/*
 * Copyright (c) 2012-2020 MIRACL UK Ltd.
 *
 * This file is part of MIRACL Core
 * (see https://github.com/miracl/core).
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

use crate::arch;
use crate::arch::Chunk;
use crate::nist521::big;
use crate::nist521::big::BIG;
use crate::nist521::dbig::DBIG;
use crate::nist521::rom;

use crate::rand::RAND;

#[derive(Copy, Clone)]
pub struct FP {
    pub x: BIG,
    pub xes: i32,
}

#[cfg(feature = "std")]
impl std::fmt::Debug for FP {
    fn fmt(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(formatter, "{}", self.tostring())
    }
}

#[cfg(feature = "std")]
impl std::fmt::Display for FP {
    fn fmt(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(formatter, "{}", self.tostring())
    }
}

pub const NOT_SPECIAL: usize = 0;
pub const PSEUDO_MERSENNE: usize = 1;
pub const MONTGOMERY_FRIENDLY: usize = 2;
pub const GENERALISED_MERSENNE: usize = 3;

pub const NEGATOWER: usize = 0;
pub const POSITOWER: usize = 1;

pub const MODBITS:usize = 521; /* Number of bits in Modulus */
pub const PM1D2: usize = 1;  /* Modulus mod 8 */
pub const RIADZ: isize = -4;  /* Z for hash-to-point */
pub const RIADZG2A: isize = 0;  /* G2 Z for hash-to-point */
pub const RIADZG2B: isize = 0;  /* G2 Z for hash-to-point */
pub const MODTYPE:usize=PSEUDO_MERSENNE;
pub const QNRI:usize=0; /* Fp2 QNR 2^i+sqrt(-1) */
pub const TOWER:usize=NEGATOWER; /* Tower type */

pub const FEXCESS:i32 = ((1 as i32)<<11)-1;
pub const OMASK: Chunk = (-1) << (MODBITS % big::BASEBITS);
pub const TBITS: usize = MODBITS % big::BASEBITS; // Number of active bits in top word
pub const TMASK: Chunk = (1 << TBITS) - 1;

pub const BIG_ENDIAN_SIGN: bool = false;

impl FP {
    /* Constructors */
    pub const fn new() -> FP {
        FP {
            x: BIG::new(),
            xes: 1,
        }
    }

    pub fn new_int(a: isize) -> FP {
        let mut f = FP::new();
        if a<0 {
            let mut m = BIG::new_ints(&rom::MODULUS);
            m.inc(a); m.norm();
            f.x.copy(&m);
        } else {
            f.x.inc(a);
        }
        f.nres();
        f
    }

    pub fn new_copy(y: &FP) -> FP {
        let mut f = FP::new();
        f.x.copy(&(y.x));
        f.xes = y.xes;
        f
    }

    pub fn new_big(y: &BIG) -> FP {
        let mut f = FP::new();
        f.x.copy(y);
        f.nres();
        f
    }

    pub fn new_rand(rng: &mut impl RAND) -> FP {
        let m = BIG::new_ints(&rom::MODULUS);
        let w = BIG::randomnum(&m,rng);
        FP::new_big(&w)
    }

    pub fn nres(&mut self) {
        if MODTYPE != PSEUDO_MERSENNE && MODTYPE != GENERALISED_MERSENNE {
            let r = BIG::new_ints(&rom::R2MODP);
            let mut d = BIG::mul(&(self.x), &r);
            self.x.copy(&FP::modulo(&mut d));
            self.xes = 2;
        } else {
            let m = BIG::new_ints(&rom::MODULUS);
            self.x.rmod(&m);
            self.xes = 1;
        }
    }

    /* convert back to regular form */
    pub fn redc(&self) -> BIG {
        if MODTYPE != PSEUDO_MERSENNE && MODTYPE != GENERALISED_MERSENNE {
            let mut d = DBIG::new_scopy(&(self.x));
            FP::modulo(&mut d)
        } else {
            BIG::new_copy(&(self.x))
        }
    }

