host-encoding 0.3.4

//! Pure DOTNS encoding and decoding functions.
//!
//! No I/O. No network calls. WASM-safe.
//!
//! Provides ENS-style namehashing, ABI encoding, SCALE encoding/decoding,
//! and contenthash → CID conversion for the DOTNS resolver protocol.

use tiny_keccak::{Hasher, Keccak};

/// Solidity function selector for `contenthash(bytes32)`.
pub const CONTENTHASH_SELECTOR: [u8; 4] = [0xbc, 0x1c, 0x58, 0xd1];

/// Compile-time hex string to 20-byte address.
pub const fn hex_addr(s: &str) -> [u8; 20] {
    let b = s.as_bytes();
    assert!(b.len() == 40, "address must be 40 hex chars");
    let mut out = [0u8; 20];
    let mut i = 0;
    while i < 20 {
        out[i] = (hex_nibble(b[i * 2]) << 4) | hex_nibble(b[i * 2 + 1]);
        i += 1;
    }
    out
}

/// Compile-time hex character to nibble value.
pub const fn hex_nibble(c: u8) -> u8 {
    match c {
        b'0'..=b'9' => c - b'0',
        b'a'..=b'f' => c - b'a' + 10,
        b'A'..=b'F' => c - b'A' + 10,
        _ => panic!("invalid hex"),
    }
}

/// Compute keccak256 hash of the given data.
pub fn keccak256(data: &[u8]) -> [u8; 32] {
    let mut hasher = Keccak::v256();
    hasher.update(data);
    let mut out = [0u8; 32];
    hasher.finalize(&mut out);
    out
}

/// ENS-style namehash: `namehash("mytestapp.dot")`.
///
/// Splits by `.`, reverses labels, and iteratively hashes to produce a
/// 32-byte node identifier compatible with the ENS/DOTNS registry.
pub fn namehash(domain: &str) -> [u8; 32] {
    if domain.is_empty() {
        return [0u8; 32];
    }
    let labels: Vec<&str> = domain.split('.').collect();
    let mut node = [0u8; 32];
    for label in labels.into_iter().rev() {
        let label_hash = keccak256(label.as_bytes());
        let mut buf = [0u8; 64];
        buf[..32].copy_from_slice(&node);
        buf[32..].copy_from_slice(&label_hash);
        node = keccak256(&buf);
    }
    node
}

/// ABI-encode `contenthash(bytes32 node)` call data.
pub fn encode_contenthash_call(node: &[u8; 32]) -> Vec<u8> {
    let mut data = Vec::with_capacity(36);
    data.extend_from_slice(&CONTENTHASH_SELECTOR);
    data.extend_from_slice(node);
    data
}

/// SCALE-encode the parameters for `ReviveApi::call()` runtime API.
///
/// Parameters (in order, from runtime metadata):
///   origin: AccountId32 ([u8; 32])
///   dest: H160 ([u8; 20])
///   value: u128 (BalanceOf<T>, 16 bytes LE)
///   gas_limit: Option<Weight> where Weight { ref_time: Compact<u64>, proof_size: Compact<u64> }
///   storage_deposit_limit: Option<u128>
///   input_data: Vec<u8>
pub fn scale_encode_revive_call(dest: &[u8; 20], input_data: &[u8]) -> Result<Vec<u8>, String> {
    let mut buf = Vec::with_capacity(128 + input_data.len());

    // origin: AccountId32 (Alice — matches dot.li's dry-run convention)
    buf.extend_from_slice(&[
        0xd4, 0x35, 0x93, 0xc7, 0x15, 0xfd, 0xd3, 0x1c, 0x61, 0x14, 0x1a, 0xbd, 0x04, 0xa9, 0x9f,
        0xd6, 0x82, 0x2c, 0x85, 0x58, 0x85, 0x4c, 0xcd, 0xe3, 0x9a, 0x56, 0x84, 0xe7, 0xa5, 0x6d,
        0xa2, 0x7d,
    ]);

    // dest: H160
    buf.extend_from_slice(dest);

    // value: u128 = 0
    buf.extend_from_slice(&0u128.to_le_bytes());

    // gas_limit: Option<Weight> = Some(Weight { ref_time: MAX, proof_size: MAX })
    buf.push(0x01); // Some
    scale_compact_u64(&mut buf, u64::MAX); // ref_time
    scale_compact_u64(&mut buf, u64::MAX); // proof_size

    // storage_deposit_limit: Option<u128> = Some(u64::MAX as u128)
    buf.push(0x01); // Some
    buf.extend_from_slice(&(u64::MAX as u128).to_le_bytes());

    // input_data: Vec<u8> = compact_len ++ bytes
    scale_compact_len(&mut buf, input_data.len())?;
    buf.extend_from_slice(input_data);

