// Package art finds and prepares album art.
//
// Sources: iTunes, Deezer and MusicBrainz/Cover Art Archive (no key, made
// for album covers), DuckDuckGo images (unofficial endpoint, best effort) and
// Google Custom Search (needs an API key and search engine id). Only square
// images are returned.
//
// Images are fetched by the server, so all fetching goes through a client
// that refuses private, loopback and link-local addresses: a crafted result
// or pasted URL cannot reach the local network.
package art

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"image"
	_ "image/gif"
	_ "image/jpeg"
	_ "image/png"
	"io"
	"net"
	"net/http"
	"net/url"
	"regexp"
	"sort"
	"strings"
	"sync"
	"syscall"
	"time"
)

// Sources.
const (
	ITunes      = "itunes"
	Deezer      = "deezer"
	MusicBrainz = "musicbrainz"
	DuckDuckGo  = "duckduckgo"
	Google      = "google"
)

var AllSources = []string{ITunes, Deezer, MusicBrainz, DuckDuckGo, Google}

// MatchSources are reliable enough for automatic matching.
var MatchSources = []string{ITunes, Deezer, MusicBrainz}

type Result struct {
	Source string `json:"source"`
	Title  string `json:"title"`
	Artist string `json:"artist,omitempty"`
	URL    string `json:"url"`
	Thumb  string `json:"thumb"`
	Width  int    `json:"width"`
	Height int    `json:"height"`
}

type Query struct {
	Artist string `json:"artist"`
	Album  string `json:"album"`
	Text   string `json:"text"` // free-form search for the web engines
}

func (q Query) text() string {
	if strings.TrimSpace(q.Text) != "" {
		return strings.TrimSpace(q.Text)
	}
	return strings.TrimSpace(q.Artist + " " + q.Album)
}

type Config struct {
	Sources   []string
	GoogleKey string
	GoogleCX  string
	MinSize   int
}

// Client talks to the art sources. The base URLs can be pointed at test
// servers.
type Client struct {
	HTTP                                                            *http.Client
	UserAgent                                                       string
	ITunesURL, DeezerURL, MusicBrainzURL, CAAURL, DDGURL, GoogleURL string
}

func New(version string) *Client {
	return &Client{
		HTTP:           SafeHTTPClient(20 * time.Second),
		UserAgent:      "playlink/" + version + " (self-hosted music library tool)",
		ITunesURL:      "https://itunes.apple.com",
		DeezerURL:      "https://api.deezer.com",
		MusicBrainzURL: "https://musicbrainz.org",
		CAAURL:         "https://coverartarchive.org",
		DDGURL:         "https://duckduckgo.com",
		GoogleURL:      "https://www.googleapis.com",
	}
}

// ---- safe fetching ----

var ErrBlockedAddress = errors.New("that address is on a private or local network and is not fetched")

func blockedIP(ip net.IP) bool {
	if ip.IsLoopback() || ip.IsPrivate() || ip.IsLinkLocalUnicast() || ip.IsLinkLocalMulticast() ||
		ip.IsMulticast() || ip.IsUnspecified() || ip.IsInterfaceLocalMulticast() {
		return true
	}
	if v4 := ip.To4(); v4 != nil && v4[0] == 100 && v4[1]&0xc0 == 64 { // 100.64.0.0/10 (CGNAT)
		return true
	}
	return false
}

// SafeHTTPClient refuses to connect to private/local addresses, including
// after redirects and DNS tricks (the check runs on the resolved address).
func SafeHTTPClient(timeout time.Duration) *http.Client {
	dialer := &net.Dialer{Timeout: 10 * time.Second, Control: func(network, address string, _ syscall.RawConn) error {
		host, _, err := net.SplitHostPort(address)
		if err != nil {
			return err
		}
		if ip := net.ParseIP(host); ip == nil || blockedIP(ip) {
			return ErrBlockedAddress
		}
		return nil
	}}
	tr := &http.Transport{Proxy: nil, DialContext: dialer.DialContext, TLSHandshakeTimeout: 10 * time.Second,
		ResponseHeaderTimeout: 15 * time.Second, MaxIdleConns: 10, IdleConnTimeout: 30 * time.Second}
	return &http.Client{Transport: tr, Timeout: timeout, CheckRedirect: func(req *http.Request, via []*http.Request) error {
		if len(via) >= 5 {
			return errors.New("too many redirects")
		}
		if req.URL.Scheme != "http" && req.URL.Scheme != "https" {
			return errors.New("only http and https are fetched")
		}
		return nil
	}}
}

