import functools
from sqlalchemy.ext.compiler import compiles
from sqlalchemy.schema import DDLElement, Column
from sqlalchemy import Integer

from sqlalchemy import types as sqltypes
class AlterTable(DDLElement):
    """Represent an ALTER TABLE statement.

    Only the string name and optional schema name of the table
    is required, not a full Table object.

    """
    def __init__(self, table_name, schema=None):
        self.table_name = table_name
        self.schema = schema

class RenameTable(AlterTable):
    def __init__(self, old_table_name, new_table_name, schema=None):
        super(RenameTable, self).__init__(old_table_name, schema=schema)
        self.new_table_name = new_table_name

class AlterColumn(AlterTable):
    def __init__(self, name, column_name, schema=None,
                        existing_type=None,
                        existing_nullable=None,
                        existing_server_default=None):
        super(AlterColumn, self).__init__(name, schema=schema)
        self.column_name = column_name
        self.existing_type=sqltypes.to_instance(existing_type) \
                        if existing_type is not None else None
        self.existing_nullable=existing_nullable
        self.existing_server_default=existing_server_default

class ColumnNullable(AlterColumn):
    def __init__(self, name, column_name, nullable, **kw):
        super(ColumnNullable, self).__init__(name, column_name, 
                        **kw)
        self.nullable = nullable

class ColumnType(AlterColumn):
    def __init__(self, name, column_name, type_, **kw):
        super(ColumnType, self).__init__(name, column_name, 
                        **kw)
        self.type_ = sqltypes.to_instance(type_)

class ColumnName(AlterColumn):
    def __init__(self, name, column_name, newname, **kw):
        super(ColumnName, self).__init__(name, column_name, **kw)
        self.newname = newname

class ColumnDefault(AlterColumn):
    def __init__(self, name, column_name, default, **kw):
        super(ColumnDefault, self).__init__(name, column_name, **kw)
        self.default = default

class AddColumn(AlterTable):
    def __init__(self, name, column, schema=None):
        super(AddColumn, self).__init__(name, schema=schema)
        self.column = column

class DropColumn(AlterTable):
    def __init__(self, name, column, schema=None):
        super(DropColumn, self).__init__(name, schema=schema)
        self.column = column


@compiles(RenameTable)
def visit_rename_table(element, compiler, **kw):
    return "%s RENAME TO %s" % (
        alter_table(compiler, element.table_name, element.schema),
        format_table_name(compiler, element.new_table_name, element.schema)
    )

@compiles(AddColumn)
def visit_add_column(element, compiler, **kw):
    return "%s %s" % (
        alter_table(compiler, element.table_name, element.schema),
        add_column(compiler, element.column, **kw)
    )

@compiles(DropColumn)
def visit_drop_column(element, compiler, **kw):
    return "%s %s" % (
        alter_table(compiler, element.table_name, element.schema),
        drop_column(compiler, element.column.name, **kw)
    )

@compiles(ColumnNullable)
def visit_column_nullable(element, compiler, **kw):
    return "%s %s %s" % (
        alter_table(compiler, element.table_name, element.schema),
        alter_column(compiler, element.column_name),
        "DROP NOT NULL" if element.nullable else "SET NOT NULL"
    )

@compiles(ColumnType)
def visit_column_type(element, compiler, **kw):
    return "%s %s %s" % (
        alter_table(compiler, element.table_name, element.schema),
        alter_column(compiler, element.column_name),
        "TYPE %s" % format_type(compiler, element.type_)
    )

@compiles(ColumnName)
def visit_column_name(element, compiler, **kw):
    return "%s RENAME %s TO %s" % (
        alter_table(compiler, element.table_name, element.schema),
        format_column_name(compiler, element.column_name),
        format_column_name(compiler, element.newname)
    )

@compiles(ColumnDefault)
def visit_column_default(element, compiler, **kw):
    return "%s %s %s" % (
        alter_table(compiler, element.table_name, element.schema),
        alter_column(compiler, element.column_name),
        "SET DEFAULT %s" % 
            format_server_default(compiler, element.default)
        if element.default is not None
        else "DROP DEFAULT"
    )

def quote_dotted(name, quote):
    """quote the elements of a dotted name"""

    result = '.'.join([quote(x) for x in name.split('.')])
    return result

def format_table_name(compiler, name, schema):
    quote = functools.partial(compiler.preparer.quote, force=None)
    if schema:
        return quote_dotted(schema, quote) + "." + quote(name)
    else:
        return quote(name)

def format_column_name(compiler, name):
    return compiler.preparer.quote(name, None)

def format_server_default(compiler, default):
    return compiler.get_column_default_string(
                Column("x", Integer, server_default=default)
            )

def format_type(compiler, type_):
    return compiler.dialect.type_compiler.process(type_)

def alter_table(compiler, name, schema):
    return "ALTER TABLE %s" % format_table_name(compiler, name, schema)

def drop_column(compiler, name):
    return 'DROP COLUMN %s' % format_column_name(compiler, name)

def alter_column(compiler, name):
    return 'ALTER COLUMN %s' % format_column_name(compiler, name)

def add_column(compiler, column, **kw):
    return "ADD COLUMN %s" % compiler.get_column_specification(column, **kw)


