Changeset 0.15.0 (#71)

server/compaction/estimator.go

@@ -0,0 +1,57 @@
+package compaction
+
+import (
+	"git.gobha.me/xcaliber/chat-switchboard/treepath"
+)
+
+// ── Token Estimation ────────────────────────
+//
+// Rough heuristic matching the frontend Tokens.estimate() (~4 chars/token).
+// Good enough for threshold checks. Swap in a real tokenizer later if
+// over/under-triggering becomes a problem.
+
+// EstimateTokens returns a rough token count for a string.
+// Uses the ~4 chars/token heuristic for English (GPT/Claude average).
+func EstimateTokens(text string) int {
+	return (len(text) + 3) / 4
+}
+
+// EstimatePath returns total estimated tokens for a message path.
+// Adds +4 per message for role/delimiter overhead, matching the frontend.
+func EstimatePath(path []treepath.PathMessage) int {
+	total := 0
+	for i := range path {
+		total += EstimateTokens(path[i].Content) + 4
+	}
+	return total
+}
+
+// EstimatePathFromSummary returns estimated tokens for messages after
+// the most recent summary boundary. Returns 0 and false if a summary
+// exists but fewer than minMessages follow it.
+func EstimatePathFromSummary(path []treepath.PathMessage, minMessages int) (tokens int, msgCount int, ok bool) {
+	startIdx := 0
+	for i := range path {
+		if treepath.IsSummaryMessage(&path[i]) {
+			startIdx = i + 1
+		}
+	}
+
+	post := path[startIdx:]
+
+	// Count non-system, non-summary messages
+	count := 0
+	est := 0
+	for i := range post {
+		if post[i].Role == "system" || treepath.IsSummaryMessage(&post[i]) {
+			continue
+		}
+		count++
+		est += EstimateTokens(post[i].Content) + 4
+	}
+
+	if count < minMessages {
+		return 0, count, false
+	}
+	return est, count, true
+}