Caching System

/**
 * In-memory cache with automatic normalization and reactive updates
 * Stores GraphQL data in a normalized format with intelligent merging
 */
class InMemoryCache extends ApolloCache<NormalizedCacheObject> {
  constructor(config?: InMemoryCacheConfig);
  
  /** Type policies for controlling cache behavior */
  policies: Policies;
}

interface InMemoryCacheConfig {
  /** Custom data ID generation function */
  dataIdFromObject?: KeyFieldsFunction;
  /** Add __typename to all objects */
  addTypename?: boolean;
  /** Type policies for cache behavior */
  typePolicies?: TypePolicies;
  /** Possible types for union/interface types */  
  possibleTypes?: PossibleTypesMap;
  /** Result caching configuration */
  resultCaching?: boolean;
  /** Canonical cache key computation */
  canonizeResults?: boolean;
}

import { InMemoryCache } from "@apollo/client/cache";

const cache = new InMemoryCache({
  typePolicies: {
    User: {
      fields: {
        posts: {
          merge(existing = [], incoming) {
            return [...existing, ...incoming];
          }
        }
      }
    },
    Post: {
      keyFields: ["slug"]
    }
  },
  possibleTypes: {
    Node: ["User", "Post", "Comment"]
  }
});

/**
 * Read query data from the cache
 * @param options - Read options with query and variables
 * @returns Query result or null if not cached
 */
readQuery<QueryType, TVariables = any>(
  options: Cache.ReadQueryOptions<QueryType, TVariables>
): QueryType | null;

/**
 * Read fragment data from the cache
 * @param options - Fragment read options with ID and fragment
 * @returns Fragment data or null if not found
 */
readFragment<FragmentType, TVariables = any>(
  options: Cache.ReadFragmentOptions<FragmentType, TVariables>
): FragmentType | null;

interface Cache.ReadQueryOptions<TQuery, TVariables> {
  query: DocumentNode | TypedDocumentNode<TQuery, TVariables>;
  variables?: TVariables;
  rootId?: string;
  previousResult?: any;
  returnPartialData?: boolean;
  optimistic?: boolean;
}

interface Cache.ReadFragmentOptions<TFragment, TVariables> {
  id: string;
  fragment: DocumentNode | TypedDocumentNode<TFragment, TVariables>;
  variables?: TVariables;
  returnPartialData?: boolean;
  optimistic?: boolean;
}

// Read query from cache
const userData = cache.readQuery({
  query: gql`
    query GetUser($id: ID!) {
      user(id: $id) {
        id
        name
        email
      }
    }
  `,
  variables: { id: '123' }
});

// Read fragment from cache
const userFragment = cache.readFragment({
  id: 'User:123',
  fragment: gql`
    fragment UserInfo on User {
      name
      email
      avatar
    }
  `
});

/**
 * Write query data to the cache
 * @param options - Write options with query, variables, and data
 */
writeQuery<TData, TVariables = any>(
  options: Cache.WriteQueryOptions<TData, TVariables>
): void;

/**
 * Write fragment data to the cache
 * @param options - Fragment write options
 * @returns Reference to the written object
 */
writeFragment<TData, TVariables = any>(
  options: Cache.WriteFragmentOptions<TData, TVariables>
): Reference | undefined;

interface Cache.WriteQueryOptions<TData, TVariables> {
  query: DocumentNode | TypedDocumentNode<TData, TVariables>;
  variables?: TVariables;
  data: TData;
  id?: string;
  broadcast?: boolean;
}

interface Cache.WriteFragmentOptions<TData, TVariables> {
  id: string;
  fragment: DocumentNode | TypedDocumentNode<TData, TVariables>;
  variables?: TVariables;
  data: TData;
  broadcast?: boolean;
}

// Write query to cache
cache.writeQuery({
  query: GET_USER,
  variables: { id: '123' },
  data: {
    user: {
      id: '123',
      name: 'John Doe',
      email: 'john@example.com',
      __typename: 'User'
    }
  }
});

// Write fragment to cache
const ref = cache.writeFragment({
  id: 'User:123',
  fragment: gql`
    fragment UserInfo on User {
      name
      email
    }
  `,
  data: {
    name: 'John Doe Updated',
    email: 'john.updated@example.com',
    __typename: 'User'
  }
});

