/*
 * Copyright (c) 2020-2023, Andreas Kling <andreas@ladybird.org>
 * Copyright (c) 2021-2022, Linus Groh <linusg@serenityos.org>
 * Copyright (c) 2021, Luke Wilde <lukew@serenityos.org>
 * Copyright (c) 2022, Ali Mohammad Pur <mpfard@serenityos.org>
 * Copyright (c) 2024, Jelle Raaijmakers <jelle@ladybird.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include "IDLParser.h"
#include <AK/Assertions.h>
#include <AK/Function.h>
#include <AK/LexicalPath.h>
#include <AK/QuickSort.h>
#include <LibCore/File.h>
#include <LibFileSystem/FileSystem.h>

[[noreturn]] static void report_parsing_error(StringView message, StringView filename, StringView input, size_t offset)
{
    // FIXME: Spaghetti code ahead.

    size_t lineno = 1;
    size_t colno = 1;
    size_t start_line = 0;
    size_t line_length = 0;
    for (size_t index = 0; index < input.length(); ++index) {
        if (offset == index)
            colno = index - start_line + 1;

        if (input[index] == '\n') {
            if (index >= offset)
                break;

            start_line = index + 1;
            line_length = 0;
            ++lineno;
        } else {
            ++line_length;
        }
    }

    StringBuilder error_message;
    error_message.appendff("{}\n", input.substring_view(start_line, line_length));
    for (size_t i = 0; i < colno - 1; ++i)
        error_message.append(' ');
    error_message.append("\033[1;31m^\n"sv);
    error_message.appendff("{}:{}: error: {}\033[0m\n", filename, lineno, message);

    warnln("{}", error_message.string_view());
    exit(EXIT_FAILURE);
}

static bool is_valid_cpp_identifier_start(char start)
{
    // https://en.cppreference.com/w/cpp/language/identifiers
    // to be a valid C++ identifier it must be a:

    // uppercase Latin letter A-Z
    // lowercase Latin letter a-z
    if (is_ascii_alpha(start)) {
        return true;
    }

    // underscore
    if (start == '_') {
        return true;
    }

    // FIXME: any Unicode character with the Unicode property XID_Start

    return false;
}

static ByteString convert_enumeration_value_to_cpp_enum_member(ByteString const& value, HashTable<ByteString>& names_already_seen)
{
    StringBuilder builder;
    GenericLexer lexer { value };

    bool first_word = true;
    while (!lexer.is_eof()) {
        lexer.ignore_while([](auto c) { return is_ascii_space(c) || c == '-' || c == '_'; });
        if (first_word) {
            auto const first_letter = lexer.peek();
            if (!is_valid_cpp_identifier_start(first_letter))
                builder.append('_');
            first_word = false;
        }

        auto word = lexer.consume_while([](auto c) { return is_ascii_alphanumeric(c); });
        if (!word.is_empty()) {
            builder.append(word.to_ascii_titlecase_string());
        } else {
            auto non_alnum_string = lexer.consume_while([](auto c) { return !is_ascii_alphanumeric(c); });
            if (!non_alnum_string.is_empty())
                builder.append('_');
        }
    }

    if (builder.is_empty())
        builder.append("Empty"sv);

    while (names_already_seen.contains(builder.string_view()))
        builder.append('_');

    names_already_seen.set(builder.string_view());
    return builder.to_byte_string();
}

namespace IDL {

void Parser::assert_specific(char ch)
{
    if (!lexer.consume_specific(ch))
        report_parsing_error(ByteString::formatted("expected '{}'", ch), filename, input, lexer.tell());
}

void Parser::consume_whitespace()
{
    bool consumed = true;
    while (consumed) {
        consumed = lexer.consume_while(is_ascii_space).length() > 0;

        if (lexer.consume_specific("//"sv)) {
            lexer.consume_until('\n');
            lexer.ignore();
            consumed = true;
        }
    }
}

void Parser::assert_string(StringView expected)
{
    if (!lexer.consume_specific(expected))
        report_parsing_error(ByteString::formatted("expected '{}'", expected), filename, input, lexer.tell());
}

ByteString Parser::parse_identifier_until(AK::Function<bool(char)> predicate)
{
    auto identifier = lexer.consume_until(move(predicate));
    return identifier.trim("_"sv, TrimMode::Left);
}

ByteString Parser::parse_identifier_ending_with_space_or(auto... possible_terminating_characters)
{
    return parse_identifier_until([&](auto ch) { return (is_ascii_space(ch) || ... || (ch == possible_terminating_characters)); });
}

ByteString Parser::parse_identifier_ending_with(auto... possible_terminating_characters)
{
    return parse_identifier_until([&](auto ch) { return (... || (ch == possible_terminating_characters)); });
}

ByteString Parser::parse_identifier_ending_with_space()
{
    return parse_identifier_ending_with_space_or();
}

HashMap<ByteString, ByteString> Parser::parse_extended_attributes()
{
    HashMap<ByteString, ByteString> extended_attributes;
    for (;;) {
        consume_whitespace();
        if (lexer.consume_specific(']'))
            break;
        auto name = parse_identifier_ending_with(']', '=', ',');
        if (lexer.consume_specific('=')) {
            bool did_open_paren = false;
            auto value = lexer.consume_until(
                [&did_open_paren](auto ch) {
                    if (ch == '(') {
                        did_open_paren = true;
                        return false;
                    }
                    if (did_open_paren)
                        return ch == ')';
                    return ch == ']' || ch == ',';
                });
            extended_attributes.set(name, value);
        } else {
            extended_attributes.set(name, {});
        }
        lexer.consume_specific(',');
    }
    consume_whitespace();
    return extended_attributes;
}

static HashTable<ByteString> import_stack;
Optional<Interface&> Parser::resolve_import(auto path)
{
    ByteString include_path;
    for (auto import_base_path : import_base_paths) {
        auto maybe_include_path = LexicalPath::join(import_base_path, path).string();
        if (!FileSystem::exists(maybe_include_path))
            continue;

        include_path = maybe_include_path;
        break;
    }

    if (include_path.is_empty()) {
        StringBuilder error_message;
        error_message.appendff("Failed to find {} in the following directories:\n", path);
        error_message.join('\n', import_base_paths);
        report_parsing_error(error_message.to_byte_string(), filename, input, lexer.tell());
    }

