# Copyright 2020 The Pigweed Authors
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may not
# use this file except in compliance with the License. You may obtain a copy of
# the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations under
# the License.
"""Script that preprocesses a Python command then runs it.

This script evaluates expressions in the Python command's arguments then invokes
the command.
"""

import argparse
import atexit
from dataclasses import dataclass
import enum
import logging
import os
from pathlib import Path
import re
import shlex
import subprocess
import sys
import time
from typing import Callable, Dict, Iterable, Iterator, List, NamedTuple
from typing import Optional, Tuple

if sys.platform != 'win32':
    import fcntl  # pylint: disable=import-error
    # TODO(b/227670947): Support Windows.

_LOG = logging.getLogger(__name__)
_LOCK_ACQUISITION_TIMEOUT = 30 * 60  # 30 minutes in seconds


def _parse_args() -> argparse.Namespace:
    """Parses arguments for this script, splitting out the command to run."""

    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('--gn-root',
                        type=Path,
                        required=True,
                        help=('Path to the root of the GN tree; '
                              'value of rebase_path("//", root_build_dir)'))
    parser.add_argument('--current-path',
                        type=Path,
                        required=True,
                        help='Value of rebase_path(".", root_build_dir)')
    parser.add_argument('--default-toolchain',
                        required=True,
                        help='Value of default_toolchain')
    parser.add_argument('--current-toolchain',
                        required=True,
                        help='Value of current_toolchain')
    parser.add_argument('--module', help='Run this module instead of a script')
    parser.add_argument('--env',
                        action='append',
                        help='Environment variables to set as NAME=VALUE')
    parser.add_argument(
        '--touch',
        type=Path,
        help='File to touch after the command is run',
    )
    parser.add_argument(
        '--capture-output',
        action='store_true',
        help='Capture subcommand output; display only on error',
    )
    parser.add_argument(
        '--working-directory',
        type=Path,
        help='Change to this working directory before running the subcommand',
    )
    parser.add_argument(
        'original_cmd',
        nargs=argparse.REMAINDER,
        help='Python script with arguments to run',
    )
    parser.add_argument(
        '--lockfile',
        type=Path,
        required=True,
        help=('Path to a pip lockfile. Any pip execution will aquire an '
              'exclusive lock on it, any other module a shared lock.'))
    return parser.parse_args()


class GnPaths(NamedTuple):
    """The set of paths needed to resolve GN paths to filesystem paths."""
    root: Path
    build: Path
    cwd: Path

    # Toolchain label or '' if using the default toolchain
    toolchain: str

    def resolve(self, gn_path: str) -> Path:
        """Resolves a GN path to a filesystem path."""
        if gn_path.startswith('//'):
            return self.root.joinpath(gn_path.lstrip('/')).resolve()

        return self.cwd.joinpath(gn_path).resolve()

    def resolve_paths(self, gn_paths: str, sep: str = ';') -> str:
        """Resolves GN paths to filesystem paths in a delimited string."""
        return sep.join(
            str(self.resolve(path)) for path in gn_paths.split(sep))


@dataclass(frozen=True)
class Label:
    """Represents a GN label."""
    name: str
    dir: Path
    relative_dir: Path
    toolchain: Optional['Label']
    out_dir: Path
    gen_dir: Path

    def __init__(self, paths: GnPaths, label: str):
        # Use this lambda to set attributes on this frozen dataclass.
        set_attr = lambda attr, val: object.__setattr__(self, attr, val)

        # Handle explicitly-specified toolchains
        if label.endswith(')'):
            label, toolchain = label[:-1].rsplit('(', 1)
        else:
            # Prevent infinite recursion for toolchains
            toolchain = paths.toolchain if paths.toolchain != label else ''

        set_attr('toolchain', Label(paths, toolchain) if toolchain else None)

        # Split off the :target, if provided, or use the last part of the path.
        try:
            directory, name = label.rsplit(':', 1)
        except ValueError:
            directory, name = label, label.rsplit('/', 1)[-1]

        set_attr('name', name)

        # Resolve the directory to an absolute path
        set_attr('dir', paths.resolve(directory))
        set_attr('relative_dir', self.dir.relative_to(paths.root.resolve()))

        set_attr(
            'out_dir',
            paths.build / self.toolchain_name() / 'obj' / self.relative_dir)
        set_attr(
            'gen_dir',
            paths.build / self.toolchain_name() / 'gen' / self.relative_dir)

    def gn_label(self) -> str:
        label = f'//{self.relative_dir.as_posix()}:{self.name}'
        return f'{label}({self.toolchain!r})' if self.toolchain else label

    def toolchain_name(self) -> str:
        return self.toolchain.name if self.toolchain else ''

    def __repr__(self) -> str:
        return self.gn_label()


class _Artifact(NamedTuple):
    path: Path
    variables: Dict[str, str]


