#!/usr/bin/env python3
"""gateway.py - host-side "link cable adapter" for gbos networking.

Wraps the emulator, owns its link-port serial (stdio), speaks SLIP, and does
the real network work the Game Boy can't (DNS/TCP/HTTP). Modes:

  echo  - bounce every frame back (loopback test)
  http  - treat each frame as a URL, HTTP GET it, stream the body back

Reply frames are typed: b'D'+chunk for data, b'E' to end the stream.

usage: tools/gateway.py [--mode echo|http] [--cmd "wget example.com"] [--rom PATH]
"""
import os, sys, subprocess, threading, time, argparse, urllib.request

EMU = os.path.expanduser("~/dev/gbc/build/sl0pboy")
END, ESC, ESC_END, ESC_ESC = 0xC0, 0xDB, 0xDC, 0xDD
CHUNK = 200
LIMIT = 800                       # cap the fetched body (link is ~1-32 KB/s)

def slip_encode(payload):
    out = bytearray([END])
    for c in payload:
        if c == END:   out += bytes([ESC, ESC_END])
        elif c == ESC: out += bytes([ESC, ESC_ESC])
        else:          out.append(c)
    out.append(END)
    return bytes(out)

def http_fetch(payload):
    url = bytes(payload).decode("latin1", "replace").strip()
    if not url.startswith("http"):
        url = "http://" + url
    sys.stderr.write("\n[gw] GET %s\n" % url)
    try:
        req = urllib.request.Request(url, headers={"User-Agent": "gbos/0.1"})
        with urllib.request.urlopen(req, timeout=8) as r:
            body = r.read(LIMIT)
    except Exception as e:
        body = ("ERR: " + str(e)).encode()
    sys.stderr.write("[gw] %d bytes\n" % len(body))
    frames = [b"D" + body[i:i+CHUNK] for i in range(0, len(body), CHUNK)]
    frames.append(b"E")
    return frames

def handle(payload, mode):
    if mode == "http":
        return http_fetch(payload)
    return [bytes(payload)]        # echo

def reader(out, inp, mode):
    buf, in_frame, esc = bytearray(), False, False
    while True:
        b = out.read(1)
        if not b:
            return
        c = b[0]
        if c == END:
            if in_frame and buf:
                for f in handle(buf, mode):
                    inp.write(slip_encode(f)); inp.flush()
                buf, in_frame, esc = bytearray(), False, False
            else:
                buf, in_frame, esc = bytearray(), True, False
        elif in_frame:
            if esc:
                c = {ESC_END: END, ESC_ESC: ESC}.get(c, c); esc = False; buf.append(c)
            elif c == ESC:
                esc = True
            else:
                buf.append(c)
        else:
            sys.stderr.write(chr(c) if 32 <= c < 127 else ("\n" if c == 10 else "."))
            sys.stderr.flush()

def main():
    ap = argparse.ArgumentParser()
    ap.add_argument("--mode", default="echo", choices=["echo", "http"])
    ap.add_argument("--cmd", default="necho")
    ap.add_argument("--rom", default=os.path.join(os.path.dirname(__file__), "..", "gbos.gb"))
    a = ap.parse_args()
    p = subprocess.Popen([EMU, "--headless", "--uncapped", a.rom],
                         stdin=subprocess.PIPE, stdout=subprocess.PIPE, bufsize=0)
    threading.Thread(target=reader, args=(p.stdout, p.stdin, a.mode), daemon=True).start()
    time.sleep(1.0)
    p.stdin.write((a.cmd + "\n").encode()); p.stdin.flush()
    time.sleep(4.0)
    p.stdin.write(b"exit\n"); p.stdin.flush()
    try: p.wait(timeout=3)
    except Exception: p.kill()

if __name__ == "__main__":
    main()