const mem = @import("../mem.zig");
const math = @import("../math/index.zig");
const endian = @import("../endian.zig");
const debug = @import("../debug/index.zig");

pub const u160 = @IntType(false, 160);

const RoundParam = struct {
    a: u32, b: u32, c: u32, d: u32, e: u32, i: u32,
};

fn Rp(a: u32, b: u32, c: u32, d: u32, e: u32, i: u32) -> RoundParam {
    return RoundParam { .a = a, .b = b, .c = c, .d = d, .e = e, .i = i };
}

pub const Sha1 = struct {
    const Self = this;

    s: [5]u32,
    // Streaming Cache
    buf: [64]u8,
    buf_len: u8,
    total_len: u64,

    pub fn init() -> Self {
        var d: Self = undefined;
        d.reset();
        return d;
    }

    pub fn reset(d: &Self) {
        d.s[0] = 0x67452301;
        d.s[1] = 0xEFCDAB89;
        d.s[2] = 0x98BADCFE;
        d.s[3] = 0x10325476;
        d.s[4] = 0xC3D2E1F0;
        d.buf_len = 0;
        d.total_len = 0;
    }

    pub fn hash(b: []const u8) -> u160 {
        var d = Sha1.init();
        d.update(b);
        return d.final();
    }

    pub fn update(d: &Self, b: []const u8) {
        var off: usize = 0;

        // Partial buffer exists from previous update. Copy into buffer then hash.
        if (d.buf_len != 0 and d.buf_len + b.len > 64) {
            off += 64 - d.buf_len;
            mem.copy(u8, d.buf[d.buf_len..], b[0..off]);

            d.round(d.buf[0..]);
            d.buf_len = 0;
        }

        // Full middle blocks.
        while (off + 64 < b.len) : (off += 64) {
            d.round(b[off..off + 64]);
        }

        // Copy any remainder for next pass.
        mem.copy(u8, d.buf[d.buf_len..], b[off..]);
        d.buf_len += u8(b[off..].len);

        d.total_len += b.len;
    }

    pub fn final(d: &Self) -> u160 {
        // The buffer here will never be completely full.
        mem.set(u8, d.buf[d.buf_len..], 0);

        // Append padding bits.
        d.buf[d.buf_len] = 0x80;
        d.buf_len += 1;

        // > 448 mod 512 so need to add an extra round to wrap around.
        if (64 - d.buf_len < 8) {
            d.round(d.buf[0..]);
            mem.set(u8, d.buf[0..], 0);
        }

        // Append message length.
        var i: usize = 1;
        var len = d.total_len >> 5;
        d.buf[63] = u8(d.total_len & 0x1f) << 3;
        while (i < 8) : (i += 1) {
            d.buf[63 - i] = u8(len & 0xff);
            len >>= 8;
        }

        d.round(d.buf[0..]);

        const r =
            (u160(d.s[0]) << 128) |
            (u160(d.s[1]) << 96)  |
            (u160(d.s[2]) << 64)  |
            (u160(d.s[3]) << 32)  |
            (u160(d.s[4]) << 0);

        return endian.swapIfBe(u160, r);
    }

    fn round(d: &Self, b: []const u8) {
        debug.assert(b.len == 64);

        var s: [16]u32 = undefined;

        var v: [5]u32 = []u32 {
            d.s[0], d.s[1], d.s[2], d.s[3], d.s[4],
        };

        const round0a = comptime []RoundParam {
            Rp(0, 1, 2, 3, 4,  0),
            Rp(4, 0, 1, 2, 3,  1),
            Rp(3, 4, 0, 1, 2,  2),
            Rp(2, 3, 4, 0, 1,  3),
            Rp(1, 2, 3, 4, 0,  4),
            Rp(0, 1, 2, 3, 4,  5),
            Rp(4, 0, 1, 2, 3,  6),
            Rp(3, 4, 0, 1, 2,  7),
            Rp(2, 3, 4, 0, 1,  8),
            Rp(1, 2, 3, 4, 0,  9),
            Rp(0, 1, 2, 3, 4, 10),
            Rp(4, 0, 1, 2, 3, 11),
            Rp(3, 4, 0, 1, 2, 12),
            Rp(2, 3, 4, 0, 1, 13),
            Rp(1, 2, 3, 4, 0, 14),
            Rp(0, 1, 2, 3, 4, 15),
        };
        inline for (round0a) |r| {
            s[r.i] = (u32(b[r.i * 4 + 0]) << 24) |
                     (u32(b[r.i * 4 + 1]) << 16) |
                     (u32(b[r.i * 4 + 2]) <<  8) |
                     (u32(b[r.i * 4 + 3]) <<  0);

