#!/usr/bin/env node
/**
 * Node.js implementation of the ChildWorker for CommTester.
 * 
 * Protocol: 4-byte little-endian length prefix + UTF-8 JSON payload
 * 
 * Usage: node child-worker.js --pipe <pipeName> --id <childId>
 */

const net = require('net');
const path = require('path');

// ─────────────────────────────────────────────────────────────────────────────
// Argument Parsing
// ─────────────────────────────────────────────────────────────────────────────

function parseArgs(args) {
    let pipeName = null;
    let childId = null;

    for (let i = 0; i < args.length; i++) {
        if (args[i] === '--pipe' && i + 1 < args.length) {
            pipeName = args[++i];
        } else if (args[i] === '--id' && i + 1 < args.length) {
            childId = parseInt(args[++i], 10);
        }
    }

    return { pipeName, childId };
}

const { pipeName, childId } = parseArgs(process.argv.slice(2));

if (!pipeName || childId === null || isNaN(childId)) {
    console.error('Usage: node child-worker.js --pipe <pipeName> --id <childId>');
    process.exit(2);
}

// ─────────────────────────────────────────────────────────────────────────────
// IPC Protocol Constants (matching IpcKinds.cs)
// ─────────────────────────────────────────────────────────────────────────────

const IpcKinds = {
    Hello: 'hello',
    Ping: 'ping',
    Pong: 'pong',
    StartWork: 'startWork',
    CancelWork: 'cancelWork',
    Log: 'log',
    Progress: 'progress',
    Result: 'result',
    Error: 'error',
};

// ─────────────────────────────────────────────────────────────────────────────
// Frame Serialization
// ─────────────────────────────────────────────────────────────────────────────

/**
 * Writes a frame to the socket with 4-byte little-endian length prefix.
 * @param {net.Socket} socket 
 * @param {object} frame 
 */
function writeFrame(socket, frame) {
    // Add timestamp if not present
    if (!frame.timestamp) {
        frame.timestamp = new Date().toISOString();
    }

    const json = Buffer.from(JSON.stringify(frame), 'utf8');
    const header = Buffer.alloc(4);
    header.writeUInt32LE(json.length, 0);

    socket.write(header);
    socket.write(json);
}

/**
 * Creates a frame reader that emits complete frames.
 * @returns {{ push: (chunk: Buffer) => void, onFrame: (callback: (frame: object) => void) => void }}
 */
function createFrameReader() {
    let buffer = Buffer.alloc(0);
    let frameCallback = null;

    return {
        push(chunk) {
            buffer = Buffer.concat([buffer, chunk]);
            
            while (buffer.length >= 4) {
                const length = buffer.readUInt32LE(0);
                
                if (length <= 0 || length > 4 * 1024 * 1024) {
                    throw new Error(`Invalid frame length: ${length}`);
                }
                
                if (buffer.length < 4 + length) {
                    break; // Wait for more data
                }

                const jsonBytes = buffer.subarray(4, 4 + length);
                buffer = buffer.subarray(4 + length);

                const frame = JSON.parse(jsonBytes.toString('utf8'));
                if (frameCallback) {
                    frameCallback(frame);
                }
            }
        },
        onFrame(callback) {
            frameCallback = callback;
        }
    };
}

// ─────────────────────────────────────────────────────────────────────────────
// Work Task Management
// ─────────────────────────────────────────────────────────────────────────────

let workAbortController = null;
let currentWorkCorrelationId = null;

async function cancelWork() {
    if (workAbortController) {
        workAbortController.abort();
        workAbortController = null;
        currentWorkCorrelationId = null;
    }
}

async function startWork(socket, correlationId, steps, delayMs) {
    await cancelWork();

    currentWorkCorrelationId = correlationId;
    workAbortController = new AbortController();
    const signal = workAbortController.signal;

