module salsa20;

private:

import std.string : format;
import std.range : isInputRange, isForwardRange, ElementType;
import std.array;

import bitmanip;
import utility;

public:

// TODO: Implement random access

auto salsa20Cipher(R)(R range, ubyte[32] key, ubyte[8] nonce)
        if (isInputRange!R && is(ElementType!R : ubyte))
{
    struct rangeResult
    {
    private:
        ulong count;
        R range;
        ubyte[64] salsaSection;
        uint salsaCounter;
    public:
        bool empty() @property
        {
            return range.empty || (count == ulong.max && salsaCounter == 64);
        }

        ubyte front() @property
        {
            assert(!empty);
            return range.front ^ salsaSection[salsaCounter];
        }

        void popFront()
        {
            assert(!empty);
            if (++salsaCounter == 64)
            {
                salsaSection = salsa20Exp(key, concat!(ubyte[16])(nonce,
                        littleEndianInv(++count)));
                salsaCounter = 0;
            }
            range.popFront();
        }

        static if (isForwardRange!R)
        {
            auto save() @property
            {
                return rangeResult(count, range.save, salsaSection, salsaCounter);
            }
        }
    }

    return rangeResult(0UL, range, salsa20Exp(key, concat!(ubyte[16])(nonce,
            littleEndianInv(0UL))));
}

// TODO: Create more unittests!!!

@safe unittest
{
    ubyte[] test = new ubyte[64];
    ubyte[32] key;
    ubyte[8] nonce;
    test = test.salsa20Cipher(key, nonce).array;
    assert(test == [154, 151, 246, 91, 155, 76, 114, 27, 150, 10, 103, 33, 69,
            252, 168, 212, 227, 46, 103, 249, 17, 30, 169, 121, 206, 156, 72,
            38, 128, 106, 238, 230, 61, 233, 192, 218, 43, 215, 249, 30, 188,
            178, 99, 155, 249, 137, 198, 37, 27, 41, 191, 56, 211, 154, 155,
            220, 231, 197, 95, 75, 42, 193, 42, 57]);
}

private:

enum string quarterRound(alias _x0, alias _x1, alias _x2, alias _x3) = q{
    %2$s ^= (%1$s + %4$s).rotateLeft(7);
    %3$s ^= (%2$s + %1$s).rotateLeft(9);
    %4$s ^= (%3$s + %2$s).rotateLeft(13);
    %1$s ^= (%4$s + %3$s).rotateLeft(18);
}.format(__traits(identifier, _x0),
            __traits(identifier, _x1), __traits(identifier, _x2), __traits(identifier, _x3));

@safe unittest
{
    uint a1 = 0x00000000, a2 = 0x00000000, a3 = 0x00000000, a4 = 0x00000000,
        b1 = 0x00000001, b2 = 0x00000000, b3 = 0x00000000, b4 = 0x00000000, c1 = 0x00000000,
        c2 = 0x00000001, c3 = 0x00000000, c4 = 0x00000000, d1 = 0x00000000, d2 = 0x00000000,
        d3 = 0x00000001, d4 = 0x00000000, e1 = 0x00000000, e2 = 0x00000000, e3 = 0x00000000,
        e4 = 0x00000001, f1 = 0xe7e8c006, f2 = 0xc4f9417d, f3 = 0x6479b4b2, f4 = 0x68c67137,
        g1 = 0xd3917c5b, g2 = 0x55f1c407, g3 = 0x52a58a7a, g4 = 0x8f887a3b;

    mixin(quarterRound!(a1, a2, a3, a4));
    mixin(quarterRound!(b1, b2, b3, b4));
    mixin(quarterRound!(c1, c2, c3, c4));
    mixin(quarterRound!(d1, d2, d3, d4));
    mixin(quarterRound!(e1, e2, e3, e4));
    mixin(quarterRound!(f1, f2, f3, f4));
    mixin(quarterRound!(g1, g2, g3, g4));

    assert([a1, a2, a3, a4] == [0x00000000, 0x00000000, 0x00000000, 0x00000000]);
    assert([b1, b2, b3, b4] == [0x08008145, 0x00000080, 0x00010200, 0x20500000]);
    assert([c1, c2, c3, c4] == [0x88000100, 0x00000001, 0x00000200, 0x00402000]);
    assert([d1, d2, d3, d4] == [0x80040000, 0x00000000, 0x00000001, 0x00002000]);
    assert([e1, e2, e3, e4] == [0x00048044, 0x00000080, 0x00010000, 0x20100001]);
    assert([f1, f2, f3, f4] == [0xe876d72b, 0x9361dfd5, 0xf1460244, 0x948541a3]);
    assert([g1, g2, g3, g4] == [0x3e2f308c, 0xd90a8f36, 0x6ab2a923, 0x2883524c]);
}

