#!/usr/bin/env python3
"""mutation_check.py -- does test_base32c.py actually have teeth?

Copies base32c.py + test_base32c.py into a scratch dir, injects one fault at a time,
runs the suite against the mutant, and reports whether the mutant was KILLED
(suite exit != 0). A suite that passes everything, including mutants, is worthless.

Run:  python3 mutation_check.py     # exit 0 iff the control passes and every mutant dies
"""

from __future__ import annotations

import os
import shutil
import subprocess
import sys
import tempfile

HERE = os.path.dirname(os.path.abspath(__file__))
MODULE = os.path.join(HERE, "base32c.py")
TEST = os.path.join(HERE, "test_base32c.py")

MUTATIONS = [
    (
        "alphabet: letter J replaced by excluded I",
        '"0123456789ABCDEFGHJKMNPQRSTVWXYZ"',
        '"0123456789ABCDEFGHIKMNPQRSTVWXYZ"',
    ),
    (
        "check symbol: modulus 37 -> 36",
        "return CHECK_ALPHABET[value % 37]",
        "return CHECK_ALPHABET[value % 36]",
    ),
    (
        "check verify: compares raw value instead of value mod 37",
        "if got != value % 37:",
        "if got != value:",
    ),
    (
        "decode: hyphens no longer stripped",
        'def decode(text: str) -> int:\n    """Decode a symbol string (hyphens ignored, case folded, i/l/o aliases honoured)."""\n    if not isinstance(text, str):\n        raise TypeError("text must be a str")\n    body = text.replace("-", "")',
        'def decode(text: str) -> int:\n    """Decode a symbol string (hyphens ignored, case folded, i/l/o aliases honoured)."""\n    if not isinstance(text, str):\n        raise TypeError("text must be a str")\n    body = text',
    ),
    (
        "encode: 5-bit slicing becomes 4-bit slicing",
        "for i in range(0, len(bits), 5)",
        "for i in range(0, len(bits), 4)",
    ),
    (
        "decode aliases: i/l/o tolerance removed",
        'for _alias, _target in (("I", "1"), ("L", "1"), ("O", "0")):\n    _SYMBOL_VALUE[_alias] = _SYMBOL_VALUE[_target]',
        'for _alias, _target in (("I", "1"), ("L", "1"), ("O", "0")):\n    pass',
    ),
]


def run_suite(directory: str) -> tuple[int, str]:
    proc = subprocess.run(
        [sys.executable, os.path.join(directory, "test_base32c.py")],
        capture_output=True,
        text=True,
        timeout=300,
        cwd=directory,
    )
    return proc.returncode, (proc.stdout + proc.stderr).strip().splitlines()[-1] if (proc.stdout + proc.stderr).strip() else ""


def main() -> int:
    root = tempfile.mkdtemp(prefix="base32c-mutants-", dir=os.environ.get("TMPDIR", "/tmp"))
    failures = []

    control = os.path.join(root, "control")
    os.makedirs(control)
    shutil.copy(MODULE, control)
    shutil.copy(TEST, control)
    code, tail = run_suite(control)
    print(f"CONTROL (unmutated copy): exit {code} -- {tail}")
    if code != 0:
        failures.append("control copy of the suite failed; results below are meaningless")

    source = open(MODULE, encoding="utf-8").read()
    killed = 0
    for index, (label, old, new) in enumerate(MUTATIONS, start=1):
        if source.count(old) != 1:
            failures.append(f"mutation {index} anchor matched {source.count(old)} times, expected 1: {label}")
            print(f"MUTANT {index} ANCHOR-BROKEN: {label}")
            continue
        directory = os.path.join(root, f"mutant{index}")
        os.makedirs(directory)
        shutil.copy(TEST, directory)
        with open(os.path.join(directory, "base32c.py"), "w", encoding="utf-8") as handle:
            handle.write(source.replace(old, new))
        code, tail = run_suite(directory)
        status = "KILLED" if code != 0 else "SURVIVED"
        if code != 0:
            killed += 1
        else:
            failures.append(f"mutant survived: {label}")
        print(f"MUTANT {index} {status}: {label}  [{tail}]")

    print()
    print(f"MUTANTS {killed}/{len(MUTATIONS)} killed")
    shutil.rmtree(root, ignore_errors=True)
    if failures:
        for line in failures:
            print(f"PROBLEM: {line}")
        return 1
    print("SUITE HAS TEETH: every injected fault was caught")
    return 0


if __name__ == "__main__":
    raise SystemExit(main())