/**
 * Zustandsuebergaenge fuer Zahlungen.
 *
 * Grundsaetze:
 * - Jede Funktion laeuft in einer Transaktion und sperrt zuerst die
 *   Buchungszeile. Doppelte, verspaetete oder ungeordnete Stripe-Events
 *   treffen dadurch immer auf einen konsistenten Stand.
 * - Uebergaenge sind monoton: Eine bezahlte Rate wird nie wieder offen, ein
 *   spaetes "expired" hebt keine bezahlte Buchung auf.
 * - Buchungsstatus (BookingStatus) und Zahlungsstatus (PaymentStatus) sind
 *   getrennt; eine bezahlte erste Rate heisst bei Ratenzahlung PARTIALLY_PAID.
 * - Was nicht automatisch sicher entschieden werden kann (verspaetete Zahlung
 *   ohne freien Platz, Doppelzahlung, Rueckbuchung), landet als
 *   NEEDS_REVIEW mit Begruendung im Adminbereich — nie still verworfen.
 */
import type { Booking, Installment, PaymentStatus } from "@/generated/prisma/client";
import { audit, type Actor } from "./audit";
import { countOccupiedSeats, lockBooking, lockCamp, releaseBookingHold } from "./booking-service";
import { getCamp } from "./camp";
import type { Tx } from "./db";
import { enqueueEmail } from "./email";
import {
  adminReviewEmail,
  bookingConfirmedEmail,
  installmentActionEmail,
  installmentPaidEmail,
  paymentFailedEmail,
  paymentProcessingEmail,
  reviewCustomerEmail,
} from "./email-templates";
import { statusTokenFor } from "./tokens";
import { countUsedRedemptions } from "./vouchers";

export type EventContext = { now: Date; secret: string; actor: Actor; adminEmail: string | null };

export type PaymentInfo = {
  paymentIntentId: string;
  chargeId: string | null;
  paymentMethodId: string | null;
  customerId: string | null;
  amountCents: number;
};

type FullBooking = Booking & { installments: Installment[] };

async function loadLocked(tx: Tx, bookingId: string) {
  await lockBooking(tx, bookingId);
  return tx.booking.findUniqueOrThrow({
    where: { id: bookingId },
    include: { installments: { orderBy: { seq: "asc" } }, reservation: true, redemption: true },
  });
}

function paymentStatusFor(paidCents: number, totalCents: number, refundedCents: number): PaymentStatus {
  if (refundedCents > 0) return refundedCents >= paidCents ? "REFUNDED" : "PARTIALLY_REFUNDED";
  if (paidCents <= 0) return "UNPAID";
  return paidCents >= totalCents ? "PAID" : "PARTIALLY_PAID";
}

async function flagForReview(tx: Tx, booking: Booking, reason: string, ctx: EventContext): Promise<void> {
  await tx.booking.update({ where: { id: booking.id }, data: { status: "NEEDS_REVIEW", reviewReason: reason } });
  await audit(tx, ctx.actor, "booking.needs_review", "Booking", booking.id, { reason });
  if (ctx.adminEmail) await enqueueEmail(tx, adminReviewEmail(ctx.adminEmail, booking, reason));
}

/** Fuer Probleme, die ausserhalb eines Zahlungsereignisses auffallen (z. B. Ratenplan bei Stripe). */
export async function flagBookingForReview(tx: Tx, bookingId: string, reason: string, ctx: EventContext): Promise<void> {
  await flagForReview(tx, await loadLocked(tx, bookingId), reason, ctx);
}

export type FirstPaymentOutcome = "confirmed" | "duplicate" | "needs_review";

/** Erste Rate (bzw. Einmalzahlung) ist bei Stripe erfolgreich eingegangen. */
export async function applyFirstPaymentSucceeded(
  tx: Tx,
  bookingId: string,
  info: PaymentInfo,
  ctx: EventContext,
): Promise<FirstPaymentOutcome> {
  const booking = await loadLocked(tx, bookingId);
  const first = booking.installments.find((i) => i.seq === 1)!;

  if (first.status === "PAID") {
    if (first.stripePaymentIntentId && first.stripePaymentIntentId !== info.paymentIntentId) {
      await flagForReview(tx, booking, "Doppelzahlung der ersten Rate – bitte eine Zahlung erstatten.", ctx);
      return "needs_review";
    }
    return "duplicate";
  }

  const problems: string[] = [];
  if (info.amountCents !== first.amountCents) {
    problems.push(`Betrag weicht ab (erwartet ${first.amountCents}, erhalten ${info.amountCents} Cent).`);
  }

