using System.Collections.Generic;
using System.Linq;

namespace AsbCloudInfrastructure.Services
{
    public static class LinearFunctionCalculator
    {
        public static double GetAForLinearFormula(IEnumerable<(double value, double timestamp)> rawData)
        {
            var (xSum, ySum, xySum, x2Sum) = GetFormulaVariables(rawData);

            var result = (xSum * ySum - rawData.Count() * xySum) /
                   (xSum * xSum - rawData.Count() * x2Sum);

            return (double)result;
        }

        public static double GetBForLinearFormula(IEnumerable<(double value, double timestamp)> rawData)
        {
            var (xSum, ySum, xySum, x2Sum) = GetFormulaVariables(rawData);

            var result = (xSum * xySum - x2Sum * ySum) /
                   (xSum * xSum - rawData.Count() * x2Sum);

            return (double)result;
        }

        public static bool IsValueNotChanges(double value, 
            (double upperBound, double lowerBound) bounds) =>
                value < bounds.upperBound && value > bounds.lowerBound;

        public static bool IsValueGoesUp(double value, double bound) =>
            value > bound;

        public static bool IsValueGoesDown(double value, double bound) =>
            value < bound;

        public static bool IsAverageLessThanBound(IEnumerable<(double Value, double TotalSeconds)> values, 
            double bound) =>
                (values.Sum(s => s.Value) / values.Count()) < bound;

        public static bool IsAverageMoreThanBound(IEnumerable<(double Value, double TotalSeconds)> values,
            double bound) =>
                (values.Sum(s => s.Value) / values.Count()) >= bound;

        private static (decimal xSum, decimal ySum, decimal xySum, decimal x2Sum) GetFormulaVariables(
            IEnumerable<(double value, double timestamp)> rawData)
        {
            var data = rawData.Select((d) => new
            {
                X = d.timestamp,
                Y = d.value
            });
            var xSum = (decimal)data.Sum(d => d.X);
            var ySum = (decimal)data.Sum(d => d.Y);
            var xySum = (decimal)data.Sum(d => d.X * d.Y);
            var x2Sum = (decimal)data.Sum(d => d.X * d.X);

            return (xSum, ySum, xySum, x2Sum);
        }
    }
}