    auto real_path_error_or = FileSystem::real_path(include_path);
    if (real_path_error_or.is_error())
        report_parsing_error(ByteString::formatted("Failed to resolve path {}: {}", include_path, real_path_error_or.error()), filename, input, lexer.tell());
    auto real_path = real_path_error_or.release_value();

    if (top_level_resolved_imports().contains(real_path))
        return *top_level_resolved_imports().find(real_path)->value;

    if (import_stack.contains(real_path))
        report_parsing_error(ByteString::formatted("Circular import detected: {}", include_path), filename, input, lexer.tell());
    import_stack.set(real_path);

    auto file_or_error = Core::File::open(real_path, Core::File::OpenMode::Read);
    if (file_or_error.is_error())
        report_parsing_error(ByteString::formatted("Failed to open {}: {}", real_path, file_or_error.error()), filename, input, lexer.tell());

    auto data_or_error = file_or_error.value()->read_until_eof();
    if (data_or_error.is_error())
        report_parsing_error(ByteString::formatted("Failed to read {}: {}", real_path, data_or_error.error()), filename, input, lexer.tell());
    auto& result = Parser(this, real_path, data_or_error.value(), import_base_paths).parse();
    import_stack.remove(real_path);

    top_level_resolved_imports().set(real_path, &result);
    return result;
}

NonnullRefPtr<Type const> Parser::parse_type()
{
    if (lexer.consume_specific('(')) {
        Vector<NonnullRefPtr<Type const>> union_member_types;
        union_member_types.append(parse_type());
        consume_whitespace();
        assert_string("or"sv);
        consume_whitespace();
        union_member_types.append(parse_type());
        consume_whitespace();

        while (lexer.consume_specific("or"sv)) {
            consume_whitespace();
            union_member_types.append(parse_type());
            consume_whitespace();
        }

        assert_specific(')');

        bool nullable = lexer.consume_specific('?');
        auto type = adopt_ref(*new UnionType("", nullable, move(union_member_types)));

        if (nullable) {
            if (type->number_of_nullable_member_types() > 0)
                report_parsing_error("nullable union type cannot contain another nullable type"sv, filename, input, lexer.tell());

            // FIXME: A nullable union type cannot include a dictionary type as one of its flattened member types.
        }

        return type;
    }

    bool unsigned_ = lexer.consume_specific("unsigned"sv);
    if (unsigned_)
        consume_whitespace();

    bool unrestricted = lexer.consume_specific("unrestricted"sv);
    if (unrestricted)
        consume_whitespace();

    VERIFY(!(unsigned_ && unrestricted));

    auto name = lexer.consume_until([](auto ch) { return !is_ascii_alphanumeric(ch) && ch != '_'; });

    if (name.equals_ignoring_ascii_case("long"sv)) {
        consume_whitespace();
        if (lexer.consume_specific("long"sv))
            name = "long long"sv;
    }

    Vector<NonnullRefPtr<Type const>> parameters;
    bool is_parameterized_type = false;
    if (lexer.consume_specific('<')) {
        is_parameterized_type = true;
        parameters.append(parse_type());
        while (lexer.consume_specific(',')) {
            consume_whitespace();
            parameters.append(parse_type());
        }
        lexer.consume_specific('>');
    }
    auto nullable = lexer.consume_specific('?');
    StringBuilder builder;
    if (unsigned_)
        builder.append("unsigned "sv);
    if (unrestricted)
        builder.append("unrestricted "sv);

    builder.append(name);

    if (nullable) {
        // https://webidl.spec.whatwg.org/#dfn-nullable-type
        // The inner type must not be:
        //   - any,
        if (name == "any"sv)
            report_parsing_error("'any' cannot be nullable"sv, filename, input, lexer.tell());

        //   - a promise type,
        if (name == "Promise"sv)
            report_parsing_error("'Promise' cannot be nullable"sv, filename, input, lexer.tell());

        //   - an observable array type,
        if (name == "ObservableArray")
            report_parsing_error("'ObservableArray' cannot be nullable"sv, filename, input, lexer.tell());

        //   - another nullable type, or

        //   - a union type that itself includes a nullable type or has a dictionary type as one of its flattened
        //     member types
        // Note: This case is handled above
    }

    if (builder.is_empty()) {
        report_parsing_error("Type can't be an empty string"sv, filename, input, lexer.tell());
    }

    if (is_parameterized_type)
        return adopt_ref(*new ParameterizedType(builder.to_byte_string(), nullable, move(parameters)));

    return adopt_ref(*new Type(builder.to_byte_string(), nullable));
}

void Parser::parse_attribute(HashMap<ByteString, ByteString>& extended_attributes, Interface& interface, IsStatic is_static)
{
    bool inherit = lexer.consume_specific("inherit"sv);
    if (inherit)
        consume_whitespace();

    bool readonly = lexer.consume_specific("readonly"sv);
    if (readonly)
        consume_whitespace();

    // FIXME: Should we parse 'readonly setlike<T>' differently than this?
    if (lexer.consume_specific("attribute"sv))
        consume_whitespace();
    else if (lexer.consume_specific("setlike"sv) && !inherit)
        parse_setlike(interface, readonly);
    else
        report_parsing_error("expected 'attribute'"sv, filename, input, lexer.tell());

    auto type = parse_type();
    consume_whitespace();
    auto name = parse_identifier_ending_with_space_or(';');
    consume_whitespace();

    assert_specific(';');

    ByteString attribute_callback_name;
    auto custom_callback_name = extended_attributes.find("AttributeCallbackName");
    if (custom_callback_name != extended_attributes.end()) {
        attribute_callback_name = custom_callback_name->value;
    } else {
        attribute_callback_name = name.to_snakecase().replace("-"sv, "_"sv, ReplaceMode::All);
    }

    auto getter_callback_name = ByteString::formatted("{}_getter", attribute_callback_name);
    auto setter_callback_name = ByteString::formatted("{}_setter", attribute_callback_name);

