package engine

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"unicode/utf8"

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

// Tag editing works on either library. A file used by only one library is
// rewritten to a new file that atomically replaces it (the old file goes to
// quarantine). A file hardlinked elsewhere (typically shared by master and
// slave) is updated in place so the link survives and every linked path sees
// the new tags; a verified backup copy goes to quarantine first. Choosing
// "separate" instead gives only this path its own edited copy.

const (
	SideMaster = "master"
	SideSlave  = "slave"

	tagModeReplace = "replace"
	tagModeInPlace = "inplace"

	maxTagFiles = 500
	maxTagValue = 2000
)

var ErrNoTagTools = errors.New("tag editing needs ffmpeg and ffprobe, which were not found")

// SetTagTools enables tag editing.
func (e *Engine) SetTagTools(t tags.Tools) { e.tagTools = t }

func (e *Engine) TagEditing() bool { return e.tagTools.FFmpeg != "" && e.tagTools.FFprobe != "" }

func sideRoot(l *libs, side string) (fsops.Root, error) {
	switch side {
	case SideMaster:
		return l.master, nil
	case SideSlave:
		return l.slave, nil
	}
	return fsops.Root{}, fmt.Errorf("%w: side must be master or slave", ErrInvalidBulk)
}

// FileEntry is one row of the library browser.
type FileEntry struct {
	Name     string `json:"name"`
	Rel      string `json:"rel"`
	Dir      bool   `json:"dir"`
	Size     int64  `json:"size,omitempty"`
	Links    int    `json:"links,omitempty"` // >1: the file is shared (hardlinked)
	Editable bool   `json:"editable,omitempty"`
}

// ListFiles lists a folder of either library: subfolders and audio files.
func (e *Engine) ListFiles(ctx context.Context, pairID int64, side, rel string) ([]FileEntry, error) {
	l, err := e.loadPair(ctx, pairID)
	if err != nil {
		return nil, err
	}
	root, err := sideRoot(l, side)
	if err != nil {
		return nil, err
	}
	dir := root.Path
	if rel != "" {
		if dir, err = root.Resolve(rel); err != nil {
			return nil, err
		}
	}
	ents, err := os.ReadDir(dir)
	if err != nil {
		return nil, err
	}
	out := []FileEntry{}
	for _, en := range ents {
		name := en.Name()
		abs := filepath.Join(dir, name)
		if strings.HasPrefix(name, ".") || en.Type()&fs.ModeSymlink != 0 || abs == l.quarantine {
			continue
		}
		child := name
		if rel != "" {
			child = filepath.Join(rel, name)
		}
		if en.IsDir() {
			out = append(out, FileEntry{Name: name, Rel: child, Dir: true})
			continue
		}
		if !l.hasExt(name) {
			continue
		}
		in, err := fsops.Lstat(abs)
		if err != nil || !in.Mode.IsRegular() {
			continue
		}
		_, editable := tags.FormatOf(name)
		out = append(out, FileEntry{Name: name, Rel: child, Size: in.Size, Links: int(in.Nlink), Editable: editable})
	}
	sort.Slice(out, func(i, j int) bool {
		if out[i].Dir != out[j].Dir {
			return out[i].Dir
		}
		return strings.ToLower(out[i].Name) < strings.ToLower(out[j].Name)
	})
	return out, nil
}

// TagFile is the editable view of one file's tags.
type TagFile struct {
	Rel      string            `json:"rel"`
	Editable bool              `json:"editable"`
	Reason   string            `json:"reason,omitempty"`
	Fields   map[string]string `json:"fields"`
	Other    map[string]string `json:"other"`
	Links    int               `json:"links"`
	Size     int64             `json:"size"`
}

func cleanRels(rels []string) ([]string, error) {
	if len(rels) == 0 {
		return nil, fmt.Errorf("%w: no files selected", ErrInvalidBulk)
	}
	if len(rels) > maxTagFiles {
		return nil, fmt.Errorf("%w: select at most %d files at a time", ErrInvalidBulk, maxTagFiles)
	}
	seen := map[string]bool{}
	var out []string
	for _, r := range rels {
		c, err := fsops.CleanRel(r)
		if err != nil {
			return nil, err
		}
		if !seen[c] {
			seen[c] = true
			out = append(out, c)
		}
	}
	return out, nil
}

