"""
 Transformation to optimize IR-code
"""

import logging
from . import ir
# Standard passes:

class FunctionPass:
    def __init__(self):
        self.logger = logging.getLogger('optimize')

    def run(self, ir):
        """ Main entry point for the pass """
        self.logger.info('Running pass {}'.format(type(self)))
        ir.check()
        self.prepare()
        for f in ir.Functions:
            self.onFunction(f)
        ir.check()

    def onFunction(self, f):
        """ Override this virtual method """
        raise NotImplementedError()

    def prepare(self):
        pass


class BasicBlockPass(FunctionPass):
    def onFunction(self, f):
        for bb in f.Blocks:
            self.onBasicBlock(bb)

    def onBasicBlock(self, bb):
        """ Override this virtual method """
        raise NotImplementedError()


class InstructionPass(BasicBlockPass):
    def onBasicBlock(self, bb):
        for ins in iter(bb.Instructions):
            self.onInstruction(ins)

    def onInstruction(self, ins):
        """ Override this virtual method """
        raise NotImplementedError()


class BasePass(BasicBlockPass):
    def onBasicBlock(self, bb):
        pass


# Usefull transforms:
class ConstantFolder(BasePass):
    def __init__(self):
        super().__init__()
        self.ops = {}
        self.ops['+'] = lambda x, y: x + y
        self.ops['-'] = lambda x, y: x - y
        self.ops['*'] = lambda x, y: x * y
        self.ops['<<'] = lambda x, y: x << y

    def postExpr(self, expr):
        if type(i) is BinaryOperator and i.operation in self.ops.keys() and type(i.a) is Const and type(i.b) is Const:
            vr = self.ops[i.operation](i.a.value, i.b.value)
            return Const(vr)
        else:
            return expr


class DeadCodeDeleter(BasicBlockPass):
    def onBasicBlock(self, bb):
        def instructionUsed(ins):
            if not type(ins) in [ImmLoad, BinaryOperator]:
                return True
            if len(ins.defs) == 0:
                # In case this instruction does not define any 
                # variables, assume it is usefull.
                return True
            return any(d.Used for d in ins.defs)

        change = True
        while change:
            change = False
            for i in bb.Instructions:
                if instructionUsed(i):
                    continue
                bb.removeInstruction(i)
                change = True


class CommonSubexpressionElimination(BasicBlockPass):
    def onBasicBlock(self, bb):
        constMap = {}
        to_remove = []
        for i in bb.Instructions:
            if isinstance(i, ImmLoad):
                if i.value in constMap:
                    t_new = constMap[i.value]
                    t_old = i.target
                    logging.debug('Replacing {} with {}'.format(t_old, t_new))
                    t_old.replaceby(t_new)
                    to_remove.append(i)
                else:
                    constMap[i.value] = i.target
            elif isinstance(i, BinaryOperator):
                k = (i.value1, i.operation, i.value2)
                if k in constMap:
                    t_old = i.result
                    t_new = constMap[k]
                    logging.debug('Replacing {} with {}'.format(t_old, t_new))
                    t_old.replaceby(t_new)
                    to_remove.append(i)
                else:
                    constMap[k] = i.result
        for i in to_remove:
            logging.debug('removing {}'.format(i))
            bb.removeInstruction(i)


class CleanPass(FunctionPass):
    def onFunction(self, f):
        removeEmptyBasicBlocks(f)


def removeEmptyBlocks(f):
    """ Remove empty basic blocks from function. """
    # If a block only contains a branch, it can be removed:
    empty = lambda b: type(b.FirstInstruction) is ir.Jump
    empty_blocks = list(filter(empty, f.Blocks))
    for b in empty_blocks:
        # Update predecessors
        preds = b.Predecessors
        if b not in preds + [f.entry]:
            # Do not remove if preceeded by itself
            tgt = b.LastInstruction.target
            for pred in preds:
                  pred.LastInstruction.changeTarget(b, tgt)
            logging.debug('Removing empty block: {}'.format(b))
            f.removeBlock(b)