    /* reduce a DBIG to a BIG using the appropriate form of the modulus */
    /* dd */
    pub fn modulo(d: &mut DBIG) -> BIG {
        if MODTYPE == PSEUDO_MERSENNE {
            let mut b = BIG::new();
            let mut t = d.split(MODBITS);
            b.dcopy(&d);
            let v = t.pmul(rom::MCONST as isize);

            t.add(&b);
            t.norm();

            let tw = t.w[big::NLEN - 1];
            t.w[big::NLEN - 1] &= TMASK;
            t.w[0] += rom::MCONST * ((tw >> TBITS) + (v << (big::BASEBITS - TBITS)));
            t.norm();
            return t;
        }

        if MODTYPE == MONTGOMERY_FRIENDLY {
            let mut b = BIG::new();
            for i in 0..big::NLEN {
                let x = d.w[i];

                let tuple = BIG::muladd(x, rom::MCONST - 1, x, d.w[big::NLEN + i - 1]);
                d.w[big::NLEN + i] += tuple.0;
                d.w[big::NLEN + i - 1] = tuple.1;
            }

            b.zero();

            for i in 0..big::NLEN {
                b.w[i] = d.w[big::NLEN + i];
            }
            b.norm();
            return b;
        }

        if MODTYPE == GENERALISED_MERSENNE {
            // GoldiLocks Only
            let mut b = BIG::new();
            let t = d.split(MODBITS);
            let rm2 = (MODBITS / 2) as usize;
            b.dcopy(&d);
            b.add(&t);
            let mut dd = DBIG::new_scopy(&t);
            dd.shl(rm2);

            let mut tt = dd.split(MODBITS);
            let lo = BIG::new_dcopy(&dd);
            b.add(&tt);
            b.add(&lo);
            b.norm();
            tt.shl(rm2);
            b.add(&tt);

            let carry = b.w[big::NLEN - 1] >> TBITS;
            b.w[big::NLEN - 1] &= TMASK;
            b.w[0] += carry;

            let ix=(224 / big::BASEBITS) as usize;
            b.w[ix] += carry << (224 % big::BASEBITS);
            b.norm();
            return b;
        }

        if MODTYPE == NOT_SPECIAL {
            let m = BIG::new_ints(&rom::MODULUS);
            return BIG::monty(&m, rom::MCONST, d);
        }
        BIG::new()
    }

    /* convert to string */
#[cfg(feature = "std")]
    pub fn tostring(&self) -> String {
        self.redc().tostring()
    }

    /* reduce this mod Modulus */
    pub fn reduce(&mut self) {
        let mut m = BIG::new_ints(&rom::MODULUS);
        let mut r = BIG::new_copy(&m);
        let mut sb: usize;
        self.x.norm();
        if self.xes > 16 {
            let q = FP::quo(&self.x, &m);
            let carry = r.pmul(q);
            r.w[big::NLEN - 1] += carry << big::BASEBITS; // correction - put any carry out back in again
            self.x.sub(&r);
            self.x.norm();
            sb = 2;
        } else {
            sb = FP::logb2((self.xes - 1) as u32);
        }
        m.fshl(sb);

        while sb > 0 {
            let sr = BIG::ssn(&mut r, &self.x, &mut m);
            self.x.cmove(&r, 1 - sr);
            sb -= 1;
        }

        self.xes = 1;
    }

    /* test this=0? */
    pub fn iszilch(&self) -> bool {
        let mut a = FP::new_copy(self);
        a.reduce();
        a.x.iszilch()
    }

    pub fn islarger(&self) -> isize {
        if self.iszilch() {
            return 0;
        }
        let mut sx = BIG::new_ints(&rom::MODULUS);
        let fx=self.redc();
        sx.sub(&fx); sx.norm();
        BIG::comp(&fx,&sx)
    }

    pub fn tobytes(&self,b: &mut [u8]) {
        self.redc().tobytes(b)
    }

    pub fn frombytes(b: &[u8]) -> FP {
        let t=BIG::frombytes(b);
        FP::new_big(&t)
    }

    /* test this=0? */
    pub fn isunity(&self) -> bool {
        let mut a = FP::new_copy(self);
        a.reduce();
        a.redc().isunity()
    }

    pub fn sign(&self) -> isize {
        if BIG_ENDIAN_SIGN {
            let mut m = BIG::new_ints(&rom::MODULUS);
            m.dec(1);
            m.fshr(1);
            let mut n = FP::new_copy(self);
            n.reduce();
            let w=n.redc();
            let cp=BIG::comp(&w,&m);
            ((cp+1)&2)>>1
        } else {
            let mut a = FP::new_copy(self);
            a.reduce();
            a.redc().parity()
        }
    }

    /* copy from FP b */
    pub fn copy(&mut self, b: &FP) {
        self.x.copy(&(b.x));
        self.xes = b.xes;
    }

    /* copy from BIG b */
    pub fn bcopy(&mut self, b: &BIG) {
        self.x.copy(&b);
        self.nres();
    }

    /* set this=0 */
    pub fn zero(&mut self) {
        self.x.zero();
        self.xes = 1;
    }

    /* set this=1 */
    pub fn one(&mut self) {
        self.x.one();
        self.nres()
    }

