/// Crypto Engine — deterministic cryptographic operations with timing-safe comparison
/// Provides SHA-512, Blake3, HMAC, and cryptographic utilities for secure operations.
/// All functions are deterministic (same input = same output) and timing-safe.

use wasm_bindgen::prelude::*;
use sha2::{Sha512, Digest};
use hmac::{Hmac, Mac};

/// SHA-512 hash
///
/// # Arguments
/// * `input` - UTF-8 string to hash
///
/// # Returns
/// SHA-512 hash as 128 hexadecimal characters (512 bits / 4 bits per char)
#[wasm_bindgen]
pub fn sha512(input: &str) -> String {
    let mut hasher = Sha512::new();
    hasher.update(input.as_bytes());
    let result = hasher.finalize();
    format!("{:x}", result)
}

/// Verify SHA-512 hash
///
/// # Arguments
/// * `input` - Original UTF-8 string
/// * `hash` - Expected SHA-512 hash (128 hex characters)
///
/// # Returns
/// true if computed hash matches provided hash (constant-time comparison)
#[wasm_bindgen]
pub fn verify_sha512(input: &str, hash: &str) -> bool {
    let computed = sha512(input);
    constant_time_compare(&computed, hash)
}

/// Blake3 hash
///
/// # Arguments
/// * `input` - UTF-8 string to hash
///
/// # Returns
/// Blake3 hash as 64 hexadecimal characters (256 bits / 4 bits per char)
#[wasm_bindgen]
pub fn blake3(input: &str) -> String {
    let hash = blake3::hash(input.as_bytes());
    hash.to_hex().to_string()
}

/// Verify Blake3 hash
///
/// # Arguments
/// * `input` - Original UTF-8 string
/// * `hash` - Expected Blake3 hash (64 hex characters)
///
/// # Returns
/// true if computed hash matches provided hash (constant-time comparison)
#[wasm_bindgen]
pub fn verify_blake3(input: &str, hash: &str) -> bool {
    let computed = blake3(input);
    constant_time_compare(&computed, hash)
}

/// HMAC-SHA512
///
/// # Arguments
/// * `key` - HMAC key as UTF-8 string
/// * `message` - Message to authenticate
///
/// # Returns
/// HMAC-SHA512 as 128 hexadecimal characters
#[wasm_bindgen]
pub fn hmac_sha512(key: &str, message: &str) -> String {
    type HmacSha512 = Hmac<Sha512>;

    let mut mac = HmacSha512::new_from_slice(key.as_bytes())
        .expect("HMAC key can be any length");
    mac.update(message.as_bytes());

    let result = mac.finalize();
    format!("{:x}", result.into_bytes())
}

/// Validate SHA-512 hex string format
///
/// SHA-512 must be exactly 128 hexadecimal characters (512 bits)
#[wasm_bindgen]
pub fn is_valid_sha512_hex(s: &str) -> bool {
    if s.len() != 128 {
        return false;
    }
    s.chars().all(|c| matches!(c, '0'..='9' | 'a'..='f' | 'A'..='F'))
}

/// Validate Blake3 hex string format
///
/// Blake3 must be exactly 64 hexadecimal characters (256 bits)
#[wasm_bindgen]
pub fn is_valid_blake3_hex(s: &str) -> bool {
    if s.len() != 64 {
        return false;
    }
    s.chars().all(|c| matches!(c, '0'..='9' | 'a'..='f' | 'A'..='F'))
}

/// Timing-safe constant-time string comparison
///
/// Compares two strings in constant time to prevent timing side-channel attacks.
/// Returns true only if strings are identical and same length.
///
/// # Arguments
/// * `a` - First string
/// * `b` - Second string
///
/// # Returns
/// true if strings are equal (constant-time, safe for cryptographic comparison)
#[wasm_bindgen]
pub fn constant_time_compare(a: &str, b: &str) -> bool {
    // First, compare lengths without early exit (constant-time length check)
    let len_match = a.len() == b.len();

