# SQL code generation

import sql

##### SQL code objects

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)

def as_Table(table):

    if table == None or isinstance(table, Table): return table

    elif isinstance(table, tuple):

        schema, table = table

        return Table(table, schema)

    else: return Table(table)

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

##### Old-style format support

def unescape_table(table):

    '''Currently only works with PostgreSQL.'''

    if table == None: return table

    assert table.count('.') <= 1

    parts = tuple((v.replace('"', '') for v in table.split('"."', 2)))

    if len(parts) == 1: parts, = parts

    return parts

def value2sql_gen(value, default_table=None, table_is_esc=False):

    '''Converts old-style (tuple-based) values to sql_gen-compatible values.

    @param table_is_esc If False, assumes any table name is not escaped or that

        re-escaping it will produce the same value.

    '''

    if isinstance(value, Code): return value # already in sql_gen form

    if table_is_esc: default_table = unescape_table(default_table)

    is_tuple = isinstance(value, tuple)

    if is_tuple and len(value) == 1: return Literal(value[0]) # value is literal

    elif is_tuple and len(value) == 2: # value is col with table

        table, col = value

        if table_is_esc: table = unescape_table(table)

        return Col(col, as_Table(table))

    else: return Col(value, as_Table(default_table)) # value is col name