from collections import OrderedDict

from migen.fhdl.std import *
from migen.fhdl.module import FinalizeError
from migen.fhdl.visit import NodeTransformer
from migen.fhdl.bitcontainer import value_bits_sign


class AnonymousState:
    pass


# do not use namedtuple here as it inherits tuple
# and the latter is used elsewhere in FHDL
class NextState:
    def __init__(self, state):
        self.state = state


class NextValue:
    def __init__(self, register, value):
        self.register = register
        self.value = value


class _LowerNext(NodeTransformer):
    def __init__(self, next_state_signal, encoding, aliases):
        self.next_state_signal = next_state_signal
        self.encoding = encoding
        self.aliases = aliases
        # register -> next_value_ce, next_value
        self.registers = OrderedDict()

    def visit_unknown(self, node):
        if isinstance(node, NextState):
            try:
                actual_state = self.aliases[node.state]
            except KeyError:
                actual_state = node.state
            return self.next_state_signal.eq(self.encoding[actual_state])
        elif isinstance(node, NextValue):
            try:
                next_value_ce, next_value = self.registers[node.register]
            except KeyError:
                related = node.register if isinstance(node.register, Signal) else None
                next_value = Signal(bits_sign=value_bits_sign(node.register), related=related)
                next_value_ce = Signal(related=related)
                self.registers[node.register] = next_value_ce, next_value
            return next_value.eq(node.value), next_value_ce.eq(1)
        else:
            return node


class FSM(Module):
    def __init__(self, reset_state=None):
        self.actions = OrderedDict()
        self.state_aliases = dict()
        self.reset_state = reset_state

        self.before_entering_signals = OrderedDict()
        self.before_leaving_signals = OrderedDict()
        self.after_entering_signals = OrderedDict()
        self.after_leaving_signals = OrderedDict()

    def act(self, state, *statements):
        if self.finalized:
            raise FinalizeError
        if self.reset_state is None:
            self.reset_state = state
        if state not in self.actions:
            self.actions[state] = []
        self.actions[state] += statements

    def delayed_enter(self, name, target, delay):
        if self.finalized:
            raise FinalizeError
        if delay:
            state = name
            for i in range(delay):
                if i == delay - 1:
                    next_state = target
                else:
                    next_state = AnonymousState()
                self.act(state, NextState(next_state))
                state = next_state
        else:
            self.state_aliases[name] = target

    def ongoing(self, state):
        is_ongoing = Signal()
        self.act(state, is_ongoing.eq(1))
        return is_ongoing

    def _get_signal(self, d, state):
        if state not in self.actions:
            self.actions[state] = []
        try:
            return d[state]
        except KeyError:
            is_el = Signal()
            d[state] = is_el
            return is_el

    def before_entering(self, state):
        return self._get_signal(self.before_entering_signals, state)

    def before_leaving(self, state):
        return self._get_signal(self.before_leaving_signals, state)

    def after_entering(self, state):
        signal = self._get_signal(self.after_entering_signals, state)
        self.sync += signal.eq(self.before_entering(state))
        return signal

    def after_leaving(self, state):
        signal = self._get_signal(self.after_leaving_signals, state)
        self.sync += signal.eq(self.before_leaving(state))
        return signal

    def do_finalize(self):
        nstates = len(self.actions)
        self.encoding = dict((s, n) for n, s in enumerate(self.actions.keys()))
        self.state = Signal(max=nstates, reset=self.encoding[self.reset_state])
        self.next_state = Signal(max=nstates)

        ln = _LowerNext(self.next_state, self.encoding, self.state_aliases)
        cases = dict((self.encoding[k], ln.visit(v)) for k, v in self.actions.items() if v)
        self.comb += [
            self.next_state.eq(self.state),
            Case(self.state, cases).makedefault(self.encoding[self.reset_state])
        ]
        self.sync += self.state.eq(self.next_state)
        for register, (next_value_ce, next_value) in ln.registers.items():
            self.sync += If(next_value_ce, register.eq(next_value))

        # drive entering/leaving signals
        for state, signal in self.before_leaving_signals.items():
            encoded = self.encoding[state]
            self.comb += signal.eq((self.state == encoded) & ~(self.next_state == encoded))
        if self.reset_state in self.after_entering_signals:
            self.after_entering_signals[self.reset_state].reset = 1
        for state, signal in self.before_entering_signals.items():
            encoded = self.encoding[state]
            self.comb += signal.eq(~(self.state == encoded) & (self.next_state == encoded))