    Attribute attribute {
        inherit,
        readonly,
        move(type),
        move(name),
        move(extended_attributes),
        move(getter_callback_name),
        move(setter_callback_name),
    };
    if (is_static == IsStatic::No)
        interface.attributes.append(move(attribute));
    else
        interface.static_attributes.append(move(attribute));
}

void Parser::parse_constant(Interface& interface)
{
    lexer.consume_specific("const"sv);
    consume_whitespace();

    auto type = parse_type();
    consume_whitespace();
    auto name = parse_identifier_ending_with_space_or('=');
    consume_whitespace();
    lexer.consume_specific('=');
    consume_whitespace();
    auto value = lexer.consume_while([](auto ch) { return !is_ascii_space(ch) && ch != ';'; });
    consume_whitespace();
    assert_specific(';');

    Constant constant {
        move(type),
        move(name),
        move(value),
    };
    interface.constants.append(move(constant));
}

Vector<Parameter> Parser::parse_parameters()
{
    consume_whitespace();
    Vector<Parameter> parameters;
    for (;;) {
        if (lexer.next_is(')'))
            break;
        HashMap<ByteString, ByteString> extended_attributes;
        if (lexer.consume_specific('['))
            extended_attributes = parse_extended_attributes();
        bool optional = lexer.consume_specific("optional"sv);
        if (optional)
            consume_whitespace();
        if (lexer.consume_specific('[')) {
            // Not explicitly forbidden by the grammar but unlikely to happen in practice - if it does,
            // we'll have to teach the parser how to merge two sets of extended attributes.
            VERIFY(extended_attributes.is_empty());
            extended_attributes = parse_extended_attributes();
        }
        auto type = parse_type();
        bool variadic = lexer.consume_specific("..."sv);
        consume_whitespace();
        auto name = parse_identifier_ending_with_space_or(',', ')', '=');
        Parameter parameter = { move(type), move(name), optional, {}, move(extended_attributes), variadic };
        consume_whitespace();
        if (variadic) {
            // Variadic parameters must be last and do not have default values.
            parameters.append(move(parameter));
            break;
        }
        if (lexer.next_is(')')) {
            parameters.append(move(parameter));
            break;
        }
        if (lexer.next_is('=') && optional) {
            assert_specific('=');
            consume_whitespace();
            auto default_value = lexer.consume_until([](auto ch) { return is_ascii_space(ch) || ch == ',' || ch == ')'; });
            parameter.optional_default_value = default_value;
        }
        parameters.append(move(parameter));
        if (lexer.next_is(')'))
            break;
        assert_specific(',');
        consume_whitespace();
    }
    return parameters;
}

Function Parser::parse_function(HashMap<ByteString, ByteString>& extended_attributes, Interface& interface, IsStatic is_static, IsSpecialOperation is_special_operation)
{
    auto position = lexer.current_position();

    auto return_type = parse_type();
    consume_whitespace();
    auto name = parse_identifier_ending_with_space_or('(');
    consume_whitespace();
    assert_specific('(');
    auto parameters = parse_parameters();
    assert_specific(')');
    consume_whitespace();
    assert_specific(';');

    Function function { move(return_type), name, move(parameters), move(extended_attributes), position, {}, false };

    // "Defining a special operation with an identifier is equivalent to separating the special operation out into its own declaration without an identifier."
    if (is_special_operation == IsSpecialOperation::No || (is_special_operation == IsSpecialOperation::Yes && !name.is_empty())) {
        if (is_static == IsStatic::No)
            interface.functions.append(function);
        else
            interface.static_functions.append(function);
    }

    return function;
}

void Parser::parse_constructor(HashMap<ByteString, ByteString>& extended_attributes, Interface& interface)
{
    assert_string("constructor"sv);
    consume_whitespace();
    assert_specific('(');
    auto parameters = parse_parameters();
    assert_specific(')');
    consume_whitespace();
    assert_specific(';');

    interface.constructors.append(Constructor { interface.name, move(parameters), move(extended_attributes) });
}

void Parser::parse_stringifier(HashMap<ByteString, ByteString>& extended_attributes, Interface& interface)
{
    assert_string("stringifier"sv);
    consume_whitespace();
    interface.has_stringifier = true;
    if (lexer.next_is("attribute"sv) || lexer.next_is("inherit"sv) || lexer.next_is("readonly"sv)) {
        parse_attribute(extended_attributes, interface);
        interface.stringifier_attribute = interface.attributes.last();
        interface.stringifier_extended_attributes = interface.stringifier_attribute->extended_attributes;
    } else {
        interface.stringifier_extended_attributes = move(extended_attributes);
        assert_specific(';');
    }
}

void Parser::parse_iterable(Interface& interface)
{
    assert_string("iterable"sv);
    assert_specific('<');
    auto first_type = parse_type();
    if (lexer.next_is(',')) {
        assert_specific(',');
        consume_whitespace();
        auto second_type = parse_type();
        interface.pair_iterator_types = Tuple { move(first_type), move(second_type) };
        interface.pair_iterator_offset = lexer.tell();
    } else {
        interface.value_iterator_type = move(first_type);
        interface.value_iterator_offset = lexer.tell();
    }

    if (interface.async_value_iterator_type.has_value())
        report_parsing_error("Interfaces with an async iterable declaration must not have an iterable declaration."sv, filename, input, lexer.tell());
    if (interface.set_entry_type.has_value())
        report_parsing_error("Interfaces with an iterable declaration must not have a setlike declaration."sv, filename, input, lexer.tell());

    assert_specific('>');
    assert_specific(';');
}

// https://webidl.spec.whatwg.org/#idl-async-iterable-declaration
void Parser::parse_async_iterable(Interface& interface)
{
    if (interface.async_value_iterator_type.has_value())
        report_parsing_error("Interfaces must not have more than one async iterable declaration."sv, filename, input, lexer.tell());
    if (interface.set_entry_type.has_value())
        report_parsing_error("Interfaces with an async iterable declaration must not have a setlike declaration."sv, filename, input, lexer.tell());
    if (interface.value_iterator_type.has_value())
        report_parsing_error("Interfaces with an async iterable declaration must not have an iterable declaration."sv, filename, input, lexer.tell());
    if (interface.supports_indexed_properties())
        report_parsing_error("Interfaces with an async iterable declaration must not support indexed properties."sv, filename, input, lexer.tell());
    // FIXME: Reject interfaces that have a maplike declaration when we support that type.

