use super::{
    super::DIGEST_SIZE, BlockWord, CellValue16, CellValue32, SpreadInputs, SpreadVar,
    Table16Assignment, ROUNDS, STATE,
};
use halo2::{
    arithmetic::FieldExt,
    circuit::Layouter,
    plonk::{Advice, Column, ConstraintSystem, Error, Fixed, Permutation},
    poly::Rotation,
};

mod compression_gates;
mod compression_util;
mod subregion_digest;
mod subregion_initial;
mod subregion_main;

use compression_gates::CompressionGate;

/// A variable that represents the `[A,B,C,D]` words of the SHA-256 internal state.
///
/// The structure of this variable is influenced by the following factors:
/// - In `Σ_0(A)` we need `A` to be split into pieces `(a,b,c,d)` of lengths `(2,11,9,10)`
///   bits respectively (counting from the little end), as well as their spread forms.
/// - `Maj(A,B,C)` requires having the bits of each input in spread form. For `A` we can
///   reuse the pieces from `Σ_0(A)`. Since `B` and `C` are assigned from `A` and `B`
///   respectively in each round, we therefore also have the same pieces in earlier rows.
///   We align the columns to make it efficient to copy-constrain these forms where they
///   are needed.
#[derive(Copy, Clone, Debug)]
pub struct AbcdVar {
    idx: i32,
    val: u32,
    a: SpreadVar,
    b: SpreadVar,
    c_lo: SpreadVar,
    c_mid: SpreadVar,
    c_hi: SpreadVar,
    d: SpreadVar,
}

/// A variable that represents the `[E,F,G,H]` words of the SHA-256 internal state.
///
/// The structure of this variable is influenced by the following factors:
/// - In `Σ_1(E)` we need `E` to be split into pieces `(a,b,c,d)` of lengths `(6,5,14,7)`
///   bits respectively (counting from the little end), as well as their spread forms.
/// - `Ch(E,F,G)` requires having the bits of each input in spread form. For `E` we can
///   reuse the pieces from `Σ_1(E)`. Since `F` and `G` are assigned from `E` and `F`
///   respectively in each round, we therefore also have the same pieces in earlier rows.
///   We align the columns to make it efficient to copy-constrain these forms where they
///   are needed.
#[derive(Copy, Clone, Debug)]
pub struct EfghVar {
    idx: i32,
    val: u32,
    a_lo: SpreadVar,
    a_hi: SpreadVar,
    b_lo: SpreadVar,
    b_hi: SpreadVar,
    c: SpreadVar,
    d: SpreadVar,
}

#[derive(Clone, Debug)]
pub struct RoundWordDense {
    dense_halves: (CellValue16, CellValue16),
}

impl RoundWordDense {
    pub fn new(dense_halves: (CellValue16, CellValue16)) -> Self {
        RoundWordDense { dense_halves }
    }
}

#[derive(Clone, Debug)]
pub struct RoundWordSpread {
    dense_halves: (CellValue16, CellValue16),
    spread_halves: (CellValue32, CellValue32),
}

impl RoundWordSpread {
    pub fn new(
        dense_halves: (CellValue16, CellValue16),
        spread_halves: (CellValue32, CellValue32),
    ) -> Self {
        RoundWordSpread {
            dense_halves,
            spread_halves,
        }
    }
}

impl Into<RoundWordDense> for RoundWordSpread {
    fn into(self) -> RoundWordDense {
        RoundWordDense::new(self.dense_halves)
    }
}

#[derive(Clone, Debug)]
pub struct RoundWordA {
    pieces: Option<AbcdVar>,
    dense_halves: (CellValue16, CellValue16),
    spread_halves: Option<(CellValue32, CellValue32)>,
}

impl RoundWordA {
    pub fn new(
        pieces: AbcdVar,
        dense_halves: (CellValue16, CellValue16),
        spread_halves: (CellValue32, CellValue32),
    ) -> Self {
        RoundWordA {
            pieces: Some(pieces),
            dense_halves,
            spread_halves: Some(spread_halves),
        }
    }

    pub fn new_dense(dense_halves: (CellValue16, CellValue16)) -> Self {
        RoundWordA {
            pieces: None,
            dense_halves,
            spread_halves: None,
        }
    }
}

impl Into<RoundWordSpread> for RoundWordA {
    fn into(self) -> RoundWordSpread {
        RoundWordSpread::new(self.dense_halves, self.spread_halves.unwrap())
    }
}