  // Platz: normalerweise noch reserviert. Wurde er inzwischen freigegeben
  // (Zahlung kam nach Ablauf an), wird er nur uebernommen, wenn noch frei.
  const reservation = booking.reservation!;
  if (reservation.status === "ACTIVE" || reservation.status === "HELD") {
    await tx.seatReservation.update({ where: { id: reservation.id }, data: { status: "CONVERTED" } });
  } else if (reservation.status === "RELEASED") {
    await lockCamp(tx);
    const camp = await getCamp(tx);
    const occupied = await countOccupiedSeats(tx, booking.livemode, ctx.now);
    if (occupied < camp.capacity) {
      await tx.seatReservation.update({
        where: { id: reservation.id },
        data: { status: "CONVERTED", releasedAt: null, releaseReason: null },
      });
      await audit(tx, ctx.actor, "seat.reacquired_after_late_payment", "Booking", booking.id, { occupiedBefore: occupied });
    } else {
      problems.push("Zahlung nach Ablauf der Reservierung eingegangen, inzwischen ist kein Platz mehr frei.");
    }
  }

  const redemption = booking.redemption;
  if (redemption?.status === "RESERVED") {
    await tx.voucherRedemption.update({ where: { id: redemption.id }, data: { status: "COMPLETED" } });
  } else if (redemption?.status === "RELEASED") {
    await tx.$queryRaw`SELECT "id" FROM "Voucher" WHERE "id" = ${redemption.voucherId} FOR UPDATE`;
    const [voucher, camp] = await Promise.all([
      tx.voucher.findUniqueOrThrow({ where: { id: redemption.voucherId } }),
      getCamp(tx),
    ]);
    const used = await countUsedRedemptions(tx, { livemode: booking.livemode, now: ctx.now, voucherId: voucher.id });
    const quotaUsed = await countUsedRedemptions(tx, { livemode: booking.livemode, now: ctx.now });
    if (used < voucher.maxRedemptions && quotaUsed < camp.stammmodelQuota) {
      await tx.voucherRedemption.update({ where: { id: redemption.id }, data: { status: "COMPLETED", releasedAt: null } });
    } else {
      problems.push("Gutscheincode war bei verspäteter Zahlung nicht mehr verfügbar.");
    }
  }

  await tx.installment.update({
    where: { id: first.id },
    data: {
      status: "PAID",
      paidAt: ctx.now,
      stripePaymentIntentId: info.paymentIntentId,
      stripeChargeId: info.chargeId,
    },
  });

  const paidCents = booking.paidCents + info.amountCents;
  const updated = await tx.booking.update({
    where: { id: booking.id },
    data: {
      status: problems.length > 0 ? "NEEDS_REVIEW" : "CONFIRMED",
      reviewReason: problems.length > 0 ? problems.join(" ") : null,
      paymentStatus: paymentStatusFor(paidCents, booking.totalCents, booking.refundedCents),
      paidCents,
      confirmedAt: problems.length > 0 ? null : ctx.now,
      stripeCustomerId: info.customerId ?? booking.stripeCustomerId,
      // Nur bei Ratenzahlung gespeichert; bei Einmalzahlung gibt es nichts
      // wiederzuverwenden.
      stripePaymentMethodId: booking.planType === "FULL" ? null : info.paymentMethodId,
    },
    include: { installments: { orderBy: { seq: "asc" } } },
  });

  await audit(tx, ctx.actor, "payment.first_succeeded", "Booking", booking.id, {
    paymentIntentId: info.paymentIntentId,
    amountCents: info.amountCents,
    paidCents,
    previousStatus: booking.status,
    problems,
  });

  const token = statusTokenFor(booking.id, ctx.secret);
  if (problems.length > 0) {
    if (ctx.adminEmail) await enqueueEmail(tx, adminReviewEmail(ctx.adminEmail, updated, problems.join(" ")));
    await enqueueEmail(tx, reviewCustomerEmail(updated, token));
    return "needs_review";
  }
  await enqueueEmail(tx, bookingConfirmedEmail(updated, token));
  return "confirmed";
}