    // Run work in the background
    (async () => {
        try {
            writeFrame(socket, {
                kind: IpcKinds.Log,
                correlationId,
                payload: { level: 'info', message: `Child ${childId}: work started (${steps} steps).` }
            });

            for (let i = 1; i <= steps; i++) {
                if (signal.aborted) {
                    return;
                }

                await sleep(delayMs, signal);

                const percent = (i * 100.0) / steps;
                writeFrame(socket, {
                    kind: IpcKinds.Progress,
                    correlationId,
                    payload: { step: i, total: steps, percent }
                });

                // Log every ~20% of progress
                if (i % Math.max(1, Math.floor(steps / 5)) === 0) {
                    writeFrame(socket, {
                        kind: IpcKinds.Log,
                        correlationId,
                        payload: { level: 'debug', message: `Child ${childId}: reached step ${i}/${steps}.` }
                    });
                }
            }

            writeFrame(socket, {
                kind: IpcKinds.Result,
                correlationId,
                payload: { message: `Child ${childId}: work finished.` }
            });
        } catch (err) {
            if (err.name !== 'AbortError') {
                writeFrame(socket, {
                    kind: IpcKinds.Error,
                    correlationId,
                    payload: { message: `Child ${childId}: work failed - ${err.message}` }
                });
            }
        } finally {
            if (currentWorkCorrelationId === correlationId) {
                workAbortController = null;
                currentWorkCorrelationId = null;
            }
        }
    })();
}

function sleep(ms, signal) {
    return new Promise((resolve, reject) => {
        const timeout = setTimeout(resolve, ms);
        if (signal) {
            signal.addEventListener('abort', () => {
                clearTimeout(timeout);
                reject(new DOMException('Aborted', 'AbortError'));
            }, { once: true });
        }
    });
}

// ─────────────────────────────────────────────────────────────────────────────
// Main
// ─────────────────────────────────────────────────────────────────────────────

const pipePath = process.platform === 'win32' 
    ? `\\\\.\\pipe\\${pipeName}` 
    : `/tmp/${pipeName}`;

const socket = net.createConnection(pipePath, () => {
    // Connection established - send hello
    writeFrame(socket, {
        kind: IpcKinds.Hello,
        payload: { childId, pid: process.pid }
    });
});

const frameReader = createFrameReader();

frameReader.onFrame((frame) => {
    switch (frame.kind) {
        case IpcKinds.Ping:
            writeFrame(socket, {
                kind: IpcKinds.Pong,
                correlationId: frame.correlationId,
                payload: { childId }
            });
            break;

        case IpcKinds.StartWork: {
            const payload = frame.payload || {};
            const steps = payload.steps || 25;
            const delayMs = payload.delayMs || 150;
            const corr = frame.correlationId || crypto.randomUUID().replace(/-/g, '');
            startWork(socket, corr, steps, delayMs);
            break;
        }

        case IpcKinds.CancelWork:
            cancelWork().then(() => {
                writeFrame(socket, {
                    kind: IpcKinds.Log,
                    correlationId: frame.correlationId || currentWorkCorrelationId,
                    payload: { level: 'info', message: `Child ${childId}: work cancelled.` }
                });
            });
            break;

        default:
            writeFrame(socket, {
                kind: IpcKinds.Error,
                correlationId: frame.correlationId,
                payload: { message: `Unknown command kind '${frame.kind}'.` }
            });
            break;
    }
});

socket.on('data', (chunk) => {
    try {
        frameReader.push(chunk);
    } catch (err) {
        console.error('Frame read error:', err.message);
        socket.destroy();
    }
});

socket.on('error', (err) => {
    console.error('Socket error:', err.message);
    process.exit(1);
});

socket.on('close', () => {
    cancelWork();
    process.exit(0);
});

// Handle graceful shutdown
process.on('SIGINT', () => {
    cancelWork();
    socket.end();
});

process.on('SIGTERM', () => {
    cancelWork();
    socket.end();
});