1 files changed, 80 insertions, 0 deletions
diff --git a/source.go b/source.go
new file mode 100644
index 0000000..577d00a
--- /dev/null
+++ b/source.go
@@ -0,0 +1,80 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+)
+
+// Spec is a parsed source as the user wrote it: a git URL and an optional ref.
+type Spec struct {
+	URL string
+	Ref string
+}
+
+var (
+	ghShorthand = regexp.MustCompile(`^[A-Za-z0-9_.-]+/[A-Za-z0-9_.-]+$`)
+	scpLike     = regexp.MustCompile(`^([A-Za-z0-9_.-]+@)?([A-Za-z0-9_.-]+):([^/].*)$`)
+	fullRev     = regexp.MustCompile(`^[0-9a-f]{40}$`)
+)
+
+// parseSpec turns what a user typed into a git URL. It accepts:
+//
+//	owner/repo, github:owner/repo     GitHub
+//	https://…, ssh://…, git://…, file://…
+//	user@host:path                    scp-like, as git understands it
+//	./path, /path, ~/path             a local repository
+//
+// each optionally followed by #ref (a branch, tag or commit).
+func parseSpec(s string) (Spec, error) {
+	raw, ref, _ := strings.Cut(s, "#")
+	if raw == "" {
+		return Spec{}, fmt.Errorf("empty source %q", s)
+	}
+	var url string
+	switch {
+	case strings.HasPrefix(raw, "github:"):
+		url = "https://github.com/" + strings.TrimPrefix(raw, "github:")
+	case strings.Contains(raw, "://"):
+		// Accept Nix's git+https:// spelling too.
+		url = strings.TrimPrefix(raw, "git+")
+	case strings.HasPrefix(raw, "/"), strings.HasPrefix(raw, "."), strings.HasPrefix(raw, "~"):
+		p := raw
+		if strings.HasPrefix(p, "~") {
+			home, err := os.UserHomeDir()
+			if err != nil {
+				return Spec{}, err
+			}
+			p = filepath.Join(home, strings.TrimPrefix(p, "~"))
+		}
+		abs, err := filepath.Abs(p)
+		if err != nil {
+			return Spec{}, err
+		}
+		url = "file://" + abs
+	case scpLike.MatchString(raw):
+		// Nix only takes URLs, and the lock is shared with it.
+		m := scpLike.FindStringSubmatch(raw)
+		url = "ssh://" + m[1] + m[2] + "/" + m[3]
+	case ghShorthand.MatchString(raw):
+		url = "https://github.com/" + raw
+	default:
+		return Spec{}, fmt.Errorf("%q is not a source; use owner/repo, a git URL or a path", s)
+	}
+	return Spec{URL: strings.TrimSuffix(url, "/"), Ref: ref}, nil
+}
+
+// defaultSourceName names a source after its only skill, or else after its
+// repository.
+func defaultSourceName(spec Spec, selected []Skill) string {
+	if len(selected) == 1 {
+		return selected[0].Name
+	}
+	u := spec.URL
+	if i := strings.LastIndexAny(u, "/:"); i >= 0 {
+		u = u[i+1:]
+	}
+	return strings.TrimSuffix(u, ".git")
+}