// Package service — episode parser for TV series.
//
// Detects season + episode numbers from filenames. Recognised patterns:
//
//	S01E02        / s1e2
//	1x02          / 01x02
//	EP02 / E02
//	第2集         / 第02集
//
// For bare episode markers such as "EP02", the parser also looks at parent
// folders like "Season 02" / "S02" / "第2季" before falling back to season 1.
//
// When neither a season nor an episode marker is present, returns (0, 0).
package service

import (
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
)

var (
	patSEnE         = regexp.MustCompile(`(?i)s(\d{1,2})e(\d{1,3})`)
	patNxE          = regexp.MustCompile(`(\d{1,2})x(\d{1,3})`)
	patEP           = regexp.MustCompile(`(?i)(?:^|[^a-z])(?:e|ep)\.?\s*(\d{1,3})(?:[^0-9]|$)`)
	patCN           = regexp.MustCompile(`第\s*(\d{1,3})\s*[集话話期]`)
	patSeasonFolder = regexp.MustCompile(`(?i)(?:^|[^a-z])(?:s|season)\.?\s*(\d{1,2})(?:[^0-9]|$)|第\s*(\d{1,2})\s*季`)
)

// ParseEpisode tries to extract (season, episode) from an arbitrary filename.
// Returns (0, 0) when nothing recognisable is found.
func ParseEpisode(path string) (season, episode int) {
	name := strings.TrimSuffix(filepath.Base(path), filepath.Ext(path))

	if m := patSEnE.FindStringSubmatch(name); len(m) == 3 {
		season = mustAtoi(m[1])
		episode = mustAtoi(m[2])
		return
	}
	if m := patNxE.FindStringSubmatch(name); len(m) == 3 {
		season = mustAtoi(m[1])
		episode = mustAtoi(m[2])
		return
	}
	if m := patEP.FindStringSubmatch(name); len(m) >= 2 {
		season = seasonFromParents(path)
		if season == 0 {
			season = 1
		}
		episode = mustAtoi(m[1])
		return
	}
	if m := patCN.FindStringSubmatch(name); len(m) >= 2 {
		season = seasonFromParents(path)
		if season == 0 {
			season = 1
		}
		episode = mustAtoi(m[1])
		return
	}
	return 0, 0
}

func seasonFromParents(path string) int {
	dir := filepath.Dir(path)
	for i := 0; i < 4; i++ {
		base := filepath.Base(dir)
		if base == "." || base == string(filepath.Separator) {
			return 0
		}
		if m := patSeasonFolder.FindStringSubmatch(base); len(m) >= 3 {
			for _, group := range m[1:] {
				if group != "" {
					return mustAtoi(group)
				}
			}
		}
		parent := filepath.Dir(dir)
		if parent == dir {
			return 0
		}
		dir = parent
	}
	return 0
}

func mustAtoi(s string) int {
	v, _ := strconv.Atoi(s)
	return v
}