parse

pub fn parse(text: []const u8) !Version {
    // Parse the required major, minor, and patch numbers.
    const extra_index = std.mem.indexOfAny(u8, text, "-+");
    const required = text[0..(extra_index orelse text.len)];
    var it = std.mem.splitScalar(u8, required, '.');
    var ver = Version{
        .major = try parseNum(it.first()),
        .minor = try parseNum(it.next() orelse return error.InvalidVersion),
        .patch = try parseNum(it.next() orelse return error.InvalidVersion),
    };
    if (it.next() != null) return error.InvalidVersion;
    if (extra_index == null) return ver;

    // Slice optional pre-release or build metadata components.
    const extra: []const u8 = text[extra_index.?..text.len];
    if (extra[0] == '-') {
        const build_index = std.mem.indexOfScalar(u8, extra, '+');
        ver.pre = extra[1..(build_index orelse extra.len)];
        if (build_index) |idx| ver.build = extra[(idx + 1)..];
    } else {
        ver.build = extra[1..];
    }

    // Check validity of optional pre-release identifiers.
    // See: https://semver.org/#spec-item-9
    if (ver.pre) |pre| {
        it = std.mem.splitScalar(u8, pre, '.');
        while (it.next()) |id| {
            // Identifiers MUST NOT be empty.
            if (id.len == 0) return error.InvalidVersion;

            // Identifiers MUST comprise only ASCII alphanumerics and hyphens [0-9A-Za-z-].
            for (id) |c| if (!std.ascii.isAlphanumeric(c) and c != '-') return error.InvalidVersion;

            // Numeric identifiers MUST NOT include leading zeroes.
            const is_num = for (id) |c| {
                if (!std.ascii.isDigit(c)) break false;
            } else true;
            if (is_num) _ = try parseNum(id);
        }
    }

    // Check validity of optional build metadata identifiers.
    // See: https://semver.org/#spec-item-10
    if (ver.build) |build| {
        it = std.mem.splitScalar(u8, build, '.');
        while (it.next()) |id| {
            // Identifiers MUST NOT be empty.
            if (id.len == 0) return error.InvalidVersion;

            // Identifiers MUST comprise only ASCII alphanumerics and hyphens [0-9A-Za-z-].
            for (id) |c| if (!std.ascii.isAlphanumeric(c) and c != '-') return error.InvalidVersion;
        }
    }

    return ver;
}