/**
 * Customer-facing post-purchase features: self-reschedule eligibility and reminders.
 */
import type { Booking, ReminderPolicy, ShopSettings } from "./types";
import { zonedToUtc } from "./time";

export function slotStartMs(b: Booking): number {
  return zonedToUtc(b.date, b.slotStart ?? "00:00", b.timezone);
}

export function canCustomerReschedule(
  b: Booking,
  policy: ShopSettings["reschedule"],
  now: number,
): { ok: true; deadline: number } | { ok: false; reason: string } {
  if (!policy.enabled) return { ok: false, reason: "Rescheduling isn't available for this store. Please contact us." };
  if (b.status !== "confirmed") return { ok: false, reason: "This booking can't be changed." };
  if ((b.rescheduleCount ?? 0) >= policy.maxChanges)
    return { ok: false, reason: `You've already changed this booking ${policy.maxChanges} time(s). Please contact us.` };
  const deadline = slotStartMs(b) - policy.minHoursBefore * 3600000;
  if (now >= deadline)
    return { ok: false, reason: `Changes are allowed up to ${policy.minHoursBefore} hours before your time slot.` };
  return { ok: true, deadline };
}

export interface PlannedReminder {
  policyId: string;
  channel: ReminderPolicy["channel"];
  sendAt: number;
  body: string;
}

export function planReminders(
  b: Booking,
  policies: ReminderPolicy[],
  now: number,
  vars: Record<string, string> = {},
): PlannedReminder[] {
  const start = slotStartMs(b);
  return policies
    .filter((p) => p.enabled && (!p.methods?.length || p.methods.includes(b.method)))
    .map((p) => ({
      policyId: p.id,
      channel: p.channel,
      sendAt: start - p.minutesBefore * 60000,
      body: renderTemplate(p.template, {
        name: b.customer?.name ?? "there",
        order: b.orderName ?? "",
        date: b.date,
        time: b.slotStart && b.slotEnd ? `${b.slotStart}–${b.slotEnd}` : "",
        method: b.method,
        ...vars,
      }),
    }))
    .filter((r) => r.sendAt > now)
    .filter((r) => {
      // Respect channel requirements.
      if (r.channel === "email") return !!b.customer?.email;
      return !!b.customer?.phone;
    });
}

/** {{var}} substitution; unknown vars render empty. */
export function renderTemplate(tpl: string, vars: Record<string, string>): string {
  return tpl.replace(/\{\{\s*(\w+)\s*\}\}/g, (_, k) => vars[k] ?? "");
}