    assert_string("async"sv);
    consume_whitespace();
    assert_string("iterable"sv);
    assert_specific('<');

    auto first_type = parse_type();

    if (lexer.next_is(',')) {
        // https://webidl.spec.whatwg.org/#pair-asynchronously-iterable-declaration
        report_parsing_error("FIXME: Support paired async iterable declarations."sv, filename, input, lexer.tell());
    } else {
        interface.async_value_iterator_type = move(first_type);
    }

    assert_specific('>');

    if (lexer.next_is('(')) {
        assert_specific('(');
        interface.async_value_iterator_parameters = parse_parameters();
        assert_specific(')');
    }

    assert_specific(';');
}

void Parser::parse_setlike(Interface& interface, bool is_readonly)
{
    if (interface.supports_indexed_properties())
        report_parsing_error("Interfaces with a setlike declaration must not support indexed properties."sv, filename, input, lexer.tell());

    if (interface.value_iterator_type.has_value() || interface.pair_iterator_types.has_value())
        report_parsing_error("Interfaces with a setlike declaration must not must not be iterable."sv, filename, input, lexer.tell());

    assert_string("setlike"sv);
    assert_specific('<');

    interface.set_entry_type = parse_type();
    interface.is_set_readonly = is_readonly;

    assert_specific('>');
    assert_specific(';');
}

void Parser::parse_getter(HashMap<ByteString, ByteString>& extended_attributes, Interface& interface)
{
    assert_string("getter"sv);
    consume_whitespace();
    auto function = parse_function(extended_attributes, interface, IsStatic::No, IsSpecialOperation::Yes);

    if (function.parameters.size() != 1)
        report_parsing_error(ByteString::formatted("Named/indexed property getters must have only 1 parameter, got {} parameters.", function.parameters.size()), filename, input, lexer.tell());

    auto& identifier = function.parameters.first();

    if (identifier.type->is_nullable())
        report_parsing_error("identifier's type must not be nullable."sv, filename, input, lexer.tell());

    if (identifier.optional)
        report_parsing_error("identifier must not be optional."sv, filename, input, lexer.tell());

    // FIXME: Disallow variadic functions once they're supported.

    if (identifier.type->name() == "DOMString") {
        if (interface.named_property_getter.has_value())
            report_parsing_error("An interface can only have one named property getter."sv, filename, input, lexer.tell());

        interface.named_property_getter = move(function);
    } else if (identifier.type->name() == "unsigned long") {
        if (interface.indexed_property_getter.has_value())
            report_parsing_error("An interface can only have one indexed property getter."sv, filename, input, lexer.tell());

        interface.indexed_property_getter = move(function);
    } else {
        report_parsing_error(ByteString::formatted("Named/indexed property getter's identifier's type must be either 'DOMString' or 'unsigned long', got '{}'.", identifier.type->name()), filename, input, lexer.tell());
    }
}

void Parser::parse_setter(HashMap<ByteString, ByteString>& extended_attributes, Interface& interface)
{
    assert_string("setter"sv);
    consume_whitespace();
    auto function = parse_function(extended_attributes, interface, IsStatic::No, IsSpecialOperation::Yes);

    if (function.parameters.size() != 2)
        report_parsing_error(ByteString::formatted("Named/indexed property setters must have only 2 parameters, got {} parameter(s).", function.parameters.size()), filename, input, lexer.tell());

    auto& identifier = function.parameters.first();

    if (identifier.type->is_nullable())
        report_parsing_error("identifier's type must not be nullable."sv, filename, input, lexer.tell());

    if (identifier.optional)
        report_parsing_error("identifier must not be optional."sv, filename, input, lexer.tell());

    // FIXME: Disallow variadic functions once they're supported.

    if (identifier.type->name() == "DOMString") {
        if (interface.named_property_setter.has_value())
            report_parsing_error("An interface can only have one named property setter."sv, filename, input, lexer.tell());

        if (!interface.named_property_getter.has_value())
            report_parsing_error("A named property setter must be accompanied by a named property getter."sv, filename, input, lexer.tell());

        interface.named_property_setter = move(function);
    } else if (identifier.type->name() == "unsigned long") {
        if (interface.indexed_property_setter.has_value())
            report_parsing_error("An interface can only have one indexed property setter."sv, filename, input, lexer.tell());

        if (!interface.indexed_property_getter.has_value())
            report_parsing_error("An indexed property setter must be accompanied by an indexed property getter."sv, filename, input, lexer.tell());

        interface.indexed_property_setter = move(function);
    } else {
        report_parsing_error(ByteString::formatted("Named/indexed property setter's identifier's type must be either 'DOMString' or 'unsigned long', got '{}'.", identifier.type->name()), filename, input, lexer.tell());
    }
}

void Parser::parse_deleter(HashMap<ByteString, ByteString>& extended_attributes, Interface& interface)
{
    assert_string("deleter"sv);
    consume_whitespace();
    auto function = parse_function(extended_attributes, interface, IsStatic::No, IsSpecialOperation::Yes);

    if (function.parameters.size() != 1)
        report_parsing_error(ByteString::formatted("Named property deleter must have only 1 parameter, got {} parameters.", function.parameters.size()), filename, input, lexer.tell());

    auto& identifier = function.parameters.first();

    if (identifier.type->is_nullable())
        report_parsing_error("identifier's type must not be nullable."sv, filename, input, lexer.tell());

    if (identifier.optional)
        report_parsing_error("identifier must not be optional."sv, filename, input, lexer.tell());

    // FIXME: Disallow variadic functions once they're supported.

    if (identifier.type->name() == "DOMString") {
        if (interface.named_property_deleter.has_value())
            report_parsing_error("An interface can only have one named property deleter."sv, filename, input, lexer.tell());

        if (!interface.named_property_getter.has_value())
            report_parsing_error("A named property deleter must be accompanied by a named property getter."sv, filename, input, lexer.tell());

        interface.named_property_deleter = move(function);
    } else {
        report_parsing_error(ByteString::formatted("Named property deleter's identifier's type must be 'DOMString', got '{}'.", identifier.type->name()), filename, input, lexer.tell());
    }
}

void Parser::parse_interface(Interface& interface)
{
    consume_whitespace();
    interface.name = parse_identifier_ending_with_space();
    consume_whitespace();
    if (lexer.consume_specific(':')) {
        consume_whitespace();
        interface.parent_name = parse_identifier_ending_with_space();
        consume_whitespace();
    }
    assert_specific('{');

    for (;;) {
        HashMap<ByteString, ByteString> extended_attributes;

        consume_whitespace();

