module unsigned

import math.bits
import encoding.binary

pub struct Uint128 {
pub mut:
    lo u64
    hi u64
}

pub const uint128_zero = Uint128{}
pub const uint128_max = Uint128{18446744073709551615, 18446744073709551615}

// is_zero returns true if u == 0
pub fn (u Uint128) is_zero() bool {
    return u == Uint128{}
}

// equals returns true if u == v.
//
// Uint128 values can be compared directly with ==, but use of the Equals method
// is preferred for consistency.
pub fn (u Uint128) equals(v Uint128) bool {
    return u == v
}

// equals_64 returns true if u == v
pub fn (u Uint128) equals_64(v u64) bool {
    return u.lo == v && u.hi == 0
}

// cmp compares u and v and returns:
//
// -1 if u <  v
//  0 if u == v
// +1 if u >  v
//
pub fn (u Uint128) cmp(v Uint128) int {
    if u == v {
        return 0
    } else if u.hi < v.hi || (u.hi == v.hi && u.lo < v.lo) {
        return -1
    } else {
        return 1
    }
}

// cmp_64 compares u and v and returns:
//
//   -1 if u <  v
//    0 if u == v
//   +1 if u >  v
//
pub fn (u Uint128) cmp_64(v u64) int {
    if u.hi == 0 && u.lo == v {
        return 0
    } else if u.hi == 0 && u.lo < v {
        return -1
    } else {
        return 1
    }
}

// and returns u & v
pub fn (u Uint128) and(v Uint128) Uint128 {
    return Uint128{u.lo & v.lo, u.hi & v.hi}
}

// and_64 returns u & v
pub fn (u Uint128) and_64(v u64) Uint128 {
    return Uint128{u.lo & v, u.hi & 0}
}

// or returns u | v
pub fn (u Uint128) or_(v Uint128) Uint128 {
    return Uint128{u.lo | v.lo, u.hi | v.hi}
}

// or returns u | v
pub fn (u Uint128) or_64(v u64) Uint128 {
    return Uint128{u.lo | v, u.hi | 0}
}

// xor returns u ^ v
pub fn (u Uint128) xor(v Uint128) Uint128 {
    return Uint128{u.lo ^ v.lo, u.hi ^ v.hi}
}

// xor_64 returns u ^ v
pub fn (u Uint128) xor_64(v u64) Uint128 {
    return Uint128{u.lo ^ v, u.hi ^ 0}
}

// add returns u + v with wraparound semantics
pub fn (u Uint128) add(v Uint128) Uint128 {
    lo, carry := bits.add_64(u.lo, v.lo, 0)
    hi, _ := bits.add_64(u.hi, v.hi, carry)
    return Uint128{lo, hi}
}

// add_128 return u + v and the carry
pub fn add_128(x Uint128, y Uint128, carry u64) (Uint128, u64) {
    mut sum := Uint128{}
    mut carry_out := u64(0)
    sum.lo, carry_out = bits.add_64(x.lo, y.lo, carry)
    sum.hi, carry_out = bits.add_64(x.hi, y.hi, carry_out)
    return sum, carry_out
}

// sub_128 returns u - v and the borrow
pub fn sub_128(x Uint128, y Uint128, borrow u64) (Uint128, u64) {
    mut diff := Uint128{}
    mut borrow_out := u64(0)
    diff.lo, borrow_out = bits.sub_64(x.lo, y.lo, borrow)
    diff.hi, borrow_out = bits.sub_64(x.hi, y.hi, borrow_out)
    return diff, borrow_out
}

// mul_128 returns u x v
pub fn mul_128(x Uint128, y Uint128) (Uint128, Uint128) {
    mut lo := Uint128{}
    mut hi := Uint128{}
    lo.hi, lo.lo = bits.mul_64(x.lo, y.lo)
    hi.hi, hi.lo = bits.mul_64(x.hi, y.hi)
    t0, t1 := bits.mul_64(x.lo, y.hi)
    t2, t3 := bits.mul_64(x.hi, y.lo)

    mut c0 := u64(0)
    mut c1 := u64(0)
    lo.hi, c0 = bits.add_64(lo.hi, t1, 0)
    lo.hi, c1 = bits.add_64(lo.hi, t3, 0)
    hi.lo, c0 = bits.add_64(hi.lo, t0, c0)
    hi.lo, c1 = bits.add_64(hi.lo, t2, c1)
    hi.hi += c0 + c1
    return hi, lo
}

// div_128 returns u / v
pub fn div_128(a_hi Uint128, a_lo Uint128, b Uint128) (Uint128, Uint128) {
    a := uint256_new(a_lo, a_hi)
    b_256 := uint256_new(b, uint128_zero)
    if a < b_256 {
        return uint128_zero, a_lo
    }
    if b.is_zero() {
        panic('Division by zero')
    }
    if a.hi.is_zero() {
        return a.lo.quo_rem(b)
    }
    shift := u32(b_256.leading_zeros() - a.leading_zeros())
    mut af := a
    mut bf := b_256.lsh(shift)
    mut quotient := uint128_zero

    for _ in 0 .. shift + 1 {
        quotient = quotient.lsh(1)
        diff_result := bf.add(af.not())
        s := u64(i64(diff_result.hi.hi) >> 63)
        quotient.lo |= s & 1
        mask := uint256_new(uint128_new(s, s), uint128_new(s, s))
        af = af.sub(bf.and(mask))
        bf = bf.rsh(1)
    }
    return quotient, af.lo
}

