/**
 * @fileoverview Shared flags for ESLint.
 */

'use strict';

//------------------------------------------------------------------------------
// Typedefs
//------------------------------------------------------------------------------

/**
 * @typedef {Object} InactiveFlagData
 * @property {string} description Flag description
 * @property {string | null} [replacedBy] Can be either:
 *   - An active flag (string) that enables the same feature.
 *   - `null` if the feature is now enabled by default.
 *   - Omitted if the feature has been abandoned.
 */

//-----------------------------------------------------------------------------
// Exports
//-----------------------------------------------------------------------------

/**
 * The set of flags that change ESLint behavior with a description.
 * @type {Map<string, string>}
 */
const activeFlags = new Map([
  ['test_only', 'Used only for testing.'],
  [
    'unstable_config_lookup_from_file',
    'Look up `eslint.config.js` from the file being linted.',
  ],
  [
    'unstable_native_nodejs_ts_config',
    'Use native Node.js to load TypeScript configuration.',
  ],
]);

/**
 * The set of flags that used to be active.
 * @type {Map<string, InactiveFlagData>}
 */
const inactiveFlags = new Map([
  [
    'test_only_replaced',
    {
      description:
        'Used only for testing flags that have been replaced by other flags.',
      replacedBy: 'test_only',
    },
  ],
  [
    'test_only_enabled_by_default',
    {
      description:
        'Used only for testing flags whose features have been enabled by default.',
      replacedBy: null,
    },
  ],
  [
    'test_only_abandoned',
    {
      description:
        'Used only for testing flags whose features have been abandoned.',
    },
  ],
  [
    'unstable_ts_config',
    {
      description: 'Enable TypeScript configuration files.',
      replacedBy: null,
    },
  ],
]);

/**
 * Creates a message that describes the reason the flag is inactive.
 * @param {InactiveFlagData} inactiveFlagData Data for the inactive flag.
 * @returns {string} Message describing the reason the flag is inactive.
 */
function getInactivityReasonMessage({ replacedBy }) {
  if (typeof replacedBy === 'undefined') {
    return 'This feature has been abandoned.';
  }

  if (typeof replacedBy === 'string') {
    return `This flag has been renamed '${replacedBy}' to reflect its stabilization. Please use '${replacedBy}' instead.`;
  }

  // null
  return 'This feature is now enabled by default.';
}

module.exports = {
  activeFlags,
  inactiveFlags,
  getInactivityReasonMessage,
};