'use strict';

const vscode = require('vscode');
const fs = require('fs');
const path = require('path');
const crypto = require('crypto');
const { spawn } = require('child_process');

const MAX_HOOK_OUTPUT = 1024 * 1024;

function projectRoot() {
  const folders = vscode.workspace.workspaceFolders || [];
  for (const folder of folders) {
    const root = folder.uri.fsPath;
    if (fs.existsSync(path.join(root, '.casan', 'config.json'))) {
      return root;
    }
  }
  return undefined;
}

function pythonCommand() {
  const configured = vscode.workspace.getConfiguration('casan').get('pythonPath', '').trim();
  if (configured) {
    return { command: configured, prefix: [] };
  }
  return process.platform === 'win32'
    ? { command: 'py', prefix: ['-3'] }
    : { command: 'python3', prefix: [] };
}

function runHook(root, event, payload, token) {
  const bootstrap = path.join(root, '.casan', 'casan-hook.py');
  if (!fs.existsSync(bootstrap)) {
    return Promise.reject(new Error('Missing .casan/casan-hook.py. Run `casan init` again.'));
  }
  const runtime = pythonCommand();
  const timeoutMs = vscode.workspace.getConfiguration('casan').get('hookTimeoutMs', 20000);
  const args = [...runtime.prefix, bootstrap, '--client', 'vscode-copilot', '--event', event];

  return new Promise((resolve, reject) => {
    const child = spawn(runtime.command, args, {
      cwd: root,
      env: { ...process.env, CASAN_APP_ROOT: root },
      windowsHide: true,
      stdio: ['pipe', 'pipe', 'pipe']
    });
    let stdout = '';
    let stderr = '';
    let settled = false;
    const finish = (error, value) => {
      if (settled) return;
      settled = true;
      clearTimeout(timer);
      cancellation.dispose();
      if (error) reject(error); else resolve(value);
    };
    const timer = setTimeout(() => {
      child.kill();
      finish(new Error(`CASAN ${event} timed out after ${timeoutMs} ms`));
    }, timeoutMs);
    const cancellation = token.onCancellationRequested(() => {
      child.kill();
      finish(new vscode.CancellationError());
    });
    child.stdout.on('data', chunk => {
      stdout += chunk.toString('utf8');
      if (stdout.length > MAX_HOOK_OUTPUT) {
        child.kill();
        finish(new Error('CASAN hook output exceeded the safety limit'));
      }
    });
    child.stderr.on('data', chunk => {
      stderr += chunk.toString('utf8');
      if (stderr.length > MAX_HOOK_OUTPUT) stderr = stderr.slice(-MAX_HOOK_OUTPUT);
    });
    child.on('error', error => finish(error));
    child.on('close', code => {
      let parsed;
      try {
        parsed = JSON.parse(stdout.trim() || '{}');
      } catch (_error) {
        finish(new Error(`CASAN ${event} returned invalid JSON${stderr ? `: ${stderr.trim()}` : ''}`));
        return;
      }
      if (code !== 0 && parsed.decision !== 'block') {
        finish(new Error(parsed.reason || stderr.trim() || `CASAN ${event} failed (${code})`));
        return;
      }
      finish(undefined, parsed);
    });
    child.stdin.end(JSON.stringify(payload));
  });
}

async function abortQuietly(root, admissionId, reason) {
  if (!admissionId) return;
  const source = new vscode.CancellationTokenSource();
  try {
    await runHook(root, 'Abort', { admission_id: admissionId, reason }, source.token);
  } catch (_error) {
    // The primary error is more useful to the user; abort remains best-effort.
  } finally {
    source.dispose();
  }
}

async function handler(request, _context, stream, token) {
  const root = projectRoot();
  if (!root) {
    stream.markdown('CASAN is not initialized in this workspace. Run `casan init` at the project root.');
    return { metadata: { certified: false, reason: 'not_initialized' } };
  }
  if (!vscode.workspace.isTrusted) {
    stream.markdown('CASAN requires a trusted VS Code workspace before it can run project governance.');
    return { metadata: { certified: false, reason: 'workspace_untrusted' } };
  }
  if (request.command === 'status') {
    stream.markdown('CASAN is initialized. Prompts sent explicitly to `@casan` use the governed route. Built-in Copilot chat is not globally intercepted.');
    return { metadata: { certified: false, reason: 'status_only' } };
  }

  const sessionId = crypto.randomUUID();
  const turnId = crypto.randomUUID();
  const started = Date.now();
  let admissionId;
  try {
    const begin = await runHook(root, 'Begin', {
      project: root,
      session_id: sessionId,
      turn_id: turnId,
      prompt: request.prompt,
      client_version: vscode.version
    }, token);
    if (begin.decision === 'block' || !begin.admission_id) {
      stream.markdown(`CASAN blocked this prompt: ${begin.reason || 'admission denied'}`);
      return { metadata: { certified: false, traceId: begin.trace_id } };
    }
    admissionId = begin.admission_id;
    stream.progress(`CASAN admission ${begin.trace_id || 'opened'}`);

    const messages = [
      vscode.LanguageModelChatMessage.User(
        'You are operating through the CASAN governed chat route. Follow the user request, do not claim to have executed tools or changed files, and clearly state when a requested side effect requires a supported agentic client.'
      ),
      vscode.LanguageModelChatMessage.User(request.prompt)
    ];
    const response = await request.model.sendRequest(messages, {}, token);
    let summary = '';
    for await (const fragment of response.text) {
      summary += fragment;
      stream.markdown(fragment);
    }
    await runHook(root, 'Telemetry', {
      admission_id: admissionId,
      model: request.model.id,
      runtime_ms: Date.now() - started,
      cost_source: 'unavailable'
    }, token);
    const finalized = await runHook(root, 'Finalize', {
      admission_id: admissionId,
      stop_reason: 'completed',
      assistant_summary: summary.slice(0, 4000)
    }, token);
    return {
      metadata: {
        certified: finalized.decision === 'certified',
        traceId: finalized.trace_id,
        certificationStrength: finalized.certification_strength
      }
    };
  } catch (error) {
    await abortQuietly(root, admissionId, token.isCancellationRequested
      ? 'vscode_cancelled'
      : `vscode_error:${error instanceof Error ? error.message : String(error)}`);
    if (error instanceof vscode.CancellationError) throw error;
    stream.markdown(`CASAN governed chat failed safely: ${error instanceof Error ? error.message : String(error)}`);
    return { metadata: { certified: false, reason: 'runtime_error' } };
  }
}

function activate(context) {
  const participant = vscode.chat.createChatParticipant('fpt-casan.casan', handler);
  context.subscriptions.push(participant);
}

function deactivate() {}

module.exports = { activate, deactivate };