# Released under the MIT License. See LICENSE for details.
#
"""Apply small text patches to packages installed in a venv.

Some Python projects need targeted modifications to third-party
packages installed via ``pip`` — bug fixes pending upstream review,
small project-specific customizations, or workarounds for
upstream-rejected behaviour. This module provides a simple,
declarative way to manage such patches.

Patches are described in a JSON file (commonly
``pconfig/venv_patches.json``) using the :class:`VenvPatches` schema
below. Each entry is a literal-string find-and-replace, validated
by an exact occurrence count so silent drift across upstream
versions surfaces immediately as a hard error.

Two operations are supported:

* :func:`apply_patches` — typically called once at the end of venv
  construction (after ``pip install``). Replaces ``srctxt`` with
  ``replacetxt`` in each target file.

* :func:`check_patches` — verifies all patches are present in the
  current venv. Designed to be called at app startup so a venv that
  was assembled without the patches (e.g. an installer that ran
  with ``allow_mismatches=True`` and skipped a broken patch) gets
  flagged via a CRITICAL log entry.

The string-search approach (rather than SHA256 of full files or
unified-diff matching) is intentional: small targeted patches stay
robust as upstream files evolve around them, as long as the
specific lines we touch don't change.
"""

import logging
import sysconfig
from pathlib import Path
from dataclasses import dataclass, field
from typing import Annotated, TYPE_CHECKING

from efro.dataclassio import ioprepped, IOAttrs, dataclass_from_json
from efro.error import CleanError

if TYPE_CHECKING:
    pass


_log = logging.getLogger(__name__)


@ioprepped
@dataclass
class VenvPatch:
    """A single string-replacement patch against a venv site-packages file."""

    #: Short human-readable identifier. Used in log/error messages so
    #: a failure points at the right patch.
    description: Annotated[str, IOAttrs('description')]

    #: Path to the target file relative to ``site-packages`` (e.g.
    #: ``google/cloud/firestore_v1/watch.py``).
    path: Annotated[str, IOAttrs('path')]

    #: Exact text to find. Must appear ``count`` times in the target.
    srctxt: Annotated[str, IOAttrs('srctxt')]

    #: Text to replace ``srctxt`` with.
    replacetxt: Annotated[str, IOAttrs('replacetxt')]

    #: Number of expected occurrences of ``srctxt``. Defaults to 1.
    #: When ``> 1``, every occurrence is replaced (so all become
    #: ``replacetxt``). To replace different occurrences with
    #: different text, split into separate patch entries with
    #: distinguishing surrounding context in ``srctxt``.
    count: Annotated[int, IOAttrs('count', soft_default=1)] = 1


@ioprepped
@dataclass
class VenvPatches:
    """Top-level container for a list of venv patches.

    This is the schema for ``pconfig/venv_patches.json``.
    """

    patches: Annotated[list[VenvPatch], IOAttrs('patches')] = field(
        default_factory=list
    )


def _validate(patches: list[VenvPatch]) -> None:
    """Validate inter-patch invariants.

    Currently checks that ``srctxt`` is non-empty and does not appear
    inside its own ``replacetxt`` (which would cause re-application
    on every run to grow indefinitely). Also disallows ``count <= 0``.
    """
    for p in patches:
        if not p.srctxt:
            raise CleanError(
                f'venv-patch {p.description!r}: srctxt must be non-empty.'
            )
        if p.count <= 0:
            raise CleanError(
                f'venv-patch {p.description!r}:'
                f' count must be positive (got {p.count}).'
            )
        if p.srctxt in p.replacetxt:
            raise CleanError(
                f'venv-patch {p.description!r}: srctxt appears'
                ' inside replacetxt; this would cause re-application'
                ' to grow without bound. Add disambiguating context'
                ' to srctxt or restructure replacetxt.'
            )


