package engine

import (
	"encoding/json"
	"errors"
	"fmt"
	"path/filepath"
	"reflect"
	"regexp"
	"strings"
	"unicode"
	"unicode/utf8"

	"github.com/cdnutter/playlink/internal/store"
	"github.com/cdnutter/playlink/internal/tags"
)

// Naming follows Lidarr's model: an artist folder, an album folder and a
// track format (with a separate format for multi-disc albums), built from
// tokens such as {Artist Name}, {Album Title} and {track:00}.

// An empty ArtistFolder means no artist folder: Album/01 Title.
type NamingConfig struct {
	ArtistFolder    string `json:"artist_folder"`
	AlbumFolder     string `json:"album_folder"`
	TrackFormat     string `json:"track_format"`
	MultiDiscFormat string `json:"multi_disc_format"`
	Colon           string `json:"colon"`   // smart, delete, dash, space_dash, space_dash_space
	Illegal         string `json:"illegal"` // replace or remove
	// Folders give part of a library its own formats, such as soundtracks in
	// "Video Games" named Album/01 Title. Files inside such a folder stay
	// inside it, and other files are never moved into it.
	Folders []FolderNaming `json:"folders"`
}

// FolderNaming is the naming for one folder of a library (relative to its root).
type FolderNaming struct {
	Folder          string `json:"folder"`
	ArtistFolder    string `json:"artist_folder"`
	AlbumFolder     string `json:"album_folder"`
	TrackFormat     string `json:"track_format"`
	MultiDiscFormat string `json:"multi_disc_format"`
}

// formats are the four path formats in effect for one file.
type formats struct{ artist, album, track, multiDisc string }

func (c NamingConfig) formats() formats {
	return formats{c.ArtistFolder, c.AlbumFolder, c.TrackFormat, c.MultiDiscFormat}
}

func (f FolderNaming) formats() formats {
	return formats{f.ArtistFolder, f.AlbumFolder, f.TrackFormat, f.MultiDiscFormat}
}

// folderOf returns the folder rule a library path falls under, if any.
func (c NamingConfig) folderOf(rel string) (FolderNaming, bool) {
	for _, f := range c.Folders {
		if inFolder(rel, f.Folder) {
			return f, true
		}
	}
	return FolderNaming{}, false
}

// inFolder reports whether rel is inside folder (compared case-insensitively).
func inFolder(rel, folder string) bool {
	return strings.HasPrefix(strings.ToLower(rel)+"/", strings.ToLower(folder)+"/") && len(rel) > len(folder)
}

func DefaultNaming() NamingConfig {
	return NamingConfig{
		ArtistFolder:    "{Artist Name}",
		AlbumFolder:     "{Album Title}",
		TrackFormat:     "{track:00} {Track Title}",
		MultiDiscFormat: "{Medium Format} {medium:00}/{track:00} {Track Title}",
		Colon:           "smart",
		Illegal:         "replace",
		Folders:         []FolderNaming{},
	}
}

// Library types. Music is organized Artist/Album/01 Title; soundtracks (games,
// films) Album/01 Title, since their "artist" is often a composer or empty.
const (
	LibraryMusic       = "music"
	LibrarySoundtracks = "soundtracks"
)

// DefaultNamingFor returns the recommended naming for a library type.
func DefaultNamingFor(libraryType string) NamingConfig {
	c := DefaultNaming()
	if libraryType == LibrarySoundtracks {
		c.ArtistFolder = ""
	}
	return c
}

// SoundtrackFolder is the suggested folder rule for game and film soundtracks.
var SoundtrackFolder = FolderNaming{Folder: "Video Games", AlbumFolder: "{Album Title}",
	TrackFormat: "{track:00} {Track Title}", MultiDiscFormat: "{Medium Format} {medium:00}/{track:00} {Track Title}"}

