//! Provides hashing abstractions and implementations including SHA256 and a default dummy hasher.

#[cfg(feature = "sha256")]
use sha2::{Digest, Sha256};

/// A trait representing a generic hash function.
///
/// This allows the Merkle tree to use any hash function that conforms to this interface.
pub trait Hasher {
    /// Hashes an input string and returns the resulting hash as a hexadecimal string.
    fn hash(&self, input: &str) -> String;
}

/// A dummy hasher used for testing or demonstration purposes.
///
/// Always returns a static hash value.
pub struct DefaultHasher;

impl Hasher for DefaultHasher {
    fn hash(&self, _input: &str) -> String {
        "0xc0ff3".to_string()
    }
}

#[cfg(feature = "sha256")]
/// A hasher implementation using the SHA-256 cryptographic hash function.
pub struct SHA256Hasher;

#[cfg(feature = "sha256")]
impl Hasher for SHA256Hasher {
    fn hash(&self, input: &str) -> String {
        let mut hasher = Sha256::new();
        hasher.update(input.as_bytes());
        hex::encode(hasher.finalize())
    }
}

#[cfg(all(test, feature = "sha256"))]
mod tests {
    use super::*;

    #[test]
    fn test_sha256_hasher_with_known_input() {
        let hasher = SHA256Hasher;
        let input = "hello";
        let expected_hash = "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824";
        let actual_hash = hasher.hash(input);
        assert_eq!(actual_hash, expected_hash);
    }

    #[test]
    fn test_sha256_hasher_empty_string() {
        let hasher = SHA256Hasher;
        let input = "";
        let expected_hash = "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855";
        let actual_hash = hasher.hash(input);
        assert_eq!(actual_hash, expected_hash);
    }
}