package metadata

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

// ComicVine matches comic series. It requires a free API key, so the provider
// is only registered when one is configured.
type ComicVine struct {
	APIKey  string
	BaseURL string
	Client  *http.Client
}

// NewComicVine builds the provider. An empty key yields a provider that finds
// nothing, so a misconfiguration degrades rather than erroring.
func NewComicVine(apiKey string) *ComicVine {
	return &ComicVine{
		APIKey:  apiKey,
		BaseURL: "https://comicvine.gamespot.com/api",
		Client:  &http.Client{Timeout: 15 * time.Second},
	}
}

func (p *ComicVine) Name() string { return "comicvine" }

func (p *ComicVine) Kinds() []string { return []string{"comics"} }

// cvResponse is the subset of the ComicVine search payload we read.
type cvResponse struct {
	StatusCode int `json:"status_code"`
	Results    []struct {
		ID          int    `json:"id"`
		Name        string `json:"name"`
		StartYear   string `json:"start_year"`
		Description string `json:"description"`
		Publisher   struct {
			Name string `json:"name"`
		} `json:"publisher"`
		Image struct {
			MediumURL   string `json:"medium_url"`
			OriginalURL string `json:"original_url"`
			SmallURL    string `json:"small_url"`
		} `json:"image"`
	} `json:"results"`
}

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

	params := url.Values{}
	params.Set("api_key", p.APIKey)
	params.Set("format", "json")
	params.Set("resources", "volume")
	params.Set("query", q.Title)
	params.Set("limit", "5")

	endpoint := strings.TrimRight(p.BaseURL, "/") + "/search/?" + params.Encode()
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
	if err != nil {
		return nil, err
	}
	// ComicVine rejects requests without a User-Agent.
	req.Header.Set("User-Agent", "Vellum/0.1 (self-hosted media server)")

	resp, err := p.Client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("comicvine: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("comicvine: status %d", resp.StatusCode)
	}

	var parsed cvResponse
	if err := json.NewDecoder(resp.Body).Decode(&parsed); err != nil {
		return nil, fmt.Errorf("comicvine: decode: %w", err)
	}
	// ComicVine returns 200 with status_code 100 for an invalid API key.
	if parsed.StatusCode != 1 {
		return nil, fmt.Errorf("comicvine: api status %d (check the API key)", parsed.StatusCode)
	}

	out := make([]Candidate, 0, len(parsed.Results))
	for _, r := range parsed.Results {
		if r.Name == "" {
			continue
		}
		cover := r.Image.MediumURL
		if cover == "" {
			cover = r.Image.SmallURL
		}
		if cover == "" {
			cover = r.Image.OriginalURL
		}
		out = append(out, Candidate{
			Provider:    p.Name(),
			ExternalID:  strconv.Itoa(r.ID),
			Title:       r.Name,
			Year:        parseYear(r.StartYear),
			Publisher:   r.Publisher.Name,
			Description: stripHTML(r.Description),
			CoverURL:    cover,
		})
	}
	return out, nil
}

// stripHTML removes the tags ComicVine embeds in descriptions. It is
// deliberately minimal: descriptions are displayed as plain text, so only the
// tags need removing, not full entity decoding.
func stripHTML(s string) string {
	var b strings.Builder
	depth := 0
	for _, r := range s {
		switch r {
		case '<':
			depth++
		case '>':
			if depth > 0 {
				depth--
			}
		default:
			if depth == 0 {
				b.WriteRune(r)
			}
		}
	}
	return strings.TrimSpace(b.String())
}