synaptic_memory/
summary_buffer.rs

1use std::{collections::HashMap, sync::Arc};
2
3use async_trait::async_trait;
4use synaptic_core::{ChatModel, ChatRequest, MemoryStore, Message, SynapseError};
5use tokio::sync::RwLock;
6
7/// Hybrid memory strategy: keeps recent messages verbatim and summarizes
8/// older messages when total estimated tokens exceed `max_token_limit`.
9///
10/// Combines the benefits of `ConversationSummaryMemory` (compact history) with
11/// `ConversationTokenBufferMemory` (recent context preserved exactly).
12pub struct ConversationSummaryBufferMemory {
13    store: Arc<dyn MemoryStore>,
14    model: Arc<dyn ChatModel>,
15    summary: Arc<RwLock<HashMap<String, String>>>,
16    max_token_limit: usize,
17}
18
19impl ConversationSummaryBufferMemory {
20    /// Create a new summary buffer memory.
21    ///
22    /// - `store` — the underlying message store
23    /// - `model` — the ChatModel used to generate summaries
24    /// - `max_token_limit` — when total estimated tokens exceed this, older messages are summarized
25    pub fn new(
26        store: Arc<dyn MemoryStore>,
27        model: Arc<dyn ChatModel>,
28        max_token_limit: usize,
29    ) -> Self {
30        Self {
31            store,
32            model,
33            summary: Arc::new(RwLock::new(HashMap::new())),
34            max_token_limit,
35        }
36    }
37
38    fn estimate_tokens(text: &str) -> usize {
39        (text.len() / 4).max(1)
40    }
41
42    async fn summarize(&self, messages: &[Message]) -> Result<String, SynapseError> {
43        let conversation = messages
44            .iter()
45            .map(|m| format!("{}: {}", m.role(), m.content()))
46            .collect::<Vec<_>>()
47            .join("\n");
48
49        let prompt = format!("Summarize the following conversation concisely:\n\n{conversation}");
50        let request = ChatRequest::new(vec![Message::human(prompt)]);
51        let response = self.model.chat(request).await?;
52        Ok(response.message.content().to_string())
53    }
54}
55
56#[async_trait]
57impl MemoryStore for ConversationSummaryBufferMemory {
58    async fn append(&self, session_id: &str, message: Message) -> Result<(), SynapseError> {
59        self.store.append(session_id, message).await?;
60
61        let messages = self.store.load(session_id).await?;
62        let total_tokens: usize = messages
63            .iter()
64            .map(|m| Self::estimate_tokens(m.content()))
65            .sum();
66
67        if total_tokens > self.max_token_limit && messages.len() > 1 {
68            // Find split point: keep as many recent messages as fit within half the limit
69            let half_limit = self.max_token_limit / 2;
70            let mut recent_tokens = 0;
71            let mut split_point = messages.len();
72
73            for (i, msg) in messages.iter().enumerate().rev() {
74                let tokens = Self::estimate_tokens(msg.content());
75                if recent_tokens + tokens > half_limit {
76                    split_point = i + 1;
77                    break;
78                }
79                recent_tokens += tokens;
80            }
81
82            // Ensure we summarize at least something
83            if split_point == 0 {
84                split_point = 1;
85            }
86            if split_point >= messages.len() {
87                split_point = messages.len() - 1;
88            }
89
90            let older = &messages[..split_point];
91            let recent = &messages[split_point..];
92
93            // Build summary incorporating existing summary
94            let existing_summary = {
95                let summaries = self.summary.read().await;
96                summaries.get(session_id).cloned()
97            };
98
99            let to_summarize = if let Some(ref existing) = existing_summary {
100                let mut with_context =
101                    vec![Message::system(format!("Previous summary: {existing}"))];
102                with_context.extend_from_slice(older);
103                with_context
104            } else {
105                older.to_vec()
106            };
107
108            let new_summary = self.summarize(&to_summarize).await?;
109
110            {
111                let mut summaries = self.summary.write().await;
112                summaries.insert(session_id.to_string(), new_summary);
113            }
114
115            // Replace store contents with just the recent messages
116            self.store.clear(session_id).await?;
117            for msg in recent {
118                self.store.append(session_id, msg.clone()).await?;
119            }
120        }
121
122        Ok(())
123    }
124
125    async fn load(&self, session_id: &str) -> Result<Vec<Message>, SynapseError> {
126        let messages = self.store.load(session_id).await?;
127        let summaries = self.summary.read().await;
128
129        if let Some(summary_text) = summaries.get(session_id) {
130            let mut result = vec![Message::system(format!(
131                "Summary of earlier conversation: {summary_text}"
132            ))];
133            result.extend(messages);
134            Ok(result)
135        } else {
136            Ok(messages)
137        }
138    }
139
140    async fn clear(&self, session_id: &str) -> Result<(), SynapseError> {
141        self.store.clear(session_id).await?;
142        let mut summaries = self.summary.write().await;
143        summaries.remove(session_id);
144        Ok(())
145    }
146}
synaptic_memory/summary_buffer.rs

synaptic_memory/
summary_buffer.rs
