#!/usr/bin/env python3
"""Fail if a push changes canvas generation without moving project.yaml's version.

`project.yaml`'s `version:` is the Atlas disk cache's only invalidation signal.
Change how a canvas is generated without moving it and every warm cache keeps
serving canvases built by code that no longer exists — silently, and only on
machines that have a warm cache, so the author never sees it. That has happened
five times (see tooling/canvas_sources.py for the roll-call); T-1239 is what the
last one cost.

The rule: if the push touches anything in the canvas-generation registry, the
`version:` line in project.yaml must change in the SAME range.

Deliberately no override flag. The ticket's ruling (T-1242) is that a false
positive is cheap — one version bump, one round of cache misses — and a false
negative is another week of a wrong map. An escape hatch would be reached for
exactly when someone is sure their change is harmless, which is the state of mind
that produced all five regressions.

Exit: 0 = fine (or nothing relevant in range), 1 = version bump required.
"""

import argparse
import subprocess
import sys
from pathlib import Path

sys.path.insert(0, str(Path(__file__).resolve().parent))
from canvas_sources import relative_paths  # noqa: E402

REPO_ROOT = Path(__file__).resolve().parent.parent
DEFAULT_BASE = "origin/main"


def git(*args: str) -> str | None:
    """Run a git command, returning stdout, or None if it failed."""
    result = subprocess.run(
        ["git", "-C", str(REPO_ROOT), *args],
        capture_output=True,
        text=True,
    )
    if result.returncode != 0:
        return None
    return result.stdout


def changed_files(commit_range: str) -> list[str] | None:
    out = git("diff", "--name-only", commit_range)
    if out is None:
        return None
    return [line for line in out.splitlines() if line]


def diff_has_version_bump(diff_text: str) -> bool:
    """Does this project.yaml diff actually move the `version:` field?

    Pure, so the property is testable without constructing git history
    (tooling/test_canvas_version_check.py).

    Matched on the diff body rather than on the file appearing in --name-only:
    project.yaml carries a long comment block documenting past bumps — including
    lines that quote old version NUMBERS — so editing that commentary, or any
    other field in the file, must NOT count as bumping the version.

    Requires the ADDED side: a lone deletion means the field was removed, not
    moved. Diff context/metadata lines such as `+++ b/project.yaml` must not
    match either, which is why this anchors on `+version:` exactly.
    """
    for line in diff_text.splitlines():
        if line.startswith("+++"):
            continue  # diff header, not content
        if line.startswith("+version:"):
            return True
    return False


def version_line_changed(commit_range: str) -> bool:
    """Did project.yaml's `version:` line itself change in this range?"""
    out = git("diff", "-U0", commit_range, "--", "project.yaml")
    if out is None:
        return False
    return diff_has_version_bump(out)


def main() -> int:
    parser = argparse.ArgumentParser(
        description="Require a project.yaml version bump alongside canvas-generation changes"
    )
    parser.add_argument(
        "--base",
        default=DEFAULT_BASE,
        help=f"Base ref to compare against (default: {DEFAULT_BASE})",
    )
    parser.add_argument(
        "--head",
        default="HEAD",
        help="Head ref to compare (default: HEAD)",
    )
    args = parser.parse_args()

    # Three-dot: what HEAD added since the merge base, matching the systems.db
    # stamp check's own convention in .config/hooks/pre-push.
    commit_range = f"{args.base}...{args.head}"

    if git("rev-parse", "--verify", args.base) is None:
        # No base to compare against (fresh clone, no remote yet). Skipping is
        # correct rather than failing: there is no "range" to judge.
        print(
            f"check-canvas-version: {args.base} not found — skipping (nothing to compare)"
        )
        return 0

    changed = changed_files(commit_range)
    if changed is None:
        print(
            f"check-canvas-version: could not diff {commit_range} — skipping",
            file=sys.stderr,
        )
        return 0

    registry = set(relative_paths())
    touched = sorted(set(changed) & registry)

    if not touched:
        print("check-canvas-version: no canvas-generation changes in range — OK")
        return 0

    if version_line_changed(commit_range):
        print(
            f"check-canvas-version: OK — {len(touched)} canvas-generation file(s) "
            "changed and project.yaml's version moved with them"
        )
        return 0

    shown = touched[:10]
    remainder = len(touched) - len(shown)
    print(
        "check-canvas-version: canvas generation changed without a version bump\n"
        "\n"
        f"  Range: {commit_range}\n"
        "  Changed canvas-generation files:\n"
        + "".join(f"    {p}\n" for p in shown)
        + (f"    ... and {remainder} more\n" if remainder else "")
        + "\n"
        "project.yaml's `version:` is the Atlas disk cache's ONLY invalidation\n"
        "signal. Without a bump, every warm cache keeps serving canvases built by\n"
        "the code you just changed — silently, and only on machines that have a\n"
        "warm cache, so you will not see it on a cold checkout.\n"
        "\n"
        "Fix: bump `version:` in project.yaml (scheme 0.{phase}.{n}), add a line to\n"
        "the comment block above it saying what the old entries carried, and mirror\n"
        "the new value into client/project.godot's config/version.\n"
        "\n"
        "If you are certain this change cannot alter canvas bytes, bump it anyway:\n"
        "the cost is one round of cache misses. That trade is the point — this has\n"
        "shipped broken five times, most recently T-1239, which took eight days to\n"
        "find.",
        file=sys.stderr,
    )
    return 1


if __name__ == "__main__":
    sys.exit(main())