def _site_packages() -> Path:
    """Return the site-packages dir of the current Python interpreter."""
    purelib = sysconfig.get_paths().get('purelib')
    if not purelib:
        raise CleanError(
            'Could not determine site-packages location from sysconfig.'
        )
    return Path(purelib)


def load_patches_from_file(path: str | Path) -> VenvPatches:
    """Load and validate a :class:`VenvPatches` JSON file."""
    src = Path(path).read_text(encoding='utf-8')
    out: VenvPatches = dataclass_from_json(VenvPatches, src)
    _validate(out.patches)
    return out


def apply_patches(
    patches: list[VenvPatch],
    *,
    site_packages: Path | None = None,
    allow_mismatches: bool = False,
) -> int:
    """Apply each patch in order to the current venv's site-packages.

    Args:
      patches: Patches to apply.
      site_packages: Optional override. If ``None``, uses the
        current interpreter's ``site-packages`` directory.
      allow_mismatches: If ``True``, mismatched or missing patches
        are logged at ERROR level and skipped instead of raising.
        Use this during installer flows on production nodes where
        a partial venv is preferable to a broken boot. The default
        ``False`` is the right choice for dev ``make env`` flows.

    Returns the number of patches that were either successfully
    applied or already present (i.e. the number that ended in the
    desired state). Errors/skips are not counted.
    """
    if site_packages is None:
        site_packages = _site_packages()
    succeeded = 0
    for p in patches:
        target = site_packages / p.path
        try:
            _apply_one(target, p)
            succeeded += 1
        except CleanError as exc:
            if allow_mismatches:
                _log.error('%s', exc)
            else:
                raise
    return succeeded


def _apply_one(target: Path, p: VenvPatch) -> None:
    if not target.exists():
        raise CleanError(
            f'venv-patch for {p.path!r}: target file does not exist.'
            ' Either remove this patch (if no longer needed) or'
            ' update path to match the current upstream layout.'
        )
    text = target.read_text(encoding='utf-8')
    src_count = text.count(p.srctxt)
    repl_count = text.count(p.replacetxt)

    # Already-applied detection: replacetxt appears the expected
    # number of times AND srctxt is gone. Idempotent re-runs are a
    # no-op in this case.
    if src_count == 0 and repl_count >= p.count:
        _log.debug('venv-patch already applied in %s; skipping.', p.path)
        return

    if src_count != p.count:
        raise CleanError(
            f'venv-patch for {p.path!r}: expected {p.count}'
            f' occurrence(s) of srctxt, found {src_count}.'
            ' Upstream may have changed; update or remove the patch.'
        )

    new_text = text.replace(p.srctxt, p.replacetxt)
    target.write_text(new_text, encoding='utf-8')
    _log.info('Applied venv-patch in %s.', p.path)


def find_patch_mismatches(
    patches: list[VenvPatch],
    *,
    site_packages: Path | None = None,
) -> list[str]:
    """Return the paths of patches not fully applied.

    Empty list means everything is in the desired state. No
    logging — callers decide severity and message format.
    """
    if site_packages is None:
        site_packages = _site_packages()
    out: list[str] = []
    for p in patches:
        target = site_packages / p.path
        if not target.exists():
            out.append(p.path)
            continue
        text = target.read_text(encoding='utf-8')
        if text.count(p.srctxt) != 0 or text.count(p.replacetxt) < p.count:
            out.append(p.path)
    return out


def check_patches(
    patches: list[VenvPatch],
    *,
    site_packages: Path | None = None,
) -> int:
    """Verify that all patches are present in the current venv.

    Logs CRITICAL for each mismatched patch. Returns the count;
    callers that want to abort on any mismatch can check the return
    value. Use :func:`find_patch_mismatches` directly if you need
    to control logging severity or message format.
    """
    paths = find_patch_mismatches(patches, site_packages=site_packages)
    for path in paths:
        _log.critical(
            'venv-patch not applied in %s. The patch may have failed'
            ' to apply during venv setup, or upstream may have'
            ' changed underneath us.',
            path,
        )
    return len(paths)