enum string rowRound(alias _x00, alias _x01, alias _x02, alias _x03, alias _x04,
            alias _x05, alias _x06, alias _x07, alias _x08, alias _x09, alias _x10,
            alias _x11, alias _x12, alias _x13, alias _x14, alias _x15) = q{
    mixin(quarterRound!(%1$s, %2$s, %3$s, %4$s));
    mixin(quarterRound!(%6$s, %7$s, %8$s, %5$s));
    mixin(quarterRound!(%11$s, %12$s, %9$s, %10$s));
    mixin(quarterRound!(%16$s, %13$s, %14$s, %15$s));
}.format(
            __traits(identifier, _x00), __traits(identifier,
            _x01), __traits(identifier, _x02), __traits(identifier, _x03),
            __traits(identifier, _x04), __traits(identifier, _x05), __traits(identifier, _x06),
            __traits(identifier, _x07), __traits(identifier, _x08), __traits(identifier, _x09),
            __traits(identifier, _x10), __traits(identifier, _x11), __traits(identifier, _x12),
            __traits(identifier, _x13), __traits(identifier, _x14), __traits(identifier, _x15));

@safe unittest
{
    uint y00 = 0x00000001, y01 = 0x00000000, y02 = 0x00000000, y03 = 0x00000000,
        y04 = 0x00000001, y05 = 0x00000000, y06 = 0x00000000, y07 = 0x00000000, y08 = 0x00000001,
        y09 = 0x00000000, y10 = 0x00000000, y11 = 0x00000000, y12 = 0x00000001,
        y13 = 0x00000000, y14 = 0x00000000, y15 = 0x00000000;

    uint x00 = 0x08521bd6, x01 = 0x1fe88837, x02 = 0xbb2aa576, x03 = 0x3aa26365,
        x04 = 0xc54c6a5b, x05 = 0x2fc74c2f, x06 = 0x6dd39cc3, x07 = 0xda0a64f6, x08 = 0x90a2f23d,
        x09 = 0x067f95a6, x10 = 0x06b35f61, x11 = 0x41e4732e, x12 = 0xe859c100,
        x13 = 0xea4d84b7, x14 = 0x0f619bff, x15 = 0xbc6e965a;

    mixin(rowRound!(y00, y01, y02, y03, y04, y05, y06, y07, y08, y09, y10,
            y11, y12, y13, y14, y15));

    mixin(rowRound!(x00, x01, x02, x03, x04, x05, x06, x07, x08, x09, x10,
            x11, x12, x13, x14, x15));

    immutable uint[16] test0 = [
        y00, y01, y02, y03, y04, y05, y06, y07, y08, y09, y10, y11, y12, y13, y14, y15
    ];

    immutable uint[16] test1 = [
        x00, x01, x02, x03, x04, x05, x06, x07, x08, x09, x10, x11, x12, x13, x14, x15
    ];

    assert(test0 == [0x08008145, 0x00000080, 0x00010200, 0x20500000, 0x20100001, 0x00048044, 0x00000080, 0x00010000,
            0x00000001, 0x00002000, 0x80040000, 0x00000000, 0x00000001,
            0x00000200, 0x00402000, 0x88000100]);

    assert(test1 == [0xa890d39d, 0x65d71596, 0xe9487daa, 0xc8ca6a86, 0x949d2192, 0x764b7754, 0xe408d9b9, 0x7a41b4d1,
            0x3402e183, 0x3c3af432, 0x50669f96, 0xd89ef0a8, 0x0040ede5,
            0xb545fbce, 0xd257ed4f, 0x1818882d]);
}

enum string colRound(alias _x00, alias _x01, alias _x02, alias _x03, alias _x04,
            alias _x05, alias _x06, alias _x07, alias _x08, alias _x09, alias _x10,
            alias _x11, alias _x12, alias _x13, alias _x14, alias _x15,) = q{
    mixin(quarterRound!(%1$s, %5$s, %9$s, %13$s));
    mixin(quarterRound!(%6$s, %10$s, %14$s, %2$s));
    mixin(quarterRound!(%11$s, %15$s, %3$s, %7$s));
    mixin(quarterRound!(%16$s, %4$s, %8$s, %12$s));
}.format(
            __traits(identifier, _x00), __traits(identifier,
            _x01), __traits(identifier, _x02), __traits(identifier, _x03),
            __traits(identifier, _x04), __traits(identifier, _x05), __traits(identifier, _x06),
            __traits(identifier, _x07), __traits(identifier, _x08), __traits(identifier, _x09),
            __traits(identifier, _x10), __traits(identifier, _x11), __traits(identifier, _x12),
            __traits(identifier, _x13), __traits(identifier, _x14), __traits(identifier, _x15));