        if (lexer.consume_specific('}')) {
            consume_whitespace();
            assert_specific(';');
            break;
        }

        if (lexer.consume_specific('[')) {
            extended_attributes = parse_extended_attributes();
            if (!interface.has_unscopable_member && extended_attributes.contains("Unscopable"))
                interface.has_unscopable_member = true;
        }

        if (lexer.next_is("async"sv)) {
            parse_async_iterable(interface);
            continue;
        }

        if (lexer.next_is("constructor"sv)) {
            parse_constructor(extended_attributes, interface);
            continue;
        }

        if (lexer.next_is("const"sv)) {
            parse_constant(interface);
            continue;
        }

        if (lexer.next_is("stringifier"sv)) {
            parse_stringifier(extended_attributes, interface);
            continue;
        }

        if (lexer.next_is("iterable"sv)) {
            parse_iterable(interface);
            continue;
        }

        if (lexer.next_is("setlike"sv)) {
            bool is_readonly = false;
            parse_setlike(interface, is_readonly);
            continue;
        }

        if (lexer.next_is("inherit"sv) || lexer.next_is("readonly"sv) || lexer.next_is("attribute"sv)) {
            parse_attribute(extended_attributes, interface);
            continue;
        }

        if (lexer.next_is("getter"sv)) {
            parse_getter(extended_attributes, interface);
            continue;
        }

        if (lexer.next_is("setter"sv)) {
            parse_setter(extended_attributes, interface);
            continue;
        }

        if (lexer.next_is("deleter"sv)) {
            parse_deleter(extended_attributes, interface);
            continue;
        }

        bool is_static = lexer.consume_specific("static"sv);
        if (!is_static) {
            parse_function(extended_attributes, interface, IsStatic::No);
        } else {
            consume_whitespace();
            if (lexer.next_is("readonly"sv) || lexer.next_is("attribute"sv)) {
                parse_attribute(extended_attributes, interface, IsStatic::Yes);
            } else {
                parse_function(extended_attributes, interface, IsStatic::Yes);
            }
        }
    }

    if (auto legacy_namespace = interface.extended_attributes.get("LegacyNamespace"sv); legacy_namespace.has_value())
        interface.namespaced_name = ByteString::formatted("{}.{}", *legacy_namespace, interface.name);
    else
        interface.namespaced_name = interface.name;

    if (auto maybe_implemented_as = interface.extended_attributes.get("ImplementedAs"); maybe_implemented_as.has_value())
        interface.implemented_name = maybe_implemented_as.release_value();
    else
        interface.implemented_name = interface.name;

    if (interface.pair_iterator_types.has_value() && interface.indexed_property_getter.has_value()) {
        VERIFY(interface.pair_iterator_offset.has_value());
        report_parsing_error("Interfaces with a pair iterator must not support indexed properties."sv, filename, input, *interface.pair_iterator_offset);
    }

    if (interface.value_iterator_type.has_value() && !interface.supports_indexed_properties()) {
        VERIFY(interface.value_iterator_offset.has_value());
        report_parsing_error("Interfaces with a value iterator must support indexed properties."sv, filename, input, *interface.value_iterator_offset);
    }

    interface.constructor_class = ByteString::formatted("{}Constructor", interface.implemented_name);
    interface.prototype_class = ByteString::formatted("{}Prototype", interface.implemented_name);
    interface.prototype_base_class = ByteString::formatted("{}Prototype", interface.parent_name.is_empty() ? "Object" : interface.parent_name);
    interface.global_mixin_class = ByteString::formatted("{}GlobalMixin", interface.name);
    consume_whitespace();
}

void Parser::parse_partial_interface(HashMap<ByteString, ByteString> extended_attributes, Interface& parent)
{
    assert_string("partial"sv);
    consume_whitespace();
    assert_string("interface"sv);

    auto partial_interface = make<Interface>();
    partial_interface->extended_attributes = move(extended_attributes);
    parse_interface(*partial_interface);
    parent.partial_interfaces.append(move(partial_interface));
}

void Parser::parse_namespace(Interface& interface)
{
    consume_whitespace();

    interface.name = parse_identifier_ending_with_space();
    interface.is_namespace = true;

    consume_whitespace();
    assert_specific('{');

    for (;;) {
        HashMap<ByteString, ByteString> extended_attributes;

        consume_whitespace();

        if (lexer.consume_specific('}')) {
            consume_whitespace();
            assert_specific(';');
            break;
        }

        if (lexer.consume_specific('[')) {
            extended_attributes = parse_extended_attributes();
            if (!interface.has_unscopable_member && extended_attributes.contains("Unscopable"))
                interface.has_unscopable_member = true;
        }

        parse_function(extended_attributes, interface);
    }

    interface.namespace_class = ByteString::formatted("{}Namespace", interface.name);
    consume_whitespace();
}

void Parser::parse_partial_namespace(Interface& parent)
{
    assert_string("partial"sv);
    consume_whitespace();
    assert_string("namespace"sv);

    auto partial_namespace = make<Interface>();
    parse_namespace(*partial_namespace);
    parent.partial_namespaces.append(move(partial_namespace));
}

// https://webidl.spec.whatwg.org/#prod-Enum
void Parser::parse_enumeration(HashMap<ByteString, ByteString> extended_attributes, Interface& interface)
{
    assert_string("enum"sv);
    consume_whitespace();

    Enumeration enumeration {};
    enumeration.extended_attributes = move(extended_attributes);

    auto name = parse_identifier_ending_with_space();
    consume_whitespace();

    assert_specific('{');

    for (; !lexer.is_eof();) {
        consume_whitespace();
        if (lexer.next_is('}'))
            break;

        assert_specific('"');
        auto string = lexer.consume_until('"');
        assert_specific('"');
        consume_whitespace();

        if (enumeration.values.contains(string))
            report_parsing_error(ByteString::formatted("Enumeration {} contains duplicate member '{}'", name, string), filename, input, lexer.tell());
        else
            enumeration.values.set(string);

        if (enumeration.first_member.is_empty())
            enumeration.first_member = move(string);

        if (!lexer.next_is('}'))
            assert_specific(',');
    }

    consume_whitespace();
    assert_specific('}');
    assert_specific(';');

