Flight-Ops/lib/sim/engine.ts

import { randomInt, randomUUID } from 'node:crypto';
import { eq } from 'drizzle-orm';
import { getGameDb, persist, type GameDb } from '@/lib/db/client';
import * as schema from '@/lib/db/schema';
import { loadAirportsGeoJson } from '@/lib/airports';
import { haversineKm } from '@/lib/geo';
import { PLANE_TYPES } from '@/lib/game/catalog';
import {
  generateContract,
  MARKET_TARGET_OPEN_CONTRACTS,
  mulberry32,
  type Rng,
  type SeedAirport,
} from '@/lib/game/seed';
import { arrivalTimeFor, fuelAt } from './movement';

// Server-authoritative sim engine (v0.7.0) — tick-on-read: there is NO background
// timer. Every read/action endpoint calls tickNow() first; the clock advances by
// (real ms since last tick) × timeScale, clamped per tick so long absences never
// fast-forward the game.

// Clamp constant: max real-time gap counted by a single tick. Chosen at 2000 ms —
// comfortably above a normal client poll interval (~1 s), so active play advances
// ~real time × scale; small enough that one stale read after an absence moves game
// time by at most 2 s × scale (≤ 2 min even at max scale 60). The sim therefore
// only meaningfully progresses while actively polled.
export const MAX_TICK_ELAPSED_MS = 2_000;

export const MIN_TIME_SCALE = 1;
export const MAX_TIME_SCALE = 60;

// Reputation gain per completed contract: BASE + PER_KM × great-circle km, rounded
// to 2 decimals (reputation is REAL). A short hop (~300 km) earns ~1.15 rep, a
// cross-Europe leg (~3000 km) ~2.5 — slow growth from the starting 10.
export const REP_BASE = 1;
export const REP_PER_KM = 0.0005;

export function reputationGainFor(km: number): number {
  return Math.round((REP_BASE + REP_PER_KM * km) * 100) / 100;
}

export interface SimControlsInput {
  timeScale?: number;
  paused?: boolean;
}

// Serialize ticks across concurrent requests (Next.js route handlers run in the
// same process): each tick re-reads sim_state after the previous one wrote it, so
// no advance is ever applied twice.
let chain: Promise<unknown> = Promise.resolve();
function withLock<T>(fn: () => Promise<T>): Promise<T> {
  const run = chain.then(fn);
  chain = run.then(
    () => undefined,
    () => undefined,
  );
  return run;
}

// --- Tick core (takes a GameDb so unit tests can inject their own instance) ---

export async function tickOnce(inst: GameDb): Promise<schema.SimStateRow> {
  const rows = await inst.db.select().from(schema.simState);
  const sim = rows[0];
  if (!sim) throw new Error('sim_state row missing');

  const nowMs = Date.now();
  const elapsed = Math.max(0, nowMs - sim.lastRealTickMs);
  // While paused the clock is frozen; lastRealTickMs still tracks real time so
  // unpausing resumes cleanly with no catch-up jump for the pause duration.
  const advanceMs = sim.paused ? 0 : Math.min(elapsed, MAX_TICK_ELAPSED_MS) * sim.timeScale;
  const clockMs = Math.round(sim.clockMs + advanceMs);

  if (advanceMs > 0) {
    await expireContracts(inst, clockMs);
    await finalizeArrivals(inst, clockMs);
    await spawnOpenContracts(inst, clockMs);
  }

  // Persist lastRealTickMs even when nothing advanced — it is the tick anchor.
  await inst.db.update(schema.simState).set({ clockMs, lastRealTickMs: nowMs });
  await persist(inst);
  const updated = (await inst.db.select().from(schema.simState))[0];
  if (!updated) throw new Error('sim_state row missing after tick');
  return updated;
}

// Open contracts whose deadline has passed become 'expired'. Accepted/in-flight
// contracts never expire — they complete. Returns the number flipped.
export async function expireContracts(inst: GameDb, clockMs: number): Promise<number> {
  const open = await inst.db.select().from(schema.contracts).where(eq(schema.contracts.status, 'open'));
  let n = 0;
  for (const c of open) {
    if (c.deadlineSimTime <= clockMs) {
      await inst.db.update(schema.contracts).set({ status: 'expired' }).where(eq(schema.contracts.id, c.id));
      n++;
    }
  }
  return n;
}

