refactor: extract core logic to a plain Go package

manager/version.go

@@ -0,0 +1,114 @@
+package manager
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+)
+
+type Version struct {
+	Version  string   `yaml:"version" json:"version"`
+	Current  bool     `yaml:"current" json:"current"`
+	Path     string   `yaml:"path" json:"path"`
+	BinDir   string   `yaml:"bin_dir" json:"bin_dir"`
+	Binaries []string `yaml:"binaries" json:"binaries"`
+}
+
+func (ver *Version) FindBin(name string) (string, error) {
+	for _, b := range ver.Binaries {
+		if filepath.Base(b) == name {
+			return b, nil
+		}
+	}
+
+	return "", fmt.Errorf(
+		`%wExecutable "%s" not found in Emacs version %s`,
+		ErrBinNotFound, name, ver.Version,
+	)
+}
+
+func newVersion(
+	ctx context.Context,
+	conf *Config,
+	version string,
+) (*Version, error) {
+	if version == "" {
+		return nil, fmt.Errorf("%wversion cannot be empty", ErrVersion)
+	}
+
+	path := filepath.Join(conf.Paths.Versions, version)
+
+	_, err := os.Stat(path)
+	if err != nil {
+		return nil, fmt.Errorf(
+			"%wVersion %s is not available in %s",
+			ErrVersionNotFound, version, conf.Paths.Versions,
+		)
+	}
+
+	ver := &Version{
+		Version: version,
+		Path:    path,
+		BinDir:  filepath.Join(path, "bin"),
+		Current: version == conf.Current.Version,
+	}
+
+	entries, err := os.ReadDir(ver.BinDir)
+	if err != nil && !errors.Is(err, fs.ErrNotExist) {
+		return nil, err
+	}
+
+	for _, entry := range entries {
+		if ctx.Err() != nil {
+			return nil, ctx.Err()
+		}
+
+		binPath := filepath.Join(ver.BinDir, entry.Name())
+
+		f, err := os.Stat(binPath)
+		if err != nil {
+			if errors.Is(err, fs.ErrNotExist) {
+				continue
+			}
+			return nil, err
+		}
+
+		// Ensure f is Regular file and executable.
+		if f.Mode().IsRegular() && f.Mode().Perm()&0111 == 0111 {
+			ver.Binaries = append(ver.Binaries, binPath)
+		}
+	}
+
+	return ver, nil
+}
+
+func newVersions(ctx context.Context, conf *Config) ([]*Version, error) {
+	results := []*Version{}
+
+	entries, err := os.ReadDir(conf.Paths.Versions)
+	if err != nil && !errors.Is(err, fs.ErrNotExist) {
+		return nil, err
+	}
+
+	for _, entry := range entries {
+		if ctx.Err() != nil {
+			return nil, ctx.Err()
+		}
+
+		if !entry.IsDir() {
+			continue
+		}
+
+		ver, err := newVersion(ctx, conf, entry.Name())
+		if err != nil {
+			return nil, err
+		}
+
+		results = append(results, ver)
+	}
+
+	return results, nil
+}