// OpenTween - Client of Twitter
// Copyright (c) 2012 kim_upsilon (@kim_upsilon) <https://upsilo.net/~upsilon/>
// All rights reserved.
//
// This file is part of OpenTween.
//
// This program is free software; you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by the Free
// Software Foundation; either version 3 of the License, or (at your option)
// any later version.
//
// This program is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
// or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
// for more details.
//
// You should have received a copy of the GNU General Public License along
// with this program. If not, see <http://www.gnu.org/licenses/>, or write to
// the Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
// Boston, MA 02110-1301, USA.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;

namespace OpenTween.Thumbnail.Services
{
    /// <summary>
    /// og:image や twitter:image をスクレイピングしてサムネイルURLを抽出する
    /// </summary>
    class MetaThumbnailService : IThumbnailService
    {
        protected static Regex metaPattern = new Regex("<meta (name|property)=[\"'](?<name>.+?)[\"'] (content|value)=[\"'](?<content>.+?)[\"']");
        protected static string[] propertyNames = { "twitter:image", "og:image" };

        protected readonly HttpClient http;
        protected readonly Regex regex;

        public MetaThumbnailService(HttpClient http, string urlPattern)
        {
            this.http = http;
            this.regex = new Regex(urlPattern);
        }

        public override async Task<ThumbnailInfo> GetThumbnailInfoAsync(string url, PostClass post, CancellationToken token)
        {
            if (!this.regex.IsMatch(url))
                return null;

            try
            {
                var content = await this.FetchImageUrlAsync(url, token)
                    .ConfigureAwait(false);

                var thumbnailUrl = this.GetThumbnailUrl(content);
                if (string.IsNullOrEmpty(thumbnailUrl)) return null;

                return new ThumbnailInfo
                {
                    ImageUrl = url,
                    ThumbnailUrl = thumbnailUrl,
                    TooltipText = null,
                };
            }
            catch (HttpRequestException) { }

            return null;
        }

        protected virtual string GetThumbnailUrl(string html)
        {
            var matches = MetaThumbnailService.metaPattern.Matches(html);

            foreach (Match match in matches)
            {
                var propertyName = match.Groups["name"].Value;
                if (MetaThumbnailService.propertyNames.Contains(propertyName))
                {
                    return match.Groups["content"].Value;
                }
            }

            return null;
        }

        protected virtual async Task<string> FetchImageUrlAsync(string url, CancellationToken token)
        {
            using (var response = await this.http.GetAsync(url, token).ConfigureAwait(false))
            {
                response.EnsureSuccessStatusCode();

                return await response.Content.ReadAsStringAsync()
                    .ConfigureAwait(false);
            }
        }
    }
}