    /* normalise this */
    pub fn norm(&mut self) {
        self.x.norm();
    }

    /* swap FPs depending on d */
    pub fn cswap(&mut self, b: &mut FP, d: isize) {
        self.x.cswap(&mut (b.x), d);
        let mut c = d as i32;
        c = !(c - 1);
        let t = c & (self.xes ^ b.xes);
        self.xes ^= t;
        b.xes ^= t;
    }

    /* copy FPs depending on d */
    pub fn cmove(&mut self, b: &FP, d: isize) {
        self.x.cmove(&(b.x), d);
        let c = d as i32;
        self.xes ^= (self.xes ^ b.xes) & (-c);
    }

    /* this*=b mod Modulus */
    pub fn mul(&mut self, b: &FP) {
        if (self.xes as i64) * (b.xes as i64) > FEXCESS as i64 {
            self.reduce()
        }

        let mut d = BIG::mul(&(self.x), &(b.x));
        self.x.copy(&FP::modulo(&mut d));
        self.xes = 2;
    }

    fn logb2(w: u32) -> usize {
        let mut v = w;
        v |= v >> 1;
        v |= v >> 2;
        v |= v >> 4;
        v |= v >> 8;
        v |= v >> 16;

        v = v - ((v >> 1) & 0x55555555);
        v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
        ((((v + (v >> 4)) & 0xF0F0F0F).wrapping_mul(0x1010101)) >> 24) as usize
    }

    // find appoximation to quotient of a/m
    // Out by at most 2.
    // Note that MAXXES is bounded to be 2-bits less than half a word
    fn quo(n: &BIG, m: &BIG) -> isize {
        let hb = arch::CHUNK / 2;

        if TBITS < hb {
            let sh = hb - TBITS;
            let num = (n.w[big::NLEN - 1] << sh) | (n.w[big::NLEN - 2] >> (big::BASEBITS - sh));
            let den = (m.w[big::NLEN - 1] << sh) | (m.w[big::NLEN - 2] >> (big::BASEBITS - sh));
            (num / (den + 1)) as isize
        } else {
            let num = n.w[big::NLEN - 1];
            let den = m.w[big::NLEN - 1];
            (num / (den + 1)) as isize
        }
    }

    /* this = -this mod Modulus */
    pub fn neg(&mut self) {
        let mut p = BIG::new_ints(&rom::MODULUS);
        let sb = FP::logb2((self.xes - 1) as u32);

        p.fshl(sb);
        self.x.rsub(&p);
        self.xes = 1 << ((sb as i32) + 1);
        if self.xes > FEXCESS {
            self.reduce()
        }
    }

    /* this*=c mod Modulus, where c is a small int */
    pub fn imul(&mut self, c: isize) {
        let mut cc = c;
        let mut s = false;
        if cc < 0 {
            cc = -cc;
            s = true;
        }

        if MODTYPE == PSEUDO_MERSENNE || MODTYPE == GENERALISED_MERSENNE {
            let mut d = self.x.pxmul(cc);
            self.x.copy(&FP::modulo(&mut d));
            self.xes = 2
        } else if self.xes * (cc as i32) <= FEXCESS {
            self.x.pmul(cc);
            self.xes *= cc as i32;
        } else {
            let n = FP::new_int(cc);
            self.mul(&n);
        }

        if s {
            self.neg();
            self.norm();
        }
    }

    /* self*=self mod Modulus */
    pub fn sqr(&mut self) {
        if (self.xes as i64) * (self.xes as i64) > FEXCESS as i64 {
            self.reduce()
        }

        let mut d = BIG::sqr(&(self.x));
        self.x.copy(&FP::modulo(&mut d));
        self.xes = 2
    }

    /* self+=b */
    pub fn add(&mut self, b: &FP) {
        self.x.add(&(b.x));
        self.xes += b.xes;
        if self.xes > FEXCESS {
            self.reduce()
        }
    }

    /* self+=self */
    pub fn dbl(&mut self) {
        self.x.dbl();
        self.xes += self.xes;
        if self.xes > FEXCESS {
            self.reduce()
        }
    }

    /* self-=b */
    pub fn sub(&mut self, b: &FP) {
        let mut n = FP::new_copy(b);
        n.neg();
        self.add(&n);
    }

    /* self=b-self */
    pub fn rsub(&mut self, b: &FP) {
        self.neg();
        self.add(&b);
    }