// NamingPresets are offered in the UI.
var NamingPresets = []struct {
	Name   string       `json:"name"`
	Config NamingConfig `json:"config"`
}{
	{"Artist/Album/01 Title", DefaultNaming()},
	{"Artist/Album (Year)/01 - Title", NamingConfig{ArtistFolder: "{Artist Name}", AlbumFolder: "{Album Title} ({Release Year})",
		TrackFormat: "{track:00} - {Track Title}", MultiDiscFormat: "{Medium Format} {medium:00}/{track:00} - {Track Title}", Colon: "smart", Illegal: "replace"}},
	{"Artist/Album/Artist - Album - 01 - Title", NamingConfig{ArtistFolder: "{Artist Name}", AlbumFolder: "{Album Title}",
		TrackFormat:     "{Artist Name} - {Album Title} - {track:00} - {Track Title}",
		MultiDiscFormat: "{Artist Name} - {Album Title} - {medium:00}-{track:00} - {Track Title}", Colon: "smart", Illegal: "replace"}},
	{"Artist/Album/1-01 Title (disc in name)", NamingConfig{ArtistFolder: "{Artist Name}", AlbumFolder: "{Album Title}",
		TrackFormat: "{track:00} {Track Title}", MultiDiscFormat: "{medium:0}-{track:00} {Track Title}", Colon: "smart", Illegal: "replace"}},
	{"Album/01 Title (no artist folder)", NamingConfig{AlbumFolder: "{Album Title}",
		TrackFormat: "{track:00} {Track Title}", MultiDiscFormat: "{Medium Format} {medium:00}/{track:00} {Track Title}", Colon: "smart", Illegal: "replace"}},
}

// NamingOf returns a pair's naming, converting the settings of earlier
// versions (one path pattern plus a disc style) when none is stored yet.
func NamingOf(p store.Pair) NamingConfig {
	c := DefaultNamingFor(p.LibraryType)
	if len(p.OrganizeConfig) > 0 && string(p.OrganizeConfig) != "{}" {
		if stored, err := parseNaming(p.OrganizeConfig); err == nil {
			return stored
		}
	}
	old := map[string]string{"{artist}": "{Artist Name}", "{album}": "{Album Title}", "{track}": "{track:00}", "{title}": "{Track Title}",
		"{year}": "{Release Year}", "{track_artist}": "{Track ArtistName}", "{genre}": "{Genre}"}
	medium := "{medium:00}"
	if p.OrganizeDiscDigits == 1 {
		medium = "{medium:0}"
	}
	old["{disc}"] = medium
	if parts := strings.Split(p.OrganizeTemplate, "/"); len(parts) == 3 {
		conv := func(s string) string {
			for k, v := range old {
				s = strings.ReplaceAll(s, k, v)
			}
			return s
		}
		c.ArtistFolder, c.AlbumFolder, c.TrackFormat = conv(parts[0]), conv(parts[1]), conv(parts[2])
	}
	switch p.OrganizeMultiDisc {
	case "prefix":
		c.MultiDiscFormat = strings.Replace(c.TrackFormat, "{track:00}", medium+"-{track:00}", 1)
	case "none":
		c.MultiDiscFormat = c.TrackFormat
	default:
		c.MultiDiscFormat = "{Medium Format} " + medium + "/" + c.TrackFormat
	}
	return c
}

// parseNaming reads stored settings. Fields missing from the JSON take the
// defaults; an artist folder that is present but empty stays empty.
func parseNaming(raw []byte) (NamingConfig, error) {
	c := DefaultNaming() // missing keys: only very old or hand-made settings
	if err := json.Unmarshal(raw, &c); err != nil {
		return c, err
	}
	fill(&c, DefaultNaming())
	return c, nil
}

// ChangeLibraryType switches a pair's naming to the new type's recommended
// naming when it still uses the old type's, so custom naming is kept.
func ChangeLibraryType(old store.Pair, p *store.Pair) {
	if old.ID == 0 || old.LibraryType == p.LibraryType {
		return
	}
	if reflect.DeepEqual(NamingOf(*p), DefaultNamingFor(old.LibraryType)) {
		p.OrganizeConfig = nil
	}
}

func fill(c *NamingConfig, d NamingConfig) {
	c.ArtistFolder = strings.TrimSpace(c.ArtistFolder)
	if c.Folders == nil {
		c.Folders = []FolderNaming{}
	}
	for i := range c.Folders {
		f := &c.Folders[i]
		f.Folder = strings.Trim(strings.TrimSpace(f.Folder), "/")
		f.ArtistFolder = strings.TrimSpace(f.ArtistFolder)
		if strings.TrimSpace(f.MultiDiscFormat) == "" {
			f.MultiDiscFormat = "{Medium Format} {medium:00}/" + f.TrackFormat
		}
	}
	if strings.TrimSpace(c.AlbumFolder) == "" {
		c.AlbumFolder = d.AlbumFolder
	}
	if strings.TrimSpace(c.TrackFormat) == "" {
		c.TrackFormat = d.TrackFormat
	}
	if strings.TrimSpace(c.MultiDiscFormat) == "" {
		c.MultiDiscFormat = d.MultiDiscFormat
	}
	if c.Colon == "" {
		c.Colon = d.Colon
	}
	if c.Illegal == "" {
		c.Illegal = d.Illegal
	}
}

