// Package providers searches external metadata services for things to rank.
package providers

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"regexp"
	"strings"
	"sync"
	"time"
)

const UserAgent = "TopDeck/0.1 (self-hosted favorites list; https://git.iamchrisama.com/cdnutter/topdeck)"

// Result is one search hit, already shaped like a list item.
type Result struct {
	Provider    string            `json:"provider"`
	ProviderID  string            `json:"providerId"`
	Title       string            `json:"title"`
	Subtitle    string            `json:"subtitle"`
	Year        string            `json:"year"`
	ImageURL    string            `json:"imageUrl"`
	ExternalURL string            `json:"externalUrl"`
	Overview    string            `json:"overview"`
	Extra       map[string]string `json:"extra,omitempty"`
}

type Searcher interface {
	// Name is the stable id stored with items, e.g. "tmdb".
	Name() string
	// Label is the human-readable service name.
	Label() string
	Search(ctx context.Context, query string) ([]Result, error)
}

// Detailer is implemented by searchers that can fill in more metadata (a
// director, a release year) once the owner picks a result.
type Detailer interface {
	Details(ctx context.Context, r Result) (Result, error)
}

// NotConfiguredError means the owner hasn't supplied credentials yet.
type NotConfiguredError struct{ Service, Hint string }

func (e NotConfiguredError) Error() string {
	return fmt.Sprintf("%s isn't set up yet. %s", e.Service, e.Hint)
}

// Credentials are resolved fresh for every search so settings changes apply
// immediately.
type Credentials struct {
	TMDBKey          string
	TVDBKey          string
	TVDBPin          string
	IGDBClientID     string
	IGDBClientSecret string
	MusicProvider    string // "deezer" or "musicbrainz"
	TVProvider       string // "tvdb" or "tmdb"
}

type Registry struct {
	creds  func(context.Context) Credentials
	client *http.Client

	tvdb *tvdbTokens
	igdb *igdbTokens
	mb   *throttle
}

func NewRegistry(creds func(context.Context) Credentials) *Registry {
	return &Registry{
		creds:  creds,
		client: &http.Client{Timeout: 20 * time.Second},
		tvdb:   &tvdbTokens{},
		igdb:   &igdbTokens{},
		mb:     &throttle{gap: 1100 * time.Millisecond},
	}
}

// For returns the searcher for a category.
func (r *Registry) For(ctx context.Context, category string) (Searcher, error) {
	c := r.creds(ctx)
	switch category {
	case "movie":
		if c.TMDBKey == "" {
			return nil, NotConfiguredError{"TMDB", "Add a TMDB API key under Settings → Integrations."}
		}
		return &tmdb{r: r, key: c.TMDBKey, kind: "movie"}, nil
	case "tv":
		if c.TVProvider == "tmdb" {
			if c.TMDBKey == "" {
				return nil, NotConfiguredError{"TMDB", "Add a TMDB API key under Settings → Integrations, or switch TV shows back to TheTVDB."}
			}
			return &tmdb{r: r, key: c.TMDBKey, kind: "tv"}, nil
		}
		if c.TVDBKey == "" {
			return nil, NotConfiguredError{"TheTVDB", "Add a TheTVDB API key under Settings → Integrations."}
		}
		return &tvdb{r: r, key: c.TVDBKey, pin: c.TVDBPin}, nil
	case "album", "song":
		if c.MusicProvider == "musicbrainz" {
			return &musicbrainz{r: r, kind: category}, nil
		}
		return &deezer{r: r, kind: category}, nil
	case "game":
		if c.IGDBClientID == "" || c.IGDBClientSecret == "" {
			return nil, NotConfiguredError{"IGDB", "Add your Twitch client ID and secret under Settings → Integrations."}
		}
		return &igdb{r: r, id: c.IGDBClientID, secret: c.IGDBClientSecret}, nil
	case "theater":
		return &wikipedia{r: r}, nil
	}
	return nil, fmt.Errorf("no provider for category %q", category)
}

// ---- HTTP helpers ----

type httpError struct {
	Status int
	Body   string
}

func (e *httpError) Error() string {
	return fmt.Sprintf("upstream returned %d: %s", e.Status, e.Body)
}

func (r *Registry) do(req *http.Request, out any) error {
	req.Header.Set("User-Agent", UserAgent)
	if req.Header.Get("Accept") == "" {
		req.Header.Set("Accept", "application/json")
	}
	resp, err := r.client.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	body, err := io.ReadAll(io.LimitReader(resp.Body, 8<<20))
	if err != nil {
		return err
	}
	if resp.StatusCode < 200 || resp.StatusCode > 299 {
		snippet := strings.TrimSpace(string(body))
		if len(snippet) > 200 {
			snippet = snippet[:200] + "…"
		}
		return &httpError{Status: resp.StatusCode, Body: snippet}
	}
	if out == nil {
		return nil
	}
	return json.Unmarshal(body, out)
}

func (r *Registry) getJSON(ctx context.Context, url string, header map[string]string, out any) error {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return err
	}
	for k, v := range header {
		req.Header.Set(k, v)
	}
	return r.do(req, out)
}

func isStatus(err error, code int) bool {
	var he *httpError
	return errors.As(err, &he) && he.Status == code
}

// throttle spaces out calls for services with strict rate limits.
type throttle struct {
	mu   sync.Mutex
	gap  time.Duration
	last time.Time
}

func (t *throttle) wait(ctx context.Context) error {
	t.mu.Lock()
	defer t.mu.Unlock()
	if d := t.gap - time.Since(t.last); d > 0 {
		select {
		case <-time.After(d):
		case <-ctx.Done():
			return ctx.Err()
		}
	}
	t.last = time.Now()
	return nil
}

var yearRe = regexp.MustCompile(`\b(1[5-9]\d\d|20\d\d)\b`)

// yearOf pulls the first plausible year out of a date or free text.
func yearOf(s string) string {
	return yearRe.FindString(s)
}

func truncate(s string, n int) string {
	s = strings.TrimSpace(s)
	if len([]rune(s)) <= n {
		return s
	}
	return strings.TrimSpace(string([]rune(s)[:n])) + "…"
}