type
  TMsgType = (event, text, image, voice, video, location, link);

  TMessage = Record
    ToUserName: String;
    FromUserName: String;
    CreateTime: Integer;
    MsgType: String;
  end;

uses System.SysUtils, System.JSON, TypInfo, Xml.XMLIntf, Xml.XMLDoc, ActiveX;

function ReplyText(Msg: TMessage; MsgText: String): RawByteString;
var
  X: IXMLDocument;
begin
  X := NewXMLDocument;
  try
    X.Xml.text := TextMsg;
    X.Active := true;
    with X.DocumentElement.ChildNodes do
    begin
      Nodes['ToUserName'].NodeValue := Msg.FromUserName;
      Nodes['FromUserName'].NodeValue := Msg.ToUserName;
      Nodes['CreateTime'].NodeValue := UnixTime(now);
      Nodes['MsgType'].NodeValue := 'text';
      Nodes['Content'].NodeValue := MsgText;
    end;
    Result := UTF8Encode(X.Xml.text);
  finally
    X.Active := False;
    X := nil;
  end;
end;

function ResponseText(M: TMessage; X: IXMLDocument): RawByteString;
begin
      Result := ReplyText(M, '有什么问题留言吧，我们会尽快答复您！');
end;

function ResponseImage(M: TMessage; X: IXMLDocument): RawByteString;
begin
  Result := ReplyText(M, '您发的图片很漂亮！');
end;

function ResponseVoice(M: TMessage; X: IXMLDocument): RawByteString;
begin
  try
    with X.DocumentElement.ChildNodes do
    begin
      Result := ReplyText(M, Format(VoiceMsg,
        [Nodes['Recognition'].NodeValue]));
    end;
  except
    Result := ReplyText(M, '没听清您说什么，不过您的声音很有磁性^_^');
  end;
end;

function ResponseVideo(M: TMessage; X: IXMLDocument): RawByteString;
begin
  Result := ReplyText(M, '什么视频？不会是A片吧？');
end;

function ResponseLocation(M: TMessage; X: IXMLDocument): RawByteString;
begin
  Result := ReplyText(M, '把你的位置发给我了，不怕我跟踪你？哈哈！');
end;

function ResponseLink(M: TMessage; X: IXMLDocument): RawByteString;
begin
  Result := ReplyText(M, '什么链接？不会木马吧？');
end;

procedure AddLog(S: String);
begin
  Form1.Log.Lines.Add(formatdatetime(TimeFormat, now) + ': ' + S);
end;

function Response(M: TMessage; X: IXMLDocument): RawByteString;
var
  MsgType: TMsgType;
begin
  MsgType := TMsgType(GetEnumValue(TypeInfo(TMsgType), M.MsgType));
  case MsgType of
    event:
      begin
        Result := ResponseEvent(M, X);
      end;
    text:
      begin
        Result := ResponseText(M, X);
        addlog('收到文本消息...' + M.MsgType + ', ' + M.FromUserName);
      end;
    image:
      begin
        Result := ResponseImage(M, X);
        addlog('收到图片消息...' + M.MsgType + ', ' + M.FromUserName);
      end;
    voice:
      begin
        Result := ResponseVoice(M, X);
        addlog('收到语音消息...' + M.MsgType + ', ' + M.FromUserName);
      end;
    video:
      begin
        Result := ResponseVideo(M, X);
        addlog('收到视频消息...' + M.MsgType + ', ' + M.FromUserName);
      end;
    location:
      begin
        Result := ResponseLocation(M, X);
        addlog('收到位置消息...' + M.MsgType + ', ' + M.FromUserName);
      end;
    link:
      begin
        Result := ResponseLink(M, X);
        addlog('收到链接消息...' + M.MsgType + ', ' + M.FromUserName);
      end
  else
    begin
      Result := '';
      addlog('收到未知消息：' + M.MsgType + ', ' + M.FromUserName);
    end;
  end;
end;

function Analysis(Stream: TStream): RawByteString;
var
  X: IXMLDocument;
  M: TMessage;
begin
  try
    X := NewXMLDocument;
    X.Xml.BeginUpdate;
    X.Xml.text := StreamToString(Stream);
    X.Xml.EndUpdate;
    X.Active := true;
    with X.DocumentElement.ChildNodes do
    begin
      M.ToUserName := Nodes['ToUserName'].NodeValue;
      M.FromUserName := Nodes['FromUserName'].NodeValue;
      M.CreateTime := Nodes['CreateTime'].NodeValue;
      M.MsgType := Nodes['MsgType'].NodeValue;
    end;
    Result := Response(M, X);
  finally
    X.Active := False;
    X := nil;
  end;
end;

procedure Form1.IdHTTPServerCommandGet(AContext: TIdContext;
  ARequestInfo: TIdHTTPRequestInfo; AResponseInfo: TIdHTTPResponseInfo);
begin
  if CheckSignature(ARequestInfo) then
    if ARequestInfo.Params.Values['echostr'] <> '' then
    begin
      AResponseInfo.ContentType := 'text/html; charset=UTF-8';
      AResponseInfo.ContentText := ARequestInfo.Params.Values['echostr'];
    end
    else
    begin
      if ARequestInfo.PostStream <> nil then
      begin
        CoInitialize(nil);
        try
          AResponseInfo.ContentType := 'text/html; charset=UTF-8';
          AResponseInfo.ContentText := Analysis(ARequestInfo.PostStream);
        finally
          CoUninitialize;
        end;
      end;
    end;
end;