package providers

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

// GoogleBooks is a fallback catalogue for books. No API key for low volume.
type GoogleBooks struct {
	Client *http.Client
}

// NewGoogleBooks builds the provider with a bounded HTTP client.
func NewGoogleBooks() *GoogleBooks {
	return &GoogleBooks{Client: &http.Client{Timeout: 10 * time.Second}}
}

func (p *GoogleBooks) Name() string { return "googlebooks" }

func (p *GoogleBooks) Kinds() []string { return []string{"ebooks"} }

type gbResponse struct {
	Items []struct {
		ID         string `json:"id"`
		VolumeInfo struct {
			Title         string   `json:"title"`
			Authors       []string `json:"authors"`
			Publisher     string   `json:"publisher"`
			Language      string   `json:"language"`
			Description   string   `json:"description"`
			PublishedDate string   `json:"publishedDate"`
			ImageLinks    struct {
				Thumbnail string `json:"thumbnail"`
			} `json:"imageLinks"`
			IndustryIdentifiers []struct {
				Type       string `json:"type"`
				Identifier string `json:"identifier"`
			} `json:"industryIdentifiers"`
		} `json:"volumeInfo"`
	} `json:"items"`
}

func (p *GoogleBooks) Search(ctx context.Context, q Query) ([]Candidate, error) {
	var terms []string
	if q.ISBN != "" {
		terms = append(terms, "isbn:"+q.ISBN)
	} else {
		if q.Title != "" {
			terms = append(terms, "intitle:"+q.Title)
		}
		if q.Author != "" {
			terms = append(terms, "inauthor:"+q.Author)
		}
	}
	if len(terms) == 0 {
		return nil, nil
	}

	params := url.Values{}
	params.Set("q", strings.Join(terms, "+"))
	params.Set("maxResults", "5")
	params.Set("printType", "books")

	endpoint := "https://www.googleapis.com/books/v1/volumes?" + params.Encode()
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
	if err != nil {
		return nil, err
	}

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

	var parsed gbResponse
	if err := json.NewDecoder(resp.Body).Decode(&parsed); err != nil {
		return nil, fmt.Errorf("googlebooks: decode: %w", err)
	}

	out := make([]Candidate, 0, len(parsed.Items))
	for _, item := range parsed.Items {
		v := item.VolumeInfo
		if v.Title == "" {
			continue
		}
		c := Candidate{
			Provider:    p.Name(),
			ExternalID:  item.ID,
			Title:       v.Title,
			Authors:     v.Authors,
			Publisher:   v.Publisher,
			Language:    v.Language,
			Description: v.Description,
			Year:        parseYear(v.PublishedDate),
		}
		// Google returns http:// thumbnail URLs; https avoids mixed content.
		if v.ImageLinks.Thumbnail != "" {
			c.CoverURL = strings.Replace(v.ImageLinks.Thumbnail, "http://", "https://", 1)
		}
		for _, id := range v.IndustryIdentifiers {
			if id.Type == "ISBN_13" || c.ISBN == "" {
				c.ISBN = id.Identifier
			}
		}
		out = append(out, c)
	}
	return out, nil
}

// parseYear extracts a leading 4-digit year from dates like "2021-05-04".
func parseYear(date string) int {
	if len(date) < 4 {
		return 0
	}
	n, err := strconv.Atoi(date[:4])
	if err != nil {
		return 0
	}
	return n
}