/**
 * stream-transform.js - chataibot JSON 流 → OpenAI/Anthropic SSE 转换器
 *
 * chataibot.pro 流式响应格式 (紧凑 JSON 对象流，无换行分隔):
 *   {"type":"botType","data":"gpt-4o"}{"type":"chunk","data":"Hello"}...
 *   {"type":"finalResult","data":{"mainText":"...","questions":[...]}}
 */

import { PassThrough } from 'stream';
import { parseToolCalls, toOpenAIToolCalls, toAnthropicToolUse, detectToolCallStart } from './tool-prompt.js';

/**
 * 流式重复内容检测器
 *
 * chataibot.pro 的搜索模型有时会返回重复内容 (同一段回答重复 2-3 次)。
 * 策略: 滑动窗口检测 — 当新增文本中出现之前已输出内容的大段重复时，截断。
 *
 * @param {number} minRepeatLen - 最小重复片段长度 (默认 150 字符)
 * @returns {{ feed(text): { emit: string, repeated: boolean }, getText(): string }}
 */
function createRepeatDetector(minRepeatLen = 150) {
  let fullText = '';

  return {
    /**
     * 送入新的 chunk 文本，返回应该输出的部分
     * @returns {{ emit: string, repeated: boolean }}
     */
    feed(chunk) {
      if (!chunk) return { emit: '', repeated: false };

      const prevLen = fullText.length;
      fullText += chunk;

      // 文本太短时不检测
      if (fullText.length < minRepeatLen * 2) {
        return { emit: chunk, repeated: false };
      }

      // 检测: 取已有文本的后 minRepeatLen 字符作为 needle，
      // 在之前的文本 (不含最后 needle 自身) 中查找
      const windowSize = Math.min(minRepeatLen, Math.floor(fullText.length / 3));
      if (windowSize < 80) return { emit: chunk, repeated: false };

      // 从新加入的文本末尾往回取 windowSize 长度的片段
      const needle = fullText.substring(fullText.length - windowSize);
      const searchArea = fullText.substring(0, fullText.length - windowSize);
      const idx = searchArea.indexOf(needle);

      if (idx >= 0) {
        // 找到重复 — 计算需要截断的位置
        // needle 在 fullText 中首次出现于 idx，第二次出现于 fullText.length - windowSize
        // 我们需要保留到第一次出现结束的部分，截掉重复
        const repeatStart = fullText.length - windowSize;

        // 只输出 chunk 中在 repeatStart 之前的部分
        const safeEnd = repeatStart - prevLen;
        const emit = safeEnd > 0 ? chunk.substring(0, safeEnd) : '';

        // 回滚 fullText 到截断点
        fullText = fullText.substring(0, repeatStart);

        console.log(`[RepeatDetect] 检测到重复 (${windowSize} chars)，截断输出`);
        return { emit, repeated: true };
      }

      return { emit: chunk, repeated: false };
    },

    getText() {
      return fullText;
    },
  };
}

/**
 * 流预检 — 缓冲流的前几个 JSON 对象，检测是否为 streamingError
 *
 * chataibot 有时在流开始后才返回 "Insufficient credits" 等错误。
 * 此函数先读取前几个对象，如果是错误就 reject (允许上层换号重试)，
 * 否则返回一个包装过的 stream (先重放缓冲的原始数据，再接续剩余流)，
 * transform 函数无需任何修改。
 *
 * @param {ReadableStream} upstreamStream
 * @returns {Promise<ReadableStream>}
 * @throws {Error} 如果流的第一个实质性对象就是 streamingError
 */
export function probeStream(upstreamStream, timeoutMs = 30000) {
  return new Promise((resolve, reject) => {
    let resolved = false;
    let rawChunks = [];

    function cleanup() {
      clearTimeout(timer);
      upstreamStream.removeListener('data', onData);
      upstreamStream.removeListener('end', onEnd);
      upstreamStream.removeListener('error', onError);
    }

