use crate::integer::block_decomposition::{BlockDecomposer, DecomposableInto};
use crate::integer::ciphertext::RadixCiphertext;
use crate::integer::server_key::CheckError;
use crate::integer::server_key::CheckError::CarryFull;
use crate::integer::ServerKey;

impl ServerKey {
    /// Computes homomorphically an addition between a scalar and a ciphertext.
    ///
    /// This function computes the operation without checking if it exceeds the capacity of the
    /// ciphertext.
    ///
    /// The result is returned as a new ciphertext.
    ///
    /// # Example
    ///
    /// ```rust
    /// use tfhe::integer::gen_keys_radix;
    /// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS;
    ///
    /// // We have 4 * 2 = 8 bits of message
    /// let size = 4;
    /// let (cks, sks) = gen_keys_radix(PARAM_MESSAGE_2_CARRY_2_KS_PBS, size);
    ///
    /// let msg = 4;
    /// let scalar = 40;
    ///
    /// let ct = cks.encrypt(msg);
    ///
    /// // Compute homomorphically an addition:
    /// let ct_res = sks.unchecked_scalar_add(&ct, scalar);
    ///
    /// // Decrypt:
    /// let dec: u64 = cks.decrypt(&ct_res);
    /// assert_eq!(msg + scalar, dec);
    /// ```
    pub fn unchecked_scalar_add<T>(&self, ct: &RadixCiphertext, scalar: T) -> RadixCiphertext
    where
        T: DecomposableInto<u8>,
    {
        let mut result = ct.clone();
        self.unchecked_scalar_add_assign(&mut result, scalar);
        result
    }

    /// Computes homomorphically an addition between a scalar and a ciphertext.
    ///
    /// This function computes the operation without checking if it exceeds the capacity of the
    /// ciphertext.
    ///
    /// The result is assigned to the `ct_left` ciphertext.
    pub fn unchecked_scalar_add_assign<T>(&self, ct: &mut RadixCiphertext, scalar: T)
    where
        T: DecomposableInto<u8>,
    {
        let bits_in_message = self.key.message_modulus.0.ilog2();
        let decomposer =
            BlockDecomposer::with_early_stop_at_zero(scalar, bits_in_message).iter_as::<u8>();
        for (ciphertext_block, scalar_block) in ct.blocks.iter_mut().zip(decomposer) {
            self.key
                .unchecked_scalar_add_assign(ciphertext_block, scalar_block);
        }
    }

    /// Verifies if a scalar can be added to a ciphertext.
    ///
    /// # Example
    ///
    ///```rust
    /// use tfhe::integer::gen_keys_radix;
    /// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS;
    ///
    /// // We have 4 * 2 = 8 bits of message
    /// let size = 4;
    /// let (cks, sks) = gen_keys_radix(PARAM_MESSAGE_2_CARRY_2_KS_PBS, size);
    ///
    /// let msg = 2u64;
    /// let scalar = 40;
    ///
    /// // Encrypt two messages:
    /// let ct1 = cks.encrypt(msg);
    /// let ct2 = cks.encrypt(msg);
    ///
    /// // Check if we can perform an addition
    /// let res = sks.is_scalar_add_possible(&ct1, scalar);
    ///
    /// assert_eq!(true, res);
    /// ```
    pub fn is_scalar_add_possible<T>(&self, ct: &RadixCiphertext, scalar: T) -> bool
    where
        T: DecomposableInto<u8>,
    {
        let bits_in_message = self.key.message_modulus.0.ilog2();
        let decomposer =
            BlockDecomposer::with_early_stop_at_zero(scalar, bits_in_message).iter_as::<u8>();

        ct.blocks
            .iter()
            .zip(decomposer)
            .all(|(ciphertext_block, scalar_block)| {
                self.key
                    .is_scalar_add_possible(ciphertext_block, scalar_block)
            })
    }

