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hookable.ts
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hookable.ts
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import Bluebird from "bluebird";
import assert from "assert";
import { EventMatcher, When } from "./event-matchers";
import { ActionName } from "../action";
import Context from "../context";
type HookProps = {
event_matcher: EventMatcher;
callback: Function;
is_blocking: boolean;
};
export class Hook {
event_matcher: EventMatcher;
callback: Function;
is_blocking: boolean;
constructor({ event_matcher, callback, is_blocking = true }: HookProps) {
assert.equal(typeof callback, "function");
assert.equal(typeof is_blocking, "boolean");
this.event_matcher = event_matcher;
this.callback = callback;
this.is_blocking = is_blocking;
}
appliesTo(event_description: EventDescription) {
return event_description.isEquivalentTo(this.event_matcher);
}
}
type EventDescriptionProps = {
when: When;
subject_path?: string;
action: ActionName;
metadata?: object;
};
export class EventDescription {
when: When;
subject_path: string;
action: ActionName;
metadata: { context: Context };
constructor({
when,
subject_path = "",
action,
metadata = {},
}: EventDescriptionProps) {
assert.equal(typeof when, "string");
assert.equal(typeof subject_path, "string");
assert.equal(typeof action, "string");
assert.equal(typeof metadata, "object");
this.when = when;
this.subject_path = subject_path;
this.action = action;
this.metadata = metadata;
}
isEquivalentTo(matcher: EventMatcher) {
return (
this.matchWhen(matcher) &&
this.matchAction(matcher) &&
this.matchSubjectPath(matcher)
);
}
matchWhen(matcher: EventMatcher) {
return this.when === matcher.when;
}
matchAction(matcher: EventMatcher) {
return matcher.actions.includes(this.action);
}
matchSubjectPath(matcher: EventMatcher) {
return matcher.subject_path.test(this.subject_path);
}
}
export class Hookable {
hooks: Hook[] = [];
addHook(
matcher: EventMatcher,
callback: (event: EventDescription, value: any) => Promise<any>, //for "before" value is the user input, for "after", `value` is system output. Both can be modified and overwritten by returning from callback
is_blocking: boolean = false
) {
const hook = new Hook({
event_matcher: matcher,
callback,
is_blocking,
});
this.hooks.push(hook);
}
async emitHook(_event_description: EventDescriptionProps, data = {}) {
const emitted_event = new EventDescription(_event_description);
return await Bluebird.reduce(
this.hooks.filter((hook) => hook.appliesTo(emitted_event)),
async (acc, hook) =>
(await hook.callback(emitted_event, acc)) || acc,
data
);
}
}

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