    // 超时保护: 防止上游永不响应导致请求永久挂起
    const timer = setTimeout(() => {
      if (resolved) return;
      resolved = true;
      cleanup();
      upstreamStream.destroy();
      reject(new Error('probeStream timeout'));
    }, timeoutMs);

    const parser = createJsonStreamParser((obj) => {
      if (resolved) return;

      if (obj.type === 'streamingError') {
        resolved = true;
        cleanup();
        upstreamStream.resume();
        reject(Object.assign(
          new Error(obj.data || 'Streaming error'),
          { statusCode: 429 }
        ));
        return;
      }

      if (obj.type === 'chunk' || obj.type === 'reasoningContent') {
        resolved = true;
        cleanup();
        upstreamStream.pause();

        const wrapped = new PassThrough();
        for (const chunk of rawChunks) wrapped.write(chunk);
        upstreamStream.pipe(wrapped);
        upstreamStream.resume();

        resolve(wrapped);
      }
    });

    function onData(chunk) {
      rawChunks.push(chunk);
      parser.feed(chunk);
    }
    function onEnd() {
      if (resolved) return;
      parser.flush();
      if (!resolved) {
        resolved = true;
        cleanup();
        const wrapped = new PassThrough();
        for (const chunk of rawChunks) wrapped.write(chunk);
        wrapped.end();
        resolve(wrapped);
      }
    }
    function onError(err) {
      if (resolved) return;
      resolved = true;
      cleanup();
      reject(err);
    }

    upstreamStream.on('data', onData);
    upstreamStream.on('end', onEnd);
    upstreamStream.on('error', onError);
  });
}

/**
 * JSON 对象流解析器 — 通过花括号计数提取完整 JSON 对象
 * chataibot 返回的不是 NDJSON（无换行），而是紧凑的 JSON 对象序列
 */
function createJsonStreamParser(onObject) {
  let buffer = '';
  let depth = 0;
  let inString = false;
  let escape = false;
  let objStart = -1;

  return {
    feed(chunk) {
      buffer += chunk;
      for (let i = 0; i < buffer.length; i++) {
        const ch = buffer[i];

        if (escape) { escape = false; continue; }
        if (ch === '\\' && inString) { escape = true; continue; }
        if (ch === '"') { inString = !inString; continue; }
        if (inString) continue;

        if (ch === '{') {
          if (depth === 0) objStart = i;
          depth++;
        } else if (ch === '}') {
          depth--;
          if (depth === 0 && objStart >= 0) {
            const jsonStr = buffer.substring(objStart, i + 1);
            try { onObject(JSON.parse(jsonStr)); } catch {}
            objStart = -1;
          }
        }
      }

      // 清理已消费的部分
      if (objStart >= 0) {
        buffer = buffer.substring(objStart);
        objStart = 0;
      } else if (depth === 0) {
        buffer = '';
      }
    },
    flush() {
      if (buffer.trim()) {
        try { onObject(JSON.parse(buffer.trim())); } catch {}
      }
      buffer = '';
    },
  };
}

/**
 * chataibot NDJSON → OpenAI SSE 格式
 * @param {Function} onStreamError - 可选回调，流中出现 streamingError 时调用
 */
export function transformToOpenAISSE(upstreamStream, res, model, requestId, onStreamError) {
  res.writeHead(200, {
    'Content-Type': 'text/event-stream',
    'Cache-Control': 'no-cache',
    'Connection': 'keep-alive',
    'Access-Control-Allow-Origin': '*',
  });

  const ts = Math.floor(Date.now() / 1000);

  function writeChunk(delta, finishReason = null) {
    const obj = {
      id: requestId,
      object: 'chat.completion.chunk',
      created: ts,
      model,
      choices: [{ index: 0, delta, finish_reason: finishReason }],
    };
    res.write(`data: ${JSON.stringify(obj)}\n\n`);
  }

  // 先发送 role chunk
  writeChunk({ role: 'assistant', content: '' });

  const detector = createRepeatDetector();
  let stopped = false;

  function finishStream() {
    if (res.writableEnded || stopped) return;
    stopped = true;
    writeChunk({}, 'stop');
    res.write('data: [DONE]\n\n');
    res.end();
  }

  const parser = createJsonStreamParser((obj) => {
    if (stopped) return;
    switch (obj.type) {
      case 'chunk': {
        const { emit, repeated } = detector.feed(obj.data);
        if (emit) writeChunk({ content: emit });
        if (repeated) finishStream();
        break;
      }

      case 'reasoningContent':
        // 兼容 OpenAI o-series reasoning 输出
        writeChunk({ reasoning_content: obj.data });
        break;

      case 'finalResult':
        finishStream();
        break;

      case 'streamingError':
        if (onStreamError) onStreamError(obj.data);
        finishStream();
        break;
    }
  });

  upstreamStream.on('data', (chunk) => parser.feed(chunk));
  upstreamStream.on('end', () => {
    parser.flush();
    finishStream();
  });
  upstreamStream.on('error', () => {
    if (!res.writableEnded) {
      res.write('data: [DONE]\n\n');
      res.end();
    }
  });
}

