/**
 * @license
 * Copyright Google LLC 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 {GitClientConfig, NgDevConfig} from '../../utils/config';
import {GithubClient} from '../../utils/git/github';

import {GithubApiMergeStrategyConfig} from './strategies/api-merge';

/** Describes possible values that can be returned for `branches` of a target label. */
export type TargetLabelBranchResult = string[]|Promise<string[]>;

/**
 * Possible merge methods supported by the Github API.
 * https://developer.github.com/v3/pulls/#merge-a-pull-request-merge-button.
 */
export type GithubApiMergeMethod = 'merge'|'squash'|'rebase';

/**
 * Target labels represent Github pull requests labels. These labels instruct the merge
 * script into which branches a given pull request should be merged to.
 */
export interface TargetLabel {
  /** Pattern that matches the given target label. */
  pattern: RegExp|string;
  /**
   * List of branches a pull request with this target label should be merged into.
   * Can also be wrapped in a function that accepts the target branch specified in the
   * Github Web UI. This is useful for supporting labels like `target: development-branch`.
   *
   * @throws {InvalidTargetLabelError} Invalid label has been applied to pull request.
   * @throws {InvalidTargetBranchError} Invalid Github target branch has been selected.
   */
  branches: TargetLabelBranchResult|((githubTargetBranch: string) => TargetLabelBranchResult);
}

/**
 * Configuration for the merge script with all remote options specified. The
 * default `MergeConfig` has does not require any of these options as defaults
 * are provided by the common dev-infra github configuration.
 */
export type MergeConfigWithRemote = MergeConfig&{remote: GitClientConfig};

/** Configuration for the merge script. */
export interface MergeConfig {
  /**
   * Configuration for the upstream remote. All of these options are optional as
   * defaults are provided by the common dev-infra github configuration.
   */
  remote?: GitClientConfig;
  /** List of target labels. */
  labels: TargetLabel[];
  /** Required base commits for given branches. */
  requiredBaseCommits?: {[branchName: string]: string};
  /** Pattern that matches labels which imply a signed CLA. */
  claSignedLabel: string|RegExp;
  /** Pattern that matches labels which imply a merge ready pull request. */
  mergeReadyLabel: string|RegExp;
  /** Label that is applied when special attention from the caretaker is required. */
  caretakerNoteLabel?: string|RegExp;
  /** Label which can be applied to fixup commit messages in the merge script. */
  commitMessageFixupLabel: string|RegExp;
  /**
   * Whether pull requests should be merged using the Github API. This can be enabled
   * if projects want to have their pull requests show up as `Merged` in the Github UI.
   * The downside is that fixup or squash commits no longer work as the Github API does
   * not support this.
   */
  githubApiMerge: false|GithubApiMergeStrategyConfig;
}

/**
 * Configuration of the merge script in the dev-infra configuration. Note that the
 * merge configuration is retrieved lazily as usually these configurations rely
 * on branch name computations. We don't want to run these immediately whenever
 * the dev-infra configuration is loaded as that could slow-down other commands.
 */
export type DevInfraMergeConfig =
    NgDevConfig<{'merge': (api: GithubClient) => MergeConfig | Promise<MergeConfig>}>;

/** Loads and validates the merge configuration. */
export async function loadAndValidateConfig(
    config: Partial<DevInfraMergeConfig>,
    api: GithubClient): Promise<{config?: MergeConfig, errors?: string[]}> {
  if (config.merge === undefined) {
    return {errors: ['No merge configuration found. Set the `merge` configuration.']};
  }

  if (typeof config.merge !== 'function') {
    return {errors: ['Expected merge configuration to be defined lazily through a function.']};
  }

  const mergeConfig = await config.merge(api);
  const errors = validateMergeConfig(mergeConfig);

  if (errors.length) {
    return {errors};
  }

  return {config: mergeConfig};
}

/** Validates the specified configuration. Returns a list of failure messages. */
function validateMergeConfig(config: Partial<MergeConfig>): string[] {
  const errors: string[] = [];
  if (!config.labels) {
    errors.push('No label configuration.');
  } else if (!Array.isArray(config.labels)) {
    errors.push('Label configuration needs to be an array.');
  }
  if (!config.claSignedLabel) {
    errors.push('No CLA signed label configured.');
  }
  if (!config.mergeReadyLabel) {
    errors.push('No merge ready label configured.');
  }
  if (config.githubApiMerge === undefined) {
    errors.push('No explicit choice of merge strategy. Please set `githubApiMerge`.');
  }
  return errors;
}