# SQL code generation

import sql

class Code:

    def to_str(self, db): raise NotImplemented()

class Literal(Code):

    def __init__(self, value): self.value = value

    def to_str(self, db): return db.esc_value(self.value)

def is_null(value): return isinstance(value, Literal) and value.value == None

class Table(Code):

    def __init__(self, name, schema=None):

        '''

        @param schema str|None (for no schema)

        '''

        self.name = name

        self.schema = schema

    def to_str(self, db): return sql.qual_name(db, self.schema, self.name)

class Col(Code):

    def __init__(self, name, table=None):

        '''

        @param table Table|None (for no table)

        '''

        assert table == None or isinstance(table, Table)

        self.name = name

        self.table = table

    def to_str(self, db):

        str_ = ''

        if self.table != None: str_ += self.table.to_str(db)+'.'

        str_ += sql.esc_name(db, self.name)

        return str_

class ValueCond:

    def __init__(self, value):

        if not isinstance(value, Literal): value = Literal(value)

        self.value = value

    def to_str(self, db, left_value):

        '''

        @param left_value The Code object that the condition is being applied on

        '''

        raise NotImplemented()

class CompareCond(ValueCond):

    def __init__(self, value, operator='='):

        ValueCond.__init__(self, value)

        self.operator = operator

    def to_str(self, db, left_value):

        if not isinstance(left_value, Code): left_value = Col(left_value)

        operator = self.operator

        if is_null(self.value): operator = 'IS'

        return left_value.to_str(db)+' '+operator+' '+self.value.to_str(db)

def as_ValueCond(value):

    if not isinstance(value, ValueCond): return CompareCond(value)

    else: return value