#[derive(Clone, Debug)]
pub struct RoundWordE {
    pieces: Option<EfghVar>,
    dense_halves: (CellValue16, CellValue16),
    spread_halves: Option<(CellValue32, CellValue32)>,
}

impl RoundWordE {
    pub fn new(
        pieces: EfghVar,
        dense_halves: (CellValue16, CellValue16),
        spread_halves: (CellValue32, CellValue32),
    ) -> Self {
        RoundWordE {
            pieces: Some(pieces),
            dense_halves,
            spread_halves: Some(spread_halves),
        }
    }

    pub fn new_dense(dense_halves: (CellValue16, CellValue16)) -> Self {
        RoundWordE {
            pieces: None,
            dense_halves,
            spread_halves: None,
        }
    }
}

impl Into<RoundWordSpread> for RoundWordE {
    fn into(self) -> RoundWordSpread {
        RoundWordSpread::new(self.dense_halves, self.spread_halves.unwrap())
    }
}

/// The internal state for SHA-256.
#[derive(Clone, Debug)]
pub struct State {
    a: Option<StateWord>,
    b: Option<StateWord>,
    c: Option<StateWord>,
    d: Option<StateWord>,
    e: Option<StateWord>,
    f: Option<StateWord>,
    g: Option<StateWord>,
    h: Option<StateWord>,
}

impl State {
    #[allow(clippy::many_single_char_names)]
    #[allow(clippy::too_many_arguments)]
    pub fn new(
        a: StateWord,
        b: StateWord,
        c: StateWord,
        d: StateWord,
        e: StateWord,
        f: StateWord,
        g: StateWord,
        h: StateWord,
    ) -> Self {
        State {
            a: Some(a),
            b: Some(b),
            c: Some(c),
            d: Some(d),
            e: Some(e),
            f: Some(f),
            g: Some(g),
            h: Some(h),
        }
    }

    pub fn empty_state() -> Self {
        State {
            a: None,
            b: None,
            c: None,
            d: None,
            e: None,
            f: None,
            g: None,
            h: None,
        }
    }
}

#[derive(Clone, Debug)]
pub enum StateWord {
    A(RoundWordA),
    B(RoundWordSpread),
    C(RoundWordSpread),
    D(RoundWordDense),
    E(RoundWordE),
    F(RoundWordSpread),
    G(RoundWordSpread),
    H(RoundWordDense),
}

#[derive(Clone, Debug)]
pub(super) struct CompressionConfig {
    lookup: SpreadInputs,
    message_schedule: Column<Advice>,
    extras: [Column<Advice>; 6],

    s_ch: Column<Fixed>,
    s_ch_neg: Column<Fixed>,
    s_maj: Column<Fixed>,
    s_h_prime: Column<Fixed>,
    s_a_new: Column<Fixed>,
    s_e_new: Column<Fixed>,

    s_upper_sigma_0: Column<Fixed>,
    s_upper_sigma_1: Column<Fixed>,

    // Decomposition gate for AbcdVar
    s_decompose_abcd: Column<Fixed>,
    // Decomposition gate for EfghVar
    s_decompose_efgh: Column<Fixed>,

    s_digest: Column<Fixed>,

    perm: Permutation,
}

impl<F: FieldExt> Table16Assignment<F> for CompressionConfig {}

impl CompressionConfig {
    pub(super) fn configure<F: FieldExt>(
        meta: &mut ConstraintSystem<F>,
        lookup: SpreadInputs,
        message_schedule: Column<Advice>,
        extras: [Column<Advice>; 6],
        perm: Permutation,
    ) -> Self {
        let s_ch = meta.fixed_column();
        let s_ch_neg = meta.fixed_column();
        let s_maj = meta.fixed_column();
        let s_h_prime = meta.fixed_column();
        let s_a_new = meta.fixed_column();
        let s_e_new = meta.fixed_column();

        let s_upper_sigma_0 = meta.fixed_column();
        let s_upper_sigma_1 = meta.fixed_column();

        // Decomposition gate for AbcdVar
        let s_decompose_abcd = meta.fixed_column();
        // Decomposition gate for EfghVar
        let s_decompose_efgh = meta.fixed_column();

        let s_digest = meta.fixed_column();

