package hooks
import (
"encoding/json"
"strings"
"github.com/sgx-labs/statelessagent/internal/store"
)
const (
// topicSimilarityThreshold: above this Jaccard score, prompts are
// considered same-topic. Tuned conservatively — better to occasionally
// re-inject than to miss a real topic change.
topicSimilarityThreshold = 0.35
// sessionStateKeyTopicTerms is the key for storing the last
// injected topic's extracted terms in session_state.
sessionStateKeyTopicTerms = "last_topic_terms"
)
// isTopicChange compares the current prompt's terms against the last
// injected topic's terms. Returns true if the topic has changed enough
// to warrant new context injection.
//
// On first prompt of a session (no stored terms), always returns true.
// Requires keyTermsPrompt to be set before calling.
func isTopicChange(db *store.DB, sessionID string) bool {
if sessionID == "" {
return true // No session tracking, always inject
}
currentTerms := collectTopicTerms()
if len(currentTerms) == 0 {
return false // No terms = low signal, already handled by hasLowSignal
}
// Read last topic terms from session state
stored, ok := db.SessionStateGet(sessionID, sessionStateKeyTopicTerms)
if !ok || stored == "" {
return true // First prompt with terms in this session
}
var lastTerms []string
if err := json.Unmarshal([]byte(stored), &lastTerms); err != nil {
return true // Corrupt data, treat as new topic
}
if len(lastTerms) == 0 {
return true
}
similarity := jaccardSimilarity(currentTerms, lastTerms)
return similarity <= topicSimilarityThreshold
}
// topicChangeScore returns the Jaccard similarity score for logging.
// Returns -1 if no comparison was possible (first prompt, no stored terms).
func topicChangeScore(db *store.DB, sessionID string) float64 {
if sessionID == "" {
return -1
}
currentTerms := collectTopicTerms()
if len(currentTerms) == 0 {
return -1
}
stored, ok := db.SessionStateGet(sessionID, sessionStateKeyTopicTerms)
if !ok || stored == "" {
return -1
}
var lastTerms []string
if err := json.Unmarshal([]byte(stored), &lastTerms); err != nil {
return -1
}
if len(lastTerms) == 0 {
return -1
}
return jaccardSimilarity(currentTerms, lastTerms)
}
// storeTopicTerms saves the current prompt's terms as the session's
// active topic. Called after a successful context injection.
func storeTopicTerms(db *store.DB, sessionID string) {
if sessionID == "" {
return
}
terms := collectTopicTerms()
data, err := json.Marshal(terms)
if err != nil {
return
}
_ = db.SessionStateSet(sessionID, sessionStateKeyTopicTerms, string(data))
}
// collectTopicTerms gathers all meaningful terms from the current prompt.
// Combines specific + broad from extractKeyTerms for maximum signal.
func collectTopicTerms() []string {
specific, broad := extractKeyTerms()
seen := make(map[string]bool)
var terms []string
for _, t := range specific {
lower := strings.ToLower(t)
if !seen[lower] {
terms = append(terms, lower)
seen[lower] = true
}
}
for _, t := range broad {
lower := strings.ToLower(t)
if !seen[lower] {
terms = append(terms, lower)
seen[lower] = true
}
}
return terms
}
// jaccardSimilarity computes |A ∩ B| / |A ∪ B| for two string slices.
func jaccardSimilarity(a, b []string) float64 {
if len(a) == 0 && len(b) == 0 {
return 1.0 // Both empty = identical
}
setA := make(map[string]bool, len(a))
for _, s := range a {
setA[s] = true
}
setB := make(map[string]bool, len(b))
for _, s := range b {
setB[s] = true
}
intersection := 0
for s := range setA {
if setB[s] {
intersection++
}
}
union := len(setA)
for s := range setB {
if !setA[s] {
union++
}
}
if union == 0 {
return 1.0
}
return float64(intersection) / float64(union)
}
