/**
 * spike.ts — Phase 0 Spike: tmux Stream PoC
 * 
 * Spawns a tmux session running pi, pipes the output via pipe-pane to a FIFO,
 * and streams it over WebSocket.
 * 
 * This is throwaway PoC code to verify the foundational assumption:
 * - pi runs cleanly in tmux
 * - pipe-pane captures ANSI output accurately
 * - WebSocket streaming has acceptable latency
 * - SSH attach and WS stream stay in sync
 */

import * as fs from "node:fs";
import * as path from "node:path";
import * as os from "node:os";
import { execSync } from "node:child_process";
import { WebSocketServer } from "ws";

const SPIKE_SESSION = "pi-spike";
const WS_PORT = 7799;
const FIFO_PATH = path.join(os.tmpdir(), `${SPIKE_SESSION}.fifo`);

/**
 * Check if a tmux session exists
 */
function sessionExists(sessionName: string): boolean {
  try {
    execSync(`tmux has-session -t ${sessionName} 2>/dev/null`);
    return true;
  } catch {
    return false;
  }
}

/**
 * Create a new tmux session running pi
 */
function createSession(sessionName: string): void {
  console.log(`[spike] Creating tmux session: ${sessionName}`);
  execSync(`tmux new-session -d -s ${sessionName} -x 120 -y 40 'pi'`);
}

/**
 * Setup pipe-pane to stream to a FIFO
 */
function setupPipePane(sessionName: string, fifoPath: string): void {
  // Remove existing FIFO if present
  if (fs.existsSync(fifoPath)) {
    fs.unlinkSync(fifoPath);
  }
  
  // Create new FIFO
  execSync(`mkfifo ${fifoPath}`);
  console.log(`[spike] Created FIFO: ${fifoPath}`);
  
  // Setup pipe-pane
  execSync(`tmux pipe-pane -t ${sessionName} -o "cat > ${fifoPath}"`);
  console.log(`[spike] Attached pipe-pane to session ${sessionName}`);
}

/**
 * Start the WebSocket server and stream from FIFO
 * Uses a single FIFO reader that broadcasts to all connected clients
 */
function startWebSocketServer(fifoPath: string): { wss: WebSocketServer, cleanup: () => void } {
  const wss = new WebSocketServer({ port: WS_PORT, host: "127.0.0.1" });
  const clients = new Set<any>();
  
  console.log(`[spike] WebSocket server listening on ws://127.0.0.1:${WS_PORT}/spike`);
  
  // Single FIFO reader that broadcasts to all clients
  const stream = fs.createReadStream(fifoPath);
  
  stream.on("data", (chunk: Buffer) => {
    for (const ws of clients) {
      if (ws.readyState === 1) { // WebSocket.OPEN
        ws.send(chunk, { binary: true });
      }
    }
  });
  
  stream.on("error", (err) => {
    console.error(`[spike] FIFO stream error:`, err);
  });
  
  stream.on("end", () => {
    console.log("[spike] FIFO stream ended");
  });
  
  wss.on("connection", (ws, req) => {
    const clientAddr = req.socket.remoteAddress;
    console.log(`[spike] Client connected: ${clientAddr}`);
    clients.add(ws);
    
    ws.on("close", () => {
      console.log(`[spike] Client disconnected: ${clientAddr}`);
      clients.delete(ws);
    });
    
    ws.on("error", (err) => {
      console.error(`[spike] WebSocket error:`, err);
    });
  });
  
  const cleanup = () => {
    stream.destroy();
    wss.close();
  };
  
  return { wss, cleanup };
}

/**
 * Print instructions for connecting to the session
 */
function printInstructions(sessionName: string): void {
  console.log("");
  console.log("=== Spike Server Running ===");
  console.log("");
  console.log("To attach to the tmux session (in another terminal):");
  console.log(`  tmux attach -t ${sessionName}`);
  console.log("");
  console.log("WebSocket endpoint:");
  console.log(`  ws://127.0.0.1:${WS_PORT}/spike`);
  console.log("");
  console.log("To test with the HTML client:");
  const clientPath = path.join(path.dirname(new URL(import.meta.url).pathname), "spike-client.html");
  console.log(`  open ${clientPath}`);
  console.log("");
  console.log("To stop: Ctrl+C in this terminal");
  console.log("");
}

/**
 * Cleanup function
 */
function cleanup(cleanupFn: (() => void) | null): void {
  console.log("\n[spike] Cleaning up...");
  
  if (cleanupFn) {
    cleanupFn();
  }
  
  // Remove FIFO
  if (fs.existsSync(FIFO_PATH)) {
    try {
      fs.unlinkSync(FIFO_PATH);
      console.log("[spike] Removed FIFO");
    } catch (err) {
      console.error("[spike] Failed to remove FIFO:", err);
    }
  }
  
  console.log("[spike] Cleanup complete");
  process.exit(0);
}

/**
 * Main spike entry point
 */
export async function runSpike(): Promise<void> {
  console.log("=== Phase 0 Spike: tmux Stream PoC ===\n");
  
  let cleanupFn: (() => void) | null = null;
  
  // Setup cleanup handlers
  const cleanupHandler = () => cleanup(cleanupFn);
  process.on("SIGINT", cleanupHandler);
  process.on("SIGTERM", cleanupHandler);
  
  try {
    // Step 1: Create or reuse tmux session
    if (sessionExists(SPIKE_SESSION)) {
      console.log(`[spike] Session ${SPIKE_SESSION} already exists, reusing it`);
    } else {
      createSession(SPIKE_SESSION);
    }
    
    // Step 2: Setup pipe-pane to FIFO
    setupPipePane(SPIKE_SESSION, FIFO_PATH);
    
    // Step 3: Start WebSocket server
    const server = startWebSocketServer(FIFO_PATH);
    cleanupFn = server.cleanup;
    
    // Give the server a moment to start
    await new Promise(resolve => setTimeout(resolve, 500));
    
    // Step 4: Print instructions
    printInstructions(SPIKE_SESSION);
    
    // Keep the process alive
    // User can Ctrl+C to stop
    await new Promise(() => {}); // Never resolves
    
  } catch (err) {
    console.error("[spike] Error:", err);
    cleanup(cleanupFn);
  }
}

// Run if invoked directly
if (import.meta.url === `file://${process.argv[1]}`) {
  runSpike();
}