import { Readable } from 'node:stream';

function parseSseDataLines(frame) {
  let data = '';
  for (const line of String(frame ?? '').split('\n')) {
    if (line.startsWith('data:')) data += line.slice(5).trim();
  }
  return data;
}

export function parseSessionStreamEvent(frame) {
  const data = parseSseDataLines(frame);
  if (!data) return null;
  try {
    return JSON.parse(data);
  } catch {
    return null;
  }
}

export function eventMatchesRequest(event, requestId) {
  if (!requestId) return true;
  const routingId = event?.chat_request_id ?? event?.request_id ?? null;
  return !routingId || routingId === requestId;
}

function messageContentItems(event) {
  const candidates = [
    event?.message?.content,
    event?.data?.message?.content,
    event?.content,
  ];
  return candidates.find((content) => Array.isArray(content)) ?? [];
}

function parseGenerateImageResult(toolResult) {
  const content = toolResult?.value?.content;
  if (!Array.isArray(content)) return null;
  for (const item of content) {
    if (item?.type !== 'text' || !String(item.text ?? '').trim()) continue;
    try {
      const result = JSON.parse(String(item.text));
      const mimeType = String(result?.source?.mimeType ?? result?.asset?.mimeType ?? '').toLowerCase();
      if (
        result?.ok === true
        && String(result?.jobId ?? '').trim()
        && /^image\/(?:png|jpeg|webp)$/.test(mimeType)
      ) {
        return {
          jobId: String(result.jobId),
          mimeType,
          assetId: String(result?.asset?.id ?? '').trim() || null,
          publicUrl: String(result?.asset?.publicUrl ?? '').trim() || null,
          workspaceRelativePath: String(result?.asset?.workspaceRelativePath ?? '').trim() || null,
        };
      }
    } catch {
      // Ignore non-JSON tool text; it cannot prove a successful image_make delivery.
    }
  }
  return null;
}

function createToolEvidenceCollector() {
  const requestNames = new Map();
  const calls = new Set();
  const successfulCalls = new Set();
  let generateImage = { called: false, succeeded: false };

  return {
    observe(event) {
      for (const item of messageContentItems(event)) {
        if (item?.type === 'toolRequest') {
          const name = String(item?.toolCall?.value?.name ?? '').trim();
          if (!name) continue;
          calls.add(name);
          if (item.id) requestNames.set(String(item.id), name);
          if (name.endsWith('generate_image')) generateImage = { called: true, succeeded: false };
          continue;
        }
        if (item?.type !== 'toolResponse') continue;
        const name = requestNames.get(String(item.id ?? '')) ?? '';
        const result = item.toolResult ?? {};
        const succeeded = result.status === 'success' && result?.value?.isError !== true;
        if (name && succeeded) successfulCalls.add(name);
        if (!name.endsWith('generate_image')) continue;
        const generated = succeeded ? parseGenerateImageResult(result) : null;
        generateImage = generated
          ? { called: true, succeeded: true, ...generated }
          : { called: true, succeeded: false };
      }
    },
    snapshot() {
      return {
        calls: [...calls],
        successfulCalls: [...successfulCalls],
        generateImage,
      };
    },
  };
}

export async function consumeSessionEventsUntilFinish(
  body,
  {
    requestId = null,
    timeoutMs = 15 * 60 * 1000,
    onEvent = null,
  } = {},
) {
  if (!body) {
    const err = new Error('session event stream unavailable');
    err.code = 'SESSION_EVENT_STREAM_UNAVAILABLE';
    throw err;
  }

  const reader = Readable.fromWeb(body);
  const decoder = new TextDecoder();
  const toolEvidence = createToolEvidenceCollector();
  let buffer = '';
  const deadline = Date.now() + Math.max(1, Number(timeoutMs) || 1);

  for await (const chunk of reader) {
    if (Date.now() > deadline) {
      const err = new Error(`session reply timed out after ${timeoutMs}ms`);
      err.code = 'SESSION_REPLY_TIMEOUT';
      err.retryable = false;
      throw err;
    }

    buffer += decoder.decode(chunk, { stream: true });
    const frames = buffer.split('\n\n');
    buffer = frames.pop() ?? '';
    for (const frame of frames) {
      const trimmed = frame.trim();
      if (!trimmed || trimmed.startsWith(':')) continue;
      const event = parseSessionStreamEvent(trimmed);
      if (!event) continue;
      if (!eventMatchesRequest(event, requestId)) continue;
      toolEvidence.observe(event);
      onEvent?.(event);
      if (event.type === 'Error') {
        const err = new Error(String(event.error ?? 'session reply failed'));
        err.code = 'SESSION_REPLY_ERROR';
        err.retryable = false;
        throw err;
      }
      if (event.type === 'Finish') {
        return {
          finishEvent: event,
          tokenState: event.token_state ?? null,
          toolEvidence: toolEvidence.snapshot(),
        };
      }
    }
  }

  const err = new Error('session event stream ended before Finish');
  err.code = 'SESSION_REPLY_INCOMPLETE';
  err.retryable = false;
  throw err;
}