// MaxImageBytes caps a downloaded image.
const MaxImageBytes = 20 << 20

// FetchImage downloads an image URL (http/https only, size capped).
func (c *Client) FetchImage(ctx context.Context, raw string) ([]byte, error) {
	u, err := url.Parse(raw)
	if err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" {
		return nil, errors.New("enter an http or https image address")
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
	if err != nil {
		return nil, err
	}
	req.Header.Set("User-Agent", c.UserAgent)
	req.Header.Set("Accept", "image/*")
	res, err := c.HTTP.Do(req)
	if err != nil {
		return nil, err
	}
	defer res.Body.Close()
	if res.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("the image server answered %s", res.Status)
	}
	if ct := res.Header.Get("Content-Type"); ct != "" && !strings.HasPrefix(ct, "image/") && !strings.HasPrefix(ct, "application/octet-stream") {
		return nil, fmt.Errorf("that address is not an image (%s)", ct)
	}
	b, err := io.ReadAll(io.LimitReader(res.Body, MaxImageBytes+1))
	if err != nil {
		return nil, err
	}
	if len(b) > MaxImageBytes {
		return nil, errors.New("the image is larger than 20 MB")
	}
	return b, nil
}

func (c *Client) getJSON(ctx context.Context, u string, header map[string]string, v any) error {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
	if err != nil {
		return err
	}
	req.Header.Set("User-Agent", c.UserAgent)
	req.Header.Set("Accept", "application/json")
	for k, val := range header {
		req.Header.Set(k, val)
	}
	res, err := c.HTTP.Do(req)
	if err != nil {
		return err
	}
	defer res.Body.Close()
	if res.StatusCode != http.StatusOK {
		return fmt.Errorf("%s", res.Status)
	}
	return json.NewDecoder(io.LimitReader(res.Body, 4<<20)).Decode(v)
}

// ---- search ----

// Square reports whether an image is square: within 0.5% or 2 pixels.
func Square(w, h int) bool {
	if w <= 0 || h <= 0 {
		return false
	}
	d := w - h
	if d < 0 {
		d = -d
	}
	return d <= max(2, max(w, h)/200)
}

// Search queries the enabled sources concurrently and returns square images
// of at least the minimum size, best first. Per-source errors are returned
// separately so one failing source does not hide the others.
func (c *Client) Search(ctx context.Context, q Query, cfg Config) ([]Result, map[string]string) {
	if cfg.MinSize <= 0 {
		cfg.MinSize = 300
	}
	type out struct {
		source string
		res    []Result
		err    error
	}
	ch := make(chan out, len(cfg.Sources))
	var wg sync.WaitGroup
	for _, s := range cfg.Sources {
		var fn func(context.Context, Query, Config) ([]Result, error)
		switch s {
		case ITunes:
			fn = c.itunes
		case Deezer:
			fn = c.deezer
		case MusicBrainz:
			fn = c.musicbrainz
		case DuckDuckGo:
			fn = c.duckduckgo
		case Google:
			if cfg.GoogleKey == "" || cfg.GoogleCX == "" {
				continue
			}
			fn = c.google
		default:
			continue
		}
		wg.Add(1)
		go func(s string, fn func(context.Context, Query, Config) ([]Result, error)) {
			defer wg.Done()
			ctx, cancel := context.WithTimeout(ctx, 25*time.Second)
			defer cancel()
			r, err := fn(ctx, q, cfg)
			ch <- out{s, r, err}
		}(s, fn)
	}
	wg.Wait()
	close(ch)
	errs := map[string]string{}
	seen := map[string]bool{}
	var all []Result
	for o := range ch {
		if o.err != nil {
			errs[o.source] = o.err.Error()
		}
		for _, r := range o.res {
			if seen[r.URL] || !Square(r.Width, r.Height) || min(r.Width, r.Height) < cfg.MinSize {
				continue
			}
			seen[r.URL] = true
			all = append(all, r)
		}
	}
	rank := map[string]int{ITunes: 0, Deezer: 1, MusicBrainz: 2, Google: 3, DuckDuckGo: 4}
	sort.SliceStable(all, func(i, j int) bool {
		if rank[all[i].Source] != rank[all[j].Source] {
			return rank[all[i].Source] < rank[all[j].Source]
		}
		return all[i].Width > all[j].Width
	})
	return all, errs
}

