const APP_NAMESPACE = "ca-frontend";

export type StorageBackend =
  | "memory"
  | "sessionStorage"
  | "localStorage"
  | "disabled"
  | "forbidden";

export type StorageValueCodec =
  | "color-scheme-v1"
  | "opaque-string-v1"
  | "none";

export type StorageKeyInput = Readonly<{
  logicalName: string;
  scope: string;
  name: string;
  backend: StorageBackend;
  classification:
    | "public-preference"
    | "opaque-cache"
    | "sensitive-forbidden";
  schemaVersion: number;
  valueCodec: StorageValueCodec;
  ttl: number | "session" | null;
  migration: "discard";
  quotaFallback: "memory" | "no-persist" | "feature-disable";
}>;

export type StorageDefinition = Readonly<
  StorageKeyInput & { physicalKey: string }
>;

export const STORAGE_REGISTRY = Object.freeze({
  COLOR_SCHEME: defineStorageKey({
    logicalName: "COLOR_SCHEME",
    scope: "preference",
    name: "color-scheme",
    backend: "localStorage",
    classification: "public-preference",
    schemaVersion: 1,
    valueCodec: "color-scheme-v1",
    ttl: null,
    migration: "discard",
    quotaFallback: "memory",
  }),
  CHUNK_RELOAD_GUARD: defineStorageKey({
    logicalName: "CHUNK_RELOAD_GUARD",
    scope: "release",
    name: "chunk-reload-guard",
    backend: "sessionStorage",
    classification: "opaque-cache",
    schemaVersion: 1,
    valueCodec: "opaque-string-v1",
    ttl: "session",
    migration: "discard",
    quotaFallback: "no-persist",
  }),
  QUERY_PERSISTENCE: defineStorageKey({
    logicalName: "QUERY_PERSISTENCE",
    scope: "cache",
    name: "query-persistence",
    backend: "disabled",
    classification: "sensitive-forbidden",
    schemaVersion: 1,
    valueCodec: "none",
    ttl: null,
    migration: "discard",
    quotaFallback: "feature-disable",
  }),
  CACHE_INVALIDATION_PULSE: defineStorageKey({
    logicalName: "CACHE_INVALIDATION_PULSE",
    scope: "cache-invalidation",
    name: "pulse",
    backend: "localStorage",
    classification: "opaque-cache",
    schemaVersion: 1,
    valueCodec: "opaque-string-v1",
    ttl: null,
    migration: "discard",
    quotaFallback: "no-persist",
  }),
  AUTH_TOKEN: defineStorageKey({
    logicalName: "AUTH_TOKEN",
    scope: "auth",
    name: "auth-token",
    backend: "forbidden",
    classification: "sensitive-forbidden",
    schemaVersion: 1,
    valueCodec: "none",
    ttl: null,
    migration: "discard",
    quotaFallback: "feature-disable",
  }),
});

export function defineStorageKey<Definition extends StorageKeyInput>(
  definition: Definition,
): Readonly<Definition & { physicalKey: string }> {
  if (
    !["color-scheme-v1", "opaque-string-v1", "none"].includes(
      definition.valueCodec,
    )
  ) {
    throw new Error("Unknown client storage value codec");
  }
  if (definition.migration !== "discard") {
    throw new Error("Unsupported client storage migration policy");
  }
  if (definition.classification === "sensitive-forbidden") {
    if (!["disabled", "forbidden"].includes(definition.backend)) {
      throw new Error("Sensitive client storage registration is forbidden");
    }
    if (definition.valueCodec !== "none") {
      throw new Error("Sensitive client storage codec is forbidden");
    }
  } else if (definition.valueCodec === "none") {
    throw new Error("Persisted storage keys require a value codec");
  }
  if (!Number.isInteger(definition.schemaVersion) || definition.schemaVersion < 1) {
    throw new Error("Storage schemaVersion must be a positive integer");
  }

  return Object.freeze({
    ...definition,
    physicalKey: buildPhysicalKey(
      definition.scope,
      definition.schemaVersion,
      definition.name,
    ),
  });
}

export function buildPhysicalKey(
  scope: string,
  schemaVersion: number,
  name: string,
): string {
  return `${APP_NAMESPACE}:${scope}:v${schemaVersion}:${name}`;
}

export function getStorageDefinition(logicalName: string): StorageDefinition {
  const registry: Readonly<Record<string, StorageDefinition>> = STORAGE_REGISTRY;
  const definition = registry[logicalName];
  if (!definition) throw new Error(`Unregistered storage key: ${logicalName}`);
  if (definition.classification === "sensitive-forbidden") {
    throw new Error(`Forbidden storage key: ${logicalName}`);
  }
  return definition;
}

export function isStorageValueAllowed(
  definition: StorageDefinition,
  value: unknown,
): boolean {
  switch (definition.valueCodec) {
    case "color-scheme-v1":
      return value === "light" || value === "dark" || value === "system";
    case "opaque-string-v1":
      return (
        typeof value === "string" &&
        value.length >= 1 &&
        value.length <= 2_048
      );
    default:
      return false;
  }
}