import {metadata, Origin} from 'aurelia-metadata';
import {RelativeViewStrategy, ConventionalViewStrategy, StaticViewStrategy, viewStrategy, NoViewStrategy, ViewStrategy } from './view-strategy';

/**
* Locates a view for an object.
*/
export class ViewLocator {
  /**
  * The metadata key for storing/finding view strategies associated with an class/object.
  */
  static viewStrategyMetadataKey = 'aurelia:view-strategy';

  /**
  * Gets the view strategy for the value.
  * @param value The value to locate the view strategy for.
  * @return The located ViewStrategy instance.
  */
  getViewStrategy(value: any): ViewStrategy {
    if (!value) {
      return null;
    }

    if (typeof value === 'object' && 'getViewStrategy' in value) {
      let origin = Origin.get(value.constructor);

      value = value.getViewStrategy();

      if (typeof value === 'string') {
        value = new RelativeViewStrategy(value);
      }

      viewStrategy.assert(value);

      if (origin.moduleId) {
        (value as RelativeViewStrategy).makeRelativeTo(origin.moduleId);
      }

      return value;
    }

    if (typeof value === 'string') {
      value = new RelativeViewStrategy(value);
    }

    if (viewStrategy.validate(value)) {
      return value;
    }

    if (typeof value !== 'function') {
      value = value.constructor;
    }

    // static view strategy
    if ('$view' in value) {
      let c = value.$view;
      let view;
      c = typeof c === 'function' ? c.call(value) : c;
      if (c === null) {
        view = new NoViewStrategy();
      } else {
        view = c instanceof StaticViewStrategy ? c : new StaticViewStrategy(c);
      }
      metadata.define(ViewLocator.viewStrategyMetadataKey, view, value);
      return view;
    }

    let origin = Origin.get(value);
    let strategy = metadata.get(ViewLocator.viewStrategyMetadataKey, value) as ViewStrategy & { moduleId?: string; };

    if (!strategy) {
      if (!origin.moduleId) {
        throw new Error('Cannot determine default view strategy for object.\n' + value);
      }

      strategy = this.createFallbackViewStrategy(origin);
    } else if (origin.moduleId) {
      strategy.moduleId = origin.moduleId;
    }

    return strategy;
  }

  /**
  * Creates a fallback View Strategy. Used when unable to locate a configured strategy.
  * The default implementation returns and instance of ConventionalViewStrategy.
  * @param origin The origin of the view model to return the strategy for.
  * @return The fallback ViewStrategy.
  */
  createFallbackViewStrategy(origin: Origin): ViewStrategy {
    return new ConventionalViewStrategy(this, origin);
  }

  /**
  * Conventionally converts a view model origin to a view url.
  * Used by the ConventionalViewStrategy.
  * @param origin The origin of the view model to convert.
  * @return The view url.
  */
  convertOriginToViewUrl(origin: Origin): string {
    let moduleId = origin.moduleId;
    let id = (moduleId.endsWith('.js') || moduleId.endsWith('.ts')) ? moduleId.substring(0, moduleId.length - 3) : moduleId;
    return id + '.html';
  }
}