    HashTable<ByteString> names_already_seen;
    for (auto& entry : enumeration.values)
        enumeration.translated_cpp_names.set(entry, convert_enumeration_value_to_cpp_enum_member(entry, names_already_seen));

    interface.enumerations.set(name, move(enumeration));
    consume_whitespace();
}

void Parser::parse_typedef(Interface& interface)
{
    assert_string("typedef"sv);
    consume_whitespace();

    HashMap<ByteString, ByteString> extended_attributes;
    if (lexer.consume_specific('['))
        extended_attributes = parse_extended_attributes();

    auto type = parse_type();
    consume_whitespace();

    auto name = parse_identifier_ending_with(';');
    assert_specific(';');

    interface.typedefs.set(move(name), Typedef { move(extended_attributes), move(type) });
    consume_whitespace();
}

void Parser::parse_dictionary(HashMap<ByteString, ByteString> extended_attributes, Interface& interface)
{
    bool partial = false;
    if (lexer.next_is("partial"sv)) {
        assert_string("partial"sv);
        consume_whitespace();
        partial = true;
    }

    assert_string("dictionary"sv);
    consume_whitespace();

    Dictionary dictionary {};
    dictionary.extended_attributes = move(extended_attributes);

    auto name = parse_identifier_ending_with_space();
    consume_whitespace();

    if (lexer.consume_specific(':')) {
        consume_whitespace();
        dictionary.parent_name = parse_identifier_ending_with_space();
        consume_whitespace();
    }
    assert_specific('{');

    for (;;) {
        consume_whitespace();

        if (lexer.consume_specific('}')) {
            consume_whitespace();
            assert_specific(';');
            break;
        }

        bool required = false;
        HashMap<ByteString, ByteString> member_extended_attributes;

        if (lexer.consume_specific('['))
            member_extended_attributes = parse_extended_attributes();

        if (lexer.consume_specific("required"sv)) {
            required = true;
            consume_whitespace();
        }

        if (lexer.consume_specific('['))
            member_extended_attributes.update(parse_extended_attributes());

        auto type = parse_type();
        consume_whitespace();

        auto name = parse_identifier_ending_with_space_or(';');
        consume_whitespace();

        Optional<StringView> default_value;

        if (lexer.consume_specific('=')) {
            VERIFY(!required);
            consume_whitespace();
            default_value = lexer.consume_until([](auto ch) { return is_ascii_space(ch) || ch == ';'; });
            consume_whitespace();
        }

        assert_specific(';');

        DictionaryMember member {
            required,
            move(type),
            move(name),
            move(member_extended_attributes),
            Optional<ByteString>(move(default_value)),
        };
        dictionary.members.append(move(member));
    }

    // dictionary members need to be evaluated in lexicographical order
    quick_sort(dictionary.members, [&](auto& one, auto& two) {
        return one.name < two.name;
    });

    if (partial) {
        auto& it = interface.partial_dictionaries.ensure(name);
        it.append(move(dictionary));
    } else {
        interface.dictionaries.set(name, move(dictionary));
    }

    consume_whitespace();
}

void Parser::parse_interface_mixin(Interface& interface)
{
    auto mixin_interface_ptr = make<Interface>();
    auto& mixin_interface = *mixin_interface_ptr;
    VERIFY(top_level_interfaces().set(move(mixin_interface_ptr)) == AK::HashSetResult::InsertedNewEntry);
    mixin_interface.module_own_path = interface.module_own_path;
    mixin_interface.is_mixin = true;

    assert_string("interface"sv);
    consume_whitespace();
    assert_string("mixin"sv);
    auto offset = lexer.tell();

    parse_interface(mixin_interface);
    if (!mixin_interface.parent_name.is_empty())
        report_parsing_error("Mixin interfaces are not allowed to have inherited parents"sv, filename, input, offset);

    auto name = mixin_interface.name;
    interface.mixins.set(move(name), &mixin_interface);
}

void Parser::parse_callback_function(HashMap<ByteString, ByteString>& extended_attributes, Interface& interface)
{
    assert_string("callback"sv);
    consume_whitespace();

    auto name = parse_identifier_ending_with_space();
    consume_whitespace();

    assert_specific('=');
    consume_whitespace();

    auto return_type = parse_type();
    consume_whitespace();
    assert_specific('(');
    auto parameters = parse_parameters();
    assert_specific(')');
    consume_whitespace();
    assert_specific(';');

    interface.callback_functions.set(move(name), CallbackFunction { move(return_type), move(parameters), extended_attributes.contains("LegacyTreatNonObjectAsNull") });
    consume_whitespace();
}

void Parser::parse_non_interface_entities(bool allow_interface, Interface& interface)
{
    consume_whitespace();

    while (!lexer.is_eof()) {
        HashMap<ByteString, ByteString> extended_attributes;
        if (lexer.consume_specific('['))
            extended_attributes = parse_extended_attributes();
        if (lexer.next_is("dictionary"sv) || lexer.next_is("partial dictionary"sv)) {
            parse_dictionary(extended_attributes, interface);
        } else if (lexer.next_is("enum"sv)) {
            parse_enumeration(extended_attributes, interface);
        } else if (lexer.next_is("typedef"sv)) {
            parse_typedef(interface);
        } else if (lexer.next_is("partial interface"sv)) {
            parse_partial_interface(extended_attributes, interface);
        } else if (lexer.next_is("interface mixin"sv)) {
            parse_interface_mixin(interface);
        } else if (lexer.next_is("partial namespace"sv)) {
            parse_partial_namespace(interface);
        } else if (lexer.next_is("callback"sv)) {
            parse_callback_function(extended_attributes, interface);
        } else if ((allow_interface && !lexer.next_is("interface"sv) && !lexer.next_is("namespace"sv)) || !allow_interface) {
            auto current_offset = lexer.tell();
            auto name = parse_identifier_ending_with_space();
            consume_whitespace();
            if (lexer.consume_specific("includes"sv)) {
                consume_whitespace();
                auto mixin_name = parse_identifier_ending_with_space_or(';');
                interface.included_mixins.ensure(name).set(mixin_name);
                consume_whitespace();
                assert_specific(';');
                consume_whitespace();
            } else {
                report_parsing_error("expected 'enum' or 'dictionary'"sv, filename, input, current_offset);
            }
        } else {
            interface.extended_attributes = move(extended_attributes);
            break;
        }
    }

    consume_whitespace();
}

static void resolve_union_typedefs(Interface& interface, UnionType& union_);

static void resolve_typedef(Interface& interface, NonnullRefPtr<Type const>& type, HashMap<ByteString, ByteString>* extended_attributes = {})
{
    if (is<ParameterizedType>(*type)) {
        auto& parameterized_type = const_cast<Type&>(*type).as_parameterized();
        auto& parameters = static_cast<Vector<NonnullRefPtr<Type const>>&>(parameterized_type.parameters());
        for (auto& parameter : parameters)
            resolve_typedef(interface, parameter);
        return;
    }

