using AngleSharp;
using AngleSharp.Dom.Html;
using Discord;
using Discord.WebSocket;
using NadekoBot.Common;
using NadekoBot.Common.Replacements;
using NadekoBot.Core.Services.Database.Models;
using NadekoBot.Extensions;
using NadekoBot.Modules.CustomReactions.Services;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace NadekoBot.Modules.CustomReactions.Extensions
{
    public static class Extensions
    {
        private static readonly Regex imgRegex = new Regex("%(img|image):(?<tag>.*?)%", RegexOptions.Compiled);

        private static readonly NadekoRandom rng = new NadekoRandom();

        public static Dictionary<Regex, Func<Match, Task<string>>> regexPlaceholders = new Dictionary<Regex, Func<Match, Task<string>>>()
        {
            { imgRegex, async (match) => {
                var tag = match.Groups["tag"].ToString();
                if(string.IsNullOrWhiteSpace(tag))
                    return "";

                var fullQueryLink = $"http://imgur.com/search?q={ tag }";
                var config = Configuration.Default.WithDefaultLoader();
                var document = await BrowsingContext.New(config).OpenAsync(fullQueryLink);

                var elems = document.QuerySelectorAll("a.image-list-link").ToArray();

                if (!elems.Any())
                    return "";

                var img = (elems.ElementAtOrDefault(new NadekoRandom().Next(0, elems.Length))?.Children?.FirstOrDefault() as IHtmlImageElement);

                if (img?.Source == null)
                    return "";

                return " " + img.Source.Replace("b.", ".") + " ";
            } }
        };

        private static string ResolveTriggerString(this string str, IUserMessage ctx, DiscordSocketClient client)
        {
            var rep = new ReplacementBuilder()
                .WithUser(ctx.Author)
                .WithClient(client)
                .Build();

            str = rep.Replace(str.ToLowerInvariant());

            return str;
        }

        private static async Task<string> ResolveResponseStringAsync(this string str, IUserMessage ctx, DiscordSocketClient client, string resolvedTrigger, bool containsAnywhere)
        {
            var substringIndex = resolvedTrigger.Length;
            if (containsAnywhere)
            {
                var pos = ctx.Content.GetWordPosition(resolvedTrigger);
                if (pos == WordPosition.Start)
                    substringIndex += 1;
                else if (pos == WordPosition.End)
                    substringIndex = ctx.Content.Length;
                else if (pos == WordPosition.Middle)
                    substringIndex += ctx.Content.IndexOf(resolvedTrigger);
            }

            var rep = new ReplacementBuilder()
                .WithDefault(ctx.Author, ctx.Channel, (ctx.Channel as ITextChannel)?.Guild, client)
                .WithOverride("%target%", () => ctx.Content.Substring(substringIndex).Trim())
                .Build();

            str = rep.Replace(str);

            foreach (var ph in regexPlaceholders)
            {
                str = await ph.Key.ReplaceAsync(str, ph.Value);
            }
            return str;
        }

        public static string TriggerWithContext(this CustomReaction cr, IUserMessage ctx, DiscordSocketClient client)
            => cr.Trigger.ResolveTriggerString(ctx, client);

        public static Task<string> ResponseWithContextAsync(this CustomReaction cr, IUserMessage ctx, DiscordSocketClient client, bool containsAnywhere)
            => cr.Response.ResolveResponseStringAsync(ctx, client, cr.Trigger.ResolveTriggerString(ctx, client), containsAnywhere);

        public static async Task<IUserMessage> Send(this CustomReaction cr, IUserMessage ctx, DiscordSocketClient client, CustomReactionsService crs)
        {
            var channel = cr.DmResponse ? await ctx.Author.GetOrCreateDMChannelAsync() : ctx.Channel;

            crs.ReactionStats.AddOrUpdate(cr.Trigger, 1, (k, old) => ++old);

            if (CREmbed.TryParse(cr.Response, out CREmbed crembed))
            {
                var trigger = cr.Trigger.ResolveTriggerString(ctx, client);
                var substringIndex = trigger.Length;
                if (cr.ContainsAnywhere)
                {
                    var pos = ctx.Content.GetWordPosition(trigger);
                    if (pos == WordPosition.Start)
                        substringIndex += 1;
                    else if (pos == WordPosition.End)
                        substringIndex = ctx.Content.Length;
                    else if (pos == WordPosition.Middle)
                        substringIndex += ctx.Content.IndexOf(trigger);
                }

                var rep = new ReplacementBuilder()
                    .WithDefault(ctx.Author, ctx.Channel, (ctx.Channel as ITextChannel)?.Guild, client)
                    .WithOverride("%target%", () => ctx.Content.Substring(substringIndex).Trim())
                    .Build();

                rep.Replace(crembed);

                return await channel.EmbedAsync(crembed.ToEmbed(), crembed.PlainText?.SanitizeMentions() ?? "");
            }
            return await channel.SendMessageAsync((await cr.ResponseWithContextAsync(ctx, client, cr.ContainsAnywhere)).SanitizeMentions());
        }

        public static WordPosition GetWordPosition(this string str, string word)
        {
            var indexOfWord = str.IndexOf(word);
            if (indexOfWord == -1)
                return WordPosition.None;

            if (indexOfWord == 0) // on start
            {
                if (word.Length < str.Length && str.isInvalidWordChar(word.Length)) // filter char after word index
                    return WordPosition.Start;
            }
            else if ((indexOfWord + word.Length) == str.Length) // on end
            {
                if (str.isInvalidWordChar(indexOfWord - 1)) // filter char before word index
                    return WordPosition.End;
            }
            else if (str.isInvalidWordChar(indexOfWord - 1) && str.isInvalidWordChar(indexOfWord + word.Length)) // on middle
                return WordPosition.Middle;

            return WordPosition.None;
        }

        private static bool isInvalidWordChar(this string str, int index)
        {
            var ch = (ushort)str[index];
            if (ch > 64 && ch <= 90) // must be A-Z
                return false;
            if (ch > 97 && ch <= 122) // a-z
                return false;

            return true;
        }
    }

    public enum WordPosition
    {
        None,
        Start,
        Middle,
        End,
    }
}