    Ok(buf)
}

/// SCALE compact encoding for a u64 value.
pub fn scale_compact_u64(buf: &mut Vec<u8>, val: u64) {
    if val < 64 {
        buf.push((val as u8) << 2);
    } else if val < 0x4000 {
        let v = ((val as u16) << 2) | 1;
        buf.extend_from_slice(&v.to_le_bytes());
    } else if val < 0x4000_0000 {
        let v = ((val as u32) << 2) | 2;
        buf.extend_from_slice(&v.to_le_bytes());
    } else {
        // Big integer mode: upper 6 bits = (byte_count - 4), lower 2 bits = 0b11
        // For u64, we need up to 8 bytes
        let bytes = val.to_le_bytes();
        let len = 8 - (val.leading_zeros() / 8) as usize;
        let len = len.max(4); // minimum 4 bytes in big mode
        let prefix = (((len - 4) as u8) << 2) | 3;
        buf.push(prefix);
        buf.extend_from_slice(&bytes[..len]);
    }
}

/// SCALE compact encoding for a length prefix.
///
/// Returns an error if `n` is >= 1 GiB, which is beyond the SCALE
/// single-byte-mode range and not expected in any RPC call this crate makes.
pub fn scale_compact_len(buf: &mut Vec<u8>, n: usize) -> Result<(), String> {
    if n < 64 {
        buf.push((n as u8) << 2);
    } else if n < 16384 {
        let v = ((n as u16) << 2) | 1;
        buf.extend_from_slice(&v.to_le_bytes());
    } else if n < 1_073_741_824 {
        let v = ((n as u32) << 2) | 2;
        buf.extend_from_slice(&v.to_le_bytes());
    } else {
        // Big mode — values >= 1 GiB are not valid for any RPC input_data this
        // crate produces; return an error instead of panicking.
        return Err(format!(
            "compact encoding: value {n} is too large (max 1_073_741_823)"
        ));
    }
    Ok(())
}

// Re-export shared hex utilities from the crate root.
pub use crate::{hex_decode, hex_encode};

/// Decode the SCALE-encoded `ContractResult` from pallet-revive's `ReviveApi::call`.
///
/// # Layout (pallet-revive, Asset Hub Paseo, 2025-03)
///
/// This is a hand-rolled positional decoder. The field order is:
/// - gas_consumed: Weight { ref_time: Compact<u64>, proof_size: Compact<u64> }
/// - gas_required: Weight { ref_time: Compact<u64>, proof_size: Compact<u64> }
/// - storage_deposit: StorageDeposit enum (1 byte tag + u128)
/// - [pallet-revive extra] Option<Balance> (1 tag + 16 if Some)
/// - [pallet-revive extra] Balance (16 bytes u128)
/// - debug_message: Vec<u8> (Compact len + bytes)
/// - result: ExecReturnValue { flags: u32, data: Vec<u8> } (no Result wrapper)
///
/// If pallet-revive changes its ContractResult layout, this decoder must be
/// updated and a new test vector captured.
pub fn decode_contract_result(response: &[u8]) -> Result<Vec<u8>, String> {
    let mut pos = 0;

    // gas_consumed: Weight { ref_time: Compact<u64>, proof_size: Compact<u64> }
    let (_, n) = decode_scale_compact(&response[pos..])?;
    pos += n;
    let (_, n) = decode_scale_compact(&response[pos..])?;
    pos += n;

    // gas_required: Weight { ref_time: Compact<u64>, proof_size: Compact<u64> }
    let (_, n) = decode_scale_compact(&response[pos..])?;
    pos += n;
    let (_, n) = decode_scale_compact(&response[pos..])?;
    pos += n;

    // storage_deposit: StorageDeposit enum (1 byte variant + u128)
    if pos + 17 > response.len() {
        return Err("response too short (storage_deposit)".into());
    }
    pos += 1 + 16;

    // pallet-revive adds extra fields not present in pallet-contracts:
    // - Option<Balance> (1 tag + 16 u128 if Some) — likely storage deposit limit
    // - Balance (16 bytes u128) — likely eth gas price or fee
    if pos >= response.len() {
        return Err("response too short (extra fields)".into());
    }
    let opt_tag = response[pos];
    pos += 1; // Option tag
    if opt_tag == 1 {
        if pos + 16 > response.len() {
            return Err("response too short (option balance)".into());
        }
        pos += 16; // Some(u128)
    }
    if pos + 16 > response.len() {
        return Err("response too short (plain balance)".into());
    }
    pos += 16; // plain u128

    // debug_message: Vec<u8>
    let (msg_len, bytes_read) = decode_scale_compact(&response[pos..])?;
    pos += bytes_read + msg_len;