func (c *Client) itunes(ctx context.Context, q Query, _ Config) ([]Result, error) {
	var d struct {
		Results []struct {
			ArtistName     string `json:"artistName"`
			CollectionName string `json:"collectionName"`
			ArtworkURL100  string `json:"artworkUrl100"`
		} `json:"results"`
	}
	u := c.ITunesURL + "/search?" + url.Values{"term": {q.text()}, "entity": {"album"}, "limit": {"25"}}.Encode()
	if err := c.getJSON(ctx, u, nil, &d); err != nil {
		return nil, err
	}
	var out []Result
	for _, r := range d.Results {
		if !strings.Contains(r.ArtworkURL100, "100x100") {
			continue
		}
		// iTunes serves the same artwork at any requested size.
		out = append(out, Result{Source: ITunes, Title: r.CollectionName, Artist: r.ArtistName, Width: 1000, Height: 1000,
			URL: strings.Replace(r.ArtworkURL100, "100x100", "1000x1000", 1), Thumb: strings.Replace(r.ArtworkURL100, "100x100", "300x300", 1)})
	}
	return out, nil
}

func (c *Client) deezer(ctx context.Context, q Query, _ Config) ([]Result, error) {
	query := q.text()
	if q.Artist != "" && q.Album != "" && q.Text == "" {
		query = fmt.Sprintf(`artist:"%s" album:"%s"`, q.Artist, q.Album)
	}
	var d struct {
		Data []struct {
			Title       string `json:"title"`
			CoverXL     string `json:"cover_xl"`
			CoverMedium string `json:"cover_medium"`
			Artist      struct {
				Name string `json:"name"`
			} `json:"artist"`
		} `json:"data"`
	}
	if err := c.getJSON(ctx, c.DeezerURL+"/search/album?"+url.Values{"q": {query}, "limit": {"25"}}.Encode(), nil, &d); err != nil {
		return nil, err
	}
	var out []Result
	for _, r := range d.Data {
		if r.CoverXL == "" {
			continue
		}
		out = append(out, Result{Source: Deezer, Title: r.Title, Artist: r.Artist.Name, URL: r.CoverXL, Thumb: r.CoverMedium, Width: 1000, Height: 1000})
	}
	return out, nil
}

func (c *Client) musicbrainz(ctx context.Context, q Query, cfg Config) ([]Result, error) {
	query := q.text()
	if q.Album != "" && q.Text == "" {
		query = fmt.Sprintf(`releasegroup:"%s"`, strings.ReplaceAll(q.Album, `"`, ""))
		if q.Artist != "" {
			query += fmt.Sprintf(` AND artist:"%s"`, strings.ReplaceAll(q.Artist, `"`, ""))
		}
	}
	var d struct {
		ReleaseGroups []struct {
			ID           string `json:"id"`
			Title        string `json:"title"`
			ArtistCredit []struct {
				Name string `json:"name"`
			} `json:"artist-credit"`
		} `json:"release-groups"`
	}
	u := c.MusicBrainzURL + "/ws/2/release-group/?" + url.Values{"query": {query}, "fmt": {"json"}, "limit": {"8"}}.Encode()
	if err := c.getJSON(ctx, u, nil, &d); err != nil {
		return nil, err
	}
	// The Cover Art Archive does not report sizes: check each front cover's
	// thumbnail to keep only square ones (and skip groups without art).
	var mu sync.Mutex
	var wg sync.WaitGroup
	var out []Result
	for _, rg := range d.ReleaseGroups {
		artist := ""
		if len(rg.ArtistCredit) > 0 {
			artist = rg.ArtistCredit[0].Name
		}
		wg.Add(1)
		go func(id, title, artist string) {
			defer wg.Done()
			thumb := c.CAAURL + "/release-group/" + id + "/front-250"
			w, h, err := c.imageSize(ctx, thumb)
			if err != nil || !Square(w, h) {
				return
			}
			mu.Lock()
			out = append(out, Result{Source: MusicBrainz, Title: title, Artist: artist, URL: c.CAAURL + "/release-group/" + id + "/front-1200",
				Thumb: thumb, Width: 1200, Height: 1200})
			mu.Unlock()
		}(rg.ID, rg.Title, artist)
	}
	wg.Wait()
	return out, nil
}