// add_64 returns u + v with wraparound semantics
pub fn (u Uint128) add_64(v u64) Uint128 {
    lo, carry := bits.add_64(u.lo, v, 0)
    hi := u.hi + carry
    return Uint128{lo, hi}
}

// sub returns u - v with wraparound semantics
pub fn (u Uint128) sub(v Uint128) Uint128 {
    lo, borrow := bits.sub_64(u.lo, v.lo, 0)
    hi, _ := bits.sub_64(u.hi, v.hi, borrow)
    return Uint128{lo, hi}
}

// sub_64 returns u - v with wraparound semantics
pub fn (u Uint128) sub_64(v u64) Uint128 {
    lo, borrow := bits.sub_64(u.lo, v, 0)
    hi := u.hi - borrow
    return Uint128{lo, hi}
}

// mul returns u * v with wraparound semantics
pub fn (u Uint128) mul(v Uint128) Uint128 {
    mut hi, lo := bits.mul_64(u.lo, v.lo)
    hi += u.hi * v.lo + u.lo * v.hi
    return Uint128{lo, hi}
}

// mul_64 returns u * v with wraparound semantics
pub fn (u Uint128) mul_64(v u64) Uint128 {
    mut hi, lo := bits.mul_64(u.lo, v)
    hi += u.hi * v
    return Uint128{lo, hi}
}

// overflowing_mul_64 returns u x v even if result size > 128
pub fn (u Uint128) overflowing_mul_64(v u64) (Uint128, bool) {
    hi, lo := bits.mul_64(u.lo, v)
    p0, p1 := bits.mul_64(u.hi, v)
    hi2, c0 := bits.add_64(hi, p1, 0)

    return Uint128{lo, hi2}, p0 != 0 || c0 != 0
}

// overflowing_add_64 returns u + v even if result size > 128
pub fn (u Uint128) overflowing_add_64(v u64) (Uint128, u64) {
    lo, carry := bits.add_64(u.lo, v, 0)
    hi, carry2 := bits.add_64(u.hi, 0, carry)

    return Uint128{lo, hi}, carry2
}

// div returns u / v
pub fn (u Uint128) div(v Uint128) Uint128 {
    q, _ := u.quo_rem(v)
    return q
}

// mod returns r = u % v
pub fn (u Uint128) mod(v Uint128) Uint128 {
    _, r := u.quo_rem(v)
    return r
}

// mod_64 returns r = u % v
pub fn (u Uint128) mod_64(v u64) u64 {
    _, r := u.quo_rem_64(v)
    return r
}

// quo_rem_64 returns q = u/v and r = u%v
pub fn (u Uint128) quo_rem_64(v u64) (Uint128, u64) {
    if u.hi < v {
        mut r := u64(0)
        mut q := Uint128{0, 0}
        q.lo, r = bits.div_64(u.hi, u.lo, v)

        return q, r
    } else {
        mut q := Uint128{0, 0}
        mut r := u64(0)
        mut r2 := u64(0)
        q.hi, r = bits.div_64(0, u.hi, v)
        q.lo, r2 = bits.div_64(r, u.lo, v)
        return q, r2
    }
}

// quo_rem returns q = u/v and r = u%v
pub fn (a Uint128) quo_rem(b Uint128) (Uint128, Uint128) {
    if a < b {
        return uint128_zero, a
    }
    if b.is_zero() {
        panic('Division by zero')
    }
    if b.hi == 0 {
        quotient, remainder := a.quo_rem_64(b.lo)
        return quotient, uint128_from_64(remainder)
    }
    shift := u32(b.leading_zeros() - a.leading_zeros())
    mut af := a
    mut bf := b.lsh(shift)
    mut quotient := uint128_zero

    for _ in 0 .. shift + 1 {
        quotient = quotient.lsh(1)
        diff_result := bf.add(af.not())
        s := u64(i64(diff_result.hi) >> 63)
        quotient.lo |= s & 1
        mask := uint128_new(s, s)
        af = af.sub(bf.and(mask))
        bf = bf.rsh(1)
    }
    return quotient, af
}

