lang: core: os: Add a simple distro uid parsing function

I had previous good success using this kind of pattern for discussing
distro UID's. Let's put this in as a reminded to see if it's worth
pursuing longer term.

lang/core/os/distro_func.go

@@ -0,0 +1,96 @@
+// Mgmt
+// Copyright (C) 2013-2024+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+// Additional permission under GNU GPL version 3 section 7
+//
+// If you modify this program, or any covered work, by linking or combining it
+// with embedded mcl code and modules (and that the embedded mcl code and
+// modules which link with this program, contain a copy of their source code in
+// the authoritative form) containing parts covered by the terms of any other
+// license, the licensors of this program grant you additional permission to
+// convey the resulting work. Furthermore, the licensors of this program grant
+// the original author, James Shubin, additional permission to update this
+// additional permission if he deems it necessary to achieve the goals of this
+// additional permission.
+
+package coreos
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/purpleidea/mgmt/lang/funcs/simple"
+	"github.com/purpleidea/mgmt/lang/types"
+)
+
+const structDistroUID = "struct{distro str; version str; arch str}"
+
+var typeParseDistroUID = types.NewType(fmt.Sprintf("func(str) %s", structDistroUID))
+
+func init() {
+	simple.ModuleRegister(ModuleName, "parse_distro_uid", &types.FuncValue{
+		T: typeParseDistroUID,
+		V: ParseDistroUID,
+	})
+}
+
+// ParseDistroUID parses a distro UID into its component values. If it cannot
+// parse correctly, all the struct fields have the zero values.
+// NOTE: The UID pattern is subject to change.
+func ParseDistroUID(input []types.Value) (types.Value, error) {
+	fn := func(distro, version, arch string) (types.Value, error) {
+		st := types.NewStruct(types.NewType(structDistroUID))
+		if err := st.Set("distro", &types.StrValue{V: distro}); err != nil {
+			return nil, err
+		}
+		if err := st.Set("version", &types.StrValue{V: version}); err != nil {
+			return nil, err
+		}
+		if err := st.Set("arch", &types.StrValue{V: arch}); err != nil {
+			return nil, err
+		}
+
+		return st, nil
+	}
+
+	distro, version, arch, err := parseDistroUID(input[0].Str())
+	//if err != nil {
+	//	return fn("", "", "") // empty
+	//}
+	_ = err
+	return fn(distro, version, arch)
+}
+
+// parseDistroUID returns distro, version, arch in that order after parsing a
+// string like: fedora39-x86_64 and returning error if it doesn't match.
+// NOTE: The UID pattern is subject to change.
+func parseDistroUID(uid string) (string, string, string, error) {
+	before, arch, found := strings.Cut(uid, "-")
+	if !found {
+		return "", "", "", fmt.Errorf("dash not found")
+	}
+
+	distro := strings.TrimRight(before, "0123456789")
+	version := before[len(distro):]
+	if distro == "" || version == "" || arch == "" {
+		return "", "", "", fmt.Errorf("got empty value")
+	}
+
+	// TODO: check for valid distro or arch?
+
+	return distro, version, arch, nil
+}