import crypto.hkdf
import crypto.rand
import crypto.sha256

// Usage example that expands one master secret into three other
// cryptographically secure keys.
fn test_usage() {
    // Underlying hash function for HMAC.
    key_len := sha256.new().size()

    // Cryptographically secure master secret.
    secret := [u8(0x00), 0x01, 0x02, 0x03] // i.e. NOT this.

    // Non-secret salt, optional (can be empty).
    // Recommended: hash-length random value.
    salt := rand.read(sha256.new().size())!

    // Non-secret context info prefix, optional (can be empty).
    info_prefix := 'hkdf example'

    // Generate three derived keys.
    mut keys := [][]u8{}
    for i in 0 .. 3 {
        info := '${info_prefix} key ${i + 1}'
        keys << hkdf.key(sha256.new, secret, salt, info, key_len)!
    }

    for derived_key in keys {
        assert derived_key != []u8{len: key_len}
    }
    assert keys[0] != keys[1]
    assert keys[1] != keys[2]
    assert keys[0] != keys[2]
}