import type { CacheScopeSnapshot } from "../../contracts/server-state-scope.ts";

export type ConditionalValidatorBinding = Readonly<{
  definitionId: string;
  identityToken: string;
  representationVersion: number;
  scope: CacheScopeSnapshot;
}>;

export type ConditionalValidatorStore = Readonly<{
  install(
    binding: ConditionalValidatorBinding,
    validator: string,
    cacheRevision: number,
  ): boolean;
  prepare(
    binding: ConditionalValidatorBinding,
    cacheRevision: number,
  ): string | null;
  acceptNotModified(
    binding: ConditionalValidatorBinding,
    cacheRevision: number,
    hasMappedValue: boolean,
  ): boolean;
  remove(binding: ConditionalValidatorBinding): void;
  clear(): void;
}>;

type ValidatorRow = {
  validator: string;
  cacheRevision: number;
  generation: number;
};

type ConditionalValidatorKeyTuple = readonly [
  scopeFingerprint: string,
  definitionId: string,
  identityToken: string,
  representationVersion: number,
];

/** The store is a trust boundary, so key components are validated and bounded. */
const MAX_KEY_COMPONENT_BYTES = 512;
const KEY_COMPONENT_ENCODER = new TextEncoder();

function isBoundedKeyComponent(value: unknown): value is string {
  return (
    typeof value === "string" &&
    value.length > 0 &&
    KEY_COMPONENT_ENCODER.encode(value).byteLength <=
      MAX_KEY_COMPONENT_BYTES
  );
}

export function createConditionalValidatorStore(
  maxEntries = 1_024,
): ConditionalValidatorStore {
  if (!Number.isSafeInteger(maxEntries) || maxEntries < 1) {
    throw new TypeError("Invalid conditional validator capacity.");
  }
  const rows = new Map<string, ValidatorRow>();

  /**
   * N-05. A delimiter join is not injective here: `definitionId`,
   * `identityToken` and the scope fingerprint may all contain the delimiter, so
   * two distinct valid bindings could encode to the same key and one
   * definition's ETag could be sent for another. The key is a validated fixed
   * tuple encoded with `JSON.stringify`, which escapes the separators.
   */
  function key(binding: ConditionalValidatorBinding): string | null {
    if (
      !binding.scope.isCurrent() ||
      !isBoundedKeyComponent(binding.scope.fingerprint) ||
      !isBoundedKeyComponent(binding.definitionId) ||
      !/^[A-Za-z0-9._:-]{16,128}$/.test(binding.identityToken) ||
      !Number.isSafeInteger(binding.representationVersion) ||
      binding.representationVersion < 1
    ) {
      return null;
    }
    const tuple: ConditionalValidatorKeyTuple = [
      binding.scope.fingerprint,
      binding.definitionId,
      binding.identityToken,
      binding.representationVersion,
    ];
    return JSON.stringify(tuple);
  }

  return Object.freeze({
    install(binding, validator, cacheRevision) {
      const selectedKey = key(binding);
      if (
        !selectedKey ||
        !isSafeEntityTag(validator) ||
        !Number.isSafeInteger(cacheRevision) ||
        cacheRevision < 0
      ) {
        return false;
      }
      if (!rows.has(selectedKey) && rows.size >= maxEntries) return false;
      rows.set(selectedKey, {
        validator,
        cacheRevision,
        generation: binding.scope.generation,
      });
      return true;
    },
    prepare(binding, cacheRevision) {
      const selectedKey = key(binding);
      if (!selectedKey) return null;
      const row = rows.get(selectedKey);
      return row &&
        row.generation === binding.scope.generation &&
        row.cacheRevision === cacheRevision
        ? row.validator
        : null;
    },
    acceptNotModified(binding, cacheRevision, hasMappedValue) {
      const selectedKey = key(binding);
      if (!selectedKey || !hasMappedValue) return false;
      const row = rows.get(selectedKey);
      return Boolean(
        row &&
          row.generation === binding.scope.generation &&
          row.cacheRevision === cacheRevision,
      );
    },
    remove(binding) {
      const selectedKey = key(binding);
      if (selectedKey) rows.delete(selectedKey);
    },
    clear() {
      rows.clear();
    },
  });
}

function isSafeEntityTag(value: string): boolean {
  if (value.length < 3 || value.length > 256) return false;
  const opaque = value.startsWith('W/"')
    ? value.slice(3, -1)
    : value.startsWith('"')
      ? value.slice(1, -1)
      : null;
  if (opaque === null || !value.endsWith('"')) return false;
  return [...opaque].every((character) => {
    const code = character.codePointAt(0) ?? 0;
    return code === 0x21 || (code >= 0x23 && code <= 0x7e) ||
      (code >= 0x80 && code <= 0xff);
  });
}