@safe unittest
{
    uint y00 = 0x00000001, y01 = 0x00000000, y02 = 0x00000000, y03 = 0x00000000,
        y04 = 0x00000001, y05 = 0x00000000, y06 = 0x00000000, y07 = 0x00000000, y08 = 0x00000001,
        y09 = 0x00000000, y10 = 0x00000000, y11 = 0x00000000, y12 = 0x00000001,
        y13 = 0x00000000, y14 = 0x00000000, y15 = 0x00000000;

    uint x00 = 0x08521bd6, x01 = 0x1fe88837, x02 = 0xbb2aa576, x03 = 0x3aa26365,
        x04 = 0xc54c6a5b, x05 = 0x2fc74c2f, x06 = 0x6dd39cc3, x07 = 0xda0a64f6, x08 = 0x90a2f23d,
        x09 = 0x067f95a6, x10 = 0x06b35f61, x11 = 0x41e4732e, x12 = 0xe859c100,
        x13 = 0xea4d84b7, x14 = 0x0f619bff, x15 = 0xbc6e965a;

    mixin(colRound!(y00, y01, y02, y03, y04, y05, y06, y07, y08, y09, y10,
            y11, y12, y13, y14, y15));

    mixin(colRound!(x00, x01, x02, x03, x04, x05, x06, x07, x08, x09, x10,
            x11, x12, x13, x14, x15));

    immutable uint[16] test0 = [
        y00, y01, y02, y03, y04, y05, y06, y07, y08, y09, y10, y11, y12, y13, y14, y15
    ];

    immutable uint[16] test1 = [
        x00, x01, x02, x03, x04, x05, x06, x07, x08, x09, x10, x11, x12, x13, x14, x15
    ];

    assert(test0 == [0x10090288, 0x00000000, 0x00000000, 0x00000000, 0x00000101, 0x00000000, 0x00000000, 0x00000000,
            0x00020401, 0x00000000, 0x00000000, 0x00000000, 0x40a04001,
            0x00000000, 0x00000000, 0x00000000]);

    assert(test1 == [0x8c9d190a, 0xce8e4c90, 0x1ef8e9d3, 0x1326a71a, 0x90a20123, 0xead3c4f3, 0x63a091a0, 0xf0708d69,
            0x789b010c, 0xd195a681, 0xeb7d5504, 0xa774135c, 0x481c2027,
            0x53a8e4b5, 0x4c1f89c5, 0x3f78c9c8]);
}

ubyte[64] salsa20(in ubyte[64] input) pure nothrow @safe @nogc
{
    auto x00 = littleEndian(input[00 .. 04]), x01 = littleEndian(input[04 .. 08]),
        x02 = littleEndian(input[08 .. 12]), x03 = littleEndian(input[12 .. 16]),
        x04 = littleEndian(input[16 .. 20]), x05 = littleEndian(input[20 .. 24]),
        x06 = littleEndian(input[24 .. 28]), x07 = littleEndian(input[28 .. 32]),
        x08 = littleEndian(input[32 .. 36]), x09 = littleEndian(input[36 .. 40]),
        x10 = littleEndian(input[40 .. 44]), x11 = littleEndian(input[44 .. 48]),
        x12 = littleEndian(input[48 .. 52]), x13 = littleEndian(input[52 .. 56]),
        x14 = littleEndian(input[56 .. 60]), x15 = littleEndian(input[60 .. 64]);

    auto y00 = x00, y01 = x01, y02 = x02, y03 = x03, y04 = x04, y05 = x05,
        y06 = x06, y07 = x07, y08 = x08, y09 = x09, y10 = x10, y11 = x11, y12 = x12,
        y13 = x13, y14 = x14, y15 = x15;

    foreach (i; 0 .. 10)
    {
        mixin(colRound!(x00, x01, x02, x03, x04, x05, x06, x07, x08, x09, x10,
                x11, x12, x13, x14, x15));

        mixin(rowRound!(x00, x01, x02, x03, x04, x05, x06, x07, x08, x09, x10,
                x11, x12, x13, x14, x15));
    }

    return concat!(ubyte[64])(littleEndianInv(x00 + y00), littleEndianInv(x01 + y01),
            littleEndianInv(x02 + y02), littleEndianInv(x03 + y03), littleEndianInv(x04 + y04),
            littleEndianInv(x05 + y05), littleEndianInv(x06 + y06), littleEndianInv(x07 + y07),
            littleEndianInv(x08 + y08), littleEndianInv(x09 + y09), littleEndianInv(x10 + y10),
            littleEndianInv(x11 + y11), littleEndianInv(x12 + y12), littleEndianInv(x13 + y13),
            littleEndianInv(x14 + y14), littleEndianInv(x15 + y15));
}