        // Rename these here for ease of matching the gates to the specification.
        let a_0 = lookup.tag;
        let a_1 = lookup.dense;
        let a_2 = lookup.spread;
        let a_3 = extras[0];
        let a_4 = extras[1];
        let a_5 = message_schedule;
        let a_6 = extras[2];
        let a_7 = extras[3];
        let a_8 = extras[4];
        let a_9 = extras[5];

        // Decompose `A,B,C,D` words into (2, 11, 9, 10)-bit chunks.
        // `c` is split into (3, 3, 3)-bit c_lo, c_mid, c_hi.
        meta.create_gate("decompose ABCD", |meta| {
            let s_decompose_abcd = meta.query_fixed(s_decompose_abcd, Rotation::cur());
            let a = meta.query_advice(a_3, Rotation::next()); // 2-bit chunk
            let spread_a = meta.query_advice(a_4, Rotation::next());
            let b = meta.query_advice(a_1, Rotation::cur()); // 11-bit chunk
            let spread_b = meta.query_advice(a_2, Rotation::cur());
            let tag_b = meta.query_advice(a_0, Rotation::cur());
            let c_lo = meta.query_advice(a_3, Rotation::cur()); // 3-bit chunk
            let spread_c_lo = meta.query_advice(a_4, Rotation::cur());
            let c_mid = meta.query_advice(a_5, Rotation::cur()); // 3-bit chunk
            let spread_c_mid = meta.query_advice(a_6, Rotation::cur());
            let c_hi = meta.query_advice(a_5, Rotation::next()); // 3-bit chunk
            let spread_c_hi = meta.query_advice(a_6, Rotation::next());
            let d = meta.query_advice(a_1, Rotation::next()); // 7-bit chunk
            let spread_d = meta.query_advice(a_2, Rotation::next());
            let tag_d = meta.query_advice(a_0, Rotation::next());
            let word_lo = meta.query_advice(a_7, Rotation::cur());
            let spread_word_lo = meta.query_advice(a_8, Rotation::cur());
            let word_hi = meta.query_advice(a_7, Rotation::next());
            let spread_word_hi = meta.query_advice(a_8, Rotation::next());

            CompressionGate::s_decompose_abcd(
                s_decompose_abcd,
                a,
                spread_a,
                b,
                spread_b,
                tag_b,
                c_lo,
                spread_c_lo,
                c_mid,
                spread_c_mid,
                c_hi,
                spread_c_hi,
                d,
                spread_d,
                tag_d,
                word_lo,
                spread_word_lo,
                word_hi,
                spread_word_hi,
            )
            .0
        });

        // Decompose `E,F,G,H` words into (6, 5, 14, 7)-bit chunks.
        // `a` is split into (3, 3)-bit a_lo, a_hi
        // `b` is split into (2, 3)-bit b_lo, b_hi
        meta.create_gate("Decompose EFGH", |meta| {
            let s_decompose_efgh = meta.query_fixed(s_decompose_efgh, Rotation::cur());
            let a_lo = meta.query_advice(a_3, Rotation::next()); // 3-bit chunk
            let spread_a_lo = meta.query_advice(a_4, Rotation::next());
            let a_hi = meta.query_advice(a_5, Rotation::next()); // 3-bit chunk
            let spread_a_hi = meta.query_advice(a_6, Rotation::next());
            let b_lo = meta.query_advice(a_3, Rotation::cur()); // 2-bit chunk
            let spread_b_lo = meta.query_advice(a_4, Rotation::cur());
            let b_hi = meta.query_advice(a_5, Rotation::cur()); // 3-bit chunk
            let spread_b_hi = meta.query_advice(a_6, Rotation::cur());
            let c = meta.query_advice(a_1, Rotation::next()); // 14-bit chunk
            let spread_c = meta.query_advice(a_2, Rotation::next());
            let tag_c = meta.query_advice(a_0, Rotation::next());
            let d = meta.query_advice(a_1, Rotation::cur()); // 7-bit chunk
            let spread_d = meta.query_advice(a_2, Rotation::cur());
            let tag_d = meta.query_advice(a_0, Rotation::cur());
            let word_lo = meta.query_advice(a_7, Rotation::cur());
            let spread_word_lo = meta.query_advice(a_8, Rotation::cur());
            let word_hi = meta.query_advice(a_7, Rotation::next());
            let spread_word_hi = meta.query_advice(a_8, Rotation::next());

