// Uses node:child_process directly instead of pi.exec() because process
// management requires long-lived streaming processes with stdin/stdout piping
// and detached process groups, which pi.exec() does not support.
import { type ChildProcess, spawn } from "node:child_process";
import { existsSync } from "node:fs";
import { isAbsolute } from "node:path";

const IS_WINDOWS = process.platform === "win32";

interface ResolveShellExecutableOptions {
  configuredShell?: string;
  knownPaths: string[];
}

const DEFAULT_KNOWN_SHELL_PATHS = [
  "/run/current-system/sw/bin/bash",
  "/bin/bash",
  "/usr/bin/bash",
  "/usr/local/bin/bash",
];

function isExistingAbsolutePath(shell: string | undefined): shell is string {
  return typeof shell === "string" && isAbsolute(shell) && existsSync(shell);
}

export function resolveShellExecutable({
  configuredShell,
  knownPaths,
}: ResolveShellExecutableOptions): string {
  // A user-configured absolute path always wins on every platform.
  if (isExistingAbsolutePath(configuredShell)) {
    return configuredShell;
  }

  // On Windows we assume Git Bash is running, so `bash` is on PATH.
  // No absolute-path probing is needed or possible with POSIX-style paths.
  if (IS_WINDOWS) {
    return "bash";
  }

  for (const path of knownPaths) {
    if (isExistingAbsolutePath(path)) {
      return path;
    }
  }

  throw new Error(
    "Unable to resolve shell executable. Checked configured shell and known shell paths.",
  );
}

export function spawnCommand(
  command: string,
  cwd: string,
  configuredShell?: string,
): ChildProcess {
  const shellExecutable = resolveShellExecutable({
    configuredShell,
    knownPaths: DEFAULT_KNOWN_SHELL_PATHS,
  });

  return spawn(shellExecutable, ["-lc", command], {
    cwd,
    env: process.env,
    stdio: ["pipe", "pipe", "pipe"],
    detached: true,
    // Suppress the console window that `detached: true` would otherwise open
    // on Windows. Has no effect on Unix.
    windowsHide: true,
  });
}