#!/usr/bin/env python3
"""CASAN Check 3 — Clean Architecture Guard (R01-T03).

Statically walks the AST of every Python file in the pure-Python layers and
fails when a file imports something the layer is not allowed to depend on.

Why AST instead of ``grep``: a regex over source text cannot tell an import
apart from the same words appearing inside a docstring, a comment or a string
literal (this repo has several docstrings that legitimately mention
``PySide6``). ``ast`` sees only real ``import`` / ``from … import`` nodes, so
the check has no false positives and needs no ``# noqa`` escape hatches.

Rules enforced (see docs/architecture/ADR-001-layered-architecture.md):

* **I1** ``domain/`` and ``application/`` must be 100% pure Python — no Qt.
* **I2** ``domain/`` must not import ``application/``, ``infrastructure/``,
  ``presentation/`` or the legacy ``ui/``.
* **I3** ``application/`` must not import ``presentation/`` or ``ui/``.

Usage::

    python scripts/check_imports.py            # scan the whole repo
    python scripts/check_imports.py domain     # scan one layer only

Exit code is 0 when clean and 1 when at least one violation is found, so it
can be wired straight into CI / ``scripts/run_quality_gate.py`` (R10-T02).
"""
from __future__ import annotations

import argparse
import ast
import sys
from dataclasses import dataclass
from pathlib import Path
from typing import Dict, Iterable, List, Sequence, Tuple

# Repository root = parent of this scripts/ folder. Everything below is resolved
# relative to it so the checker works no matter what the checkout folder is
# named or which directory the developer runs it from.
REPO_ROOT = Path(__file__).resolve().parents[1]

# The distribution package name. Absolute imports may be written either as
# ``from cowork_local.ui import x`` or ``from ui import x`` depending on how the
# module was reached; we normalise the prefix away so both spellings are caught.
PACKAGE_NAME = "cowork_local"

# Any import whose first dotted segment is one of these is a GUI toolkit.
QT_ROOTS = frozenset({"PySide6", "PySide2", "PyQt5", "PyQt6", "shiboken6", "shiboken2"})

# Per-layer rules: layer directory -> top-level package names it may not import.
# Kept as a plain table so adding a layer later is a one-line change and the
# rules stay readable next to the ADR they implement.
LAYER_RULES: Dict[str, frozenset] = {
    # I1 + I2: domain is the innermost layer and depends on nothing but stdlib.
    "domain": frozenset({"application", "infrastructure", "presentation", "ui", "core"}),
    # I1 + I3: application may use domain, but never anything that draws pixels.
    "application": frozenset({"presentation", "ui"}),
}

# Directories that are never production code and therefore never scanned.
SKIP_DIRS = frozenset({".git", "__pycache__", ".pytest_cache", "tests", "build", "dist"})


@dataclass(frozen=True)
class Violation:
    """One forbidden import, carrying enough context to fix it without grepping."""

    path: Path
    line: int
    imported: str
    rule: str

    def render(self) -> str:
        """Format as ``file:line: message`` — the shape editors turn into a
        clickable link, so a CI failure lands the developer on the exact line."""
        rel = self.path.relative_to(REPO_ROOT).as_posix()
        # ASCII-only on purpose: this line is printed to a console that may run a
        # legacy code page (cp932 on the team's Windows boxes), where a non-ASCII
        # dash raises UnicodeEncodeError and would crash the gate on the very
        # failure path it exists to report.
        return f"{rel}:{self.line}: imports '{self.imported}' - {self.rule}"


def iter_python_files(layer_dir: Path) -> Iterable[Path]:
    """Yield every production ``.py`` file under ``layer_dir``.

    Test files are excluded on purpose: a test for a pure-Python service is
    allowed to import Qt (an integration test may need a headless widget), and
    holding tests to the production rule would push people to disable the gate.
    """
    if not layer_dir.is_dir():
        return
    for path in sorted(layer_dir.rglob("*.py")):
        # Reject a path as soon as ANY of its parent folder names is skippable,
        # which also covers nested __pycache__ inside a sub-package.
        if any(part in SKIP_DIRS for part in path.parts):
            continue
        yield path


def module_parts(path: Path) -> List[str]:
    """Dotted package path of ``path`` relative to the repo root, as a list.

    ``domain/agents/agent_event.py``   -> ``["domain", "agents", "agent_event"]``
    ``domain/agents/__init__.py``      -> ``["domain", "agents"]``

    Needed to resolve *relative* imports: ``from ..models import X`` inside
    ``domain/agents/foo.py`` really means ``domain.models``, and only the file's
    own position tells us that.
    """
    rel = path.relative_to(REPO_ROOT)
    parts = list(rel.parts)
    if parts[-1] == "__init__.py":
        parts.pop()
    else:
        parts[-1] = parts[-1][: -len(".py")]
    return parts


def resolve_relative(parts: Sequence[str], level: int, module: str) -> str:
    """Turn a relative import into the absolute top-level package it points at.