            CompressionGate::s_decompose_efgh(
                s_decompose_efgh,
                a_lo,
                spread_a_lo,
                a_hi,
                spread_a_hi,
                b_lo,
                spread_b_lo,
                b_hi,
                spread_b_hi,
                c,
                spread_c,
                tag_c,
                d,
                spread_d,
                tag_d,
                word_lo,
                spread_word_lo,
                word_hi,
                spread_word_hi,
            )
            .0
        });

        // s_upper_sigma_0 on abcd words
        // (2, 11, 9, 10)-bit chunks
        meta.create_gate("s_upper_sigma_0", |meta| {
            let s_upper_sigma_0 = meta.query_fixed(s_upper_sigma_0, Rotation::cur());
            let spread_r0_even = meta.query_advice(a_2, Rotation::prev());
            let spread_r0_odd = meta.query_advice(a_2, Rotation::cur());
            let spread_r1_even = meta.query_advice(a_2, Rotation::next());
            let spread_r1_odd = meta.query_advice(a_3, Rotation::cur());

            let spread_a = meta.query_advice(a_3, Rotation::next());
            let spread_b = meta.query_advice(a_5, Rotation::cur());
            let spread_c_lo = meta.query_advice(a_3, Rotation::prev());
            let spread_c_mid = meta.query_advice(a_4, Rotation::prev());
            let spread_c_hi = meta.query_advice(a_4, Rotation::next());
            let spread_d = meta.query_advice(a_4, Rotation::cur());

            CompressionGate::s_upper_sigma_0(
                s_upper_sigma_0,
                spread_r0_even,
                spread_r0_odd,
                spread_r1_even,
                spread_r1_odd,
                spread_a,
                spread_b,
                spread_c_lo,
                spread_c_mid,
                spread_c_hi,
                spread_d,
            )
            .0
        });

        // s_upper_sigma_1 on efgh words
        // (6, 5, 14, 7)-bit chunks
        meta.create_gate("s_upper_sigma_1", |meta| {
            let s_upper_sigma_1 = meta.query_fixed(s_upper_sigma_1, Rotation::cur());
            let spread_r0_even = meta.query_advice(a_2, Rotation::prev());
            let spread_r0_odd = meta.query_advice(a_2, Rotation::cur());
            let spread_r1_even = meta.query_advice(a_2, Rotation::next());
            let spread_r1_odd = meta.query_advice(a_3, Rotation::cur());
            let spread_a_lo = meta.query_advice(a_3, Rotation::next());
            let spread_a_hi = meta.query_advice(a_4, Rotation::next());
            let spread_b_lo = meta.query_advice(a_3, Rotation::prev());
            let spread_b_hi = meta.query_advice(a_4, Rotation::prev());
            let spread_c = meta.query_advice(a_5, Rotation::cur());
            let spread_d = meta.query_advice(a_4, Rotation::cur());

            CompressionGate::s_upper_sigma_1(
                s_upper_sigma_1,
                spread_r0_even,
                spread_r0_odd,
                spread_r1_even,
                spread_r1_odd,
                spread_a_lo,
                spread_a_hi,
                spread_b_lo,
                spread_b_hi,
                spread_c,
                spread_d,
            )
            .0
        });

        // s_ch on efgh words
        // First part of choice gate on (E, F, G), E ∧ F
        meta.create_gate("s_ch", |meta| {
            let s_ch = meta.query_fixed(s_ch, Rotation::cur());
            let spread_p0_even = meta.query_advice(a_2, Rotation::prev());
            let spread_p0_odd = meta.query_advice(a_2, Rotation::cur());
            let spread_p1_even = meta.query_advice(a_2, Rotation::next());
            let spread_p1_odd = meta.query_advice(a_3, Rotation::cur());
            let spread_e_lo = meta.query_advice(a_3, Rotation::prev());
            let spread_e_hi = meta.query_advice(a_4, Rotation::prev());
            let spread_f_lo = meta.query_advice(a_3, Rotation::next());
            let spread_f_hi = meta.query_advice(a_4, Rotation::next());

