package main

import (
	"errors"
	"fmt"
	"io"
	"io/fs"
	"log"
	"os"
	"path"
	"path/filepath"
	"slices"
	"strings"

	"github.com/gabriel-vasile/mimetype"
	"github.com/pelletier/go-toml/v2"
)

type Config struct {
	Paths []string
}

// Define a map of MIME types to their correct extensions.
var conversionMap = map[string][]string{
	"image/png":              {".png"},
	"image/vnd.mozilla.apng": {".png"},
	"image/jpeg":             {".jpg", ".jpeg"},
	"image/webp":             {".webp"},
	"video/mp4":              {".mp4"},
	"video/quicktime":        {".mp4"},
	"video/3gpp":             {".3gp", ".3gpp", ".mp4"},
	"video/x-m4v":            {".m4v", ".mp4"},
	"video/webm":             {".webm"},
	"video/x-matroska":       {".mkv"},
	"image/gif":              {".gif"},
}

var suffixesToCheck []string

func loadConfiguration() (*Config, error) {
	dir, err := os.UserConfigDir()
	if err != nil {
		return nil, err
	}

	configFilePath := path.Join(dir, "justanyone", "fix-mime-types", "config.toml")
	_, err = os.Stat(configFilePath)
	if err != nil {
		// If it's an error that is not for file not existing, send it upwards
		if !errors.Is(err, os.ErrNotExist) {
			return nil, err
		}

		// Otherwise, create the parent directories
		if err := os.MkdirAll(filepath.Dir(configFilePath), 0770); err != nil {
			return nil, err
		}

		// Marshal a default object
		bytes, _ := toml.Marshal(&Config{Paths: []string{}})

		file, err := os.Create(configFilePath)
		if err != nil {
			return nil, err
		}
		defer file.Close()
		file.Write(bytes)
	}

	file, err := os.Open(configFilePath)
	if err != nil {
		return nil, err
	}

	bytes, err := io.ReadAll(file)
	if err != nil {
		return nil, err
	}

	var config Config
	err = toml.Unmarshal(bytes, &config)
	if err != nil {
		return nil, err
	}
	return &config, nil
}

func loadSuffixes() {
	for _, extensions := range conversionMap {
		// Only add unique extensions to the suffixesToCheck list.
		for _, ext := range extensions {
			if !slices.Contains(suffixesToCheck, ext) {
				suffixesToCheck = append(suffixesToCheck, ext)
			}
		}
	}
}

func main() {
	loadSuffixes()
	config, err := loadConfiguration()
	if err != nil {
		log.Fatal("Failed to load configuration:", err)
	}

	if len(config.Paths) == 0 {
		fmt.Println("Warning: you have no configured directory paths")
	}

	for _, directory := range config.Paths {
		fixExtensionsInDirectory(directory)
	}
}

// This function returns true if the entry is a regular file and has an extension that is in the suffixesToCheck list.
func shouldEntryBeChecked(entry fs.DirEntry) bool {
	if !entry.Type().IsRegular() {
		return false
	}
	for _, suffix := range suffixesToCheck {
		if strings.HasSuffix(entry.Name(), suffix) {
			return true
		}
	}
	return false
}

func getFileMimeType(pathToFile string) *mimetype.MIME {
	mimeType, err := mimetype.DetectFile(pathToFile)
	if err != nil {
		panic(err)
	}
	return mimeType
}

func changeFileExtension(originalPath string, newExtension string) {
	oldExt := filepath.Ext(originalPath)
	newPath := originalPath[0:len(originalPath)-len(oldExt)] + newExtension
	os.Rename(originalPath, newPath)
}

func isFileExtensionExpected(currentExt string, expectedExts []string) bool {
	return slices.Contains(expectedExts, currentExt)
}

func fixExtensionsInDirectory(directory string) {
	entries, err := os.ReadDir(directory)
	if err != nil {
		fmt.Println(err)
		return
	}

	for _, v := range entries {
		if shouldEntryBeChecked(v) {
			path := filepath.Join(directory, v.Name())
			fileExt := filepath.Ext(path)
			mimeType := getFileMimeType(path).String()

			expectedExtensions, ok := conversionMap[mimeType]
			if !ok {
				fmt.Println("File at", path, "has unrecognized MIME type", mimeType)
				continue
			}
			// Check if the file's extension is in the list of expected extensions for its MIME type.
			if !isFileExtensionExpected(fileExt, expectedExtensions) {
				fmt.Println("File at", path, "has MIME", mimeType, "and expects", expectedExtensions, "but got", fileExt)
				changeFileExtension(path, expectedExtensions[0])
			}
		} else if v.IsDir() {
			fixExtensionsInDirectory(path.Join(directory, v.Name()))
		}
	}
}