// Package syncer contains the diff/apply logic that reconciles a local
// audio folder with the chapters of a Kreativ-Tonie.
package syncer

import (
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"

	"github.com/arnef/toni-sync/internal/config"
	"github.com/arnef/toni-sync/internal/tonieapi"
)

// TonieClient is the subset of tonieapi.Client used by the syncer, extracted
// as an interface so it can be faked in tests.
type TonieClient interface {
	GetCreativeTonie(tonieID string) (*tonieapi.CreativeTonie, error)
	UploadFileToTonie(tonie tonieapi.CreativeTonie, filePath, title string) error
	SortChaptersOfTonie(tonie tonieapi.CreativeTonie, chapters []tonieapi.Chapter) error
}

const maxTitleLength = 100

var audioExtensions = map[string]bool{
	".mp3":  true,
	".m4a":  true,
	".aac":  true,
	".ogg":  true,
	".flac": true,
	".wav":  true,
}

// Track is a local audio file considered for syncing.
type Track struct {
	Path  string
	Title string
}

// TitleFromFilename derives a chapter title from a filename (its stem, length-capped).
func TitleFromFilename(name string) string {
	title := strings.TrimSuffix(name, filepath.Ext(name))
	title = strings.TrimSpace(title)
	if len(title) > maxTitleLength {
		title = title[:maxTitleLength]
	}
	return title
}

// ListLocalTracks returns audio files in folder, sorted by filename (defines chapter order).
func ListLocalTracks(folder string) ([]Track, error) {
	entries, err := os.ReadDir(folder)
	if err != nil {
		return nil, fmt.Errorf("folder does not exist: %s: %w", folder, err)
	}

	var tracks []Track
	for _, e := range entries {
		if e.IsDir() {
			continue
		}
		ext := strings.ToLower(filepath.Ext(e.Name()))
		if !audioExtensions[ext] {
			continue
		}
		tracks = append(tracks, Track{
			Path:  filepath.Join(folder, e.Name()),
			Title: TitleFromFilename(e.Name()),
		})
	}
	sort.Slice(tracks, func(i, j int) bool { return tracks[i].Path < tracks[j].Path })
	return tracks, nil
}

// Plan describes the changes needed to bring a Kreativ-Tonie in sync with a local folder.
type Plan struct {
	Tonie            tonieapi.CreativeTonie
	LocalTracks      []Track
	ToUpload         []Track
	ToRemove         []tonieapi.Chapter
	FinalOrderTitles []string
}

// NeedsChanges reports whether applying the plan would change anything on the tonie.
func (p *Plan) NeedsChanges() bool {
	if len(p.ToUpload) > 0 || len(p.ToRemove) > 0 {
		return true
	}
	removed := make(map[string]bool, len(p.ToRemove))
	for _, c := range p.ToRemove {
		removed[c.Title] = true
	}
	var kept []string
	for _, c := range p.Tonie.Chapters {
		if !removed[c.Title] {
			kept = append(kept, c.Title)
		}
	}
	limit := len(kept)
	if limit > len(p.FinalOrderTitles) {
		limit = len(p.FinalOrderTitles)
	}
	for i := 0; i < limit; i++ {
		if kept[i] != p.FinalOrderTitles[i] {
			return true
		}
	}
	return len(kept) != len(p.FinalOrderTitles)
}

// BuildPlan fetches the current state of the tonie and computes the diff against the local folder.
func BuildPlan(client TonieClient, m config.Mapping) (*Plan, error) {
	tonie, err := client.GetCreativeTonie(m.TonieID)
	if err != nil {
		return nil, err
	}

	tracks, err := ListLocalTracks(m.Folder)
	if err != nil {
		return nil, err
	}

	localTitles := make(map[string]bool, len(tracks))
	orderedTitles := make([]string, 0, len(tracks))
	for _, t := range tracks {
		localTitles[t.Title] = true
		orderedTitles = append(orderedTitles, t.Title)
	}

	existingTitles := make(map[string]bool, len(tonie.Chapters))
	for _, c := range tonie.Chapters {
		existingTitles[c.Title] = true
	}

	var toUpload []Track
	for _, t := range tracks {
		if !existingTitles[t.Title] {
			toUpload = append(toUpload, t)
		}
	}

	var toRemove []tonieapi.Chapter
	finalOrder := append([]string{}, orderedTitles...)
	if m.Prune {
		for _, c := range tonie.Chapters {
			if !localTitles[c.Title] {
				toRemove = append(toRemove, c)
			}
		}
	} else {
		for _, c := range tonie.Chapters {
			if !localTitles[c.Title] {
				finalOrder = append(finalOrder, c.Title)
			}
		}
	}

	return &Plan{
		Tonie:            *tonie,
		LocalTracks:      tracks,
		ToUpload:         toUpload,
		ToRemove:         toRemove,
		FinalOrderTitles: finalOrder,
	}, nil
}

// ApplyPlan uploads missing tracks, then reorders/prunes chapters to match the local folder.
func ApplyPlan(client TonieClient, m config.Mapping, plan *Plan) error {
	for _, track := range plan.ToUpload {
		if err := client.UploadFileToTonie(plan.Tonie, track.Path, track.Title); err != nil {
			return fmt.Errorf("uploading %s: %w", track.Path, err)
		}
	}

	refreshed, err := client.GetCreativeTonie(m.TonieID)
	if err != nil {
		return fmt.Errorf("refetching tonie after upload: %w", err)
	}

	chaptersByTitle := make(map[string]tonieapi.Chapter, len(refreshed.Chapters))
	currentOrder := make([]string, 0, len(refreshed.Chapters))
	for _, c := range refreshed.Chapters {
		chaptersByTitle[c.Title] = c
		currentOrder = append(currentOrder, c.Title)
	}

	var ordered []tonieapi.Chapter
	var desiredOrder []string
	for _, title := range plan.FinalOrderTitles {
		if c, ok := chaptersByTitle[title]; ok {
			ordered = append(ordered, c)
			desiredOrder = append(desiredOrder, title)
		}
	}

	if !equalStrings(currentOrder, desiredOrder) {
		if err := client.SortChaptersOfTonie(*refreshed, ordered); err != nil {
			return fmt.Errorf("reordering chapters: %w", err)
		}
	}
	return nil
}

func equalStrings(a, b []string) bool {
	if len(a) != len(b) {
		return false
	}
	for i := range a {
		if a[i] != b[i] {
			return false
		}
	}
	return true
}