/** Checkout abgeschlossen, Zahlung aber noch unterwegs (z. B. SEPA-Lastschrift). */
export async function applyFirstPaymentProcessing(
  tx: Tx,
  bookingId: string,
  info: { paymentIntentId: string | null; customerId: string | null },
  ctx: EventContext,
): Promise<"processing" | "ignored"> {
  const booking = await loadLocked(tx, bookingId);
  const first = booking.installments.find((i) => i.seq === 1)!;
  if (booking.status !== "PENDING" || first.status !== "PENDING") return "ignored";

  await tx.seatReservation.updateMany({ where: { bookingId, status: "ACTIVE" }, data: { status: "HELD" } });
  await tx.installment.update({
    where: { id: first.id },
    data: { status: "PROCESSING", stripePaymentIntentId: info.paymentIntentId },
  });
  const updated = await tx.booking.update({
    where: { id: bookingId },
    data: { paymentStatus: "PROCESSING", stripeCustomerId: info.customerId ?? booking.stripeCustomerId },
  });
  await audit(tx, ctx.actor, "payment.first_processing", "Booking", bookingId, { paymentIntentId: info.paymentIntentId });
  await enqueueEmail(tx, paymentProcessingEmail(updated, statusTokenFor(bookingId, ctx.secret)));
  return "processing";
}

/** Verzoegerte erste Zahlung endgueltig fehlgeschlagen: Platz freigeben. */
export async function applyFirstPaymentFailed(tx: Tx, bookingId: string, ctx: EventContext): Promise<"failed" | "ignored"> {
  const booking = await loadLocked(tx, bookingId);
  const first = booking.installments.find((i) => i.seq === 1)!;
  if (first.status === "PAID" || booking.status === "CANCELED") return "ignored";

  await tx.installment.update({ where: { id: first.id }, data: { status: "FAILED", failureCode: "async_payment_failed" } });
  await releaseBookingHold(tx, bookingId, { status: "EXPIRED", reason: "payment_failed", now: ctx.now });
  const updated = await tx.booking.update({ where: { id: bookingId }, data: { paymentStatus: "FAILED" } });
  await audit(tx, ctx.actor, "payment.first_failed", "Booking", bookingId);
  await enqueueEmail(tx, paymentFailedEmail(updated));
  return "failed";
}

/** Checkout-Session abgelaufen oder abgebrochen: nur unbezahlte Buchungen freigeben. */
export async function applyCheckoutExpired(
  tx: Tx,
  bookingId: string,
  sessionId: string | null,
  ctx: EventContext & { reason?: string },
): Promise<"released" | "ignored"> {
  const booking = await loadLocked(tx, bookingId);
  if (sessionId && booking.stripeCheckoutSessionId && booking.stripeCheckoutSessionId !== sessionId) return "ignored";
  if (booking.status !== "PENDING" || booking.paymentStatus !== "UNPAID") return "ignored";
  await releaseBookingHold(tx, bookingId, { status: "EXPIRED", reason: ctx.reason ?? "checkout_expired", now: ctx.now });
  await audit(tx, ctx.actor, "booking.expired", "Booking", bookingId, { sessionId, reason: ctx.reason ?? "checkout_expired" });
  return "released";
}

export type InstallmentPaidOutcome = { outcome: "paid" | "duplicate" | "needs_review"; fullyPaid: boolean };

