SnapOtter/packages/ai/python/dispatcher.py

"""
Persistent Python sidecar dispatcher.

Runs as a long-lived process. Reads JSON requests from stdin (one per line),
dispatches to the appropriate AI handler, writes JSON responses to stdout.
Progress emissions continue via stderr (unchanged from the standalone scripts).

Request format:  {"id": "uuid", "script": "remove_bg", "args": [...]}
Response format: {"id": "uuid", "stdout": "...", "exitCode": 0}

Pre-imports heavy libraries at startup to eliminate cold-start latency.
"""
import sys
import json
import io
import os
import traceback


def emit_progress(percent, stage):
    """Emit structured progress to stderr."""
    print(json.dumps({"progress": percent, "stage": stage}), file=sys.stderr, flush=True)


# ── Pre-import heavy libraries ──────────────────────────────────────
# These imports are the main source of cold-start latency.
# By importing once at startup, subsequent requests skip the import cost.

available_modules = {}


def _try_import(name, import_fn):
    try:
        available_modules[name] = import_fn()
    except ImportError:
        pass


_try_import("PIL", lambda: __import__("PIL"))
_try_import("cv2", lambda: __import__("cv2"))
_try_import("numpy", lambda: __import__("numpy"))

# Heavy ML libraries - import but don't fail if unavailable
_try_import("rembg", lambda: __import__("rembg"))


# ── Script handlers ─────────────────────────────────────────────────
# Each handler sets sys.argv and calls the script's main() function,
# capturing stdout. The scripts remain unchanged.


def _run_script_main(script_name, args):
    """
    Import and run a script's main() function, capturing its stdout output.

    Since some scripts (like remove_bg.py) manipulate file descriptors directly
    (os.dup2), we use a pipe at the fd level rather than StringIO.
    """
    script_dir = os.path.dirname(os.path.abspath(__file__))

    # Save original state
    old_argv = sys.argv

    # Create a pipe to capture stdout at the fd level
    read_fd, write_fd = os.pipe()

    # Save the real stdout fd
    real_stdout_fd = os.dup(1)

    # Redirect fd 1 to our pipe's write end
    os.dup2(write_fd, 1)
    os.close(write_fd)

    # Also redirect sys.stdout to the same fd
    old_sys_stdout = sys.stdout
    sys.stdout = os.fdopen(1, "w", closefd=False)

    exit_code = 0
    try:
        sys.argv = ["script.py"] + args

        # Load and run the script
        script_path = os.path.join(script_dir, script_name + ".py")

        module_globals = {"__name__": "__main__", "__file__": script_path}

        with open(script_path) as f:
            code = compile(f.read(), script_path, "exec")

        # Run the compiled script in its own namespace
        exec(code, module_globals)  # noqa: S102 - trusted internal scripts only

    except SystemExit as e:
        exit_code = e.code if isinstance(e.code, int) else 1
    except Exception as e:
        # Write error to the captured stdout
        sys.stdout.write(json.dumps({"success": False, "error": str(e)}) + "\n")
        sys.stdout.flush()
        exit_code = 1
    finally:
        # Flush before restoring
        sys.stdout.flush()

        # Restore stdout fd
        os.dup2(real_stdout_fd, 1)
        os.close(real_stdout_fd)

        # Restore sys.stdout
        sys.stdout = old_sys_stdout

        # Restore sys.argv
        sys.argv = old_argv

    # Read captured output from the pipe
    read_file = os.fdopen(read_fd, "r")
    captured = read_file.read()
    read_file.close()

    return captured.strip(), exit_code


# ── Main loop ───────────────────────────────────────────────────────


def main():
    # Signal readiness
    print(json.dumps({"ready": True}), file=sys.stderr, flush=True)

    for line in sys.stdin:
        line = line.strip()
        if not line:
            continue

        try:
            request = json.loads(line)
        except json.JSONDecodeError:
            continue

        request_id = request.get("id", "unknown")
        script_name = request.get("script", "")
        args = request.get("args", [])

        try:
            stdout_output, exit_code = _run_script_main(script_name, args)
            response = {
                "id": request_id,
                "stdout": stdout_output,
                "exitCode": exit_code,
            }
        except Exception as e:
            response = {
                "id": request_id,
                "stdout": json.dumps({"success": False, "error": str(e)}),
                "exitCode": 1,
            }

        # Write response as a single JSON line to stdout
        sys.stdout.write(json.dumps(response) + "\n")
        sys.stdout.flush()


if __name__ == "__main__":
    main()