from __future__ import print_function

import ast
import os
import os.path
import sys

import pycommand

__version__ = '0.1.0'


def get_setting_specs(module):
    sys.path.insert(0, os.getcwd())
    return __import__(module)


def write_settings(specs, out, values=None):
    values = values or {}

    print('# {file} file generated by topple v{version}'
          .format(file=specs.OUTPUT_FILE, version=__version__), file=out)

    for key, spec in specs.SETTINGS:
        value = values.get(key, spec[1])
        print(key, repr(value), sep=' = ', file=out)


def get_node_value(node):
    if isinstance(node, ast.Name):
        return ast.literal_eval(node.id)
    elif isinstance(node, ast.Str):
        return node.s
    elif isinstance(node, ast.Num):
        return node.n
    else:
        return node


def get_settings_from(filename):
    res = {}

    with open(filename, 'r') as f:
        tree = ast.parse('\n'.join(f.readlines()), filename)
        for node in ast.iter_child_nodes(tree):
            if isinstance(node, ast.Assign):
                for target in node.targets:
                    res[target.id] = get_node_value(node.value)
            else:
                print(node, node._fields)

    return res


class PreviewMixin(object):
    optionList = (
        ('preview', ('p', None, 'Print generated file to stdout')),
    )

    def __new__(cls, *args, **kwargs):
        cls.optionList = (cls.optionList or tuple()) + PreviewMixin.optionList
        instance = super(PreviewMixin, cls).__new__(cls, *args, **kwargs)
        return instance

    def write(self, output, specs, values=None):
        preview = self.flags['preview']

        if not preview:
            with open(output, 'w') as f:
                write_settings(specs, f, values)
        else:
            write_settings(specs, sys.stdout, values)


class Generate(pycommand.CommandBase, PreviewMixin):
    usagestr = 'usage: topple generate [--preview|-p]'

    def run(self):
        sys.path.insert(0, os.getcwd())

        specs = get_setting_specs(self.parentFlags['module'] or 'toppler')
        self.write(specs.OUTPUT_FILE, specs)


class Update(pycommand.CommandBase, PreviewMixin):
    usagestr = 'usage: topple update [--preview|-p]'

    def run(self):
        sys.path.insert(0, os.getcwd())
        filename = 'settings_local.py'
        res = get_settings_from(filename)
        specs = get_setting_specs(self.parentFlags['module'] or 'toppler')
        self.write(specs.OUTPUT_FILE, specs, res)


class Check(pycommand.CommandBase):
    usagestr = 'usage: topple check'

    def run(self):
        sys.path.insert(0, os.getcwd())
        filename = 'settings_local.py'
        res = get_settings_from(filename)
        specs = get_setting_specs(self.parentFlags['module'] or 'toppler')

        for key, spec in specs.SETTINGS:
            if key not in res:
                print('Missing setting:', key)
            elif not spec[0](res[key]):
                print('Value "%s" for %s does not pass predicate `%s\''
                      % (res[key], key, spec[0].func_name))


class Topple(pycommand.CommandBase):
    usagestr = 'usage: topple [--module=modulename|-m modulename] generate'
    description = (
        'Commands:\n'
        '  generate   Generate a new settings file.\n'
        '  update     Update an existing settings file.\n'
        '  check      Check the validity of an existing settings file.'
    )
    optionList = (('module', ('m', '<modulename>',
                              'Use specified python module.')),)

    def run(self):
        module = self.flags['module'] or 'toppler'

        if not os.path.exists(module + '.py'):
            print('No {module}.py module found!'.format(module=module))
            return 1
        if not self.args:
            print(self.usage)
            return 2

        if self.args[0] == 'generate':
            cmd = Generate(argv=self.args[1:])
        elif self.args[0] == 'update':
            cmd = Update(argv=self.args[1:])
        elif self.args[0] == 'check':
            cmd = Check(argv=self.args[1:])
        else:
            print('Undefined command: {cmd}'.format(cmd=self.args[0]))
            return 1

        cmd.registerParentFlag('module', self.flags['module'])

        if cmd.error:
            print('Error during {cmd}: {err}'.format(cmd=self.args[0],
                                                     err=cmd.error))
            return 1
        else:
            return cmd.run()