// ---- tokens ----

var (
	tokenPat  = regexp.MustCompile(`\{([^{}]+)\}`)
	numberTok = regexp.MustCompile(`(?i)^(track|medium):(0+)$`)
)

// TokenHelp documents the tokens (with example values) for the UI.
var TokenHelp = [][2]string{
	{"{Artist Name}", "Avenged Sevenfold"}, {"{Artist NameThe}", "Beatles, The"}, {"{Artist CleanName}", "ACDC"},
	{"{Artist NameFirstCharacter}", "A"}, {"{Album Title}", "Nightmare"}, {"{Album TitleThe}", "White Album, The"},
	{"{Album CleanTitle}", "Nightmare"}, {"{Release Year}", "2010"}, {"{track:00}", "01"}, {"{track:0}", "1"},
	{"{medium:00}", "01"}, {"{medium:0}", "1"}, {"{Medium Format}", "Disc"}, {"{Track Title}", "Nightmare"},
	{"{Track CleanTitle}", "Nightmare"}, {"{Track ArtistName}", "Avenged Sevenfold"}, {"{Genre}", "Metal"},
}

var knownTokens = map[string]bool{
	"artistname": true, "artistnamethe": true, "artistcleanname": true, "artistnamefirstcharacter": true,
	"albumtitle": true, "albumtitlethe": true, "albumcleantitle": true, "releaseyear": true,
	"tracktitle": true, "trackcleantitle": true, "trackartistname": true, "mediumformat": true, "genre": true,
}

// tokenKey normalizes "Artist Name", "Artist.Name" and "ARTIST_NAME".
func tokenKey(t string) string {
	var b strings.Builder
	for _, r := range strings.ToLower(t) {
		if unicode.IsLetter(r) || unicode.IsDigit(r) {
			b.WriteRune(r)
		}
	}
	return b.String()
}

// styleOf returns the word separator and case a token is written in.
func styleOf(t string) (sep string, cased string) {
	sep = " "
	switch {
	case strings.Contains(t, "."):
		sep = "."
	case strings.Contains(t, "_"):
		sep = "_"
	}
	letters := strings.Map(func(r rune) rune {
		if unicode.IsLetter(r) {
			return r
		}
		return -1
	}, t)
	switch {
	case letters != "" && letters == strings.ToUpper(letters):
		cased = "upper"
	case letters != "" && letters == strings.ToLower(letters):
		cased = "lower"
	}
	return
}

// ValidateNaming checks the formats.
func ValidateNaming(c NamingConfig) error {
	if err := checkFormats("", c.formats()); err != nil {
		return err
	}
	seen := map[string]bool{}
	for _, f := range c.Folders {
		label := fmt.Sprintf("Folder %q", f.Folder)
		switch {
		case f.Folder == "":
			return errors.New("a folder rule has no folder")
		case strings.Contains(f.Folder, "\\") || strings.HasPrefix(f.Folder, "/") || filepath.Clean(f.Folder) != f.Folder ||
			f.Folder == "." || strings.HasPrefix(f.Folder, ".."):
			return fmt.Errorf("%s must be a folder inside the library, like Video Games", label)
		case strings.HasPrefix(filepath.Base(f.Folder), "."):
			return fmt.Errorf("%s: hidden folders can't have naming rules", label)
		case seen[strings.ToLower(f.Folder)]:
			return fmt.Errorf("%s is listed twice", label)
		}
		seen[strings.ToLower(f.Folder)] = true
		for _, o := range c.Folders {
			if inFolder(f.Folder, o.Folder) {
				return fmt.Errorf("%s is inside %q; folder rules can't be nested", label, o.Folder)
			}
		}
		if err := checkFormats(label+": ", f.formats()); err != nil {
			return err
		}
	}
	switch c.Colon {
	case "smart", "delete", "dash", "space_dash", "space_dash_space":
	default:
		return errors.New("unknown colon replacement")
	}
	if c.Illegal != "replace" && c.Illegal != "remove" {
		return errors.New("illegal characters must be replace or remove")
	}
	return nil
}

