install-cfg

#!/usr/bin/python
# INTENDED TO BE EXECUTED WITH `python install-cfg src dest verbose`

import os
import sys

import curses           # Used by the std cfg.

def scan_cfg(src_cfg, dest_cfg):
    '''Does `src_cfg` have something new that `dest_cfg` doesn't?'''
    for key in src_cfg:
        if key not in dest_cfg:
            return True
        if isinstance(src_cfg[key], dict):
            if not isinstance(dest_cfg[key], dict):
                return True
            if scan_cfg(src_cfg[key], dest_cfg[key]):
                return True
        # Tuple check doesn't work.
        if isinstance(src_cfg[key], tuple):
            try:
                if len(src_cfg[key]) != len(dest_cfg[key]):
                    return True
            except:
                return True
    return False

def decide(src, dest, verbose=True):
    '''
    Decide what needs to be done to install the configuration file
    from `src` to `dest`.
    
    Returns
        'install'       if the `dest` should be overwritten with `src`.
        'fail'          if it can't be installed automatically.
        'skip'          if it should not be installed/overwritten.
    '''
    try:
        src_cfg = eval(open(src).read())
    except:
        sys.stderr.write(
            "\nERROR:\n"
            "Cannot load the source configuration files.\n"
            "\n"
        )
        return 'fail'
    # Install the file if it hasn't already been installed.
    try:
        dest_file = open(dest)
    except IOError:
        return 'install'
    try:
        content = dest_file.read()
    except:
        sys.stderr.write(
            "\nERROR:\n"
            "Cannot open the pre-existing configuration file.\n"
            "\n"
        )
    # Install if file has not been modified.
    magic = '#@not-modified@\n'
    if '\n'+magic in content or content.startswith(magic):
        if verbose:
            sys.stderr.write(
                "\nINFORMATIONAL:\n"
                "The already existing configuration file is at its default\n"
                "and will therefore be overwritten to install any changes.\n"
                "\n"
            )
        return 'install'
    # Check if the pre-existing configuration is usable.
    try:
        dest_cfg = eval(content)
    except:
        sys.stderr.write(
            "\nERROR:\n"
            "Cannot parse the pre-existing configuration.\n"
            "\n"
        )
        return 'fail'
    dest_file.close()
    if scan_cfg(src_cfg, dest_cfg):
        sys.stderr.write(
            "\nNOTICE:\n"
            "The format of the configuration file has been changed in this\n"
            "version.  The configuration file must be modified manually.\n"
            "\n"
        )
        return 'fail'
    else:
        if verbose:
            sys.stderr.write(
                "\nINFORMATIONAL:\n"
                "The altered configuration file should be usable\n"
                "by the newly installed version of the program.\n"
                "\n"
            )
        return 'skip'

def main():
    if len(sys.argv) != 5:
        sys.stderr.write(
            "Usage: python install-cfg install-cmd src dest verbose\n"
        )
        sys.exit(1)
    install_cmd, src, dest = sys.argv[1], sys.argv[2], sys.argv[3]
    if sys.argv[4] == 'true':
        verbose = True
    elif sys.argv[4] == 'false':
        verbose = False
    else:
        verbose = True
        sys.stderr.write(
            'The <verbose> parameter must be "true" or "false".\n'
        )
    
    status = decide(src, dest, verbose)
    if status == 'fail':
        sys.stderr.write("Error: Cannot install automatically.\n")
        sys.stderr.write(
            '"{0}" is incompatible and must be edited\n'.format(dest)
        )
        sys.stderr.write(
            'Look at "{0}" to know what changes must be made.\n'.format(src)
        )
        sys.exit(1)
    elif status == 'install':
        os.system('{0} -m 644 "{1}" "{2}"'.format(install_cmd, src, dest))
    elif status == 'skip':
        pass
    else:
        sys.stderr.write('Internal error!\n')

if __name__ == '__main__':
    main()