import { ENTITY_HANDLE, isHandleEnabled, type PointerState, worldPositionOf } from '../core/graph';
import { newId } from '../core/ids';
import type { Asset } from '../core/model/Asset';
import { isPlaceableType } from '../core/model/AssetTypes';
import { bakeInstances, materializeInstance, objectRef, resolveObjects } from '../core/model/instance';
import { treeOrder } from '../core/model/hierarchy';
import { descendantsBelow } from '../core/model/walk';
import { findAsset, findScene, type Project } from '../core/model/Project';
import { createSceneObject, type SceneObject } from '../core/model/SceneObject';
import { footprintContains } from '../core/properties/bounds';
import { colliderShape, shapeContains } from '../core/properties/collider';
import { resolveSceneObjectProps } from '../core/properties/resolve';
import type { Entity } from './Entity';
import type { System } from './systems/System';

export interface WorldOptions {
  /**
   * Whether a placed container's content may be written into the scene (see `syncFromModel`).
   * Baking is a real, irreversible edit, so the editor run switches it off; its content still runs,
   * but what it writes goes into the instance edits and it cannot destroy itself for good.
   */
  bakeContainers?: boolean;
}

/** What `syncToModel` wrote: `structure` = objects appeared or vanished, `values` = the rest. */
export interface ModelWrite {
  structure: boolean;
  values: boolean;
}

/**
 * The running game: entities of one scene plus the systems ticking them. Built on the play copy
 * (discarded on stop) or, for the editor run, on the saved model, where its writes stay.
 */
export class World {
  readonly entities: Entity[] = [];
  backgroundColor = 0x000000;
  /** Set by a behavior (Stop game node); the editor leaves play mode on the next tick. */
  stopRequested = false;
  /** Set by a behavior (Restart game node); the editor restarts the scene on the next tick. */
  restartRequested = false;
  /**
   * Mouse state in world units, fed by the game view (the only place with the camera
   * transform). `pressed`/`released` last for one tick, like the keyboard edges.
   */
  readonly pointer: PointerState = {
    x: 0,
    y: 0,
    inside: false,
    down: false,
    pressed: false,
    released: false,
  };
  /** Messages logged by behaviors (Log node), newest last. */
  readonly log: string[] = [];
  private readonly systems: System[] = [];
  private elapsed = 0;
  /** Set when `spawn` added an object; reported (and cleared) by the next `syncToModel`. */
  private structureChanged = false;

  private constructor(
    readonly project: Project,
    readonly sceneId: string,
    private readonly bakeContainers: boolean,
  ) {}

  /** Builds a world from the given scene. Throws when the scene does not exist. */
  static instantiate(project: Project, sceneId: string, options: WorldOptions = {}): World {
    if (!findScene(project, sceneId)) throw new Error(`Scene ${sceneId} not found`);
    const world = new World(project, sceneId, options.bakeContainers ?? true);
    world.syncFromModel();
    return world;
  }

  /** Seconds since the world started. */
  get time(): number {
    return this.elapsed;
  }

  /** Makes the entities match the scene; props are updated in place so systems holding a bag stay current. */
  syncFromModel(): void {
    const scene = findScene(this.project, this.sceneId);
    if (!scene) return;
    // Baking spells a placed container's content out as stored objects, which is what lets a
    // behavior destroy one of them for good. Play does it (on its throwaway copy); the editor run
    // must not, so there the content stays resolved and `objectRef` writes into the instance edits.
    if (this.bakeContainers && bakeInstances(this.project, scene)) this.structureChanged = true;
    const background = scene.props.backgroundColor;
    this.backgroundColor = typeof background === 'number' ? background : 0x000000;
    const objects = new Map(resolveObjects(this.project, scene).map((o) => [o.id, o]));
    const keep = new Set<Entity>();
    for (const object of objects.values()) {
      const asset = findAsset(this.project, object.assetId);
      if (!asset || !isPlaceableType(asset.type)) continue;
      keep.add(this.materialize(object, asset));
    }
    for (let i = this.entities.length - 1; i >= 0; i--)
      if (!keep.has(this.entities[i]!)) this.entities.splice(i, 1);
    // Link parents once every entity exists (storage order is not guaranteed to be parent-first).
    for (const entity of this.entities) {
      const object = objects.get(entity.objectId);
      entity.parent = object?.parentId ? (this.findByObjectId(object.parentId) ?? null) : null;
    }
  }

