/**
 * Opportunity Domain - Helpers
 *
 * Utility functions for cancellation date calculations and validation.
 * Implements the "25th rule" and rental return deadline logic.
 */

import {
  CANCELLATION_DEADLINE_DAY,
  RENTAL_RETURN_DEADLINE_DAY,
  CANCELLATION_NOTICE,
  LINE_RETURN_STATUS,
  type CancellationFormData,
  type CancellationOpportunityData,
  type CancellationEligibility,
  type CancellationMonthOption,
} from "./contract.js";

// ============================================================================
// Date Utilities
// ============================================================================

/**
 * Get the last day of a month
 * @param year - Full year (e.g., 2025)
 * @param month - Month (1-12)
 * @returns Date string in YYYY-MM-DD format
 */
export function getLastDayOfMonth(year: number, month: number): string {
  // Day 0 of next month = last day of current month
  const lastDay = new Date(year, month, 0).getDate();
  const monthStr = String(month).padStart(2, "0");
  const dayStr = String(lastDay).padStart(2, "0");
  return `${year}-${monthStr}-${dayStr}`;
}

/**
 * Get the rental return deadline (10th of following month)
 * @param year - Year of cancellation month
 * @param month - Month of cancellation (1-12)
 * @returns Date string in YYYY-MM-DD format
 */
export function getRentalReturnDeadline(year: number, month: number): string {
  // Move to next month
  let nextYear = year;
  let nextMonth = month + 1;
  if (nextMonth > 12) {
    nextMonth = 1;
    nextYear += 1;
  }

  const monthStr = String(nextMonth).padStart(2, "0");
  const dayStr = String(RENTAL_RETURN_DEADLINE_DAY).padStart(2, "0");
  return `${nextYear}-${monthStr}-${dayStr}`;
}

/**
 * Parse YYYY-MM format to year and month
 */
export function parseYearMonth(value: string): { year: number; month: number } | null {
  const match = value.match(/^(\d{4})-(0[1-9]|1[0-2])$/);
  if (!match) return null;
  return {
    year: parseInt(match[1], 10),
    month: parseInt(match[2], 10),
  };
}

/**
 * Format a date as YYYY-MM
 */
export function formatYearMonth(date: Date): string {
  const year = date.getFullYear();
  const month = String(date.getMonth() + 1).padStart(2, "0");
  return `${year}-${month}`;
}

/**
 * Format a month for display (e.g., "January 2025")
 */
export function formatMonthLabel(year: number, month: number): string {
  const date = new Date(year, month - 1, 1);
  return date.toLocaleDateString("en-US", { year: "numeric", month: "long" });
}

/**
 * Format a date for display (e.g., "January 31, 2025")
 */
export function formatDateLabel(dateStr: string): string {
  const date = new Date(dateStr);
  return date.toLocaleDateString("en-US", {
    year: "numeric",
    month: "long",
    day: "numeric",
  });
}

// ============================================================================
// Cancellation Deadline Logic
// ============================================================================

/**
 * Check if current date is before the cancellation deadline for a given month
 *
 * Rule: Cancellation form must be received by the 25th of the cancellation month
 *
 * @param cancellationYear - Year of cancellation
 * @param cancellationMonth - Month of cancellation (1-12)
 * @param today - Current date (for testing, defaults to now)
 * @returns true if can still cancel for this month
 */
export function isBeforeCancellationDeadline(
  cancellationYear: number,
  cancellationMonth: number,
  today: Date = new Date()
): boolean {
  const deadlineDate = new Date(
    cancellationYear,
    cancellationMonth - 1,
    CANCELLATION_DEADLINE_DAY,
    23,
    59,
    59
  );
  return today <= deadlineDate;
}

/**
 * Get the cancellation deadline date for a month
 *
 * @param year - Year
 * @param month - Month (1-12)
 * @returns Date string in YYYY-MM-DD format
 */
export function getCancellationDeadline(year: number, month: number): string {
  const monthStr = String(month).padStart(2, "0");
  const dayStr = String(CANCELLATION_DEADLINE_DAY).padStart(2, "0");
  return `${year}-${monthStr}-${dayStr}`;
}

/**
 * Calculate the earliest month that can be selected for cancellation
 *
 * If today is on or after the 25th, earliest is next month.
 * Otherwise, earliest is current month.
 *
 * @param today - Current date (for testing, defaults to now)
 * @returns YYYY-MM format string
 */
export function getEarliestCancellationMonth(today: Date = new Date()): string {
  const year = today.getFullYear();
  const month = today.getMonth() + 1; // 1-indexed
  const day = today.getDate();

  if (day > CANCELLATION_DEADLINE_DAY) {
    // After 25th - earliest is next month
    let nextMonth = month + 1;
    let nextYear = year;
    if (nextMonth > 12) {
      nextMonth = 1;
      nextYear += 1;
    }
    return `${nextYear}-${String(nextMonth).padStart(2, "0")}`;
  } else {
    // On or before 25th - can cancel this month
    return `${year}-${String(month).padStart(2, "0")}`;
  }
}

/**
 * Generate available cancellation months
 *
 * Returns 12 months starting from the earliest available month.
 *
 * @param today - Current date (for testing)
 * @returns Array of month options
 */
export function generateCancellationMonthOptions(
  today: Date = new Date()
): CancellationMonthOption[] {
  const earliestMonth = getEarliestCancellationMonth(today);
  const parsed = parseYearMonth(earliestMonth);
  if (!parsed) return [];

  let { year, month } = parsed;
  const currentYearMonth = formatYearMonth(today);
  const options: CancellationMonthOption[] = [];

  for (let i = 0; i < 12; i++) {
    const value = `${year}-${String(month).padStart(2, "0")}`;
    const serviceEndDate = getLastDayOfMonth(year, month);
    const rentalReturnDeadline = getRentalReturnDeadline(year, month);
    const isCurrentMonth = value === currentYearMonth;

    options.push({
      value,
      label: formatMonthLabel(year, month),
      serviceEndDate,
      rentalReturnDeadline,
      isCurrentMonth,
    });