    // result: ExecReturnValue { flags: u32, data: Vec<u8> } (no Result wrapper in pallet-revive)
    if pos + 4 > response.len() {
        return Err("response too short (flags)".into());
    }
    pos += 4; // flags: u32

    // data: Vec<u8>
    let (data_len, bytes_read) = decode_scale_compact(&response[pos..])?;
    pos += bytes_read;

    if pos + data_len > response.len() {
        return Err(format!(
            "data extends beyond response (pos={pos}, data_len={data_len}, total={})",
            response.len()
        ));
    }

    Ok(response[pos..pos + data_len].to_vec())
}

/// Decode a SCALE compact-encoded integer, returning (value, bytes_consumed).
pub fn decode_scale_compact(data: &[u8]) -> Result<(usize, usize), String> {
    if data.is_empty() {
        return Err("empty data for compact decode".into());
    }
    let mode = data[0] & 0b11;
    match mode {
        0 => Ok(((data[0] >> 2) as usize, 1)),
        1 => {
            if data.len() < 2 {
                return Err("compact: need 2 bytes".into());
            }
            let v = u16::from_le_bytes([data[0], data[1]]) >> 2;
            Ok((v as usize, 2))
        }
        2 => {
            if data.len() < 4 {
                return Err("compact: need 4 bytes".into());
            }
            let v = u32::from_le_bytes([data[0], data[1], data[2], data[3]]) >> 2;
            Ok((v as usize, 4))
        }
        3 => {
            // Big integer mode
            let bytes_needed = (data[0] >> 2) as usize + 4;
            if data.len() < 1 + bytes_needed {
                return Err("compact: big mode insufficient data".into());
            }
            let mut val: usize = 0;
            for i in (0..bytes_needed).rev() {
                val = (val << 8) | data[1 + i] as usize;
            }
            Ok((val, 1 + bytes_needed))
        }
        _ => unreachable!(),
    }
}

/// Decode ABI-encoded bytes return value from Solidity.
///
/// The `contenthash` function returns `bytes` which is ABI-encoded as:
///   offset (32 bytes, = 0x20)
///   length (32 bytes)
///   data (padded to 32-byte boundary)
pub fn decode_abi_bytes(data: &[u8]) -> Result<Vec<u8>, String> {
    if data.len() < 64 {
        return Err(format!("ABI bytes too short: {} bytes", data.len()));
    }
    // First 32 bytes: offset (should be 0x20 = 32)
    // Next 32 bytes: length
    let len = u32::from_be_bytes([data[60], data[61], data[62], data[63]]) as usize;
    if 64 + len > data.len() {
        return Err(format!("ABI bytes: length {len} exceeds data"));
    }
    Ok(data[64..64 + len].to_vec())
}

/// Parse a contenthash value to extract an IPFS CIDv1.
///
/// The contenthash format follows EIP-1577:
///   0xe3 0x01 0x01 <multihash>  (IPFS, codec dag-pb, CIDv1)
///   0xe5 0x01 ...               (Swarm)
///
/// We decode the CID and return it as a base32-encoded string (multibase prefix `b`).
pub fn contenthash_to_cid(data: &[u8]) -> Result<String, String> {
    if data.is_empty() {
        return Err("empty contenthash".into());
    }

    // EIP-1577 contenthash uses multicodec varint prefix.
    // IPFS namespace = 0xe3 = 227, encoded as varint `e3 01` (2 bytes).
    // Swarm namespace = 0xe5 = 229, encoded as varint `e5 01` (2 bytes).
    let (codec, varint_len) = decode_unsigned_varint(data);
    match codec {
        0xe3 => {
            // IPFS — skip the namespace varint, rest is the CID
            let cid_bytes = &data[varint_len..];
            Ok(format!("b{}", base32_encode(cid_bytes)))
        }
        0xe5 => Err("Swarm contenthash not supported".into()),
        _ => Err(format!(
            "contenthash_to_cid: unrecognized codec varint 0x{codec:02x}; only IPFS dag-pb (0x70) is supported"
        )),
    }
}

/// Decode an unsigned varint (LEB128), returning (value, bytes_consumed).
pub fn decode_unsigned_varint(data: &[u8]) -> (u64, usize) {
    let mut value: u64 = 0;
    let mut shift = 0;
    for (i, &byte) in data.iter().enumerate() {
        if shift >= 64 {
            break;
        }
        value |= ((byte & 0x7f) as u64) << shift;
        if byte & 0x80 == 0 {
            return (value, i + 1);
        }
        shift += 7;
    }
    (value, data.len())
}

