watch-party/backend/internal/danime/danime.go

package danime

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"net/url"
	"regexp"
	"strconv"
	"strings"
	"time"
)

// RawPartInfo mirrors the subset of fields we need from WS030101.
type RawPartInfo struct {
	WorkTitle      string `json:"workTitle"`      // Season / series title
	PartTitle      string `json:"partTitle"`      // Episode title
	PartDispNumber string `json:"partDispNumber"` // Display episode number, e.g. "第21話" or "＃２１"
	PartMeasure    string `json:"partMeasure"`    // Duration string, e.g. "23分50秒"
}

// Episode is the normalized representation we use internally and/or output as JSON.
type Episode struct {
	EpNum          int    `json:"ep_num"`
	EpTitle        string `json:"ep_title"`
	SeasonName     string `json:"season_name"`
	PlaybackLength string `json:"playback_length"` // format: "HH:MM:SS"
}

var (
	baseURL    = "https://animestore.docomo.ne.jp/animestore/rest/WS030101"
	httpClient = &http.Client{Timeout: 10 * time.Second}
	epNumRe    = regexp.MustCompile(`\d+`)
	hourRe     = regexp.MustCompile(`(\d+)時間`)
	minRe      = regexp.MustCompile(`(\d+)分`)
	secRe      = regexp.MustCompile(`(\d+)秒`)
)

// FetchEpisode fetches metadata for a single episode (partId) and returns normalized Episode.
func FetchEpisode(ctx context.Context, partID string) (*Episode, error) {
	partID = strings.TrimSpace(partID)
	if partID == "" {
		return nil, fmt.Errorf("partId is required")
	}

	u, err := url.Parse(baseURL)
	if err != nil {
		return nil, fmt.Errorf("parse base url: %w", err)
	}
	q := u.Query()
	q.Set("partId", partID)
	u.RawQuery = q.Encode()

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
	if err != nil {
		return nil, fmt.Errorf("create request: %w", err)
	}

	resp, err := httpClient.Do(req)
	if err != nil {
		return nil, fmt.Errorf("fetching WS030101 for partId=%s: %w", partID, err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("WS030101 status %d for partId=%s", resp.StatusCode, partID)
	}

	var raw RawPartInfo
	if err := json.NewDecoder(resp.Body).Decode(&raw); err != nil {
		return nil, fmt.Errorf("decoding WS030101: %w", err)
	}

	ep, err := normalizeEpisode(raw)
	if err != nil {
		return nil, fmt.Errorf("normalizing WS030101: %w", err)
	}
	return &ep, nil
}

func normalizeEpisode(raw RawPartInfo) (Episode, error) {
	num := parseEpisodeNumber(raw.PartDispNumber)
	length, err := parsePartMeasure(raw.PartMeasure)
	if err != nil {
		return Episode{}, err
	}

	return Episode{
		EpNum:          num,
		EpTitle:        raw.PartTitle,
		SeasonName:     raw.WorkTitle,
		PlaybackLength: length,
	}, nil
}

func parseEpisodeNumber(s string) int {
	s = toHalfWidthDigits(s)
	match := epNumRe.FindString(s)
	if match == "" {
		return 0
	}
	n, err := strconv.Atoi(match)
	if err != nil {
		return 0
	}
	return n
}

func parsePartMeasure(s string) (string, error) {
	s = strings.TrimSpace(toHalfWidthDigits(s))
	if s == "" {
		return "", fmt.Errorf("partMeasure missing")
	}

	hours := extractInt(hourRe, s)
	minutes := extractInt(minRe, s)
	seconds := extractInt(secRe, s)

	if hours == 0 && minutes == 0 && seconds == 0 {
		return "", fmt.Errorf("could not parse partMeasure %q", s)
	}

	dur := time.Duration(hours)*time.Hour + time.Duration(minutes)*time.Minute + time.Duration(seconds)*time.Second
	totalSeconds := int(dur.Seconds())
	h := totalSeconds / 3600
	m := (totalSeconds % 3600) / 60
	sec := totalSeconds % 60
	return fmt.Sprintf("%02d:%02d:%02d", h, m, sec), nil
}

func extractInt(re *regexp.Regexp, s string) int {
	m := re.FindStringSubmatch(s)
	if len(m) < 2 {
		return 0
	}
	n, err := strconv.Atoi(m[1])
	if err != nil {
		return 0
	}
	return n
}

func toHalfWidthDigits(s string) string {
	return strings.Map(func(r rune) rune {
		// Convert full-width digits to ASCII digits.
		if r >= '０' && r <= '９' {
			return r - '０' + '0'
		}
		return r
	}, s)
}