using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Threading.Tasks;
using Bit.Icons.Models;
using AngleSharp.Parser.Html;

namespace Bit.Icons.Services
{
    public class IconFetchingService : IIconFetchingService
    {
        private readonly HashSet<string> _iconRels =
            new HashSet<string> { "icon", "apple-touch-icon", "shortcut icon" };
        private readonly HashSet<string> _iconExtensions =
            new HashSet<string> { ".ico", ".png", ".jpg", ".jpeg" };

        private readonly string _pngMediaType = "image/png";
        private readonly byte[] _pngHeader = new byte[] { 137, 80, 78, 71 };

        private readonly string _icoMediaType = "image/x-icon";
        private readonly string _icoAltMediaType = "image/vnd.microsoft.icon";
        private readonly byte[] _icoHeader = new byte[] { 00, 00, 01, 00 };

        private readonly string _jpegMediaType = "image/jpeg";
        private readonly byte[] _jpegHeader = new byte[] { 255, 216, 255 };

        private readonly HashSet<string> _allowedMediaTypes;
        private readonly HttpClient _httpClient;

        public IconFetchingService()
        {
            _allowedMediaTypes = new HashSet<string>
            {
                _pngMediaType,
                _icoMediaType,
                _icoAltMediaType,
                _jpegMediaType
            };

            _httpClient = new HttpClient(new HttpClientHandler
            {
                AllowAutoRedirect = false,
                AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate,
            });
            _httpClient.Timeout = TimeSpan.FromSeconds(20);
        }

        public async Task<IconResult> GetIconAsync(string domain)
        {
            if(!Uri.TryCreate($"https://{domain}", UriKind.Absolute, out var parsedUri))
            {
                return null;
            }

            var uri = parsedUri;
            var response = await GetAndFollowAsync(uri, 2);
            if(response == null || !response.IsSuccessStatusCode)
            {
                Cleanup(response);
                uri = new Uri($"http://{domain}");
                response = await GetAndFollowAsync(uri, 2);
                if(response == null || !response.IsSuccessStatusCode)
                {
                    Cleanup(response);
                    uri = new Uri($"https://www.{domain}");
                    response = await GetAndFollowAsync(uri, 2);
                }
            }

            if(response?.Content == null || !response.IsSuccessStatusCode)
            {
                Cleanup(response);
                return null;
            }

            var parser = new HtmlParser();
            using(response)
            using(var htmlStream = await response.Content.ReadAsStreamAsync())
            using(var document = await parser.ParseAsync(htmlStream))
            {
                uri = response.RequestMessage.RequestUri;
                if(document.DocumentElement == null)
                {
                    return null;
                }

                var baseUrl = "/";
                var baseUrlNode = document.QuerySelector("head base[href]");
                if(baseUrlNode != null)
                {
                    var hrefAttr = baseUrlNode.Attributes["href"];
                    if(!string.IsNullOrWhiteSpace(hrefAttr?.Value))
                    {
                        baseUrl = hrefAttr.Value;
                    }

                    baseUrlNode = null;
                    hrefAttr = null;
                }

                var icons = new List<IconResult>();
                var links = document.QuerySelectorAll("head link[href]");
                if(links != null)
                {
                    foreach(var link in links.Take(200))
                    {
                        var hrefAttr = link.Attributes["href"];
                        if(string.IsNullOrWhiteSpace(hrefAttr?.Value))
                        {
                            continue;
                        }

                        var relAttr = link.Attributes["rel"];
                        var sizesAttr = link.Attributes["sizes"];
                        if(relAttr != null && _iconRels.Contains(relAttr.Value.ToLower()))
                        {
                            icons.Add(new IconResult(hrefAttr.Value, sizesAttr?.Value));
                        }
                        else
                        {
                            try
                            {
                                var extension = Path.GetExtension(hrefAttr.Value);
                                if(_iconExtensions.Contains(extension.ToLower()))
                                {
                                    icons.Add(new IconResult(hrefAttr.Value, sizesAttr?.Value));
                                }
                            }
                            catch(ArgumentException) { }
                        }

                        sizesAttr = null;
                        relAttr = null;
                        hrefAttr = null;
                    }

                    links = null;
                }

                var iconResultTasks = new List<Task>();
                foreach(var icon in icons.OrderBy(i => i.Priority).Take(10))
                {
                    Uri iconUri = null;
                    if(icon.Path.StartsWith("//") && Uri.TryCreate($"{GetScheme(uri)}://{icon.Path.Substring(2)}",
                        UriKind.Absolute, out var slashUri))
                    {
                        iconUri = slashUri;
                    }
                    else if(Uri.TryCreate(icon.Path, UriKind.Relative, out var relUri))
                    {
                        iconUri = ResolveUri($"{GetScheme(uri)}://{uri.Host}", baseUrl, relUri.OriginalString);
                    }
                    else if(Uri.TryCreate(icon.Path, UriKind.Absolute, out var absUri))
                    {
                        iconUri = absUri;
                    }

                    if(iconUri != null)
                    {
                        var task = GetIconAsync(iconUri).ContinueWith(async (r) =>
                        {
                            var result = await r;
                            if(result != null)
                            {
                                icon.Path = iconUri.ToString();
                                icon.Icon = result.Icon;
                            }
                        });
                        iconResultTasks.Add(task);
                    }
                }

