# 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.
"""Generates compile fail test GN targets.

Scans source files for PW_NC_TEST(...) statements and generates a
BUILD.gn file with a target for each test. This allows the compilation failure
tests to run in parallel in Ninja.

This file is executed during gn gen, so it cannot rely on any setup that occurs
during the build.
"""

import argparse
import base64
from collections import defaultdict
from dataclasses import dataclass
from enum import Enum
from pathlib import Path
import pickle
import re
import sys
from typing import (Iterable, Iterator, List, NamedTuple, NoReturn, Optional,
                    Pattern, Sequence, Set, Tuple)

# Matches the #if or #elif statement that starts a compile fail test.
_TEST_START = re.compile(r'^[ \t]*#[ \t]*(?:el)?if[ \t]+PW_NC_TEST\([ \t]*')

# Matches the name of a test case.
_TEST_NAME = re.compile(
    r'(?P<name>[a-zA-Z0-9_]+)[ \t]*\)[ \t]*(?://.*|/\*.*)?$')

# Negative compilation test commands take the form PW_NC_EXPECT("regex"),
# PW_NC_EXPECT_GCC("regex"), or PW_NC_EXPECT_CLANG("regex"). PW_NC_EXPECT() is
# an error.
_EXPECT_START = re.compile(r'^[ \t]*PW_NC_EXPECT(?P<compiler>_GCC|_CLANG)?\(')

# EXPECT statements are regular expressions that must match the compiler output.
# They must fit on a single line.
_EXPECT_REGEX = re.compile(r'(?P<regex>"[^\n]+")\);[ \t]*(?://.*|/\*.*)?$')


class Compiler(Enum):
    ANY = 0
    GCC = 1
    CLANG = 2

    @staticmethod
    def from_command(command: str) -> 'Compiler':
        if command.endswith(('clang', 'clang++')):
            return Compiler.CLANG

        if command.endswith(('gcc', 'g++')):
            return Compiler.GCC

        raise ValueError(
            f"Unrecognized compiler '{command}'; update the Compiler enum "
            f'in {Path(__file__).name} to account for this')

    def matches(self, other: 'Compiler') -> bool:
        return self is other or self is Compiler.ANY or other is Compiler.ANY


@dataclass(frozen=True)
class Expectation:
    compiler: Compiler
    pattern: Pattern[str]
    line: int


@dataclass(frozen=True)
class TestCase:
    suite: str
    case: str
    expectations: Tuple[Expectation, ...]
    source: Path
    line: int

    def name(self) -> str:
        return f'{self.suite}.{self.case}'

    def serialize(self) -> str:
        return base64.b64encode(pickle.dumps(self)).decode()

    @classmethod
    def deserialize(cls, serialized: str) -> 'Expectation':
        return pickle.loads(base64.b64decode(serialized))


class ParseError(Exception):
    """Failed to parse a PW_NC_TEST."""
    def __init__(self, message: str, file: Path, lines: Sequence[str],
                 error_lines: Sequence[int]) -> None:
        for i in error_lines:
            message += f'\n{file.name}:{i + 1}: {lines[i]}'
        super().__init__(message)


class _ExpectationParser:
    """Parses expecatations from 'PW_NC_EXPECT(' to the final ');'."""
    class _State:
        SPACE = 0  # Space characters, which are ignored
        COMMENT_START = 1  # First / in a //-style comment
        COMMENT = 2  # Everything after // on a line
        OPEN_QUOTE = 3  # Starting quote for a string literal
        CHARACTERS = 4  # Characters within a string literal
        ESCAPE = 5  # \ within a string literal, which may escape a "
        CLOSE_PAREN = 6  # Closing parenthesis to the PW_NC_EXPECT statement.

