import { execFile } from "node:child_process";
import { promisify } from "node:util";

const execFileAsync = promisify(execFile);
const wait = (ms) => new Promise((resolve) => setTimeout(resolve, ms));
const TYPE_CHUNK_SIZE = 18;
const TYPE_CHUNK_DELAY_MS = 22;

function shellEscape(value) {
  return `'${String(value).replace(/'/g, `'\\''`)}'`;
}

function buildLaunchCommand(command, args, env) {
  const exports = Object.entries(env)
    .filter(([, value]) => value != null && value !== "")
    .map(([key, value]) => `export ${key}=${shellEscape(value)}`)
    .join("; ");

  const commandPart = [command, ...args].map((part) => shellEscape(part)).join(" ");
  return `${exports}; exec ${commandPart}`;
}

async function runTmux(args) {
  return execFileAsync("/opt/homebrew/bin/tmux", args);
}

async function typeLikeHuman(sessionName, text) {
  for (let index = 0; index < text.length; index += TYPE_CHUNK_SIZE) {
    const chunk = text.slice(index, index + TYPE_CHUNK_SIZE);
    if (chunk) {
      await runTmux(["send-keys", "-t", sessionName, "-l", chunk]);
      await wait(TYPE_CHUNK_DELAY_MS);
    }
  }
}

export class PtyService {
  constructor({ cwd, env }) {
    this.cwd = cwd;
    this.env = env;
    this.sessionName = null;
    this.pollTimer = null;
    this.lastSnapshot = "";
    this.onData = null;
    this.onExit = null;
  }

  async start({ command, args = [], onData, onExit }) {
    if (this.sessionName) {
      throw new Error("PTY session is already running");
    }

    this.onData = onData;
    this.onExit = onExit;
    this.lastSnapshot = "";
    this.sessionName = `retro_claude_${Date.now()}`;
    const launchCommand = buildLaunchCommand(command, args, this.env);

    await runTmux([
      "new-session",
      "-d",
      "-s",
      this.sessionName,
      "-c",
      this.cwd,
      "/bin/zsh",
      "-lc",
      launchCommand
    ]);

    this.startPolling();
  }

  async write(input) {
    if (!this.sessionName) {
      throw new Error("No active PTY session");
    }

    const normalized = String(input ?? "");
    const chunks = normalized.split(/\r\n|\r|\n/);
    const shouldPressEnterAtEnd = /[\r\n]$/.test(normalized);

    for (let index = 0; index < chunks.length; index += 1) {
      const chunk = chunks[index];
      if (chunk) {
        await typeLikeHuman(this.sessionName, chunk);
      }

      if (index < chunks.length - 1) {
        await runTmux(["send-keys", "-t", this.sessionName, "Enter"]);
        await wait(35);
      }
    }

    if (shouldPressEnterAtEnd) {
      await wait(60);
      await runTmux(["send-keys", "-t", this.sessionName, "Enter"]);
    }
  }

  resize(cols, rows) {
    void cols;
    void rows;
  }

  async stop() {
    if (!this.sessionName) {
      return;
    }

    const sessionName = this.sessionName;
    this.stopPolling();
    this.sessionName = null;
    this.lastSnapshot = "";
    await runTmux(["kill-session", "-t", sessionName]).catch(() => {});
  }

  isRunning() {
    return Boolean(this.sessionName);
  }

  startPolling() {
    this.stopPolling();
    this.pollTimer = setInterval(async () => {
      if (!this.sessionName) {
        return;
      }

      try {
        const { stdout } = await runTmux(["capture-pane", "-p", "-t", this.sessionName, "-S", "-200"]);
        const snapshot = stdout ?? "";
        if (!snapshot || snapshot === this.lastSnapshot) {
          return;
        }

        const payload = snapshot.startsWith(this.lastSnapshot)
          ? snapshot.slice(this.lastSnapshot.length)
          : snapshot;

        this.lastSnapshot = snapshot;
        this.onData?.(payload);
      } catch (error) {
        const message = String(error.stderr ?? error.message ?? "");
        if (message.includes("can't find session")) {
          const previous = this.sessionName;
          this.stopPolling();
          this.sessionName = null;
          this.lastSnapshot = "";
          this.onExit?.({
            exitCode: 0,
            signal: 0,
            error: previous ? undefined : "tmux session missing"
          });
        } else {
          this.onData?.(`\n[tmux-error] ${message}\n`);
        }
      }
    }, 500);
  }

  stopPolling() {
    if (this.pollTimer) {
      clearInterval(this.pollTimer);
      this.pollTimer = null;
    }
  }
}