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// This file is part of the laron-crypto
//
// Copyright 2023 Ade M Ramdani
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

use k256::{AffinePoint, NonZeroScalar};
use k256::elliptic_curve::group::prime::PrimeCurveAffine;
use k256::elliptic_curve::sec1::ToEncodedPoint;
use crate::error::{Error, Result};

/// Byte size of the public key
const SIZE: usize = 65;

/// Public key
#[derive(Debug, Clone, Copy, Eq, PartialEq)]
pub struct PublicKey {
    bytes: [u8; SIZE],
}

impl PublicKey {
    /// Create public key from bytes
    pub fn from_bytes(bytes: [u8; SIZE]) -> Self {
        Self { bytes }
    }

    /// Create public key from slice
    pub fn from_slice(slice: &[u8]) -> Result<Self> {
        if slice.len() != SIZE {
            Err(Error::LengthError(format!(
                "PublicKey size must be {} bytes got {} bytes.",
                SIZE,
                slice.len()
            )))
        } else {
            let mut new_bytes = [0u8; SIZE];
            new_bytes.copy_from_slice(slice);
            Ok(Self::from_bytes(new_bytes))
        }
    }

    /// Create public key from hex string
    pub fn from_hex(hex: &str) -> Result<Self> {
        if hex.len() != SIZE * 2 {
            Err(Error::LengthError(format!(
                "PublicKey hex must be {} characters got {} characters.",
                SIZE * 2,
                hex.len()
            )))
        } else {
            let bytes = hex::decode(hex)?;
            Self::from_slice(&bytes)
        }
    }

    /// Get public key as bytes
    pub fn as_bytes(&self) -> [u8; SIZE] {
        self.bytes
    }

    /// Get public key as slice
    pub fn as_slice(&self) -> &[u8] {
        &self.bytes
    }

    /// Get public key as hex string
    pub fn as_hex(&self) -> String {
        hex::encode(&self.bytes)
    }

    /// Derive child key from parent key.
    pub fn derive_child(&self, other: [u8; 32]) -> Result<Self> {
        let current = k256::PublicKey::from_sec1_bytes(&self.bytes).unwrap();
        let child_scalar = Option::<NonZeroScalar>::from(NonZeroScalar::from_repr(other.into())).ok_or(Error::InvalidPublicKey)?;
        let child_point = current.to_projective() + (AffinePoint::generator() * *child_scalar);
        let derived = k256::PublicKey::from_affine(child_point.into()).map_err(|_| Error::InvalidPublicKey)?;
        let bytes = derived.to_encoded_point(false);
        Self::from_slice(bytes.as_bytes())
    }
}