#!/usr/bin/env python3
"""Merge gate for lint on a change — the narrow rule set a change must pass.

This is deliberately *not* the repo's full `ruff.toml` selection. The policy, decided from the
measured findings rather than from taste:

  * ``BLE001`` (blind except) is **allowed**. A broad ``except Exception`` is the right choice
    around device I/O, GL teardown and camera probing, and this codebase already records that
    choice inline as ``# noqa: BLE001 - <reason>``. Gating it would produce ~100 findings whose
    only correct fix is "add a reasoned suppression".
  * ``S110``/``S112`` (a handler that is only ``pass``/``continue``) and ``E722`` (bare
    ``except:``) **are** gated: the complaint is not the breadth of the catch, it is that the
    failure becomes invisible. Silence is acceptable only with a reasoned suppression or a
    handler that reports/re-raises.
  * ``RUF100`` (unused suppression) is reported for triage but is configured ``unfixable``: a
    machine must never delete a suppression whose comment records why it exists.

Run over the files a change touches, never the whole tree, so an AI-authored diff is not
drowned in pre-existing style churn.

Usage::

    tools/lint_gate.py                     # files changed vs HEAD (staged + unstaged)
    tools/lint_gate.py --base origin/main  # files changed vs a ref
    tools/lint_gate.py --files a.py b.py   # explicit files
    tools/lint_gate.py --all               # gate rules over the whole repo
    tools/lint_gate.py --json              # machine-readable result on stdout

Exit codes: 0 clean, 1 findings, 2 a usage or environment problem (e.g. ruff missing).
"""

from __future__ import annotations

import argparse
import json
import os
import shutil
import subprocess
import sys
from pathlib import Path

#: The gate. Explicit, so a rule added to `ruff.toml` cannot silently start failing builds.
#: `E4`/`E7` are deliberately absent: `E402` fires on the intentional "set the environment before
#: importing Qt" pattern in scripts, and `E701`/`E702` are style, which `ruff format` handles.
GATE_SELECT = "E9,E722,F,S110,S112,B023,PLW1510"

#: Rules we report but never let a tool auto-fix (RUF100 is `unfixable` in ruff.toml too).
REPORT_ONLY = "RUF100"

REPO = Path(__file__).resolve().parents[1]


def find_ruff() -> str:
    """Locate ruff: $RUFF, then PATH, then the interpreter environment."""
    for candidate in (os.environ.get("RUFF"), shutil.which("ruff")):
        if candidate and Path(candidate).is_file():
            return candidate
    beside = Path(sys.executable).parent / ("ruff.exe" if os.name == "nt" else "ruff")
    if beside.is_file():
        return str(beside)
    print(
        "lint_gate: ruff not found. Set $RUFF, install it beside the interpreter, or put it on "
        "PATH. The pin matters: findings differ between ruff versions, so the gate names its "
        "version below when it runs.",
        file=sys.stderr,
    )
    raise SystemExit(2)


def git(*args: str) -> list[str]:
    result = subprocess.run(
        ["git", "-C", str(REPO), *args],
        capture_output=True,
        text=True,
        check=False,
    )
    if result.returncode != 0:
        print(f"lint_gate: git {' '.join(args)} failed: {result.stderr.strip()}", file=sys.stderr)
        raise SystemExit(2)
    return [line for line in result.stdout.splitlines() if line.strip()]


def changed_python_files(base: str | None) -> list[str]:
    """The .py files this change touches: working tree, index, and new files."""
    paths: set[str] = set()
    if base:
        paths.update(git("diff", "--name-only", "--diff-filter=ACMR", f"{base}...HEAD"))
    paths.update(git("diff", "--name-only", "--diff-filter=ACMR"))
    paths.update(git("diff", "--name-only", "--cached", "--diff-filter=ACMR"))
    paths.update(git("ls-files", "--others", "--exclude-standard"))
    return sorted(p for p in paths if p.endswith(".py") and (REPO / p).is_file())


def run_ruff(ruff: str, args: list[str]) -> tuple[list[dict], str]:
    version = subprocess.run(
        [ruff, "--version"], capture_output=True, text=True, check=False
    ).stdout.strip()
    result = subprocess.run(
        [ruff, "check", "--no-cache", "--output-format", "json", *args],
        capture_output=True,
        text=True,
        check=False,
    )
    if result.returncode not in (0, 1):
        print(f"lint_gate: ruff failed ({result.returncode}): {result.stderr.strip()}", file=sys.stderr)
        raise SystemExit(2)
    try:
        findings = json.loads(result.stdout or "[]")
    except json.JSONDecodeError:
        print(f"lint_gate: could not parse ruff output: {result.stdout[:400]}", file=sys.stderr)
        raise SystemExit(2)
    return findings, version


def describe(finding: dict) -> str:
    code = finding.get("code") or "?"
    location = finding.get("location") or {}
    path = str(finding.get("filename", "")).replace(str(REPO) + os.sep, "")
    return (
        f"{path}:{location.get('row', '?')}:{location.get('column', '?')}: {code}: "
        f"{finding.get('message', '')}"
    )


def main(argv: list[str] | None = None) -> int:
    parser = argparse.ArgumentParser(description=__doc__.splitlines()[0])
    parser.add_argument("--base", default=None, help="compare against this ref (e.g. origin/main)")
    parser.add_argument("--files", nargs="*", default=None, help="explicit files to check")
    parser.add_argument("--all", action="store_true", help="run the gate rules over the whole repo")
    parser.add_argument("--json", action="store_true", help="machine-readable result on stdout")
    args = parser.parse_args(argv)

    ruff = find_ruff()

    if args.all:
        targets = [str(REPO)]
    else:
        targets = args.files or changed_python_files(args.base)
        if not targets:
            print("lint_gate: no changed Python files; nothing to check.")
            if args.json:
                print(json.dumps({"findings": [], "checked": [], "status": "clean"}))
            return 0

    findings, version = run_ruff(ruff, ["--select", GATE_SELECT, *targets])
    report_only, _ = run_ruff(ruff, ["--select", REPORT_ONLY, *targets])

    if args.json:
        print(
            json.dumps(
                {
                    "ruff": version,
                    "select": GATE_SELECT,
                    "checked": targets,
                    "findings": [
                        {
                            "file": str(f.get("filename", "")).replace(str(REPO) + os.sep, ""),
                            "row": (f.get("location") or {}).get("row"),
                            "column": (f.get("location") or {}).get("column"),
                            "code": f.get("code"),
                            "message": f.get("message"),
                            "fixable": bool((f.get("fix") or {}).get("applicability") == "safe"),
                        }
                        for f in findings
                    ],
                    "unused_suppressions": [describe(f) for f in report_only],
                    "status": "findings" if findings else "clean",
                },
                indent=2,
            )
        )
        return 1 if findings else 0

    print(f"lint_gate: {version}")
    print(f"  select   {GATE_SELECT}  (BLE001 is allowed by policy; see ruff.toml)")
    print(f"  checked  {len(targets)} target(s)")
    if findings:
        print(f"\n{len(findings)} finding(s):")
        for finding in sorted(findings, key=describe):
            hint = " [safe fix: ruff check --fix]" if (finding.get("fix") or {}).get("applicability") == "safe" else ""
            print(f"  {describe(finding)}{hint}")
    else:
        print("  no findings")
    if report_only:
        print(f"\n{len(report_only)} unused suppression(s) to triage by hand (never auto-removed):")
        for finding in report_only:
            print(f"  {describe(finding)}")
    print(f"\nstatus: {'FINDINGS' if findings else 'clean'}")
    return 1 if findings else 0


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