/*
 * Copyright (c) 2025, Tim Flynn <trflynn89@ladybird.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibCore/DirIterator.h>
#include <LibCore/StandardPaths.h>
#include <LibFileSystem/FileSystem.h>
#include <LibURL/URL.h>
#include <RequestServer/Cache/DiskCache.h>
#include <RequestServer/Cache/Utilities.h>
#include <RequestServer/Request.h>

namespace RequestServer {

static constexpr auto INDEX_DATABASE = "INDEX"sv;

ErrorOr<DiskCache> DiskCache::create()
{
    auto cache_directory = LexicalPath::join(Core::StandardPaths::cache_directory(), "Ladybird"sv, "Cache"sv);

    auto database = TRY(Database::Database::create(cache_directory.string(), INDEX_DATABASE));
    auto index = TRY(CacheIndex::create(database));

    return DiskCache { move(database), move(cache_directory), move(index) };
}

DiskCache::DiskCache(NonnullRefPtr<Database::Database> database, LexicalPath cache_directory, CacheIndex index)
    : m_database(move(database))
    , m_cache_directory(move(cache_directory))
    , m_index(move(index))
{
}

Variant<Optional<CacheEntryWriter&>, DiskCache::CacheHasOpenEntry> DiskCache::create_entry(Request& request)
{
    if (!is_cacheable(request.method()))
        return Optional<CacheEntryWriter&> {};

    auto serialized_url = serialize_url_for_cache_storage(request.url());
    auto cache_key = create_cache_key(serialized_url, request.method());

    if (check_if_cache_has_open_entry(request, cache_key, CheckReaderEntries::Yes))
        return CacheHasOpenEntry {};

    auto cache_entry = CacheEntryWriter::create(*this, m_index, cache_key, move(serialized_url), request.request_start_time());
    if (cache_entry.is_error()) {
        dbgln("\033[31;1mUnable to create cache entry for\033[0m {}: {}", request.url(), cache_entry.error());
        return Optional<CacheEntryWriter&> {};
    }

    dbgln("\033[32;1mCreated disk cache entry for\033[0m {}", request.url());

    auto* cache_entry_pointer = cache_entry.value().ptr();
    m_open_cache_entries.ensure(cache_key).append(cache_entry.release_value());

    return Optional<CacheEntryWriter&> { *cache_entry_pointer };
}

Variant<Optional<CacheEntryReader&>, DiskCache::CacheHasOpenEntry> DiskCache::open_entry(Request& request)
{
    if (!is_cacheable(request.method()))
        return Optional<CacheEntryReader&> {};

    auto serialized_url = serialize_url_for_cache_storage(request.url());
    auto cache_key = create_cache_key(serialized_url, request.method());

    if (check_if_cache_has_open_entry(request, cache_key, CheckReaderEntries::No))
        return CacheHasOpenEntry {};

    auto index_entry = m_index.find_entry(cache_key);
    if (!index_entry.has_value()) {
        dbgln("\033[35;1mNo disk cache entry for\033[0m {}", request.url());
        return Optional<CacheEntryReader&> {};
    }

    auto cache_entry = CacheEntryReader::create(*this, m_index, cache_key, index_entry->response_headers, index_entry->data_size);
    if (cache_entry.is_error()) {
        dbgln("\033[31;1mUnable to open cache entry for\033[0m {}: {}", request.url(), cache_entry.error());
        m_index.remove_entry(cache_key);

        return Optional<CacheEntryReader&> {};
    }

    auto const& response_headers = cache_entry.value()->response_headers();
    auto freshness_lifetime = calculate_freshness_lifetime(response_headers);
    auto current_age = calculate_age(response_headers, index_entry->request_time, index_entry->response_time);

    switch (cache_lifetime_status(response_headers, freshness_lifetime, current_age)) {
    case CacheLifetimeStatus::Fresh:
        dbgln("\033[32;1mOpened disk cache entry for\033[0m {} (lifetime={}s age={}s) ({} bytes)", request.url(), freshness_lifetime.to_seconds(), current_age.to_seconds(), index_entry->data_size);
        break;

    case CacheLifetimeStatus::Expired:
        dbgln("\033[33;1mCache entry expired for\033[0m {} (lifetime={}s age={}s)", request.url(), freshness_lifetime.to_seconds(), current_age.to_seconds());
        cache_entry.value()->remove();

