// Utility hashing module copied from `solana_program::program::hash`, since we
// can't import solana_program for compile time hashing for some reason.

use serde::{Deserialize, Serialize};
use sha2::{Digest, Sha256};
use std::{convert::TryFrom, fmt, mem, str::FromStr};
use thiserror::Error;

pub const HASH_BYTES: usize = 32;
#[derive(Serialize, Deserialize, Clone, Copy, Default, Eq, PartialEq, Ord, PartialOrd, Hash)]
#[repr(transparent)]
pub struct Hash(pub [u8; HASH_BYTES]);

#[derive(Clone, Default)]
pub struct Hasher {
    hasher: Sha256,
}

impl Hasher {
    pub fn hash(&mut self, val: &[u8]) {
        self.hasher.update(val);
    }
    pub fn hashv(&mut self, vals: &[&[u8]]) {
        for val in vals {
            self.hash(val);
        }
    }
    pub fn result(self) -> Hash {
        // At the time of this writing, the sha2 library is stuck on an old version
        // of generic_array (0.9.0). Decouple ourselves with a clone to our version.
        Hash(<[u8; HASH_BYTES]>::try_from(self.hasher.finalize().as_slice()).unwrap())
    }
}

impl AsRef<[u8]> for Hash {
    fn as_ref(&self) -> &[u8] {
        &self.0[..]
    }
}

impl fmt::Debug for Hash {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", bs58::encode(self.0).into_string())
    }
}

impl fmt::Display for Hash {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", bs58::encode(self.0).into_string())
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Error)]
pub enum ParseHashError {
    #[error("string decoded to wrong size for hash")]
    WrongSize,
    #[error("failed to decoded string to hash")]
    Invalid,
}

impl FromStr for Hash {
    type Err = ParseHashError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let bytes = bs58::decode(s)
            .into_vec()
            .map_err(|_| ParseHashError::Invalid)?;
        if bytes.len() != mem::size_of::<Hash>() {
            Err(ParseHashError::WrongSize)
        } else {
            Ok(Hash::new(&bytes))
        }
    }
}

impl Hash {
    pub fn new(hash_slice: &[u8]) -> Self {
        Hash(<[u8; HASH_BYTES]>::try_from(hash_slice).unwrap())
    }

    pub fn to_bytes(self) -> [u8; HASH_BYTES] {
        self.0
    }
}

/// Return a Sha256 hash for the given data.
pub fn hashv(vals: &[&[u8]]) -> Hash {
    // Perform the calculation inline, calling this from within a program is
    // not supported
    #[cfg(not(target_arch = "bpf"))]
    {
        let mut hasher = Hasher::default();
        hasher.hashv(vals);
        hasher.result()
    }
    // Call via a system call to perform the calculation
    #[cfg(target_arch = "bpf")]
    {
        extern "C" {
            fn sol_sha256(vals: *const u8, val_len: u64, hash_result: *mut u8) -> u64;
        };
        let mut hash_result = [0; HASH_BYTES];
        unsafe {
            sol_sha256(
                vals as *const _ as *const u8,
                vals.len() as u64,
                &mut hash_result as *mut _ as *mut u8,
            );
        }
        Hash::new_from_array(hash_result)
    }
}

/// Return a Sha256 hash for the given data.
pub fn hash(val: &[u8]) -> Hash {
    hashv(&[val])
}