from .astnodes import *
from .scope import *
from .visitor import Visitor

def theType(t):
    """
        Recurse until a 'real' type is found
    """
    if type(t) is DefinedType:
        return theType(t.typ)
    return t

def equalTypes(a, b):
    """
        Compare types a and b for equality.
        Not equal until proven otherwise.
    """
    # Recurse into named types:
    a = theType(a)
    b = theType(b)

    # Compare for structural equivalence:
    if type(a) is type(b):
        if type(a) is BaseType:
            return a.name == b.name
        elif type(a) is PointerType:
            return equalTypes(a.ptype, b.ptype)
        elif type(a) is StructureType:
            if len(a.mems) != len(b.mems):
                return False
            for amem, bmem in zip(a.mems, b.mems):
                if not equalTypes(amem.typ, bmem.typ):
                    return False
            return True
        else:
            raise Exception('Type compare not implemented')
    return False

def canCast(fromT, toT):
    fromT = theType(fromT)
    toT = theType(toT)
    if isinstance(fromT, PointerType) and isinstance(toT, PointerType):
        return True
    elif fromT is intType and isinstance(toT, PointerType):
        return True
    return False

def expectRval(s):
    # TODO: solve this better
    s.expect_rvalue = True

class TypeChecker:
    def __init__(self, diag):
        self.diag = diag

    def error(self, msg, loc):
        """
            Wrapper that registers the message and marks the result invalid
        """
        self.diag.error(msg, loc)
        self.ok = False

    def checkPackage(self, pkg):
        self.ok = True
        visitor = Visitor()
        visitor.visit(pkg, f_post=self.check2)
        return self.ok

    def check2(self, sym):
        if type(sym) in [IfStatement, WhileStatement]:
            if not equalTypes(sym.condition.typ, boolType):
                msg = 'Condition must be of type {}'.format(boolType)
                self.error(msg, sym.condition.loc)
        elif type(sym) is Assignment:
            l, r = sym.lval, sym.rval
            if not equalTypes(l.typ, r.typ):
                msg = 'Cannot assign {} to {}'.format(r.typ, l.typ)
                self.error(msg, sym.loc)
            if not l.lvalue:
                self.error('No valid lvalue {}'.format(l), l.loc)
            #if sym.rval.lvalue:
            #    self.error('Right hand side must be an rvalue', sym.rval.loc)
            expectRval(sym.rval)
        elif type(sym) is ReturnStatement:
            pass
        elif type(sym) is FunctionCall:
            # Check arguments:
            ngiv = len(sym.args)
            ptypes = sym.proc.typ.parametertypes
            nreq = len(ptypes)
            if ngiv != nreq:
               self.error('Function {2}: {0} arguments required, {1} given'.format(nreq, ngiv, sym.proc.name), sym.loc)
            else:
               for a, at in zip(sym.args, ptypes):
                  expectRval(a)
                  if not equalTypes(a.typ, at):
                     self.error('Got {0}, expected {1}'.format(a.typ, at), a.loc)
            # determine return type:
            sym.typ = sym.proc.typ.returntype
        elif type(sym) is VariableUse:
            sym.lvalue = True
            if type(sym.target) is Variable:
                sym.typ = sym.target.typ
            else:
                print('warning {} has no target, defaulting to int'.format(sym))
                sym.typ = intType
        elif type(sym) is Literal:
            sym.lvalue = False
            if type(sym.val) is int:
                sym.typ = intType
            elif type(sym.val) is float:
                sym.typ = doubleType
            elif type(sym.val) is bool:
                sym.typ = boolType
            else:
                raise Exception('Unknown literal type'.format(sym.val))
        elif type(sym) is Unop:
            if sym.op == '&':
                sym.typ = PointerType(sym.a.typ)
                sym.lvalue = False
            else:
                raise Exception('Unknown unop {0}'.format(sym.op))
        elif type(sym) is Deref:
            # pointer deref
            sym.lvalue = True
            # check if the to be dereferenced variable is a pointer type:
            ptype = theType(sym.ptr.typ)
            if type(ptype) is PointerType:
                sym.typ = ptype.ptype
            else:
                self.error('Cannot dereference non-pointer type {}'.format(ptype), sym.loc)
                sym.typ = intType
        elif type(sym) is FieldRef:
            basetype = sym.base.typ
            sym.lvalue = sym.base.lvalue
            basetype = theType(basetype)
            if type(basetype) is StructureType:
                if basetype.hasField(sym.field):
                    sym.typ = basetype.fieldType(sym.field)
                else:
                    self.error('{} does not contain field {}'.format(basetype, sym.field), sym.loc)
                    sym.typ = intType
            else:
                self.error('Cannot select field {} of non-structure type {}'.format(sym.field, basetype), sym.loc)
                sym.typ = intType
        elif type(sym) is Binop:
            sym.lvalue = False
            if sym.op in ['+', '-', '*', '/', '<<', '>>', '|', '&']:
                expectRval(sym.a)
                expectRval(sym.b)
                if equalTypes(sym.a.typ, sym.b.typ):
                   if equalTypes(sym.a.typ, intType):
                      sym.typ = sym.a.typ
                   else:
                      self.error('Can only add integers', sym.loc)
                      sym.typ = intType
                else:
                   # assume void here? TODO: throw exception!
                   sym.typ = intType
                   self.error('Types unequal {} != {}'.format(sym.a.typ, sym.b.typ), sym.loc)
            elif sym.op in ['>', '<', '==', '<=', '>=']:
                expectRval(sym.a)
                expectRval(sym.b)
                sym.typ = boolType
                if not equalTypes(sym.a.typ, sym.b.typ):
                   self.error('Types unequal {} != {}'.format(sym.a.typ, sym.b.typ), sym.loc)
            elif sym.op in ['or', 'and']:
                sym.typ = boolType
                if not equalTypes(sym.a.typ, boolType):
                   self.error('Must be {0}'.format(boolType), sym.a.loc)
                if not equalTypes(sym.b.typ, boolType):
                   self.error('Must be {0}'.format(boolType), sym.b.loc)
            else:
                raise Exception('Unknown binop {0}'.format(sym.op))
        elif type(sym) is Variable:
            # check initial value type:
            # TODO
            pass
        elif type(sym) is TypeCast:
            if canCast(sym.a.typ, sym.to_type):
                sym.typ = sym.to_type
            else:
                self.error('Cannot cast {} to {}'.format(sym.a.typ, sym.to_type), sym.loc)
                sym.typ = intType
        elif type(sym) is Constant:
            if not equalTypes(sym.typ, sym.value.typ):
                self.error('Cannot assign {0} to {1}'.format(sym.value.typ, sym.typ), sym.loc)
        elif type(sym) in [CompoundStatement, Package, Function, FunctionType, ExpressionStatement, DefinedType]:
            pass
        else:
            raise NotImplementedError('Unknown type check {0}'.format(sym))