module daque.math.linear;

enum MatrixOrder
{
	RowMajor, ColumnMajor
}

struct Matrix(RealType, uint Rows, uint Columns, MatrixOrder Order = MatrixOrder.ColumnMajor)
{
	private RealType[Rows * Columns] m_element;
	
	ref RealType opIndex(uint i, uint j)
	{
		static if(Order == MatrixOrder.RowMajor)
		{
			return m_element[j * Rows + i];
		}
		else
		{
			return m_element[i * Columns + j];
		}
	}

	RealType[] linearize(MatrixOrder order = Order)()
	{
		RealType[] linearization;

		static if(order == Order)
		{
			linearization = m_element;
		}
		else
		{
			static if(order == MatrixOrder.RowMajor)
			{
				for(uint i; i < Rows; i++)
					for(uint j; j < Columns; j++)
						linearization ~= this[i, j];
			}
			else
			{
				for(uint j; j < Columns; j++)
					for(uint i; i < Rows; i++)
						linearization ~= this[i, j];
			}
		}

		return linearization;
	}

	static Matrix!(RealType, Rows, Columns, Order) Identity()
	{
		Matrix!(RealType, Rows, Columns, Order) identity;
		for(uint i; i < Rows; i++)
			for(uint j; j < Columns; j++)
				identity[i, j] = i == j;
		return identity;
	}
}

unittest
{
	import std.algorithm;
	import std.range;
	import std.stdio;
	auto identityColumn = Matrix!(real, 3, 3, MatrixOrder.ColumnMajor).Identity();
	auto identityRow = Matrix!(real, 3, 3, MatrixOrder.RowMajor).Identity();
	writeln(identityColumn.linearize!(MatrixOrder.RowMajor)());
	writeln(identityRow);
}