#!/usr/bin/env python3
"""Structural regression test for unmarked post-EXE code discovery."""

from pathlib import Path
import re
import sys


ROOT = Path(__file__).resolve().parents[2]
SOURCE = ROOT / "runtime" / "src" / "dirty_ram_interp.c"


def function_body(source: str, name: str) -> str:
    match = re.search(rf"\bstatic\s+int\s+{re.escape(name)}\s*\([^;]*?\)\s*\{{", source, re.S)
    if not match:
        raise AssertionError(f"missing function definition: {name}")
    start = match.end()
    depth = 1
    for pos in range(start, len(source)):
        if source[pos] == "{":
            depth += 1
        elif source[pos] == "}":
            depth -= 1
            if depth == 0:
                return source[start:pos]
    raise AssertionError(f"unterminated function definition: {name}")


def main() -> int:
    source = SOURCE.read_text(encoding="utf-8")
    body = function_body(source, "dirty_ram_dispatch_inner")

    dirty_gate = body.find("!dirty_ram_is_dirty(phys) && !clean_game_text_miss")
    floor_gate = body.find("phys >= g_overlay_region_floor", dirty_gate)
    ram_gate = body.find("phys < (2u * 1024u * 1024u)", dirty_gate)
    decode_gate = body.find("dirty_ram_word_looks_decodable(fetch_word(phys))", dirty_gate)
    mark = body.find("dirty_ram_mark_executable_range(phys, 4u)", dirty_gate)
    if min(dirty_gate, floor_gate, ram_gate, decode_gate, mark) < 0:
        raise AssertionError("missing dirty/floor/RAM/decode/mark fallback chain")
    if not (dirty_gate < floor_gate < decode_gate < mark and dirty_gate < ram_gate < mark):
        raise AssertionError("fallback checks or executable marking are out of order")

    fallback = body[dirty_gate:mark + 200]
    if "else {\n            return 0;" not in fallback:
        raise AssertionError("invalid/data targets do not fail closed")

    print("PASS: decodable post-EXE dispatch fallback is guarded and fail-closed")
    return 0


if __name__ == "__main__":
    try:
        sys.exit(main())
    except AssertionError as exc:
        print(f"FAIL: {exc}")
        sys.exit(1)