            CompressionGate::s_ch(
                s_ch,
                spread_p0_even,
                spread_p0_odd,
                spread_p1_even,
                spread_p1_odd,
                spread_e_lo,
                spread_e_hi,
                spread_f_lo,
                spread_f_hi,
            )
            .0
        });

        // s_ch_neg on efgh words
        // Second part of Choice gate on (E, F, G), ¬E ∧ G
        meta.create_gate("s_ch_neg", |meta| {
            let s_ch_neg = meta.query_fixed(s_ch_neg, Rotation::cur());
            let spread_q0_even = meta.query_advice(a_2, Rotation::prev());
            let spread_q0_odd = meta.query_advice(a_2, Rotation::cur());
            let spread_q1_even = meta.query_advice(a_2, Rotation::next());
            let spread_q1_odd = meta.query_advice(a_3, Rotation::cur());
            let spread_e_lo = meta.query_advice(a_5, Rotation::prev());
            let spread_e_hi = meta.query_advice(a_5, Rotation::cur());
            let spread_e_neg_lo = meta.query_advice(a_3, Rotation::prev());
            let spread_e_neg_hi = meta.query_advice(a_4, Rotation::prev());
            let spread_g_lo = meta.query_advice(a_3, Rotation::next());
            let spread_g_hi = meta.query_advice(a_4, Rotation::next());

            CompressionGate::s_ch_neg(
                s_ch_neg,
                spread_q0_even,
                spread_q0_odd,
                spread_q1_even,
                spread_q1_odd,
                spread_e_lo,
                spread_e_hi,
                spread_e_neg_lo,
                spread_e_neg_hi,
                spread_g_lo,
                spread_g_hi,
            )
            .0
        });

        // s_maj on abcd words
        meta.create_gate("s_maj", |meta| {
            let s_maj = meta.query_fixed(s_maj, Rotation::cur());
            let spread_m0_even = meta.query_advice(a_2, Rotation::prev());
            let spread_m0_odd = meta.query_advice(a_2, Rotation::cur());
            let spread_m1_even = meta.query_advice(a_2, Rotation::next());
            let spread_m1_odd = meta.query_advice(a_3, Rotation::cur());
            let spread_a_lo = meta.query_advice(a_4, Rotation::prev());
            let spread_a_hi = meta.query_advice(a_5, Rotation::prev());
            let spread_b_lo = meta.query_advice(a_4, Rotation::cur());
            let spread_b_hi = meta.query_advice(a_5, Rotation::cur());
            let spread_c_lo = meta.query_advice(a_4, Rotation::next());
            let spread_c_hi = meta.query_advice(a_5, Rotation::next());

            CompressionGate::s_maj(
                s_maj,
                spread_m0_even,
                spread_m0_odd,
                spread_m1_even,
                spread_m1_odd,
                spread_a_lo,
                spread_a_hi,
                spread_b_lo,
                spread_b_hi,
                spread_c_lo,
                spread_c_hi,
            )
            .0
        });

        // s_h_prime to compute H' = H + Ch(E, F, G) + s_upper_sigma_1(E) + K + W
        meta.create_gate("s_h_prime", |meta| {
            let s_h_prime = meta.query_fixed(s_h_prime, Rotation::cur());
            let h_prime_lo = meta.query_advice(a_7, Rotation::next());
            let h_prime_hi = meta.query_advice(a_8, Rotation::next());
            let h_prime_carry = meta.query_advice(a_9, Rotation::next());
            let sigma_e_lo = meta.query_advice(a_4, Rotation::cur());
            let sigma_e_hi = meta.query_advice(a_5, Rotation::cur());
            let ch_lo = meta.query_advice(a_1, Rotation::cur());
            let ch_hi = meta.query_advice(a_6, Rotation::next());
            let ch_neg_lo = meta.query_advice(a_5, Rotation::prev());
            let ch_neg_hi = meta.query_advice(a_5, Rotation::next());
            let h_lo = meta.query_advice(a_7, Rotation::prev());
            let h_hi = meta.query_advice(a_7, Rotation::cur());
            let k_lo = meta.query_advice(a_6, Rotation::prev());
            let k_hi = meta.query_advice(a_6, Rotation::cur());
            let w_lo = meta.query_advice(a_8, Rotation::prev());
            let w_hi = meta.query_advice(a_8, Rotation::cur());