// checkFormats validates one set of formats. The artist folder may be empty.
func checkFormats(prefix string, f formats) error {
	if f.artist != "" {
		if err := checkFormat(prefix+"Artist folder format", f.artist, true); err != nil {
			return err
		}
	}
	if err := checkFormat(prefix+"Album folder format", f.album, true); err != nil {
		return err
	}
	for _, t := range []struct{ label, v string }{{"Track format", f.track}, {"Multi-disc track format", f.multiDisc}} {
		if err := checkFormat(prefix+t.label, t.v, false); err != nil {
			return err
		}
		if !strings.Contains(tokenKeys(t.v), "|tracktitle|") && !strings.Contains(tokenKeys(t.v), "|trackcleantitle|") {
			return fmt.Errorf("%s%s must contain {Track Title}", prefix, t.label)
		}
	}
	return nil
}

func checkFormat(label, f string, folder bool) error {
	if strings.TrimSpace(f) == "" {
		return fmt.Errorf("%s is empty", label)
	}
	if strings.Contains(f, "..") || strings.Contains(f, "\\") || strings.HasPrefix(f, "/") || strings.HasSuffix(f, "/") {
		return fmt.Errorf("%s must be a relative name without .. or backslashes", label)
	}
	if folder && strings.Contains(f, "/") {
		return fmt.Errorf("%s must be a single folder name (no /)", label)
	}
	for _, m := range tokenPat.FindAllStringSubmatch(f, -1) {
		if numberTok.MatchString(m[1]) {
			continue
		}
		if !knownTokens[tokenKey(m[1])] {
			return fmt.Errorf("%s: unknown token {%s}", label, m[1])
		}
	}
	if strings.Count(f, "{") != strings.Count(f, "}") {
		return fmt.Errorf("%s has an unclosed {", label)
	}
	return nil
}

func tokenKeys(f string) string {
	var b strings.Builder
	b.WriteString("|")
	for _, m := range tokenPat.FindAllStringSubmatch(f, -1) {
		b.WriteString(tokenKey(m[1]) + "|")
	}
	return b.String()
}

// ---- value transforms ----

var articles = []string{"The ", "A ", "An "}

// nameThe moves a leading article to the end: "The Beatles" -> "Beatles, The".
func nameThe(s string) string {
	for _, a := range articles {
		if len(s) > len(a) && strings.EqualFold(s[:len(a)], a) {
			return strings.TrimSpace(s[len(a):]) + ", " + strings.TrimSpace(s[:len(a)])
		}
	}
	return s
}

// cleanName keeps letters, digits and spaces: "AC/DC" -> "ACDC".
func cleanName(s string) string {
	s = strings.Map(func(r rune) rune {
		switch {
		case unicode.IsLetter(r), unicode.IsDigit(r), r == ' ':
			return r
		case r == '&':
			return r
		}
		return -1
	}, s)
	return strings.TrimSpace(spaces.ReplaceAllString(s, " "))
}

func firstChar(s string) string {
	for _, r := range nameThe(s) {
		if unicode.IsLetter(r) {
			return string(unicode.ToUpper(r))
		}
		if unicode.IsDigit(r) {
			return "#"
		}
	}
	return ""
}

func colonReplace(s, mode string) string {
	switch mode {
	case "delete":
		return strings.ReplaceAll(s, ":", "")
	case "dash":
		return strings.ReplaceAll(s, ":", "-")
	case "space_dash":
		return strings.ReplaceAll(s, ":", " -")
	case "space_dash_space":
		return strings.ReplaceAll(strings.ReplaceAll(s, " :", ":"), ":", " - ")
	}
	// smart: "Title: Sub" -> "Title - Sub", "10:30" -> "10-30"
	s = strings.ReplaceAll(s, ": ", " - ")
	return strings.ReplaceAll(s, ":", "-")
}

var (
	illegalReplace = strings.NewReplacer("/", "-", "\\", "-", "|", "-", "*", "-", "?", "", "\"", "'", "<", "", ">", "")
	illegalRemove  = strings.NewReplacer("/", "", "\\", "", "|", "", "*", "", "?", "", "\"", "", "<", "", ">", "")
)