            v[r.e] = v[r.e] +% math.rotl(u32, v[r.a], u32(5)) +% 0x5A827999 +% s[r.i & 0xf]
                        +% ((v[r.b] & v[r.c]) | (~v[r.b] & v[r.d]));
            v[r.b] = math.rotl(u32, v[r.b], u32(30));
        }

        const round0b = comptime []RoundParam {
            Rp(4, 0, 1, 2, 3, 16),
            Rp(3, 4, 0, 1, 2, 17),
            Rp(2, 3, 4, 0, 1, 18),
            Rp(1, 2, 3, 4, 0, 19),
        };
        inline for (round0b) |r| {
            const t = s[(r.i-3) & 0xf] ^ s[(r.i-8) & 0xf] ^ s[(r.i-14) & 0xf] ^ s[(r.i-16) & 0xf];
            s[r.i & 0xf] = math.rotl(u32, t, u32(1));

            v[r.e] = v[r.e] +% math.rotl(u32, v[r.a], u32(5)) +% 0x5A827999 +% s[r.i & 0xf]
                        +% ((v[r.b] & v[r.c]) | (~v[r.b] & v[r.d]));
            v[r.b] = math.rotl(u32, v[r.b], u32(30));
        }

        const round1 = comptime []RoundParam {
            Rp(0, 1, 2, 3, 4, 20),
            Rp(4, 0, 1, 2, 3, 21),
            Rp(3, 4, 0, 1, 2, 22),
            Rp(2, 3, 4, 0, 1, 23),
            Rp(1, 2, 3, 4, 0, 24),
            Rp(0, 1, 2, 3, 4, 25),
            Rp(4, 0, 1, 2, 3, 26),
            Rp(3, 4, 0, 1, 2, 27),
            Rp(2, 3, 4, 0, 1, 28),
            Rp(1, 2, 3, 4, 0, 29),
            Rp(0, 1, 2, 3, 4, 30),
            Rp(4, 0, 1, 2, 3, 31),
            Rp(3, 4, 0, 1, 2, 32),
            Rp(2, 3, 4, 0, 1, 33),
            Rp(1, 2, 3, 4, 0, 34),
            Rp(0, 1, 2, 3, 4, 35),
            Rp(4, 0, 1, 2, 3, 36),
            Rp(3, 4, 0, 1, 2, 37),
            Rp(2, 3, 4, 0, 1, 38),
            Rp(1, 2, 3, 4, 0, 39),
        };
        inline for (round1) |r| {
            const t = s[(r.i-3) & 0xf] ^ s[(r.i-8) & 0xf] ^ s[(r.i-14) & 0xf] ^ s[(r.i-16) & 0xf];
            s[r.i & 0xf] = math.rotl(u32, t, u32(1));

            v[r.e] = v[r.e] +% math.rotl(u32, v[r.a], u32(5)) +% 0x6ED9EBA1 +% s[r.i & 0xf]
                        +% (v[r.b] ^ v[r.c] ^ v[r.d]);
            v[r.b] = math.rotl(u32, v[r.b], u32(30));
        }

