#!/usr/bin/env python3

# Copyright 2016 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

import os
import os.path
import shutil
import subprocess
import sys

# Prefix for all custom linker driver arguments.
LINKER_DRIVER_ARG_PREFIX = '-Wcrl,'

# The linker_driver.py is responsible for forwarding a linker invocation to
# the compiler driver, while processing special arguments itself.
#
# Usage: linker_driver.py clang++ main.o -L. -llib -o prog -Wcrl,dsym,out
#
# On Mac, the logical step of linking is handled by three discrete tools to
# perform the image link, debug info link, and strip. The linker_driver.py
# combines these three steps into a single tool.
#
# The command passed to the linker_driver.py should be the compiler driver
# invocation for the linker. It is first invoked unaltered (except for the
# removal of the special driver arguments, described below). Then the driver
# performs additional actions, based on these arguments:
#
# -Wcrl,installnametoolpath,<install_name_tool_path>
#    Sets the path to the `install_name_tool` to run with
#    -Wcrl,installnametool, in which case `xcrun` is not used to invoke it.
#
# -Wcrl,installnametool,<arguments,...>
#    After invoking the linker, this will run install_name_tool on the linker's
#    output. |arguments| are comma-separated arguments to be passed to the
#    install_name_tool command.
#
# -Wcrl,dsym,<dsym_path_prefix>
#    After invoking the linker, this will run `dsymutil` on the linker's
#    output, producing a dSYM bundle, stored at dsym_path_prefix. As an
#    example, if the linker driver were invoked with:
#        "... -o out/gn/obj/foo/libbar.dylib ... -Wcrl,dsym,out/gn ..."
#    The resulting dSYM would be out/gn/libbar.dylib.dSYM/.
#
# -Wcrl,dsymutilpath,<dsymutil_path>
#    Sets the path to the dsymutil to run with -Wcrl,dsym, in which case
#    `xcrun` is not used to invoke it.
#
# -Wcrl,unstripped,<unstripped_path_prefix>
#    After invoking the linker, and before strip, this will save a copy of
#    the unstripped linker output in the directory unstripped_path_prefix.
#
# -Wcrl,strip,<strip_arguments>
#    After invoking the linker, and optionally dsymutil, this will run
#    the strip command on the linker's output. strip_arguments are
#    comma-separated arguments to be passed to the strip command.
#
# -Wcrl,strippath,<strip_path>
#    Sets the path to the strip to run with -Wcrl,strip, in which case
#    `xcrun` is not used to invoke it.


class LinkerDriver(object):
    def __init__(self, args):
        """Creates a new linker driver.

        Args:
            args: list of string, Arguments to the script.
        """
        if len(args) < 2:
            raise RuntimeError("Usage: linker_driver.py [linker-invocation]")
        self._args = args

        # List of linker driver actions. **The sort order of this list affects
        # the order in which the actions are invoked.**
        # The first item in the tuple is the argument's -Wcrl,<sub_argument>
        # and the second is the function to invoke.
        self._actions = [
            ('installnametoolpath,', self.set_install_name_tool_path),
            ('installnametool,', self.run_install_name_tool),
            ('dsymutilpath,', self.set_dsymutil_path),
            ('dsym,', self.run_dsymutil),
            ('unstripped,', self.run_save_unstripped),
            ('strippath,', self.set_strip_path),
            ('strip,', self.run_strip),
        ]

        # Linker driver actions can modify the these values.
        self._install_name_tool_cmd = ['xcrun', 'install_name_tool']
        self._dsymutil_cmd = ['xcrun', 'dsymutil']
        self._strip_cmd = ['xcrun', 'strip']

        # The linker output file, lazily computed in self._get_linker_output().
        self._linker_output = None

    def run(self):
        """Runs the linker driver, separating out the main compiler driver's
        arguments from the ones handled by this class. It then invokes the
        required tools, starting with the compiler driver to produce the linker
        output.
        """
        # Collect arguments to the linker driver (this script) and remove them
        # from the arguments being passed to the compiler driver.
        linker_driver_actions = {}
        compiler_driver_args = []
        for index, arg in enumerate(self._args[1:]):
            if arg.startswith(LINKER_DRIVER_ARG_PREFIX):
                # Convert driver actions into a map of name => lambda to invoke.
                driver_action = self._process_driver_arg(arg)
                assert driver_action[0] not in linker_driver_actions
                linker_driver_actions[driver_action[0]] = driver_action[1]
            else:
                compiler_driver_args.append(arg)

        if self._get_linker_output() is None:
            raise ValueError(
                'Could not find path to linker output (-o or --output)')

        linker_driver_outputs = [self._get_linker_output()]

        try:
            # Zero the mtime in OSO fields for deterministic builds.
            # https://crbug.com/330262.
            env = os.environ.copy()
            env['ZERO_AR_DATE'] = '1'
            # Run the linker by invoking the compiler driver.
            subprocess.check_call(compiler_driver_args, env=env)

            # Run the linker driver actions, in the order specified by the
            # actions list.
            for action in self._actions:
                name = action[0]
                if name in linker_driver_actions:
                    linker_driver_outputs += linker_driver_actions[name]()
        except:
            # If a linker driver action failed, remove all the outputs to make
            # the build step atomic.
            map(_remove_path, linker_driver_outputs)

            # Re-report the original failure.
            raise

    def _get_linker_output(self):
        """Returns the value of the output argument to the linker."""
        if not self._linker_output:
            for index, arg in enumerate(self._args):
                if arg in ('-o', '-output', '--output'):
                    self._linker_output = self._args[index + 1]
                    break
        return self._linker_output

    def _process_driver_arg(self, arg):
        """Processes a linker driver argument and returns a tuple containing the
        name and unary lambda to invoke for that linker driver action.

