/**
 * Backend-neutral terminal surface facade.
 *
 * Herdr is selected when Pi is running in a Herdr-managed pane, Orca when Pi
 * is running in an Orca-managed terminal. tmux remains the fallback when Pi is
 * running inside tmux. Selection is automatic so a process uses one backend
 * consistently for its whole lifetime.
 */
import { existsSync, mkdirSync, readFileSync, rmSync, writeFileSync } from "node:fs";
import { tmpdir } from "node:os";
import { dirname, join } from "node:path";
import * as herdr from "./herdr.ts";
import * as orca from "./orca.ts";
import * as tmux from "./tmux.ts";

export type MuxBackend = "herdr" | "orca" | "tmux";
type Direction = "left" | "right" | "up" | "down";

type SurfaceBackend = {
  createSurface(name: string): string;
  createSurfaceSplit(name: string, direction: Direction, fromSurface?: string): string;
  sendCommand(surface: string, command: string): void;
  readScreen(surface: string, lines?: number): string;
  readScreenAsync(surface: string, lines?: number): Promise<string>;
  isSurfaceAlive(surface: string, signal?: AbortSignal): Promise<boolean>;
  closeSurface(surface: string): void;
};

export function selectMuxBackend(availability: {
  herdr: boolean;
  orca: boolean;
  tmux: boolean;
}): MuxBackend | null {
  if (availability.herdr) return "herdr";
  if (availability.orca) return "orca";
  if (availability.tmux) return "tmux";
  return null;
}

export function getMuxBackend(): MuxBackend | null {
  return selectMuxBackend({
    herdr: herdr.isAvailable(),
    orca: orca.isAvailable(),
    tmux: tmux.isAvailable(),
  });
}

function getBackend(): SurfaceBackend {
  const backend = getMuxBackend();
  if (backend === "herdr") return herdr;
  if (backend === "orca") return orca;
  if (backend === "tmux") return tmux;
  throw new Error(`No supported terminal multiplexer is available. ${muxSetupHint()}`);
}

export function isMuxAvailable(): boolean {
  return getMuxBackend() !== null;
}

export function muxSetupHint(): string {
  if (process.env.HERDR_ENV === "1") return herdr.setupHint();
  if (process.env.ORCA_TERMINAL_HANDLE) return orca.setupHint();
  if (process.env.TMUX) return tmux.setupHint();
  return "Start pi inside Herdr, Orca, or tmux.";
}

export function createSurface(name: string): string {
  return getBackend().createSurface(name);
}

export function createSurfaceSplit(
  name: string,
  direction: Direction,
  fromSurface?: string,
): string {
  return getBackend().createSurfaceSplit(name, direction, fromSurface);
}

export function sendCommand(surface: string, command: string): void {
  getBackend().sendCommand(surface, command);
}

export function readScreen(surface: string, lines = 50): string {
  return getBackend().readScreen(surface, lines);
}

export function readScreenAsync(surface: string, lines = 50): Promise<string> {
  return getBackend().readScreenAsync(surface, lines);
}

export function isSurfaceAlive(surface: string, signal?: AbortSignal): Promise<boolean> {
  return getBackend().isSurfaceAlive(surface, signal);
}

export function closeSurface(surface: string): void {
  getBackend().closeSurface(surface);
}

export function shellEscape(value: string): string {
  return "'" + value.replace(/'/g, "'\\''") + "'";
}

export function wrapWithCompletionFile(command: string, completionFile: string): string {
  return (
    `${command}; exit_code=$?; ` +
    `printf '%s\\n' "$exit_code" > ${shellEscape(completionFile)}; ` +
    `echo "__SUBAGENT_DONE_\${exit_code}__"`
  );
}

export function sendLongCommand(
  surface: string,
  command: string,
  options?: { scriptPath?: string; scriptPreamble?: string; replaceShell?: boolean },
): string {
  const scriptPath =
    options?.scriptPath ??
    join(
      tmpdir(),
      "pi-subagent-scripts",
      `cmd-${Date.now()}-${Math.random().toString(16).slice(2, 8)}.sh`,
    );
  mkdirSync(dirname(scriptPath), { recursive: true });

  const scriptParts = ["#!/bin/bash"];
  if (options?.scriptPreamble) scriptParts.push(options.scriptPreamble.trimEnd());
  scriptParts.push(command);

  writeFileSync(scriptPath, scriptParts.join("\n") + "\n", { mode: 0o755 });
  const launch = `${options?.replaceShell ? "exec " : ""}bash ${shellEscape(scriptPath)}`;
  sendCommand(surface, launch);
  return scriptPath;
}

