from ppci import CompilerError

"""
  Base classes for defining a target
"""

class Instruction:
    """ Base instruction class """
    def encode(self):
        return bytes()

    def relocations(self):
        return []

    def symbols(self):
        return []


class Nop(Instruction):
    """ Instruction that does nothing and has zero size """
    def encode(self):
        return bytes()


class PseudoInstruction(Instruction):
    pass


class Label(PseudoInstruction):
    def __init__(self, name):
        self.name = name

    def __repr__(self):
        return '{}:'.format(self.name)

    def symbols(self):
        return [self.name]


class Comment(PseudoInstruction):
    def __init__(self, txt):
        self.txt = txt

    def encode(self):
        return bytes()

    def __repr__(self):
        return '; {}'.format(self.txt)


class Alignment(PseudoInstruction):
    def __init__(self, a):
        self.align = a

    def __repr__(self):
        return 'ALIGN({})'.format(self.align)

    def encode(self):
        pad = []
        # TODO
        address = 0
        while (address % self.align) != 0:
            address += 1
            pad.append(0)
        return bytes(pad)


class DebugInfo(PseudoInstruction):
    def __init__(self, i):
        self.info = i

    def __repr__(self):
        return 'DebugInfo: {}'.format(self.info)


class Register:
    def __init__(self, name):
        self.name = name


class Target:
    def __init__(self, name, desc=''):
        self.name = name
        self.desc = desc
        self.registers = []
        self.byte_sizes = {'int' : 4}  # For front end!

        # For lowering:
        self.lower_functions = {}

        # For assembler:
        self.assembler_rules = []
        self.asm_keywords = []

        self.generate_base_rules()

    def generate_base_rules(self):
        # Base rules for constants:
        self.add_rule('imm32', ['val32'], lambda x: x[0].val)
        self.add_rule('imm32', ['imm16'], lambda x: x[0])

        self.add_rule('imm16', ['val16'], lambda x: x[0].val)
        self.add_rule('imm16', ['imm12'], lambda x: x[0])

        self.add_rule('imm12', ['val12'], lambda x: x[0].val)
        self.add_rule('imm12', ['imm8'], lambda x: x[0])

        self.add_rule('imm8', ['val8'], lambda x: x[0].val)
        self.add_rule('imm8', ['imm5'], lambda x: x[0])

        self.add_rule('imm5', ['val5'], lambda x: x[0].val)
        self.add_rule('imm5', ['imm3'], lambda x: x[0])

        self.add_rule('imm3', ['val3'], lambda x: x[0].val)

    def add_keyword(self, kw):
        self.asm_keywords.append(kw)

    def add_instruction(self, rhs, f):
        self.add_rule('instruction', rhs, f)

    def add_rule(self, lhs, rhs, f):
        self.assembler_rules.append((lhs, rhs, f))

    def lower_frame_to_stream(self, frame, outs):
        """ Lower instructions from frame to output stream """
        for im in frame.instructions:
            if isinstance(im.assem, Instruction):
                outs.emit(im.assem)
            else:
                ins = self.lower_functions[im.assem](im)
                outs.emit(ins)

    def add_lowering(self, cls, f):
        """ Add a function to the table of lowering options for this target """
        self.lower_functions[cls] = f