package metadata

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

// IGDB matches games. It uses Twitch's client-credentials flow: the app
// exchanges its client id and secret for a bearer token that lasts about two
// months, so the token is cached rather than re-fetched per search.
type IGDB struct {
	ClientID     string
	ClientSecret string

	// BaseURL and TokenURL are overridable so tests can point at a local server.
	BaseURL  string
	TokenURL string

	Client *http.Client

	mu          sync.Mutex
	token       string
	tokenExpiry time.Time
}

// NewIGDB builds the provider.
func NewIGDB(clientID, clientSecret string) *IGDB {
	return &IGDB{
		ClientID:     clientID,
		ClientSecret: clientSecret,
		BaseURL:      "https://api.igdb.com/v4",
		TokenURL:     "https://id.twitch.tv/oauth2/token",
		Client:       &http.Client{Timeout: 15 * time.Second},
	}
}

func (p *IGDB) Name() string { return "igdb" }

func (p *IGDB) Kinds() []string { return []string{"games"} }

type igdbGame struct {
	ID               int    `json:"id"`
	Name             string `json:"name"`
	Summary          string `json:"summary"`
	FirstReleaseDate int64  `json:"first_release_date"`
	Cover            struct {
		URL string `json:"url"`
	} `json:"cover"`
}

func (p *IGDB) Search(ctx context.Context, q Query) ([]Candidate, error) {
	if p.ClientID == "" || p.ClientSecret == "" || strings.TrimSpace(q.Title) == "" {
		return nil, nil
	}

	token, err := p.accessToken(ctx)
	if err != nil {
		return nil, err
	}

	// IGDB uses its own query language (Apicalypse) sent as the request body.
	body := fmt.Sprintf(
		`search %q; fields name,summary,first_release_date,cover.url; limit 5;`,
		q.Title)

	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
		strings.TrimRight(p.BaseURL, "/")+"/games", strings.NewReader(body))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Client-ID", p.ClientID)
	req.Header.Set("Authorization", "Bearer "+token)
	req.Header.Set("Accept", "application/json")

	resp, err := p.Client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("igdb: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode == http.StatusUnauthorized {
		// The cached token was rejected; drop it so the next call re-auths.
		p.mu.Lock()
		p.token, p.tokenExpiry = "", time.Time{}
		p.mu.Unlock()
		return nil, fmt.Errorf("igdb: unauthorized (token rejected)")
	}
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("igdb: status %d", resp.StatusCode)
	}

	var games []igdbGame
	if err := json.NewDecoder(resp.Body).Decode(&games); err != nil {
		return nil, fmt.Errorf("igdb: decode: %w", err)
	}

	out := make([]Candidate, 0, len(games))
	for _, g := range games {
		if g.Name == "" {
			continue
		}
		c := Candidate{
			Provider:    p.Name(),
			ExternalID:  strconv.Itoa(g.ID),
			Title:       g.Name,
			Description: g.Summary,
		}
		if g.FirstReleaseDate > 0 {
			c.Year = time.Unix(g.FirstReleaseDate, 0).UTC().Year()
		}
		if g.Cover.URL != "" {
			c.CoverURL = igdbCover(g.Cover.URL)
		}
		out = append(out, c)
	}
	return out, nil
}

// accessToken returns a cached bearer token, fetching a new one when absent or
// near expiry.
func (p *IGDB) accessToken(ctx context.Context) (string, error) {
	p.mu.Lock()
	defer p.mu.Unlock()

	// Refresh a minute early to avoid racing the expiry.
	if p.token != "" && time.Now().Before(p.tokenExpiry.Add(-time.Minute)) {
		return p.token, nil
	}

	params := url.Values{}
	params.Set("client_id", p.ClientID)
	params.Set("client_secret", p.ClientSecret)
	params.Set("grant_type", "client_credentials")

	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
		p.TokenURL+"?"+params.Encode(), nil)
	if err != nil {
		return "", err
	}
	resp, err := p.Client.Do(req)
	if err != nil {
		return "", fmt.Errorf("igdb: token request: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return "", fmt.Errorf("igdb: token status %d", resp.StatusCode)
	}

	var parsed struct {
		AccessToken string `json:"access_token"`
		ExpiresIn   int    `json:"expires_in"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&parsed); err != nil {
		return "", fmt.Errorf("igdb: token decode: %w", err)
	}
	if parsed.AccessToken == "" {
		return "", fmt.Errorf("igdb: empty access token")
	}
	p.token = parsed.AccessToken
	p.tokenExpiry = time.Now().Add(time.Duration(parsed.ExpiresIn) * time.Second)
	return p.token, nil
}

// igdbCover normalises an IGDB image URL: protocol-relative to https, and the
// thumbnail size swapped for a larger one.
func igdbCover(u string) string {
	u = strings.Replace(u, "t_thumb", "t_cover_big", 1)
	if strings.HasPrefix(u, "//") {
		u = "https:" + u
	}
	return u
}