    // Resolve anonymous union types until we get named types that can be resolved in the next step.
    if (is<UnionType>(*type) && type->name().is_empty()) {
        resolve_union_typedefs(interface, const_cast<Type&>(*type).as_union());
        return;
    }

    auto it = interface.typedefs.find(type->name());
    if (it == interface.typedefs.end())
        return;
    bool nullable = type->is_nullable();
    type = it->value.type;
    const_cast<Type&>(*type).set_nullable(nullable);
    if (extended_attributes) {
        for (auto& attribute : it->value.extended_attributes)
            extended_attributes->set(attribute.key, attribute.value);
    }

    // Recursively resolve typedefs in unions after we resolved the type itself - e.g. for this:
    // typedef (A or B) Union1;
    // typedef (C or D) Union2;
    // typedef (Union1 or Union2) NestedUnion;
    // We run:
    // - resolve_typedef(NestedUnion) -> NestedUnion gets replaced by UnionType(Union1, Union2)
    //   - resolve_typedef(Union1) -> Union1 gets replaced by UnionType(A, B)
    //   - resolve_typedef(Union2) -> Union2 gets replaced by UnionType(C, D)
    // So whatever referenced NestedUnion ends up with the following resolved union:
    // UnionType(UnionType(A, B), UnionType(C, D))
    // Note that flattening unions is handled separately as per the spec.
    if (is<UnionType>(*type))
        resolve_union_typedefs(interface, const_cast<Type&>(*type).as_union());
}

static void resolve_union_typedefs(Interface& interface, UnionType& union_)
{
    auto& member_types = static_cast<Vector<NonnullRefPtr<Type const>>&>(union_.member_types());
    for (auto& member_type : member_types)
        resolve_typedef(interface, member_type);
}

static void resolve_parameters_typedefs(Interface& interface, Vector<Parameter>& parameters)
{
    for (auto& parameter : parameters)
        resolve_typedef(interface, parameter.type, &parameter.extended_attributes);
}

template<typename FunctionType>
void resolve_function_typedefs(Interface& interface, FunctionType& function)
{
    resolve_typedef(interface, function.return_type);
    resolve_parameters_typedefs(interface, function.parameters);
}

Interface& Parser::parse()
{
    auto this_module_or_error = FileSystem::real_path(filename);
    if (this_module_or_error.is_error()) {
        report_parsing_error(ByteString::formatted("Failed to resolve path '{}': {}", filename, this_module_or_error.error()), filename, input, 0);
        VERIFY_NOT_REACHED();
    }
    auto this_module = this_module_or_error.release_value();

    auto interface_ptr = make<Interface>();
    auto& interface = *interface_ptr;
    VERIFY(top_level_interfaces().set(move(interface_ptr)) == AK::HashSetResult::InsertedNewEntry);
    interface.module_own_path = this_module;
    top_level_resolved_imports().set(this_module, &interface);

    Vector<Interface&> imports;
    {
        while (lexer.consume_specific("#import"sv)) {
            consume_whitespace();
            assert_specific('<');
            auto path = lexer.consume_until('>');
            lexer.ignore();
            auto maybe_interface = resolve_import(path);
            if (maybe_interface.has_value()) {
                imports.append(maybe_interface.release_value());
            }
            consume_whitespace();
        }
    }

    parse_non_interface_entities(true, interface);

    if (lexer.consume_specific("interface"sv))
        parse_interface(interface);
    else if (lexer.consume_specific("namespace"sv))
        parse_namespace(interface);

    parse_non_interface_entities(false, interface);

    for (auto& import : imports) {
        // FIXME: Instead of copying every imported entity into the current interface, query imports directly
        for (auto& partial_interface : import.partial_interfaces) {
            if (partial_interface->name == interface.name)
                interface.extend_with_partial_interface(*partial_interface);
        }

        for (auto& dictionary : import.dictionaries) {
            auto dictionary_copy = dictionary.value;
            dictionary_copy.is_original_definition = false;
            interface.dictionaries.set(dictionary.key, move(dictionary_copy));
        }

        for (auto& partial_dictionary : import.partial_dictionaries) {
            auto& it = interface.partial_dictionaries.ensure(partial_dictionary.key);
            it.extend(partial_dictionary.value);
        }

        for (auto& enumeration : import.enumerations) {
            auto enumeration_copy = enumeration.value;
            enumeration_copy.is_original_definition = false;
            interface.enumerations.set(enumeration.key, move(enumeration_copy));
        }

        for (auto& partial_namespace : import.partial_namespaces) {
            if (partial_namespace->namespace_class == interface.namespace_class)
                interface.extend_with_partial_interface(*partial_namespace);
        }

        interface.typedefs.update(import.typedefs);

        for (auto& mixin : import.mixins) {
            if (auto it = interface.mixins.find(mixin.key); it != interface.mixins.end() && it->value != mixin.value)
                report_parsing_error(ByteString::formatted("Mixin '{}' was already defined in {}", mixin.key, mixin.value->module_own_path), filename, input, lexer.tell());
            interface.mixins.set(mixin.key, mixin.value);
        }

        interface.callback_functions.update(import.callback_functions);
    }

    // Resolve mixins
    if (auto it = interface.included_mixins.find(interface.name); it != interface.included_mixins.end()) {
        for (auto& entry : it->value) {
            auto mixin_it = interface.mixins.find(entry);
            if (mixin_it == interface.mixins.end())
                report_parsing_error(ByteString::formatted("Mixin '{}' was never defined", entry), filename, input, lexer.tell());

            auto& mixin = mixin_it->value;
            interface.attributes.extend(mixin->attributes);
            interface.constants.extend(mixin->constants);
            interface.functions.extend(mixin->functions);
            interface.static_functions.extend(mixin->static_functions);
            if (interface.has_stringifier && mixin->has_stringifier)
                report_parsing_error(ByteString::formatted("Both interface '{}' and mixin '{}' have defined stringifier attributes", interface.name, mixin->name), filename, input, lexer.tell());

            if (mixin->has_stringifier) {
                interface.stringifier_attribute = mixin->stringifier_attribute;
                interface.has_stringifier = true;
            }

            if (mixin->has_unscopable_member)
                interface.has_unscopable_member = true;
        }
    }