/** Folgerate bezahlt (ueber ihre Stripe-Rechnung, siehe applyInstallmentInvoicePaid). */
export async function applyInstallmentPaid(
  tx: Tx,
  installmentId: string,
  info: PaymentInfo,
  ctx: EventContext,
): Promise<InstallmentPaidOutcome> {
  const target = await tx.installment.findUniqueOrThrow({ where: { id: installmentId } });
  const booking = await loadLocked(tx, target.bookingId);
  const installment = booking.installments.find((i) => i.id === installmentId)!;

  if (installment.status === "PAID") {
    if (installment.stripePaymentIntentId !== info.paymentIntentId) {
      await flagForReview(tx, booking, `Rate ${installment.seq} wurde doppelt bezahlt – bitte eine Zahlung erstatten.`, ctx);
      return { outcome: "needs_review", fullyPaid: booking.paidCents >= booking.totalCents };
    }
    return { outcome: "duplicate", fullyPaid: booking.paidCents >= booking.totalCents };
  }

  const paidCents = booking.paidCents + info.amountCents;
  await tx.installment.update({
    where: { id: installmentId },
    data: {
      status: "PAID",
      paidAt: ctx.now,
      stripePaymentIntentId: info.paymentIntentId,
      stripeChargeId: info.chargeId,
      nextAttemptAt: null,
      failureCode: null,
    },
  });
  const updated = await tx.booking.update({
    where: { id: booking.id },
    data: {
      paidCents,
      paymentStatus: paymentStatusFor(paidCents, booking.totalCents, booking.refundedCents),
      ...(info.paymentMethodId && booking.planType !== "FULL" && !booking.paymentMethodDetachedAt
        ? { stripePaymentMethodId: info.paymentMethodId }
        : {}),
    },
    include: { installments: { orderBy: { seq: "asc" } } },
  });
  await audit(tx, ctx.actor, "payment.installment_succeeded", "Installment", installmentId, {
    bookingId: booking.id,
    seq: installment.seq,
    paymentIntentId: info.paymentIntentId,
    amountCents: info.amountCents,
    paidCents,
  });

  const problems: string[] = [];
  if (info.amountCents !== installment.amountCents) problems.push(`Betrag von Rate ${installment.seq} weicht ab.`);
  if (installment.status === "CANCELED" || booking.status === "CANCELED") problems.push(`Rate ${installment.seq} ging nach Stornierung ein.`);
  if (paidCents > booking.totalCents) problems.push("Es wurde mehr als der Gesamtpreis gezahlt.");
  if (problems.length > 0) {
    await flagForReview(tx, updated, problems.join(" "), ctx);
    return { outcome: "needs_review", fullyPaid: paidCents >= booking.totalCents };
  }

  await enqueueEmail(tx, installmentPaidEmail(updated, { ...installment, status: "PAID" }, statusTokenFor(booking.id, ctx.secret)));
  return { outcome: "paid", fullyPaid: paidCents >= booking.totalCents };
}

/**
 * Ordnet eine Rechnung des Stripe-Zeitplans ihrer Folgerate zu. Stripe
 * erzeugt die Rechnungen nacheinander (die naechste erst im naechsten
 * Abrechnungszeitraum), deshalb gehoert eine neue Rechnung zur ersten noch
 * nicht verknuepften, unbezahlten Rate.
 */
async function installmentForInvoice(tx: Tx, booking: FullBooking, invoiceId: string): Promise<Installment | null> {
  const linked = booking.installments.find((i) => i.stripeInvoiceId === invoiceId);
  if (linked) return linked;
  const next = booking.installments.find((i) => i.seq > 1 && !i.stripeInvoiceId && i.status !== "PAID");
  if (!next) return null;
  return tx.installment.update({ where: { id: next.id }, data: { stripeInvoiceId: invoiceId } });
}

/** Stripe Billing hat eine Folgerate eingezogen (automatisch oder von der Kundin ueber die Rechnungsseite bezahlt). */
export async function applyInstallmentInvoicePaid(
  tx: Tx,
  bookingId: string,
  invoiceId: string,
  info: PaymentInfo,
  ctx: EventContext,
): Promise<InstallmentPaidOutcome | "unmatched"> {
  const booking = await loadLocked(tx, bookingId);
  const installment = await installmentForInvoice(tx, booking, invoiceId);
  if (!installment) {
    await flagForReview(tx, booking, `Zahlung über Rechnung ${invoiceId} passt zu keiner offenen Rate – bitte prüfen und ggf. erstatten.`, ctx);
    return "unmatched";
  }
  return applyInstallmentPaid(tx, installment.id, info, ctx);
}

