drive-between-the-lines/src/sim/garage.ts

/**
 * The cars you can be driving, and which of them you own. Pure — no engine
 * imports.
 *
 * This is the loop's central decision, and it exists because the old one had
 * none. Condition used to be health, capability, currency sink and fail state
 * all at once, so every event pushed the same way: damage made the car slower
 * and harder to hold straight, which made it worse at earning, which meant
 * fewer repairs, which meant more damage. A spiral with no negative term in it
 * anywhere, and no decision inside it either.
 *
 * A garage breaks that apart. Damage is now a *sortie* resource — you are
 * patched up when you get home — and money buys **cars**, permanently. So
 * progress climbs while any given drive still declines.
 *
 * The choice itself is the point, and the axis is not capability. It is
 * whether the vehicle *belongs here*:
 *
 *   A lorry is huge and tough and nobody looks twice, because lorries exist.
 *   A sports car is quick and flimsy and everybody looks, because who drives
 *   that, here, now.
 *
 * So the civilian half of the catalogue — runabout, tractor, estate, lorry —
 * stays quiet however capable it gets, and you pay for protection and speed in
 * money and in handling rather than in attention. The military half buys you
 * out of that at a price nothing else charges.
 *
 * There is deliberately no best car, and it is checked rather than asserted:
 * no vehicle may beat another on speed, protection, discretion *and* handling
 * at once. A quiet errand down cold roads wants the thing nobody reports; a run
 * into a district that already knows your face wants the thing that survives
 * what happens next. Picking wrong is supposed to be how you lose.
 */

export interface CarSpec {
  id: string;
  name: string;
  /** One line, in the words somebody handing you the keys would use. */
  blurb: string;
  /** What it costs to put one in the garage. The first is free. */
  cost: number;

  // --- How it drives ---
  /** Kilograms. Heavier shrugs off shunts and takes far longer to stop. */
  mass: number;
  /** Newtons per driven wheel at full throttle, in good condition. */
  engineForce: number;
  /** Braking impulse per wheel, in good condition. */
  brakeForce: number;
  /** Steering lock in radians, in good condition. Big things turn like barges. */
  maxSteer: number;
  /** Tyre grip, in good condition. Lower slides. */
  grip: number;

  // --- What it costs you ---
  /**
   * Share of incoming damage the car actually takes. Armour is this number.
   * Above 1 is worse than bare metal; 0.22 is something built to be shot at.
   */
  fragility: number;
  /**
   * How much attention it draws, as a multiplier on how fast anyone watching
   * makes their mind up about you.
   *
   * Deliberately *not* correlated with how good the vehicle is. An ordinary
   * thing doing an ordinary thing is invisible whatever its specification; the
   * two that cost you here are the one nobody in this country drives and the
   * one with a gun mount.
   */
  presence: number;

  // --- What it looks like ---
  colour: number;
  /** Scale on the body mesh, so a lorry reads as a lorry from the mirror. */
  size: { width: number; height: number; length: number };
}

/** The catalogue, cheapest first. */
export const CARS: CarSpec[] = [
  {
    id: 'runabout',
    name: 'Small runabout',
    blurb: 'Somebody’s second car. Slow, tinny, and completely unremarkable.',
    cost: 0,
    mass: 950,
    engineForce: 1900,
    brakeForce: 30,
    maxSteer: 0.64,
    grip: 4.6,
    fragility: 1.3,
    presence: 0.5,
    colour: 0x9aa2a8,
    size: { width: 0.9, height: 0.88, length: 0.86 },
  },
  {
    id: 'tractor',
    name: 'Field tractor',
    blurb: 'Barely faster than walking, built out of girders, part of the scenery.',
    cost: 220,
    mass: 1600,
    engineForce: 1300,
    brakeForce: 24,
    maxSteer: 0.7,
    grip: 3.4,
    fragility: 0.8,
    presence: 0.45,
    colour: 0x6a7042,
    size: { width: 1.02, height: 1.24, length: 0.9 },
  },
  {
    id: 'estate',
    name: 'Large estate',
    blurb: 'A family car with some weight to it. Quick enough, dull enough.',
    cost: 520,
    mass: 1350,
    engineForce: 3000,
    brakeForce: 33,
    maxSteer: 0.56,
    grip: 4.5,
    fragility: 0.85,
    presence: 0.7,
    colour: 0x7c8378,
    size: { width: 1.02, height: 1, length: 1.12 },
  },
  {
    id: 'lorry',
    name: 'Lorry',
    blurb: 'Three tonnes of cab and flatbed. Steers like a barge, stops like one.',
    cost: 950,
    mass: 3200,
    engineForce: 4200,
    brakeForce: 26,
    maxSteer: 0.38,
    grip: 3.8,
    fragility: 0.5,
    presence: 0.8,
    colour: 0x4f6068,
    size: { width: 1.16, height: 1.34, length: 1.5 },
  },
  {
    id: 'sports',
    name: 'Sports coupe',
    blurb: 'Nothing here goes this fast. That is the problem with it.',
    cost: 1500,
    mass: 1000,
    engineForce: 5200,
    brakeForce: 42,
    maxSteer: 0.6,
    grip: 5.8,
    fragility: 1.35,
    presence: 2.4,
    colour: 0xb03a2e,
    size: { width: 1, height: 0.8, length: 1.06 },
  },
  {
    id: 'apc',
    name: 'Armoured carrier',
    blurb: 'Nothing short of a tower will stop it. Everybody phones it in.',
    cost: 2600,
    mass: 4000,
    engineForce: 3000,
    brakeForce: 28,
    maxSteer: 0.34,
    grip: 3.6,
    fragility: 0.22,
    presence: 3.8,
    colour: 0x4d5348,
    size: { width: 1.2, height: 1.32, length: 1.22 },
  },
];

/** The four ways a vehicle can be good, for the no-dominance check. */
export const virtues = (c: CarSpec) => ({
  /** Acceleration, which is what actually gets you away. */
  speed: c.engineForce / c.mass,
  protection: 1 / c.fragility,
  discretion: 1 / c.presence,
  /** Lock times grip: how well it will actually take a junction. */
  handling: c.maxSteer * c.grip,
});

export const carById = (id: string): CarSpec => CARS.find((c) => c.id === id) ?? CARS[0]!;

export interface GarageState {
  /** Ids of every car in the garage. The first one is always there. */
  owned: string[];
  /** What is being driven right now. */
  driving: string;
}

export const createGarage = (): GarageState => ({
  owned: [CARS[0]!.id],
  driving: CARS[0]!.id,
});

export const owns = (garage: GarageState, id: string): boolean => garage.owned.includes(id);

export const current = (garage: GarageState): CarSpec => carById(garage.driving);

/**
 * Buys a car, if it is not already owned and the money is there.
 * Returns what is left. Money is only ever spent here.
 */
export function buy(
  garage: GarageState,
  id: string,
  funds: number,
): { bought: boolean; funds: number } {
  const spec = CARS.find((c) => c.id === id);
  if (!spec || owns(garage, id) || funds < spec.cost) return { bought: false, funds };
  garage.owned.push(id);
  return { bought: true, funds: funds - spec.cost };
}

/** Takes a different car out. Only ones you own, and only at a base. */
export function take(garage: GarageState, id: string): boolean {
  if (!owns(garage, id)) return false;
  garage.driving = id;
  return true;
}

/**
 * The next thing worth saving for: cheapest car not yet owned.
 * Null once the garage is complete.
 */
export const nextUnlock = (garage: GarageState): CarSpec | null =>
  CARS.find((c) => !owns(garage, c.id)) ?? null;