package media

import (
	"fmt"
	"path/filepath"
	"strings"
	"unicode"
)

const (
	maxSeriesBytes    = 90
	maxEpisodeBytes   = 140
	maxEpisodeIDBytes = 64
	maxFilenameBytes  = 255
)

// RelativeVideoPath は worker と web が共有する保存先の相対パスを返す。
func RelativeVideoPath(seriesTitle, episodeTitle, episodeID string) (string, error) {
	series := sanitizeComponent(seriesTitle, maxSeriesBytes)
	episode := sanitizeComponent(episodeTitle, maxEpisodeBytes)
	id := sanitizeComponent(episodeID, -1)
	if len(id) > maxEpisodeIDBytes {
		return "", fmt.Errorf("エピソードIDはサニタイズ後%dバイト以下である必要があります: %dバイト", maxEpisodeIDBytes, len(id))
	}

	// A directory entry must fit within the NFS namlen limit. Keep the episode
	// ID intact and use the remaining bytes for the episode title.
	const separators = "  [].mp4"
	seriesInFilename := series
	titleBytes := maxFilenameBytes - len(seriesInFilename) - len(id) - len(separators)
	if titleBytes < 0 {
		titleBytes = 0
	}
	episode = truncateComponent(episode, titleBytes, false)
	return filepath.Join(series, seriesInFilename+" "+episode+" ["+id+"].mp4"), nil
}

func sanitizeComponent(value string, maxBytes int) string {
	var result []rune
	lastReplacement := false
	for _, r := range value {
		invalid := unicode.IsControl(r) || strings.ContainsRune(`<>:"/\|?*`, r)
		if invalid {
			if !lastReplacement {
				result = append(result, '_')
				lastReplacement = true
			}
			continue
		}
		if unicode.IsSpace(r) {
			r = ' '
		}
		result = append(result, r)
		lastReplacement = false
	}
	clean := strings.Trim(string(result), " .")
	if clean == "" || clean == "." || clean == ".." {
		return "名称未設定"
	}
	return truncateComponent(clean, maxBytes, true)
}

func truncateComponent(value string, maxBytes int, fallback bool) string {
	if maxBytes < 0 {
		return value
	}
	var limited []rune
	bytes := 0
	for _, r := range value {
		size := len(string(r))
		if bytes+size > maxBytes {
			break
		}
		limited = append(limited, r)
		bytes += size
	}
	clean := strings.Trim(string(limited), " .")
	if fallback && (clean == "" || clean == "." || clean == "..") {
		return "名称未設定"
	}
	return clean
}