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operation - like Result and various other ADTs in Haskell etc
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| export type Operation<T, E = Error> = typeof NotStarted | typeof Waiting | Complete<T> | Failed<E>; | |
| export enum OperationState { | |
| NotStartedState = "NotStarted", | |
| WaitingState = "Waiting", | |
| CompleteState = "Complete", | |
| FailedState = "Failed", | |
| } | |
| export const NotStarted = { | |
| opState: OperationState.NotStartedState, | |
| } as const; | |
| export const Waiting = { | |
| opState: OperationState.WaitingState, | |
| } as const; | |
| export class Complete<T> { | |
| readonly opState = OperationState.CompleteState; | |
| constructor(readonly value: T) {} | |
| } | |
| export class Failed<E> { | |
| readonly opState = OperationState.FailedState; | |
| constructor(readonly error: E) {} | |
| static fromCatch(e: Error | any): Failed<{ name: string; message: string }> { | |
| if (e instanceof Error) { | |
| const { name, message } = e; | |
| return new Failed({ name, message }); | |
| } | |
| return new Failed({ | |
| name: "Unknown", | |
| message: "An unknown error occurred", | |
| }); | |
| } | |
| static fromError(e: Error): Failed<{ name: string; message: string }> { | |
| const { name, message } = e; | |
| return new Failed({ name, message }); | |
| } | |
| } | |
| export type Handler<T, E, R> = { | |
| notStarted: () => R; | |
| waiting: () => R; | |
| complete: (t: T) => R; | |
| failed: (e: E) => R; | |
| }; | |
| type BooleanHandler<T, R> = { | |
| present: (t: T) => R; | |
| absent: () => R; | |
| }; | |
| export function isWaiting<T, E>(op: Operation<T, E>): op is typeof Waiting { | |
| return op.opState === OperationState.WaitingState; | |
| } | |
| export function isComplete<T, E>(op: Operation<T, E>): op is Complete<T> { | |
| return op.opState === OperationState.CompleteState; | |
| } | |
| export function isFailed<E>(op: Operation<any, E>): op is Failed<E> { | |
| return op.opState === OperationState.FailedState; | |
| } | |
| export function handle<T, E, R>(op: Operation<T, E>, handler: Handler<T, E, R>): R { | |
| switch (op.opState) { | |
| case OperationState.CompleteState: | |
| return handler.complete(op.value); | |
| case OperationState.FailedState: | |
| return handler.failed(op.error); | |
| case OperationState.NotStartedState: | |
| return handler.notStarted(); | |
| case OperationState.WaitingState: | |
| return handler.waiting(); | |
| } | |
| } | |
| // transform both value containing cases of the operation - useful for turning a complex op type into a displayable one | |
| export const mapOperation = <T, U, E, F>( | |
| op: Operation<T, E>, | |
| mapComplete: (t: T) => U, | |
| mapFailed: (e: E) => F, | |
| ): Operation<U, F> => | |
| op.opState === OperationState.CompleteState | |
| ? new Complete(mapComplete(op.value)) | |
| : op.opState === OperationState.FailedState | |
| ? new Failed(mapFailed(op.error)) | |
| : op; | |
| export const handlePresence = <T, E, R>(op: Operation<T, E>, handler: BooleanHandler<T, R>): R => | |
| op.opState === OperationState.CompleteState ? handler.present(op.value) : handler.absent(); | |
| export const mapComplete = <T, E, U>(op: Operation<T, E>, fn: (t: T) => U): Operation<U, E> => | |
| op.opState === OperationState.CompleteState ? new Complete(fn(op.value)) : op; | |
| export const mapCompleteAndGet = <T, E, U>( | |
| op: Operation<T, E>, | |
| fn: (t: T) => U, | |
| getAbsent: () => U, | |
| ): U => (op.opState === OperationState.CompleteState ? fn(op.value) : getAbsent()); | |
| export const mapAndGetPresence = <T, E, R>( | |
| op: Operation<T, E>, | |
| handler: BooleanHandler<T, R>, | |
| ): R => | |
| op.opState === OperationState.CompleteState ? handler.present(op.value) : handler.absent(); |
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