    def __init__(self, index: int, compiler: Compiler) -> None:
        self.index = index
        self._compiler = compiler
        self._state = self._State.SPACE
        self._contents: List[str] = []

    def parse(self, chars: str) -> Optional[Expectation]:
        """State machine that parses characters in PW_NC_EXPECT()."""
        for char in chars:
            if self._state is self._State.SPACE:
                if char == '"':
                    self._state = self._State.CHARACTERS
                elif char == ')':
                    self._state = self._State.CLOSE_PAREN
                elif char == '/':
                    self._state = self._State.COMMENT_START
                elif not char.isspace():
                    raise ValueError(f'Unexpected character "{char}"')
            elif self._state is self._State.COMMENT_START:
                if char == '*':
                    raise ValueError(
                        '"/* */" comments are not supported; use // instead')
                if char != '/':
                    raise ValueError(f'Unexpected character "{char}"')
                self._state = self._State.COMMENT
            elif self._state is self._State.COMMENT:
                if char == '\n':
                    self._state = self._State.SPACE
            elif self._state is self._State.CHARACTERS:
                if char == '"':
                    self._state = self._State.SPACE
                elif char == '\\':
                    self._state = self._State.ESCAPE
                else:
                    self._contents.append(char)
            elif self._state is self._State.ESCAPE:
                # Include escaped " directly. Restore the \ for other chars.
                if char != '"':
                    self._contents.append('\\')
                self._contents.append(char)
                self._state = self._State.CHARACTERS
            elif self._state is self._State.CLOSE_PAREN:
                if char != ';':
                    raise ValueError(f'Expected ";", found "{char}"')

                return self._expectation(''.join(self._contents))

        return None

    def _expectation(self, regex: str) -> Expectation:
        if '"""' in regex:
            raise ValueError('The regular expression cannot contain """')

        # Evaluate the string from the C++ source as a raw literal.
        re_string = eval(f'r"""{regex}"""')  # pylint: disable=eval-used
        if not isinstance(re_string, str):
            raise ValueError('The regular expression must be a string!')

        try:
            return Expectation(self._compiler, re.compile(re_string),
                               self.index + 1)
        except re.error as error:
            raise ValueError('Invalid regular expression: ' + error.msg)


class _NegativeCompilationTestSource:
    def __init__(self, file: Path) -> None:
        self._file = file
        self._lines = self._file.read_text().splitlines(keepends=True)

        self._parsed_expectations: Set[int] = set()

    def _error(self, message: str, *error_lines: int) -> NoReturn:
        raise ParseError(message, self._file, self._lines, error_lines)

    def _parse_expectations(self, start: int) -> Iterator[Expectation]:
        expectation: Optional[_ExpectationParser] = None

        for index in range(start, len(self._lines)):
            line = self._lines[index]

            # Skip empty or comment lines
            if not line or line.isspace() or line.lstrip().startswith('//'):
                continue

            # Look for a 'PW_NC_EXPECT(' in the code.
            if not expectation:
                expect_match = _EXPECT_START.match(line)
                if not expect_match:
                    break  # No expectation found, stop processing.

                compiler = expect_match['compiler'] or 'ANY'
                expectation = _ExpectationParser(
                    index, Compiler[compiler.lstrip('_')])

                self._parsed_expectations.add(index)

                # Remove the 'PW_NC_EXPECT(' so the line starts with the regex.
                line = line[expect_match.end():]

            # Find the regex after previously finding 'PW_NC_EXPECT('.
            try:
                if parsed_expectation := expectation.parse(line.lstrip()):
                    yield parsed_expectation

                    expectation = None
            except ValueError as err:
                self._error(
                    f'Failed to parse PW_NC_EXPECT() statement:\n\n  {err}.\n\n'
                    'PW_NC_EXPECT() statements must contain only a string '
                    'literal with a valid Python regular expression and '
                    'optional //-style comments.', index)

        if expectation:
            self._error('Unterminated PW_NC_EXPECT() statement!',
                        expectation.index)

    def _check_for_stray_expectations(self) -> None:
        all_expectations = frozenset(i for i in range(len(self._lines))
                                     if _EXPECT_START.match(self._lines[i]))
        stray = all_expectations - self._parsed_expectations
        if stray:
            self._error(f'Found {len(stray)} stray PW_NC_EXPECT() commands!',
                        *sorted(stray))

    def parse(self, suite: str) -> Iterator[TestCase]:
        """Finds all negative compilation tests in this source file."""
        for index, line in enumerate(self._lines):
            case_match = _TEST_START.match(line)
            if not case_match:
                continue

            name_match = _TEST_NAME.match(line, case_match.end())
            if not name_match:
                self._error(
                    'Negative compilation test syntax error. '
                    f"Expected test name, found '{line[case_match.end():]}'",
                    index)

            expectations = tuple(self._parse_expectations(index + 1))
            yield TestCase(suite, name_match['name'], expectations, self._file,
                           index + 1)