/**
 * chataibot NDJSON → Anthropic SSE 格式
 * @param {Function} onStreamError - 可选回调，流中出现 streamingError 时调用
 */
export function transformToAnthropicSSE(upstreamStream, res, model, requestId, onStreamError) {
  res.writeHead(200, {
    'Content-Type': 'text/event-stream',
    'Cache-Control': 'no-cache',
    'Connection': 'keep-alive',
    'Access-Control-Allow-Origin': '*',
  });

  function writeEvent(event, data) {
    res.write(`event: ${event}\ndata: ${JSON.stringify(data)}\n\n`);
  }

  let headerSent = false;
  let blockIndex = 0;

  function ensureHeader() {
    if (headerSent) return;
    headerSent = true;

    writeEvent('message_start', {
      type: 'message_start',
      message: {
        id: requestId,
        type: 'message',
        role: 'assistant',
        model,
        content: [],
        stop_reason: null,
        usage: { input_tokens: 0, output_tokens: 0 },
      },
    });

    writeEvent('content_block_start', {
      type: 'content_block_start',
      index: blockIndex,
      content_block: { type: 'text', text: '' },
    });
  }

  const detector = createRepeatDetector();
  let stopped = false;

  function finishAnthropicStream() {
    if (res.writableEnded || stopped) return;
    stopped = true;
    ensureHeader();
    writeEvent('content_block_stop', { type: 'content_block_stop', index: blockIndex });
    writeEvent('message_delta', {
      type: 'message_delta',
      delta: { stop_reason: 'end_turn' },
      usage: { output_tokens: 0 },
    });
    writeEvent('message_stop', { type: 'message_stop' });
    res.end();
  }

  const parser = createJsonStreamParser((obj) => {
    if (stopped) return;
    switch (obj.type) {
      case 'chunk': {
        const { emit, repeated } = detector.feed(obj.data);
        if (emit) {
          ensureHeader();
          writeEvent('content_block_delta', {
            type: 'content_block_delta',
            index: blockIndex,
            delta: { type: 'text_delta', text: emit },
          });
        }
        if (repeated) finishAnthropicStream();
        break;
      }

      case 'reasoningContent':
        ensureHeader();
        writeEvent('content_block_delta', {
          type: 'content_block_delta',
          index: blockIndex,
          delta: { type: 'text_delta', text: obj.data },
        });
        break;

      case 'finalResult':
        finishAnthropicStream();
        break;

      case 'streamingError':
        if (onStreamError) onStreamError(obj.data);
        finishAnthropicStream();
        break;
    }
  });

  upstreamStream.on('data', (chunk) => parser.feed(chunk));
  upstreamStream.on('end', () => {
    parser.flush();
    finishAnthropicStream();
  });
  upstreamStream.on('error', () => {
    if (!res.writableEnded) res.end();
  });
}

/**
 * chataibot → OpenAI SSE (带工具调用检测)
 *
 * 策略: 先正常流式输出文本。当检测到 ```tool_calls 开头时，
 * 停止流式文本输出，缓冲剩余内容。流结束后解析完整文本，
 * 如果包含工具调用则发送 tool_calls chunk，否则补发剩余文本。
 */
export function transformToOpenAISSEWithTools(upstreamStream, res, model, requestId, onStreamError) {
  res.writeHead(200, {
    'Content-Type': 'text/event-stream',
    'Cache-Control': 'no-cache',
    'Connection': 'keep-alive',
    'Access-Control-Allow-Origin': '*',
  });

  const ts = Math.floor(Date.now() / 1000);
  let fullText = '';
  let toolCallDetected = false;
  let streamError = false;

  function writeChunk(delta, finishReason = null) {
    const obj = {
      id: requestId,
      object: 'chat.completion.chunk',
      created: ts,
      model,
      choices: [{ index: 0, delta, finish_reason: finishReason }],
    };
    res.write(`data: ${JSON.stringify(obj)}\n\n`);
  }

  writeChunk({ role: 'assistant', content: '' });

  const detector = createRepeatDetector();

  const parser = createJsonStreamParser((obj) => {
    switch (obj.type) {
      case 'chunk':
        fullText += obj.data;
        if (!toolCallDetected) {
          if (detectToolCallStart(fullText)) {
            toolCallDetected = true;
          } else {
            const { emit, repeated } = detector.feed(obj.data);
            if (emit) writeChunk({ content: emit });
            if (repeated) {
              // 重复内容，停止流式输出但不影响 tool call 解析
            }
          }
        }
        break;

      case 'reasoningContent':
        if (!toolCallDetected) {
          writeChunk({ reasoning_content: obj.data });
        }
        break;

      case 'finalResult':
        if (obj.data?.mainText) fullText = obj.data.mainText;
        // 最终处理在 end 事件中
        break;

      case 'streamingError':
        streamError = true;
        if (onStreamError) onStreamError(obj.data);
        break;
    }
  });

  upstreamStream.on('data', (chunk) => parser.feed(chunk));
  upstreamStream.on('end', () => {
    parser.flush();
    if (res.writableEnded) return;

    if (streamError) {
      writeChunk({}, 'stop');
      res.write('data: [DONE]\n\n');
      res.end();
      return;
    }

