/**
 * The answer of a validate endpoint: problems maps a field of the validated value to a message; message describes what
 * the value would break elsewhere, or is empty.
 */
export type Validation = {
  problems: Record<string, string>
  message: string
}

/** A failed call: the server's message and status, with the problems and message of a refused write (422). */
export class ApiError extends Error {
  status: number
  problems: Record<string, string>
  detail: string

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

/** Calls the backend and returns the decoded JSON; a failed call throws ApiError with the backend's message. */
export async function request<T>(method: string, path: string, body?: unknown): Promise<T> {
  const response = await fetch(path, {
    method,
    headers: body === undefined ? {} : { 'Content-Type': 'application/json' },
    body: body === undefined ? undefined : JSON.stringify(body),
  })
  if (!response.ok) {
    const payload = (await response.json().catch(() => null)) as { error?: string; problems?: Record<string, string>; message?: string } | null
    throw new ApiError(payload?.error ?? `${method} ${path} failed (${response.status}).`, response.status, payload?.problems, payload?.message)
  }
  return (await response.json()) as T
}