const TARGETS = new Set(['stable', 'candidate']);

function csvSet(value) {
  return new Set(
    String(value ?? '')
      .split(',')
      .map((item) => item.trim())
      .filter(Boolean),
  );
}

function normalizeIdentity(identity = {}) {
  identity = identity ?? {};
  return {
    id: String(identity.id ?? '').trim(),
    username: String(identity.username ?? '').trim().toLowerCase(),
    wechatUserId: String(identity.wechatUserId ?? identity.wechat_user_id ?? '').trim(),
  };
}

/**
 * Build a fail-closed, immutable-identity canary policy. Display names are
 * intentionally not accepted: nicknames are not unique enough for production
 * routing (there may be multiple users named “唐”).
 */
export function createCanaryPolicy({
  userIds = [],
  usernames = [],
  wechatUserIds = [],
  candidateTarget = 'candidate',
} = {}) {
  if (!TARGETS.has(candidateTarget) || candidateTarget === 'stable') {
    throw new Error('candidateTarget must be candidate');
  }
  const policy = {
    userIds: userIds instanceof Set ? new Set(userIds) : csvSet(userIds),
    usernames: usernames instanceof Set
      ? new Set([...usernames].map((item) => String(item).trim().toLowerCase()))
      : new Set([...csvSet(usernames)].map((item) => item.toLowerCase())),
    wechatUserIds: wechatUserIds instanceof Set ? new Set(wechatUserIds) : csvSet(wechatUserIds),
    candidateTarget,
  };
  if (!policy.userIds.size && !policy.usernames.size && !policy.wechatUserIds.size) {
    throw new Error('canary policy must contain at least one immutable user selector');
  }
  return Object.freeze(policy);
}

export function canaryPolicyFromEnv(env = process.env) {
  return createCanaryPolicy({
    userIds: csvSet(env.MEMIND_RELEASE_CANARY_USER_IDS),
    usernames: csvSet(env.MEMIND_RELEASE_CANARY_USERNAMES),
    wechatUserIds: csvSet(env.MEMIND_RELEASE_CANARY_WECHAT_USER_IDS),
  });
}

export function resolveCanaryTarget(identity, policy) {
  if (!policy || typeof policy !== 'object') return 'stable';
  const normalized = normalizeIdentity(identity);
  const matched = policy.userIds?.has(normalized.id)
    || policy.usernames?.has(normalized.username)
    || policy.wechatUserIds?.has(normalized.wechatUserId);
  return matched ? policy.candidateTarget : 'stable';
}

export function describeCanaryMatch(identity, policy) {
  const normalized = normalizeIdentity(identity);
  const target = resolveCanaryTarget(normalized, policy);
  return {
    target,
    identity: normalized,
    matched: target === 'candidate',
  };
}