/**
 * Stripe konnte eine Folgerate nicht einziehen. Stripe versucht es selbst
 * erneut (Smart Retries) und schickt bei verlangter Bestaetigung (3-D
 * Secure) einen Link. Hier wird nur der Stand festgehalten, die Kundin
 * informiert und — wenn Stripe aufgibt — ein Mensch eingeschaltet.
 */
export async function applyInstallmentInvoiceFailed(
  tx: Tx,
  bookingId: string,
  invoice: { id: string; attemptCount: number; nextPaymentAttempt: Date | null },
  info: { requiresAction: boolean },
  ctx: EventContext,
): Promise<"recorded" | "ignored"> {
  const booking = await loadLocked(tx, bookingId);
  const installment = await installmentForInvoice(tx, booking, invoice.id);
  if (!installment || installment.status === "PAID" || installment.status === "CANCELED") return "ignored";

  const status = info.requiresAction ? "REQUIRES_ACTION" : "FAILED";
  // Dasselbe Ergebnis desselben Versuchs (doppelt zugestellt oder als
  // payment_failed UND payment_action_required gemeldet) nur einmal zaehlen.
  if (installment.attemptCount >= invoice.attemptCount && installment.status === status) return "ignored";

  const updatedInstallment = await tx.installment.update({
    where: { id: installment.id },
    data: {
      status,
      attemptCount: Math.max(invoice.attemptCount, installment.attemptCount),
      lastAttemptAt: ctx.now,
      failureCode: info.requiresAction ? "authentication_required" : "payment_failed",
      nextAttemptAt: invoice.nextPaymentAttempt,
    },
  });
  await audit(tx, ctx.actor, "payment.installment_failed", "Installment", installment.id, {
    bookingId: booking.id,
    seq: installment.seq,
    invoiceId: invoice.id,
    attempt: invoice.attemptCount,
    requiresAction: info.requiresAction,
    nextAttemptAt: invoice.nextPaymentAttempt?.toISOString() ?? null,
  });
  await enqueueEmail(
    tx,
    installmentActionEmail(booking, updatedInstallment, statusTokenFor(booking.id, ctx.secret), info.requiresAction),
  );
  if (!info.requiresAction && !invoice.nextPaymentAttempt) {
    await flagForReview(tx, booking, `Rate ${installment.seq} ist nach ${invoice.attemptCount} Versuchen nicht eingegangen.`, ctx);
  }
  return "recorded";
}

/**
 * Erstattungsstand einer Zahlung. Stripe liefert den kumulierten Betrag
 * (amount_refunded) — absolute Werte machen ungeordnete Events harmlos.
 */
export async function applyRefundState(
  tx: Tx,
  params: { paymentIntentId: string; amountRefundedCents: number },
  ctx: EventContext,
): Promise<"updated" | "ignored"> {
  const target = await tx.installment.findUnique({ where: { stripePaymentIntentId: params.paymentIntentId } });
  if (!target) return "ignored";
  const booking = await loadLocked(tx, target.bookingId);
  await tx.installment.update({ where: { id: target.id }, data: { refundedCents: params.amountRefundedCents } });
  const refundedCents = booking.installments.reduce(
    (sum, i) => sum + (i.id === target.id ? params.amountRefundedCents : i.refundedCents),
    0,
  );
  await tx.booking.update({
    where: { id: booking.id },
    data: { refundedCents, paymentStatus: paymentStatusFor(booking.paidCents, booking.totalCents, refundedCents) },
  });
  await audit(tx, ctx.actor, "payment.refund_state", "Booking", booking.id, {
    paymentIntentId: params.paymentIntentId,
    installmentRefundedCents: params.amountRefundedCents,
    bookingRefundedCents: refundedCents,
  });
  return "updated";
}

export async function applyDispute(tx: Tx, paymentIntentId: string, ctx: EventContext): Promise<"flagged" | "ignored"> {
  const target = await tx.installment.findUnique({ where: { stripePaymentIntentId: paymentIntentId } });
  if (!target) return "ignored";
  const booking = await loadLocked(tx, target.bookingId);
  await flagForReview(tx, booking, `Rückbuchung (Dispute) zu Rate ${target.seq} eröffnet.`, ctx);
  return "flagged";
}

export type { FullBooking };