    // Move to next month
    month += 1;
    if (month > 12) {
      month = 1;
      year += 1;
    }
  }

  return options;
}

/**
 * Get full cancellation eligibility information
 *
 * @param today - Current date (for testing)
 * @returns Cancellation eligibility details
 */
export function getCancellationEligibility(today: Date = new Date()): CancellationEligibility {
  const availableMonths = generateCancellationMonthOptions(today);
  const earliestMonth = getEarliestCancellationMonth(today);
  const day = today.getDate();

  // Check if current month is still available
  const canCancelThisMonth = day <= CANCELLATION_DEADLINE_DAY;
  const currentMonthDeadline = canCancelThisMonth
    ? getCancellationDeadline(today.getFullYear(), today.getMonth() + 1)
    : null;

  return {
    canCancel: true,
    earliestCancellationMonth: earliestMonth,
    availableMonths,
    currentMonthDeadline,
  };
}

/**
 * Validate that a selected cancellation month is allowed
 *
 * @param selectedMonth - YYYY-MM format
 * @param today - Current date (for testing)
 * @returns Validation result
 */
export function validateCancellationMonth(
  selectedMonth: string,
  today: Date = new Date()
): { valid: boolean; error?: string } {
  const parsed = parseYearMonth(selectedMonth);
  if (!parsed) {
    return { valid: false, error: "Invalid month format" };
  }

  const earliestMonth = getEarliestCancellationMonth(today);
  const earliestParsed = parseYearMonth(earliestMonth);
  if (!earliestParsed) {
    return { valid: false, error: "Unable to determine earliest month" };
  }

  // Compare dates
  const selectedDate = new Date(parsed.year, parsed.month - 1, 1);
  const earliestDate = new Date(earliestParsed.year, earliestParsed.month - 1, 1);

  if (selectedDate < earliestDate) {
    const deadline = CANCELLATION_DEADLINE_DAY;
    return {
      valid: false,
      error: `Cancellation requests for this month must be submitted by the ${deadline}th. The earliest available month is ${formatMonthLabel(earliestParsed.year, earliestParsed.month)}.`,
    };
  }

  return { valid: true };
}

// ============================================================================
// Data Transformation
// ============================================================================

/**
 * Transform cancellation form data to Opportunity update data
 *
 * @param formData - Customer form submission
 * @returns Data to update on Opportunity
 */
export function transformCancellationFormToOpportunityData(
  formData: CancellationFormData
): CancellationOpportunityData {
  const parsed = parseYearMonth(formData.cancellationMonth);
  if (!parsed) {
    throw new Error("Invalid cancellation month format");
  }

  const scheduledCancellationDate = getLastDayOfMonth(parsed.year, parsed.month);

  // NOTE: alternativeEmail and comments go to the Cancellation Case, not to Opportunity
  return {
    scheduledCancellationDate,
    cancellationNotice: CANCELLATION_NOTICE.RECEIVED,
    lineReturnStatus: LINE_RETURN_STATUS.NOT_YET,
  };
}

/**
 * Calculate rental return deadline from scheduled cancellation date
 *
 * @param scheduledCancellationDate - End of cancellation month (YYYY-MM-DD)
 * @returns Rental return deadline (10th of following month)
 */
export function calculateRentalReturnDeadline(scheduledCancellationDate: string): string {
  const date = new Date(scheduledCancellationDate);
  const year = date.getFullYear();
  const month = date.getMonth() + 1; // 1-indexed

  return getRentalReturnDeadline(year, month);
}

// ============================================================================
// Display Helpers
// ============================================================================

/**
 * Get human-readable status for line return
 */
export function getLineReturnStatusLabel(status: string | undefined): {
  label: string;
  description: string;
} {
  switch (status) {
    case LINE_RETURN_STATUS.NOT_YET:
      return {
        label: "Return Pending",
        description: "A return kit will be sent to you",
      };
    case LINE_RETURN_STATUS.SENT_KIT:
      return {
        label: "Return Kit Sent",
        description: "Please return equipment using the provided kit",
      };
    case LINE_RETURN_STATUS.PICKUP_SCHEDULED:
      return {
        label: "Pickup Scheduled",
        description: "Equipment pickup has been scheduled",
      };
    case LINE_RETURN_STATUS.RETURNED:
    case "Returned1":
      return {
        label: "Returned",
        description: "Equipment has been returned successfully",
      };
    case LINE_RETURN_STATUS.NTT_DISPATCH:
      return {
        label: "NTT Dispatch",
        description: "NTT will handle equipment return",
      };
    case LINE_RETURN_STATUS.COMPENSATED:
      return {
        label: "Compensated",
        description: "Compensation fee has been charged for unreturned equipment",
      };
    case LINE_RETURN_STATUS.NA:
      return {
        label: "Not Applicable",
        description: "No rental equipment to return",
      };
    default:
      return {
        label: "Unknown",
        description: "",
      };
  }
}

/**
 * Check if rental equipment is applicable for a product type
 */
export function hasRentalEquipment(productType: string): boolean {
  // Internet typically has rental equipment (router, modem)
  // SIM and VPN do not
  return productType === "Internet";
}