// ReadTags reads the tags of files in one library.
func (e *Engine) ReadTags(ctx context.Context, pairID int64, side string, rels []string) ([]TagFile, error) {
	if !e.TagEditing() {
		return nil, ErrNoTagTools
	}
	rels, err := cleanRels(rels)
	if err != nil {
		return nil, err
	}
	l, err := e.loadPair(ctx, pairID)
	if err != nil {
		return nil, err
	}
	root, err := sideRoot(l, side)
	if err != nil {
		return nil, err
	}
	out := make([]TagFile, 0, len(rels))
	for _, rel := range rels {
		tf := TagFile{Rel: rel, Fields: map[string]string{}, Other: map[string]string{}}
		abs, err := root.Resolve(rel)
		if err == nil {
			var in fsops.Info
			if in, err = fsops.RegularFile(abs); err == nil {
				tf.Links, tf.Size = int(in.Nlink), in.Size
				var f tags.File
				if f, err = e.tagTools.Read(ctx, abs); err == nil {
					tf.Editable, tf.Fields, tf.Other = true, f.Fields, f.Other
				}
			}
		}
		if err != nil {
			tf.Reason = err.Error()
		}
		out = append(out, tf)
	}
	return out, nil
}

// TagEdit is one tag edit request.
type TagEdit struct {
	Side  string            `json:"side"`
	Paths []string          `json:"paths"`
	Set   map[string]string `json:"set"` // field -> new value ("" removes the tag)
	// Separate gives a hardlinked file its own edited copy instead of
	// updating it in place for every linked path.
	Separate bool `json:"separate"`
}

func validTagChanges(set map[string]string) error {
	if len(set) == 0 {
		return fmt.Errorf("%w: no tags changed", ErrInvalidBulk)
	}
	known := map[string]bool{}
	for _, id := range tags.FieldIDs {
		known[id] = true
	}
	for id, v := range set {
		if !known[id] {
			return fmt.Errorf("%w: unknown tag field %q", ErrInvalidBulk, id)
		}
		if len(v) > maxTagValue || !utf8.ValidString(v) || strings.ContainsRune(v, 0) {
			return fmt.Errorf("%w: invalid value for %s", ErrInvalidBulk, id)
		}
	}
	return nil
}

// StartTagEdit applies a tag edit to each selected file in a background job.
func (e *Engine) StartTagEdit(pairID int64, req TagEdit) (*Job, error) {
	if !e.TagEditing() {
		return nil, ErrNoTagTools
	}
	if req.Side != SideMaster && req.Side != SideSlave {
		return nil, fmt.Errorf("%w: side must be master or slave", ErrInvalidBulk)
	}
	rels, err := cleanRels(req.Paths)
	if err != nil {
		return nil, err
	}
	if err := validTagChanges(req.Set); err != nil {
		return nil, err
	}
	return e.startJob(pairID, "edit-tags", func(ctx context.Context, j *Job) error {
		l, err := e.loadPair(ctx, pairID)
		if err != nil {
			return err
		}
		j.phase("Editing tags", int64(len(rels)))
		for _, rel := range rels {
			if ctx.Err() != nil {
				return ctx.Err()
			}
			if err := e.editTagsOne(ctx, j, l, req.Side, rel, req.Set, req.Separate); err != nil {
				j.skip(rel + ": " + err.Error())
			}
			j.tick()
		}
		return nil
	})
}

type tagDetail struct {
	Side    string               `json:"side"`
	Mode    string               `json:"mode"`
	Changes map[string][2]string `json:"changes"` // field -> [old, new]
}