        self._check_for_stray_expectations()


def enumerate_tests(suite: str, paths: Iterable[Path]) -> Iterator[TestCase]:
    """Parses PW_NC_TEST statements from a file."""
    for path in paths:
        yield from _NegativeCompilationTestSource(path).parse(suite)


class SourceFile(NamedTuple):
    gn_path: str
    file_path: Path


def generate_gn_target(base: str, source_list: str, test: TestCase,
                       all_tests: str) -> Iterator[str]:
    yield f'''\
pw_python_action("{test.name()}.negative_compilation_test") {{
  script = "$dir_pw_compilation_testing/py/pw_compilation_testing/runner.py"
  inputs = [{source_list}]
  args = [
    "--toolchain-ninja=$_toolchain_ninja",
    "--target-ninja=$_target_ninja",
    "--test-data={test.serialize()}",
    "--all-tests={all_tests}",
  ]
  deps = ["{base}"]
  python_deps = [
    "$dir_pw_cli/py",
    "$dir_pw_compilation_testing/py",
  ]
  stamp = true
}}
'''


def generate_gn_build(base: str, sources: Iterable[SourceFile],
                      tests: List[TestCase], all_tests: str) -> Iterator[str]:
    """Generates the BUILD.gn file with compilation failure test targets."""
    _, base_name = base.rsplit(':', 1)

    yield 'import("//build_overrides/pigweed.gni")'
    yield ''
    yield 'import("$dir_pw_build/python_action.gni")'
    yield ''
    yield ('_toolchain_ninja = '
           'rebase_path("$root_out_dir/toolchain.ninja", root_build_dir)')
    yield ('_target_ninja = '
           f'rebase_path(get_label_info("{base}", "target_out_dir") +'
           f'"/{base_name}.ninja", root_build_dir)')
    yield ''

    gn_source_list = ', '.join(f'"{gn_path}"' for gn_path, _ in sources)
    for test in tests:
        yield from generate_gn_target(base, gn_source_list, test, all_tests)


def _main(name: str, base: str, sources: Iterable[SourceFile],
          output: Path) -> int:
    print_stderr = lambda s: print(s, file=sys.stderr)

    try:
        tests = list(enumerate_tests(name, (s.file_path for s in sources)))
    except ParseError as error:
        print_stderr(f'ERROR: {error}')
        return 1

    if not tests:
        print_stderr(f'The test "{name}" has no negative compilation tests!')
        print_stderr('Add PW_NC_TEST() cases or remove this negative '
                     'compilation test')
        return 1

    tests_by_case = defaultdict(list)
    for test in tests:
        tests_by_case[test.case].append(test)

    duplicates = [tests for tests in tests_by_case.values() if len(tests) > 1]
    if duplicates:
        print_stderr('There are duplicate negative compilation test cases!')
        print_stderr('The following test cases appear more than once:')
        for tests in duplicates:
            print_stderr(f'\n    {tests[0].case} ({len(tests)} occurrences):')
            for test in tests:
                print_stderr(f'        {test.source.name}:{test.line}')
        return 1

    output.mkdir(parents=True, exist_ok=True)
    build_gn = output.joinpath('BUILD.gn')
    with build_gn.open('w') as fd:
        for line in generate_gn_build(base, sources, tests,
                                      output.joinpath('tests.txt').as_posix()):
            print(line, file=fd)

    with output.joinpath('tests.txt').open('w') as fd:
        for test in tests:
            print(test.case, file=fd)

    # Print the test case names to stdout for consumption by GN.
    for test in tests:
        print(test.case)

    return 0


def _parse_args() -> dict:
    """Parses command-line arguments."""
    def source_file(arg: str) -> SourceFile:
        gn_path, file_path = arg.split(';', 1)
        return SourceFile(gn_path, Path(file_path))

    parser = argparse.ArgumentParser(
        description='Emits an error when a facade has a null backend')
    parser.add_argument('--output', type=Path, help='Output directory')
    parser.add_argument('--name', help='Name of the NC test')
    parser.add_argument('--base', help='GN label for the base target to build')
    parser.add_argument('sources',
                        nargs='+',
                        type=source_file,
                        help='Source file with the no-compile tests')
    return vars(parser.parse_args())


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