// imageSize reads just enough of an image to learn its dimensions.
func (c *Client) imageSize(ctx context.Context, u string) (int, int, error) {
	b, err := c.FetchImage(ctx, u)
	if err != nil {
		return 0, 0, err
	}
	cfg, _, err := image.DecodeConfig(bytes.NewReader(b))
	return cfg.Width, cfg.Height, err
}

var vqdRe = regexp.MustCompile(`vqd=["']?([0-9-]+)`)

func (c *Client) duckduckgo(ctx context.Context, q Query, _ Config) ([]Result, error) {
	text := q.Text
	if strings.TrimSpace(text) == "" {
		text = q.text() + " album cover"
	}
	// DuckDuckGo has no official image API: a page request yields the token
	// its own image search uses. This can break if they change their site.
	req, _ := http.NewRequestWithContext(ctx, http.MethodGet, c.DDGURL+"/?"+url.Values{"q": {text}, "iax": {"images"}, "ia": {"images"}}.Encode(), nil)
	req.Header.Set("User-Agent", "Mozilla/5.0 (X11; Linux x86_64) playlink")
	res, err := c.HTTP.Do(req)
	if err != nil {
		return nil, err
	}
	page, _ := io.ReadAll(io.LimitReader(res.Body, 2<<20))
	res.Body.Close()
	m := vqdRe.FindSubmatch(page)
	if m == nil {
		return nil, errors.New("DuckDuckGo did not return a search token (their site may have changed)")
	}
	var d struct {
		Results []struct {
			Title     string `json:"title"`
			Image     string `json:"image"`
			Thumbnail string `json:"thumbnail"`
			Width     int    `json:"width"`
			Height    int    `json:"height"`
		} `json:"results"`
	}
	u := c.DDGURL + "/i.js?" + url.Values{"q": {text}, "vqd": {string(m[1])}, "o": {"json"}, "l": {"us-en"}, "f": {",,,,,layout:Square"}, "p": {"1"}}.Encode()
	if err := c.getJSON(ctx, u, map[string]string{"Referer": c.DDGURL + "/", "User-Agent": "Mozilla/5.0 (X11; Linux x86_64) playlink"}, &d); err != nil {
		return nil, err
	}
	var out []Result
	for _, r := range d.Results {
		out = append(out, Result{Source: DuckDuckGo, Title: r.Title, URL: r.Image, Thumb: r.Thumbnail, Width: r.Width, Height: r.Height})
	}
	return out, nil
}

func (c *Client) google(ctx context.Context, q Query, cfg Config) ([]Result, error) {
	text := q.Text
	if strings.TrimSpace(text) == "" {
		text = q.text() + " album cover"
	}
	var d struct {
		Items []struct {
			Title string `json:"title"`
			Link  string `json:"link"`
			Image struct {
				Width         int    `json:"width"`
				Height        int    `json:"height"`
				ThumbnailLink string `json:"thumbnailLink"`
			} `json:"image"`
		} `json:"items"`
		Error *struct {
			Message string `json:"message"`
		} `json:"error"`
	}
	u := c.GoogleURL + "/customsearch/v1?" + url.Values{"key": {cfg.GoogleKey}, "cx": {cfg.GoogleCX}, "q": {text},
		"searchType": {"image"}, "num": {"10"}, "imgSize": {"large"}}.Encode()
	if err := c.getJSON(ctx, u, nil, &d); err != nil {
		return nil, fmt.Errorf("Google: %v (check the API key and search engine id)", err)
	}
	var out []Result
	for _, it := range d.Items {
		out = append(out, Result{Source: Google, Title: it.Title, URL: it.Link, Thumb: it.Image.ThumbnailLink, Width: it.Image.Width, Height: it.Image.Height})
	}
	return out, nil
}