func (e *Engine) editTagsOne(ctx context.Context, j *Job, l *libs, side, rel string, set map[string]string, separate bool) error {
	e.mu.Lock()
	defer e.mu.Unlock()
	root, _ := sideRoot(l, side)
	abs, err := root.Resolve(rel)
	if err != nil {
		return err
	}
	info, err := fsops.RegularFile(abs)
	if err != nil {
		return err
	}
	f, err := e.tagTools.Read(ctx, abs)
	if err != nil {
		return err
	}
	changes := map[string]string{}
	d := tagDetail{Side: side, Mode: tagModeReplace, Changes: map[string][2]string{}}
	for id, v := range set {
		if f.Fields[id] != v {
			changes[id] = v
			d.Changes[id] = [2]string{f.Fields[id], v}
		}
	}
	if len(changes) == 0 {
		j.count("unchanged")
		return nil
	}
	plan, err := f.Plan(changes)
	if err != nil {
		return err
	}
	if info.Nlink > 1 && !separate {
		d.Mode = tagModeInPlace
	}
	o := store.Operation{PairID: l.pair.ID, Action: store.ActTags, QuarantineSide: side, Trigger: "tags"}
	if side == SideMaster {
		o.RelMaster = rel
	} else {
		o.RelSlave = rel
	}
	o.Detail, _ = json.Marshal(d)
	if err := e.begin(ctx, &o); err != nil {
		return err
	}
	if o.DryRun {
		j.count("planned")
		return nil
	}

	var b [8]byte
	_, _ = rand.Read(b[:])
	tmp := filepath.Join(filepath.Dir(abs), fsops.TmpPrefix+hex.EncodeToString(b[:])+filepath.Ext(abs))
	defer os.Remove(tmp)
	err = func() error {
		if err := e.tagTools.Write(ctx, abs, tmp, f, plan); err != nil {
			return err
		}
		if err := e.tagTools.Verify(ctx, abs, tmp, changes); err != nil {
			return err
		}
		// Nothing may have touched the original while the new file was made.
		if now, err := fsops.RegularFile(abs); err != nil || !now.SameInode(info) || !now.Unchanged(info.Size, info.MtimeNs) {
			return fmt.Errorf("%s %w", rel, fsops.ErrChanged)
		}
		q := quarantinePath(l, o.ID, side, rel)
		if err := fsops.MkdirAllLike(filepath.Dir(q)); err != nil {
			return err
		}
		if d.Mode == tagModeReplace {
			// Keep the old file (as a hardlink, no extra space) and swap in
			// the new one atomically, with the original's permissions.
			if err := fsops.LinkNew(abs, info, q); err != nil {
				return fmt.Errorf("quarantine: %w", err)
			}
			e.setQuarantine(ctx, o.ID, q)
			if err := os.Chmod(tmp, info.Mode.Perm()); err != nil {
				dropQuarantine(l, q, info)
				e.clearQuarantine(ctx, o.ID)
				return err
			}
			if err := os.Rename(tmp, abs); err != nil {
				dropQuarantine(l, q, info)
				e.clearQuarantine(ctx, o.ID)
				return err
			}
			return fsops.SyncDir(filepath.Dir(abs))
		}
		// In place: a verified backup copy first, then overwrite the shared
		// file's contents; restore from the backup if anything goes wrong.
		if err := fsops.CopyNew(abs, q, info.Mode); err != nil {
			return fmt.Errorf("backup: %w", err)
		}
		e.setQuarantine(ctx, o.ID, q)
		if err := fsops.OverwriteInPlace(abs, tmp); err != nil {
			if rerr := fsops.OverwriteInPlace(abs, q); rerr != nil {
				return fmt.Errorf("%v; restoring the original also failed (%v): the original is at %s", err, rerr, q)
			}
			_ = os.Remove(q)
			e.clearQuarantine(ctx, o.ID)
			return fmt.Errorf("could not write the new tags, the original was restored: %w", err)
		}
		return nil
	}()
	if err = e.finish(ctx, &o, err); err != nil {
		return err
	}
	j.count("edited")
	e.refreshTagged(ctx, l, side, rel)
	return nil
}

func (e *Engine) setQuarantine(ctx context.Context, opID int64, q string) {
	_, _ = e.st.DB.ExecContext(ctx, `UPDATE operations SET quarantine_path = ? WHERE id = ?`, q, opID)
}

