use anyhow::Result;
use bitreader::BitReader;
use openssl::{
    bn::{BigNum, BigNumContext, MsbOption},
    ec::{EcGroup, EcPoint},
    sha::sha1,
};

use crate::key::{base24_decode, base24_encode};

const FIELD_BITS: i32 = 512;
const FIELD_BYTES: usize = 64;
const SHA_MSG_LENGTH: usize = 3 + 2 * FIELD_BYTES;

#[derive(Clone, Copy, Debug)]
struct ProductKey {
    upgrade: bool,
    channel_id: u32,
    hash: u32,
    signature: u64,
    auth_info: u32,
}

pub fn verify(
    e_curve: &EcGroup,
    base_point: &EcPoint,
    public_key: &EcPoint,
    cd_key: &str,
    verbose: bool,
) -> Result<bool> {
    let mut num_context = BigNumContext::new()?;

    let b_key = base24_decode(cd_key);
    let product_key = unpack(&b_key)?;

    let p_data = product_key.channel_id << 1 | product_key.upgrade as u32;

    if verbose {
        println!("Validation results:");
        println!("   Upgrade: {}", product_key.upgrade);
        println!("Channel ID: {}", product_key.channel_id);
        println!("      Hash: {}", product_key.hash);
        println!(" Signature: {}", product_key.signature);
        println!("  AuthInfo: {}", product_key.auth_info);
        println!();
    }

    let mut msg_buffer: [u8; SHA_MSG_LENGTH] = [0; SHA_MSG_LENGTH];

    msg_buffer[0x00] = 0x5D;
    msg_buffer[0x01] = (p_data & 0x00FF) as u8;
    msg_buffer[0x02] = ((p_data & 0xFF00) >> 8) as u8;
    msg_buffer[0x03] = (product_key.hash & 0x000000FF) as u8;
    msg_buffer[0x04] = ((product_key.hash & 0x0000FF00) >> 8) as u8;
    msg_buffer[0x05] = ((product_key.hash & 0x00FF0000) >> 16) as u8;
    msg_buffer[0x06] = ((product_key.hash & 0xFF000000) >> 24) as u8;
    msg_buffer[0x07] = (product_key.auth_info & 0x00FF) as u8;
    msg_buffer[0x08] = ((product_key.auth_info & 0xFF00) >> 8) as u8;
    msg_buffer[0x09] = 0x00;
    msg_buffer[0x0A] = 0x00;

    let msg_digest = sha1(&msg_buffer[..=0x0A]);

    let i_signature = next_sn_bits(by_dword(&msg_digest[4..8]) as u64, 30, 2) << 32
        | by_dword(&msg_digest[0..4]) as u64;

    let e = BigNum::from_slice(&i_signature.to_be_bytes())?;
    let s = BigNum::from_slice(&product_key.signature.to_be_bytes())?;

    let mut x = BigNum::new()?;
    let mut y = BigNum::new()?;

    let mut p = EcPoint::new(e_curve)?;
    let mut t = EcPoint::new(e_curve)?;

    t.mul(e_curve, base_point, &s, &num_context)?;
    p.mul(e_curve, public_key, &e, &num_context)?;
    let p_2 = p.to_owned(e_curve)?;

    p.add(e_curve, &t, &p_2, &mut num_context)?;
    let p_2 = p.to_owned(e_curve)?;

    p.mul(e_curve, &p_2, &s, &num_context)?;

    p.affine_coordinates(e_curve, &mut x, &mut y, &mut num_context)?;

    let mut x_bin = x.to_vec_padded(FIELD_BYTES as i32)?;
    x_bin.reverse();
    let mut y_bin = y.to_vec_padded(FIELD_BYTES as i32)?;
    y_bin.reverse();

    msg_buffer[0x00] = 0x79;
    msg_buffer[0x01] = (p_data & 0x00FF) as u8;
    msg_buffer[0x02] = ((p_data & 0xFF00) >> 8) as u8;

    msg_buffer[3..3 + FIELD_BYTES].copy_from_slice(&x_bin);
    msg_buffer[3 + FIELD_BYTES..3 + FIELD_BYTES * 2].copy_from_slice(&y_bin);

    let msg_digest = sha1(&msg_buffer);

    let hash: u32 = by_dword(&msg_digest[0..4]) & bitmask(31) as u32;