/// RFC 4648 base32 encoding (lowercase, no padding).
pub fn base32_encode(data: &[u8]) -> String {
    const ALPHABET: &[u8] = b"abcdefghijklmnopqrstuvwxyz234567";
    let mut result = String::new();
    let mut bits: u32 = 0;
    let mut num_bits: u32 = 0;
    for &byte in data {
        bits = (bits << 8) | byte as u32;
        num_bits += 8;
        while num_bits >= 5 {
            num_bits -= 5;
            result.push(ALPHABET[((bits >> num_bits) & 0x1f) as usize] as char);
        }
    }
    if num_bits > 0 {
        result.push(ALPHABET[((bits << (5 - num_bits)) & 0x1f) as usize] as char);
    }
    result
}

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

    #[test]
    fn test_hex_nibble_digits() {
        assert_eq!(hex_nibble(b'0'), 0);
        assert_eq!(hex_nibble(b'9'), 9);
        assert_eq!(hex_nibble(b'a'), 10);
        assert_eq!(hex_nibble(b'f'), 15);
        assert_eq!(hex_nibble(b'A'), 10);
        assert_eq!(hex_nibble(b'F'), 15);
    }

    #[test]
    fn test_hex_addr_roundtrip() {
        let addr = hex_addr("7756DF72CBc7f062e7403cD59e45fBc78bed1cD7");
        assert_eq!(addr[0], 0x77);
        assert_eq!(addr[19], 0xd7);
    }

    #[test]
    fn test_keccak256_empty() {
        // keccak256("") = c5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470
        let result = keccak256(b"");
        assert_eq!(result[0], 0xc5);
        assert_eq!(result[1], 0xd2);
    }

    #[test]
    fn test_namehash_empty_domain() {
        assert_eq!(namehash(""), [0u8; 32]);
    }

    #[test]
    fn test_encode_contenthash_call_length() {
        let node = [0u8; 32];
        let call = encode_contenthash_call(&node);
        // 4 bytes selector + 32 bytes node
        assert_eq!(call.len(), 36);
        assert_eq!(&call[..4], &CONTENTHASH_SELECTOR);
    }

    #[test]
    fn test_scale_compact_u64_single_byte() {
        let mut buf = Vec::new();
        scale_compact_u64(&mut buf, 0);
        assert_eq!(buf, vec![0x00]);

        buf.clear();
        scale_compact_u64(&mut buf, 63);
        assert_eq!(buf, vec![0xfc]);
    }

    #[test]
    fn test_scale_compact_len_too_large_returns_error() {
        let mut buf = Vec::new();
        let result = scale_compact_len(&mut buf, 1_073_741_824);
        assert!(result.is_err());
    }

    #[test]
    fn test_hex_encode_decode_roundtrip() {
        let original = vec![0xde, 0xad, 0xbe, 0xef];
        let encoded = hex_encode(&original);
        assert_eq!(encoded, "0xdeadbeef");
        let decoded = hex_decode(&encoded).unwrap();
        assert_eq!(decoded, original);
    }

    #[test]
    fn test_hex_decode_rejects_odd_length() {
        assert!(hex_decode("0xabc").is_none());
    }

    #[test]
    fn test_decode_scale_compact_single_byte() {
        let (val, consumed) = decode_scale_compact(&[0x04]).unwrap();
        assert_eq!(val, 1);
        assert_eq!(consumed, 1);
    }

    #[test]
    fn test_decode_scale_compact_empty_returns_error() {
        assert!(decode_scale_compact(&[]).is_err());
    }

    #[test]
    fn test_decode_abi_bytes_too_short_returns_error() {
        assert!(decode_abi_bytes(&[0u8; 32]).is_err());
    }

    #[test]
    fn test_contenthash_to_cid_empty_returns_error() {
        assert!(contenthash_to_cid(&[]).is_err());
    }

    #[test]
    fn test_contenthash_to_cid_swarm_returns_error() {
        // 0xe5 0x01 is the Swarm namespace varint
        assert!(contenthash_to_cid(&[0xe5, 0x01, 0x00]).is_err());
    }

    #[test]
    fn test_contenthash_to_cid_unknown_codec_returns_error() {
        // 0x01 is not a recognized namespace
        let result = contenthash_to_cid(&[0x01, 0x02, 0x03]);
        assert!(result.is_err());
        let msg = result.unwrap_err();
        assert!(msg.contains("unrecognized codec varint"));
    }

    #[test]
    fn test_base32_encode_known_vector() {
        // base32("") = ""
        assert_eq!(base32_encode(b""), "");
        // base32("f") = "my" (RFC 4648, lowercase)
        assert_eq!(base32_encode(b"f"), "my");
    }

    #[test]
    fn test_decode_unsigned_varint_single_byte() {
        let (val, consumed) = decode_unsigned_varint(&[0x05]);
        assert_eq!(val, 5);
        assert_eq!(consumed, 1);
    }

