package main

import (
	"encoding/json"
	"fmt"
	"net/url"
	"strings"
	"tweetdistributor/output"
)

// findYouTubeURL returns the first YouTube video link in content, or "" if
// there is none.
func findYouTubeURL(content string) string {
	for _, match := range urlPattern.FindAllString(content, -1) {
		raw := trimURL(match)
		u, err := url.Parse(raw)
		if err != nil {
			continue
		}
		switch strings.ToLower(u.Hostname()) {
		case "youtu.be":
			if strings.Trim(u.Path, "/") != "" {
				return raw
			}
		case "youtube.com", "www.youtube.com", "m.youtube.com", "music.youtube.com":
			if u.Path == "/watch" && u.Query().Get("v") != "" {
				return raw
			}
			if strings.HasPrefix(u.Path, "/shorts/") || strings.HasPrefix(u.Path, "/live/") {
				return raw
			}
		}
	}
	return ""
}

// oEmbedResponse is the part of YouTube's oEmbed document we care about.
type oEmbedResponse struct {
	Title        string `json:"title"`
	AuthorName   string `json:"author_name"`
	ThumbnailURL string `json:"thumbnail_url"`
}

// youtubePreview builds the preview card for a YouTube link by asking
// YouTube's oEmbed endpoint for the title, channel and thumbnail.
func youtubePreview(videoURL string) (*output.Preview, error) {
	endpoint := "https://www.youtube.com/oembed?format=json&url=" + url.QueryEscape(videoURL)
	body, err := fetch(endpoint)
	if err != nil {
		return nil, fmt.Errorf("fetching preview for %s: %w", videoURL, err)
	}

	var oembed oEmbedResponse
	if err := json.Unmarshal(body, &oembed); err != nil {
		return nil, fmt.Errorf("parsing preview for %s: %w", videoURL, err)
	}

	preview := &output.Preview{
		URL:         videoURL,
		Title:       oembed.Title,
		Description: oembed.AuthorName,
	}

	if oembed.ThumbnailURL != "" {
		thumb, err := downloadImage(oembed.ThumbnailURL, "thumbnail.jpg", "image/jpeg")
		if err != nil {
			// A card without its thumbnail is still worth posting.
			return preview, nil
		}
		preview.Thumb = &thumb
	}

	return preview, nil
}