    /// Computes homomorphically an addition between a scalar and a ciphertext.
    ///
    /// If the operation can be performed, the result is returned in a new ciphertext.
    /// Otherwise [CheckError::CarryFull] is returned.
    ///
    /// # Example
    ///
    /// ```rust
    /// # fn main() -> Result<(), Box<dyn std::error::Error>> {
    /// use tfhe::integer::gen_keys_radix;
    /// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS;
    ///
    /// // We have 4 * 2 = 8 bits of message
    /// let size = 4;
    /// let (cks, sks) = gen_keys_radix(PARAM_MESSAGE_2_CARRY_2_KS_PBS, size);
    ///
    /// let msg = 4;
    /// let scalar = 40;
    ///
    /// let mut ct = cks.encrypt(msg);
    ///
    /// // Compute homomorphically an addition:
    /// let ct_res = sks.checked_scalar_add(&mut ct, scalar)?;
    ///
    /// // Decrypt:
    /// let dec: u64 = cks.decrypt(&ct_res);
    /// assert_eq!(msg + scalar, dec);
    /// # Ok(())
    /// # }
    /// ```
    pub fn checked_scalar_add<T>(
        &self,
        ct: &RadixCiphertext,
        scalar: T,
    ) -> Result<RadixCiphertext, CheckError>
    where
        T: DecomposableInto<u8>,
    {
        if self.is_scalar_add_possible(ct, scalar) {
            Ok(self.unchecked_scalar_add(ct, scalar))
        } else {
            Err(CarryFull)
        }
    }

    /// Computes homomorphically an addition between a scalar and a ciphertext.
    ///
    /// If the operation can be performed, the result is stored in the `ct_left` ciphertext.
    /// Otherwise [CheckError::CarryFull] is returned, and `ct_left` is not modified.
    pub fn checked_scalar_add_assign<T>(
        &self,
        ct: &mut RadixCiphertext,
        scalar: T,
    ) -> Result<(), CheckError>
    where
        T: DecomposableInto<u8>,
    {
        if self.is_scalar_add_possible(ct, scalar) {
            self.unchecked_scalar_add_assign(ct, scalar);
            Ok(())
        } else {
            Err(CarryFull)
        }
    }

    /// Computes homomorphically the addition of ciphertext with a scalar.
    ///
    /// The result is returned in a new ciphertext.
    ///
    /// # Example
    ///
    /// ```rust
    /// use tfhe::integer::gen_keys_radix;
    /// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS;
    ///
    /// // We have 4 * 2 = 8 bits of message
    /// let size = 4;
    /// let (cks, sks) = gen_keys_radix(PARAM_MESSAGE_2_CARRY_2_KS_PBS, size);
    ///
    /// let msg = 4;
    /// let scalar = 40;
    ///
    /// let mut ct = cks.encrypt(msg);
    ///
    /// // Compute homomorphically an addition:
    /// let ct_res = sks.smart_scalar_add(&mut ct, scalar);
    ///
    /// // Decrypt:
    /// let dec: u64 = cks.decrypt(&ct_res);
    /// assert_eq!(msg + scalar, dec);
    /// ```
    pub fn smart_scalar_add<T>(&self, ct: &mut RadixCiphertext, scalar: T) -> RadixCiphertext
    where
        T: DecomposableInto<u8>,
    {
        if !self.is_scalar_add_possible(ct, scalar) {
            self.full_propagate(ct);
        }

        let mut ct = ct.clone();
        self.unchecked_scalar_add_assign(&mut ct, scalar);
        ct
    }

    /// Computes homomorphically the addition of ciphertext with a scalar.
    ///
    /// The result is assigned to the `ct_left` ciphertext.
    ///
    /// # Example
    ///
    /// ```rust
    /// use tfhe::integer::gen_keys_radix;
    /// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS;
    ///
    /// // We have 4 * 2 = 8 bits of message
    /// let size = 4;
    /// let (cks, sks) = gen_keys_radix(PARAM_MESSAGE_2_CARRY_2_KS_PBS, size);
    ///
    /// let msg = 129;
    /// let scalar = 40;
    ///
    /// let mut ct = cks.encrypt(msg);
    ///
    /// // Compute homomorphically an addition:
    /// sks.smart_scalar_add_assign(&mut ct, scalar);
    ///
    /// // Decrypt:
    /// let dec: u64 = cks.decrypt(&ct);
    /// assert_eq!(msg + scalar, dec);
    /// ```
    pub fn smart_scalar_add_assign<T>(&self, ct: &mut RadixCiphertext, scalar: T)
    where
        T: DecomposableInto<u8>,
    {
        if !self.is_scalar_add_possible(ct, scalar) {
            self.full_propagate(ct);
        }
        self.unchecked_scalar_add_assign(ct, scalar);
    }
}