// Finalize in-flight planes whose arrival time has passed: award the contract
// reward (cash) + reputation gain exactly once, mark the contract completed, and
// ground the plane at the destination with its remaining fuel. Idempotent — a
// finalized plane leaves the 'flying' state, so it can never be awarded twice.
export async function finalizeArrivals(inst: GameDb, clockMs: number): Promise<number> {
  const [planeRows, contractRows] = await Promise.all([
    inst.db.select().from(schema.planes),
    inst.db.select().from(schema.contracts),
  ]);

  const fc = await loadAirportsGeoJson();
  const byIcao = new Map(fc.features.map((f) => [f.properties.icao, f.properties]));
  const contractById = new Map(contractRows.map((c) => [c.id, c]));

  let n = 0;
  for (const p of planeRows) {
    if (p.status !== 'flying' || p.departureSimTime == null || !p.contractId) continue;
    const contract = contractById.get(p.contractId);
    const type = PLANE_TYPES[p.model];
    const from = contract ? byIcao.get(contract.originIcao) : undefined;
    const to = contract ? byIcao.get(contract.destIcao) : undefined;
    if (!contract || !type || !from || !to) continue; // no route info — leave alone

    const distanceKm = haversineKm(from.lat, from.lon, to.lat, to.lon);
    if (clockMs < arrivalTimeFor(p.departureSimTime, distanceKm, type.speedKmh)) continue;

    // Arrived: progress is exactly 1 here, so remaining fuel is the full-leg burn.
    await inst.db.update(schema.planes)
      .set({
        status: 'available',
        locationIcao: to.icao,
        lat: to.lat,
        lon: to.lon,
        fuel: fuelAt(p.fuel, type.burnPerKm, distanceKm, 1),
        departureSimTime: null,
      })
      .where(eq(schema.planes.id, p.id));
    await inst.db.update(schema.contracts)
      .set({ status: 'completed' })
      .where(eq(schema.contracts.id, contract.id));
    // Fresh account read per award so multiple arrivals in one tick all count.
    const fresh = (await inst.db.select().from(schema.account))[0];
    if (!fresh) throw new Error('account row missing');
    await inst.db.update(schema.account).set({
      cash: fresh.cash + contract.reward,
      reputation: Math.round((fresh.reputation + reputationGainFor(distanceKm)) * 100) / 100,
    });
    n++;
  }
  return n;
}

// Top the market back up to MARKET_TARGET_OPEN_CONTRACTS open contracts using the
// SAME builder as the first-run seed (generateContract), so spawned contracts are
// indistinguishable from seeded ones. RNG is injectable for deterministic tests.
export async function spawnOpenContracts(
  inst: GameDb,
  clockMs: number,
  rng?: Rng,
): Promise<number> {
  const openCount = (
    await inst.db.select().from(schema.contracts).where(eq(schema.contracts.status, 'open'))
  ).length;
  const needed = MARKET_TARGET_OPEN_CONTRACTS - openCount;
  if (needed <= 0) return 0;

  const fc = await loadAirportsGeoJson();
  const airports: SeedAirport[] = fc.features.map((f) => ({
    icao: f.properties.icao,
    name: f.properties.name,
    lat: f.properties.lat,
    lon: f.properties.lon,
  }));
  const rand = rng ?? mulberry32(randomInt(0, 2 ** 31));

  for (let i = 0; i < needed; i++) {
    await inst.db.insert(schema.contracts).values(generateContract({ id: randomUUID(), airports, rng: rand, nowMs: clockMs }));
  }
  return needed;
}

// --- Public API (singleton DB + lock) — call from every read/action endpoint ---

export function tickNow(): Promise<schema.SimStateRow> {
  return withLock(async () => tickOnce(await getGameDb()));
}

// Tick first so the returned state reflects current time, then apply the new
// controls. timeScale is clamped to [1, 60]; validation of raw input happens in
// the route handler (400 on non-number / non-boolean).
export function applyTimeControls(input: SimControlsInput): Promise<schema.SimStateRow> {
  return withLock(async () => {
    const inst = await getGameDb();
    await tickOnce(inst);
    const sets: Partial<Pick<schema.SimStateRow, 'timeScale' | 'paused'>> = {};
    if (input.timeScale !== undefined) sets.timeScale = clampTimeScale(input.timeScale);
    if (input.paused !== undefined) sets.paused = input.paused;
    if (Object.keys(sets).length > 0) await inst.db.update(schema.simState).set(sets);
    await persist(inst);
    const updated = (await inst.db.select().from(schema.simState))[0];
    if (!updated) throw new Error('sim_state row missing');
    return updated;
  });
}

export function clampTimeScale(v: number): number {
  return Math.min(MAX_TIME_SCALE, Math.max(MIN_TIME_SCALE, v));
}