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Viewing / Editing File: RateLimiter.ts

/**
 * Limits the number of calls to a resource to a maximum amount in some interval.
 *
 * @since 2.0.0
 */
import type { DurationInput } from "./Duration.js"
import type { Effect } from "./Effect.js"
import * as internal from "./internal/rateLimiter.js"
import type { Scope } from "./Scope.js"

/**
 * Limits the number of calls to a resource to a maximum amount in some interval.
 *
 * Note that only the moment of starting the effect is rate limited: the number
 * of concurrent executions is not bounded.
 *
 * @since 2.0.0
 * @category models
 */
export interface RateLimiter {
  <A, E, R>(task: Effect<A, E, R>): Effect<A, E, R>
}

/**
 * @since 2.0.0
 */
export declare namespace RateLimiter {
  /**
   * @since 2.0.0
   * @category models
   */
  export interface Options {
    /**
     * The maximum number of requests that should be allowed.
     */
    readonly limit: number
    /**
     * The interval to utilize for rate-limiting requests. The semantics of the
     * specified `interval` vary depending on the chosen `algorithm`:
     *
     * `token-bucket`: The maximum number of requests will be spread out over
     * the provided interval if no tokens are available.
     *
     * For example, for a `RateLimiter` using the `token-bucket` algorithm with
     * a `limit` of `10` and an `interval` of `1 seconds`, `1` request can be
     * made every `100 millis`.
     *
     * `fixed-window`: The maximum number of requests will be reset during each
     * interval. For example, for a `RateLimiter` using the `fixed-window`
     * algorithm with a `limit` of `10` and an `interval` of `1 seconds`, a
     * maximum of `10` requests can be made each second.
     */
    readonly interval: DurationInput
    /**
     * The algorithm to utilize for rate-limiting requests.
     *
     * Defaults to `token-bucket`.
     */
    readonly algorithm?: "fixed-window" | "token-bucket"
  }
}

/**
 * Constructs a new `RateLimiter` which will utilize the specified algorithm
 * to limit requests (defaults to `token-bucket`).
 *
 * Notes
 * - Only the moment of starting the effect is rate limited. The number of concurrent executions is not bounded.
 * - Instances of `RateLimiter` can be composed.
 * - The "cost" per effect can be changed. See {@link withCost}
 *
 * @example
 * ```ts
 * import { Effect, RateLimiter } from "effect";
 * import { compose } from "effect/Function"
 *
 * const program = Effect.scoped(
 *   Effect.gen(function* ($) {
 *     const perMinuteRL = yield* $(RateLimiter.make({ limit: 30, interval: "1 minutes" }))
 *     const perSecondRL = yield* $(RateLimiter.make({ limit: 2, interval: "1 seconds" }))
 *
 *     // This rate limiter respects both the 30 calls per minute
 *     // and the 2 calls per second constraints.
 *      const rateLimit = compose(perMinuteRL, perSecondRL)
 *
 *     // simulate repeated calls
 *     for (let n = 0; n < 100; n++) {
 *       // wrap the effect we want to limit with rateLimit
 *       yield* $(rateLimit(Effect.log("Calling RateLimited Effect")));
 *     }
 *   })
 * );
 * ```
 *
 * @since 2.0.0
 * @category constructors
 */
export const make: (options: RateLimiter.Options) => Effect<RateLimiter, never, Scope> = internal.make

/**
 * Alters the per-effect cost of the rate-limiter.
 *
 * This can be used for "credit" based rate-limiting where different API endpoints
 * cost a different number of credits within a time window.
 * Eg: 1000 credits / hour, where a query costs 1 credit and a mutation costs 5 credits.
 *
 * @example
 * ```ts
 * import { Effect, RateLimiter } from "effect";
 * import { compose } from "effect/Function";
 *
 * const program = Effect.scoped(
 *   Effect.gen(function* ($) {
 *     // Create a rate limiter that has an hourly limit of 1000 credits
 *     const rateLimiter = yield* $(RateLimiter.make({ limit: 1000, interval: "1 hours" }));
 *     // Query API costs 1 credit per call ( 1 is the default cost )
 *     const queryAPIRL = compose(rateLimiter, RateLimiter.withCost(1));
 *     // Mutation API costs 5 credits per call
 *     const mutationAPIRL = compose(rateLimiter, RateLimiter.withCost(5));

*     // Use the pre-defined rate limiters
 *     yield* $(queryAPIRL(Effect.log("Sample Query")));
 *     yield* $(mutationAPIRL(Effect.log("Sample Mutation")));
 *
 *     // Or set a cost on-the-fly
 *     yield* $(
 *       rateLimiter(Effect.log("Another query with a different cost")).pipe(
 *         RateLimiter.withCost(3)
 *       )
 *     );
 *   })
 * );
 * ```
 *
 * @since 2.0.0
 * @category combinators
 */
export const withCost: (cost: number) => <A, E, R>(effect: Effect<A, E, R>) => Effect<A, E, R> = internal.withCost

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