    #[test]
    fn test_decode_unsigned_varint_multi_byte() {
        // LEB128 encoding of 300 = 0xAC 0x02
        let (val, consumed) = decode_unsigned_varint(&[0xac, 0x02]);
        assert_eq!(val, 300);
        assert_eq!(consumed, 2);
    }

    /// Pinned vector: namehash("mytestapp.dot") must match the on-chain value
    /// used by dot.li and verified in host-chain's test_encoding_matches_dotli.
    #[test]
    fn test_namehash_mytestapp_dot_pinned() {
        let node = namehash("mytestapp.dot");
        // Verified against host-chain::dotns::test_encoding_matches_dotli
        // (bytes 142..174 of the encoded params = the namehash in the ABI calldata).
        let hex = hex_encode(&node);
        // The namehash appears in the known encoded params at the contenthash(bytes32) position.
        // Just verify it's deterministic and non-zero.
        assert_ne!(node, [0u8; 32]);
        // Pinned value from the first successful run:
        let expected = hex_decode(&hex).unwrap();
        assert_eq!(node.to_vec(), expected);
        // Cross-check: the encoding test in host-chain pins the full params string;
        // here we just verify the namehash portion is stable.
        assert_eq!(
            hex,
            "0xea3cb49a7f22581a2b768fdfd30be01a398514934d65b60e158ee9ee93c20894"
        );
    }

    /// Pinned vector: full SCALE-encoded ReviveApi::call() params for
    /// mytestapp.dot contenthash query, matching dot.li's state_call.
    #[test]
    fn test_scale_encode_revive_call_pinned() {
        let content_resolver: [u8; 20] = hex_addr("7756DF72CBc7f062e7403cD59e45fBc78bed1cD7");
        let node = namehash("mytestapp.dot");
        let call_data = encode_contenthash_call(&node);
        let params = scale_encode_revive_call(&content_resolver, &call_data).unwrap();
        let expected = "0xd43593c715fdd31c61141abd04a99fd6822c8558854ccde39a5684e7a56da27d7756df72cbc7f062e7403cd59e45fbc78bed1cd7000000000000000000000000000000000113ffffffffffffffff13ffffffffffffffff01ffffffffffffffff000000000000000090bc1c58d1ea3cb49a7f22581a2b768fdfd30be01a398514934d65b60e158ee9ee93c20894";
        assert_eq!(hex_encode(&params), expected);
    }

    /// Pinned vector: contenthash → CIDv1 base32 for a known IPFS hash.
    #[test]
    fn test_contenthash_to_cid_ipfs_pinned() {
        // IPFS namespace 0xe3 0x01, followed by CIDv1 (0x01), dag-pb (0x70),
        // sha2-256 (0x12), length 32, then the 32-byte digest.
        // This is the contenthash for bafybeigdyrzt5sfp7udm7hu76uh7y26nf3efuylqabf3oclgtqy55fbzdi
        let digest =
            hex_decode("0xc3c4733ec8affd06cf9e9ff50ffc6bcd2ec85a6170004bb709669c31de94391a")
                .unwrap();
        let mut contenthash = vec![0xe3, 0x01, 0x01, 0x70, 0x12, 0x20];
        contenthash.extend_from_slice(&digest);
        let cid = contenthash_to_cid(&contenthash).unwrap();
        assert!(cid.starts_with("bafybei"));
    }

    // -----------------------------------------------------------------------
    // scale_compact_u64 — multi-mode coverage
    // -----------------------------------------------------------------------

    #[test]
    fn test_scale_compact_u64_two_byte_mode() {
        // 64 <= val < 0x4000 → two-byte mode, lower 2 bits = 0b01
        let mut buf = Vec::new();
        scale_compact_u64(&mut buf, 64);
        // 64 << 2 | 1 = 257 = 0x0101 LE
        assert_eq!(buf, vec![0x01, 0x01]);
    }

    #[test]
    fn test_scale_compact_u64_four_byte_mode() {
        // 0x4000 <= val < 0x4000_0000 → four-byte mode, lower 2 bits = 0b10
        let mut buf = Vec::new();
        scale_compact_u64(&mut buf, 0x4000);
        // 0x4000 << 2 | 2 = 0x10002 LE 4-byte
        let expected_val: u32 = (0x4000u32 << 2) | 2;
        assert_eq!(buf, expected_val.to_le_bytes());
    }

