using System;
using System.IO;
using System.Text;
using System.Reflection;
using BestHTTP;
using HarmonyLib;

/// <summary>
/// Fabric-level repairs for two things the game cannot survive as-is:
/// a chunked response the server truncated, and two responses whose shape the
/// client's reader rejects.
/// </summary>
internal static class HttpTolerancePatches
{
    private static long _healed;
    private static int _lastHealReport;

    internal static void Apply(Harmony harmony)
    {
        try
        {
            var target = TargetMethod();
            if (target == null)
            {
                Diag.Warn("[Http] BestHTTP.HTTPResponse.ReadChunkLength(Stream) was not found: " +
                    "a truncated chunked body will keep failing its request.");
                return;
            }

            harmony.Patch(target,
                finalizer: new HarmonyMethod(AccessTools.Method(typeof(HttpTolerancePatches), nameof(Finalizer))));
            Diag.Info("[Http] truncated chunked responses are completed instead of failing their request.");
        }
        catch (Exception ex)
        {
            Diag.Warn("[Http] could not arm the tolerant chunked reader (" + ex.GetType().Name + ": " + ex.Message + ").");
        }
    }

    internal static MethodBase TargetMethod() =>
        AccessTools.Method(typeof(HTTPResponse), "ReadChunkLength", new[] { typeof(Stream) });

    /// <summary>
    /// "Can't parse '' as a hex number" is BestHTTP reading a chunk-size line from a
    /// connection the server had already closed - the pooled keep-alive connection
    /// it picked was dead. Ending the body there (chunk length 0) delivers the
    /// response that did arrive instead of failing the request, which is what the
    /// heartbeats need: their ack body is empty anyway.
    /// </summary>
    private static Exception Finalizer(Exception __exception, ref int __result)
    {
        try
        {
            if (__exception == null) return null;
            if (!ResponseRepair.IsTruncatedChunkFailure(__exception.Message)) return __exception;

            ReportHealed();
            __result = 0;
            __exception = null;
            return null;
        }
        catch
        {
            return __exception;
        }
    }

    private static void ReportHealed()
    {
        var count = System.Threading.Interlocked.Increment(ref _healed);
        var now = Environment.TickCount;
        if (count != 1 && unchecked(now - _lastHealReport) < 60000) return;
        _lastHealReport = now;
        Diag.Warn("[Http] a chunked response ended early (dead pooled connection); the request was completed "
            + "with the bytes that arrived instead of failing. Occurrences so far: " + count + ".");
    }

    /// <summary>
    /// Applies <see cref="ResponseRepair"/> to a live response before the client's own
    /// callback reads it. Called from the request funnel, always on the transport
    /// thread that owns the response.
    /// </summary>
    internal static void RepairResponse(HTTPResponse response, string path, string query)
    {
        try
        {
            if (response == null || string.IsNullOrEmpty(path)) return;
            if (response.StatusCode != 200) return;

            string body;
            try { body = response.DataAsText; }
            catch { return; }

            var repaired = ResponseRepair.RepairBody(path, query, body, out var note);
            if (repaired == null) return;

            response.Data = Encoding.UTF8.GetBytes(repaired);

            if (Diag.FirstTime("repair:" + path))
                Diag.Warn("[Repair] " + path + ": " + note + ".");
        }
        catch (Exception ex)
        {
            Diag.Warn("[Repair] could not repair a " + path + " response: " + ex.GetType().Name + ": " + ex.Message);
        }
    }
}