/// This example does the hash chain but in the naive approach: instead of using folding, it does a
/// big circuit containing n instantiations of the sha256 constraints.

#[cfg(test)]
mod tests {
    use ark_bn254::{Bn254, Fr};

    use ark_groth16::Groth16;
    use ark_snark::SNARK;

    use ark_ff::PrimeField;

    use std::time::Instant;

    use ark_crypto_primitives::crh::sha256::{constraints::Sha256Gadget, digest::Digest, Sha256};
    use ark_r1cs_std::fields::fp::FpVar;
    use ark_r1cs_std::{alloc::AllocVar, eq::EqGadget};
    use ark_r1cs_std::{bits::uint8::UInt8, boolean::Boolean, ToBitsGadget, ToBytesGadget};
    use ark_relations::r1cs::{
        ConstraintSynthesizer, ConstraintSystem, ConstraintSystemRef, SynthesisError,
    };

    use crate::utils::tests::*;

    /// Test circuit to be folded
    #[derive(Clone, Debug)]
    pub struct SHA256ChainCircuit<F: PrimeField, const N: usize, const HASHES_PER_STEP: usize> {
        z_0: Option<Vec<F>>,
        z_n: Option<Vec<F>>,
    }
    impl<F: PrimeField, const N: usize, const HASHES_PER_STEP: usize> ConstraintSynthesizer<F>
        for SHA256ChainCircuit<F, N, HASHES_PER_STEP>
    {
        fn generate_constraints(self, cs: ConstraintSystemRef<F>) -> Result<(), SynthesisError> {
            let z_0 = Vec::<FpVar<F>>::new_witness(cs.clone(), || {
                Ok(self.z_0.unwrap_or(vec![F::zero()]))
            })?;
            let z_n =
                Vec::<FpVar<F>>::new_input(cs.clone(), || Ok(self.z_n.unwrap_or(vec![F::zero()])))?;
            let mut z_i: Vec<FpVar<F>> = z_0.clone();
            for _ in 0..N {
                let mut b: Vec<UInt8<F>> = z_i
                    .iter()
                    .map(|f| UInt8::<F>::from_bits_le(&f.to_bits_le().unwrap()[..8]))
                    .collect::<Vec<_>>();

                for _ in 0..HASHES_PER_STEP {
                    let mut sha256_var = Sha256Gadget::default();
                    sha256_var.update(&b).unwrap();
                    b = sha256_var.finalize()?.to_bytes()?;
                }

                // update z_i = z_{i+1}
                z_i = b
                    .iter()
                    .map(|e| {
                        let bits = e.to_bits_le().unwrap();
                        Boolean::<F>::le_bits_to_fp_var(&bits).unwrap()
                    })
                    .collect();
            }

            z_i.enforce_equal(&z_n)?;
            Ok(())
        }
    }
    // compute natively in rust the expected result
    fn rust_native_result(z_0: Vec<Fr>, n_steps: usize, hashes_per_step: usize) -> Vec<Fr> {
        let mut z_i: Vec<Fr> = z_0.clone();
        for _ in 0..n_steps {
            let mut b = f_vec_to_bytes(z_i.to_vec());

            for _ in 0..hashes_per_step {
                let mut sha256 = Sha256::default();
                sha256.update(b);
                b = sha256.finalize().to_vec();
            }

            z_i = bytes_to_f_vec(b.to_vec()).unwrap();
        }
        z_i.clone()
    }

    #[test]
    fn full_flow() {
        // set how many iterations of the SHA256ChainCircuit circuit internal loop we want to
        // compute
        const N_STEPS: usize = 50;
        const HASHES_PER_STEP: usize = 10;
        println!("running the 'naive' SHA256ChainCircuit, with N_STEPS={}, HASHES_PER_STEP={}. Total hashes = {}", N_STEPS, HASHES_PER_STEP, N_STEPS* HASHES_PER_STEP);

        // set the initial state
        // let z_0_aux: Vec<u32> = vec![0_u32; 32 * 8];
        let z_0_aux: Vec<u8> = vec![0_u8; 32];
        let z_0: Vec<Fr> = z_0_aux.iter().map(|v| Fr::from(*v)).collect::<Vec<Fr>>();

        // run the N iterations 'natively' in rust to compute the expected `z_n`
        let z_n = rust_native_result(z_0.clone(), N_STEPS, HASHES_PER_STEP);

        let circuit = SHA256ChainCircuit::<Fr, N_STEPS, HASHES_PER_STEP> {
            z_0: Some(z_0),
            z_n: Some(z_n.clone()),
        };

        let cs = ConstraintSystem::<Fr>::new_ref();
        circuit.clone().generate_constraints(cs.clone()).unwrap();
        println!(
            "number of constraints of the (naive) SHA256ChainCircuit with N={} hash iterations: {}",
            N_STEPS,
            cs.num_constraints()
        );

        // now let's generate an actual Groth16 proof
        let mut rng = rand::rngs::OsRng;
        let (g16_pk, g16_vk) =
            Groth16::<Bn254>::circuit_specific_setup(circuit.clone(), &mut rng).unwrap();

        let start = Instant::now();
        let proof = Groth16::<Bn254>::prove(&g16_pk, circuit.clone(), &mut rng).unwrap();
        println!(
            "Groth16 proof generation (for the naive SHA256ChainCircuit): {:?}",
            start.elapsed()
        );

        let public_inputs = z_n;
        let valid_proof = Groth16::<Bn254>::verify(&g16_vk, &public_inputs, &proof).unwrap();

        assert!(valid_proof);

        println!("finished running the 'naive' SHA256ChainCircuit, with N_STEPS={}, HASHES_PER_STEP={}. Total hashes = {}", N_STEPS, HASHES_PER_STEP, N_STEPS* HASHES_PER_STEP);
    }
}