package engine

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

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

// PlexIgnoreName is the file Plex reads to skip content in a folder.
const PlexIgnoreName = ".plexignore"

// plexIgnoreMarker identifies a .plexignore written by playlink, so only
// that file is ever replaced or removed; a user's own file is left alone.
const plexIgnoreMarker = "# Created by playlink"

// plexIgnoreDepth covers quarantine paths like <op>/<side>/Artist/Album/Disc/Song.
const plexIgnoreDepth = 12

func plexIgnoreContent() []byte {
	var b strings.Builder
	b.WriteString(plexIgnoreMarker + ": keeps Plex from scanning files in playlink's quarantine.\n")
	b.WriteString("# Turn off \"Hide quarantine from Plex\" in playlink's settings to remove it.\n")
	for i := 1; i <= plexIgnoreDepth; i++ {
		b.WriteString(strings.TrimSuffix(strings.Repeat("*/", i), "/") + "\n")
	}
	return []byte(b.String())
}

// ErrForeignIgnore means a .plexignore exists that playlink did not write.
var ErrForeignIgnore = errors.New("a .plexignore not created by playlink already exists; it was left unchanged")

// syncPlexIgnore makes the quarantine folder's .plexignore match the setting.
func syncPlexIgnore(quarantine string, enabled bool) error {
	p := filepath.Join(quarantine, PlexIgnoreName)
	cur, err := os.ReadFile(p)
	exists := err == nil
	if err != nil && !errors.Is(err, fs.ErrNotExist) {
		return err
	}
	ours := exists && bytes.HasPrefix(cur, []byte(plexIgnoreMarker))
	want := plexIgnoreContent()
	switch {
	case enabled && exists && !ours:
		return ErrForeignIgnore
	case enabled && ours && bytes.Equal(cur, want):
		return nil
	case enabled:
		// Write via a temporary file so Plex never sees a half-written file.
		tmp := filepath.Join(quarantine, fsops.TmpPrefix+"plexignore")
		if err := os.WriteFile(tmp, want, 0o644); err != nil {
			return err
		}
		if err := os.Rename(tmp, p); err != nil {
			_ = os.Remove(tmp)
			return err
		}
		return nil
	case ours:
		return os.Remove(p)
	}
	return nil
}

// IgnoreResult reports what happened to one pair's quarantine folder.
type IgnoreResult struct {
	Pair  string `json:"pair"`
	Path  string `json:"path"`
	Error string `json:"error,omitempty"`
}

// ApplyPlexIgnore adds or removes the .plexignore in every pair's quarantine.
func (e *Engine) ApplyPlexIgnore(ctx context.Context, enabled bool) []IgnoreResult {
	pairs, err := e.st.Pairs(ctx)
	if err != nil {
		return []IgnoreResult{{Error: err.Error()}}
	}
	out := []IgnoreResult{}
	for _, p := range pairs {
		r := IgnoreResult{Pair: p.Name, Path: filepath.Join(p.QuarantineDir, PlexIgnoreName)}
		// open re-validates the pair and syncs the file as a side effect.
		l, err := e.open(p)
		if err == nil {
			err = syncPlexIgnore(l.quarantine, enabled)
		}
		if err != nil {
			r.Error = err.Error()
			e.log.Warn(".plexignore not updated", "pair", p.Name, "err", err)
		}
		out = append(out, r)
	}
	e.log.Info(".plexignore setting applied", "enabled", enabled, "pairs", len(pairs))
	return out
}

func (e *Engine) plexIgnoreEnabled() bool {
	return e.st.Setting(context.Background(), "plex_ignore", "0") == "1"
}

func plexIgnoreError(quarantine string, err error) error {
	return fmt.Errorf("%s: %w", filepath.Join(quarantine, PlexIgnoreName), err)
}