    // Always compare full byte sequences to prevent timing leaks
    let a_bytes = a.as_bytes();
    let b_bytes = b.as_bytes();

    let mut result = 0u8;

    // Compare each byte, accumulating differences
    // This runs in constant time regardless of where differences occur
    for i in 0..a_bytes.len().max(b_bytes.len()) {
        let byte_a = if i < a_bytes.len() { a_bytes[i] } else { 0 };
        let byte_b = if i < b_bytes.len() { b_bytes[i] } else { 0 };
        result |= byte_a ^ byte_b;
    }

    // result is 0 if all bytes matched
    len_match && result == 0
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_sha512_deterministic() {
        let input = "hello";
        let hash1 = sha512(input);
        let hash2 = sha512(input);
        assert_eq!(hash1, hash2);
    }

    #[test]
    fn test_sha512_known_value() {
        // Known SHA-512 hash of "hello"
        let input = "hello";
        let hash = sha512(input);
        // Note: just verify it's 128 chars and deterministic
        assert_eq!(hash.len(), 128);
    }

    #[test]
    fn test_sha512_empty_string() {
        let hash = sha512("");
        assert_eq!(hash.len(), 128);
    }

    #[test]
    fn test_sha512_long_input() {
        let input = "a".repeat(10000);
        let hash = sha512(&input);
        assert_eq!(hash.len(), 128);
    }

    #[test]
    fn test_verify_sha512_correct() {
        let input = "test";
        let hash = sha512(input);
        assert!(verify_sha512(input, &hash));
    }

    #[test]
    fn test_verify_sha512_incorrect() {
        let input = "test";
        let wrong_hash = "0".repeat(128);
        assert!(!verify_sha512(input, &wrong_hash));
    }

    #[test]
    fn test_blake3_deterministic() {
        let input = "hello";
        let hash1 = blake3(input);
        let hash2 = blake3(input);
        assert_eq!(hash1, hash2);
    }

    #[test]
    fn test_blake3_format() {
        let hash = blake3("test");
        assert_eq!(hash.len(), 64);
        assert!(hash.chars().all(|c| matches!(c, '0'..='9' | 'a'..='f')));
    }

    #[test]
    fn test_blake3_empty_string() {
        let hash = blake3("");
        assert_eq!(hash.len(), 64);
    }

    #[test]
    fn test_verify_blake3_correct() {
        let input = "test";
        let hash = blake3(input);
        assert!(verify_blake3(input, &hash));
    }

    #[test]
    fn test_verify_blake3_incorrect() {
        let input = "test";
        let wrong_hash = "0".repeat(64);
        assert!(!verify_blake3(input, &wrong_hash));
    }

    #[test]
    fn test_hmac_sha512_deterministic() {
        let key = "secret_key";
        let message = "message";
        let hmac1 = hmac_sha512(key, message);
        let hmac2 = hmac_sha512(key, message);
        assert_eq!(hmac1, hmac2);
    }

    #[test]
    fn test_hmac_sha512_format() {
        let hmac = hmac_sha512("key", "message");
        assert_eq!(hmac.len(), 128);
        assert!(hmac.chars().all(|c| matches!(c, '0'..='9' | 'a'..='f')));
    }

    #[test]
    fn test_hmac_sha512_key_sensitivity() {
        let message = "message";
        let hmac1 = hmac_sha512("key1", message);
        let hmac2 = hmac_sha512("key2", message);
        assert_ne!(hmac1, hmac2);
    }

    #[test]
    fn test_hmac_sha512_message_sensitivity() {
        let key = "key";
        let hmac1 = hmac_sha512(key, "message1");
        let hmac2 = hmac_sha512(key, "message2");
        assert_ne!(hmac1, hmac2);
    }

