feat: reorganize packages

pkg/command/command.go

@@ -0,0 +1,93 @@
+package command
+
+import (
+	"fmt"
+	"strings"
+)
+
+const separator = "/"
+
+var _ fmt.Stringer = (*Command)(nil)
+
+// Command is a concrete messages (a "verb") that MUST be unambiguously
+// interpretable by the Subject of a UCAN.
+//
+// A [Command] is composed of a leading slash which is optionally followed
+// by one or more slash-separated Segments of lowercase characters.
+//
+// [Command]: https://github.com/ucan-wg/spec#command
+type Command struct {
+	segments []string
+}
+
+// New creates a validated command from the provided list of segment strings.
+// An error is returned if an invalid Command would be formed
+func New(segments ...string) Command {
+	return Command{segments: segments}
+}
+
+// Parse verifies that the provided string contains the required
+// [segment structure] and, if valid, returns the resulting
+// Command.
+//
+// [segment structure]: https://github.com/ucan-wg/spec#segment-structure
+func Parse(s string) (Command, error) {
+	if !strings.HasPrefix(s, "/") {
+		return Command{}, ErrRequiresLeadingSlash
+	}
+
+	if len(s) > 1 && strings.HasSuffix(s, "/") {
+		return Command{}, ErrDisallowsTrailingSlash
+	}
+
+	if s != strings.ToLower(s) {
+		return Command{}, ErrRequiresLowercase
+	}
+
+	// The leading slash will result in the first element from strings.Split
+	// being an empty string which is removed as strings.Join will ignore it.
+	return Command{strings.Split(s, "/")[1:]}, nil
+}
+
+// MustParse is the same as Parse, but panic() if the parsing fail.
+func MustParse(s string) Command {
+	c, err := Parse(s)
+	if err != nil {
+		panic(err)
+	}
+	return c
+}
+
+// [Top] is the most powerful capability.
+//
+// This function returns a Command that is a wildcard and therefore represents the
+// most powerful ability. As such, it should be handled with care and used sparingly.
+//
+// [Top]: https://github.com/ucan-wg/spec#-aka-top
+func Top() Command {
+	return New()
+}
+
+// IsValid returns true if the provided string is a valid UCAN command.
+func IsValid(s string) bool {
+	_, err := Parse(s)
+	return err == nil
+}
+
+// Join appends segments to the end of this command using the required
+// segment separator.
+func (c Command) Join(segments ...string) Command {
+	return Command{append(c.segments, segments...)}
+}
+
+// Segments returns the ordered segments that comprise the Command as a
+// slice of strings.
+func (c Command) Segments() []string {
+	return c.segments
+}
+
+// String returns the composed representation the command.  This is also
+// the required wire representation (before IPLD encoding occurs.)
+func (c Command) String() string {
+	return "/" + strings.Join(c.segments, "/")
+}