    // 解析完整文本中的 tool calls
    const { hasToolCalls, toolCalls, textContent } = parseToolCalls(fullText);

    if (hasToolCalls) {
      // 如果之前已经流式输出了部分文本 (tool_calls 标记之前的文本)
      // 而解析后 textContent 为空或很少，无需额外处理

      // 发送 tool_calls
      const openaiToolCalls = toOpenAIToolCalls(toolCalls);
      for (let i = 0; i < openaiToolCalls.length; i++) {
        const tc = openaiToolCalls[i];
        // 首个 chunk: 含 tool call id, type, function.name, function.arguments 开始部分
        writeChunk({
          tool_calls: [{
            index: i,
            id: tc.id,
            type: 'function',
            function: { name: tc.function.name, arguments: tc.function.arguments },
          }],
        });
      }
      writeChunk({}, 'tool_calls');
    } else {
      // 没有工具调用 — 如果之前因检测到 ```tool_calls 停了输出
      // 需要补发被缓冲的文本
      if (toolCallDetected) {
        // 找到之前已输出的部分，补发剩余
        const markerIdx = fullText.indexOf('```tool_calls');
        if (markerIdx >= 0) {
          writeChunk({ content: fullText.substring(markerIdx) });
        }
      }
      writeChunk({}, 'stop');
    }

    res.write('data: [DONE]\n\n');
    res.end();
  });

  upstreamStream.on('error', () => {
    if (!res.writableEnded) {
      res.write('data: [DONE]\n\n');
      res.end();
    }
  });
}

/**
 * chataibot → Anthropic SSE (带工具调用检测)
 *
 * 同 OpenAI 版本，先流式输出文本，检测到工具调用后缓冲，
 * 最终解析并发送 tool_use content blocks。
 */
export function transformToAnthropicSSEWithTools(upstreamStream, res, model, requestId, onStreamError) {
  res.writeHead(200, {
    'Content-Type': 'text/event-stream',
    'Cache-Control': 'no-cache',
    'Connection': 'keep-alive',
    'Access-Control-Allow-Origin': '*',
  });

  function writeEvent(event, data) {
    res.write(`event: ${event}\ndata: ${JSON.stringify(data)}\n\n`);
  }

  let headerSent = false;
  let textBlockIndex = 0;
  let fullText = '';
  let toolCallDetected = false;
  let streamError = false;

  function ensureHeader() {
    if (headerSent) return;
    headerSent = true;
    writeEvent('message_start', {
      type: 'message_start',
      message: {
        id: requestId,
        type: 'message',
        role: 'assistant',
        model,
        content: [],
        stop_reason: null,
        usage: { input_tokens: 0, output_tokens: 0 },
      },
    });
    writeEvent('content_block_start', {
      type: 'content_block_start',
      index: textBlockIndex,
      content_block: { type: 'text', text: '' },
    });
  }

  const detector = createRepeatDetector();

  const parser = createJsonStreamParser((obj) => {
    switch (obj.type) {
      case 'chunk':
        fullText += obj.data;
        if (!toolCallDetected) {
          if (detectToolCallStart(fullText)) {
            toolCallDetected = true;
          } else {
            const { emit, repeated } = detector.feed(obj.data);
            if (emit) {
              ensureHeader();
              writeEvent('content_block_delta', {
                type: 'content_block_delta',
                index: textBlockIndex,
                delta: { type: 'text_delta', text: emit },
              });
            }
            // repeated 时停止流式输出，但不影响 tool call 解析
          }
        }
        break;

      case 'reasoningContent':
        if (!toolCallDetected) {
          ensureHeader();
          writeEvent('content_block_delta', {
            type: 'content_block_delta',
            index: textBlockIndex,
            delta: { type: 'text_delta', text: obj.data },
          });
        }
        break;

      case 'finalResult':
        if (obj.data?.mainText) fullText = obj.data.mainText;
        break;

      case 'streamingError':
        streamError = true;
        if (onStreamError) onStreamError(obj.data);
        break;
    }
  });