@safe unittest
{
    ubyte[64] test0 = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
    test0 = salsa20(test0);

    ubyte[64] test1 = [211, 159, 13, 115, 76, 55, 82, 183, 3, 117, 222, 37,
        191, 187, 234, 136, 49, 237, 179, 48, 1, 106, 178, 219, 175, 199,
        166, 48, 86, 16, 179, 207, 31, 240, 32, 63, 15, 83, 93, 161, 116, 147,
        48, 113, 238, 55, 204, 36, 79, 201, 235, 79, 3, 81, 156, 47, 203, 26,
        244, 243, 88, 118, 104, 54];
    test1 = salsa20(test1);

    ubyte[64] test2 = [88, 118, 104, 54, 79, 201, 235, 79, 3, 81, 156, 47, 203,
        26, 244, 243, 191, 187, 234, 136, 211, 159, 13, 115, 76, 55, 82, 183,
        3, 117, 222, 37, 86, 16, 179, 207, 49, 237, 179, 48, 1, 106, 178, 219,
        175, 199, 166, 48, 238, 55, 204, 36, 31, 240, 32, 63, 15, 83, 93, 161, 116, 147, 48, 113];
    test2 = salsa20(test2);

    ubyte[64] test3 = [6, 124, 83, 146, 38, 191, 9, 50, 4, 161, 47, 222, 122,
        182, 223, 185, 75, 27, 0, 216, 16, 122, 7, 89, 162, 104, 101, 147, 213,
        21, 54, 95, 225, 253, 139, 176, 105, 132, 23, 116, 76, 41, 176, 207,
        221, 34, 157, 108, 94, 94, 99, 52, 90, 117, 91, 220, 146, 190, 239,
        143, 196, 176, 130, 186];
    foreach (i; 0 .. 1_000_000)
        test3 = salsa20(test3);

    assert(test0 == [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]);

    assert(test1 == [109, 42, 178, 168, 156, 240, 248, 238, 168, 196, 190, 203,
            26, 110, 170, 154, 29, 29, 150, 26, 150, 30, 235, 249, 190, 163,
            251, 48, 69, 144, 51, 57, 118, 40, 152, 157, 180, 57, 27, 94,
            107, 42, 236, 35, 27, 111, 114, 114, 219, 236, 232, 135, 111,
            155, 110, 18, 24, 232, 95, 158, 179, 19, 48, 202]);

    assert(test2 == [179, 19, 48, 202, 219, 236, 232, 135, 111, 155, 110, 18,
            24, 232, 95, 158, 26, 110, 170, 154, 109, 42, 178, 168, 156, 240,
            248, 238, 168, 196, 190, 203, 69, 144, 51, 57, 29, 29, 150, 26,
            150, 30, 235, 249, 190, 163, 251, 48, 27, 111, 114, 114, 118, 40,
            152, 157, 180, 57, 27, 94, 107, 42, 236, 35]);

    assert(test3 == [8, 18, 38, 199, 119, 76, 215, 67, 173, 127, 144, 162,
            103, 212, 176, 217, 192, 19, 233, 33, 159, 197, 154, 160, 128, 243,
            219, 65, 171, 136, 135, 225, 123, 11, 68, 86, 237, 82, 20, 155,
            133, 189, 9, 83, 167, 116, 194, 78, 122, 127, 195, 185, 185, 204,
            188, 90, 245, 9, 183, 248, 226, 85, 245, 104]);
}

static immutable ubyte[4] sigma0 = [101, 120, 112, 97];
static immutable ubyte[4] sigma1 = [110, 100, 32, 51];
static immutable ubyte[4] sigma2 = [50, 45, 98, 121];
static immutable ubyte[4] sigma3 = [116, 101, 32, 107];

ubyte[64] salsa20Exp(in ref ubyte[32] key, in ubyte[16] n) @safe pure nothrow @nogc
{
    return salsa20(concat!(ubyte[64])(sigma0, key[0 .. 16], sigma1, n,
            sigma2, key[16 .. $], sigma3));
}

@safe unittest
{
    immutable ubyte[32] key = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
        15, 16, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216];

    immutable ubyte[16] n = [
        101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116
    ];

    assert(salsa20Exp(key, n) == [69, 37, 68, 39, 41, 15, 107, 193, 255, 139,
            122, 6, 170, 233, 217, 98, 89, 144, 182, 106, 21, 51, 200, 65, 239,
            49, 222, 34, 215, 114, 40, 126, 104, 197, 7, 225, 197, 153, 31,
            2, 102, 78, 76, 176, 84, 245, 246, 184, 177, 160, 133, 130, 6, 72,
            149, 119, 192, 195, 132, 236, 234, 103, 246, 74]);
}