"""Static packaging linter for Lambda container images.

Every Lambda here ships as a Docker image that copies a *subset* of the repo
(``COPY utils/ utils/``, ``COPY backend/ backend/``, ...) and then runs a
handler via ``CMD ["<module>.handler"]``. If the handler's import graph reaches
a top-level package the Dockerfile forgot to ``COPY``, the function dies at cold
start with ``Runtime.ImportModuleError: No module named '<pkg>'`` — but only
*inside the image*. In the dev/test tree every package is present, so a plain
``import`` test can't see the gap. This is exactly how ``No module named
'domain'`` reached a deployed address2UPRN.

The RIE smoke tests (.github/workflows/_smoke_test_lambda.yml) catch this too,
but only by building the full image (minutes) and only for hand-listed services.
This test catches the same class of bug in milliseconds, locally, for *every*
handler Dockerfile — by statically computing each handler's import-time module
graph and asserting every repo file it reaches is copied into the image.

Scope: import-time (module-level) imports only — the ones that run at Lambda
init, which is what ImportModuleError is about. Imports inside function bodies
and under ``if TYPE_CHECKING:`` are deliberately ignored. Third-party / stdlib
imports are out of scope (that's requirements.txt's job, covered by the RIE
smoke test actually installing and importing).
"""

from __future__ import annotations

import ast
import json
import re
from pathlib import Path
from typing import Optional

import pytest

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

# Dockerfiles that are not Lambda handlers (test harness, dev containers).
_SKIP_DOCKERFILES = {"Dockerfile.test", "Dockerfile.test.dockerignore"}
_SKIP_PARTS = {".git", "node_modules", ".devcontainer"}


def _toplevel_names() -> set[str]:
    """Top-level repo packages/modules — the namespace handler imports resolve
    against (imports are absolute: ``domain.x``, ``backend.y``)."""
    names: set[str] = set()
    for p in REPO_ROOT.iterdir():
        if p.name.startswith(".") or p.name == "__pycache__":
            continue
        if p.is_dir():
            names.add(p.name)
        elif p.suffix == ".py":
            names.add(p.stem)
    return names


_TOP = _toplevel_names()


def _is_type_checking(test: ast.expr) -> bool:
    if isinstance(test, ast.Name):
        return test.id == "TYPE_CHECKING"
    if isinstance(test, ast.Attribute):
        return test.attr == "TYPE_CHECKING"
    return False


def _import_time_imports(path: Path) -> list[str]:
    """Absolute module names imported when ``path`` is imported (i.e. at Lambda
    init). Descends into module-level if/try/with and class bodies, but not into
    function bodies (lazy) or ``if TYPE_CHECKING:`` blocks (never executed)."""
    try:
        tree = ast.parse(path.read_text(encoding="utf-8"), str(path))
    except (SyntaxError, UnicodeDecodeError):
        return []
    out: list[str] = []

    def visit(stmts: list[ast.stmt]) -> None:
        for node in stmts:
            if isinstance(node, ast.Import):
                out.extend(alias.name for alias in node.names)
            elif isinstance(node, ast.ImportFrom):
                if not node.level and node.module:  # absolute imports only
                    out.append(node.module)
            elif isinstance(node, ast.If):
                if _is_type_checking(node.test):
                    continue
                visit(node.body)
                visit(node.orelse)
            elif isinstance(node, ast.Try):
                visit(node.body)
                visit(node.orelse)
                visit(node.finalbody)
                for handler in node.handlers:
                    visit(handler.body)
            elif isinstance(node, ast.With):
                visit(node.body)
            elif isinstance(node, ast.ClassDef):
                visit(node.body)
            # FunctionDef / AsyncFunctionDef bodies are intentionally skipped.

    visit(tree.body)
    return out


def _module_to_file(module: str) -> Optional[Path]:
    """Resolve a dotted module to its repo source file (``foo.bar`` ->
    ``foo/bar.py`` or ``foo/bar/__init__.py``)."""
    base = REPO_ROOT.joinpath(*module.split("."))
    py = base.with_suffix(".py")
    if py.is_file():
        return py
    init = base / "__init__.py"
    if init.is_file():
        return init
    return None


def _import_closure(start: Path) -> dict[Path, Optional[Path]]:
    """Repo files reachable from ``start`` via import-time imports, mapped to the
    first file that imported each (for blame in failure messages)."""
    reached: dict[Path, Optional[Path]] = {}
    stack: list[tuple[Path, Optional[Path]]] = [(start, None)]
    while stack:
        path, importer = stack.pop()
        if path in reached:
            continue
        reached[path] = importer
        for module in _import_time_imports(path):
            if module.split(".")[0] not in _TOP:
                continue  # stdlib / third-party — not our concern here
            target = _module_to_file(module)
            if target is not None and target not in reached:
                stack.append((target, path))
    return reached


def _norm(path_token: str) -> str:
    return path_token.lstrip("./").rstrip("/")