    Ok(hash == product_key.hash)
}

pub fn generate(
    e_curve: &EcGroup,
    base_point: &EcPoint,
    gen_order: &BigNum,
    private_key: &BigNum,
    p_channel_id: u32,
    p_auth_info: u32,
    p_upgrade: bool,
) -> Result<String> {
    let mut num_context = BigNumContext::new().unwrap();

    let mut c = BigNum::new()?;
    let mut x = BigNum::new()?;
    let mut y = BigNum::new()?;

    let p_data = p_channel_id << 1 | p_upgrade as u32;

    let mut no_square = false;
    let p_raw: Vec<u8> = loop {
        let mut r = EcPoint::new(e_curve)?;

        c.rand(FIELD_BITS, MsbOption::MAYBE_ZERO, false)?;

        r.mul(e_curve, base_point, &c, &num_context)?;

        r.affine_coordinates(e_curve, &mut x, &mut y, &mut num_context)?;

        let mut msg_buffer: [u8; SHA_MSG_LENGTH] = [0; SHA_MSG_LENGTH];

        let mut x_bin = x.to_vec_padded(FIELD_BYTES as i32)?;
        x_bin.reverse();
        let mut y_bin = y.to_vec_padded(FIELD_BYTES as i32)?;
        y_bin.reverse();

        msg_buffer[0x00] = 0x79;
        msg_buffer[0x01] = (p_data & 0x00FF) as u8;
        msg_buffer[0x02] = ((p_data & 0xFF00) >> 8) as u8;

        msg_buffer[3..3 + FIELD_BYTES].copy_from_slice(&x_bin);
        msg_buffer[3 + FIELD_BYTES..3 + FIELD_BYTES * 2].copy_from_slice(&y_bin);

        let msg_digest = sha1(&msg_buffer);

        let p_hash: u32 = by_dword(&msg_digest[0..4]) & bitmask(31) as u32;

        msg_buffer[0x00] = 0x5D;
        msg_buffer[0x01] = (p_data & 0x00FF) as u8;
        msg_buffer[0x02] = ((p_data & 0xFF00) >> 8) as u8;
        msg_buffer[0x03] = (p_hash & 0x000000FF) as u8;
        msg_buffer[0x04] = ((p_hash & 0x0000FF00) >> 8) as u8;
        msg_buffer[0x05] = ((p_hash & 0x00FF0000) >> 16) as u8;
        msg_buffer[0x06] = ((p_hash & 0xFF000000) >> 24) as u8;
        msg_buffer[0x07] = (p_auth_info & 0x00FF) as u8;
        msg_buffer[0x08] = ((p_auth_info & 0xFF00) >> 8) as u8;
        msg_buffer[0x09] = 0x00;
        msg_buffer[0x0A] = 0x00;

        let msg_digest = sha1(&msg_buffer[..=0x0A]);

        let i_signature = next_sn_bits(by_dword(&msg_digest[4..8]) as u64, 30, 2) << 32
            | by_dword(&msg_digest[0..4]) as u64;

        let mut e = BigNum::from_slice(&i_signature.to_be_bytes())?;

        let e_2 = e.to_owned()?;
        e.mod_mul(&e_2, private_key, gen_order, &mut num_context)?;

        let mut s = e.to_owned()?;

        let s_2 = s.to_owned()?;
        s.mod_sqr(&s_2, gen_order, &mut num_context)?;

        let c_2 = c.to_owned()?;
        c.lshift(&c_2, 2)?;

        s = &s + &c;

        let s_2 = s.to_owned()?;
        if s.mod_sqrt(&s_2, gen_order, &mut num_context).is_err() {
            no_square = true;
        };

        let s_2 = s.to_owned()?;
        s.mod_sub(&s_2, &e, gen_order, &mut num_context)?;

        if s.is_bit_set(0) {
            s = &s + gen_order;
        }

        let s_2 = s.to_owned()?;
        s.rshift1(&s_2)?;

        let p_signature = u64::from_be_bytes(s.to_vec_padded(8)?.try_into().unwrap());

        let product_key = ProductKey {
            upgrade: p_upgrade,
            channel_id: p_channel_id,
            hash: p_hash,
            signature: p_signature,
            auth_info: p_auth_info,
        };

        if p_signature <= bitmask(62) && !no_square {
            break pack(product_key);
        }

        no_square = false;
    };

