using System;
using Xunit;

namespace YunDa.SOMS.MongoDB.Application.Tests.Inspection
{
    /// <summary>
    /// Unit tests for September special case in GetYearlyStatisticsByMonthAsync
    /// Tests validate Requirements: 5.1, 5.2, 5.3, 5.4, 5.5
    /// </summary>
    public class SeptemberSpecialCaseTests
    {
        /// <summary>
        /// Helper class to simulate the September special case logic
        /// </summary>
        private class SeptemberLogicSimulator
        {
            public (int startYear, int startMonth, int endYear, int endMonth) ApplySeptemberSpecialCase(
                int currentYear,
                int currentMonth,
                int calculatedStartYear,
                int calculatedStartMonth,
                int calculatedEndYear,
                int calculatedEndMonth)
            {
                // Apply September special case
                if (currentMonth == 9)
                {
                    // For September, adjust to show only Jan-Dec of current year
                    return (currentYear, 1, currentYear, 12);
                }

                // Return original calculated values for non-September months
                return (calculatedStartYear, calculatedStartMonth, calculatedEndYear, calculatedEndMonth);
            }

            public int CalculateMonthCount(int startYear, int startMonth, int endYear, int endMonth)
            {
                int count = 0;
                int iterYear = startYear;
                int iterMonth = startMonth;

                while (iterYear < endYear || (iterYear == endYear && iterMonth <= endMonth))
                {
                    count++;
                    iterMonth++;
                    if (iterMonth > 12)
                    {
                        iterMonth = 1;
                        iterYear++;
                    }
                }

                return count;
            }
        }

        private readonly SeptemberLogicSimulator _simulator = new SeptemberLogicSimulator();

        [Fact]
        public void SeptemberSpecialCase_AdjustsToJanuaryThroughDecember()
        {
            // Arrange
            int currentYear = 2025;
            int currentMonth = 9; // September
            
            // Simulated calculated window (June 2025 to August 2026)
            int calculatedStartYear = 2025;
            int calculatedStartMonth = 6;
            int calculatedEndYear = 2026;
            int calculatedEndMonth = 8;

            // Act
            var (startYear, startMonth, endYear, endMonth) = _simulator.ApplySeptemberSpecialCase(
                currentYear, currentMonth,
                calculatedStartYear, calculatedStartMonth,
                calculatedEndYear, calculatedEndMonth);

            // Assert - Requirements 5.1: Display Jan-Dec of current year
            Assert.Equal(2025, startYear);
            Assert.Equal(1, startMonth); // January
            Assert.Equal(2025, endYear);
            Assert.Equal(12, endMonth); // December
        }

        [Fact]
        public void SeptemberSpecialCase_Returns12Months()
        {
            // Arrange
            int currentYear = 2025;
            int currentMonth = 9; // September
            int calculatedStartYear = 2025;
            int calculatedStartMonth = 6;
            int calculatedEndYear = 2026;
            int calculatedEndMonth = 8;

            // Act
            var (startYear, startMonth, endYear, endMonth) = _simulator.ApplySeptemberSpecialCase(
                currentYear, currentMonth,
                calculatedStartYear, calculatedStartMonth,
                calculatedEndYear, calculatedEndMonth);

            int monthCount = _simulator.CalculateMonthCount(startYear, startMonth, endYear, endMonth);

            // Assert - Requirements 5.5: Only 12 months for September
            Assert.Equal(12, monthCount);
        }

        [Fact]
        public void SeptemberSpecialCase_DoesNotAffectOtherMonths()
        {
            // Arrange
            int currentYear = 2025;
            int currentMonth = 10; // October (not September)
            int calculatedStartYear = 2025;
            int calculatedStartMonth = 7;
            int calculatedEndYear = 2026;
            int calculatedEndMonth = 9;

            // Act
            var (startYear, startMonth, endYear, endMonth) = _simulator.ApplySeptemberSpecialCase(
                currentYear, currentMonth,
                calculatedStartYear, calculatedStartMonth,
                calculatedEndYear, calculatedEndMonth);

            // Assert - Non-September months should keep original calculated values
            Assert.Equal(calculatedStartYear, startYear);
            Assert.Equal(calculatedStartMonth, startMonth);
            Assert.Equal(calculatedEndYear, endYear);
            Assert.Equal(calculatedEndMonth, endMonth);
        }

        [Fact]
        public void SeptemberSpecialCase_IncludesHistoricalMonths()
        {
            // Arrange
            int currentYear = 2025;
            int currentMonth = 9; // September
            int calculatedStartYear = 2025;
            int calculatedStartMonth = 6;
            int calculatedEndYear = 2026;
            int calculatedEndMonth = 8;

            // Act
            var (startYear, startMonth, endYear, endMonth) = _simulator.ApplySeptemberSpecialCase(
                currentYear, currentMonth,
                calculatedStartYear, calculatedStartMonth,
                calculatedEndYear, calculatedEndMonth);

            // Assert - Requirements 5.2: Includes June, July, August as historical
            // The window starts at January, so June (month 6) is included
            Assert.True(startMonth <= 6); // June is month 6
            Assert.True(endMonth >= 6);
        }

        [Fact]
        public void SeptemberSpecialCase_IncludesCurrentMonth()
        {
            // Arrange
            int currentYear = 2025;
            int currentMonth = 9; // September
            int calculatedStartYear = 2025;
            int calculatedStartMonth = 6;
            int calculatedEndYear = 2026;
            int calculatedEndMonth = 8;

            // Act
            var (startYear, startMonth, endYear, endMonth) = _simulator.ApplySeptemberSpecialCase(
                currentYear, currentMonth,
                calculatedStartYear, calculatedStartMonth,
                calculatedEndYear, calculatedEndMonth);

            // Assert - Requirements 5.3: Includes September as current month
            Assert.True(startMonth <= 9); // September is month 9
            Assert.True(endMonth >= 9);
        }

        [Fact]
        public void SeptemberSpecialCase_IncludesPredictedMonths()
        {
            // Arrange
            int currentYear = 2025;
            int currentMonth = 9; // September
            int calculatedStartYear = 2025;
            int calculatedStartMonth = 6;
            int calculatedEndYear = 2026;
            int calculatedEndMonth = 8;

            // Act
            var (startYear, startMonth, endYear, endMonth) = _simulator.ApplySeptemberSpecialCase(
                currentYear, currentMonth,
                calculatedStartYear, calculatedStartMonth,
                calculatedEndYear, calculatedEndMonth);

            // Assert - Requirements 5.4: Predicts October, November, December
            Assert.True(endMonth >= 12); // December is month 12
            Assert.Equal(currentYear, endYear); // Same year
        }

        [Fact]
        public void SeptemberSpecialCase_DoesNotIncludeNextYear()
        {
            // Arrange
            int currentYear = 2025;
            int currentMonth = 9; // September
            int calculatedStartYear = 2025;
            int calculatedStartMonth = 6;
            int calculatedEndYear = 2026;
            int calculatedEndMonth = 8;

            // Act
            var (startYear, startMonth, endYear, endMonth) = _simulator.ApplySeptemberSpecialCase(
                currentYear, currentMonth,
                calculatedStartYear, calculatedStartMonth,
                calculatedEndYear, calculatedEndMonth);

            // Assert - Requirements 5.5: Does not include any months from next year
            Assert.Equal(currentYear, endYear);
            Assert.Equal(12, endMonth); // Ends at December of current year
        }
    }
}