#!/usr/bin/python2.4
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"""Search and replace builder for SCons."""


import re
import SCons.Script


def ReplaceStrings(target, source, env):
  """Replace Strings builder, does regex substitution on files.

  Args:
    target: A single target file node.
    source: A single input file node.
    env: Environment in which to build.

  From env:
    REPLACE_STRINGS: A list of pairs of regex search and replacement strings.
        The body of the source file has substitution performed on each
        pair (search_regex, replacement) in order.  SCons variables in the
        replacement strings will be evaluated.

  Returns:
    The target node, a file with contents from source, with the substitutions
    from REPLACE_STRINGS performed on it.

  For example:
    env.ReplaceStrings('out', 'in',
                       REPLACE_STRINGS = [('a*', 'b'), ('b', 'CCC')])
    With 'in' having contents: Haaapy.
    Outputs: HCCCpy.
  """
  # Load text.
  fh = open(source[0].abspath, 'rb')
  text = fh.read()
  fh.close()
  # Do replacements.
  for r in env['REPLACE_STRINGS']:
    text = re.sub(r[0], env.subst(r[1]), text)
  # Write it out.
  fh = open(target[0].abspath, 'wb')
  fh.write(text)
  fh.close()


def generate(env):
  # NOTE: SCons requires the use of this name, which fails gpylint.
  """SCons entry point for this tool."""

  # Add the builder
  act = SCons.Script.Action(ReplaceStrings, varlist=['REPLACE_STRINGS'])
  bld = SCons.Script.Builder(action=act, single_source=True)
  env.Append(BUILDERS={'ReplaceStrings': bld})