    /* self/=2 mod Modulus */
    pub fn div2(&mut self) {
        let p = BIG::new_ints(&rom::MODULUS);
        let pr = self.x.parity();
        let mut w = BIG::new_copy(&self.x);
        self.x.fshr(1);
        w.add(&p); w.norm();
        w.fshr(1);
        self.x.cmove(&w,pr);
    }
    /* return jacobi symbol (this/Modulus) */
    pub fn jacobi(&mut self) -> isize {
        let p = BIG::new_ints(&rom::MODULUS);
        let mut w = self.redc();
        w.jacobi(&p)
    }
    /* return TRUE if self==a */
    pub fn equals(&self, a: &FP) -> bool {
        let mut f = FP::new_copy(self);
        let mut s = FP::new_copy(a);
        f.reduce();
        s.reduce();
        BIG::comp(&(f.x), &(s.x)) == 0
    }

    /* return self^e mod Modulus */
    pub fn pow(&self, e: &BIG) -> FP {
        let mut tb: [FP; 16] = [
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
        ];
        const CT: usize = 1 + (big::NLEN * (big::BASEBITS as usize) + 3) / 4;
        let mut w: [i8; CT] = [0; CT];

        let mut s = FP::new_copy(&self);
        s.norm();
        let mut t = BIG::new_copy(e);
        t.norm();
        let nb = 1 + (t.nbits() + 3) / 4;

        for i in 0..nb {
            let lsbs = t.lastbits(4);
            t.dec(lsbs);
            t.norm();
            w[i] = lsbs as i8;
            t.fshr(4);
        }
        tb[0].one();
        tb[1].copy(&s);

        let mut c = FP::new();
        for i in 2..16 {
            c.copy(&tb[i - 1]);
            tb[i].copy(&c);
            tb[i].mul(&s);
        }
        let mut r = FP::new_copy(&tb[w[nb - 1] as usize]);
        for i in (0..nb - 1).rev() {
            r.sqr();
            r.sqr();
            r.sqr();
            r.sqr();
            r.mul(&tb[w[i] as usize])
        }
        r.reduce();
        r
    }

    // See eprint paper https://eprint.iacr.org/2018/1038
    // return this^(p-3)/4 or this^(p-5)/8
    pub fn fpow(&self) -> FP {
        let ac: [isize; 11] = [1, 2, 3, 6, 12, 15, 30, 60, 120, 240, 255];
        let mut xp: [FP; 11] = [
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
            FP::new(),
        ];
        // phase 1
        let mut t = FP::new();
        xp[0].copy(&self); // 1
        xp[1].copy(&self);
        xp[1].sqr(); // 2
        t.copy(&xp[1]);
        xp[2].copy(&t);
        xp[2].mul(&self); // 3
        t.copy(&xp[2]);
        xp[3].copy(&t);
        xp[3].sqr(); // 6
        t.copy(&xp[3]);
        xp[4].copy(&t);
        xp[4].sqr(); // 12
        t.copy(&xp[4]);
        t.mul(&xp[2]);
        xp[5].copy(&t); // 15
        t.copy(&xp[5]);
        xp[6].copy(&t);
        xp[6].sqr(); // 30
        t.copy(&xp[6]);
        xp[7].copy(&t);
        xp[7].sqr(); // 60
        t.copy(&xp[7]);
        xp[8].copy(&t);
        xp[8].sqr(); // 120
        t.copy(&xp[8]);
        xp[9].copy(&t);
        xp[9].sqr(); // 240
        t.copy(&xp[9]);
        t.mul(&xp[5]);
        xp[10].copy(&t); // 255

        let mut n = MODBITS as isize;
        let mut c: isize;

        if MODTYPE == GENERALISED_MERSENNE {
            // Goldilocks ONLY
            n /= 2;
        }

        let e = PM1D2 as isize;

        n-=e+1;
        c=((rom::MCONST as isize)+(1<<e)+1)/(1<<(e+1));

        let mut nd=0;
        while c%2==0 {
            c/=2;
            n-=1;
            nd+=1;
        }

        let mut bw = 0;
        let mut w = 1;
        while w < c {
            w *= 2;
            bw += 1;
        }
        let mut k = w - c;

        let mut i = 10;
        let mut key = FP::new();
        if k != 0 {
            while ac[i] > k {
                i -= 1;
            }
            key.copy(&xp[i]);
            k -= ac[i];
        }
        while k != 0 {
            i -= 1;
            if ac[i] > k {
                continue;
            }
            key.mul(&xp[i]);
            k -= ac[i];
        }
        // phase 2
        t.copy(&xp[2]);
        xp[1].copy(&t);
        t.copy(&xp[5]);
        xp[2].copy(&t);
        t.copy(&xp[10]);
        xp[3].copy(&t);

