metatrondelivery/app/services/rates.server.ts

import type { Method } from "@prisma/client";

// Pure rate resolution — no DB calls (CLAUDE.md: inject data). The caller
// (apps.scheduling.availability.tsx) fetches the shop's Rate rows for the
// method and passes them in here.

export interface RateLike {
  id: string;
  method: Method;
  zoneId: string | null;
  name: string;
  priceCents: number;
  keyedBy: string; // "zone" | "distance"
  minDistanceKm: number | null;
  maxDistanceKm: number | null;
}

export interface RateContext {
  method: Method;
  zoneId?: string;
  distanceKm?: number;
}

/**
 * Picks the rate that applies to a given method/zone/distance. Zone-keyed
 * rates are matched by exact zoneId; distance-keyed rates by falling within
 * [minDistanceKm, maxDistanceKm) (open-ended bounds are unbounded on that
 * side). When more than one rate matches, the cheapest wins — a merchant
 * with overlapping bands almost certainly wants the shopper quoted the best
 * available price, not an arbitrary one.
 */
export function resolveRate(rates: RateLike[], context: RateContext): RateLike | null {
  const candidates = rates.filter((rate) => {
    if (rate.method !== context.method) return false;

    if (rate.keyedBy === "zone") {
      return context.zoneId !== undefined && rate.zoneId === context.zoneId;
    }

    if (rate.keyedBy === "distance") {
      if (context.distanceKm === undefined) return false;
      const min = rate.minDistanceKm ?? 0;
      const max = rate.maxDistanceKm ?? Infinity;
      return context.distanceKm >= min && context.distanceKm < max;
    }

    return false;
  });

  if (candidates.length === 0) return null;

  return candidates.reduce((cheapest, candidate) => (candidate.priceCents < cheapest.priceCents ? candidate : cheapest));
}

// formatPriceLabel moved to app/lib/currency.ts (2026-08-24): it's pure/
// no-I/O, but a route *component* needs it (app.rates._index.tsx), and
// Remix refuses to bundle anything imported from a .server.ts path for the
// client — import it from lib/currency directly, not re-exported here.