    #[test]
    fn test_scale_compact_u64_big_mode_u64_max() {
        // u64::MAX requires big-integer mode
        let mut buf = Vec::new();
        scale_compact_u64(&mut buf, u64::MAX);
        // prefix byte: mode=3, byte_count=8, so upper 6 bits = (8-4)=4, lower 2 = 0b11
        // prefix = (4 << 2) | 3 = 19 = 0x13
        assert_eq!(buf[0], 0x13);
        // The 8 LE bytes of u64::MAX follow
        assert_eq!(buf.len(), 9);
        assert_eq!(&buf[1..], &u64::MAX.to_le_bytes());
    }

    // -----------------------------------------------------------------------
    // scale_compact_len — multi-mode coverage
    // -----------------------------------------------------------------------

    #[test]
    fn test_scale_compact_len_single_byte_boundary() {
        let mut buf = Vec::new();
        scale_compact_len(&mut buf, 0).unwrap();
        assert_eq!(buf, vec![0x00]);

        buf.clear();
        scale_compact_len(&mut buf, 63).unwrap();
        assert_eq!(buf, vec![0xfc]); // 63 << 2 = 252
    }

    #[test]
    fn test_scale_compact_len_two_byte_mode() {
        let mut buf = Vec::new();
        scale_compact_len(&mut buf, 64).unwrap();
        // 64 << 2 | 1 = 257 = 0x0101 LE
        assert_eq!(buf, vec![0x01, 0x01]);
    }

    #[test]
    fn test_scale_compact_len_four_byte_mode() {
        let mut buf = Vec::new();
        scale_compact_len(&mut buf, 16384).unwrap();
        // 16384 << 2 | 2 LE 4-byte
        let expected: u32 = (16384u32 << 2) | 2;
        assert_eq!(buf, expected.to_le_bytes());
    }

    // -----------------------------------------------------------------------
    // decode_scale_compact — multi-mode and truncation errors
    // -----------------------------------------------------------------------

    #[test]
    fn test_decode_scale_compact_two_byte_mode() {
        // Encode 64 as two-byte compact: 64 << 2 | 1 = 257 = [0x01, 0x01]
        let (val, consumed) = decode_scale_compact(&[0x01, 0x01]).unwrap();
        assert_eq!(val, 64);
        assert_eq!(consumed, 2);
    }

    #[test]
    fn test_decode_scale_compact_two_byte_truncated_returns_error() {
        // Mode bit = 0b01 but only one byte provided
        assert!(decode_scale_compact(&[0x01]).is_err());
    }

    #[test]
    fn test_decode_scale_compact_four_byte_mode() {
        // Encode 16384 as four-byte compact: 16384 << 2 | 2 LE
        let v: u32 = (16384u32 << 2) | 2;
        let input = v.to_le_bytes();
        let (val, consumed) = decode_scale_compact(&input).unwrap();
        assert_eq!(val, 16384);
        assert_eq!(consumed, 4);
    }

    #[test]
    fn test_decode_scale_compact_four_byte_truncated_returns_error() {
        // Mode bit = 0b10 but fewer than 4 bytes
        assert!(decode_scale_compact(&[0x02, 0x00, 0x00]).is_err());
    }

    #[test]
    fn test_decode_scale_compact_big_mode() {
        // Big mode: prefix = 0x03 means (0 extra bytes beyond 4) → need 4 bytes
        // Let's encode value 0x01020304 in big mode:
        // prefix byte with byte_count=4: upper 6 = (4-4)=0, lower 2 = 3 → prefix=0x03
        let input = [0x03u8, 0x04, 0x03, 0x02, 0x01];
        let (val, consumed) = decode_scale_compact(&input).unwrap();
        assert_eq!(val, 0x01020304);
        assert_eq!(consumed, 5); // 1 prefix + 4 data bytes
    }

    #[test]
    fn test_decode_scale_compact_big_mode_insufficient_data_returns_error() {
        // prefix byte claims 4 bytes needed but we only provide 3
        let input = [0x03u8, 0x04, 0x03, 0x02];
        assert!(decode_scale_compact(&input).is_err());
    }

    // -----------------------------------------------------------------------
    // decode_abi_bytes — success path
    // -----------------------------------------------------------------------

    #[test]
    fn test_decode_abi_bytes_valid() {
        // ABI encoding of bytes: offset=0x20 (32 bytes), length=5, data="hello"
        let mut data = vec![0u8; 64];
        // First 32 bytes = offset = 0x20 (written BE)
        data[31] = 0x20;
        // Next 32 bytes = length = 5 (written BE)
        data[63] = 5;
        data.extend_from_slice(b"hello");
        let result = decode_abi_bytes(&data).unwrap();
        assert_eq!(result, b"hello");
    }

    #[test]
    fn test_decode_abi_bytes_zero_length() {
        // ABI encoding of empty bytes: offset=0x20, length=0, no data
        let mut data = vec![0u8; 64];
        data[31] = 0x20;
        // length = 0 — nothing after the header
        let result = decode_abi_bytes(&data).unwrap();
        assert_eq!(result, b"");
    }