export interface PollResult {
  reason: "done" | "sentinel" | "error";
  exitCode: number;
  errorMessage?: string;
}

function interpretExitSidecar(data: unknown): PollResult {
  const payload = data as { type?: unknown; errorMessage?: unknown } | null;
  if (payload?.type === "error") {
    const errorMessage =
      typeof payload.errorMessage === "string" && payload.errorMessage.trim() !== ""
        ? payload.errorMessage
        : "Subagent exited with stopReason=error (no errorMessage in sidecar).";
    return { reason: "error", exitCode: 1, errorMessage };
  }
  return { reason: "done", exitCode: 0 };
}

function readCompletionFile(path: string): PollResult | null {
  if (!existsSync(path)) return null;
  const raw = readFileSync(path, "utf8").trim();
  const exitCode = Number.parseInt(raw, 10);
  if (!/^\d+$/.test(raw) || !Number.isSafeInteger(exitCode)) return null;
  rmSync(path, { force: true });
  return { reason: "sentinel", exitCode };
}

type PollOptions = {
  interval: number;
  sessionFile?: string;
  sentinelFile?: string;
  completionFile?: string;
  onTick?: (elapsed: number) => void;
  onExitDetected?: () => void;
  livenessCheck?: (surface: string, signal?: AbortSignal) => Promise<boolean>;
  livenessIntervalMs?: number;
  livenessFailureThreshold?: number;
};

/** Avoid launching a terminal CLI reader when a local completion signal is authoritative. */
function shouldPollSurface(
  options: Pick<PollOptions, "sessionFile" | "sentinelFile" | "completionFile">,
): boolean {
  return !options.sessionFile && !options.sentinelFile && !options.completionFile;
}

export const __pollForExitTest__ = { interpretExitSidecar, readCompletionFile };

export async function pollForExit(
  surface: string,
  signal: AbortSignal,
  options: PollOptions,
  readSurface: (surface: string, lines?: number) => Promise<string> = readScreenAsync,
): Promise<PollResult> {
  const start = Date.now();
  const livenessCheck = options.livenessCheck ?? isSurfaceAlive;
  const livenessIntervalMs = options.livenessIntervalMs ?? 5_000;
  const livenessFailureThreshold = options.livenessFailureThreshold ?? 3;
  let nextLivenessCheck = start + livenessIntervalMs;
  let livenessFailures = 0;

  for (;;) {
    if (signal.aborted) throw new Error("Aborted while waiting for subagent to finish");

    if (options.sessionFile) {
      try {
        const exitFile = `${options.sessionFile}.exit`;
        if (existsSync(exitFile)) {
          const result = interpretExitSidecar(JSON.parse(readFileSync(exitFile, "utf8")));
          options.onExitDetected?.();
          rmSync(exitFile, { force: true });
          return result;
        }
      } catch {}
    }

    if (options.sentinelFile) {
      try {
        if (existsSync(options.sentinelFile)) {
          options.onExitDetected?.();
          return { reason: "sentinel", exitCode: 0 };
        }
      } catch {}
    }

    if (options.completionFile) {
      try {
        const result = readCompletionFile(options.completionFile);
        if (result) {
          options.onExitDetected?.();
          return result;
        }
      } catch {}
    }

    if (shouldPollSurface(options)) {
      try {
        const screen = await readSurface(surface, 5);
        const match = screen.match(/__SUBAGENT_DONE_(\d+)__/);
        if (match) {
          options.onExitDetected?.();
          return { reason: "sentinel", exitCode: Number.parseInt(match[1], 10) };
        }
      } catch {
        // Surface reads are a best-effort fallback when no completion file is available.
      }
    } else if (Date.now() >= nextLivenessCheck) {
      nextLivenessCheck = Date.now() + livenessIntervalMs;
      try {
        livenessFailures = await livenessCheck(surface, signal) ? 0 : livenessFailures + 1;
      } catch {
        livenessFailures += 1;
      }
      if (signal.aborted) throw new Error("Aborted while checking subagent surface liveness");
      if (livenessFailures >= livenessFailureThreshold) {
        throw new Error("Subagent terminal surface closed before completion.");
      }
    }

    const elapsed = Math.floor((Date.now() - start) / 1000);
    options.onTick?.(elapsed);

    await new Promise<void>((resolve, reject) => {
      if (signal.aborted) return reject(new Error("Aborted"));
      const timer = setTimeout(() => {
        signal.removeEventListener("abort", onAbort);
        resolve();
      }, options.interval);
      function onAbort() {
        clearTimeout(timer);
        reject(new Error("Aborted"));
      }
      signal.addEventListener("abort", onAbort, { once: true });
    });
  }
}