import type {} from '@fastify/static'
import type { FastifyError, FastifyReply, FastifyRequest } from 'fastify'
import { existsSync } from 'node:fs'
import { join } from 'node:path'
import type { Log } from './log.ts'

/**
 * An error answered with its status code and message as { error }. A refused write also carries the problems by
 * field and a message about what it would break elsewhere, answered as { error, problems, message }.
 */
export class HttpError extends Error {
  statusCode: number
  problems?: Record<string, string>
  detail?: string

  constructor(statusCode: number, message: string, problems?: Record<string, string>, detail?: string) {
    super(message)
    this.statusCode = statusCode
    this.problems = problems
    this.detail = detail
  }
}

/**
 * A JSON schema of an object with exactly the properties given, all required. With Fastify's removeAdditional off, a
 * body with another property is refused with 400.
 */
export function strict(properties: Record<string, unknown>) {
  return { type: 'object', required: Object.keys(properties), additionalProperties: false, properties }
}

/**
 * The error handler of setErrorHandler: the status of the error, 500 when it has none, with { error }, and the
 * problems and message of an HttpError that has problems. An error of 500 or more that is not an HttpError is logged
 * with its stack. A request that fails its schema is answered with "The request is not valid".
 */
export function errorHandler(log: Log) {
  return (error: FastifyError, request: FastifyRequest, reply: FastifyReply) => {
    const status = error.statusCode ?? 500
    if (status >= 500 && !(error instanceof HttpError)) {
      log.error(`${request.method} ${request.url}: ${error.stack ?? error.message}`)
    }
    const message = error.validation ? `The request is not valid (${error.message}).` : error.message
    if (error instanceof HttpError && error.problems !== undefined) {
      return reply.code(status).send({ error: message, problems: error.problems, message: error.detail ?? '' })
    }
    return reply.code(status).send({ error: message })
  }
}

/**
 * The not-found handler of setNotFoundHandler for an application of webDir, the built frontend served by
 * @fastify/static: a path under /api is 404 with { error }; any other path answers index.html, so the frontend's
 * routes work on a reload, or 503 with buildHint while the frontend is not built.
 */
export function notFoundHandler(webDir: string, buildHint: string) {
  return (request: FastifyRequest, reply: FastifyReply) => {
    if (request.url === '/api' || request.url.startsWith('/api/')) {
      return reply.code(404).send({ error: `'${request.method} ${request.url.split('?')[0]}' is not an endpoint of this tool.` })
    }
    if (!existsSync(join(webDir, 'index.html'))) {
      return reply.code(503).type('text/plain; charset=utf-8').send(`${buildHint}\n`)
    }
    return reply.type('text/html; charset=utf-8').sendFile('index.html')
  }
}