// HMAC: Keyed-Hashing for Message Authentication  implemented in v
// implementation based on https://tools.ietf.org/html/rfc2104
module hmac

import crypto.internal.subtle

// new returns a HMAC byte array, depending on the hash algorithm used.
pub fn new(key []u8, data []u8, hash_func fn ([]u8) []u8, blocksize int) []u8 {
    mut inner := []u8{len: blocksize, init: 0x36}
    mut outer := []u8{len: blocksize, init: 0x5C}

    mut b_key := []u8{}
    if key.len <= blocksize {
        b_key =
            key.clone() // TODO: remove .clone() once https://github.com/vlang/v/issues/6604 gets fixed
    } else {
        b_key = hash_func(key)
    }
    if b_key.len > blocksize {
        b_key = b_key[..blocksize].clone()
    }
    for i, b in b_key {
        inner[i] = b ^ 0x36
        outer[i] = b ^ 0x5c
    }
    inner << data
    inner_hash := hash_func(inner)
    outer << inner_hash
    digest := hash_func(outer)
    return digest
}

// equal compares 2 MACs for equality, without leaking timing info.
// Note: if the lengths of the 2 MACs are different, probably a completely different
// hash function was used to generate them => no useful timing information.
pub fn equal(mac1 []u8, mac2 []u8) bool {
    return subtle.constant_time_compare(mac1, mac2) == 1
}