polaris-task-force/src/lib/market/negotiations.ts

import type { MarketListing } from "@/payload-types";
import { notifyUser } from "@/lib/notifications";
import { negotiationRange } from "@/lib/market";
import { npcDialogue, type NpcDialogueKind } from "@/lib/market/npcDialogue";

export { npcDialogue, type NpcDialogueKind };

type PayloadType = Awaited<ReturnType<typeof import("payload").getPayload>>;

export const NPC_PATIENCE = {
  /** Patience gained every round the buyer keeps bargaining. */
  roundCost: 12,
  /** Extra patience burned when the offer is below the vendor's floor. */
  lowballPenalty: 25,
  /** Extra patience burned when the offer barely budges from the previous one. */
  stallPenalty: 35,
  /** An offer that moves less than this fraction of the asking price counts as a "stall". */
  stallRatio: 0.01,
  /** Patience relieved when the offer is close to the asking price. */
  goodOfferRelief: 9,
  /** An offer at or above this fraction of the asking price counts as "good". */
  goodOfferRatio: 0.85,
  /** When patience reaches this, the negotiation closes. */
  cap: 100,
} as const;

export const NPC_ACCEPT = {
  /** The vendor concedes this fraction of the gap toward the buyer's offer each round. */
  concedeRatio: 0.3,
  /** Offers within this fraction of the vendor's current stance may be accepted outright. */
  marginRatio: 0.02,
  /** Chance the vendor accepts an offer inside the margin. */
  chance: 0.85,
} as const;

export interface NpcState {
  /** The vendor's patience meter (0–100). */
  patience?: number;
  /** The vendor's most recent counteroffer (null before the first round). */
  lastCounter?: number | null;
  /** The buyer offer that drew lastCounter (null before the first round). */
  lastBuyerOffer?: number | null;
}

export type NpcAcceptReason = "accept" | "good" | "overpay";

export type NpcCounterReason = Exclude<NpcDialogueKind, "closed" | "accept" | "good" | "overpay">;

export type NpcResponse =
  | { action: "accept"; amount: number; reason: NpcAcceptReason }
  | {
      action: "counter";
      amount: number;
      patience: number;
      closed: boolean;
      reason: NpcCounterReason;
    };

/**
 * Auto-response of an NPC vendor to a buyer's offer.
 *
 * The vendor keeps a private "stance" price that starts at the asking price and
 * only ever moves down. Offers at/above the stance are accepted outright;
 * offers within a small margin of the stance are accepted with high chance
 * (`NPC_ACCEPT.chance`) and otherwise the vendor holds firm. Offers well below
 * the stance draw a concession — the stance moves a fraction of the gap toward
 * the buyer, but never rises past its previous counter, never drops below the
 * vendor's floor (`minPrice`), and the vendor holds firm if the buyer offers
 * *less* than their previous offer. Offers that barely budge from the buyer's
 * previous offer ("stalls", < 1% of the asking price) burn extra patience. The patience meter
 * advances with every round: lowballs burn a lot, reasonable offers cost a
 * little, and near-asking offers ease the vendor's mind. At the cap the
 * negotiation closes — the buyer can only buy at the asking price.
 */
export function npcResponseToOffer(
  listing: Pick<MarketListing, "price" | "desiredPrice" | "minPrice">,
  amount: number,
  state: NpcState = {},
  rng: () => number = Math.random,
): NpcResponse {
  const { min, desired } = negotiationRange(listing);
  const patience = state.patience ?? 0;
  const lastCounter = state.lastCounter ?? null;
  const lastBuyerOffer = state.lastBuyerOffer ?? null;

  const good = (n: number) =>
    n >= desired * NPC_PATIENCE.goodOfferRatio ? ("good" as const) : ("accept" as const);

  if (amount >= desired) {
    return { action: "accept", amount: desired, reason: amount > desired ? "overpay" : "good" };
  }

  const stance = lastCounter ?? desired;
  const margin = Math.round(stance * NPC_ACCEPT.marginRatio);
  const movedBackward = lastBuyerOffer != null && amount < lastBuyerOffer;
  const stall =
    lastBuyerOffer != null &&
    amount > lastBuyerOffer &&
    amount - lastBuyerOffer < desired * NPC_PATIENCE.stallRatio;

  if (amount >= stance)
    return { action: "accept", amount: Math.min(amount, desired), reason: good(amount) };
  if (amount >= stance - margin) {
    if (rng() < NPC_ACCEPT.chance) {
      return { action: "accept", amount: Math.min(amount, desired), reason: good(amount) };
    }
    // Declined inside the margin: hold firm at the current stance.
    const nextPatience = advancePatience(patience, amount, min, desired, lastBuyerOffer);
    return {
      action: "counter",
      amount: stance,
      patience: nextPatience,
      closed: nextPatience >= NPC_PATIENCE.cap,
      reason: stall ? "stall" : "firm",
    };
  }

  const counter = movedBackward
    ? stance
    : Math.max(amount, min, Math.round(stance - (stance - amount) * NPC_ACCEPT.concedeRatio));

  const nextPatience = advancePatience(patience, amount, min, desired, lastBuyerOffer);
  return {
    action: "counter",
    amount: counter,
    patience: nextPatience,
    closed: nextPatience >= NPC_PATIENCE.cap,
    reason: movedBackward ? "backward" : stall ? "stall" : amount < min ? "lowball" : "concede",
  };
}

function advancePatience(
  patience: number,
  amount: number,
  min: number,
  desired: number,
  previous: number | null,
): number {
  let delta: number;
  if (
    previous != null &&
    amount > previous &&
    amount - previous < desired * NPC_PATIENCE.stallRatio
  ) {
    delta = NPC_PATIENCE.roundCost + NPC_PATIENCE.stallPenalty;
  } else if (amount < min) {
    delta = NPC_PATIENCE.roundCost + NPC_PATIENCE.lowballPenalty;
  } else if (amount >= desired * NPC_PATIENCE.goodOfferRatio) {
    delta = -NPC_PATIENCE.goodOfferRelief;
  } else {
    delta = NPC_PATIENCE.roundCost;
  }
  return Math.max(0, Math.min(NPC_PATIENCE.cap, patience + delta));
}

export interface ExpireOptions {
  /** Reason shown in the buyer notification. */
  reason?: string;
}

/**
 * Close every open negotiation thread on a listing (e.g. when it is sold or
 * expired) and notify each interested buyer.
 */
export async function expireNegotiationsForListing(
  payload: PayloadType,
  listingId: number,
  listingName: string,
  options?: ExpireOptions,
): Promise<void> {
  const open = await payload.find({
    collection: "market-negotiations",
    where: { and: [{ listing: { equals: listingId } }, { status: { equals: "open" } }] },
    limit: 100,
    depth: 1,
    overrideAccess: true,
  });

  const reason = options?.reason ?? "was sold";

  for (const negotiation of open.docs) {
    await payload.update({
      collection: "market-negotiations",
      id: negotiation.id,
      data: { status: "expired" },
      overrideAccess: true,
      depth: 0,
    });

    const buyerId =
      typeof negotiation.buyer === "object" && negotiation.buyer
        ? negotiation.buyer.id
        : (negotiation.buyer as number | null);

    if (buyerId != null) {
      await notifyUser(payload, {
        userId: buyerId,
        type: "market:expired",
        title: "Negotiation closed",
        message: `${listingName} ${reason} before you could close the deal.`,
        link: "/logistics/market",
      });
    }
  }
}