src/utils/fareCalculator.ts

/**
 * Offline fare estimation based on distance and vehicle type.
 *
 * Rates (INR):
 *   Bike: ₹10 base + ₹8/km
 *   Auto: ₹20 base + ₹12/km
 *   Car:  ₹30 base + ₹15/km
 *
 * The estimate returns a min/max range to account for traffic, route
 * variations, and surge considerations. The buffer is configurable via
 * FARE_ESTIMATE_BUFFER in constants.
 */
import type { VehicleType } from '../types/user';
import { VEHICLE_TYPES, FARE_ESTIMATE_BUFFER } from './constants';

export interface FareEstimate {
  min: number;
  max: number;
  baseFare: number;
  perKmRate: number;
  total: number;
}

/**
 * Calculate fare estimate for a given distance and vehicle type.
 *
 * @param distanceKm - Distance in kilometers
 * @param vehicleType - Vehicle type (bike, auto, car)
 * @returns Fare estimate with min/max range and breakdown
 */
export function estimateFare(
  distanceKm: number,
  vehicleType: VehicleType,
): FareEstimate {
  const vehicle = VEHICLE_TYPES.find((v) => v.type === vehicleType);

  if (!vehicle) {
    throw new Error(`Unknown vehicle type: ${vehicleType}`);
  }

  if (distanceKm <= 0) {
    return {
      min: vehicle.baseFare,
      max: vehicle.baseFare,
      baseFare: vehicle.baseFare,
      perKmRate: vehicle.perKmRate,
      total: vehicle.baseFare,
    };
  }

  const total = vehicle.baseFare + vehicle.perKmRate * distanceKm;
  const buffer = total * FARE_ESTIMATE_BUFFER;

  return {
    min: Math.round(total - buffer),
    max: Math.round(total + buffer),
    baseFare: vehicle.baseFare,
    perKmRate: vehicle.perKmRate,
    total: Math.round(total),
  };
}

/**
 * Calculate the fare per person when sharing a ride.
 *
 * @param totalFare - The total fare estimate
 * @param passengers - Number of passengers (minimum 1)
 * @returns Per-passenger fare
 */
export function farePerPerson(totalFare: number, passengers: number): number {
  const count = Math.max(1, passengers);
  return Math.ceil(totalFare / count);
}

/**
 * Format fare in Indian Rupees.
 *
 * @param amount - Amount in INR
 * @returns Formatted string like "₹125"
 */
export function formatFare(amount: number): string {
  return `₹${Math.round(amount)}`;
}

/**
 * Format fare range.
 *
 * @param min - Minimum amount
 * @param max - Maximum amount
 * @returns Formatted string like "₹100 - ₹130"
 */
export function formatFareRange(min: number, max: number): string {
  return `${formatFare(min)} - ${formatFare(max)}`;
}