def _parse_handler_spec(dockerfile_text: str) -> Optional[str]:
    """The ``<module>.handler`` string from the ``CMD`` line, or None if this
    isn't a Lambda handler image."""
    match = re.search(r"^CMD\s+(\[.*\]|.+)$", dockerfile_text, re.MULTILINE)
    if not match:
        return None
    raw = match.group(1).strip()
    try:
        parsed = json.loads(raw)
        spec = parsed[0] if isinstance(parsed, list) and parsed else raw
    except json.JSONDecodeError:
        spec = raw.strip('"')
    return spec if isinstance(spec, str) and spec.endswith(".handler") else None


def _parse_copies(dockerfile_text: str) -> list[tuple[list[str], str]]:
    """``COPY`` instructions as (sources, dest), dropping ``--flag`` tokens."""
    copies: list[tuple[list[str], str]] = []
    for match in re.finditer(r"^COPY\s+(.+)$", dockerfile_text, re.MULTILINE):
        tokens = [t for t in match.group(1).split() if not t.startswith("--")]
        if len(tokens) < 2:
            continue
        *sources, dest = tokens
        copies.append((sources, dest))
    return copies


def _resolve_handler_file(
    spec: str, copies: list[tuple[list[str], str]]
) -> Optional[Path]:
    """Map a handler spec to its repo source file.

    Handles both in-place layouts (``backend.foo.handler`` -> ``backend/foo/
    handler.py``, present via ``COPY backend/ backend/``) and root-placed
    handlers (``main.handler`` where a ``COPY <src> /var/task/main.py`` or
    ``COPY <src>/main.py .`` puts the file at the image root)."""
    module_path, _func = spec.rsplit(".", 1)

    direct = REPO_ROOT / (module_path.replace(".", "/") + ".py")
    if direct.is_file():
        return direct

    # Root-placed module: find the COPY whose destination basename matches.
    wanted = module_path.split("/")[-1] + ".py"
    for sources, dest in copies:
        dest_norm = _norm(dest)
        dest_is_named_file = Path(dest_norm).name == wanted
        dest_is_dir = dest_norm in ("", module_path.split("/")[-1]) or dest.endswith("/")
        for src in sources:
            src_path = REPO_ROOT / _norm(src)
            if not src_path.is_file():
                continue
            if dest_is_named_file or (dest_is_dir and src_path.name == wanted):
                return src_path
    return None


def _is_copied(rel_path: str, copies: list[tuple[list[str], str]]) -> bool:
    """Whether a repo-relative file path lands in the image via some COPY."""
    rel_path = _norm(rel_path)
    for sources, _dest in copies:
        for src in sources:
            src_norm = _norm(src)
            if src_norm == "" or src_norm == rel_path or rel_path.startswith(src_norm + "/"):
                return True
    return False


def _discover_handler_dockerfiles() -> list[Path]:
    found: list[Path] = []
    for path in REPO_ROOT.rglob("*Dockerfile*"):
        if path.name in _SKIP_DOCKERFILES:
            continue
        if any(part in _SKIP_PARTS for part in path.relative_to(REPO_ROOT).parts):
            continue
        try:
            text = path.read_text(encoding="utf-8")
        except OSError:
            continue
        if _parse_handler_spec(text):
            found.append(path)
    return sorted(found)


_HANDLER_DOCKERFILES = _discover_handler_dockerfiles()


def test_handler_dockerfiles_discovered() -> None:
    """Guard against the discovery silently finding nothing (e.g. a refactor
    that renames Dockerfiles), which would make every check below vacuous."""
    assert _HANDLER_DOCKERFILES, "no Lambda handler Dockerfiles found under repo root"


@pytest.mark.parametrize(
    "dockerfile",
    _HANDLER_DOCKERFILES,
    ids=[str(p.relative_to(REPO_ROOT)) for p in _HANDLER_DOCKERFILES],
)
def test_lambda_image_copies_full_import_closure(dockerfile: Path) -> None:
    """Every repo file the handler imports at init must be COPYed into the image."""
    text = dockerfile.read_text(encoding="utf-8")
    spec = _parse_handler_spec(text)
    assert spec is not None  # discovery guaranteed this
    copies = _parse_copies(text)

    handler_file = _resolve_handler_file(spec, copies)
    assert handler_file is not None, (
        f"{dockerfile.relative_to(REPO_ROOT)}: could not locate the source file "
        f"for CMD handler {spec!r}. Update _resolve_handler_file if this is a new "
        f"handler layout."
    )

    missing: list[str] = []
    for reached, importer in _import_closure(handler_file).items():
        rel = str(reached.relative_to(REPO_ROOT))
        if not _is_copied(rel, copies):
            blame = (
                str(importer.relative_to(REPO_ROOT)) if importer else "(handler entrypoint)"
            )
            missing.append(f"  - {rel}\n      imported by {blame}")

    assert not missing, (
        f"{dockerfile.relative_to(REPO_ROOT)} runs `{spec}` but does not COPY "
        f"{len(missing)} file(s) it imports at init. The Lambda will fail at cold "
        f"start with Runtime.ImportModuleError. Add the missing top-level "
        f"package(s) as `COPY <pkg>/ <pkg>/`:\n" + "\n".join(sorted(missing))
    )