FieldErrors.ts

import * as t from './io-ts'

type FieldErrors<T = Record<string, any>> = Partial<Record<keyof T, string>>

/** Creates an empty FieldErrors object for the specified entity type. */
function FieldErrors<T = Record<string, any>>() {
	return {} as FieldErrors<T>
}

// Helpers
namespace FieldErrors {
	/**
	 * Creates a FieldErrors object from an io-ts ValidationError array.
	 * Provide the record type that the field error keys should match.
	 * @param errors The array of errors
	 * @param formatter An optional callback that returns an error message.
	 */
	export function from<T = Record<string, any>>(
		errors: t.ValidationError[],
		formatter?: (field: keyof T, value: any) => string
	): FieldErrors<T> {
		return errors.map(
			e => [validationErrorKey<T>(e), e.value] as [keyof T, any]
		).reduce((fieldErrors, [key, value]) => {
			// Only count non-empty, non-numeric keys
			if (key && !Number.isSafeInteger(Number(key))) {
				if (!fieldErrors[key]) {
					fieldErrors[key] = formatter
						? formatter(key, value)
						: `Invalid ${key}.`
				}
			}
			return fieldErrors
		}, FieldErrors<T>())
	}
}

/** Helper function returns the field name from the ValidationError */
function validationErrorKey<T> (error: t.ValidationError) {
	let key = ''
	// Use the entry with longest key to get the field name
	for (const c of error.context) {
		if (c.key.length > key.length) {
			key = c.key
		}
	}
	return key
}