        const round2 = comptime []RoundParam {
            Rp(0, 1, 2, 3, 4, 40),
            Rp(4, 0, 1, 2, 3, 41),
            Rp(3, 4, 0, 1, 2, 42),
            Rp(2, 3, 4, 0, 1, 43),
            Rp(1, 2, 3, 4, 0, 44),
            Rp(0, 1, 2, 3, 4, 45),
            Rp(4, 0, 1, 2, 3, 46),
            Rp(3, 4, 0, 1, 2, 47),
            Rp(2, 3, 4, 0, 1, 48),
            Rp(1, 2, 3, 4, 0, 49),
            Rp(0, 1, 2, 3, 4, 50),
            Rp(4, 0, 1, 2, 3, 51),
            Rp(3, 4, 0, 1, 2, 52),
            Rp(2, 3, 4, 0, 1, 53),
            Rp(1, 2, 3, 4, 0, 54),
            Rp(0, 1, 2, 3, 4, 55),
            Rp(4, 0, 1, 2, 3, 56),
            Rp(3, 4, 0, 1, 2, 57),
            Rp(2, 3, 4, 0, 1, 58),
            Rp(1, 2, 3, 4, 0, 59),
        };
        inline for (round2) |r| {
            const t = s[(r.i-3) & 0xf] ^ s[(r.i-8) & 0xf] ^ s[(r.i-14) & 0xf] ^ s[(r.i-16) & 0xf];
            s[r.i & 0xf] = math.rotl(u32, t, u32(1));

            v[r.e] = v[r.e] +% math.rotl(u32, v[r.a], u32(5)) +% 0x8F1BBCDC  +% s[r.i & 0xf]
                        +% ((v[r.b] & v[r.c]) ^ (v[r.b] & v[r.d]) ^ (v[r.c] & v[r.d]));
            v[r.b] = math.rotl(u32, v[r.b], u32(30));
        }

        const round3 = comptime []RoundParam {
            Rp(0, 1, 2, 3, 4, 60),
            Rp(4, 0, 1, 2, 3, 61),
            Rp(3, 4, 0, 1, 2, 62),
            Rp(2, 3, 4, 0, 1, 63),
            Rp(1, 2, 3, 4, 0, 64),
            Rp(0, 1, 2, 3, 4, 65),
            Rp(4, 0, 1, 2, 3, 66),
            Rp(3, 4, 0, 1, 2, 67),
            Rp(2, 3, 4, 0, 1, 68),
            Rp(1, 2, 3, 4, 0, 69),
            Rp(0, 1, 2, 3, 4, 70),
            Rp(4, 0, 1, 2, 3, 71),
            Rp(3, 4, 0, 1, 2, 72),
            Rp(2, 3, 4, 0, 1, 73),
            Rp(1, 2, 3, 4, 0, 74),
            Rp(0, 1, 2, 3, 4, 75),
            Rp(4, 0, 1, 2, 3, 76),
            Rp(3, 4, 0, 1, 2, 77),
            Rp(2, 3, 4, 0, 1, 78),
            Rp(1, 2, 3, 4, 0, 79),
        };
        inline for (round3) |r| {
            const t = s[(r.i-3) & 0xf] ^ s[(r.i-8) & 0xf] ^ s[(r.i-14) & 0xf] ^ s[(r.i-16) & 0xf];
            s[r.i & 0xf] = math.rotl(u32, t, u32(1));

            v[r.e] = v[r.e] +% math.rotl(u32, v[r.a], u32(5)) +% 0xCA62C1D6 +% s[r.i & 0xf]
                        +% (v[r.b] ^ v[r.c] ^ v[r.d]);
            v[r.b] = math.rotl(u32, v[r.b], u32(30));
        }

        d.s[0] +%= v[0];
        d.s[1] +%= v[1];
        d.s[2] +%= v[2];
        d.s[3] +%= v[3];
        d.s[4] +%= v[4];
    }
};

test "sha1 single" {
    debug.assert(0xda39a3ee5e6b4b0d3255bfef95601890afd80709 == Sha1.hash(""));
    debug.assert(0xa9993e364706816aba3e25717850c26c9cd0d89d == Sha1.hash("abc"));
    debug.assert(0xa49b2446a02c645bf419f995b67091253a04a259 == Sha1.hash("abcdefghbcdefghicdefghijdefghijkefghijklfghijklmghijklmnhijklmnoijklmnopjklmnopqklmnopqrlmnopqrsmnopqrstnopqrstu"));
}

test "sha1 streaming" {
    var h = Sha1.init();

    debug.assert(0xda39a3ee5e6b4b0d3255bfef95601890afd80709 == h.final());

    h.reset();
    h.update("abc");
    debug.assert(0xa9993e364706816aba3e25717850c26c9cd0d89d == h.final());

    h.reset();
    h.update("a");
    h.update("b");
    h.update("c");
    debug.assert(0xa9993e364706816aba3e25717850c26c9cd0d89d == h.final());
}