/**
 * The body a snapshot must carry, stated once.
 *
 * The client renderer (`scene.js`, `topdown.js`, `presence.js`, `gun.js`)
 * reads fixed fields off every body in `snap.players` and off `snap.me`. A
 * game that renames one — `down` for `alive` — is not refused by anything at
 * runtime: every enemy simply draws as a corpse. So the shape is a contract
 * here, and each game tests its real snapshot against it.
 *
 * Every body in `snap.players` has:
 *   id: string        who; `me` is skipped in the scene by this id
 *   name: string      the tag over the body
 *   x, y: number      where, in world units
 *   angle: number     which way it faces, radians
 *   alive: boolean    false draws a corpse
 *   hp: number        0..100; a bar shows under 100
 *   mate: boolean     on the viewer's side
 *
 * `snap.me` has, besides id, x, y, angle, alive and hp:
 *   ammo: number        rounds in the magazine
 *   reloading: boolean  mid-reload
 */

type Kind = "string" | "number" | "boolean";

const BODY: Record<string, Kind> = {
  id: "string",
  name: "string",
  x: "number",
  y: "number",
  angle: "number",
  alive: "boolean",
  hp: "number",
  mate: "boolean",
};

const ME: Record<string, Kind> = {
  id: "string",
  x: "number",
  y: "number",
  angle: "number",
  alive: "boolean",
  hp: "number",
  ammo: "number",
  reloading: "boolean",
};

function problems(value: unknown, shape: Record<string, Kind>, label: string): string[] {
  if (typeof value !== "object" || value === null) return [`${label} is not an object`];
  const out: string[] = [];
  for (const [field, kind] of Object.entries(shape)) {
    const got = (value as Record<string, unknown>)[field];
    if (typeof got !== kind || (kind === "number" && !Number.isFinite(got))) out.push(`${label}.${field} should be a ${kind}, is ${String(got)}`);
  }
  return out;
}

/** What is wrong with one body of `snap.players`; empty when it is fit to draw. */
export const bodyProblems = (body: unknown, label = "body"): string[] => problems(body, BODY, label);

/** What is wrong with `snap.me`; empty when the gun and the camera can read it. */
export const meProblems = (me: unknown): string[] => problems(me, ME, "me");

/** Every problem in a snapshot's bodies and `me`. */
export function snapshotProblems(snap: { me?: unknown; players?: unknown }): string[] {
  const players = Array.isArray(snap.players) ? snap.players : null;
  return [
    ...meProblems(snap.me),
    ...(players ? players.flatMap((p, i) => bodyProblems(p, `players[${i}]`)) : ["players is not an array"]),
  ];
}