#!/usr/bin/env python
# -*- coding: utf-8 -*-

import shutil
import warnings
import logging
import inspect
from StringIO import StringIO

from kallithea.lib.dbmigrate import migrate
from kallithea.lib.dbmigrate.migrate.versioning import genmodel, schemadiff
from kallithea.lib.dbmigrate.migrate.versioning.config import operations
from kallithea.lib.dbmigrate.migrate.versioning.template import Template
from kallithea.lib.dbmigrate.migrate.versioning.script import base
from kallithea.lib.dbmigrate.migrate.versioning.util import import_path, load_model, with_engine
from kallithea.lib.dbmigrate.migrate.exceptions import MigrateDeprecationWarning, InvalidScriptError, ScriptError

log = logging.getLogger(__name__)
__all__ = ['PythonScript']


class PythonScript(base.BaseScript):
    """Base for Python scripts"""

    @classmethod
    def create(cls, path, **opts):
        """Create an empty migration script at specified path

        :returns: :class:`PythonScript instance <migrate.versioning.script.py.PythonScript>`"""
        cls.require_notfound(path)

        src = Template(opts.pop('templates_path', None)).get_script(theme=opts.pop('templates_theme', None))
        shutil.copy(src, path)

        return cls(path)

    @classmethod
    def make_update_script_for_model(cls, engine, oldmodel,
                                     model, repository, **opts):
        """Create a migration script based on difference between two SA models.

        :param repository: path to migrate repository
        :param oldmodel: dotted.module.name:SAClass or SAClass object
        :param model: dotted.module.name:SAClass or SAClass object
        :param engine: SQLAlchemy engine
        :type repository: string or :class:`Repository instance <migrate.versioning.repository.Repository>`
        :type oldmodel: string or Class
        :type model: string or Class
        :type engine: Engine instance
        :returns: Upgrade / Downgrade script
        :rtype: string
        """

        if isinstance(repository, basestring):
            # oh dear, an import cycle!
            from kallithea.lib.dbmigrate.migrate.versioning.repository import Repository
            repository = Repository(repository)

        oldmodel = load_model(oldmodel)
        model = load_model(model)

        # Compute differences.
        diff = schemadiff.getDiffOfModelAgainstModel(
            model,
            oldmodel,
            excludeTables=[repository.version_table])
        # TODO: diff can be False (there is no difference?)
        decls, upgradeCommands, downgradeCommands = \
            genmodel.ModelGenerator(diff,engine).genB2AMigration()

        # Store differences into file.
        src = Template(opts.pop('templates_path', None)).get_script(opts.pop('templates_theme', None))
        f = open(src)
        contents = f.read()
        f.close()

        # generate source
        search = 'def upgrade(migrate_engine):'
        contents = contents.replace(search, '\n\n'.join((decls, search)), 1)
        if upgradeCommands:
            contents = contents.replace('    pass', upgradeCommands, 1)
        if downgradeCommands:
            contents = contents.replace('    pass', downgradeCommands, 1)
        return contents

    @classmethod
    def verify_module(cls, path):
        """Ensure path is a valid script

        :param path: Script location
        :type path: string
        :raises: :exc:`InvalidScriptError <migrate.exceptions.InvalidScriptError>`
        :returns: Python module
        """
        # Try to import and get the upgrade() func
        module = import_path(path)
        try:
            assert callable(module.upgrade)
        except Exception, e:
            raise InvalidScriptError(path + ': %s' % str(e))
        return module

    def preview_sql(self, url, step, **args):
        """Mocks SQLAlchemy Engine to store all executed calls in a string
        and runs :meth:`PythonScript.run <migrate.versioning.script.py.PythonScript.run>`

        :returns: SQL file
        """
        buf = StringIO()
        args['engine_arg_strategy'] = 'mock'
        args['engine_arg_executor'] = lambda s, p = '': buf.write(str(s) + p)

        @with_engine
        def go(url, step, **kw):
            engine = kw.pop('engine')
            self.run(engine, step)
            return buf.getvalue()

        return go(url, step, **args)

    def run(self, engine, step):
        """Core method of Script file.
        Exectues :func:`update` or :func:`downgrade` functions

        :param engine: SQLAlchemy Engine
        :param step: Operation to run
        :type engine: string
        :type step: int
        """
        if step > 0:
            op = 'upgrade'
        elif step < 0:
            op = 'downgrade'
        else:
            raise ScriptError("%d is not a valid step" % step)

        funcname = base.operations[op]
        script_func = self._func(funcname)

        # check for old way of using engine
        if not inspect.getargspec(script_func)[0]:
            raise TypeError("upgrade/downgrade functions must accept engine"
                " parameter (since version 0.5.4)")

        script_func(engine)

    @property
    def module(self):
        """Calls :meth:`migrate.versioning.script.py.verify_module`
        and returns it.
        """
        if not hasattr(self, '_module'):
            self._module = self.verify_module(self.path)
        return self._module

    def _func(self, funcname):
        if not hasattr(self.module, funcname):
            msg = "Function '%s' is not defined in this script"
            raise ScriptError(msg % funcname)
        return getattr(self.module, funcname)