const RECOVERABLE_KINDS = new Set(["CHUNK_LOAD_FAILURE", "DEPLOY_MISMATCH"]);

/**
 * @typedef {{action: "reload-once", releasePair: string} |
 *   {action: "support", reason: string}} ChunkRecoveryDecision
 */

/**
 * @param {{
 *   failureKind: string,
 *   manifestLoaded: boolean,
 *   currentBuildId: string,
 *   currentReleaseId: string,
 *   activeBuildId: string,
 *   activeReleaseId: string,
 *   storage: import("../ports/storage-port.js").StoragePort
 * }} input
 * @returns {ChunkRecoveryDecision}
 */
export function decideChunkRecovery(input) {
  if (!RECOVERABLE_KINDS.has(input.failureKind)) {
    return { action: "support", reason: "not-recoverable" };
  }
  if (!input.manifestLoaded) {
    return { action: "support", reason: "manifest-unavailable" };
  }
  if (
    input.activeBuildId === input.currentBuildId &&
    input.activeReleaseId === input.currentReleaseId
  ) {
    return { action: "support", reason: "same-release" };
  }

  const releasePair =
    `${input.currentBuildId}/${input.currentReleaseId}` +
    `->${input.activeBuildId}/${input.activeReleaseId}`;
  const guard = input.storage.read("CHUNK_RELOAD_GUARD");
  if (!guard.ok) {
    return { action: "support", reason: "guard-read-failed" };
  }
  if (guard.value === releasePair) {
    return { action: "support", reason: "reload-already-attempted" };
  }

  const recorded = input.storage.write("CHUNK_RELOAD_GUARD", releasePair);
  if (!recorded.ok) {
    return { action: "support", reason: "guard-write-failed" };
  }
  return { action: "reload-once", releasePair };
}