            CompressionGate::s_h_prime(
                s_h_prime,
                h_prime_lo,
                h_prime_hi,
                h_prime_carry,
                sigma_e_lo,
                sigma_e_hi,
                ch_lo,
                ch_hi,
                ch_neg_lo,
                ch_neg_hi,
                h_lo,
                h_hi,
                k_lo,
                k_hi,
                w_lo,
                w_hi,
            )
            .0
        });

        // s_a_new
        meta.create_gate("s_a_new", |meta| {
            let s_a_new = meta.query_fixed(s_a_new, Rotation::cur());
            let a_new_lo = meta.query_advice(a_8, Rotation::cur());
            let a_new_hi = meta.query_advice(a_8, Rotation::next());
            let a_new_carry = meta.query_advice(a_9, Rotation::cur());
            let sigma_a_lo = meta.query_advice(a_6, Rotation::cur());
            let sigma_a_hi = meta.query_advice(a_6, Rotation::next());
            let maj_abc_lo = meta.query_advice(a_1, Rotation::cur());
            let maj_abc_hi = meta.query_advice(a_3, Rotation::prev());
            let h_prime_lo = meta.query_advice(a_7, Rotation::prev());
            let h_prime_hi = meta.query_advice(a_8, Rotation::prev());

            CompressionGate::s_a_new(
                s_a_new,
                a_new_lo,
                a_new_hi,
                a_new_carry,
                sigma_a_lo,
                sigma_a_hi,
                maj_abc_lo,
                maj_abc_hi,
                h_prime_lo,
                h_prime_hi,
            )
            .0
        });

        // s_e_new
        meta.create_gate("s_e_new", |meta| {
            let s_e_new = meta.query_fixed(s_e_new, Rotation::cur());
            let e_new_lo = meta.query_advice(a_8, Rotation::cur());
            let e_new_hi = meta.query_advice(a_8, Rotation::next());
            let e_new_carry = meta.query_advice(a_9, Rotation::next());
            let d_lo = meta.query_advice(a_7, Rotation::cur());
            let d_hi = meta.query_advice(a_7, Rotation::next());
            let h_prime_lo = meta.query_advice(a_7, Rotation::prev());
            let h_prime_hi = meta.query_advice(a_8, Rotation::prev());

            CompressionGate::s_e_new(
                s_e_new,
                e_new_lo,
                e_new_hi,
                e_new_carry,
                d_lo,
                d_hi,
                h_prime_lo,
                h_prime_hi,
            )
            .0
        });

        // s_digest for final round
        meta.create_gate("s_digest", |meta| {
            let s_digest = meta.query_fixed(s_digest, Rotation::cur());
            let lo_0 = meta.query_advice(a_3, Rotation::cur());
            let hi_0 = meta.query_advice(a_4, Rotation::cur());
            let word_0 = meta.query_advice(a_5, Rotation::cur());
            let lo_1 = meta.query_advice(a_6, Rotation::cur());
            let hi_1 = meta.query_advice(a_7, Rotation::cur());
            let word_1 = meta.query_advice(a_8, Rotation::cur());
            let lo_2 = meta.query_advice(a_3, Rotation::next());
            let hi_2 = meta.query_advice(a_4, Rotation::next());
            let word_2 = meta.query_advice(a_5, Rotation::next());
            let lo_3 = meta.query_advice(a_6, Rotation::next());
            let hi_3 = meta.query_advice(a_7, Rotation::next());
            let word_3 = meta.query_advice(a_8, Rotation::next());

            CompressionGate::s_digest(
                s_digest, lo_0, hi_0, word_0, lo_1, hi_1, word_1, lo_2, hi_2, word_2, lo_3, hi_3,
                word_3,
            )
            .0
        });

        CompressionConfig {
            lookup,
            message_schedule,
            extras,
            s_ch,
            s_ch_neg,
            s_maj,
            s_h_prime,
            s_a_new,
            s_e_new,
            s_upper_sigma_0,
            s_upper_sigma_1,
            s_decompose_abcd,
            s_decompose_efgh,
            s_digest,
            perm,
        }
    }