// safeValue makes a tag value safe inside a file or folder name.
func safeValue(s string, c NamingConfig) string {
	s = colonReplace(s, c.Colon)
	if c.Illegal == "remove" {
		s = illegalRemove.Replace(s)
	} else {
		s = illegalReplace.Replace(s)
	}
	return strings.Map(func(r rune) rune {
		if unicode.IsControl(r) {
			return -1
		}
		return r
	}, s)
}

var emptyBrackets = regexp.MustCompile(`\(\s*\)|\[\s*\]|\{\s*\}`)

// finishComponent tidies a rendered name: empty brackets and separators left
// by missing optional values are removed, and leading dots (hidden files)
// and trailing dots/spaces (invalid on Windows) are trimmed.
func finishComponent(s string) string {
	s = emptyBrackets.ReplaceAllString(s, "")
	s = spaces.ReplaceAllString(s, " ")
	for _, dup := range []string{" - - ", " -  - "} {
		for strings.Contains(s, dup) {
			s = strings.ReplaceAll(s, dup, " - ")
		}
	}
	s = strings.Trim(s, " -._")
	s = strings.TrimLeft(s, ".")
	for len(s) > maxComponent {
		_, size := utf8.DecodeLastRuneInString(s)
		s = strings.TrimRight(s[:len(s)-size], ". ")
	}
	return s
}

// songValues are the raw values tokens draw from.
type songValues struct {
	artist, trackArtist, album, title, year, genre string
	track, disc, discTotal                         int
}

func valuesOf(f map[string]string) songValues {
	v := songValues{
		artist: strings.TrimSpace(f[tags.AlbumArtist]), trackArtist: strings.TrimSpace(f[tags.Artist]),
		album: strings.TrimSpace(f[tags.Album]), title: strings.TrimSpace(f[tags.Title]), genre: strings.TrimSpace(f[tags.Genre]),
		track: leadingNumber(f[tags.Track]), disc: leadingNumber(f[tags.Disc]), discTotal: leadingNumber(f[tags.DiscTotal]),
	}
	if v.artist == "" {
		v.artist = v.trackArtist
	}
	if d := strings.TrimSpace(f[tags.Date]); len(d) >= 4 && leadingNumber(d[:4]) > 0 {
		v.year = d[:4]
	}
	return v
}

func (v songValues) multiDisc() bool { return v.discTotal > 1 || v.disc > 1 }

// renderPath builds the organized relative path of a song at rel. Songs in
// a folder with its own naming stay in that folder. It returns why the song
// can't be renamed instead when a tag is missing or the new path would enter
// a folder that has its own naming.
func renderPath(c NamingConfig, rel string, f map[string]string) (string, string) {
	ext := filepath.Ext(rel)
	if rule, ok := c.folderOf(rel); ok {
		to, why := renderFormats(c, rule.formats(), ext, f)
		if why != "" {
			return "", why
		}
		// Keep the folder as it is spelled on disk.
		return filepath.Join(rel[:len(rule.Folder)], to), ""
	}
	to, why := renderFormats(c, c.formats(), ext, f)
	if why != "" {
		return "", why
	}
	for _, rule := range c.Folders {
		if inFolder(to, rule.Folder) {
			return "", "would move into " + rule.Folder + ", which has its own naming"
		}
	}
	return to, ""
}

var artistTokens = []string{"|artistname|", "|artistnamethe|", "|artistcleanname|", "|artistnamefirstcharacter|"}

func renderFormats(c NamingConfig, fm formats, ext string, f map[string]string) (string, string) {
	v := valuesOf(f)
	track := fm.track
	if v.multiDisc() {
		track = fm.multiDisc
	}
	used := tokenKeys(fm.artist + fm.album + track)
	for _, t := range artistTokens {
		if v.artist == "" && strings.Contains(used, t) {
			return "", "missing artist or album artist tag"
		}
	}
	if v.album == "" {
		return "", "missing album tag"
	}
	if v.title == "" {
		return "", "missing title tag"
	}
	var parts []string
	for _, f := range []string{fm.artist, fm.album, track} {
		if f == "" {
			continue // no artist folder
		}
		for _, part := range strings.Split(f, "/") {
			out := tokenPat.ReplaceAllStringFunc(part, func(tok string) string { return renderToken(tok[1:len(tok)-1], v, c) })
			out = finishComponent(out)
			if out == "" {
				return "", "missing tags for " + part
			}
			parts = append(parts, out)
		}
	}
	return filepath.Join(parts...) + strings.ToLower(ext), ""
}

