cesrox 2.0.0-beta.5

Implementation of Composable Event Streaming Representation (CESR)
Documentation 
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use base64::prelude::*;

use super::error::Error;

pub fn from_text_to_bytes(text: &str) -> Result<Vec<u8>, Error> {
    let lead_size = (4 - (text.len() % 4)) % 4;
    let full_derivative = [&"A".repeat(lead_size), text].concat();

    Ok(BASE64_URL_SAFE.decode(full_derivative)?.to_vec())
}

pub fn from_bytes_to_text(bytes: &[u8]) -> String {
    let lead_size = (3 - (bytes.len() % 3)) % 3;
    let full_derivative: Vec<_> = std::iter::repeat_n(0, lead_size)
        .chain(bytes.iter().copied())
        .collect();

    BASE64_URL_SAFE.encode(full_derivative)
}

/// Parses the number from radix 64 using digits from url-safe base64 (`A` = 0, `_` = 63)
pub fn b64_to_num(b64: &str) -> Result<u16, Error> {
    let slice = from_text_to_bytes(b64)?;
    let len = slice.len();

    Ok(u16::from_be_bytes(match len {
        0 => [0u8; 2],
        1 => [0, slice[0]],
        _ => [slice[len - 2], slice[len - 1]],
    }))
}

/// Formats the number in radix 64 using digits from url-safe base64 (`A` = 0, `_` = 63)
pub fn num_to_b64(num: u16) -> String {
    let b64 = from_bytes_to_text(num.to_be_bytes().as_ref());
    // remove leading A's
    if num < 64 {
        b64[3..].to_string()
    } else if num < 4096 {
        b64[2..].to_string()
    } else {
        todo!()
    }
}

pub fn adjust_with_num(sn: u16, expected_length: usize) -> String {
    if expected_length > 0 {
        let i = num_to_b64(sn);
        if i.len() < expected_length {
            // refill string to have proper size
            let missing_part = "A".repeat(expected_length - i.len());
            [missing_part, i].join("")
        } else {
            [i].join("")
        }
    } else {
        "".to_string()
    }
}

pub fn check_first_three_bits(byte: &u8) -> u8 {
    (byte >> 5) & 0b111 // Shift right by 5 and mask the first 3 bits
}

#[test]
fn num_to_b64_test() {
    assert_eq!("A", num_to_b64(0));
    assert_eq!("B", num_to_b64(1));
    assert_eq!("C", num_to_b64(2));
    assert_eq!("D", num_to_b64(3));
    assert_eq!("b", num_to_b64(27));
    assert_eq!("BQ", num_to_b64(80));
    assert_eq!("__", num_to_b64(4095));
}

#[test]
fn b64_to_num_test() {
    assert_eq!(b64_to_num("AAAA").unwrap(), 0);
    assert_eq!(b64_to_num("A").unwrap(), 0);
    assert_eq!(b64_to_num("B").unwrap(), 1);
    assert_eq!(b64_to_num("C").unwrap(), 2);
    assert_eq!(b64_to_num("D").unwrap(), 3);
    assert_eq!(b64_to_num("b").unwrap(), 27);
    assert_eq!(b64_to_num("BQ").unwrap(), 80);
    assert_eq!(b64_to_num("__").unwrap(), 4095);
}

#[test]
fn test_from_text_to_bytes() {
    assert_eq!(hex::encode(from_text_to_bytes("MP__").unwrap()), "30ffff");
    assert_eq!(hex::encode(from_text_to_bytes("MAAA").unwrap()), "300000");
    assert_eq!(hex::encode(from_text_to_bytes("MAAB").unwrap()), "300001");
}

#[test]
fn test_from_bytes_to_text() {
    let b_bytes = from_text_to_bytes("B").unwrap();
    assert_eq!("AAAB", from_bytes_to_text(&b_bytes));

    assert_eq!(
        from_bytes_to_text(&hex::decode("300000").unwrap()),
        "MAAA".to_string()
    );
    assert_eq!(
        from_bytes_to_text(&hex::decode("300001").unwrap()),
        "MAAB".to_string()
    );
    assert_eq!(
        from_bytes_to_text(&hex::decode("30ffff").unwrap()),
        "MP__".to_string()
    );
}

#[test]
fn test_adjust_with_num() {
    assert_eq!(adjust_with_num(2, 4), "AAAC");
    assert_eq!(adjust_with_num(27, 6), "AAAAAb");
}