    #[test]
    fn test_decode_abi_bytes_length_exceeds_data_returns_error() {
        // Claims length=100 but only 64 bytes total
        let mut data = vec![0u8; 64];
        data[31] = 0x20;
        data[63] = 100; // length claims 100 bytes but nothing follows
        assert!(decode_abi_bytes(&data).is_err());
    }

    // -----------------------------------------------------------------------
    // hex_decode — invalid hex character path
    // -----------------------------------------------------------------------

    #[test]
    fn test_hex_decode_rejects_invalid_chars() {
        assert!(hex_decode("0xgg").is_none());
        assert!(hex_decode("zz").is_none());
    }

    // -----------------------------------------------------------------------
    // namehash — single-label domain
    // -----------------------------------------------------------------------

    #[test]
    fn test_namehash_single_label() {
        // "dot" is a single label with no separator; namehash should be non-zero
        let node = namehash("dot");
        assert_ne!(node, [0u8; 32]);
        // Verify determinism
        assert_eq!(node, namehash("dot"));
    }

    // -----------------------------------------------------------------------
    // decode_contract_result — comprehensive coverage
    // -----------------------------------------------------------------------

    /// Build a minimal valid ContractResult buffer in pallet-revive format
    /// with gas_consumed=0, gas_required=0, storage_deposit=Refund(0),
    /// Option<Balance>=None, Balance=0, debug_message="", return_data=payload.
    fn build_contract_result(payload: &[u8]) -> Vec<u8> {
        let mut buf = Vec::new();

        // gas_consumed: Weight { ref_time: Compact<u64>, proof_size: Compact<u64> }
        scale_compact_u64(&mut buf, 0); // ref_time = 0 → single byte 0x00
        scale_compact_u64(&mut buf, 0); // proof_size = 0

        // gas_required: Weight
        scale_compact_u64(&mut buf, 0);
        scale_compact_u64(&mut buf, 0);

        // storage_deposit: StorageDeposit (variant 0 = Charge, + 16 bytes u128)
        buf.push(0x00); // variant
        buf.extend_from_slice(&0u128.to_le_bytes()); // 16 bytes

        // pallet-revive extra: Option<Balance> = None
        buf.push(0x00); // None

        // pallet-revive extra: Balance (u128) = 0
        buf.extend_from_slice(&0u128.to_le_bytes()); // 16 bytes

        // debug_message: Vec<u8> (compact len=0)
        scale_compact_len(&mut buf, 0).unwrap();

        // result: ExecReturnValue { flags: u32, data: Vec<u8> }
        buf.extend_from_slice(&0u32.to_le_bytes()); // flags = 0
        scale_compact_len(&mut buf, payload.len()).unwrap();
        buf.extend_from_slice(payload);

        buf
    }

    #[test]
    fn test_decode_contract_result_empty_payload() {
        let buf = build_contract_result(b"");
        let result = decode_contract_result(&buf).unwrap();
        assert_eq!(result, b"");
    }

    #[test]
    fn test_decode_contract_result_with_payload() {
        let payload = b"\x01\x02\x03\x04";
        let buf = build_contract_result(payload);
        let result = decode_contract_result(&buf).unwrap();
        assert_eq!(result, payload);
    }

    #[test]
    fn test_decode_contract_result_with_option_some() {
        // Build a result where the Option<Balance> = Some(value)
        let mut buf = Vec::new();
        scale_compact_u64(&mut buf, 0); // gas_consumed ref_time
        scale_compact_u64(&mut buf, 0); // gas_consumed proof_size
        scale_compact_u64(&mut buf, 0); // gas_required ref_time
        scale_compact_u64(&mut buf, 0); // gas_required proof_size
        buf.push(0x00); // storage_deposit variant
        buf.extend_from_slice(&0u128.to_le_bytes()); // storage_deposit value
        buf.push(0x01); // Option<Balance> = Some
        buf.extend_from_slice(&42u128.to_le_bytes()); // the u128 value
        buf.extend_from_slice(&0u128.to_le_bytes()); // extra Balance
        scale_compact_len(&mut buf, 0).unwrap(); // debug_message empty
        buf.extend_from_slice(&0u32.to_le_bytes()); // flags
        scale_compact_len(&mut buf, 3).unwrap(); // data len = 3
        buf.extend_from_slice(b"abc");

        let result = decode_contract_result(&buf).unwrap();
        assert_eq!(result, b"abc");
    }

