module mtclass;

import std.range, std.traits;

final class MersenneTwisterClass(UIntType, size_t w, size_t n, size_t m, size_t r,
                                 UIntType a, size_t u, size_t s,
                                 UIntType b, size_t t,
                                 UIntType c, size_t l)
    if(isUnsigned!UIntType)
{
    ///Mark this as a Rng
    enum bool isUniformRandom = true;
/**
Parameter for the generator.
*/
    enum size_t wordSize = w;
    enum size_t stateSize = n;
    enum size_t shiftSize = m;
    enum size_t maskBits = r;
    enum UIntType xorMask = a;
    enum UIntType temperingU = u;
    enum size_t temperingS = s;
    enum UIntType temperingB = b;
    enum size_t temperingT = t;
    enum UIntType temperingC = c;
    enum size_t temperingL = l;

    /// Smallest generated value (0).
    enum UIntType min = 0;
    /// Largest generated value.
    enum UIntType max =
        w == UIntType.sizeof * 8 ? UIntType.max : (1u << w) - 1;
    /// The default seed value.
    enum UIntType defaultSeed = 5489u;

    static assert(1 <= m && m <= n);
    static assert(0 <= r && 0 <= u && 0 <= s && 0 <= t && 0 <= l);
    static assert(r <= w && u <= w && s <= w && t <= w && l <= w);
    static assert(0 <= a && 0 <= b && 0 <= c);
    static assert(a <= max && b <= max && c <= max);

/**
   Constructs a MersenneTwisterEngine object.
*/
    this(UIntType value)
    {
        seed(value);
    }

    this(typeof(this) source)
    {
        this.mt[] = source.mt[];
        this.mti = source.mti;
        this._y = source._y;
    }

/**
   Seeds a MersenneTwisterEngine object.
   Note:
   This seed function gives 2^32 starting points. To allow the RNG to be started in any one of its
   internal states use the seed overload taking an InputRange.
*/
    void seed()(UIntType value = defaultSeed)
    {
        static if (w == UIntType.sizeof * 8)
        {
            mt[0] = value;
        }
        else
        {
            static assert(max + 1 > 0);
            mt[0] = value % (max + 1);
        }
        for (mti = 1; mti < n; ++mti)
        {
            mt[mti] =
                cast(UIntType)
                (1812433253UL * (mt[mti-1] ^ (mt[mti-1] >> (w - 2))) + mti);
            /* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
            /* In the previous versions, MSBs of the seed affect   */
            /* only MSBs of the array mt[].                        */
            /* 2002/01/09 modified by Makoto Matsumoto             */
            //mt[mti] &= ResultType.max;
            /* for >32 bit machines */
        }
        popFront();
    }

/**
   Seeds a MersenneTwisterEngine object using an InputRange.

   Throws:
   $(D Exception) if the InputRange didn't provide enough elements to seed the generator.
   The number of elements required is the 'n' template parameter of the MersenneTwisterEngine struct.

   Examples:
   ----------------
   Mt19937 gen;
   gen.seed(map!((a) => unpredictableSeed)(repeat(0)));
   ----------------
 */
    void seed(T)(T range) if(isInputRange!T && is(Unqual!(ElementType!T) == UIntType))
    {
        size_t j;
        for(j = 0; j < n && !range.empty; ++j, range.popFront())
        {
            mt[j] = range.front;
        }

        mti = n;
        if(range.empty && j < n)
        {
            throw new Exception(format("MersenneTwisterEngine.seed: Input range didn't provide enough"
                " elements: Need %s elemnets.", n));
        }

        popFront();
    }

/**
   Advances the generator.
*/
    void popFront()
    {
        if (mti == size_t.max) seed();
        enum UIntType
            upperMask = ~((cast(UIntType) 1u <<
                           (UIntType.sizeof * 8 - (w - r))) - 1),
            lowerMask = (cast(UIntType) 1u << r) - 1;
        static immutable UIntType mag01[2] = [0x0UL, a];

        ulong y = void;

        if (mti >= n)
        {
            /* generate N words at one time */

            int kk = 0;
            const limit1 = n - m;
            for (; kk < limit1; ++kk)
            {
                y = (mt[kk] & upperMask)|(mt[kk + 1] & lowerMask);
                mt[kk] = cast(UIntType) (mt[kk + m] ^ (y >> 1)
                        ^ mag01[cast(UIntType) y & 0x1U]);
            }
            const limit2 = n - 1;
            for (; kk < limit2; ++kk)
            {
                y = (mt[kk] & upperMask)|(mt[kk + 1] & lowerMask);
                mt[kk] = cast(UIntType) (mt[kk + (m -n)] ^ (y >> 1)
                                         ^ mag01[cast(UIntType) y & 0x1U]);
            }
            y = (mt[n -1] & upperMask)|(mt[0] & lowerMask);
            mt[n - 1] = cast(UIntType) (mt[m - 1] ^ (y >> 1)
                                        ^ mag01[cast(UIntType) y & 0x1U]);

            mti = 0;
        }

        y = mt[mti++];

        /* Tempering */
        y ^= (y >> temperingU);
        y ^= (y << temperingS) & temperingB;
        y ^= (y << temperingT) & temperingC;
        y ^= (y >> temperingL);

        _y = cast(UIntType) y;
    }

/**
   Returns the current random value.
 */
    @property UIntType front()
    {
        if (mti == size_t.max) seed();
        return _y;
    }

///
    @property typeof(this) save()
    {
        return new typeof(this)(this);
    }

/**
Always $(D false).
 */
    enum bool empty = false;

    private UIntType mt[n];
    private size_t mti = size_t.max; /* means mt is not initialized */
    UIntType _y = UIntType.max;
}

alias MersenneTwisterClass!(uint, 32, 624, 397, 31, 0x9908b0df, 11, 7,
                             0x9d2c5680, 15, 0xefc60000, 18)
    MtClass19937;