cinny/src/app/utils/decryptionReason.ts

import { DecryptionFailureCode } from 'matrix-js-sdk/lib/crypto-api';

/**
 * [Gitea #159] What to tell the user about an undecryptable message, and the
 * one thing that fixes it (if anything does). Raw codes never reach the UI
 * text — they go in the tooltip for support.
 */
export type DecryptionAction = 'setup-backup' | 'retry' | 'verify-session' | 'none';

export type DecryptionReason = {
  text: string;
  action: DecryptionAction;
  actionLabel?: string;
};

export const describeDecryptionFailure = (
  code: DecryptionFailureCode | string | null | undefined,
): DecryptionReason => {
  switch (code) {
    case DecryptionFailureCode.HISTORICAL_MESSAGE_NO_KEY_BACKUP:
      // No backup exists on the server at all: this key is gone for this
      // session (another signed-in device may still share it), and the fix is
      // for the future.
      return {
        text: 'Sent before you signed in here, and no key backup exists — set one up so your next session can read history.',
        action: 'setup-backup',
        actionLabel: 'Set up key backup',
      };
    case DecryptionFailureCode.HISTORICAL_MESSAGE_BACKUP_UNCONFIGURED:
      // A backup exists but this session can't open it (needs the recovery key
      // / verification).
      return {
        text: "Sent before you signed in here. Your key backup exists but this session can't open it yet.",
        action: 'verify-session',
        actionLabel: 'Unlock key backup',
      };
    case DecryptionFailureCode.HISTORICAL_MESSAGE_WORKING_BACKUP:
      return {
        text: 'Waiting for the key from your backup…',
        action: 'retry',
        actionLabel: 'Retry',
      };
    case DecryptionFailureCode.HISTORICAL_MESSAGE_USER_NOT_JOINED:
      return { text: 'Sent before you joined this room.', action: 'none' };
    case DecryptionFailureCode.MEGOLM_KEY_WITHHELD_FOR_UNVERIFIED_DEVICE:
      return {
        text: "The sender's device won't share keys with unverified sessions.",
        action: 'verify-session',
        actionLabel: 'Verify this session',
      };
    case DecryptionFailureCode.MEGOLM_KEY_WITHHELD:
      return { text: 'The sender chose not to share the key for this message.', action: 'none' };
    case DecryptionFailureCode.MEGOLM_UNKNOWN_INBOUND_SESSION_ID:
    case DecryptionFailureCode.OLM_UNKNOWN_MESSAGE_INDEX:
      // rust-crypto re-requests the key from our other devices by itself
      // (there is no public re-request API any more); a retry re-runs the
      // decryption in case it has arrived since.
      return {
        text: "This session doesn't have the key yet — it is being requested from your other devices.",
        action: 'retry',
        actionLabel: 'Retry',
      };
    case DecryptionFailureCode.SENDER_IDENTITY_PREVIOUSLY_VERIFIED:
      return {
        text: "The sender's identity changed since you verified them — re-verify to read this.",
        action: 'none',
      };
    case DecryptionFailureCode.UNSIGNED_SENDER_DEVICE:
      return { text: "Sent from a device the sender hasn't verified.", action: 'none' };
    case DecryptionFailureCode.UNKNOWN_SENDER_DEVICE:
      return { text: "Sent from a device we don't know about.", action: 'none' };
    default:
      return { text: 'Unable to decrypt this message.', action: 'none' };
  }
};