import { PrismaClient, Prisma } from "@prisma/client";
import { fromZonedTime, toZonedTime } from "date-fns-tz";

const DAY_MS = 24 * 60 * 60 * 1000;

export type PaymentSchedule = {
  frequency: "monthly" | "weekly" | "biweekly" | "daily" | "custom";
  dayOfMonth?: number;      // For monthly (1-31)
  dayOfWeek?: number;       // For weekly/biweekly (0=Sunday, 6=Saturday)
  everyNDays?: number;      // For custom cadence (fallback to periodDays)
  minFundingPercent: number; // 0-100, minimum funding required before auto-pay
};

export type AutoPaymentReport = {
  planId: string;
  userId: string;
  name: string;
  paymentAmountCents: number;
  success: boolean;
  error?: string;
  retryCount: number;
  nextRetryDate?: string;
};

const isProd = process.env.NODE_ENV === "production";

/**
 * Check if auto-payment should run for a user based on their timezone
 * Auto-payment runs at 9 AM in the user's timezone
 */
function shouldProcessPaymentForUser(userTimezone: string, asOf: Date): boolean {
  const zonedTime = toZonedTime(asOf, userTimezone);
  const hour = zonedTime.getHours();
  // Process if we're past 9 AM in user's timezone
  return hour >= 9;
}

/**
 * Process auto-scheduled payments for fixed plans
 */
export async function processAutoPayments(
  prisma: PrismaClient,
  asOfInput?: Date | string,
  { dryRun = false }: { dryRun?: boolean } = {}
): Promise<AutoPaymentReport[]> {
  const asOf = asOfInput ? new Date(asOfInput) : new Date();
  
  // Find plans with auto-payments enabled and due for payment
  const candidates = await prisma.fixedPlan.findMany({
    where: {
      autoPayEnabled: true,
      nextPaymentDate: { lte: asOf },
      paymentSchedule: { not: Prisma.DbNull },
    },
    orderBy: { nextPaymentDate: "asc" },
    select: {
      id: true,
      userId: true,
      name: true,
      totalCents: true,
      fundedCents: true,
      currentFundedCents: true,
      paymentSchedule: true,
      nextPaymentDate: true,
      lastAutoPayment: true,
      maxRetryAttempts: true,
      periodDays: true,
      user: {
        select: {
          timezone: true,
        },
      },
    },
  });

  const reports: AutoPaymentReport[] = [];

  for (const plan of candidates) {
    // Check if it's time for auto-payment in this user's timezone
    const userTimezone = plan.user.timezone ?? "America/New_York";
    if (!shouldProcessPaymentForUser(userTimezone, asOf)) {
      if (!isProd) {
        console.log(
          `[auto-payment] Skipping plan ${plan.id} for user ${plan.userId} - not yet 9 AM in ${userTimezone}`
        );
      }
      continue;
    }
    
    const schedule = plan.paymentSchedule as PaymentSchedule | null;
    if (!schedule) continue;
    const funded = Number(plan.currentFundedCents ?? plan.fundedCents ?? 0n);
    const total = Number(plan.totalCents ?? 0n);
    const fundingPercent = total > 0 ? (funded / total) * 100 : 0;
    const minFunding = schedule.minFundingPercent ?? 100;

    // Check if plan meets minimum funding requirement
    if (fundingPercent < minFunding) {
      reports.push({
        planId: plan.id,
        userId: plan.userId,
        name: plan.name,
        paymentAmountCents: 0,
        success: false,
        error: `Insufficient funding: ${fundingPercent.toFixed(1)}% < ${minFunding}%`,
        retryCount: 0,
      });
      
      // Schedule next retry (1 day later)
      const nextRetry = new Date(asOf.getTime() + DAY_MS);
      if (!dryRun) {
        await prisma.fixedPlan.update({
          where: { id: plan.id },
          data: { nextPaymentDate: nextRetry },
        });
      }
      continue;
    }

