using System;
using System.Collections.Generic;
using System.IO;
using System.Text.Json;
using System.Threading;
using System.Threading.Tasks;
using ArcaneLibs.Extensions;
using LibMatrix.Extensions;
using Microsoft.Extensions.Logging;

namespace LibMatrix.Services;

public class HomeserverResolverService {
    private readonly MatrixHttpClient _httpClient = new();
    private readonly ILogger<HomeserverResolverService> _logger;

    private static readonly Dictionary<string, string> _wellKnownCache = new();
    private static readonly Dictionary<string, SemaphoreSlim> _wellKnownSemaphores = new();

    public HomeserverResolverService(ILogger<HomeserverResolverService> logger) {
        _logger = logger;
    }

    public async Task<string> ResolveHomeserverFromWellKnown(string homeserver) {
        var res = await _resolveHomeserverFromWellKnown(homeserver);
        if (!res.StartsWith("http")) res = "https://" + res;
        if (res.EndsWith(":443")) res = res[..^4];
        return res;
    }

    private async Task<string> _resolveHomeserverFromWellKnown(string homeserver) {
        if (homeserver is null) throw new ArgumentNullException(nameof(homeserver));
        var sem = _wellKnownSemaphores.GetOrCreate(homeserver, _ => new SemaphoreSlim(1, 1));
        await sem.WaitAsync();
        if (_wellKnownCache.TryGetValue(homeserver, out var known)) {
            sem.Release();
            return known;
        }

        string? result = null;
        _logger.LogInformation("Attempting to resolve homeserver: {}", homeserver);
        result ??= await _tryResolveFromClientWellknown(homeserver);
        result ??= await _tryResolveFromServerWellknown(homeserver);
        result ??= await _tryCheckIfDomainHasHomeserver(homeserver);

        if (result is null) throw new InvalidDataException($"Failed to resolve homeserver for {homeserver}! Is it online and configured correctly?");

        //success!
        _logger.LogInformation("Resolved homeserver: {} -> {}", homeserver, result);
        _wellKnownCache[homeserver] = result;
        sem.Release();
        return result;
    }

    private async Task<string?> _tryResolveFromClientWellknown(string homeserver) {
        if (!homeserver.StartsWith("http")) homeserver = "https://" + homeserver;
        if (await _httpClient.CheckSuccessStatus($"{homeserver}/.well-known/matrix/client")) {
            var resp = await _httpClient.GetFromJsonAsync<JsonElement>($"{homeserver}/.well-known/matrix/client");
            var hs = resp.GetProperty("m.homeserver").GetProperty("base_url").GetString();
            return hs;
        }

        _logger.LogInformation("No client well-known...");
        return null;
    }

    private async Task<string?> _tryResolveFromServerWellknown(string homeserver) {
        if (!homeserver.StartsWith("http")) homeserver = "https://" + homeserver;
        if (await _httpClient.CheckSuccessStatus($"{homeserver}/.well-known/matrix/server")) {
            var resp = await _httpClient.GetFromJsonAsync<JsonElement>($"{homeserver}/.well-known/matrix/server");
            var hs = resp.GetProperty("m.server").GetString();
            return hs;
        }

        _logger.LogInformation("No server well-known...");
        return null;
    }

    private async Task<string?> _tryCheckIfDomainHasHomeserver(string homeserver) {
        _logger.LogInformation("Checking if {} hosts a homeserver...", homeserver);
        if (await _httpClient.CheckSuccessStatus($"{homeserver}/_matrix/client/versions"))
            return homeserver;
        _logger.LogInformation("No homeserver on shortname...");
        return null;
    }

    private async Task<string?> _tryCheckIfSubDomainHasHomeserver(string homeserver, string subdomain) {
        homeserver = homeserver.Replace("https://", $"https://{subdomain}.");
        return await _tryCheckIfDomainHasHomeserver(homeserver);
    }
}