  /** The entity for a scene object, created when missing; position, name and props re-read. */
  private materialize(object: SceneObject, asset: Asset): Entity {
    let entity = this.findByObjectId(object.id);
    if (!entity) {
      entity = {
        [ENTITY_HANDLE]: true,
        id: `e-${object.id}`,
        objectId: object.id,
        assetId: asset.id,
        type: asset.type,
        name: '',
        x: 0,
        y: 0,
        z: 0,
        props: {},
        parent: null,
      };
      this.entities.push(entity);
    }
    entity.assetId = asset.id;
    entity.type = asset.type;
    entity.name = object.name || asset.name;
    entity.x = object.position.x;
    entity.y = object.position.y;
    entity.z = object.position.z;
    const resolved = resolveSceneObjectProps(asset, object);
    for (const key of Object.keys(entity.props)) if (!(key in resolved)) delete entity.props[key];
    Object.assign(entity.props, resolved);
    return entity;
  }

  /**
   * Adds the object to the scene and creates only its entity, leaving the others alone (they may have
   * moved this tick already). Position is local to `parent`, world when there is none.
   */
  spawn(
    assetId: string,
    position: { x: number; y: number; z: number },
    parent: Entity | null,
  ): Entity | null {
    const scene = findScene(this.project, this.sceneId);
    const asset = findAsset(this.project, assetId);
    if (!scene || !asset || !isPlaceableType(asset.type)) return null;
    const parentEntity = parent && this.entities.includes(parent) ? parent : null;
    const object = createSceneObject(newId(), asset.id, position, parentEntity?.objectId ?? '');
    scene.objects.push(object);
    // A container brings its content along (parented below it, in template order).
    const created = asset.type === 'container' ? materializeInstance(this.project, scene, object) : [];
    scene.objects.push(...created);
    const entity = this.materialize(object, asset);
    entity.parent = parentEntity;
    for (const child of created) {
      const childAsset = findAsset(this.project, child.assetId);
      if (!childAsset || !isPlaceableType(childAsset.type)) continue;
      this.materialize(child, childAsset).parent = this.findByObjectId(child.parentId) ?? null;
    }
    this.structureChanged = true;
    return entity;
  }

  /**
   * Writes the entities' state into the scene: positions, property values that differ from
   * what the model resolves (stored as overrides, so the inspector marks them) and removed
   * entities (their objects are dropped – only stored ones, see `WorldOptions.bakeContainers`).
   */
  syncToModel(): ModelWrite {
    const scene = findScene(this.project, this.sceneId);
    if (!scene) return { structure: false, values: false };
    let values = false;
    const spawned = this.structureChanged;
    this.structureChanged = false;
    const alive = new Set(this.entities.map((e) => e.objectId));
    const before = scene.objects.length;
    for (let i = scene.objects.length - 1; i >= 0; i--) {
      const object = scene.objects[i]!;
      const asset = findAsset(this.project, object.assetId);
      if (asset && isPlaceableType(asset.type) && !alive.has(object.id)) scene.objects.splice(i, 1);
    }
    for (const object of resolveObjects(this.project, scene)) {
      const entity = this.findByObjectId(object.id);
      const asset = entity && findAsset(this.project, entity.assetId);
      if (!entity || !asset) continue;
      const p = object.position;
      const moved = p.x !== entity.x || p.y !== entity.y || p.z !== entity.z;
      const base = resolveSceneObjectProps(asset, object);
      const drifted = Object.keys(entity.props).filter((k) => k in base && base[k] !== entity.props[k]);
      if (!moved && drifted.length === 0) continue;
      // Only now, because a ref for resolved content costs a resolve of its own – and because a
      // direct write to such an object would land in the freshly built copy and be lost.
      const ref = objectRef(this.project, scene, object.id);
      if (!ref) continue;
      if (moved) ref.setPosition({ x: entity.x, y: entity.y, z: entity.z });
      for (const key of drifted) ref.setOverride(key, entity.props[key]);
      values = true;
    }
    return { structure: spawned || scene.objects.length !== before, values };
  }