                await Task.WhenAll(iconResultTasks);
                if(!icons.Any(i => i.Icon != null))
                {
                    var faviconUri = ResolveUri($"{GetScheme(uri)}://{uri.Host}", "favicon.ico");
                    var result = await GetIconAsync(faviconUri);
                    if(result != null)
                    {
                        icons.Add(result);
                    }
                    else
                    {
                        return null;
                    }
                }

                return icons.Where(i => i.Icon != null).OrderBy(i => i.Priority).First();
            }
        }

        private async Task<IconResult> GetIconAsync(Uri uri)
        {
            using(var response = await GetAndFollowAsync(uri, 2))
            {
                if(response?.Content?.Headers == null || !response.IsSuccessStatusCode)
                {
                    response?.Content?.Dispose();
                    return null;
                }

                var format = response.Content.Headers?.ContentType?.MediaType;
                var bytes = await response.Content.ReadAsByteArrayAsync();
                response.Content.Dispose();
                if(format == null || !_allowedMediaTypes.Contains(format))
                {
                    if(HeaderMatch(bytes, _icoHeader))
                    {
                        format = _icoMediaType;
                    }
                    else if(HeaderMatch(bytes, _pngHeader))
                    {
                        format = _pngMediaType;
                    }
                    else if(HeaderMatch(bytes, _jpegHeader))
                    {
                        format = _jpegMediaType;
                    }
                    else
                    {
                        return null;
                    }
                }

                return new IconResult(uri, bytes, format);
            }
        }

        private async Task<HttpResponseMessage> GetAndFollowAsync(Uri uri, int maxRedirectCount)
        {
            var response = await GetAsync(uri);
            if(response == null)
            {
                return null;
            }
            return await FollowRedirectsAsync(response, maxRedirectCount);
        }

        private async Task<HttpResponseMessage> GetAsync(Uri uri)
        {
            using(var message = new HttpRequestMessage())
            {
                message.RequestUri = uri;
                message.Method = HttpMethod.Get;

                // Let's add some headers to look like we're coming from a web browser request. Some websites
                // will block our request without these.
                message.Headers.Add("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 " +
                    "(KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36 Edge/16.16299");
                message.Headers.Add("Accept-Language", "en-US,en;q=0.8");
                message.Headers.Add("Cache-Control", "no-cache");
                message.Headers.Add("Pragma", "no-cache");
                message.Headers.Add("Accept", "text/html,application/xhtml+xml,application/xml;" +
                    "q=0.9,image/webp,image/apng,*/*;q=0.8");

                try
                {
                    return await _httpClient.SendAsync(message);
                }
                catch
                {
                    return null;
                }
            }
        }

        private async Task<HttpResponseMessage> FollowRedirectsAsync(HttpResponseMessage response,
            int maxFollowCount, int followCount = 0)
        {
            if(response == null || response.IsSuccessStatusCode || followCount > maxFollowCount)
            {
                return response;
            }

            if(!(response.StatusCode == HttpStatusCode.Redirect ||
                response.StatusCode == HttpStatusCode.MovedPermanently ||
                response.StatusCode == HttpStatusCode.RedirectKeepVerb ||
                response.StatusCode == HttpStatusCode.SeeOther) ||
                response.Headers.Location == null)
            {
                Cleanup(response);
                return null;
            }

            Uri location = null;
            if(response.Headers.Location.IsAbsoluteUri)
            {
                if(response.Headers.Location.Scheme != "http" && response.Headers.Location.Scheme != "https")
                {
                    if(Uri.TryCreate($"https://{response.Headers.Location.OriginalString}",
                        UriKind.Absolute, out var newUri))
                    {
                        location = newUri;
                    }
                }
                else
                {
                    location = response.Headers.Location;
                }
            }
            else
            {
                var requestUri = response.RequestMessage.RequestUri;
                location = ResolveUri($"{GetScheme(requestUri)}://{requestUri.Host}",
                    response.Headers.Location.OriginalString);
            }

            Cleanup(response);
            var newResponse = await GetAsync(location);
            if(newResponse != null)
            {
                followCount++;
                var redirectedResponse = await FollowRedirectsAsync(newResponse, maxFollowCount, followCount);
                if(redirectedResponse != null)
                {
                    if(redirectedResponse != newResponse)
                    {
                        Cleanup(newResponse);
                    }
                    return redirectedResponse;
                }
            }

            return null;
        }

        private bool HeaderMatch(byte[] imageBytes, byte[] header)
        {
            return imageBytes.Length >= header.Length && header.SequenceEqual(imageBytes.Take(header.Length));
        }

        private Uri ResolveUri(string baseUrl, params string[] paths)
        {
            var url = baseUrl;
            foreach(var path in paths)
            {
                if(Uri.TryCreate(new Uri(url), path, out var r))
                {
                    url = r.ToString();
                }
            }
            return new Uri(url);
        }

        private void Cleanup(IDisposable obj)
        {
            obj?.Dispose();
            obj = null;
        }

        private string GetScheme(Uri uri)
        {
            return uri != null && uri.Scheme == "http" ? "http" : "https";
        }
    }
}