# Copyright 2014 Pants project contributors (see CONTRIBUTORS.md).
# Licensed under the Apache License, Version 2.0 (see LICENSE).

import errno
import subprocess


class Xargs:
    """A subprocess execution wrapper in the spirit of the xargs command line tool.

    Specifically allows encapsulated commands to be passed very large argument lists by chunking up
    the argument lists into a minimal set and then invoking the encapsulated command against each
    chunk in turn.
    """

    @classmethod
    def subprocess(cls, cmd, **kwargs):
        """Creates an xargs engine that uses subprocess.call to execute the given cmd array with
        extra arg chunks."""

        def call(args):
            return subprocess.call(cmd + args, **kwargs)

        return cls(call)

    def __init__(self, cmd):
        """Creates an xargs engine that calls cmd with argument chunks.

        :param cmd: A function that can execute a command line in the form of a list of strings
          passed as its sole argument.
        """
        self._cmd = cmd

    def _split_args(self, args):
        half = len(args) // 2
        return args[:half], args[half:]

    def execute(self, args):
        """Executes the configured cmd passing args in one or more rounds xargs style.

        :param list args: Extra arguments to pass to cmd.
        """
        all_args = list(args)
        try:
            return self._cmd(all_args)
        except OSError as e:
            if errno.E2BIG == e.errno:
                args1, args2 = self._split_args(all_args)
                result = self.execute(args1)
                if result != 0:
                    return result
                return self.execute(args2)
            else:
                raise e