        Args:
            arg: string, The linker driver argument.

        Returns:
            A 2-tuple:
                0: The driver action name, as in |self._actions|.
                1: A lambda that calls the linker driver action with its direct
                   argument and returns a list of outputs from the action.
        """
        if not arg.startswith(LINKER_DRIVER_ARG_PREFIX):
            raise ValueError('%s is not a linker driver argument' % (arg, ))

        sub_arg = arg[len(LINKER_DRIVER_ARG_PREFIX):]

        for driver_action in self._actions:
            (name, action) = driver_action
            if sub_arg.startswith(name):
                return (name, lambda: action(sub_arg[len(name):]))

        raise ValueError('Unknown linker driver argument: %s' % (arg, ))

    def set_install_name_tool_path(self, install_name_tool_path):
        """Linker driver action for -Wcrl,installnametoolpath,<path>.

        Sets the invocation command for install_name_tool, which allows the
        caller to specify an alternate path. This action is always
        processed before the run_install_name_tool action.

        Args:
            install_name_tool_path: string, The path to the install_name_tool
                binary to run

        Returns:
            No output - this step is run purely for its side-effect.
        """
        self._install_name_tool_cmd = [install_name_tool_path]
        return []

    def run_install_name_tool(self, args_string):
        """Linker driver action for -Wcrl,installnametool,<args>. Invokes
        install_name_tool on the linker's output.

        Args:
            args_string: string, Comma-separated arguments for
                `install_name_tool`.

        Returns:
            No output - this step is run purely for its side-effect.
        """
        command = list(self._install_name_tool_cmd)
        command.extend(args_string.split(','))
        command.append(self._get_linker_output())
        subprocess.check_call(command)
        return []

    def run_dsymutil(self, dsym_path_prefix):
        """Linker driver action for -Wcrl,dsym,<dsym-path-prefix>. Invokes
        dsymutil on the linker's output and produces a dsym file at |dsym_file|
        path.

        Args:
            dsym_path_prefix: string, The path at which the dsymutil output
                should be located.

        Returns:
            list of string, Build step outputs.
        """
        if not len(dsym_path_prefix):
            raise ValueError('Unspecified dSYM output file')

        linker_output = self._get_linker_output()
        base = os.path.basename(linker_output)
        dsym_out = os.path.join(dsym_path_prefix, base + '.dSYM')

        # Remove old dSYMs before invoking dsymutil.
        _remove_path(dsym_out)

        tools_paths = _find_tools_paths(self._args)
        if os.environ.get('PATH'):
            tools_paths.append(os.environ['PATH'])
        dsymutil_env = os.environ.copy()
        dsymutil_env['PATH'] = ':'.join(tools_paths)
        subprocess.check_call(self._dsymutil_cmd +
                              ['-o', dsym_out, linker_output],
                              env=dsymutil_env)
        return [dsym_out]

    def set_dsymutil_path(self, dsymutil_path):
        """Linker driver action for -Wcrl,dsymutilpath,<dsymutil_path>.

        Sets the invocation command for dsymutil, which allows the caller to
        specify an alternate dsymutil. This action is always processed before
        the RunDsymUtil action.

        Args:
            dsymutil_path: string, The path to the dsymutil binary to run

        Returns:
            No output - this step is run purely for its side-effect.
        """
        self._dsymutil_cmd = [dsymutil_path]
        return []

    def run_save_unstripped(self, unstripped_path_prefix):
        """Linker driver action for -Wcrl,unstripped,<unstripped_path_prefix>.
        Copies the linker output to |unstripped_path_prefix| before stripping.

        Args:
            unstripped_path_prefix: string, The path at which the unstripped
                output should be located.

        Returns:
            list of string, Build step outputs.
        """
        if not len(unstripped_path_prefix):
            raise ValueError('Unspecified unstripped output file')

        base = os.path.basename(self._get_linker_output())
        unstripped_out = os.path.join(unstripped_path_prefix,
                                      base + '.unstripped')

        shutil.copyfile(self._get_linker_output(), unstripped_out)
        return [unstripped_out]

    def run_strip(self, strip_args_string):
        """Linker driver action for -Wcrl,strip,<strip_arguments>.

        Args:
            strip_args_string: string, Comma-separated arguments for `strip`.

        Returns:
            list of string, Build step outputs.
        """
        strip_command = list(self._strip_cmd)
        if len(strip_args_string) > 0:
            strip_command += strip_args_string.split(',')
        strip_command.append(self._get_linker_output())
        subprocess.check_call(strip_command)
        return []

    def set_strip_path(self, strip_path):
        """Linker driver action for -Wcrl,strippath,<strip_path>.

        Sets the invocation command for strip, which allows the caller to
        specify an alternate strip. This action is always processed before the
        RunStrip action.

        Args:
            strip_path: string, The path to the strip binary to run

        Returns:
            No output - this step is run purely for its side-effect.
        """
        self._strip_cmd = [strip_path]
        return []


def _find_tools_paths(full_args):
    """Finds all paths where the script should look for additional tools."""
    paths = []
    for idx, arg in enumerate(full_args):
        if arg in ['-B', '--prefix']:
            paths.append(full_args[idx + 1])
        elif arg.startswith('-B'):
            paths.append(arg[2:])
        elif arg.startswith('--prefix='):
            paths.append(arg[9:])
    return paths


def _remove_path(path):
    """Removes the file or directory at |path| if it exists."""
    if os.path.exists(path):
        if os.path.isdir(path):
            shutil.rmtree(path)
        else:
            os.unlink(path)


if __name__ == '__main__':
    LinkerDriver(sys.argv).run()
    sys.exit(0)
