cmd/hakurei: short identifier from lower half

The upper half is now a nanosecond timestamp. Lower half is still random bytes, so use lower half for short identifier.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/hakurei/parse.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"encoding/hex"
 	"errors"
 	"io"
 	"log"
@@ -15,6 +16,9 @@ import (
 	"hakurei.app/message"
 )
 
+// tryPath attempts to read [hst.Config] from multiple sources.
+// tryPath reads from [os.Stdin] if name has value "-".
+// Otherwise, name is passed to tryFd, and if that returns nil, name is passed to [os.Open].
 func tryPath(msg message.Msg, name string) (config *hst.Config) {
 	var r io.ReadCloser
 	config = new(hst.Config)
@@ -42,6 +46,7 @@ func tryPath(msg message.Msg, name string) (config *hst.Config) {
 	return
 }
 
+// tryFd returns a [io.ReadCloser] if name represents an integer corresponding to a valid file descriptor.
 func tryFd(msg message.Msg, name string) io.ReadCloser {
 	if v, err := strconv.Atoi(name); err != nil {
 		if !errors.Is(err, strconv.ErrSyntax) {
@@ -61,10 +66,48 @@ func tryFd(msg message.Msg, name string) io.ReadCloser {
 	}
 }
 
-func tryShort(msg message.Msg, name string) (config *hst.Config, entry *hst.State) {
-	likePrefix := false
-	if len(name) <= 32 {
-		likePrefix = true
+// shortLengthMin is the minimum length a short form identifier can have and still be interpreted as an identifier.
+const shortLengthMin = 1 << 3
+
+// shortIdentifier returns an eight character short representation of [hst.ID] from its random bytes.
+func shortIdentifier(id *hst.ID) string {
+	return shortIdentifierString(id.String())
+}
+
+// shortIdentifierString implements shortIdentifier on an arbitrary string.
+func shortIdentifierString(s string) string {
+	return s[len(hst.ID{}) : len(hst.ID{})+shortLengthMin]
+}
+
+// tryIdentifier attempts to match [hst.State] from a [hex] representation of [hst.ID] or a prefix of its lower half.
+func tryIdentifier(msg message.Msg, name string) (config *hst.Config, entry *hst.State) {
+	return tryIdentifierEntries(msg, name, func() map[hst.ID]*hst.State {
+		var sc hst.Paths
+		app.CopyPaths().Copy(&sc, new(app.Hsu).MustID(nil))
+		s := state.NewMulti(msg, sc.RunDirPath.String())
+		if entries, err := state.Join(s); err != nil {
+			msg.GetLogger().Printf("cannot join store: %v", err) // not fatal
+			return nil
+		} else {
+			return entries
+		}
+	})
+}
+
+// tryIdentifierEntries implements tryIdentifier with a custom entries pair getter.
+func tryIdentifierEntries(
+	msg message.Msg,
+	name string,
+	getEntries func() map[hst.ID]*hst.State,
+) (config *hst.Config, entry *hst.State) {
+	const (
+		likeShort = 1 << iota
+		likeFull
+	)
+
+	var likely uintptr
+	if len(name) >= shortLengthMin && len(name) <= len(hst.ID{}) { // half the hex representation
+		// cannot safely decode here due to unknown alignment
 		for _, c := range name {
 			if c >= '0' && c <= '9' {
 				continue
@@ -72,35 +115,50 @@ func tryShort(msg message.Msg, name string) (config *hst.Config, entry *hst.Stat
 			if c >= 'a' && c <= 'f' {
 				continue
 			}
-			likePrefix = false
-			break
+			return
 		}
+		likely |= likeShort
+	} else if len(name) == hex.EncodedLen(len(hst.ID{})) {
+		likely |= likeFull
 	}
 
-	// try to match from state store
-	if likePrefix && len(name) >= 8 {
-		msg.Verbose("argument looks like prefix")
+	if likely == 0 {
+		return
+	}
+	entries := getEntries()
+	if entries == nil {
+		return
+	}
 
-		var sc hst.Paths
-		app.CopyPaths().Copy(&sc, new(app.Hsu).MustID(nil))
-		s := state.NewMulti(msg, sc.RunDirPath.String())
-		if entries, err := state.Join(s); err != nil {
-			log.Printf("cannot join store: %v", err)
-			// drop to fetch from file
-		} else {
-			for id := range entries {
-				v := id.String()
-				if strings.HasPrefix(v, name) {
-					// match, use config from this state entry
-					entry = entries[id]
-					config = entry.Config
-					break
-				}
-
-				msg.Verbosef("instance %s skipped", v)
+	switch {
+	case likely&likeShort != 0:
+		msg.Verbose("argument looks like short identifier")
+		for id := range entries {
+			v := id.String()
+			if strings.HasPrefix(v[len(hst.ID{}):], name) {
+				// match, use config from this state entry
+				entry = entries[id]
+				config = entry.Config
+				break
 			}
-		}
-	}
 
-	return
+			msg.Verbosef("instance %s skipped", v)
+		}
+		return
+
+	case likely&likeFull != 0:
+		var likelyID hst.ID
+		if likelyID.UnmarshalText([]byte(name)) != nil {
+			return
+		}
+		msg.Verbose("argument looks like identifier")
+		if ent, ok := entries[likelyID]; ok {
+			entry = ent
+			config = ent.Config
+		}
+		return
+
+	default:
+		panic("unreachable")
+	}
 }