diff --git a/src/message.rs b/src/message.rs
new file mode 100644
index 0000000..9865ebc
--- /dev/null
+++ b/src/message.rs
@@ -0,0 +1,318 @@
+use std::{ptr::NonNull, marker::PhantomPinned, pin::Pin, cmp::min, num::NonZeroUsize, fmt::Display, error::Error};
+
+use openai_rs::{chat::{ChatMessage, Role, ChatHistoryBuilder}, context::Context as OpenAIContext};
+use tiktoken::CoreBPE;
+
+const PROMPT_COMPRESS: &str = "Summarize the chat history precisely and concisely";
+
+type UserAliases = Vec<String>;
+
+#[derive(Debug)]
+struct ContextOverrunError {
+    max_tokens: usize,
+    context_budget: usize,
+    history_budget: usize,
+    alias_budget: usize
+}
+
+impl Display for ContextOverrunError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(&format!("Context budget overrun. Context ({}), history ({}) and alias ({}) budgets must be at most {} tokens", self.context_budget, self.history_budget, self.alias_budget, self.max_tokens))?;
+        Ok(())
+    }
+}
+
+impl Error for ContextOverrunError {}
+
+impl ContextOverrunError {
+    fn new(max_tokens: usize, context_budget: usize, history_budget: usize, alias_budget: usize) -> Self {
+        Self {
+            max_tokens,
+            context_budget,
+            history_budget,
+            alias_budget
+        }
+    }
+}
+
+pub struct UserList {
+    pub users: Vec<UserAliases>,
+    _pin: PhantomPinned
+}
+
+pub enum User {
+    Assistant,
+    System,
+    User {
+        aliases: NonNull<UserAliases>
+    }
+}
+
+pub struct Message {
+    pub sender: User,
+    pub message: String
+}
+
+impl Message {
+    fn new(sender: User, message: String) -> Self {
+        Self {
+            sender,
+            message
+        }
+    }
+    
+    fn to_chat_message(&self, user_index: Option<usize>) -> ChatMessage {
+        ChatMessage::new(
+            match self.sender {
+                User::System => Role::System,
+                User::Assistant => Role::Assistant,
+                User::User { aliases } => Role::User
+            },
+            self.message,
+            if let Some(user_index) = user_index {
+                Some(format!("u{user_index}"))
+            } else {
+                None
+            }
+        )
+    }
+}
+
+pub struct Context {
+    pub users: Pin<Box<UserList>>,
+    messages: Vec<Message>,
+    openai_context: OpenAIContext,
+    summary: Option<String>,
+    max_tokens: usize,
+    model: String,
+    encoding: CoreBPE,
+    summary_budget: usize,
+    summary_instruction_budget: usize,
+    history_target: usize,
+    alias_budget: usize,
+}
+
+impl UserList {
+    fn new() -> Pin<Box<Self>> {
+        Box::pin(Self {
+            users: Vec::new(),
+            _pin: PhantomPinned
+        })
+    }
+
+    fn add_user(&mut self) {
+        self.users.push(Vec::new());
+    }
+
+    fn add_existing_user(&mut self, aliases: UserAliases) {
+        self.users.push(aliases);
+    }
+}
+
+impl Context {
+    fn new(max_tokens: NonZeroUsize, model: String, encoding: CoreBPE, openai_context: OpenAIContext, summary_budget: NonZeroUsize, history_target: NonZeroUsize, alias_budget: NonZeroUsize) -> Result<Self, impl Error> {
+        let summary_instruction_budget = count_message_tokens(&get_summary_instruction(), &encoding, &model) as usize;
+        let summary_budget = summary_budget.get() + count_message_tokens(&get_summary_message(None), &encoding, &model) as usize;
+        if history_target.get() + summary_budget + alias_budget.get() + summary_instruction_budget >= max_tokens.get() {
+            Err(ContextOverrunError::new(max_tokens.get(), history_target.get(), summary_budget, alias_budget.get()))
+        } else {
+            Ok(Self {
+                users: UserList::new(),
+                messages: Vec::new(),
+                openai_context,
+                summary: None,
+                max_tokens: max_tokens.get(),
+                model,
+                encoding,
+                summary_budget: summary_budget,
+                summary_instruction_budget,
+                history_target: history_target.get(),
+                alias_budget: alias_budget.get()
+            })
+        }
+    }
+
+    fn find_user_by_alias(&self, find: NonNull<UserAliases>) -> Option<usize> {
+        for (index, user) in self.users.users.iter().enumerate() {
+            if unsafe { find.as_ref() == user } {
+                return Some(index);
+            }
+        }
+        return None;
+    }
+
+    fn find_user(&self, find: &User) -> Option<usize> {
+        if let User::User { aliases } = find {
+            self.find_user_by_alias(*aliases)
+        } else {
+            None
+        }
+    }
+
+    fn update_user_list(&mut self, user: &User) -> Option<usize> {
+        if let User::User { aliases } = user {
+            Some(if let Some(index) = self.find_user_by_alias(*aliases) {
+                index
+            } else {
+                eprintln!("Attempt to add unregistered user to history! This is probably a bug.");
+
+                let copy = unsafe { (*aliases.as_ptr()).clone() };
+                self.users.add_existing_user(copy);
+                self.users.users.len() - 1
+            })
+        } else {
+            None
+        }
+    }
+
+    fn history_token_limit(&self) -> usize {
