Add enum parser utility

This commit is contained in:
Evan Hahn 2021-03-31 11:14:45 -05:00 committed by Josh Perez
parent 73a8c3ff95
commit bd48dea613
3 changed files with 73 additions and 14 deletions

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@ -1,6 +1,8 @@
// Copyright 2021 Signal Messenger, LLC
// SPDX-License-Identifier: AGPL-3.0-only
import { makeEnumParser } from './util/enum';
// Many places rely on this enum being a string.
export enum Environment {
Development = 'development',
@ -33,17 +35,7 @@ export function setEnvironment(env: Environment): void {
environment = env;
}
const ENVIRONMENTS_BY_STRING = new Map<string, Environment>([
['development', Environment.Development],
['production', Environment.Production],
['staging', Environment.Staging],
['test', Environment.Test],
['test-lib', Environment.TestLib],
]);
export function parseEnvironment(value: unknown): Environment {
if (typeof value !== 'string') {
return Environment.Production;
}
const result = ENVIRONMENTS_BY_STRING.get(value);
return result || Environment.Production;
}
export const parseEnvironment = makeEnumParser(
Environment,
Environment.Production
);

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@ -0,0 +1,37 @@
// Copyright 2021 Signal Messenger, LLC
// SPDX-License-Identifier: AGPL-3.0-only
import { assert } from 'chai';
import { makeEnumParser } from '../../util/enum';
describe('enum utils', () => {
describe('makeEnumParser', () => {
enum Color {
Red = 'red',
Green = 'green',
Blue = 'blue',
}
const parse = makeEnumParser(Color, Color.Blue);
it('returns a parser that returns the default value if passed a non-string', () => {
[undefined, null, 0, 1, 123].forEach(serializedValue => {
const result: Color = parse(serializedValue);
assert.strictEqual(result, Color.Blue);
});
});
it('returns a parser that returns the default value if passed a string not in the enum', () => {
['', 'garbage', 'RED'].forEach(serializedValue => {
const result: Color = parse(serializedValue);
assert.strictEqual(result, Color.Blue);
});
});
it('returns a parser that parses enum values', () => {
const result: Color = parse('green');
assert.strictEqual(result, Color.Green);
});
});
});

30
ts/util/enum.ts Normal file
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@ -0,0 +1,30 @@
// Copyright 2021 Signal Messenger, LLC
// SPDX-License-Identifier: AGPL-3.0-only
/**
* Turn a string (like "green") into its enum type (like `Color.Green`). Useful when
* deserializing strings into enum types.
*
* It only supports enums with string values. It could theoretically support more, but:
*
* 1. It's easier to debug. A serialized value of "Green" is easier to associate with
* `Color.Green` than a serialized value of 2.
* 2. TypeScript's default uses numeric enum values. Because the stability of values is
* important and it's easy to mess up the stability of values (e.g., by reordering the
* enum), these are discouraged here.
*
* Again: no "hard" technical reason why this only supports strings; it's to encourage
* good behavior.
*/
export function makeEnumParser<
TEnumKey extends string,
TEnumValue extends string
>(
enumToParse: Record<TEnumKey, TEnumValue>,
defaultValue: TEnumValue
): (value: unknown) => TEnumValue {
const enumValues = new Set(Object.values(enumToParse));
const isEnumValue = (value: unknown): value is TEnumValue =>
typeof value === 'string' && enumValues.has(value);
return value => (isEnumValue(value) ? value : defaultValue);
}