# -*- coding: utf-8 -*-

import os
import time

import sqlalchemy as sqla
from sqlalchemy.ext.compiler import compiles

## @file sqlalter.py
# This file defines all DDL (data definition langage) for the ALTER TABLE instructions
#
# It uses the SqlAlchemy compilation and quoting methos to generate SQL


class AddColumn(sqla.schema.DDLElement):
    """ Defines the ddl for adding a column to a table """
    def __init__(self, table, column):
        """ Instanciate the DDL
            @param table sqlalchemy.Table: A sqlalchemy table object
            @param column sqlalchemy.Column: A sqlalchemy column object
        """
        self.col = column
        self.table = table


@compiles(AddColumn, 'mysql')
@compiles(AddColumn, 'postgresql')
@compiles(AddColumn, 'sqlite')
def visit_add_column(element, ddlcompiler, **kw):
    """ Compiles the AddColumn DDL for mysql, postgresql and sqlite"""
    prep = ddlcompiler.sql_compiler.preparer
    tname = prep.format_table(element.table)
    colname = prep.format_column(element.col)
    return 'ALTER TABLE %s ADD COLUMN %s %s' % (tname, colname, element.col.type)


@compiles(AddColumn)
def visit_add_column(element, ddlcompiler, **kw):
    raise NotImplementedError('Add column not yet implemented for ' + str(ddlcompiler.dialect.name))


class DropColumn(sqla.schema.DDLElement):
    """ Defines the DDL for droping a column from a table """
    def __init__(self, table, column):
        """ Instanciate the DDL
            @param table sqlalchemy.Table: A sqlalchemy table object
            @param column sqlalchemy.Column: A sqlalchemy column object representing the column to drop
        """
        self.col = column
        self.table = table


@compiles(DropColumn, 'mysql')
@compiles(DropColumn, 'postgresql')
def visit_drop_column(element, ddlcompiler, **kw):
    """ Compiles the DropColumn DDL for mysql & postgresql """
    prep = ddlcompiler.sql_compiler.preparer
    tname = prep.format_table(element.table)
    colname = prep.format_column(element.col)
    return 'ALTER TABLE %s DROP COLUMN %s' % (tname, colname)


@compiles(DropColumn)
##
# @warning Returns more than one query @ref Database.sqlutils.ddl_execute
def visit_drop_column(element, ddlcompiler, **kw):
    prep = ddlcompiler.sql_compiler.preparer
    tname = prep.format_table(element.table)

    #Temporary table
    tmpname = str(element.table) + '_copydropcol'
    tmpTable = sqla.Table(tmpname, sqla.MetaData())
    tmptname = prep.format_table(tmpTable)

    query = 'ALTER TABLE %s RENAME TO %s; ' % (tname, tmptname)

    colname = prep.format_column(element.col)

    meta = sqla.MetaData()
    newtable = sqla.Table(element.table, meta)
    clist = element.table.columns

    cols = []
    for col in clist:
        if col.name != element.col.name:
            newtable.append_column(col.copy())
            cols.append(prep.format_column(col))
    cols = ', '.join(cols)

    query += str(sqla.schema.CreateTable(newtable).compile(dialect=ddlcompiler.dialect)) + ';'

    query += 'INSERT INTO %s ( %s ) SELECT %s FROM %s;' % (newtable, cols, cols, tmptname)

    query += 'DROP TABLE %s' % (tmpname)

    return query


    #raise NotImplementedError('Drop column not yet implemented for '+str(ddlcompiler.dialect.name))

class AlterColumn(sqla.schema.DDLElement):
    """ Defines the DDL for changing the type of a column """
    def __init__(self, table, column):
        """ Instanciate the DDL
            @param table sqlalchemy.Table: A sqlalchemy Table object
            @param column sqlalchemy.Column: A sqlalchemy Column object representing the new column
        """
        self.col = column
        self.table = table


@compiles(AlterColumn, 'mysql')
def visit_alter_column(element, ddlcompiler, **kw):
    """ Compiles the AlterColumn DDL for mysql """
    prep = ddlcompiler.sql_compiler.preparer
    tname = prep.format_table(element.table)
    colname = prep.format_column(element.col)
    return 'ALTER TABLE %s ALTER COLUMN %s %s' % (tname, colname, element.col.type)


@compiles(AlterColumn, 'postgresql')
def visit_alter_column(element, ddlcompiler, **kw):
    """ Compiles the AlterColumn DDL for postgresql """
    prep = ddlcompiler.sql_compiler.preparer
    tname = prep.format_table(element.table)
    colname = prep.format_column(element.col)
    return 'ALTER TABLE %s ALTER COLUMN %s TYPE %s' % (tname, colname, element.col.type)


@compiles(AlterColumn)
def visit_alter_column(element, ddlcompiler, **kw):
    raise NotImplementedError('Alter column not yet implemented for ' + str(ddlcompiler.dialect.name))