# Copyright 2022 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.
"""Evaluates target expressions within a GN build context."""

import argparse
from dataclasses import dataclass
import enum
import logging
import os
import re
import sys
from pathlib import Path
from typing import (Callable, Dict, List, Iterable, Iterator, NamedTuple,
                    Optional, Tuple)

_LOG = logging.getLogger(__name__)


def abspath(path: Path) -> Path:
    """Turns a path into an absolute path, not resolving symlinks."""
    return Path(os.path.abspath(path))


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 abspath(self.root.joinpath(gn_path.lstrip('/')))

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

    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(abspath(paths.root)))

        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)')

_OBJECTS_EXTENSIONS = ('.o', )

# 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, _ in _parse_build_artifacts(fd):
            # Older GN used .stamp files when there is no build artifact.
            if path.suffix == '.stamp':
                continue

            if str(path).endswith(_OBJECTS_EXTENSIONS):
                objects.append(Path(path))
            else:
                assert not artifact, f'Multiple artifacts for {target}!'
                artifact = 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(b/234886742): 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)


def _parse_args() -> argparse.Namespace:
    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('files',
                        metavar='FILE',
                        nargs='+',
                        type=Path,
                        help='Files to scan for expressions to evaluate')
    return parser.parse_args()


def _resolve_expressions_in_file(file: Path, paths: GnPaths):
    source = file.read_text()
    file.write_text(''.join(expand_expressions(paths, source)))


def main(
    gn_root: Path,
    current_path: Path,
    default_toolchain: str,
    current_toolchain: str,
    files: Iterable[Path],
) -> int:
    """Evaluates GN target expressions within a list of files.

    Modifies the files in-place with their resolved contents.
    """
    tool = current_toolchain if current_toolchain != default_toolchain else ''
    paths = GnPaths(root=abspath(gn_root),
                    build=Path.cwd(),
                    cwd=abspath(current_path),
                    toolchain=tool)

    for file in files:
        try:
            _resolve_expressions_in_file(file, paths)
        except ExpressionError as err:
            _LOG.error('Error evaluating expressions in %s:', file)
            _LOG.error('  %s', err)
            return 1

    return 0


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