# SQL code generation

import operator

import objects

import sql

import strings

import util

##### SQL code objects

class MockDb:

    def esc_value(self, value): return repr(value)

    def esc_name(self, name): return name

mockDb = MockDb()

class Code(objects.BasicObject):

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

    def __str__(self): return self.to_str(mockDb)

class CustomCode(Code):

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

    def to_str(self, db): return self.str_

##### Literal values

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

##### Tables

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):

        str_ = ''

        if self.schema != None: str_ += db.esc_name(self.schema)+'.'

        str_ += db.esc_name(self.name)

        return str_

    def to_Table(self): return self

def as_Table(table):

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

    else: return Table(table)

class NamedTable(Table):

    def __init__(self, name, code, cols=None):

        Table.__init__(self, name)

        if not isinstance(code, Code): code = Table(code)

        self.code = code

        self.cols = cols

    def to_str(self, db):

        str_ = self.code.to_str(db)+' AS '+Table.to_str(self, db)

        if self.cols != None: str_ += ' ('+(', '.join(self.cols))+')'

        return str_

    def to_Table(self): return Table(self.name)

##### Columns

class Col(Code):

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

        '''

        @param table Table|None (for no table)

        '''

        if util.is_str(table): table = Table(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_ += db.esc_name(self.name)

        return str_

    def to_Col(self): return self

def as_Col(col, table=None):

    assert col != None

    if isinstance(col, Code): return col

    else: return Col(col, table)

class NamedCol(Col):

    def __init__(self, name, code):

        Col.__init__(self, name)

        if not isinstance(code, Code): code = Literal(code)

        self.code = code

    def to_str(self, db):

        return self.code.to_str(db)+' AS '+Col.to_str(self, db)

    def to_Col(self): return Col(self.name)

##### Conditions

class ValueCond(objects.BasicObject):

    def __init__(self, value):

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

        if isinstance(value, NamedCol): value = value.code

        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()

    def __str__(self): return self.to_str(mockDb, '<left_value>')

class CompareCond(ValueCond):

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

        '''

        @param operator By default, compares NULL values literally. Use '~=' or

            '~!=' to pass NULLs through.

        '''

        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)

        right_value = self.value

        left = left_value.to_str(db)

        right = right_value.to_str(db)

        # Parse operator

        operator = self.operator

        passthru_null_ref = [False]

        operator = strings.remove_prefix('~', operator, passthru_null_ref)

        neg_ref = [False]

        operator = strings.remove_prefix('!', operator, neg_ref)

        equals = operator.endswith('=')

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

        # Create str

        str_ = left+' '+operator+' '+right

        if equals and not passthru_null_ref[0] and isinstance(right_value, Col):

            str_ += ' OR ('+left+' IS NULL AND '+right+' IS NULL)'

        if neg_ref[0]: str_ = 'NOT ('+str_+')'

        return str_

# Tells as_ValueCond() to assume a non-ValueCond is a literal value

assume_literal = object()

def as_ValueCond(value, default_table=assume_literal):

    if not isinstance(value, ValueCond):

        if default_table is not assume_literal:

            value = as_Col(value, default_table)

        return CompareCond(value)

    else: return value

##### Joins

join_same = object() # tells Join the left and right columns have the same name

# Tells Join the left and right columns have the same name and are never NULL

join_same_not_null = object()

filter_out = object() # tells Join to filter out rows that match the join

class Join(objects.BasicObject):

    def __init__(self, table, mapping, type_=None):

        '''

        @param mapping dict(right_table_col=left_table_col, ...)

            * if left_table_col is join_same: left_table_col = right_table_col

              * Note that right_table_col must be a string

            * if left_table_col is join_same_not_null:

              left_table_col = right_table_col and both have NOT NULL constraint

              * Note that right_table_col must be a string

        @param type_ None (for plain join)|str (e.g. 'LEFT')|filter_out

            * filter_out: equivalent to 'LEFT' with the query filtered by

              `table_pkey IS NULL` (indicating no match)

        '''

        if util.is_str(table): table = Table(table)

        assert type_ == None or util.is_str(type_) or type_ is filter_out

        self.table = table

        self.mapping = mapping

        self.type_ = type_

    def to_str(self, db, left_table):

        # Switch order (left_table is on the right in the comparison)

        right_table = left_table

        left_table = self.table # note left_table is reassigned

        def join(entry):

            '''Parses non-USING joins'''

            right_table_col, left_table_col = entry

            # Switch order (right_table_col is on the left in the comparison)

            left = right_table_col

            right = left_table_col

            # Parse special values

            if right is join_same: right = left

            elif right is join_same_not_null:

                right = CompareCond(as_Col(left, right_table), '~=')

            right = as_ValueCond(right, right_table)

            return right.to_str(db, as_Col(left, left_table))

        # Create join condition

        type_ = self.type_

        joins = self.mapping

        if type_ is not filter_out and reduce(operator.and_,

            (v is join_same for v in joins.itervalues())):

            # all cols w/ USING, so can use simpler USING syntax

            cols = (as_Col(v).to_str(db) for v in joins.iterkeys())

            join_cond = 'USING ('+(', '.join(cols))+')'

        else: join_cond = 'ON '+(' AND '.join(map(join, joins.iteritems())))

        # Create join

        if type_ is filter_out: type_ = 'LEFT'

        str_ = ''

        if type_ != None: str_ += type_+' '

        str_ += 'JOIN '+left_table.to_str(db)+' '+join_cond

        return str_

    def __str__(self): return self.to_str(mockDb, '<left_table>')