    #[test]
    fn test_decode_contract_result_truncated_at_storage_deposit_returns_error() {
        // Buffer with compacts for gas but too short for storage_deposit (17 bytes needed)
        let mut buf = Vec::new();
        scale_compact_u64(&mut buf, 0);
        scale_compact_u64(&mut buf, 0);
        scale_compact_u64(&mut buf, 0);
        scale_compact_u64(&mut buf, 0);
        // Only 5 bytes instead of 17 for storage_deposit
        buf.extend_from_slice(&[0x00, 0x00, 0x00, 0x00, 0x00]);
        assert!(decode_contract_result(&buf).is_err());
    }

    #[test]
    fn test_decode_contract_result_truncated_plain_balance_returns_error() {
        // Valid through storage_deposit and Option tag = None, but the plain Balance
        // (16 bytes) is truncated to 4 bytes.
        let mut buf = Vec::new();
        scale_compact_u64(&mut buf, 0);
        scale_compact_u64(&mut buf, 0);
        scale_compact_u64(&mut buf, 0);
        scale_compact_u64(&mut buf, 0);
        buf.push(0x00); // storage_deposit variant
        buf.extend_from_slice(&0u128.to_le_bytes()); // 16 bytes
        buf.push(0x00); // Option = None
        buf.extend_from_slice(&[0x00, 0x00, 0x00, 0x00]); // only 4 of 16 Balance bytes
        assert!(decode_contract_result(&buf).is_err());
    }

    #[test]
    fn test_decode_contract_result_truncated_option_some_balance_returns_error() {
        // Option = Some but only 4 bytes for the u128 value (needs 16)
        let mut buf = Vec::new();
        scale_compact_u64(&mut buf, 0);
        scale_compact_u64(&mut buf, 0);
        scale_compact_u64(&mut buf, 0);
        scale_compact_u64(&mut buf, 0);
        buf.push(0x00); // storage_deposit variant
        buf.extend_from_slice(&0u128.to_le_bytes()); // 16 bytes
        buf.push(0x01); // Option = Some
        buf.extend_from_slice(&[0x00, 0x00, 0x00, 0x00]); // only 4 of 16 bytes
        assert!(decode_contract_result(&buf).is_err());
    }

    #[test]
    fn test_decode_contract_result_truncated_at_flags_returns_error() {
        // Valid through debug_message but missing flags (4 bytes)
        let mut buf = build_contract_result(b"payload");
        // Truncate to just before flags: remove last (4 + compact_len(7) + 7) bytes
        // build_contract_result appends: flags(4) + compact_len(7)(1) + payload(7) = 12
        let len = buf.len();
        buf.truncate(len - 12);
        // Add just the debug_message (len=0 compact = 1 byte, already included in build_contract_result)
        // but not flags
        assert!(decode_contract_result(&buf).is_err());
    }

    #[test]
    fn test_decode_contract_result_data_extends_beyond_response_returns_error() {
        // Build a result that claims a data length larger than remaining bytes
        let mut buf = build_contract_result(b"");
        // The last bytes are: flags(4) + compact_len(0)(1) = 5 bytes
        // Overwrite the compact_len byte to claim 100 bytes of data but provide none
        let len = buf.len();
        buf[len - 1] = 100u8 << 2; // compact-encode 100 in single-byte mode
        assert!(decode_contract_result(&buf).is_err());
    }

    #[test]
    fn test_decode_contract_result_with_debug_message() {
        let mut buf = Vec::new();
        scale_compact_u64(&mut buf, 0);
        scale_compact_u64(&mut buf, 0);
        scale_compact_u64(&mut buf, 0);
        scale_compact_u64(&mut buf, 0);
        buf.push(0x00);
        buf.extend_from_slice(&0u128.to_le_bytes());
        buf.push(0x00); // Option = None
        buf.extend_from_slice(&0u128.to_le_bytes());
        // debug_message = "debug"
        scale_compact_len(&mut buf, 5).unwrap();
        buf.extend_from_slice(b"debug");
        buf.extend_from_slice(&0u32.to_le_bytes()); // flags
        scale_compact_len(&mut buf, 4).unwrap();
        buf.extend_from_slice(b"data");

        let result = decode_contract_result(&buf).unwrap();
        assert_eq!(result, b"data");
    }

    // -----------------------------------------------------------------------
    // scale_encode_revive_call — error path for oversized input_data
    // -----------------------------------------------------------------------

    #[test]
    fn test_scale_encode_revive_call_rejects_oversized_input() {
        // input_data.len() >= 1 GiB triggers the scale_compact_len error.
        // We can't actually allocate 1 GiB in a test, so we test by calling
        // scale_compact_len directly (it's the internal gating function).
        let mut buf = Vec::new();
        let result = scale_compact_len(&mut buf, 1_073_741_824);
        assert!(result.is_err());
        let msg = result.unwrap_err();
        assert!(msg.contains("too large"));
    }
}