import { DrawingSurface } from "./drawing-core.js";
import { validateOptionalHandler } from "./diagram-component.js";
import { DiagramLink } from "./diagram-link.js";
import { DiagramNode } from "./diagram-node.js";
import { DiagramGroup } from "./diagram-group.js";

/**
 * Render and interact with a diagram of nodes and links.
 *
 * DiagramEngine is the complete public boundary of the drawing engine. It
 * translates low-level hit-test results to DiagramNode and DiagramLink
 * handles and owns every rendering object's lifetime.
 */
export class DiagramEngine {
  constructor(element) {
    this.drawingSurface = new DrawingSurface(element);
    this.handles = new Map();
    this.selectionHandler = null;
    this.activationHandler = null;
    this.filter = null;
    this.groups = new Set();
    this.destroyed = false;

    this.drawingSurface.selectionHandler = (component, event) => {
      if (this.selectionHandler) {
        this.selectionHandler(component ? this.handleFor(component) : null, event);
      }
    };
    this.drawingSurface.activationHandler = (component, event) => {
      if (this.activationHandler) {
        this.activationHandler(component ? this.handleFor(component) : null, event);
      }
    };
  }

  /** Register a callback for a single hit-tested component selection. */
  onSelection(handler) {
    validateOptionalHandler(handler, "selection");
    this.selectionHandler = handler || null;
    return this;
  }

  /** Register a callback for activation of one hit-tested component. */
  onActivation(handler) {
    validateOptionalHandler(handler, "activation");
    this.activationHandler = handler || null;
    return this;
  }

  /** Create and render a node owned by this engine. */
  node(attributes) {
    this.ensureActive();
    const node = new DiagramNode(this, attributes);
    this.addComponent(node);
    return node;
  }

  /** Create and render a link owned by this engine. */
  link(attributes) {
    this.ensureActive();
    const link = new DiagramLink(this, attributes);
    this.addComponent(link);
    return link;
  }

  /**
   * Create a generic group frame for nodes and nested groups.
   * @returns {DiagramGroup} A group owned by this engine.
   */
  group(options) {
    this.ensureActive();
    const group = new DiagramGroup(this, options);
    this.groups.add(group);
    return group;
  }

  /**
   * goal   : Install a policy that controls component visibility.
   * pre    : filter is null or a function receiving a public component handle.
   * post   : All existing components use the new policy immediately.
   * result : This engine, for fluent setup.
   * internals : A policy may return a boolean or `{ visible }`; the component's
   * own visibility remains the base value and is combined with the policy.
   */
  setFilter(filter) {
    if (filter !== null && filter !== undefined && typeof filter !== "function") {
      throw new TypeError("A diagram filter must be a function");
    }
    this.filter = filter || null;
    for (const handle of this.handles.values()) this.applyFilter(handle);
    for (const group of this.groups) group.redraw();
    return this;
  }

  /** Read or update the diagram zoom factor. */
  zoom(value) {
    if (value === undefined) return this.drawingSurface.zoomFactor;

    const factor = Number(value);
    if (!Number.isFinite(factor) || factor <= 0) {
      throw new TypeError("Invalid zoom factor");
    }

    this.drawingSurface.zoomFactor = factor;
    const element = this.drawingSurface.element();
    if (element) element.style.zoom = String(factor);
    return factor;
  }

  /** Destroy the surface and all nodes and links created through this engine. */
  destroy() {
    if (this.destroyed) return;

    const element = this.drawingSurface.element();
    this.selectionHandler = null;
    this.activationHandler = null;
    this.drawingSurface.selectionHandler = null;
    this.drawingSurface.activationHandler = null;
    for (const group of this.groups) group.destroy();
    this.groups.clear();
    for (const component of this.drawingSurface.componentList().toArray()) {
      component.dispose();
      component.parentElement(null);
    }
    this.drawingSurface.dispose();
    this.handles.clear();
    this.destroyed = true;

    if (element && element.parentNode) element.parentNode.removeChild(element);
  }

  /** Return the public handle associated with a low-level drawing object. */
  handleFor(component) {
    return this.handles.get(component) || null;
  }

  /** Add a newly constructed public component to the drawing surface. */
  addComponent(handle) {
    this.handles.set(handle.component, handle);
    this.drawingSurface.add(handle.component);
    this.applyFilter(handle);
  }

  /** Remove a public component and forget its low-level drawing object. */
  removeComponent(handle) {
    if (!handle || handle.engine !== this || !this.handles.has(handle.component)) return;
    this.drawingSurface.remove(handle.component);
    this.handles.delete(handle.component);
  }

  /** Return the DOM surface on which components and group frames are drawn. */
  surfaceElement() {
    return this.drawingSurface.element();
  }

  /** Apply the current base visibility and optional external filter to a handle. */
  applyFilter(handle) {
    const decision = this.filter ? this.filter(handle) : true;
    let visible = typeof decision === "boolean" ? decision : decision?.visible !== false;
    if (handle instanceof DiagramLink) {
      const source = handle.sourceNode();
      const target = handle.targetNode();
      visible = visible && (!source || source.visible()) && (!target || target.visible());
    }
    handle.component.visible = handle.baseVisible && visible;
    handle.component.redraw();
    if (handle instanceof DiagramNode) {
      for (const candidate of this.handles.values()) {
        if (!(candidate instanceof DiagramLink)) continue;
        if (candidate.sourceNode() === handle || candidate.targetNode() === handle) {
          this.applyFilter(candidate);
        }
      }
    }
    for (const group of this.groups) {
      if (group.members.has(handle)) group.redraw();
    }
  }

  /** Reject operations after the engine and its DOM surface were destroyed. */
  ensureActive() {
    if (this.destroyed) throw new Error("The diagram engine has been destroyed");
  }
}