/**
 * Modify cached fields with granular control
 * @param options - Modification options with ID and field modifiers
 * @returns Boolean indicating if any modifications were made
 */
modify(options: Cache.ModifyOptions): boolean;

interface Cache.ModifyOptions {
  /** ID of the object to modify */
  id?: string;
  /** Field modification functions */
  fields?: Modifiers | Modifier<any>;
  /** Whether to broadcast changes */
  broadcast?: boolean;
  /** Optimistic modification */
  optimistic?: boolean;
}

type Modifiers = {
  [fieldName: string]: Modifier<any>;
};

type Modifier<T> = (value: T, details: ModifierDetails) => T | typeof INVALIDATE | typeof DELETE;

interface ModifierDetails {
  /** Field name being modified */
  fieldName: string;
  /** Storage key for the field */
  storeFieldName: string;
  /** Arguments for the field */
  args?: Record<string, any>;
  /** Check if value is a cache reference */
  isReference: (value: any) => value is Reference;
  /** Convert cache reference to object */
  toReference: typeof toReference;
  /** Read field from another object */
  readField: ReadFieldFunction;
}

// Add item to a list
cache.modify({
  id: 'User:123',
  fields: {
    posts(existingPosts = [], { readField }) {
      const newPost = cache.writeFragment({
        data: {
          id: 'post-456',
          title: 'New Post',
          __typename: 'Post'
        },
        fragment: gql`
          fragment NewPost on Post {
            id
            title
          }
        `
      });
      
      return [...existingPosts, newPost];
    },
    postCount(existing) {
      return existing + 1;
    }
  }
});

// Remove item from cache
cache.modify({
  id: 'ROOT_QUERY',
  fields: {
    posts(existingPosts, { readField }) {
      return existingPosts.filter(
        post => readField('id', post) !== 'post-to-remove'
      );
    }
  }
});

/**
 * Reset the cache, clearing all data
 * @returns Promise that resolves when reset is complete
 */
reset(): Promise<void>;

/**
 * Evict objects or fields from the cache
 * @param options - Eviction options
 * @returns Boolean indicating if anything was evicted
 */
evict(options: Cache.EvictOptions): boolean;

/**
 * Garbage collect unreferenced objects
 * @returns Array of IDs that were collected
 */
gc(): string[];

/**
 * Retain a cache object to prevent garbage collection
 * @param id - Object ID to retain
 * @returns Release function
 */
retain(id: string): number;

/**
 * Release a retained object
 * @param id - Object ID to release
 * @returns Remaining retain count
 */
release(id: string): number;

/**
 * Extract the entire cache state
 * @param optimistic - Include optimistic data
 * @returns Complete cache state
 */
extract(optimistic?: boolean): NormalizedCacheObject;

/**
 * Restore cache state from extracted data
 * @param serializedState - Previously extracted cache state
 */
restore(serializedState: NormalizedCacheObject): this;

interface Cache.EvictOptions {
  /** ID of object to evict from */
  id?: string;
  /** Specific field name to evict */
  fieldName?: string;
  /** Arguments for the field to evict */
  args?: Record<string, any>;
  /** Broadcast the eviction */
  broadcast?: boolean;
}

// Evict specific object
cache.evict({ id: 'User:123' });

// Evict specific field
cache.evict({
  id: 'User:123',
  fieldName: 'posts',
  args: { limit: 10 }
});

// Garbage collect unreferenced objects
const collected = cache.gc();
console.log(`Collected ${collected.length} objects`);

// Extract and restore cache
const state = cache.extract();
const newCache = new InMemoryCache();
newCache.restore(state);

/**
 * Create a reactive variable for local state
 * @param initialValue - Initial value for the variable
 * @returns Reactive variable function
 */
function makeVar<T>(initialValue: T): ReactiveVar<T>;

interface ReactiveVar<T> {
  /** Get current value */
  (): T;
  /** Set new value */
  (newValue: T): T;
  /** Listen for changes (internal use) */
  onNextChange(listener: (value: T) => void): () => void;
}

import { makeVar } from "@apollo/client/cache";

