"""Process-level cached filesystem helpers for project-tree scans.

Many integration/lint tests and CLI tools walk the whole repo and read every
matching file. Doing that N times per process is wasteful — the tree doesn't
change during a run. These helpers walk the tree once per process and memoise
both the path list and file contents, so every caller after the first one pays
near-zero cost.

Usage:

    from utils.cache.files import iter_project_files, read_text

    for path in iter_project_files(extensions=(".yml", ".yml.j2"), exclude_tests=True):
        content = read_text(path)
        ...

`PROJECT_ROOT` is the repo root derived from this file's location.

Gitignore-filtered iteration
----------------------------

The matcher itself lives in :mod:`utils.cache.gitignore` (single SPOT for
``.gitignore`` parsing and matching). :func:`iter_non_ignored_files`
here composes the cached project walk with that matcher and is the
recommended helper for lint tests that want the "files git would track"
view without subprocessing.
"""

from __future__ import annotations

import os
from functools import lru_cache
from pathlib import Path
from typing import TYPE_CHECKING

from . import PROJECT_ROOT
from .gitignore import is_path_gitignored, load_gitignore_patterns

if TYPE_CHECKING:
    from collections.abc import Iterable, Iterator

_DEFAULT_SKIP_DIRS: frozenset[str] = frozenset(
    {
        ".git",
        ".cache",
        ".pytest_cache",
        ".ruff_cache",
        ".venv",
        "venv",
        "__pycache__",
        "node_modules",
        "vendor",
    }
)


@lru_cache(maxsize=1)
def _local_exclude_dirs() -> frozenset[str]:
    """Directory names from ``.git/info/exclude`` (git's local-only ignore).

    Untracked local tooling output listed there is by definition not part of
    the project, so project-tree scans must not descend into it. Only plain
    single-component directory entries are honored — file patterns and globs
    stay with git.
    """
    exclude = Path(str(PROJECT_ROOT)) / ".git" / "info" / "exclude"
    names: set[str] = set()
    try:
        lines = exclude.read_text(encoding="utf-8").splitlines()
    except OSError:
        return frozenset()
    for raw in lines:
        line = raw.strip()
        if not line or line.startswith(("#", "!")):
            continue
        token = line.strip("/")
        if token and not any(c in token for c in "/*?["):
            names.add(token)
    return frozenset(names)


@lru_cache(maxsize=4)
def _all_project_files(root_str: str) -> tuple[str, ...]:
    """One-shot filesystem walk from *root_str*.

    Returns absolute paths as a tuple (immutable → safe to cache).
    Pruned at walk-time by `_DEFAULT_SKIP_DIRS` plus git's local exclude
    file, since those dirs are never relevant for any project-tree test and
    descending into them is pure waste.
    """
    skip_dirs = _DEFAULT_SKIP_DIRS | _local_exclude_dirs()
    paths: list[str] = []
    for dirpath, dirnames, filenames in os.walk(root_str, topdown=True):
        dirnames[:] = [d for d in dirnames if d not in skip_dirs]
        paths.extend(str(Path(dirpath) / fn) for fn in filenames)
    return tuple(paths)


def iter_project_files(
    *,
    extensions: Iterable[str] | None = None,
    exclude_tests: bool = False,
    exclude_dirs: Iterable[str] | None = None,
) -> Iterator[str]:
    """Yield absolute paths of project files matching the filter.

    Args:
        extensions: Suffix strings (e.g. ``(".yml", ".yaml.j2")``). Matching is
            case-insensitive via plain string suffix. ``None`` yields all files.
        exclude_tests: Skip everything under ``<root>/tests/``.
        exclude_dirs: Additional top-level-or-nested directory names to skip.
            Matched by path-component containment, not by prefix. E.g.
            ``exclude_dirs=("docs",)`` skips any file whose path contains a
            ``docs`` segment.
    """
    all_files = _all_project_files(str(PROJECT_ROOT))
    tests_prefix = str(Path(str(PROJECT_ROOT)) / "tests") + os.sep
    ext_lower = tuple(e.lower() for e in extensions) if extensions else None
    exclude_dirs_set = set(exclude_dirs) if exclude_dirs else None

    for path in all_files:
        if exclude_tests and path.startswith(tests_prefix):
            continue
        if exclude_dirs_set is not None:
            rel = os.path.relpath(path, str(PROJECT_ROOT))
            if exclude_dirs_set.intersection(Path(rel).parts):
                continue
        if ext_lower is not None:
            lower = path.lower()
            if not any(lower.endswith(e) for e in ext_lower):
                continue
        yield path


@lru_cache(maxsize=8192)
def read_text(path: str) -> str:
    """Return the UTF-8 text content of a file; cached process-wide.

    Raises OSError / UnicodeDecodeError unchanged — callers that scan arbitrary
    files can wrap this in try/except if non-UTF-8 blobs may appear.
    """
    with Path(path).open(encoding="utf-8") as f:
        return f.read()


def iter_project_files_with_content(
    *,
    extensions: Iterable[str] | None = None,
    exclude_tests: bool = False,
    exclude_dirs: Iterable[str] | None = None,
) -> Iterator[tuple[str, str]]:
    """Yield ``(path, content)`` for matching files; content is cached.

    Files that fail to read (permission errors, non-UTF-8) are silently
    skipped — that matches the prior caller behaviour of wrapping
    ``open().read()`` in a bare ``try/except Exception: continue``.
    """
    for path in iter_project_files(
        extensions=extensions,
        exclude_tests=exclude_tests,
        exclude_dirs=exclude_dirs,
    ):
        try:
            content = read_text(path)
        except (OSError, UnicodeDecodeError):
            continue
        yield path, content


def iter_non_ignored_files(
    *,
    extensions: Iterable[str] | None = None,
    exclude_tests: bool = False,
    exclude_dirs: Iterable[str] | None = None,
    root: str | None = None,
) -> Iterator[str]:
    """Yield project files filtered through ``.gitignore``.

    Combines :func:`iter_project_files` with :func:`is_path_gitignored`
    so callers get the "files git would track" view without spawning a
    git subprocess. ``root`` defaults to :data:`PROJECT_ROOT`.

    A path is yielded iff it survives both the in-process skip-dir
    pruning of :func:`iter_project_files` and the ``.gitignore`` match.
    """
    base = Path(root) if root else PROJECT_ROOT
    patterns = load_gitignore_patterns(str(base))
    for path in iter_project_files(
        extensions=extensions,
        exclude_tests=exclude_tests,
        exclude_dirs=exclude_dirs,
    ):
        rel = os.path.relpath(path, str(base)).replace(os.sep, "/")
        if is_path_gitignored(rel, patterns):
            continue
        yield path


def _reset() -> None:
    """Test-only helper: clear the project-walk and file-content caches.

    Named ``_reset`` for parity with the per-domain reset helpers in
    sibling modules; ``utils.cache._reset_cache_for_tests`` orchestrates
    calls to all of them.
    """
    _all_project_files.cache_clear()
    _local_exclude_dirs.cache_clear()
    read_text.cache_clear()