func renderToken(t string, v songValues, c NamingConfig) string {
	if m := numberTok.FindStringSubmatch(t); m != nil {
		n := v.track
		if strings.EqualFold(m[1], "medium") {
			n = v.disc
			if n == 0 {
				n = 1
			}
		}
		if n <= 0 {
			return ""
		}
		width := len(m[2])
		if strings.EqualFold(m[1], "track") && n >= 100 && width < 3 {
			width = 3
		}
		return fmt.Sprintf("%0*d", width, n)
	}
	var val string
	switch tokenKey(t) {
	case "artistname":
		val = v.artist
	case "artistnamethe":
		val = nameThe(v.artist)
	case "artistcleanname":
		val = cleanName(v.artist)
	case "artistnamefirstcharacter":
		val = firstChar(v.artist)
	case "albumtitle":
		val = v.album
	case "albumtitlethe":
		val = nameThe(v.album)
	case "albumcleantitle":
		val = cleanName(v.album)
	case "releaseyear":
		val = v.year
	case "tracktitle":
		val = v.title
	case "trackcleantitle":
		val = cleanName(v.title)
	case "trackartistname":
		val = v.trackArtist
	case "mediumformat":
		val = "Disc"
	case "genre":
		val = v.genre
	}
	val = safeValue(val, c)
	sep, cased := styleOf(t)
	if sep != " " {
		val = strings.ReplaceAll(val, " ", sep)
	}
	switch cased {
	case "upper":
		val = strings.ToUpper(val)
	case "lower":
		val = strings.ToLower(val)
	}
	return val
}

// NamingExample is one sample rendering for the settings page.
type NamingExample struct {
	Label string `json:"label"`
	Path  string `json:"path"`
}

// NamingExamples renders sample songs with a naming config, using exactly
// the code that renames real files.
func NamingExamples(c NamingConfig) []NamingExample {
	samples := []struct {
		label, ext string
		f          map[string]string
	}{
		{"Album track", ".flac", map[string]string{tags.Artist: "Avenged Sevenfold", tags.Album: "Nightmare", tags.Title: "Nightmare",
			tags.Track: "1", tags.Date: "2010", tags.Genre: "Metal"}},
		{"Multi-disc album, disc 1", ".flac", map[string]string{tags.Artist: "The Beatles", tags.Album: "The Beatles (White Album)",
			tags.Title: "Back in the U.S.S.R.", tags.Track: "1", tags.Disc: "1", tags.DiscTotal: "2", tags.Date: "1968"}},
		{"Multi-disc album, disc 2", ".flac", map[string]string{tags.Artist: "The Beatles", tags.Album: "The Beatles (White Album)",
			tags.Title: "Birthday", tags.Track: "1", tags.Disc: "2", tags.DiscTotal: "2", tags.Date: "1968"}},
		{"Colon and slash in names", ".mp3", map[string]string{tags.Artist: "AC/DC", tags.Album: "Who Made Who", tags.Title: "Hells Bells: Live",
			tags.Track: "7", tags.Date: "1986"}},
	}
	out := []NamingExample{}
	add := func(label, rel string, f map[string]string) {
		p, why := renderPath(c, rel, f)
		if why != "" {
			p = "(skipped: " + why + ")"
		}
		out = append(out, NamingExample{Label: label, Path: p})
	}
	for _, s := range samples {
		add(s.label, "x"+s.ext, s.f)
	}
	for _, rule := range c.Folders {
		add("In "+rule.Folder, rule.Folder+"/x.flac", map[string]string{tags.Artist: "Koji Kondo", tags.Album: "Super Mario Galaxy",
			tags.Title: "Gusty Garden Galaxy", tags.Track: "3", tags.Date: "2007"})
	}
	return out
}