Added project files

core/errors.go

@@ -0,0 +1,55 @@
+// Copyright (c) 2025, Julian Müller (ChaoticByte)
+
+package core
+
+import "fmt"
+
+type HttpStatusCodeError struct {
+	Url        string
+	StatusCode int
+}
+
+func (err *HttpStatusCodeError) Error() string {
+	var e string
+	switch err.StatusCode {
+	case 400:
+		e = "Bad Request"
+	case 401:
+		e = "Unauthorized"
+	case 403:
+		e = "Forbidden"
+	case 404:
+		e = "Not Found"
+	case 500, 502, 504:
+		e = "Server Error"
+	case 503:
+		e = "Service Unavailable"
+	default:
+		e = "Request failed"
+	}
+	return fmt.Sprintf("%v - got status code %v while fetching %v", e, err.StatusCode, err.Url)
+}
+
+type FileExistsError struct {
+	Filename string
+}
+
+func (err *FileExistsError) Error() string {
+	return "File '" + err.Filename + "' already exists. See the available options on how to proceed."
+}
+
+type FormatNotFoundError struct {
+	FormatName string
+}
+
+func (err *FormatNotFoundError) Error() string {
+	return "Format " + err.FormatName + " is not available."
+}
+
+type ChapterNotFoundError struct {
+	ChapterNum int
+}
+
+func (err *ChapterNotFoundError) Error() string {
+	return fmt.Sprintf("Chapter %v not found.", err.ChapterNum)
+}