"""Base classes for states."""

from __future__ import annotations

from typing import Protocol, TypeAlias

import attrs
import tcod.console
import tcod.event

import g


class State(Protocol):
    """An abstract game state."""

    __slots__ = ()

    def on_event(self, event: tcod.event.Event) -> StateResult:
        """Called on events."""

    def on_draw(self, console: tcod.console.Console) -> None:
        """Called when the state is being drawn."""


@attrs.define()
class Push:
    """Push a new state on top of the stack."""

    state: State


@attrs.define()
class Pop:
    """Remove the current state from the stack."""


@attrs.define()
class Reset:
    """Replace the entire stack with a new state."""

    state: State


StateResult: TypeAlias = "Push | Pop | Reset | None"
"""Union of state results."""


def main_draw() -> None:
    """Render and present the active state."""
    if not g.states:
        return
    g.console.clear()
    g.states[-1].on_draw(g.console)
    g.context.present(g.console)


def apply_state_result(result: StateResult) -> None:
    """Apply a StateResult to `g.states`."""
    match result:
        case Push(state=state):
            g.states.append(state)
        case Pop():
            g.states.pop()
        case Reset(state=state):
            while g.states:
                apply_state_result(Pop())
            apply_state_result(Push(state))
        case None:
            pass
        case _:
            raise TypeError(result)


def main_loop() -> None:
    """Run the active state forever."""
    while g.states:
        main_draw()
        for event in tcod.event.wait():
            tile_event = g.context.convert_event(event)
            if g.states:
                apply_state_result(g.states[-1].on_event(tile_event))


def get_previous_state(state: State) -> State | None:
    """Return the state before `state` in the stack if it exists."""
    current_index = next(index for index, value in enumerate(g.states) if value is state)
    return g.states[current_index - 1] if current_index > 0 else None


def draw_previous_states(state: State, console: tcod.console.Console, dim: bool = True) -> None:
    """Draw previous states, optionally dimming all but the active state."""
    prev_state = get_previous_state(state)
    if prev_state is None:
        return
    prev_state.on_draw(console)
    if dim and state is g.states[-1]:
        console.rgb["fg"] //= 4
        console.rgb["bg"] //= 4