    // Resolve typedefs
    for (auto& attribute : interface.attributes)
        resolve_typedef(interface, attribute.type, &attribute.extended_attributes);
    for (auto& attribute : interface.static_attributes)
        resolve_typedef(interface, attribute.type, &attribute.extended_attributes);
    for (auto& constant : interface.constants)
        resolve_typedef(interface, constant.type);
    for (auto& constructor : interface.constructors)
        resolve_parameters_typedefs(interface, constructor.parameters);
    for (auto& function : interface.functions)
        resolve_function_typedefs(interface, function);
    for (auto& static_function : interface.static_functions)
        resolve_function_typedefs(interface, static_function);
    if (interface.value_iterator_type.has_value())
        resolve_typedef(interface, *interface.value_iterator_type);
    if (interface.pair_iterator_types.has_value()) {
        resolve_typedef(interface, interface.pair_iterator_types->get<0>());
        resolve_typedef(interface, interface.pair_iterator_types->get<1>());
    }
    if (interface.named_property_getter.has_value())
        resolve_function_typedefs(interface, *interface.named_property_getter);
    if (interface.named_property_setter.has_value())
        resolve_function_typedefs(interface, *interface.named_property_setter);
    if (interface.indexed_property_getter.has_value())
        resolve_function_typedefs(interface, *interface.indexed_property_getter);
    if (interface.indexed_property_setter.has_value())
        resolve_function_typedefs(interface, *interface.indexed_property_setter);
    if (interface.named_property_deleter.has_value())
        resolve_function_typedefs(interface, *interface.named_property_deleter);
    if (interface.named_property_getter.has_value())
        resolve_function_typedefs(interface, *interface.named_property_getter);
    for (auto& dictionary : interface.dictionaries) {
        for (auto& dictionary_member : dictionary.value.members)
            resolve_typedef(interface, dictionary_member.type, &dictionary_member.extended_attributes);
    }
    for (auto& dictionaries : interface.partial_dictionaries) {
        for (auto& dictionary : dictionaries.value)
            for (auto& dictionary_member : dictionary.members)
                resolve_typedef(interface, dictionary_member.type, &dictionary_member.extended_attributes);
    }
    for (auto& callback_function : interface.callback_functions)
        resolve_function_typedefs(interface, callback_function.value);

    // Create overload sets
    for (auto& function : interface.functions) {
        if (function.extended_attributes.contains("FIXME"))
            continue;
        auto& overload_set = interface.overload_sets.ensure(function.name);
        function.overload_index = overload_set.size();
        overload_set.append(function);
    }
    for (auto& overload_set : interface.overload_sets) {
        if (overload_set.value.size() == 1)
            continue;
        for (auto& overloaded_function : overload_set.value)
            overloaded_function.is_overloaded = true;
    }
    for (auto& function : interface.static_functions) {
        if (function.extended_attributes.contains("FIXME"))
            continue;
        auto& overload_set = interface.static_overload_sets.ensure(function.name);
        function.overload_index = overload_set.size();
        overload_set.append(function);
    }
    for (auto& overload_set : interface.static_overload_sets) {
        if (overload_set.value.size() == 1)
            continue;
        for (auto& overloaded_function : overload_set.value)
            overloaded_function.is_overloaded = true;
    }
    for (auto& constructor : interface.constructors) {
        if (constructor.extended_attributes.contains("FIXME"))
            continue;
        auto& overload_set = interface.constructor_overload_sets.ensure(constructor.name);
        constructor.overload_index = overload_set.size();
        overload_set.append(constructor);
    }
    for (auto& overload_set : interface.constructor_overload_sets) {
        if (overload_set.value.size() == 1)
            continue;
        for (auto& overloaded_constructor : overload_set.value)
            overloaded_constructor.is_overloaded = true;
    }

    // Check overload sets for repeated instances of the same function
    // as these will produce very cryptic errors if left alone.
    for (auto& overload_set : interface.overload_sets) {
        auto& functions = overload_set.value;
        for (size_t i = 0; i < functions.size(); ++i) {
            for (size_t j = i + 1; j < functions.size(); ++j) {
                if (functions[i].parameters.size() != functions[j].parameters.size())
                    continue;
                auto same = true;
                for (size_t k = 0; k < functions[i].parameters.size(); ++k) {
                    if (functions[i].parameters[k].type->is_distinguishable_from(interface, functions[j].parameters[k].type)) {
                        same = false;
                        break;
                    }
                }
                if (same) {
                    report_parsing_error(
                        ByteString::formatted("Overload set '{}' contains multiple identical declarations", overload_set.key),
                        filename,
                        input,
                        functions[j].source_position.offset);
                }
            }
        }
    }

    interface.imported_modules = move(imports);

    if (top_level_parser() == this)
        VERIFY(import_stack.is_empty());

    return interface;
}

Parser::Parser(ByteString filename, StringView contents, Vector<ByteString> import_base_paths)
    : import_base_paths(move(import_base_paths))
    , filename(move(filename))
    , input(contents)
    , lexer(input)
{
}

Parser::Parser(Parser* parent, ByteString filename, StringView contents, Vector<ByteString> import_base_paths)
    : import_base_paths(move(import_base_paths))
    , filename(move(filename))
    , input(contents)
    , lexer(input)
    , parent(parent)
{
}

Parser* Parser::top_level_parser()
{
    Parser* current = this;
    for (Parser* next = this; next; next = next->parent)
        current = next;
    return current;
}

HashMap<ByteString, Interface*>& Parser::top_level_resolved_imports()
{
    return top_level_parser()->resolved_imports;
}

HashTable<NonnullOwnPtr<Interface>>& Parser::top_level_interfaces()
{
    return top_level_parser()->interfaces;
}

Vector<ByteString> Parser::imported_files() const
{
    return const_cast<Parser*>(this)->top_level_resolved_imports().keys();
}

}
