@clipboard-health/rules-engine/src/lib/rule.d.ts

A pure functional rules engine to keep logic-dense code simple, reliable, understandable, and explainable.

import { type ReadonlyDeep } from "type-fest";
export interface RuleContext<TInput, TOutput> {
    /**
     * Input is immutable, rules must not modify it.
     */
    input: ReadonlyDeep<TInput>;
    /**
     * Output is immutable, do not modify existing items, only append using {@link appendOutput}.
     */
    output: ReadonlyArray<ReadonlyDeep<TOutput>>;
}
export interface Rule<TInput, TOutput, TContext extends RuleContext<TInput, TOutput> = RuleContext<TInput, TOutput>> {
    /**
     * Returns whether the rule should run or not.
     *
     * Only the `input` and not the full `context` is passed to `runIf`. This prevents rules from
     * relying on `output`, which may be appended to by previous rules by the time `run` is called.
     */
    runIf: (input: ReadonlyDeep<TInput>) => boolean;
    /**
     * A pure function that runs rule logic and returns a new context by appending to the output
     * array.
     *
     * @see {@link appendOutput}
     */
    run: (context: TContext) => TContext;
}