// Package service — TMDb discovery (trending / popular).
//
// DiscoverService surfaces curated lists from TMDb so the React home
// page can show "Trending" and "Popular" rails alongside the user's own
// library. All methods gracefully no-op when the TMDb provider is
// disabled.
package service

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"net/url"
	"time"

	"go.uber.org/zap"
)

// DiscoverService talks to TMDb's /trending and /movie/popular endpoints.
type DiscoverService struct {
	log    *zap.Logger
	tmdb   *TMDbProvider
	client *http.Client
}

// NewDiscoverService is the constructor.
func NewDiscoverService(log *zap.Logger, tmdb *TMDbProvider) *DiscoverService {
	return &DiscoverService{
		log:    log,
		tmdb:   tmdb,
		client: &http.Client{Timeout: 15 * time.Second},
	}
}

// Trending returns the daily trending movies (TMDb /trending/movie/day).
func (d *DiscoverService) Trending(ctx context.Context) ([]Match, error) {
	return d.fetch(ctx, "/trending/movie/day")
}

// Popular returns the popular movies list (TMDb /movie/popular).
func (d *DiscoverService) Popular(ctx context.Context) ([]Match, error) {
	return d.fetch(ctx, "/movie/popular")
}

// fetch is the shared helper that paginates page=1 only — that's all the
// home page needs and it keeps us under TMDb's 50 rps limit.
func (d *DiscoverService) fetch(ctx context.Context, path string) ([]Match, error) {
	if d.tmdb == nil || !d.tmdb.Enabled() {
		return nil, nil
	}
	q := url.Values{}
	q.Set("api_key", d.tmdb.cfg.Secrets.TMDbAPIKey)
	q.Set("language", "zh-CN")
	q.Set("page", "1")
	u := d.tmdb.base + path + "?" + q.Encode()

	type result struct {
		ID           int     `json:"id"`
		Title        string  `json:"title"`
		Name         string  `json:"name"`
		Overview     string  `json:"overview"`
		PosterPath   string  `json:"poster_path"`
		BackdropPath string  `json:"backdrop_path"`
		ReleaseDate  string  `json:"release_date"`
		FirstAirDate string  `json:"first_air_date"`
		VoteAverage  float32 `json:"vote_average"`
	}
	type page struct {
		Results []result `json:"results"`
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
	if err != nil {
		return nil, err
	}
	resp, err := d.client.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	if resp.StatusCode >= 400 {
		return nil, fmt.Errorf("tmdb %s: %d", path, resp.StatusCode)
	}
	var p page
	if err := json.NewDecoder(resp.Body).Decode(&p); err != nil {
		return nil, err
	}
	out := make([]Match, 0, len(p.Results))
	for _, r := range p.Results {
		title := r.Title
		if title == "" {
			title = r.Name
		}
		m := Match{
			TMDbID:   r.ID,
			Title:    title,
			Overview: r.Overview,
			Rating:   r.VoteAverage,
		}
		if r.PosterPath != "" {
			m.PosterURL = d.tmdb.imgCDN + "/w500" + r.PosterPath
		}
		if r.BackdropPath != "" {
			m.BackdropURL = d.tmdb.imgCDN + "/w1280" + r.BackdropPath
		}
		date := r.ReleaseDate
		if date == "" {
			date = r.FirstAirDate
		}
		if len(date) >= 4 {
			fmt.Sscanf(date[:4], "%d", &m.Year)
		}
		out = append(out, m)
	}
	return out, nil
}