// Create reactive variables
const isLoggedInVar = makeVar(false);
const currentUserVar = makeVar(null);
const themeVar = makeVar('light');

// Use in components (with useReactiveVar)
function LoginStatus() {
  const isLoggedIn = useReactiveVar(isLoggedInVar);
  
  return (
    <div>
      Status: {isLoggedIn ? 'Logged In' : 'Logged Out'}
      <button onClick={() => isLoggedInVar(!isLoggedIn)}>
        Toggle Status
      </button>
    </div>
  );
}

// Use in type policies
const cache = new InMemoryCache({
  typePolicies: {
    Query: {
      fields: {
        isLoggedIn: {
          read() {
            return isLoggedInVar();
          }
        },
        currentUser: {
          read() {
            return currentUserVar();
          }
        }
      }
    }
  }
});

interface TypePolicies {
  [typename: string]: TypePolicy;
}

interface TypePolicy {
  /** Fields used to identify objects of this type */
  keyFields?: KeySpecifier | KeyFieldsFunction | false;
  /** Field-specific policies */
  fields?: {
    [fieldName: string]: FieldPolicy<any>;
  };
  /** Custom merge function for this type */
  merge?: FieldMergeFunction<any, any>;
}

interface FieldPolicy<TExisting = any, TIncoming = TExisting, TReadResult = TIncoming> {
  /** Custom field read function */
  read?: FieldReadFunction<TExisting, TReadResult>;
  /** Custom field merge function */
  merge?: FieldMergeFunction<TExisting, TIncoming>;
  /** Key arguments that affect field identity */
  keyArgs?: KeySpecifier | KeyArgsFunction | false;
}

type FieldReadFunction<TExisting, TReadResult = TExisting> = (
  existing: TExisting | undefined,
  options: FieldFunctionOptions
) => TReadResult;

type FieldMergeFunction<TExisting, TIncoming = TExisting> = (
  existing: TExisting | undefined,
  incoming: TIncoming,
  options: FieldFunctionOptions
) => TExisting | TIncoming;

const cache = new InMemoryCache({
  typePolicies: {
    User: {
      keyFields: ["email"], // Use email instead of id
      fields: {
        posts: {
          merge(existing = [], incoming) {
            // Merge arrays without duplicates
            const existingIds = existing.map(ref => readField('id', ref));
            return [
              ...existing,
              ...incoming.filter(ref => 
                !existingIds.includes(readField('id', ref))
              )
            ];
          }
        },
        fullName: {
          read(_, { readField }) {
            // Computed field
            const firstName = readField('firstName');
            const lastName = readField('lastName');
            return `${firstName} ${lastName}`;
          }
        }
      }
    },
    Post: {
      keyFields: ["slug"],
      fields: {
        comments: relayStylePagination() // Use built-in pagination
      }
    }
  }
});

interface NormalizedCacheObject {
  [dataId: string]: StoreObject | undefined;
}

interface StoreObject {
  __typename?: string;
  [storeFieldName: string]: StoreValue;
}

type StoreValue = 
  | number 
  | string 
  | boolean 
  | null 
  | undefined 
  | StoreObject 
  | StoreObject[] 
  | Reference 
  | Reference[];

interface Reference {
  readonly __ref: string;
}

type KeySpecifier = (string | KeySpecifier)[];
type KeyFieldsFunction = (object: Readonly<StoreObject>, context: {
  typename: string;
  selectionSet?: SelectionSetNode;
  fragmentMap?: FragmentMap;
}) => string | null | void;

interface PossibleTypesMap {
  [supertype: string]: string[];
}

interface FieldFunctionOptions {
  args?: Record<string, any> | null;
  fieldName: string;
  storeFieldName: string;
  field?: FieldNode;
  typename?: string;
  cache: InMemoryCache;
  canRead: CanReadFunction;
  readField: ReadFieldFunction;
  mergeObjects: MergeObjectsFunction;
  variables?: Record<string, any>;
  isReference: (obj: any) => obj is Reference;
  toReference: ToReferenceFunction;
  storage: StorageType;
}