# Matches a non-phony build statement.
_GN_NINJA_BUILD_STATEMENT = re.compile(r'^build (.+):[ \n](?!phony\b)')

# Extensions used for compilation artifacts.
_MAIN_ARTIFACTS = '', '.elf', '.a', '.so', '.dylib', '.exe', '.lib', '.dll'


def _get_artifact(entries: List[str]) -> _Artifact:
    """Attempts to resolve which artifact to use if there are multiple.

    Selects artifacts based on extension. This will not work if a toolchain
    creates multiple compilation artifacts from one command (e.g. .a and .elf).
    """
    assert entries, "There should be at least one entry here!"

    if len(entries) == 1:
        return _Artifact(Path(entries[0]), {})

    filtered = [p for p in entries if Path(p).suffix in _MAIN_ARTIFACTS]

    if len(filtered) == 1:
        return _Artifact(Path(filtered[0]), {})

    raise ExpressionError(
        f'Expected 1, but found {len(filtered)} artifacts, after filtering for '
        f'extensions {", ".join(repr(e) for e in _MAIN_ARTIFACTS)}: {entries}')


def _parse_build_artifacts(fd) -> Iterator[_Artifact]:
    """Partially parses the build statements in a Ninja file."""
    lines = iter(fd)

    def next_line():
        try:
            return next(lines)
        except StopIteration:
            return None

    # Serves as the parse state (only two states)
    artifact: Optional[_Artifact] = None

    line = next_line()

    while line is not None:
        if artifact:
            if line.startswith('  '):  # build variable statements are indented
                key, value = (a.strip() for a in line.split('=', 1))
                artifact.variables[key] = value
                line = next_line()
            else:
                yield artifact
                artifact = None
        else:
            match = _GN_NINJA_BUILD_STATEMENT.match(line)
            if match:
                artifact = _get_artifact(match.group(1).split())

            line = next_line()

    if artifact:
        yield artifact


def _search_target_ninja(ninja_file: Path,
                         target: Label) -> Tuple[Optional[Path], List[Path]]:
    """Parses the main output file and object files from <target>.ninja."""

    artifact: Optional[Path] = None
    objects: List[Path] = []

    _LOG.debug('Parsing target Ninja file %s for %s', ninja_file, target)

    with ninja_file.open() as fd:
        for path, variables in _parse_build_artifacts(fd):
            # Older GN used .stamp files when there is no build artifact.
            if path.suffix == '.stamp':
                continue

            if variables:
                assert not artifact, f'Multiple artifacts for {target}!'
                artifact = Path(path)
            else:
                objects.append(Path(path))

    return artifact, objects


def _search_toolchain_ninja(ninja_file: Path, paths: GnPaths,
                            target: Label) -> Optional[Path]:
    """Searches the toolchain.ninja file for outputs from the provided target.

    Files created by an action appear in toolchain.ninja instead of in their own
    <target>.ninja. If the specified target has a single output file in
    toolchain.ninja, this function returns its path.
    """

    _LOG.debug('Searching toolchain Ninja file %s for %s', ninja_file, target)

    # Older versions of GN used a .stamp file to signal completion of a target.
    stamp_dir = target.out_dir.relative_to(paths.build).as_posix()
    stamp_tool = 'stamp'
    if target.toolchain_name() != '':
        stamp_tool = f'{target.toolchain_name()}_stamp'
    stamp_statement = f'build {stamp_dir}/{target.name}.stamp: {stamp_tool} '

    # Newer GN uses a phony Ninja target to signal completion of a target.
    phony_dir = Path(target.toolchain_name(), 'phony',
                     target.relative_dir).as_posix()
    phony_statement = f'build {phony_dir}/{target.name}: phony '

    with ninja_file.open() as fd:
        for line in fd:
            for statement in (phony_statement, stamp_statement):
                if line.startswith(statement):
                    output_files = line[len(statement):].strip().split()
                    if len(output_files) == 1:
                        return Path(output_files[0])

                    break

    return None


def _search_ninja_files(
        paths: GnPaths,
        target: Label) -> Tuple[bool, Optional[Path], List[Path]]:
    ninja_file = target.out_dir / f'{target.name}.ninja'
    if ninja_file.exists():
        return (True, *_search_target_ninja(ninja_file, target))

    ninja_file = paths.build / target.toolchain_name() / 'toolchain.ninja'
    if ninja_file.exists():
        return True, _search_toolchain_ninja(ninja_file, paths, target), []

    return False, None, []


