// Copyright (c) 2022, 2023 blackshirt. All rights reserved.
// Use of this source code is governed by a MIT License
// that can be found in the LICENSE file.
module asn1

// default_null_tag is the default tag of ASN.1 NULL type.
pub const default_null_tag = Tag{.universal, false, int(TagType.null)}

// ASN.1 UNIVERSAL CLASS OF NULL TYPE.
//
// The ASN.1 NULL type is a placeholder used when there is no value.
// It's a simple, non-string type with the UNIVERSAL TAG number 5.
// The NULL type can be used in situations where the presence of a type is important, but no concrete value is needed.
pub struct Null {}

// tag returns the tag of Null element.
pub fn (n Null) tag() Tag {
    return default_null_tag
}

// payload returns the payload of the Null element, its should empty bytes.
pub fn (n Null) payload() ![]u8 {
    return []u8{}
}

fn (n Null) str() string {
    return 'NULL'
}

// `Null.parse` tries to read into Null type from ongoing parser.
fn Null.parse(mut p Parser) !Null {
    tag := p.read_tag()!
    if !tag.equal(default_null_tag) {
        return error('Get unexpected null tag')
    }
    length := p.read_length()!
    if length != 0 {
        return error('Get unexpected non-null length for Null type')
    }
    return Null{}
}

// Null.decode read Null from bytes.
fn Null.decode(bytes []u8) !(Null, int) {
    tag, length_pos := Tag.decode(bytes)!
    if !tag.equal(default_null_tag) {
        return error('Null: get unexpected tag')
    }
    length, content_pos := Length.decode_from_offset(bytes, length_pos)!
    if length != 0 {
        return error('Null with non-null length')
    }
    next := content_pos + length
    return Null{}, next
}

fn Null.from_bytes(b []u8) !Null {
    if b.len != 0 {
        return error('Null: bad non-null bytes')
    }
    return Null{}
}