        let mut j = 3;
        let mut m = 8;
        let nw = n - bw;
        let mut r = FP::new();

        while 2 * m < nw {
            t.copy(&xp[j]);
            j += 1;
            for _ in 0..m {
                t.sqr();
            }
            r.copy(&xp[j - 1]);
            r.mul(&t);
            xp[j].copy(&r);
            m *= 2;
        }
        let mut lo = nw - m;
        r.copy(&xp[j]);

        while lo != 0 {
            m /= 2;
            j -= 1;
            if lo < m {
                continue;
            }
            lo -= m;
            t.copy(&r);
            for _ in 0..m {
                t.sqr();
            }
            r.copy(&t);
            r.mul(&xp[j]);
        }
        // phase 3
        if bw != 0 {
            for _ in 0..bw {
                r.sqr();
            }
            r.mul(&key);
        }
        if MODTYPE == GENERALISED_MERSENNE {
            // Goldilocks ONLY
            key.copy(&r);
            r.sqr();
            r.mul(&self);
            for _ in 0..n + 1 {
                r.sqr();
            }
            r.mul(&key);
        }
        while nd>0 {
            r.sqr();
            nd-=1;
        }
        r
    }

    /* Pseudo_inverse square root */
    pub fn progen(&mut self) {
        if MODTYPE == PSEUDO_MERSENNE || MODTYPE == GENERALISED_MERSENNE {
            self.copy(&self.fpow());
            return;
        }
        let e=PM1D2 as usize;
        let mut m = BIG::new_ints(&rom::MODULUS);
        m.dec(1);
        m.shr(e);
        m.dec(1);
        m.fshr(1);

        self.copy(&self.pow(&m));
    }

    /* self=1/self mod Modulus */
    pub fn inverse(&mut self,take_hint: Option<&FP>) {
        let e=PM1D2 as isize;
        self.norm();
        let mut s=FP::new_copy(self);
        for _ in 0..e-1 {
            s.sqr();
            s.mul(self);
        }
        if let Some(hint) = take_hint {
            self.copy(&hint);
        } else {
            self.progen();
        }
        for _ in 0..=e {
            self.sqr();
        }
        self.mul(&s);
        self.reduce();
    }

    /* Test for Quadratic Residue */
    pub fn qr(&self,give_hint: Option<&mut FP>) -> isize {
        let e=PM1D2 as isize;
        let mut r=FP::new_copy(self);
        r.progen();
        if let Some(hint) = give_hint {
            hint.copy(&r);
        }

        r.sqr();
        r.mul(self);
        for _ in 0..e-1 {
            r.sqr();
        }

        r.isunity() as isize
    }

    pub fn invsqrt(&self,i: &mut FP,s: &mut FP) -> isize {
        let mut h=FP::new();
        let qr=self.qr(Some(&mut h));
        s.copy(&self.sqrt(Some(&h)));
        i.copy(self);
        i.inverse(Some(&h));
        qr
    }

// Two for the price of One  - See Hamburg https://eprint.iacr.org/2012/309.pdf
// Calculate inverse of i and square root of s, return QR
    pub fn tpo(mut i: &mut FP,mut s: &mut FP) -> isize {
        let mut w = FP::new_copy(s);
        let mut t = FP::new_copy(i);
        w.mul(&i);
        t.mul(&w);
        let qr=t.invsqrt(&mut i,&mut s);
        i.mul(&w);
        s.mul(&i);
        qr
    }

    /* return sqrt(this) mod Modulus */
    pub fn sqrt(&self,take_hint: Option<&FP>) -> FP {
        let e=PM1D2 as isize;
        let mut g=FP::new_copy(self);

        if let Some(hint) = take_hint {
            g.copy(&hint);
        } else {
            g.progen();
        }
        let m = BIG::new_ints(&rom::ROI);
        let mut v=FP::new_big(&m);
        let mut t=FP::new_copy(&g);
        t.sqr();
        t.mul(self);

        let mut r=FP::new_copy(self);
        r.mul(&g);
        let mut b=FP::new_copy(&t);

        for k in (2..=e).rev()   //(int k=e;k>1;k--)
        {
            for _ in 1..k-1 {
                b.sqr();
            }
            let u=!b.isunity() as isize;
            g.copy(&r); g.mul(&v);
            r.cmove(&g,u);
            v.sqr();
            g.copy(&t); g.mul(&v);
            t.cmove(&g,u);
            b.copy(&t);
        }
        let sgn=r.sign();
        let mut nr=FP::new_copy(&r);
        nr.neg(); nr.norm();
        r.cmove(&nr,sgn);
        r
    }

}