package transfer

import (
	"context"
	"fmt"
	"strings"
	"sync"
	"time"

	"navimigrate/internal/model"
)

type Writer interface {
	CreatePlaylist(ctx context.Context, name string) (string, error)
	AddTracksToPlaylist(ctx context.Context, playlistID string, trackIDs []string) error
}

type TrackMatcher interface {
	MatchTrack(ctx context.Context, src model.Track) model.MatchedTrack
}

type Config struct {
	DryRun      bool
	Concurrency int
	Progress    ProgressFunc
}

type ProgressFunc func(message string)

func Run(ctx context.Context, cfg Config, writer Writer, matcher TrackMatcher, playlists []model.Playlist) (model.TransferReport, error) {
	rep := model.TransferReport{
		StartedAt: time.Now().UTC().Format(time.RFC3339),
		DryRun:    cfg.DryRun,
	}

	totalPlaylists := len(playlists)
	for i, pl := range playlists {
		result := processPlaylist(ctx, cfg, writer, matcher, pl, i+1, totalPlaylists)
		rep.Results = append(rep.Results, result)
		notify(cfg, fmt.Sprintf(
			"Transfer %d/%d done: %s | matched %d/%d | added %d | unmatched %d",
			i+1,
			totalPlaylists,
			shortName(pl.Name),
			result.MatchedTracks,
			result.TotalTracks,
			result.AddedTracks,
			len(result.Unmatched),
		))
	}

	rep.EndedAt = time.Now().UTC().Format(time.RFC3339)
	notify(cfg, "Transfer processing complete")
	return rep, nil
}

func processPlaylist(ctx context.Context, cfg Config, writer Writer, matcher TrackMatcher, pl model.Playlist, playlistIndex, playlistTotal int) model.PlaylistTransferResult {
	res := model.PlaylistTransferResult{
		Name:        pl.Name,
		TotalTracks: len(pl.Tracks),
		Errors:      []string{},
		Unmatched:   []model.MatchedTrack{},
	}

	notify(cfg, fmt.Sprintf("Transfer %d/%d matching: %s (0/%d)", playlistIndex, playlistTotal, shortName(pl.Name), len(pl.Tracks)))

	matched, unmatched := matchTracks(ctx, matcher, pl.Tracks, cfg.Concurrency, func(done, total int) {
		notify(cfg, fmt.Sprintf("Transfer %d/%d matching: %s (%d/%d)", playlistIndex, playlistTotal, shortName(pl.Name), done, total))
	})
	res.MatchedTracks = len(matched)
	res.Unmatched = unmatched

	if cfg.DryRun {
		res.AddedTracks = len(uniqueIDs(matched))
		notify(cfg, fmt.Sprintf("Transfer %d/%d dry-run: %s resolved %d matches", playlistIndex, playlistTotal, shortName(pl.Name), res.AddedTracks))
		return res
	}

	notify(cfg, fmt.Sprintf("Transfer %d/%d creating playlist: %s", playlistIndex, playlistTotal, shortName(pl.Name)))
	playlistID, err := writer.CreatePlaylist(ctx, pl.Name)
	if err != nil {
		res.Errors = append(res.Errors, fmt.Sprintf("create playlist: %v", err))
		notify(cfg, fmt.Sprintf("Transfer %d/%d failed creating playlist: %s", playlistIndex, playlistTotal, shortName(pl.Name)))
		return res
	}
	res.TargetID = playlistID

	ids := uniqueIDs(matched)
	if len(ids) == 0 {
		notify(cfg, fmt.Sprintf("Transfer %d/%d no matched tracks to add: %s", playlistIndex, playlistTotal, shortName(pl.Name)))
		return res
	}

	notify(cfg, fmt.Sprintf("Transfer %d/%d adding %d track(s): %s", playlistIndex, playlistTotal, len(ids), shortName(pl.Name)))
	if err := writer.AddTracksToPlaylist(ctx, playlistID, ids); err != nil {
		res.Errors = append(res.Errors, fmt.Sprintf("add tracks: %v", err))
		notify(cfg, fmt.Sprintf("Transfer %d/%d failed adding tracks: %s", playlistIndex, playlistTotal, shortName(pl.Name)))
		return res
	}

	res.AddedTracks = len(ids)
	notify(cfg, fmt.Sprintf("Transfer %d/%d added %d track(s): %s", playlistIndex, playlistTotal, res.AddedTracks, shortName(pl.Name)))
	return res
}

func matchTracks(ctx context.Context, matcher TrackMatcher, tracks []model.Track, concurrency int, progress func(done, total int)) ([]string, []model.MatchedTrack) {
	if concurrency < 1 {
		concurrency = 1
	}

	type job struct {
		idx int
		trk model.Track
	}
	type out struct {
		idx int
		res model.MatchedTrack
	}

	jobs := make(chan job)
	results := make(chan out)

	var wg sync.WaitGroup
	for i := 0; i < concurrency; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			for j := range jobs {
				m := matcher.MatchTrack(ctx, j.trk)
				results <- out{idx: j.idx, res: m}
			}
		}()
	}

	go func() {
		for i, t := range tracks {
			jobs <- job{idx: i, trk: t}
		}
		close(jobs)
		wg.Wait()
		close(results)
	}()

	ordered := make([]model.MatchedTrack, len(tracks))
	total := len(tracks)
	step := 1
	if total > 100 {
		step = total / 100
	}
	done := 0
	for r := range results {
		ordered[r.idx] = r.res
		done++
		if progress != nil {
			if done == 1 || done == total || done%step == 0 {
				progress(done, total)
			}
		}
	}

	matched := make([]string, 0, len(tracks))
	unmatched := make([]model.MatchedTrack, 0)
	for _, r := range ordered {
		if r.Matched && strings.TrimSpace(r.TargetID) != "" {
			matched = append(matched, r.TargetID)
		} else {
			unmatched = append(unmatched, r)
		}
	}
	return matched, unmatched
}

func uniqueIDs(ids []string) []string {
	seen := map[string]struct{}{}
	out := make([]string, 0, len(ids))
	for _, id := range ids {
		id = strings.TrimSpace(id)
		if id == "" {
			continue
		}
		if _, ok := seen[id]; ok {
			continue
		}
		seen[id] = struct{}{}
		out = append(out, id)
	}
	return out
}

func notify(cfg Config, msg string) {
	if cfg.Progress != nil {
		cfg.Progress(msg)
	}
}

func shortName(s string) string {
	const limit = 48
	s = strings.TrimSpace(s)
	if len(s) <= limit {
		return s
	}
	if limit <= 3 {
		return s[:limit]
	}
	return s[:limit-3] + "..."
}