  upstreamStream.on('data', (chunk) => parser.feed(chunk));
  upstreamStream.on('end', () => {
    parser.flush();
    if (res.writableEnded) return;
    ensureHeader();

    if (streamError) {
      writeEvent('content_block_stop', { type: 'content_block_stop', index: textBlockIndex });
      writeEvent('message_delta', {
        type: 'message_delta',
        delta: { stop_reason: 'end_turn' },
        usage: { output_tokens: 0 },
      });
      writeEvent('message_stop', { type: 'message_stop' });
      res.end();
      return;
    }

    const { hasToolCalls, toolCalls, textContent } = parseToolCalls(fullText);

    if (hasToolCalls) {
      // 关闭文本 block
      writeEvent('content_block_stop', { type: 'content_block_stop', index: textBlockIndex });

      // 发送 tool_use blocks
      const toolUseBlocks = toAnthropicToolUse(toolCalls);
      for (let i = 0; i < toolUseBlocks.length; i++) {
        const blockIdx = textBlockIndex + 1 + i;
        const tu = toolUseBlocks[i];
        writeEvent('content_block_start', {
          type: 'content_block_start',
          index: blockIdx,
          content_block: { type: 'tool_use', id: tu.id, name: tu.name, input: {} },
        });
        writeEvent('content_block_delta', {
          type: 'content_block_delta',
          index: blockIdx,
          delta: { type: 'input_json_delta', partial_json: JSON.stringify(tu.input) },
        });
        writeEvent('content_block_stop', { type: 'content_block_stop', index: blockIdx });
      }

      writeEvent('message_delta', {
        type: 'message_delta',
        delta: { stop_reason: 'tool_use' },
        usage: { output_tokens: 0 },
      });
    } else {
      // 没有工具调用 — 补发被缓冲的文本
      if (toolCallDetected) {
        const markerIdx = fullText.indexOf('```tool_calls');
        if (markerIdx >= 0) {
          writeEvent('content_block_delta', {
            type: 'content_block_delta',
            index: textBlockIndex,
            delta: { type: 'text_delta', text: fullText.substring(markerIdx) },
          });
        }
      }
      writeEvent('content_block_stop', { type: 'content_block_stop', index: textBlockIndex });
      writeEvent('message_delta', {
        type: 'message_delta',
        delta: { stop_reason: 'end_turn' },
        usage: { output_tokens: 0 },
      });
    }

    writeEvent('message_stop', { type: 'message_stop' });
    res.end();
  });

  upstreamStream.on('error', () => {
    if (!res.writableEnded) res.end();
  });
}

/**
 * 消费 NDJSON 流，收集完整响应 (用于非流式请求)
 */
export function collectFullResponse(upstreamStream) {
  return new Promise((resolve, reject) => {
    let text = '';
    let reasoning = '';
    let actualModel = '';

    const parser = createJsonStreamParser((obj) => {
      switch (obj.type) {
        case 'botType':
          actualModel = obj.data;
          break;
        case 'chunk':
          text += obj.data;
          break;
        case 'reasoningContent':
          reasoning += obj.data;
          break;
        case 'finalResult':
          if (obj.data?.mainText) text = obj.data.mainText;
          break;
        case 'streamingError':
          reject(new Error(obj.data || 'Streaming error'));
          break;
      }
    });

    upstreamStream.on('data', (chunk) => parser.feed(chunk));
    upstreamStream.on('end', () => {
      parser.flush();
      // 去重: 检测并移除重复的大段文本
      text = deduplicateText(text);
      resolve({ text, reasoning, model: actualModel });
    });
    upstreamStream.on('error', reject);
  });
}

/**
 * 对完整文本做后处理去重
 * 检测是否有大段内容重复出现，保留第一次出现
 */
function deduplicateText(text) {
  if (!text || text.length < 300) return text;

  // 策略: 尝试不同的片段长度 (200, 300, 500)，
  // 从文本中间位置取一个 needle，看后半部分是否有重复
  for (const windowSize of [500, 300, 200]) {
    if (text.length < windowSize * 2) continue;

    // 取文本前 1/3 处的片段作为 needle
    const start = Math.floor(text.length / 3);
    const needle = text.substring(start, start + windowSize);

    // 在 needle 之后的文本中查找重复
    const searchFrom = start + windowSize;
    const repeatIdx = text.indexOf(needle, searchFrom);

    if (repeatIdx >= 0) {
      // 找到重复 — 截断到重复开始处
      console.log(`[Dedup] 非流式去重: ${text.length} → ${repeatIdx} (window=${windowSize})`);
      return text.substring(0, repeatIdx).trimEnd();
    }
  }

  return text;
}