import {
  WEB_PUSH_PROTOCOLS,
  webPushFailure,
  webPushSuccess,
  type PushAuthoritySnapshot,
  type WebPushResult,
} from "../../contracts/web-push.ts";

const OPAQUE_ID = /^[A-Za-z0-9][A-Za-z0-9._:-]{0,127}$/u;

export const WEB_PUSH_REGISTRATION_OPERATIONS = Object.freeze({
  register: "REGISTER_WEB_PUSH_SUBSCRIPTION",
  reconcile: "RECONCILE_WEB_PUSH_SUBSCRIPTION",
  revoke: "REVOKE_WEB_PUSH_ASSOCIATION",
} as const);

export type NativePushSubscriptionMaterial = Readonly<{
  endpoint: string;
  p256dh: string;
  auth: string;
  expirationTime: number | null;
}>;

export type WebPushRegistrationExecutor = Readonly<{
  execute(input: Readonly<{
    operationId:
      (typeof WEB_PUSH_REGISTRATION_OPERATIONS)[keyof typeof WEB_PUSH_REGISTRATION_OPERATIONS];
    body: unknown;
    idempotencyKey?: string;
    signal?: AbortSignal;
  }>): Promise<WebPushResult<unknown>>;
}>;

export type WebPushRegistrationCommit = Readonly<{
  associationEpoch: string;
  sessionBindingEpoch: string;
}>;

export type WebPushReconciliation =
  | Readonly<{ state: "ABSENT" }>
  | Readonly<{
      state: "ACTIVE";
      associationEpoch: string;
      sessionBindingEpoch: string;
    }>;

export interface WebPushRegistrationGateway {
  register(input: Readonly<{
    material: NativePushSubscriptionMaterial;
    authority: PushAuthoritySnapshot;
    idempotencyKey: string;
    signal?: AbortSignal;
  }>): Promise<WebPushResult<WebPushRegistrationCommit>>;

  reconcile(input: Readonly<{
    material: NativePushSubscriptionMaterial;
    authority: PushAuthoritySnapshot;
    signal?: AbortSignal;
  }>): Promise<WebPushResult<WebPushReconciliation>>;

  revoke(input: Readonly<{
    associationEpoch: string;
    signal?: AbortSignal;
  }>): Promise<WebPushResult<Readonly<{
    state: "REVOKED" | "ALREADY_GONE";
  }>>>;
}

export function createWebPushRegistrationGateway(
  executor: WebPushRegistrationExecutor,
): WebPushRegistrationGateway {
  const gateway: WebPushRegistrationGateway = {
    async register(input) {
      if (
        !validMaterial(input.material) ||
        !validAuthority(input.authority) ||
        !validOpaqueId(input.idempotencyKey)
      ) {
        return webPushFailure("INVALID_INPUT", "SUBSCRIPTION_CREATE");
      }
      const response = await execute(
        {
          operationId: WEB_PUSH_REGISTRATION_OPERATIONS.register,
          body: Object.freeze({
            protocol: "WEB_PUSH_REGISTER_COMMAND_V1",
            subscription: snapshotMaterial(input.material),
            fenceGeneration: input.authority.fenceGeneration,
            sessionBindingEpoch: input.authority.sessionBindingEpoch,
            releaseEpoch: input.authority.releaseEpoch,
          }),
          idempotencyKey: input.idempotencyKey,
          signal: input.signal,
        },
        "SUBSCRIPTION_CREATE",
      );
      if (!response.ok) return response;
      const decoded = decodeRegistration(response.value);
      return decoded
        ? webPushSuccess(decoded)
        : webPushFailure("CONTRACT_REJECTED", "SUBSCRIPTION_CREATE");
    },

    async reconcile(input) {
      if (
        !validMaterial(input.material) ||
        !validAuthority(input.authority)
      ) {
        return webPushFailure("INVALID_INPUT", "SUBSCRIPTION_RECONCILE");
      }
      const response = await execute(
        {
          operationId: WEB_PUSH_REGISTRATION_OPERATIONS.reconcile,
          body: Object.freeze({
            protocol: "WEB_PUSH_RECONCILE_COMMAND_V1",
            subscription: snapshotMaterial(input.material),
            fenceGeneration: input.authority.fenceGeneration,
            sessionBindingEpoch: input.authority.sessionBindingEpoch,
            releaseEpoch: input.authority.releaseEpoch,
          }),
          signal: input.signal,
        },
        "SUBSCRIPTION_RECONCILE",
      );
      if (!response.ok) return response;
      const decoded = decodeReconciliation(response.value);
      return decoded
        ? webPushSuccess(decoded)
        : webPushFailure("CONTRACT_REJECTED", "SUBSCRIPTION_RECONCILE");
    },

    async revoke(input) {
      if (!validOpaqueId(input.associationEpoch)) {
        return webPushFailure("INVALID_INPUT", "SUBSCRIPTION_REVOKE");
      }
      const response = await execute(
        {
          operationId: WEB_PUSH_REGISTRATION_OPERATIONS.revoke,
          body: Object.freeze({
            protocol: "WEB_PUSH_REVOKE_COMMAND_V1",
            associationEpoch: input.associationEpoch,
          }),
          signal: input.signal,
        },
        "SUBSCRIPTION_REVOKE",
      );
      if (!response.ok) return response;
      const decoded = decodeRevoke(response.value);
      return decoded
        ? webPushSuccess(decoded)
        : webPushFailure("CONTRACT_REJECTED", "SUBSCRIPTION_REVOKE");
    },
  };
  return Object.freeze(gateway);

