From f609cda61e42bafb343186673e086c96045258ac Mon Sep 17 00:00:00 2001
From: Paul Buetow <paul@buetow.org>
Date: Fri, 27 Feb 2026 17:03:04 +0200
Subject: flamegraph: add live trie scaffold

---
 internal/flamegraph/livetrie.go | 61 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)
 create mode 100644 internal/flamegraph/livetrie.go

(limited to 'internal/flamegraph')

diff --git a/internal/flamegraph/livetrie.go b/internal/flamegraph/livetrie.go
new file mode 100644
index 0000000..11d5c1b
--- /dev/null
+++ b/internal/flamegraph/livetrie.go
@@ -0,0 +1,61 @@
+package flamegraph
+
+import (
+	"slices"
+	"sync"
+	"sync/atomic"
+)
+
+// LiveTrie is a thread-safe, append-only trie used for live flamegraph snapshots.
+type LiveTrie struct {
+	mu         sync.RWMutex
+	root       *trieNode
+	maxDepth   int
+	version    atomic.Uint64
+	fields     []string
+	countField string
+
+	// Snapshot cache avoids recomputing JSON when version is unchanged.
+	cacheMu      sync.Mutex
+	cacheVersion uint64
+	cacheJSON    []byte
+}
+
+// NewLiveTrie constructs an empty live trie with the configured frame/count fields.
+func NewLiveTrie(fields []string, countField string) *LiveTrie {
+	return &LiveTrie{
+		root: &trieNode{
+			childMap: make(map[string]*trieNode),
+		},
+		fields:     slices.Clone(fields),
+		countField: countField,
+	}
+}
+
+func (lt *LiveTrie) addLocked(frames []string, value uint64) {
+	node := lt.root
+	for _, frame := range frames {
+		if node.childMap == nil {
+			node.childMap = make(map[string]*trieNode)
+		}
+		child, ok := node.childMap[frame]
+		if !ok {
+			child = &trieNode{
+				name:     frame,
+				childMap: make(map[string]*trieNode),
+			}
+			node.children = append(node.children, child)
+			node.childMap[frame] = child
+		}
+		node = child
+	}
+	node.value += value
+	if len(frames) > lt.maxDepth {
+		lt.maxDepth = len(frames)
+	}
+}
+
+// Version returns the current ingest version of the trie.
+func (lt *LiveTrie) Version() uint64 {
+	return lt.version.Load()
+}
-- 
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