/**
 * Process Log Writer
 *
 * Handles per-process stdout/stderr capture to individual log files.
 * Optionally emits log events to an EventBus for real-time streaming.
 */

import { createWriteStream, type WriteStream } from 'node:fs';
import type { LogManager } from './manager.js';
import type { EventBus, LogEntryEvent } from '../events/index.js';

/**
 * Formats a timestamp for log output.
 * Format: [YYYY-MM-DD HH:mm:ss.SSS]
 */
function formatTimestamp(date: Date): string {
  const pad = (n: number, w = 2) => n.toString().padStart(w, '0');
  const year = date.getFullYear();
  const month = pad(date.getMonth() + 1);
  const day = pad(date.getDate());
  const hours = pad(date.getHours());
  const minutes = pad(date.getMinutes());
  const seconds = pad(date.getSeconds());
  const ms = pad(date.getMilliseconds(), 3);
  return `[${year}-${month}-${day} ${hours}:${minutes}:${seconds}.${ms}]`;
}

/**
 * Writes stdout/stderr output to per-process log files.
 *
 * Each line of output is prefixed with a timestamp.
 * Handles backpressure by exposing drain events on the underlying streams.
 */
export class ProcessLogWriter {
  private readonly processId: string;
  private readonly logManager: LogManager;
  private readonly eventBus: EventBus | undefined;
  private stdoutStream: WriteStream | null = null;
  private stderrStream: WriteStream | null = null;

  /**
   * Creates a new ProcessLogWriter.
   * @param processId - Unique identifier for the process
   * @param logManager - LogManager instance for directory management
   * @param eventBus - Optional EventBus for emitting log entry events
   */
  constructor(processId: string, logManager: LogManager, eventBus?: EventBus) {
    this.processId = processId;
    this.logManager = logManager;
    this.eventBus = eventBus;
  }

  /**
   * Opens file handles for stdout and stderr log files.
   * Creates the process log directory if it doesn't exist.
   */
  async open(): Promise<void> {
    // Ensure the process directory exists
    await this.logManager.ensureProcessDir(this.processId);

    // Open write streams in append mode
    const stdoutPath = this.logManager.getLogPath(this.processId, 'stdout');
    const stderrPath = this.logManager.getLogPath(this.processId, 'stderr');

    this.stdoutStream = createWriteStream(stdoutPath, { flags: 'a' });
    this.stderrStream = createWriteStream(stderrPath, { flags: 'a' });

    // Wait for both streams to be ready
    await Promise.all([
      new Promise<void>((resolve, reject) => {
        this.stdoutStream!.once('open', () => resolve());
        this.stdoutStream!.once('error', reject);
      }),
      new Promise<void>((resolve, reject) => {
        this.stderrStream!.once('open', () => resolve());
        this.stderrStream!.once('error', reject);
      }),
    ]);
  }

  /**
   * Writes data to the stdout log file with timestamps.
   * Also emits a LogEntry event if an EventBus was provided.
   * @param data - String or Buffer to write
   * @returns Promise that resolves when write is complete (including drain if needed)
   */
  async writeStdout(data: string | Buffer): Promise<void> {
    if (!this.stdoutStream) {
      throw new Error('Log writer not open. Call open() first.');
    }
    await this.writeWithTimestamp(this.stdoutStream, data);

    // Emit log entry event for real-time streaming
    if (this.eventBus) {
      const content = typeof data === 'string' ? data : data.toString('utf-8');
      const event: LogEntryEvent = {
        type: 'log:entry',
        timestamp: new Date(),
        payload: {
          processId: this.processId,
          stream: 'stdout',
          data: content,
        },
      };
      this.eventBus.emit(event);
    }
  }

  /**
   * Writes data to the stderr log file with timestamps.
   * Also emits a LogEntry event if an EventBus was provided.
   * @param data - String or Buffer to write
   * @returns Promise that resolves when write is complete (including drain if needed)
   */
  async writeStderr(data: string | Buffer): Promise<void> {
    if (!this.stderrStream) {
      throw new Error('Log writer not open. Call open() first.');
    }
    await this.writeWithTimestamp(this.stderrStream, data);

    // Emit log entry event for real-time streaming
    if (this.eventBus) {
      const content = typeof data === 'string' ? data : data.toString('utf-8');
      const event: LogEntryEvent = {
        type: 'log:entry',
        timestamp: new Date(),
        payload: {
          processId: this.processId,
          stream: 'stderr',
          data: content,
        },
      };
      this.eventBus.emit(event);
    }
  }

  /**
   * Writes data with timestamp prefix, handling backpressure.
   */
  private async writeWithTimestamp(
    stream: WriteStream,
    data: string | Buffer
  ): Promise<void> {
    const content = typeof data === 'string' ? data : data.toString('utf-8');
    const timestamp = formatTimestamp(new Date());

    // Prefix each line with timestamp
    const lines = content.split('\n');
    const timestampedLines = lines
      .map((line, index) => {
        // Don't add timestamp to empty trailing line from split
        if (index === lines.length - 1 && line === '') {
          return '';
        }
        return `${timestamp} ${line}`;
      })
      .join('\n');

    // Write with backpressure handling
    const canWrite = stream.write(timestampedLines);
    if (!canWrite) {
      // Wait for drain event before continuing
      await new Promise<void>((resolve) => {
        stream.once('drain', resolve);
      });
    }
  }

  /**
   * Flushes and closes both file handles.
   */
  async close(): Promise<void> {
    const closePromises: Promise<void>[] = [];

    if (this.stdoutStream) {
      closePromises.push(
        new Promise<void>((resolve, reject) => {
          this.stdoutStream!.end(() => {
            this.stdoutStream = null;
            resolve();
          });
          this.stdoutStream!.once('error', reject);
        })
      );
    }

    if (this.stderrStream) {
      closePromises.push(
        new Promise<void>((resolve, reject) => {
          this.stderrStream!.end(() => {
            this.stderrStream = null;
            resolve();
          });
          this.stderrStream!.once('error', reject);
        })
      );
    }

    await Promise.all(closePromises);
  }

  /**
   * Gets the stdout write stream for direct piping.
   * @returns The stdout WriteStream or null if not open
   */
  getStdoutStream(): WriteStream | null {
    return this.stdoutStream;
  }

  /**
   * Gets the stderr write stream for direct piping.
   * @returns The stderr WriteStream or null if not open
   */
  getStderrStream(): WriteStream | null {
    return this.stderrStream;
  }

  /**
   * Gets the process ID for this writer.
   */
  getProcessId(): string {
    return this.processId;
  }
}