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// Copyright 2019 Stichting Organism
// Copyright 2018 The Grin Developers
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

/// Implements hex-encoding from bytes to string and decoding of strings
/// to bytes. Given that rustc-serialize is deprecated and serde doesn't
/// provide easy hex encoding, hex is a bit in limbo right now in Rust-
/// land. It's simple enough that we can just have our own.
use std::fmt::Write;
use std::num;

/// Encode the provided bytes into a hex string
pub fn to_hex(bytes: &[u8]) -> String {
    let mut s = String::new();
    for byte in bytes {
        write!(&mut s, "{:02x}", byte).expect("Unable to write");
    }

    s
}

/// Decode a hex string into bytes.
pub fn from_hex(hex_str: String) -> Result<Vec<u8>, num::ParseIntError> {
    if hex_str.len() % 2 == 1 {
        // TODO: other way to instantiate a ParseIntError?
        let err = ("QQQ").parse::<u64>();
        if let Err(e) = err {
            return Err(e);
        }
    }
    let hex_trim = if &hex_str[..2] == "0x" {
        hex_str[2..].to_owned()
    } else {
        hex_str.clone()
    };
    split_n(&hex_trim.trim()[..], 2)
        .iter()
        .map(|b| u8::from_str_radix(b, 16))
        .collect::<Result<Vec<u8>, _>>()
}

fn split_n(s: &str, n: usize) -> Vec<&str> {
    (0..(s.len() - n + 1) / 2 + 1)
        .map(|i| &s[2 * i..2 * i + n])
        .collect()
}

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

    #[test]
    fn test_to_hex() {
        assert_eq!(to_hex(&[0, 0, 0, 0]), "00000000");
        assert_eq!(to_hex(&[10, 11, 12, 13]), "0a0b0c0d");
        assert_eq!(to_hex(&[0, 0, 0, 255]), "000000ff");
    }

    #[test]
    fn test_from_hex() {
        assert_eq!(from_hex("00000000".to_string()).unwrap(), &[0, 0, 0, 0]);
        assert_eq!(
            from_hex("0a0b0c0d".to_string()).unwrap(),
            vec![10, 11, 12, 13]
        );
        assert_eq!(
            from_hex("000000ff".to_string()).unwrap(),
            vec![0, 0, 0, 255]
        );
    }
}