@dataclass(frozen=True)
class TargetInfo:
    """Provides information about a target parsed from a .ninja file."""

    label: Label
    generated: bool  # True if the Ninja files for this target were generated.
    artifact: Optional[Path]
    object_files: Tuple[Path]

    def __init__(self, paths: GnPaths, target: str):
        object.__setattr__(self, 'label', Label(paths, target))

        generated, artifact, objects = _search_ninja_files(paths, self.label)

        object.__setattr__(self, 'generated', generated)
        object.__setattr__(self, 'artifact', artifact)
        object.__setattr__(self, 'object_files', tuple(objects))

    def __repr__(self) -> str:
        return repr(self.label)


class ExpressionError(Exception):
    """An error occurred while parsing an expression."""


class _ArgAction(enum.Enum):
    APPEND = 0
    OMIT = 1
    EMIT_NEW = 2


class _Expression:
    def __init__(self, match: re.Match, ending: int):
        self._match = match
        self._ending = ending

    @property
    def string(self):
        return self._match.string

    @property
    def end(self) -> int:
        return self._ending + len(_ENDING)

    def contents(self) -> str:
        return self.string[self._match.end():self._ending]

    def expression(self) -> str:
        return self.string[self._match.start():self.end]


_Actions = Iterator[Tuple[_ArgAction, str]]


def _target_file(paths: GnPaths, expr: _Expression) -> _Actions:
    target = TargetInfo(paths, expr.contents())

    if not target.generated:
        raise ExpressionError(f'Target {target} has not been generated by GN!')

    if target.artifact is None:
        raise ExpressionError(f'Target {target} has no output file!')

    yield _ArgAction.APPEND, str(target.artifact)


def _target_file_if_exists(paths: GnPaths, expr: _Expression) -> _Actions:
    target = TargetInfo(paths, expr.contents())

    if target.generated:
        if target.artifact is None:
            raise ExpressionError(f'Target {target} has no output file!')

        if paths.build.joinpath(target.artifact).exists():
            yield _ArgAction.APPEND, str(target.artifact)
            return

    yield _ArgAction.OMIT, ''


def _target_objects(paths: GnPaths, expr: _Expression) -> _Actions:
    if expr.expression() != expr.string:
        raise ExpressionError(
            f'The expression "{expr.expression()}" in "{expr.string}" may '
            'expand to multiple arguments, so it cannot be used alongside '
            'other text or expressions')

    target = TargetInfo(paths, expr.contents())
    if not target.generated:
        raise ExpressionError(f'Target {target} has not been generated by GN!')

    for obj in target.object_files:
        yield _ArgAction.EMIT_NEW, str(obj)


# TODO(pwbug/347): Replace expressions with native GN features when possible.
_FUNCTIONS: Dict['str', Callable[[GnPaths, _Expression], _Actions]] = {
    'TARGET_FILE': _target_file,
    'TARGET_FILE_IF_EXISTS': _target_file_if_exists,
    'TARGET_OBJECTS': _target_objects,
}

_START_EXPRESSION = re.compile(fr'<({"|".join(_FUNCTIONS)})\(')
_ENDING = ')>'


def _expand_arguments(paths: GnPaths, string: str) -> _Actions:
    pos = 0

    for match in _START_EXPRESSION.finditer(string):
        if pos != match.start():
            yield _ArgAction.APPEND, string[pos:match.start()]

        ending = string.find(_ENDING, match.end())
        if ending == -1:
            raise ExpressionError(f'Parse error: no terminating "{_ENDING}" '
                                  f'was found for "{string[match.start():]}"')

        expression = _Expression(match, ending)
        yield from _FUNCTIONS[match.group(1)](paths, expression)

        pos = expression.end

    if pos < len(string):
        yield _ArgAction.APPEND, string[pos:]


def expand_expressions(paths: GnPaths, arg: str) -> Iterable[str]:
    """Expands <FUNCTION(...)> expressions; yields zero or more arguments."""
    if arg == '':
        return ['']

    expanded_args: List[List[str]] = [[]]

    for action, piece in _expand_arguments(paths, arg):
        if action is _ArgAction.OMIT:
            return []

        expanded_args[-1].append(piece)
        if action is _ArgAction.EMIT_NEW:
            expanded_args.append([])

    return (''.join(arg) for arg in expanded_args if arg)


class LockAcquisitionTimeoutError(Exception):
    """Raised on a timeout."""


def acquire_lock(lockfile: Path, exclusive: bool):
    """Attempts to acquire the lock.