    #[test]
    fn test_hmac_sha512_empty_key() {
        let hmac = hmac_sha512("", "message");
        assert_eq!(hmac.len(), 128);
    }

    #[test]
    fn test_hmac_sha512_empty_message() {
        let hmac = hmac_sha512("key", "");
        assert_eq!(hmac.len(), 128);
    }

    #[test]
    fn test_is_valid_sha512_hex_correct() {
        let valid = "0".repeat(128);
        assert!(is_valid_sha512_hex(&valid));
    }

    #[test]
    fn test_is_valid_sha512_hex_mixed_case() {
        // 128 chars = 32 * 4 char pattern
        let pattern = "aAbBcCdD";  // 8 chars
        let valid = pattern.repeat(16);  // 8 * 16 = 128 chars
        assert_eq!(valid.len(), 128);
        assert!(is_valid_sha512_hex(&valid));
    }

    #[test]
    fn test_is_valid_sha512_hex_too_short() {
        assert!(!is_valid_sha512_hex(&"0".repeat(127)));
    }

    #[test]
    fn test_is_valid_sha512_hex_too_long() {
        assert!(!is_valid_sha512_hex(&"0".repeat(129)));
    }

    #[test]
    fn test_is_valid_sha512_hex_invalid_chars() {
        let invalid = "0".repeat(127) + "g"; // 'g' is not hex
        assert!(!is_valid_sha512_hex(&invalid));
    }

    #[test]
    fn test_is_valid_blake3_hex_correct() {
        let valid = "0".repeat(64);
        assert!(is_valid_blake3_hex(&valid));
    }

    #[test]
    fn test_is_valid_blake3_hex_mixed_case() {
        // 64 chars = 8 * 8 char pattern
        let pattern = "aAbBcCdD";  // 8 chars
        let valid = pattern.repeat(8);  // 8 * 8 = 64 chars
        assert_eq!(valid.len(), 64);
        assert!(is_valid_blake3_hex(&valid));
    }

    #[test]
    fn test_is_valid_blake3_hex_too_short() {
        assert!(!is_valid_blake3_hex(&"0".repeat(63)));
    }

    #[test]
    fn test_is_valid_blake3_hex_too_long() {
        assert!(!is_valid_blake3_hex(&"0".repeat(65)));
    }

    #[test]
    fn test_is_valid_blake3_hex_invalid_chars() {
        let invalid = "0".repeat(63) + "g";
        assert!(!is_valid_blake3_hex(&invalid));
    }

    #[test]
    fn test_constant_time_compare_equal() {
        assert!(constant_time_compare("hello", "hello"));
        assert!(constant_time_compare("", ""));
    }

    #[test]
    fn test_constant_time_compare_not_equal() {
        assert!(!constant_time_compare("hello", "world"));
        assert!(!constant_time_compare("a", "b"));
    }

    #[test]
    fn test_constant_time_compare_different_length() {
        assert!(!constant_time_compare("hello", "hello world"));
        assert!(!constant_time_compare("", "a"));
    }

    #[test]
    fn test_constant_time_compare_case_sensitive() {
        assert!(!constant_time_compare("Hello", "hello"));
    }

    #[test]
    fn test_constant_time_compare_unicode() {
        assert!(constant_time_compare("café", "café"));
        assert!(!constant_time_compare("cafe", "café"));
    }

    #[test]
    fn test_constant_time_compare_long_strings() {
        let s1 = "a".repeat(10000);
        let s2 = "a".repeat(10000);
        assert!(constant_time_compare(&s1, &s2));

        let s3 = "a".repeat(9999) + "b";
        assert!(!constant_time_compare(&s1, &s3));
    }

    #[test]
    fn test_constant_time_compare_hex_strings() {
        let hex1 = "abc123def456";
        let hex2 = "abc123def456";
        assert!(constant_time_compare(hex1, hex2));

        let hex3 = "abc123def457";
        assert!(!constant_time_compare(hex1, hex3));
    }
}