use sha2::{Digest, Sha256};

/// Compute SHA-256 hash as: SHA256(timestamp_bytes + content_bytes).
/// The timestamp is serialized as its string representation's bytes,
/// matching the spec: `SHA256([timestamp_bytes] + [raw_file_content_bytes])`.
pub fn compute_hash(timestamp_ms: i64, content: &[u8]) -> String {
    let mut hasher = Sha256::new();
    hasher.update(timestamp_ms.to_be_bytes());
    hasher.update(content);
    hex::encode(hasher.finalize())
}

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

    #[test]
    fn test_deterministic_hash() {
        let ts = 1773014400123i64;
        let content = b"hello world";
        let h1 = compute_hash(ts, content);
        let h2 = compute_hash(ts, content);
        assert_eq!(h1, h2);
        assert_eq!(h1.len(), 64); // SHA-256 hex = 64 chars
    }

    #[test]
    fn test_different_timestamp_different_hash() {
        let content = b"same content";
        let h1 = compute_hash(1000, content);
        let h2 = compute_hash(2000, content);
        assert_ne!(h1, h2);
    }

    #[test]
    fn test_different_content_different_hash() {
        let ts = 1234567890i64;
        let h1 = compute_hash(ts, b"content A");
        let h2 = compute_hash(ts, b"content B");
        assert_ne!(h1, h2);
    }

    #[test]
    fn test_empty_content() {
        let h = compute_hash(0, b"");
        assert_eq!(h.len(), 64);
    }
}