from __future__ import annotations

from dataclasses import dataclass, field

from engine.defs import DefRegistry
from engine.map_loader import MapLoader
from engine.world import World


@dataclass(frozen=True)
class WorldTemplate:
    """One selectable starting-world option on the 'create world' screen.

    For now every template is just a fixed map file this engine ships with. Planned follow-up
    game modes (campaign/survival/creative) will add templates that build a World from
    procedural generation instead of a map_file - map_file is left optional so those can slot
    in as templates with map_file=None and their own generator, without changing this shape.
    """

    id: str
    name: str
    description: str = ""
    map_file: str | None = None  # resources/defs/maps/*.json, loaded via MapLoader


AVAILABLE_WORLD_TEMPLATES: list[WorldTemplate] = [
    WorldTemplate(
        id="test_map",
        name="Test Map",
        description="A small sample field with a docked, rotatable two-deck ship - exercises "
        "the engine's core mechanics (embedding, steering, staircases, weather).",
        map_file="harbor_world.json",
    ),
]


@dataclass
class WorldCreationMenu:
    """Pure interaction state for the 'create world' screen: pick which starting world template
    to build a fresh World from. No rendering here - same boundary as StartScreen/CharacterMenu
    (see their docstrings in this module and engine/ui.py) - this is the state/logic side: which
    templates exist, which is selected, and handing back the chosen template once confirmed.
    """

    templates: list[WorldTemplate] = field(default_factory=lambda: list(AVAILABLE_WORLD_TEMPLATES))
    selected_index: int | None = None

    def select(self, index: int) -> None:
        if 0 <= index < len(self.templates):
            self.selected_index = index

    def selected_template(self) -> WorldTemplate | None:
        if self.selected_index is None:
            return None
        return self.templates[self.selected_index]


def build_world_from_template(template: WorldTemplate, registry: DefRegistry, map_loader: MapLoader) -> World:
    """Builds an empty (player-less) World from a template's map - the "confirm" action once a
    WorldCreationMenu selection is made. Spawning/joining a character into it is a separate
    step - see engine/start_screen.py::join_world_with_character.
    """
    if template.map_file is None:
        raise NotImplementedError(f"world template {template.id!r} has no map_file and no generator yet")
    world = World(registry=registry)
    root_map = map_loader.load(template.map_file)
    world.add_map(root_map)
    for embedding in root_map.embeddings:
        world.add_map(embedding.child_map)
    return world