package importer

import (
	"context"
	"errors"
	"io/fs"
	"os"
	"path/filepath"
	"sort"
	"strings"

	"github.com/dhowden/tag"

	"git.fabledsword.com/bvandeusen/minstrel/internal/acoustid"
	"git.fabledsword.com/bvandeusen/minstrel/internal/library"
)

// Printer says which MusicBrainz recordings a file's audio is. ErrNoPrints:
// it cannot say for any file (AcoustID is not set up, or not answering), so
// the check rests on lengths and tags.
type Printer interface {
	Recordings(ctx context.Context, path string) ([]string, error)
}

// ErrNoPrints: fingerprints are not available for this download.
var ErrNoPrints = errors.New("importer: fingerprints are not available")

// AcoustIDPrinter fingerprints with fpcalc and asks AcoustID, under the
// operator's settings (key, minimum score). Each call reads the settings, so
// a change takes effect on the next file.
type AcoustIDPrinter struct {
	Settings interface {
		Get() library.AcoustIDSettings
	}
	Client *acoustid.Client
}

// Recordings is every recording AcoustID gives at or above the minimum score:
// one audio can be several recordings (the album track and the single).
func (p *AcoustIDPrinter) Recordings(ctx context.Context, path string) ([]string, error) {
	s := p.Settings.Get()
	if !s.Ready() || p.Client == nil {
		return nil, ErrNoPrints
	}
	fp, dur, err := library.LookupFingerprint(ctx, path)
	if err != nil {
		if library.IsInconclusive(err) {
			return nil, ErrNoPrints
		}
		return nil, nil // fpcalc rejected the file: no evidence either way
	}
	cands, err := p.Client.Lookup(ctx, s.APIKey, fp, dur)
	switch {
	case errors.Is(err, acoustid.ErrInvalidKey), errors.Is(err, acoustid.ErrUnavailable):
		return nil, ErrNoPrints
	case err != nil:
		return nil, nil
	}
	var out []string
	for _, c := range cands {
		if c.Score >= float64(s.MinScore) && c.ID != "" {
			out = append(out, c.ID)
		}
	}
	return out, nil
}

// formatRank picks which format's files are the album when a download holds
// more than one (a FLAC folder and an MP3 folder): the most files, then the
// better format.
var formatRank = map[string]int{".flac": 6, ".wav": 5, ".m4a": 4, ".opus": 3, ".ogg": 2, ".mp3": 1, ".aac": 0}

// audioFiles lists the audio files under root (a folder, or one file), in
// the one format that is the album. Dot-named files and folders are skipped:
// they are partial downloads, OS litter or Minstrel's own temp files.
func audioFiles(root string) ([]string, error) {
	info, err := os.Stat(root)
	if err != nil {
		return nil, err
	}
	if !info.IsDir() {
		if library.IsAudioFile(root) {
			return []string{root}, nil
		}
		return nil, nil
	}
	byExt := map[string][]string{}
	err = filepath.WalkDir(root, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if strings.HasPrefix(d.Name(), ".") && path != root {
			if d.IsDir() {
				return filepath.SkipDir
			}
			return nil
		}
		if !d.IsDir() && library.IsAudioFile(path) {
			ext := strings.ToLower(filepath.Ext(path))
			byExt[ext] = append(byExt[ext], path)
		}
		return nil
	})
	if err != nil {
		return nil, err
	}
	best := ""
	for ext, paths := range byExt {
		if best == "" || len(paths) > len(byExt[best]) ||
			(len(paths) == len(byExt[best]) && formatRank[ext] > formatRank[best]) {
			best = ext
		}
	}
	out := byExt[best]
	sort.Strings(out)
	return out, nil
}

// readFile reads what one file's tags and length say. A file whose tags
// cannot be read still counts, by its length and name.
func readFile(ctx context.Context, root, path string) File {
	f := File{Path: path, Rel: rel(root, path), Video: len(library.SourceMarkersFor(path)) > 0}
	if ms, err := library.ProbeDurationMs(ctx, path); err == nil {
		f.LengthMs = int(ms)
	}
	h, err := os.Open(path)
	if err != nil {
		return f
	}
	defer func() { _ = h.Close() }()
	m, err := tag.ReadFrom(h)
	if err != nil {
		return f
	}
	f.Title, f.Artist, f.AlbumArtist, f.Album = m.Title(), m.Artist(), m.AlbumArtist(), m.Album()
	f.Track, f.Disc = library.ReadTrackAndDisc(m)
	ids := library.ReadTagMBIDs(m)
	f.GroupMBID, f.ReleaseMBID, f.RecordingMBID = ids.ReleaseGroup, ids.Release, ids.Recording
	return f
}

func rel(root, path string) string {
	if r, err := filepath.Rel(root, path); err == nil && r != "." {
		return r
	}
	return filepath.Base(path)
}

// inspect reads every audio file under root and asks the printer about each.
// fingerprinted reports whether the printer answered at all.
func inspect(ctx context.Context, root string, p Printer) (files []File, fingerprinted bool, err error) {
	paths, err := audioFiles(root)
	if err != nil {
		return nil, false, err
	}
	fingerprinted = p != nil
	for _, path := range paths {
		if ctx.Err() != nil {
			return nil, false, ctx.Err()
		}
		f := readFile(ctx, root, path)
		if fingerprinted && len(paths) <= maxFiles {
			recs, err := p.Recordings(ctx, path)
			if errors.Is(err, ErrNoPrints) {
				fingerprinted = false
				for i := range files {
					files[i].Recordings = nil
				}
			} else {
				f.Recordings = recs
			}
		}
		files = append(files, f)
	}
	return files, fingerprinted, nil
}