  /** Registers a system; it starts immediately and is ticked in registration order. */
  addSystem(system: System): this {
    this.systems.push(system);
    system.start?.(this);
    return this;
  }

  /** Advances the simulation by `dt` seconds. */
  tick(dt: number): void {
    this.elapsed += dt;
    for (const system of this.systems) system.update(this, dt);
    // The pointer edges belong to exactly one tick, whatever the systems did with them.
    this.dropPointerEdges();
  }

  /** Forgets a pending click edge without running a tick (used while paused). */
  dropPointerEdges(): void {
    this.pointer.pressed = false;
    this.pointer.released = false;
  }

  /** Game view: where the mouse is (world units) and whether it is over the view at all. */
  movePointer(x: number, y: number, inside: boolean): void {
    this.pointer.x = x;
    this.pointer.y = y;
    this.pointer.inside = inside;
  }

  /** Game view: the mouse button changed. Sets the edge flag the current tick reports. */
  setPointerDown(down: boolean): void {
    if (down === this.pointer.down) return;
    this.pointer.down = down;
    if (down) this.pointer.pressed = true;
    else this.pointer.released = true;
  }

  /** Stops the systems and drops every entity; the world is unusable afterwards. */
  destroy(): void {
    for (const system of this.systems) system.stop?.(this);
    this.systems.length = 0;
    this.entities.length = 0;
  }

  /**
   * Whether a world point lies on an entity: on the colliders of its subtree when it has
   * any, otherwise on the box of a sprite or text in it. Disabled parts never answer, so a
   * hidden screen cannot swallow clicks meant for what is drawn behind it.
   */
  hitTest(entity: Entity, x: number, y: number): boolean {
    const point = { x, y };
    const parts = [entity, ...this.descendantsOf(entity)].filter((e) => isHandleEnabled(e));
    const colliders = parts.filter((e) => e.type === 'collider');
    if (colliders.length > 0)
      return colliders.some((c) => shapeContains(colliderShape(c.props, worldPositionOf(c)), point));
    return parts.some(
      (e) =>
        (e.type === 'sprite' || e.type === 'text') &&
        footprintContains(e.type, e.props, worldPositionOf(e), point),
    );
  }

  childrenOf(entity: Entity): Entity[] {
    return this.entities.filter((e) => e.parent === entity);
  }

  descendantsOf(entity: Entity): Entity[] {
    return descendantsBelow(
      entity,
      (parent) => this.childrenOf(parent),
      (child) => child,
    );
  }

  findByObjectId(objectId: string): Entity | undefined {
    return this.entities.find((e) => e.objectId === objectId);
  }

  /** The first entity with that name; an object without a name of its own carries its asset's name. */
  findByName(name: string): Entity | undefined {
    return this.entities.find((e) => e.name === name);
  }

  /**
   * The camera the game is seen through: of the cameras that are switched on (itself and every
   * parent, see `properties/enabled.ts`) the first one in hierarchy order. Undefined while none
   * is on, and then nothing is rendered – switching one off is how a scene hands the view over.
   */
  activeCamera(): Entity | undefined {
    const on = this.entities.filter((e) => e.type === 'camera' && isHandleEnabled(e));
    if (on.length < 2) return on[0];
    // Ranked only when the order can decide something, since this runs per frame.
    const scene = findScene(this.project, this.sceneId);
    const order = scene ? treeOrder(scene).map(({ object }) => object.id) : [];
    const rank = (camera: Entity) => {
      const index = order.indexOf(camera.objectId);
      return index < 0 ? order.length : index;
    };
    return on.reduce((first, camera) => (rank(camera) < rank(first) ? camera : first));
  }

  /** Removes an entity and, recursively, everything parented to it. */
  remove(entity: Entity): void {
    for (const child of this.childrenOf(entity)) this.remove(child);
    const index = this.entities.indexOf(entity);
    if (index >= 0) this.entities.splice(index, 1);
  }
}