    // Calculate payment amount (use full funded amount)
    const paymentAmount = funded;
    
    try {
      if (!dryRun) {
        // Create the payment transaction
        await prisma.$transaction(async (tx) => {
          // Create fixed_payment transaction
          await tx.transaction.create({
            data: {
              userId: plan.userId,
              kind: "fixed_payment",
              amountCents: BigInt(paymentAmount),
              occurredAt: asOf,
              planId: plan.id,
              note: `Auto-payment (${schedule.frequency})`,
              isAutoPayment: true,
            },
          });

          // Update plan funding
          await tx.fixedPlan.update({
            where: { id: plan.id },
            data: {
              fundedCents: BigInt(funded - paymentAmount),
              currentFundedCents: BigInt(funded - paymentAmount),
              lastAutoPayment: asOf,
              nextPaymentDate: calculateNextPaymentDate(asOf, schedule, plan.periodDays, userTimezone),
            },
          });
        });
      }

      reports.push({
        planId: plan.id,
        userId: plan.userId,
        name: plan.name,
        paymentAmountCents: paymentAmount,
        success: true,
        retryCount: 0,
      });

    } catch (error) {
      const errorMessage = error instanceof Error ? error.message : 'Unknown error';
      
      reports.push({
        planId: plan.id,
        userId: plan.userId,
        name: plan.name,
        paymentAmountCents: paymentAmount,
        success: false,
        error: errorMessage,
        retryCount: 0,
      });

      // Schedule retry (1 hour later)
      const nextRetry = new Date(asOf.getTime() + 60 * 60 * 1000);
      if (!dryRun) {
        await prisma.fixedPlan.update({
          where: { id: plan.id },
          data: { nextPaymentDate: nextRetry },
        });
      }
    }
  }

  return reports;
}

/**
 * Calculate the next payment date based on schedule
 */
export function calculateNextPaymentDate(
  currentDate: Date,
  schedule: PaymentSchedule,
  periodDays: number,
  timezone: string
): Date {
  const next = toZonedTime(currentDate, timezone);
  const hours = next.getUTCHours();
  const minutes = next.getUTCMinutes();
  const seconds = next.getUTCSeconds();
  const ms = next.getUTCMilliseconds();

  switch (schedule.frequency) {
    case "daily":
      next.setUTCDate(next.getUTCDate() + 1);
      break;
      
    case "weekly":
      // Move to next occurrence of specified day of week
      {
        const targetDay = schedule.dayOfWeek ?? 0;
        const currentDay = next.getUTCDay();
        const daysUntilTarget = (targetDay - currentDay + 7) % 7;
        next.setUTCDate(next.getUTCDate() + (daysUntilTarget || 7));
      }
      break;

    case "biweekly":
      {
        const targetDay = schedule.dayOfWeek ?? next.getUTCDay();
        const currentDay = next.getUTCDay();
        let daysUntilTarget = (targetDay - currentDay + 7) % 7;
        // ensure at least one full week gap to make it biweekly
        daysUntilTarget = daysUntilTarget === 0 ? 14 : daysUntilTarget + 7;
        next.setUTCDate(next.getUTCDate() + daysUntilTarget);
      }
      break;
      
    case "monthly":
      {
        const targetDay = schedule.dayOfMonth ?? next.getUTCDate();
        // Avoid month overflow (e.g., Jan 31 -> Feb) by resetting to day 1 before adding months.
        next.setUTCDate(1);
        next.setUTCMonth(next.getUTCMonth() + 1);
        const lastDay = getLastDayOfMonth(next);
        next.setUTCDate(Math.min(targetDay, lastDay));
      }
      break;

    case "custom":
      {
        const days = schedule.everyNDays && schedule.everyNDays > 0 ? schedule.everyNDays : periodDays;
        next.setUTCDate(next.getUTCDate() + days);
      }
      break;
      
    default:
      // Fallback to periodDays
      next.setUTCDate(next.getUTCDate() + periodDays);
  }

  next.setUTCHours(hours, minutes, seconds, ms);
  return fromZonedTime(next, timezone);
}

function getLastDayOfMonth(date: Date): number {
  return new Date(Date.UTC(date.getUTCFullYear(), date.getUTCMonth() + 1, 0)).getUTCDate();
}