// lsh returns u << n
pub fn (u Uint128) lsh(n u32) Uint128 {
    mut s := Uint128{}
    if n == 0 {
        s.lo = u.lo
        s.hi = u.hi
    } else if n >= 128 {
        s.lo = 0
        s.hi = 0
    } else if n == 64 {
        s.lo = 0
        s.hi = u.lo
    } else if n > 64 {
        s.lo = 0
        s.hi = u.lo << (n - 64)
    } else {
        s.lo = u.lo << n
        s.hi = u.hi << n | u.lo >> (64 - n)
    }

    return s
}

// rsh returns u >> n
pub fn (u Uint128) rsh(n u32) Uint128 {
    mut s := Uint128{}
    if n == 0 {
        s.lo = u.lo
        s.hi = u.hi
    } else if n >= 128 {
        s.lo = 0
        s.hi = 0
    } else if n == 64 {
        s.hi = 0
        s.lo = u.hi
    } else if n > 64 {
        s.hi = 0
        s.lo = u.hi >> (n - 64)
    } else {
        s.lo = u.lo >> n | u.hi << (64 - n)
        s.hi = u.hi >> n
    }

    return s
}

// leading_zeros returns the number of leading zero bits in u; the result is 128
// for u == 0.
pub fn (u Uint128) leading_zeros() int {
    if u.hi > 0 {
        return bits.leading_zeros_64(u.hi)
    }
    return 64 + bits.leading_zeros_64(u.lo)
}

// trailing_zeros returns the number of trailing zero bits in u; the result is
// 128 for u == 0.
pub fn (u Uint128) trailing_zeros() int {
    if u.lo > 0 {
        return bits.trailing_zeros_64(u.lo)
    }
    return 64 + bits.trailing_zeros_64(u.hi)
}

// ones_count returns the number of one bits ("population count" in u)
pub fn (u Uint128) ones_count() int {
    return bits.ones_count_64(u.hi) + bits.ones_count_64(u.lo)
}

// rotate_left returns the value of u rotated left by (k mod 128) bits.
pub fn (u Uint128) rotate_left(k int) Uint128 {
    n := u32(128)
    s := u32(k) & (n - 1)
    return u.lsh(s).or_(u.rsh(n - s))
}

// rotate_right returns the value of u rotated right by (k mod 128) bits.
pub fn (u Uint128) rotate_right(k int) Uint128 {
    return u.rotate_left(-k)
}

// reverse returns the value of u with its bits in reversed order.
pub fn (u Uint128) reverse() Uint128 {
    return Uint128{bits.reverse_64(u.hi), bits.reverse_64(u.lo)}
}

// reverse_bytes returns the value of u with its bytes in reversed order.
pub fn (u Uint128) reverse_bytes() Uint128 {
    return Uint128{bits.reverse_bytes_64(u.hi), bits.reverse_bytes_64(u.lo)}
}

// not returns a binary negation of the Uint128 value
pub fn (u Uint128) not() Uint128 {
    return Uint128{~u.lo, ~u.hi}
}

// len returns the minimum number of bits required to represent u; the result is
// 0 for u == 0.
pub fn (u Uint128) len() int {
    return 128 - u.leading_zeros()
}

// string returns the base-10 representation of u as a string
pub fn (u_ Uint128) str() string {
    mut u := u_
    if u.is_zero() {
        return '0'
    }

    mut buf := '0000000000000000000000000000000000000000'.bytes() // log10(2^128) < 40

    for i := buf.len; true; i -= 19 {
        q, mut r := u.quo_rem_64(u64(1e19))

        mut n := int(0)
        for ; r != 0; r /= 10 {
            n++
            buf[i - n] += u8(r % 10)
        }
        if q.is_zero() {
            return buf[i - n..].bytestr()
        }
        u = q
    }

    return ''
}

// put_bytes stores u in b in little-endian order
pub fn (u Uint128) put_bytes(mut b []u8) {
    binary.little_endian_put_u64(mut b[..8], u.lo)
    binary.little_endian_put_u64(mut b[8..], u.hi)
}

// uint128_from_64 converts v to a Uint128 value
pub fn uint128_from_64(v u64) Uint128 {
    return uint128_new(v, 0)
}

// uint128_new creates new Uint128 with given `lo` and `hi`
pub fn uint128_new(lo u64, hi u64) Uint128 {
    return Uint128{lo, hi}
}

// unint_from_dec_str returns an error or new Uint128 from given string.
// The `_` character is allowed as a separator.
pub fn uint128_from_dec_str(value string) !Uint128 {
    mut res := uint128_zero
    underscore := `_`

    for b_ in value {
        b := b_ - `0`
        if b > 9 {
            // allow _ as a separator in decimal strings
            if b_ == underscore {
                continue
            }

            return error('invalid character "${b}"')
        }

        r, overflow := res.overflowing_mul_64(10)

        if overflow {
            return error('invalid length')
        }
        r2, overflow2 := r.overflowing_add_64(u64(b))

        if overflow2 > 0 {
            return error('invalid length')
        }

        res = r2
    }
    return res
}

// / -> returns u / v
pub fn (u Uint128) / (v Uint128) Uint128 {
    return u.div(v)
}

// % -> returns u % v
pub fn (u Uint128) % (v Uint128) Uint128 {
    return u.mod(v)
}

// + -> returns u + v
pub fn (u Uint128) + (v Uint128) Uint128 {
    return u.add(v)
}

// - -> returns u - v
pub fn (u Uint128) - (v Uint128) Uint128 {
    return u.sub(v)
}

// * -> returns u * v
pub fn (u Uint128) * (v Uint128) Uint128 {
    return u.mul(v)
}

// < -> returns true if u < v
pub fn (u Uint128) < (v Uint128) bool {
    return u.cmp(v) == -1
}