using System;
using Xunit;

namespace YunDa.SOMS.MongoDB.Application.Tests.Inspection
{
    /// <summary>
    /// Unit tests for CalculateDisplayWindow helper method
    /// Tests validate Requirements: 1.1, 1.2, 1.3, 1.4, 5.1, 6.1, 7.1, 8.1, 9.1, 10.1
    /// </summary>
    public class CalculateDisplayWindowTests
    {
        /// <summary>
        /// Helper class to expose the internal CalculateDisplayWindow method for testing
        /// </summary>
        private class TestableService
        {
            public (int startYear, int startMonth, int endYear, int endMonth) CalculateDisplayWindow(
                int currentYear,
                int currentMonth)
            {
                // Calculate historical start (3 months before current)
                int historicalStartMonth = currentMonth - 3;
                int startYear;
                int startMonth;

                if (historicalStartMonth <= 0)
                {
                    // Year boundary: go back to previous year
                    startYear = currentYear - 1;
                    startMonth = 12 + historicalStartMonth; // historicalStartMonth is negative or 0
                }
                else
                {
                    startYear = currentYear;
                    startMonth = historicalStartMonth;
                }

                // Calculate end month (11 months after current)
                int endMonthOffset = currentMonth + 11;
                int endYear;
                int endMonth;

                if (endMonthOffset > 12)
                {
                    // Year boundary: go to next year
                    endYear = currentYear + 1;
                    endMonth = endMonthOffset - 12;
                }
                else
                {
                    endYear = currentYear;
                    endMonth = endMonthOffset;
                }

                return (startYear, startMonth, endYear, endMonth);
            }
        }

        private readonly TestableService _service = new TestableService();

        [Fact]
        public void CalculateDisplayWindow_January_ReturnsCorrectWindow()
        {
            // Arrange
            int currentYear = 2025;
            int currentMonth = 1; // January

            // Act
            var (startYear, startMonth, endYear, endMonth) = _service.CalculateDisplayWindow(currentYear, currentMonth);

            // Assert
            // January: 3 months before = Oct, Nov, Dec of previous year
            // 11 months after = December of current year
            Assert.Equal(2024, startYear);
            Assert.Equal(10, startMonth); // October
            Assert.Equal(2025, endYear);
            Assert.Equal(12, endMonth); // December
        }

        [Fact]
        public void CalculateDisplayWindow_March_ReturnsCorrectWindow()
        {
            // Arrange
            int currentYear = 2025;
            int currentMonth = 3; // March

            // Act
            var (startYear, startMonth, endYear, endMonth) = _service.CalculateDisplayWindow(currentYear, currentMonth);

            // Assert
            // March: 3 months before = Dec of previous year, Jan, Feb of current year
            // 11 months after = February of next year
            Assert.Equal(2024, startYear);
            Assert.Equal(12, startMonth); // December
            Assert.Equal(2026, endYear);
            Assert.Equal(2, endMonth); // February
        }

        [Fact]
        public void CalculateDisplayWindow_September_ReturnsCorrectWindow()
        {
            // Arrange
            int currentYear = 2025;
            int currentMonth = 9; // September

            // Act
            var (startYear, startMonth, endYear, endMonth) = _service.CalculateDisplayWindow(currentYear, currentMonth);

            // Assert
            // September: 3 months before = June, July, August
            // 11 months after = August of next year
            Assert.Equal(2025, startYear);
            Assert.Equal(6, startMonth); // June
            Assert.Equal(2026, endYear);
            Assert.Equal(8, endMonth); // August
        }

        [Fact]
        public void CalculateDisplayWindow_October_ReturnsCorrectWindow()
        {
            // Arrange
            int currentYear = 2025;
            int currentMonth = 10; // October

            // Act
            var (startYear, startMonth, endYear, endMonth) = _service.CalculateDisplayWindow(currentYear, currentMonth);

            // Assert
            // October: 3 months before = July, August, September
            // 11 months after = September of next year
            Assert.Equal(2025, startYear);
            Assert.Equal(7, startMonth); // July
            Assert.Equal(2026, endYear);
            Assert.Equal(9, endMonth); // September
        }

        [Fact]
        public void CalculateDisplayWindow_December_ReturnsCorrectWindow()
        {
            // Arrange
            int currentYear = 2025;
            int currentMonth = 12; // December

            // Act
            var (startYear, startMonth, endYear, endMonth) = _service.CalculateDisplayWindow(currentYear, currentMonth);

            // Assert
            // December: 3 months before = September, October, November
            // 11 months after = November of next year
            Assert.Equal(2025, startYear);
            Assert.Equal(9, startMonth); // September
            Assert.Equal(2026, endYear);
            Assert.Equal(11, endMonth); // November
        }

        [Fact]
        public void CalculateDisplayWindow_February_HandlesYearBoundary()
        {
            // Arrange
            int currentYear = 2025;
            int currentMonth = 2; // February

            // Act
            var (startYear, startMonth, endYear, endMonth) = _service.CalculateDisplayWindow(currentYear, currentMonth);

            // Assert
            // February: 3 months before = Nov, Dec of previous year, Jan of current year
            // 11 months after = January of next year
            Assert.Equal(2024, startYear);
            Assert.Equal(11, startMonth); // November
            Assert.Equal(2026, endYear);
            Assert.Equal(1, endMonth); // January
        }

        [Fact]
        public void CalculateDisplayWindow_April_NoYearBoundary()
        {
            // Arrange
            int currentYear = 2025;
            int currentMonth = 4; // April

            // Act
            var (startYear, startMonth, endYear, endMonth) = _service.CalculateDisplayWindow(currentYear, currentMonth);

            // Assert
            // April: 3 months before = January, February, March (same year)
            // 11 months after = March of next year
            Assert.Equal(2025, startYear);
            Assert.Equal(1, startMonth); // January
            Assert.Equal(2026, endYear);
            Assert.Equal(3, endMonth); // March
        }
    }
}