    /// Initialize compression with a constant Initialization Vector of 32-byte words.
    /// Returns an initialized state.
    pub(super) fn initialize_with_iv<F: FieldExt>(
        &self,
        layouter: &mut impl Layouter<F>,
        init_state: [u32; STATE],
    ) -> Result<State, Error> {
        let mut new_state = State::empty_state();
        layouter.assign_region(
            || "initialize_with_iv",
            |mut region| {
                new_state = self.initialize_iv(&mut region, init_state)?;
                Ok(())
            },
        )?;
        Ok(new_state)
    }

    /// Initialize compression with some initialized state. This could be a state
    /// output from a previous compression round.
    pub(super) fn initialize_with_state<F: FieldExt>(
        &self,
        layouter: &mut impl Layouter<F>,
        init_state: State,
    ) -> Result<State, Error> {
        let mut new_state = State::empty_state();
        layouter.assign_region(
            || "initialize_with_state",
            |mut region| {
                new_state = self.initialize_state(&mut region, init_state.clone())?;
                Ok(())
            },
        )?;
        Ok(new_state)
    }

    /// Given an initialized state and a message schedule, perform 64 compression rounds.
    pub(super) fn compress<F: FieldExt>(
        &self,
        layouter: &mut impl Layouter<F>,
        initialized_state: State,
        w_halves: [(CellValue16, CellValue16); ROUNDS],
    ) -> Result<State, Error> {
        let mut state = State::empty_state();
        layouter.assign_region(
            || "compress",
            |mut region| {
                state = initialized_state.clone();
                for idx in 0..64 {
                    state =
                        self.assign_round(&mut region, idx, state.clone(), w_halves[idx as usize])?;
                }
                Ok(())
            },
        )?;
        Ok(state)
    }

    /// After the final round, convert the state into the final digest.
    pub(super) fn digest<F: FieldExt>(
        &self,
        layouter: &mut impl Layouter<F>,
        state: State,
    ) -> Result<[BlockWord; DIGEST_SIZE], Error> {
        let mut digest = [BlockWord::new(0); DIGEST_SIZE];
        layouter.assign_region(
            || "digest",
            |mut region| {
                digest = self.assign_digest(&mut region, state.clone())?;

                Ok(())
            },
        )?;
        Ok(digest)
    }
}

#[cfg(test)]
mod tests {
    use super::super::{
        super::BLOCK_SIZE, get_msg_schedule_test_input, BlockWord, Table16Chip, Table16Config, IV,
    };
    use halo2::{
        arithmetic::FieldExt,
        circuit::layouter::SingleChipLayouter,
        dev::MockProver,
        pasta::Fp,
        plonk::{Assignment, Circuit, ConstraintSystem, Error},
    };

    #[test]
    fn compress() {
        struct MyCircuit {}

        impl<F: FieldExt> Circuit<F> for MyCircuit {
            type Config = Table16Config;

            fn configure(meta: &mut ConstraintSystem<F>) -> Self::Config {
                Table16Chip::configure(meta)
            }

            fn synthesize(
                &self,
                cs: &mut impl Assignment<F>,
                config: Self::Config,
            ) -> Result<(), Error> {
                let mut layouter = SingleChipLayouter::new(cs)?;
                Table16Chip::<F>::load(config.clone(), &mut layouter)?;

                // Test vector: "abc"
                let input: [BlockWord; BLOCK_SIZE] = get_msg_schedule_test_input();

                let (_, w_halves) = config.message_schedule.process(&mut layouter, input)?;

                let compression = config.compression.clone();
                let initial_state = compression.initialize_with_iv(&mut layouter, IV)?;

                let state =
                    config
                        .compression
                        .compress(&mut layouter, initial_state.clone(), w_halves)?;

                let digest = config.compression.digest(&mut layouter, state)?;
                for (idx, digest_word) in digest.iter().enumerate() {
                    assert_eq!(
                        (digest_word.value.unwrap() as u64 + IV[idx] as u64) as u32,
                        super::compression_util::COMPRESSION_OUTPUT[idx]
                    );
                }

                Ok(())
            }
        }

        let circuit: MyCircuit = MyCircuit {};

        let prover = match MockProver::<Fp>::run(16, &circuit, vec![]) {
            Ok(prover) => prover,
            Err(e) => panic!("{:?}", e),
        };
        assert_eq!(prover.verify(), Ok(()));
    }
}