        return Optional<CacheEntryReader&> {};

    case CacheLifetimeStatus::MustRevalidate:
        // We will hold an exclusive lock on the cache entry for revalidation requests.
        if (check_if_cache_has_open_entry(request, cache_key, CheckReaderEntries::Yes))
            return Optional<CacheEntryReader&> {};

        dbgln("\033[36;1mMust revalidate disk cache entry for\033[0m {} (lifetime={}s age={}s)", request.url(), freshness_lifetime.to_seconds(), current_age.to_seconds());
        cache_entry.value()->set_must_revalidate();
        break;
    }

    auto* cache_entry_pointer = cache_entry.value().ptr();
    m_open_cache_entries.ensure(cache_key).append(cache_entry.release_value());

    return Optional<CacheEntryReader&> { *cache_entry_pointer };
}

bool DiskCache::check_if_cache_has_open_entry(Request& request, u64 cache_key, CheckReaderEntries check_reader_entries)
{
    auto open_entries = m_open_cache_entries.get(cache_key);
    if (!open_entries.has_value())
        return false;

    for (auto const& open_entry : *open_entries) {
        if (is<CacheEntryWriter>(*open_entry)) {
            dbgln("\033[36;1mDeferring disk cache entry for\033[0m {} (waiting for existing writer)", request.url());
            m_requests_waiting_completion.ensure(cache_key).append(request);
            return true;
        }

        // We allow concurrent readers unless another reader is open for revalidation. That reader will issue the network
        // request, which may then result in the cache entry being updated or deleted.
        if (check_reader_entries == CheckReaderEntries::Yes || as<CacheEntryReader>(*open_entry).must_revalidate()) {
            dbgln("\033[36;1mDeferring disk cache entry for\033[0m {} (waiting for existing reader)", request.url());
            m_requests_waiting_completion.ensure(cache_key).append(request);
            return true;
        }
    }

    return false;
}

Requests::CacheSizes DiskCache::estimate_cache_size_accessed_since(UnixDateTime since) const
{
    return m_index.estimate_cache_size_accessed_since(since);
}

void DiskCache::clear_cache()
{
    for (auto const& [_, open_entries] : m_open_cache_entries) {
        for (auto const& open_entry : open_entries)
            open_entry->mark_for_deletion({});
    }

    m_index.remove_all_entries();

    Core::DirIterator it { m_cache_directory.string(), Core::DirIterator::SkipDots };
    size_t cache_entries { 0 };

    while (it.has_next()) {
        auto entry = it.next_full_path();
        if (LexicalPath { entry }.title() == INDEX_DATABASE)
            continue;

        (void)FileSystem::remove(entry, FileSystem::RecursionMode::Disallowed);
        ++cache_entries;
    }

    dbgln("Cleared {} disk cache entries", cache_entries);
}

void DiskCache::cache_entry_closed(Badge<CacheEntry>, CacheEntry const& cache_entry)
{
    auto cache_key = cache_entry.cache_key();

    auto open_entries = m_open_cache_entries.get(cache_key);
    if (!open_entries.has_value())
        return;

    open_entries->remove_first_matching([&](auto const& open_entry) { return open_entry.ptr() == &cache_entry; });
    if (open_entries->size() > 0)
        return;

    m_open_cache_entries.remove(cache_key);

    // FIXME: This creates a bit of a first-past-the-post situation if a resumed request causes other pending requests
    //        to become delayed again. We may want to come up with some method to control the order of resumed requests.
    if (auto pending_requests = m_requests_waiting_completion.take(cache_key); pending_requests.has_value()) {
        // We defer resuming requests to ensure we are outside of any internal curl callbacks. For example, when curl
        // invokes the CURLOPT_WRITEFUNCTION callback, we will flush pending HTTP headers to the disk cache. If that
        // does not succeed, we delete the cache entry, and end up here. We must queue the new request outside of that
        // callback, otherwise curl will return CURLM_RECURSIVE_API_CALL error codes.
        Core::deferred_invoke([pending_requests = pending_requests.release_value()]() {
            for (auto const& request : pending_requests) {
                if (request)
                    request->notify_request_unblocked({});
            }
        });
    }
}

}