PdfPig/src/UglyToad.PdfPig/Core/TransformationMatrix.cs

namespace UglyToad.PdfPig.Core
{
    using System;
    using System.Collections.Generic;
    using System.Diagnostics.Contracts;
    using Geometry;

    /// <summary>
    /// Specifies the conversion from the transformed coordinate space to the original untransformed coordinate space.
    /// </summary>
    internal struct TransformationMatrix
    {
        public static TransformationMatrix Identity = new TransformationMatrix(new decimal[]
        {
            1,0,0,
            0,1,0,
            0,0,1
        });

        private readonly decimal[] value;

        /// <summary>
        /// The scale for the X dimension.
        /// </summary>
        public decimal A => value[0];
        public decimal B => value[1];
        public decimal C => value[3];
        /// <summary>
        /// The scale for the Y dimension.
        /// </summary>
        public decimal D => value[4];
        public decimal E => value[6];
        public decimal F => value[7];

        public decimal this[int row, int col]
        {
            get
            {
                if (row >= Rows)
                {
                    throw new ArgumentOutOfRangeException($"The transformation matrix only contains {Rows} rows and is zero indexed, you tried to access row {row}.");
                }

                if (row < 0)
                {
                    throw new ArgumentOutOfRangeException("Cannot access negative rows in a matrix.");
                }

                if (col >= Columns)
                {
                    throw new ArgumentOutOfRangeException($"The transformation matrix only contains {Columns} columns and is zero indexed, you tried to access column {col}.");
                }

                if (col < 0)
                {
                    throw new ArgumentOutOfRangeException("Cannot access negative columns in a matrix.");
                }

                var resultIndex = row * Rows + col;

                if (resultIndex > value.Length - 1)
                {
                    throw new ArgumentOutOfRangeException($"Trying to access {row}, {col} mapped to the index {resultIndex} which was not in the value array.");
                }

                return value[resultIndex];
            }
        }

        public const int Rows = 3;
        public const int Columns = 3;
        
        public TransformationMatrix(decimal[] value)
        {
            if (value == null)
            {
                throw new ArgumentNullException(nameof(value));
            }

            if (value.Length != 9)
            {
                throw new ArgumentException("The constructor for the PDF transformation matrix must contain 9 elements. Instead got: " + value);
            }

            this.value = value;
        }
        
        public PdfPoint Transform(PdfPoint original)
        {
            var x = A * original.X + C * original.Y + E;
            var y = B * original.X + D * original.Y + F;

            return new PdfPoint(x, y);
        }

        [Pure]
        public PdfVector Transform(PdfVector original)
        {
            var x = A * original.X + C * original.Y + E;
            var y = B * original.X + D * original.Y + F;

            return new PdfVector(x, y);
        }

        [Pure]
        public PdfRectangle Transform(PdfRectangle original)
        {
            return new PdfRectangle(
                Transform(original.TopLeft.ToVector()),
                Transform(original.TopRight.ToVector()),
                Transform(original.BottomLeft.ToVector()),
                Transform(original.BottomRight.ToVector())
            );
        }

        public static TransformationMatrix FromValues(decimal a, decimal b, decimal c, decimal d, decimal e, decimal f)
            => FromArray(new[] {a, b, c, d, e, f});
        public static TransformationMatrix FromArray(decimal[] values)
        {
            if (values.Length == 9)
            {
                return new TransformationMatrix(values);
            }

            if (values.Length == 6)
            {
                return new TransformationMatrix(new []
                {
                    values[0], values[1], 0,
                    values[2], values[3], 0,
                    values[4], values[5], 1
                });
            }

            throw new ArgumentException("The array must either define all 9 elements of the matrix or all 6 key elements. Instead array was: " + values);
        }

        public TransformationMatrix Multiply(TransformationMatrix matrix)
        {
            var result = new decimal[9];

            for (int i = 0; i < Rows; i++)
            {
                for (int j = 0; j < Columns; j++)
                {
                    var index = (i * Rows) + j;

                    for (int x = 0; x < Rows; x++)
                    {
                        result[index] += this[i, x] * matrix[x, j];
                    }
                }
            }

            return new TransformationMatrix(result);
        }

        public TransformationMatrix Multiply(decimal scalar)
        {
            var result = new decimal[9];

            for (int i = 0; i < Rows; i++)
            {
                for (int j = 0; j < Columns; j++)
                {
                    var index = (i * Rows) + j;

                    for (int x = 0; x < Rows; x++)
                    {
                        result[index] += this[i, x] * scalar;
                    }
                }
            }

            return new TransformationMatrix(result);
        }

        public decimal GetScalingFactorX()
        {
            var xScale = A;

            /*
             * BM: if the trm is rotated, the calculation is a little more complicated
             *
             * The rotation matrix multiplied with the scaling matrix is:
             * (   x   0   0)    ( cos  sin  0)    ( x*cos x*sin   0)
             * (   0   y   0) *  (-sin  cos  0)  = (-y*sin y*cos   0)
             * (   0   0   1)    (   0    0  1)    (     0     0   1)
             *
             * So, if you want to deduce x from the matrix you take
             * M(0,0) = x*cos and M(0,1) = x*sin and use the theorem of Pythagoras
             *
             * sqrt(M(0,0)^2+M(0,1)^2) =
             * sqrt(x2*cos2+x2*sin2) =
             * sqrt(x2*(cos2+sin2)) = (here is the trick cos2+sin2 = 1)
             * sqrt(x2) =
             * abs(x)
             */
            if (!(B == 0m && C == 0m))
            {
                xScale = (decimal)Math.Sqrt((double)(A*A + B*B));
            }

            return xScale;
        }

        public override bool Equals(object obj)
        {
            if (!(obj is TransformationMatrix m))
            {
                return false;
            }

            return Equals(this, m);
        }

        public static bool Equals(TransformationMatrix a, TransformationMatrix b)
        {
            for (int i = 0; i < Rows; i++)
            {
                for (int j = 0; j < Columns; j++)
                {
                    if (a[i, j] != b[i, j])
                    {
                        return false;
                    }
                }
            }

            return true;
        }

        public override int GetHashCode()
        {
            var hashCode = 1113510858;
            hashCode = hashCode * -1521134295 + base.GetHashCode();
            hashCode = hashCode * -1521134295 + EqualityComparer<decimal[]>.Default.GetHashCode(value);
            return hashCode;
        }

        public override string ToString()
        {
            return $"{A}, {B}, 0\r\n{C}, {D}, 0\r\n{E}, {F}, 1";
        }

        public static TransformationMatrix GetTranslationMatrix(decimal x, decimal y)
        {
            return new TransformationMatrix(new []
            {
                1, 0, 0,
                0, 1, 0,
                x, y, 1
            });
        }
    }
}