  async function execute(
    input: Parameters<WebPushRegistrationExecutor["execute"]>[0],
    operation:
      | "SUBSCRIPTION_CREATE"
      | "SUBSCRIPTION_RECONCILE"
      | "SUBSCRIPTION_REVOKE",
  ): Promise<WebPushResult<unknown>> {
    try {
      return await executor.execute(input);
    } catch {
      return webPushFailure("NATIVE_FAILURE", operation, true);
    }
  }
}

function decodeRegistration(
  value: unknown,
): WebPushRegistrationCommit | null {
  if (!exactRecord(value, [
    "associationEpoch",
    "protocol",
    "sessionBindingEpoch",
  ])) {
    return null;
  }
  return value.protocol === WEB_PUSH_PROTOCOLS.registration &&
    validOpaqueId(value.associationEpoch) &&
    validOpaqueId(value.sessionBindingEpoch)
    ? Object.freeze({
        associationEpoch: value.associationEpoch,
        sessionBindingEpoch: value.sessionBindingEpoch,
      })
    : null;
}

function decodeReconciliation(
  value: unknown,
): WebPushReconciliation | null {
  if (
    exactRecord(value, ["protocol", "state"]) &&
    value.protocol === WEB_PUSH_PROTOCOLS.reconciliation &&
    value.state === "ABSENT"
  ) {
    return Object.freeze({ state: "ABSENT" });
  }
  if (
    !exactRecord(value, [
      "associationEpoch",
      "protocol",
      "sessionBindingEpoch",
      "state",
    ]) ||
    value.protocol !== WEB_PUSH_PROTOCOLS.reconciliation ||
    value.state !== "ACTIVE" ||
    !validOpaqueId(value.associationEpoch) ||
    !validOpaqueId(value.sessionBindingEpoch)
  ) {
    return null;
  }
  return Object.freeze({
    state: "ACTIVE",
    associationEpoch: value.associationEpoch,
    sessionBindingEpoch: value.sessionBindingEpoch,
  });
}

function decodeRevoke(
  value: unknown,
): Readonly<{ state: "REVOKED" | "ALREADY_GONE" }> | null {
  return exactRecord(value, ["protocol", "state"]) &&
    value.protocol === WEB_PUSH_PROTOCOLS.revoke &&
    (value.state === "REVOKED" || value.state === "ALREADY_GONE")
    ? Object.freeze({ state: value.state })
    : null;
}

function exactRecord(
  value: unknown,
  keys: readonly string[],
): value is Record<string, unknown> {
  if (!value || typeof value !== "object" || Array.isArray(value)) return false;
  const actual = Object.keys(value).sort();
  return (
    actual.length === keys.length &&
    actual.every((key, index) => key === keys[index])
  );
}

function validOpaqueId(value: unknown): value is string {
  return typeof value === "string" && OPAQUE_ID.test(value);
}

function validAuthority(value: PushAuthoritySnapshot): boolean {
  return (
    validOpaqueId(value.fenceGeneration) &&
    validOpaqueId(value.sessionBindingEpoch) &&
    validOpaqueId(value.releaseEpoch)
  );
}

function validMaterial(value: NativePushSubscriptionMaterial): boolean {
  const p256dh = base64UrlDecode(value?.p256dh);
  const auth = base64UrlDecode(value?.auth);
  if (
    !value ||
    typeof value !== "object" ||
    typeof value.endpoint !== "string" ||
    value.endpoint.length > 4_096 ||
    !/^[A-Za-z0-9_-]{87}$/u.test(value.p256dh) ||
    !/^[A-Za-z0-9_-]{22}$/u.test(value.auth) ||
    p256dh?.byteLength !== 65 ||
    p256dh[0] !== 4 ||
    auth?.byteLength !== 16 ||
    (value.expirationTime !== null &&
      (!Number.isFinite(value.expirationTime) ||
        value.expirationTime <= 0))
  ) {
    return false;
  }
  try {
    const endpoint = new URL(value.endpoint);
    return (
      endpoint.protocol === "https:" &&
      !endpoint.username &&
      !endpoint.password &&
      !endpoint.hash
    );
  } catch {
    return false;
  }
}

function snapshotMaterial(
  value: NativePushSubscriptionMaterial,
): NativePushSubscriptionMaterial {
  return Object.freeze({
    endpoint: value.endpoint,
    p256dh: value.p256dh,
    auth: value.auth,
    expirationTime: value.expirationTime,
  });
}

function base64UrlDecode(value: unknown): Uint8Array | null {
  if (typeof value !== "string") return null;
  const alphabet =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
  const output = new Uint8Array(
    new ArrayBuffer(Math.floor((value.length * 6) / 8)),
  );
  let accumulator = 0;
  let bitCount = 0;
  let outputIndex = 0;
  for (const character of value) {
    const digit = alphabet.indexOf(character);
    if (digit < 0) return null;
    accumulator = (accumulator << 6) | digit;
    bitCount += 6;
    if (bitCount >= 8) {
      bitCount -= 8;
      output[outputIndex] = (accumulator >> bitCount) & 0xff;
      outputIndex += 1;
    }
  }
  return bitCount < 6 &&
    outputIndex === output.length &&
    (bitCount === 0 ||
      (accumulator & ((1 << bitCount) - 1)) === 0)
    ? output
    : null;
}