    Args:
      lockfile: pathlib.Path to the lock.
      exclusive: whether this needs to be an exclusive lock.

    Raises:
      LockAcquisitionTimeoutError: If the lock is not acquired after a
        reasonable time.
    """
    if sys.platform == 'win32':
        # No-op on Windows, which doesn't have POSIX file locking.
        # TODO(b/227670947): Get this working on Windows, too.
        return

    start_time = time.monotonic()
    if exclusive:
        lock_type = fcntl.LOCK_EX  # type: ignore[name-defined]
    else:
        lock_type = fcntl.LOCK_SH  # type: ignore[name-defined]
    fd = os.open(lockfile, os.O_RDWR | os.O_CREAT)

    # Make sure we close the file when the process exits. If we manage to
    # acquire the lock below, closing the file will release it.
    def cleanup():
        os.close(fd)

    atexit.register(cleanup)

    backoff = 1
    while time.monotonic() - start_time < _LOCK_ACQUISITION_TIMEOUT:
        try:
            fcntl.flock(  # type: ignore[name-defined]
                fd, lock_type | fcntl.LOCK_NB)  # type: ignore[name-defined]
            return  # Lock acquired!
        except BlockingIOError:
            pass  # Keep waiting.

        time.sleep(backoff * 0.05)
        backoff += 1

    raise LockAcquisitionTimeoutError(
        f"Failed to acquire lock {lockfile} in {_LOCK_ACQUISITION_TIMEOUT}")


def main(  # pylint: disable=too-many-arguments
    gn_root: Path,
    current_path: Path,
    original_cmd: List[str],
    default_toolchain: str,
    current_toolchain: str,
    module: Optional[str],
    env: Optional[List[str]],
    capture_output: bool,
    touch: Optional[Path],
    working_directory: Optional[Path],
    lockfile: Path,
) -> int:
    """Script entry point."""

    if not original_cmd or original_cmd[0] != '--':
        _LOG.error('%s requires a command to run', sys.argv[0])
        return 1

    # GN build scripts are executed from the root build directory.
    root_build_dir = Path.cwd().resolve()

    tool = current_toolchain if current_toolchain != default_toolchain else ''
    paths = GnPaths(root=gn_root.resolve(),
                    build=root_build_dir,
                    cwd=current_path.resolve(),
                    toolchain=tool)

    command = [sys.executable]

    if module is not None:
        command += ['-m', module]

    run_args: dict = dict()

    if env is not None:
        environment = os.environ.copy()
        environment.update((k, v) for k, v in (a.split('=', 1) for a in env))
        run_args['env'] = environment

    if capture_output:
        # Combine stdout and stderr so that error messages are correctly
        # interleaved with the rest of the output.
        run_args['stdout'] = subprocess.PIPE
        run_args['stderr'] = subprocess.STDOUT

    try:
        for arg in original_cmd[1:]:
            command += expand_expressions(paths, arg)
    except ExpressionError as err:
        _LOG.error('%s: %s', sys.argv[0], err)
        return 1

    if working_directory:
        run_args['cwd'] = working_directory

    try:
        acquire_lock(lockfile, module == 'pip')
    except LockAcquisitionTimeoutError as exception:
        _LOG.error('%s', exception)
        return 1

    _LOG.debug('RUN %s', ' '.join(shlex.quote(arg) for arg in command))

    completed_process = subprocess.run(command, **run_args)

    if completed_process.returncode != 0:
        _LOG.debug('Command failed; exit code: %d',
                   completed_process.returncode)
        if capture_output:
            sys.stdout.buffer.write(completed_process.stdout)
    elif touch:
        # If a stamp file is provided and the command executed successfully,
        # touch the stamp file to indicate a successful run of the command.
        touch = touch.resolve()
        _LOG.debug('TOUCH %s', touch)

        # Create the parent directory in case GN / Ninja hasn't created it.
        touch.parent.mkdir(parents=True, exist_ok=True)
        touch.touch()

    return completed_process.returncode


if __name__ == '__main__':
    sys.exit(main(**vars(_parse_args())))