🎨 Port package to types

This refactors DefaultPackage into types.Package and gets rid of the
interface. This is a preceeding for a follow up where accessors will be
removed from the code.
It also does several cleanup, so we get rid also of some unneeded
dependencies.

pkg/solver/explainer.go

@@ -0,0 +1,135 @@
+// Copyright © 2021-2022 Ettore Di Giacinto <mudler@mocaccino.org>
+//
+// 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 2 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 <http://www.gnu.org/licenses/>.
+
+package solver
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/crillab/gophersat/bf"
+	"github.com/crillab/gophersat/explain"
+	types "github.com/mudler/luet/pkg/api/core/types"
+	"github.com/pkg/errors"
+)
+
+type Explainer struct{}
+
+func decodeDimacs(vars map[string]string, dimacs string) (string, error) {
+	res := ""
+	sc := bufio.NewScanner(bytes.NewBufferString(dimacs))
+	lines := strings.Split(dimacs, "\n")
+	linenum := 1
+SCAN:
+	for sc.Scan() {
+
+		line := sc.Text()
+		fields := strings.Fields(line)
+		if len(fields) == 0 {
+			continue
+		}
+		switch fields[0] {
+		case "p":
+			continue SCAN
+		default:
+			for i := 0; i < len(fields)-1; i++ {
+				v := fields[i]
+				negative := false
+				if strings.HasPrefix(fields[i], "-") {
+					v = strings.TrimLeft(fields[i], "-")
+					negative = true
+				}
+				variable := vars[v]
+				if negative {
+					res += fmt.Sprintf("!(%s)", variable)
+				} else {
+					res += variable
+				}
+
+				if i != len(fields)-2 {
+					res += fmt.Sprintf(" or ")
+				}
+			}
+			if linenum != len(lines)-1 {
+				res += fmt.Sprintf(" and \n")
+			}
+		}
+		linenum++
+	}
+	if err := sc.Err(); err != nil {
+		return res, fmt.Errorf("could not parse problem: %v", err)
+	}
+	return res, nil
+}
+
+func parseVars(r io.Reader) (map[string]string, error) {
+	sc := bufio.NewScanner(r)
+	res := map[string]string{}
+	for sc.Scan() {
+		line := sc.Text()
+		fields := strings.Fields(line)
+		if len(fields) == 0 {
+			continue
+		}
+		switch fields[0] {
+		case "c":
+			data := strings.Split(fields[1], "=")
+			res[data[1]] = data[0]
+
+		default:
+			continue
+
+		}
+	}
+	if err := sc.Err(); err != nil {
+		return nil, fmt.Errorf("could not parse problem: %v", err)
+	}
+	return res, nil
+}
+
+// Solve tries to find the MUS (minimum unsat) formula from the original problem.
+// it returns an error with the decoded dimacs
+func (*Explainer) Solve(f bf.Formula, s types.PackageSolver) (types.PackagesAssertions, error) {
+	buf := bytes.NewBufferString("")
+	if err := bf.Dimacs(f, buf); err != nil {
+		return nil, errors.Wrap(err, "cannot extract dimacs from formula")
+	}
+
+	copy := *buf
+
+	pb, err := explain.ParseCNF(&copy)
+	if err != nil {
+		return nil, errors.Wrap(err, "could not parse problem")
+	}
+	pb2, err := pb.MUS()
+	if err != nil {
+		return nil, errors.Wrap(err, "could not extract subset")
+	}
+
+	variables, err := parseVars(buf)
+	if err != nil {
+		return nil, errors.Wrap(err, "could not parse variables")
+	}
+
+	res, err := decodeDimacs(variables, pb2.CNF())
+	if err != nil {
+		return nil, errors.Wrap(err, "could not parse dimacs")
+	}
+
+	return nil, fmt.Errorf("could not satisfy the constraints: \n%s", res)
+}