/**
 * @license
 * Copyright Google Inc. All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */

import {Expression} from '@angular/compiler';
import * as ts from 'typescript';

import {identifierOfNode} from '../../util/src/typescript';

export enum ImportMode {
  UseExistingImport,
  ForceNewImport,
}

export interface OwningModule {
  specifier: string;
  resolutionContext: string;
}

/**
 * A `ts.Node` plus the context in which it was discovered.
 *
 * A `Reference` is a pointer to a `ts.Node` that was extracted from the program somehow. It
 * contains not only the node itself, but the information regarding how the node was located. In
 * particular, it might track different identifiers by which the node is exposed, as well as
 * potentially a module specifier which might expose the node.
 *
 * The Angular compiler uses `Reference`s instead of `ts.Node`s when tracking classes or generating
 * imports.
 */
export class Reference<T extends ts.Node = ts.Node> {
  /**
   * The compiler's best guess at an absolute module specifier which owns this `Reference`.
   *
   * This is usually determined by tracking the import statements which led the compiler to a given
   * node. If any of these imports are absolute, it's an indication that the node being imported
   * might come from that module.
   *
   * It is not _guaranteed_ that the node in question is exported from its `bestGuessOwningModule` -
   * that is mostly a convention that applies in certain package formats.
   *
   * If `bestGuessOwningModule` is `null`, then it's likely the node came from the current program.
   */
  readonly bestGuessOwningModule: OwningModule|null;

  private identifiers: ts.Identifier[] = [];

  private _alias: Expression|null = null;

  constructor(readonly node: T, bestGuessOwningModule: OwningModule|null = null) {
    this.bestGuessOwningModule = bestGuessOwningModule;

    const id = identifierOfNode(node);
    if (id !== null) {
      this.identifiers.push(id);
    }
  }

  /**
   * The best guess at which module specifier owns this particular reference, or `null` if there
   * isn't one.
   */
  get ownedByModuleGuess(): string|null {
    if (this.bestGuessOwningModule !== null) {
      return this.bestGuessOwningModule.specifier;
    } else {
      return null;
    }
  }

  /**
   * Whether this reference has a potential owning module or not.
   *
   * See `bestGuessOwningModule`.
   */
  get hasOwningModuleGuess(): boolean { return this.bestGuessOwningModule !== null; }

  /**
   * A name for the node, if one is available.
   *
   * This is only suited for debugging. Any actual references to this node should be made with
   * `ts.Identifier`s (see `getIdentityIn`).
   */
  get debugName(): string|null {
    const id = identifierOfNode(this.node);
    return id !== null ? id.text : null;
  }

  get alias(): Expression|null { return this._alias; }


  /**
   * Record a `ts.Identifier` by which it's valid to refer to this node, within the context of this
   * `Reference`.
   */
  addIdentifier(identifier: ts.Identifier): void { this.identifiers.push(identifier); }

  /**
   * Get a `ts.Identifier` within this `Reference` that can be used to refer within the context of a
   * given `ts.SourceFile`, if any.
   */
  getIdentityIn(context: ts.SourceFile): ts.Identifier|null {
    return this.identifiers.find(id => id.getSourceFile() === context) || null;
  }

  cloneWithAlias(alias: Expression): Reference<T> {
    const ref = new Reference(this.node, this.bestGuessOwningModule);
    ref.identifiers = [...this.identifiers];
    ref._alias = alias;
    return ref;
  }

  cloneWithNoIdentifiers(): Reference<T> {
    const ref = new Reference(this.node, this.bestGuessOwningModule);
    ref._alias = this._alias;
    ref.identifiers = [];
    return ref;
  }
}