// refreshTagged updates the matches that involve an edited file.
func (e *Engine) refreshTagged(ctx context.Context, l *libs, side, rel string) {
	if side == SideSlave {
		e.refresh(ctx, l, rel)
		return
	}
	ms, _ := e.st.MatchesByMaster(ctx, l.pair.ID, rel)
	for _, m := range ms {
		e.refresh(ctx, l, m.RelSlave, m)
	}
}

func tagOpPath(l *libs, o store.Operation) (string, tagDetail, error) {
	var d tagDetail
	if err := json.Unmarshal(o.Detail, &d); err != nil {
		return "", d, fmt.Errorf("unreadable operation details: %w", err)
	}
	root, err := sideRoot(l, d.Side)
	if err != nil {
		return "", d, err
	}
	rel := o.RelSlave
	if d.Side == SideMaster {
		rel = o.RelMaster
	}
	abs, err := root.Resolve(rel)
	return abs, d, err
}

// undoTags puts the file back the way it was before the edit.
func (e *Engine) undoTags(ctx context.Context, l *libs, o store.Operation) error {
	abs, d, err := tagOpPath(l, o)
	if err != nil {
		return err
	}
	qi, err := e.quarantined(l, o.QuarantinePath)
	if err != nil {
		return err
	}
	cur, err := fsops.RegularFile(abs)
	if err != nil {
		return err
	}
	if d.Mode == tagModeReplace {
		if cur.SameInode(qi) {
			return errors.New("the file is already the original")
		}
		// The original inode comes back, rejoining any links it had.
		if err := fsops.ReplaceWithLink(o.QuarantinePath, qi, abs); err != nil {
			return err
		}
		dropQuarantine(l, o.QuarantinePath, qi)
	} else {
		if err := fsops.OverwriteInPlace(abs, o.QuarantinePath); err != nil {
			return err
		}
		if err := os.Remove(o.QuarantinePath); err == nil {
			pruneEmpty(filepath.Dir(o.QuarantinePath), l.quarantine)
		}
	}
	rel := o.RelSlave
	if d.Side == SideMaster {
		rel = o.RelMaster
	}
	e.refreshTagged(ctx, l, d.Side, rel)
	return nil
}

// recoverTags handles a tag edit cut short by a crash. An in-place edit may
// have left a partially written file, so the backup is written back. A
// replace edit either happened (atomic rename) or did not; an unused
// quarantine link is dropped.
func (e *Engine) recoverTags(ctx context.Context, o store.Operation) string {
	l, err := e.loadPair(ctx, o.PairID)
	if err != nil || o.QuarantinePath == "" {
		return "interrupted before any change"
	}
	abs, d, err := tagOpPath(l, o)
	if err != nil {
		return err.Error()
	}
	// The half-written new file is disposable.
	if ents, err := os.ReadDir(filepath.Dir(abs)); err == nil {
		for _, en := range ents {
			if strings.HasPrefix(en.Name(), fsops.TmpPrefix) && en.Type().IsRegular() {
				_ = os.Remove(filepath.Join(filepath.Dir(abs), en.Name()))
			}
		}
	}
	qi, err := e.quarantined(l, o.QuarantinePath)
	if err != nil {
		return "interrupted; " + err.Error()
	}
	if d.Mode == tagModeInPlace {
		if err := fsops.OverwriteInPlace(abs, o.QuarantinePath); err != nil {
			return fmt.Sprintf("interrupted; could not restore the original (%v), it is kept at %s", err, o.QuarantinePath)
		}
		_ = os.Remove(o.QuarantinePath)
		e.clearQuarantine(ctx, o.ID)
		return "interrupted by shutdown; the original tags were restored"
	}
	if cur, err := fsops.Lstat(abs); err == nil && cur.SameInode(qi) {
		dropQuarantine(l, o.QuarantinePath, qi) // rename never happened
		e.clearQuarantine(ctx, o.ID)
		return "interrupted by shutdown before the file was replaced; nothing changed"
	}
	return "interrupted by shutdown after the new tags were written"
}