    ``level`` is the number of leading dots. Level 1 means "the package this
    module lives in", so we drop the module's own name plus ``level - 1``
    further parents. Returns the FIRST segment of the resolved path, because
    the rules are expressed in terms of top-level layers.

    Walking off the top of the tree (more dots than there are parents) yields
    an empty string, which simply never matches a rule — a malformed import
    like that is a syntax/packaging problem, not an architecture violation.
    """
    base = list(parts[:-1])  # the package containing this module
    if level > 1:
        drop = level - 1
        if drop > len(base):
            return ""
        base = base[: len(base) - drop]
    tail = module.split(".") if module else []
    resolved = base + tail
    return resolved[0] if resolved else ""


def top_level(name: str) -> str:
    """First dotted segment of an absolute import, with the distribution package
    prefix stripped so ``cowork_local.ui.chat_panel`` and ``ui.chat_panel`` are
    treated as the same dependency."""
    segments = name.split(".")
    if segments and segments[0] == PACKAGE_NAME:
        segments = segments[1:]
    return segments[0] if segments else ""


def imported_roots(tree: ast.AST, parts: Sequence[str]) -> Iterable[Tuple[str, int, str]]:
    """Yield ``(top_level_package, line_number, as_written)`` for every import.

    ``as_written`` is kept so the error message shows what the developer
    actually typed rather than the normalised root, which makes the violation
    obvious at a glance.

    ``ast.walk`` (not just the module body) is deliberate: this repo defers many
    heavy imports into function bodies to keep app start-up fast, and a
    function-local ``from PySide6 import QtWidgets`` breaks the layer exactly
    the same way a top-level one does.
    """
    for node in ast.walk(tree):
        if isinstance(node, ast.Import):
            for alias in node.names:
                yield top_level(alias.name), node.lineno, alias.name
        elif isinstance(node, ast.ImportFrom):
            if node.level:
                written = "." * node.level + (node.module or "")
                yield resolve_relative(parts, node.level, node.module or ""), node.lineno, written
            else:
                module = node.module or ""
                yield top_level(module), node.lineno, module


def check_file(path: Path, layer: str, banned: frozenset) -> List[Violation]:
    """Collect every rule violation in one file.

    A file that cannot be parsed is reported as a violation rather than skipped:
    silently passing a file the checker could not read would make the gate lie.
    """
    try:
        tree = ast.parse(path.read_text(encoding="utf-8"), filename=str(path))
    except (SyntaxError, UnicodeDecodeError) as exc:
        return [Violation(path, getattr(exc, "lineno", 0) or 0, "<unparseable>",
                          f"cannot be parsed by the architecture guard ({exc})")]

    parts = module_parts(path)
    out: List[Violation] = []
    for root, lineno, written in imported_roots(tree, parts):
        if root in QT_ROOTS:
            out.append(Violation(path, lineno, written,
                                 f"'{layer}/' must be 100% pure Python (ADR-001 I1)"))
        elif root in banned:
            out.append(Violation(path, lineno, written,
                                 f"'{layer}/' must not depend on '{root}/' (ADR-001 I2/I3)"))
    return out


def run(layers: Sequence[str]) -> List[Violation]:
    """Scan the requested layers and return every violation found, in file order."""
    found: List[Violation] = []
    for layer in layers:
        banned = LAYER_RULES[layer]
        for path in iter_python_files(REPO_ROOT / layer):
            found.extend(check_file(path, layer, banned))
    return found


def main(argv: Sequence[str] | None = None) -> int:
    parser = argparse.ArgumentParser(
        description="CASAN Check 3 - Clean Architecture Guard (see ADR-001).")
    parser.add_argument(
        "layers", nargs="*", choices=sorted(LAYER_RULES) or None, default=None,
        help="Layers to scan (default: every layer with a rule).",
    )
    args = parser.parse_args(argv)
    layers = args.layers or sorted(LAYER_RULES)

    violations = run(layers)
    scanned = sum(1 for layer in layers for _ in iter_python_files(REPO_ROOT / layer))

    if violations:
        print(f"FAIL - {len(violations)} architecture violation(s) in {scanned} file(s):\n")
        for v in violations:
            print("  " + v.render())
        # Point at the rationale instead of just the rule id, so someone hitting
        # this for the first time knows where the decision was made.
        print("\nSee docs/architecture/ADR-001-layered-architecture.md")
        return 1

    print(f"PASS - 0 Qt imports in {', '.join(layers)} ({scanned} file(s) scanned)")
    return 0


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