    Ok(base24_encode(&p_raw))
}

const SIGNATURE_LENGTH_BITS: u8 = 62;
const HASH_LENGTH_BITS: u8 = 31;
const CHANNEL_ID_LENGTH_BITS: u8 = 10;
const UPGRADE_LENGTH_BITS: u8 = 1;
const EVERYTHING_ELSE: u8 =
    SIGNATURE_LENGTH_BITS + HASH_LENGTH_BITS + CHANNEL_ID_LENGTH_BITS + UPGRADE_LENGTH_BITS;

fn unpack(p_raw: &[u8]) -> Result<ProductKey> {
    let mut reader = BitReader::new(p_raw);
    let auth_info_length_bits = (p_raw.len() * 8) as u8 - EVERYTHING_ELSE;

    let p_auth_info = reader.read_u32(auth_info_length_bits)?;
    let p_signature = reader.read_u64(SIGNATURE_LENGTH_BITS)?;
    let p_hash = reader.read_u32(HASH_LENGTH_BITS)?;
    let p_channel_id = reader.read_u32(CHANNEL_ID_LENGTH_BITS)?;
    let p_upgrade = reader.read_bool()?;

    Ok(ProductKey {
        upgrade: p_upgrade,
        channel_id: p_channel_id,
        hash: p_hash,
        signature: p_signature,
        auth_info: p_auth_info,
    })
}

fn pack(p_key: ProductKey) -> Vec<u8> {
    let mut p_raw: u128 = 0;

    p_raw |= (p_key.auth_info as u128)
        << (SIGNATURE_LENGTH_BITS
            + HASH_LENGTH_BITS
            + CHANNEL_ID_LENGTH_BITS
            + UPGRADE_LENGTH_BITS);
    p_raw |= (p_key.signature as u128)
        << (HASH_LENGTH_BITS + CHANNEL_ID_LENGTH_BITS + UPGRADE_LENGTH_BITS);
    p_raw |= (p_key.hash as u128) << (CHANNEL_ID_LENGTH_BITS + UPGRADE_LENGTH_BITS);
    p_raw |= (p_key.channel_id as u128) << UPGRADE_LENGTH_BITS;
    p_raw |= p_key.upgrade as u128;

    p_raw
        .to_be_bytes()
        .into_iter()
        .skip_while(|&x| x == 0)
        .collect()
}

fn bitmask(n: u64) -> u64 {
    (1 << n) - 1
}

fn next_sn_bits(field: u64, n: u32, offset: u32) -> u64 {
    (field >> offset) & ((1u64 << n) - 1)
}

fn by_dword(n: &[u8]) -> u32 {
    (n[0] as u32) | (n[1] as u32) << 8 | (n[2] as u32) << 16 | (n[3] as u32) << 24
}

#[cfg(test)]
mod tests {
    use std::{fs::File, io::BufReader};

    use serde_json::from_reader;

    use crate::crypto::initialize_elliptic_curve;

    #[test]
    fn verify_test() {
        // Example product key and its BINK ID
        let product_key = "R882X-YRGC8-4KYTG-C3FCC-JCFDY";
        let bink_id = "54";

        // Load keys.json
        let path = "keys.json";
        let file = File::open(path).unwrap();
        let reader = BufReader::new(file);
        let keys: serde_json::Value = from_reader(reader).unwrap();

        let bink = &keys["BINK"][&bink_id];

        let p = bink["p"].as_str().unwrap();
        let a = bink["a"].as_str().unwrap();
        let b = bink["b"].as_str().unwrap();
        let gx = bink["g"]["x"].as_str().unwrap();
        let gy = bink["g"]["y"].as_str().unwrap();
        let kx = bink["pub"]["x"].as_str().unwrap();
        let ky = bink["pub"]["y"].as_str().unwrap();

        let (e_curve, gen_point, pub_point) = initialize_elliptic_curve(p, a, b, gx, gy, kx, ky);

        assert!(super::verify(&e_curve, &gen_point, &pub_point, product_key, true).unwrap());
    }
}