module Prism::Pack

static VALUE
pack_parse(VALUE self, VALUE version_symbol, VALUE variant_symbol, VALUE format_string) {
    if (version_symbol != v3_2_0_symbol) {
        rb_raise(rb_eArgError, "invalid version");
    }

    pm_pack_variant variant;
    if (variant_symbol == pack_symbol) {
        variant = PM_PACK_VARIANT_PACK;
    } else if (variant_symbol == unpack_symbol) {
        variant = PM_PACK_VARIANT_UNPACK;
    } else {
        rb_raise(rb_eArgError, "invalid variant");
    }

    StringValue(format_string);

    const char *format = RSTRING_PTR(format_string);
    const char *format_end = format + RSTRING_LEN(format_string);
    pm_pack_encoding encoding = PM_PACK_ENCODING_START;

    VALUE directives_array = rb_ary_new();

    while (format < format_end) {
        pm_pack_type type;
        pm_pack_signed signed_type;
        pm_pack_endian endian;
        pm_pack_size size;
        pm_pack_length_type length_type;
        uint64_t length;

        const char *directive_start = format;

        pm_pack_result parse_result = pm_pack_parse(variant, &format, format_end, &type, &signed_type, &endian,
                                                    &size, &length_type, &length, &encoding);

        const char *directive_end = format;

        switch (parse_result) {
            case PM_PACK_OK:
                break;
            case PM_PACK_ERROR_UNSUPPORTED_DIRECTIVE:
                rb_raise(rb_eArgError, "unsupported directive");
            case PM_PACK_ERROR_UNKNOWN_DIRECTIVE:
                rb_raise(rb_eArgError, "unsupported directive");
            case PM_PACK_ERROR_LENGTH_TOO_BIG:
                rb_raise(rb_eRangeError, "pack length too big");
            case PM_PACK_ERROR_BANG_NOT_ALLOWED:
                rb_raise(rb_eRangeError, "bang not allowed");
            case PM_PACK_ERROR_DOUBLE_ENDIAN:
                rb_raise(rb_eRangeError, "double endian");
            default:
                rb_bug("parse result");
        }

        if (type == PM_PACK_END) {
            break;
        }

        VALUE directive_args[9] = {
            version_symbol,
            variant_symbol,
            rb_usascii_str_new(directive_start, directive_end - directive_start),
            pack_type_to_symbol(type),
            pack_signed_to_symbol(signed_type),
            pack_endian_to_symbol(endian),
            pack_size_to_symbol(size),
            pack_length_type_to_symbol(length_type),
            UINT64T2NUM(length)
        };

        rb_ary_push(directives_array, rb_class_new_instance(9, directive_args, rb_cPrismPackDirective));
    }

    VALUE format_args[2];
    format_args[0] = directives_array;
    format_args[1] = pack_encoding_to_ruby(encoding);
    return rb_class_new_instance(2, format_args, rb_cPrismPackFormat);
}