code-api-web/src/packages/fastify-compliant-http-errors/index.ts

import { FastifyReply, FastifyRequest } from 'fastify'

type AppErrorOptions = {
	cause?: Error,
}

export class AppError extends Error {
	public readonly cause?: Error

	constructor(message?: string, options?: AppErrorOptions) {
		super(message)
		if (typeof options === 'object') {
			this.cause = options.cause
		}
	}
}

const httpErrorClassFactory = (statusCode: number, statusMessage?: string) => class HttpError extends AppError {
	readonly statusCode = statusCode
	readonly statusMessage = statusMessage
}

interface CustomFastifyError extends Error {
	statusMessage?: string;
	validation: {
		keyword: string,
		instancePath: string,
		params: Record<string, unknown>,
		message: string,
	}[];
	statusCode?: number;
	errors: Record<string, unknown>[];
	detail?: string;
}

export const fastifyErrorHandler = (error: CustomFastifyError, _request: FastifyRequest, reply: FastifyReply) => {
	reply.headers({
		'Content-Type': 'application/problem+json',
	})

	if (error.validation) {
		reply.status(400)
		reply.raw.statusMessage = 'Invalid Request'
		reply.send({
			title: 'There are errors in the request body.',
			'invalid-params': error.validation.map(v => ({
				name: (
					v.keyword === 'required'
						? `${v.instancePath}/${v.params.missingProperty}`
						: v.instancePath
				).replaceAll('/', '.'),
				reason: v.message,
			})),
		})
		return
	}

	if (Number.isNaN(reply.raw.statusCode)) {
		reply.status(error?.statusCode ?? 500)
	}
	reply.raw.statusMessage = error.statusMessage ?? 'Unknown Error'
	reply.send({
		title: reply.raw.statusMessage,
		detail: error.message,
	})
}

export { httpErrorClassFactory as HttpError }