+        self.max_tokens - self.alias_budget - self.summary_budget - self.summary_instruction_budget
+    }
+
+    pub async fn add_message(&mut self, message: String, user: User) {
+        let user_index = self.update_user_list(&user);
+        let total_tokens = self.count_message_tokens();
+        let message = Message::new(user, message);
+
+        let message_tokens = count_message_tokens(&message.to_chat_message(user_index), &self.encoding, &self.model);
+
+        if (total_tokens + message_tokens) as usize >= self.history_token_limit() {
+            self.compress_history(message_tokens as usize).await;
+        }
+        
+        self.messages.push(message);
+    }
+
+    pub async fn add_message_0(&mut self, message: Message) {
+        self.add_message(message.message, message.sender).await
+    }
+
+    pub async fn generate_response(&self) -> anyhow::Result<Option<Message>> {
+        let mut history = self.chat_to_history(None);
+        if let Some(ref summary) = self.summary {
+            history.insert(0, get_summary_message(Some(summary.clone())));
+        }
+
+        let response = self.openai_context.create_chat_completion_sync(
+            ChatHistoryBuilder::default()
+                .messages(history)
+                .max_tokens(self.history_token_limit() as u64)
+                .model(self.model.clone())
+        ).await?.choices.remove(0).message.content;
+
+        Ok(if response.len() > 0 {
+            Some(Message::new(User::Assistant, response))
+        } else {
+            None
+        })
+    }
+
+    pub fn get_user_aliases(&self, id: usize) -> Option<&mut UserAliases> {
+        if id >= self.users.users.len() {
+            None
+        } else {
+            Some(&mut self.users.users[id])
+        }
+    }
+
+    pub fn chat_to_history(&self, last_n: Option<usize>) -> Vec<ChatMessage> {
+        let last_n = min(if let Some(value) = last_n { value } else { self.messages.len() }, self.messages.len());
+
+        let mut history = Vec::new();
+
+        for (index, msg) in self.messages[self.messages.len() - last_n..self.messages.len()].iter().enumerate() {
+            history.push(msg.to_chat_message(if let User::User { aliases } = msg.sender {
+                Some(index)
+            } else {
+                None
+            }));
+        }
+
+        return history;
+    }
+
+    fn count_message_tokens(&self) -> i64 {
+        let history = self.chat_to_history(None);
+        let mut total = 0i64;
+
+        for ref message in history {
+            total += count_message_tokens(message, &self.encoding, &self.model);
+        }
+
+        return total;
+    }
+
+    async fn compress_history(&mut self, new_tokens: usize) -> anyhow::Result<()> {
+        let mut permitted_history_size = if new_tokens > self.history_target {
+            0
+        } else {
+            self.history_target - new_tokens
+        };
+
+        let mut skip_count = 0;
+
+        for (index, message) in self.messages.iter().enumerate() {
+            let tokens = count_message_tokens(&message.to_chat_message(self.find_user(&message.sender)), &self.encoding, &self.model) as usize;
+            if tokens > permitted_history_size {
+                break;
+            }
+
+            permitted_history_size -= tokens;
+            skip_count = index + 1;
+        }
+
+        let mut history = self.chat_to_history(Some(self.messages.len() - skip_count));
+        history.push(get_summary_instruction());
+        self.summary = Some(self.openai_context.create_chat_completion_sync(
+            ChatHistoryBuilder::default()
+                .max_tokens(self.summary_budget as u64)
+                .model(self.model.clone())
+                .messages(history)
+        ).await?.choices.remove(0).message.content);
+
+        self.messages.drain(skip_count..);
+
+        Ok(())
+    }
+}
+
+fn get_summary_instruction() -> ChatMessage {
+    ChatMessage::new(Role::System, PROMPT_COMPRESS, None)
+}
+fn get_summary_message(summary: Option<String>) -> ChatMessage {
+    ChatMessage::new(Role::System, if let Some(ref message) = summary { message } else { "" }, Some("Context".to_string()))
+}
+
+
+fn get_tokens_per_message(model: &str) -> Option<i64> {
+    match model {
+        "gpt-4" | "gpt-4-32k" => Some(3),
+        "gpt-3.5-turbo" => Some(4),
+        _ => None
+    }
+}
+
+fn get_tokens_per_name(model: &str) -> Option<i64> {
+    match model {
+        "gpt-4" | "gpt-4-32k" => Some(1),
+        "gpt-3.5-turbo" => Some(-1),
+        _ => None
+    }
+}
+
+fn role_str(role: &Role) -> &str {
+    match role {
+        Role::Assistant => "Assistant",
+        Role::System => "System",
+        Role::User => "User",
+    }
+}
+
+fn count_message_tokens(message: &ChatMessage, encoding: &CoreBPE, model: &str) -> i64 {
+    let tpm = get_tokens_per_message(model).expect("Unknown tokens-per-message value");
+    let tpn = get_tokens_per_name(model).expect("Unknown tokens-per-name value");
+
+    return tpm + encoding.encode_ordinary(&message.content).len() as i64 + encoding.encode_ordinary(role_str(&message.role)).len() as i64 + if let Some(ref name) = message.name {
+        tpn + encoding.encode_ordinary(name).len() as i64
+    } else { 0i64 };
+}
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