//! In-memory conversation state: message history plus the system prompt and
//! model parameters used to drive the LLM.

use serde::{Deserialize, Serialize};

/// A single conversation's message history and generation settings.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Conversation {
    pub messages: Vec<crate::dto::chat::message::ChatMessage>,
    pub system_prompt: String,
    pub session_id: String,
    pub model: String,
    pub max_tokens: u32,
    pub temperature: f32,
}

impl Conversation {
    /// Create an empty conversation with the given system prompt and
    /// session id, using default model/token/temperature settings.
    pub fn new(system_prompt: String, session_id: String) -> Self {
        Conversation {
            messages: Vec::new(),
            system_prompt,
            session_id,
            model: "anthropic/claude-opus-4-8".to_string(),
            max_tokens: 8192,
            temperature: 0.7,
        }
    }

    /// Append a message to the conversation history.
    pub fn push(&mut self, msg: crate::dto::chat::message::ChatMessage) {
        self.messages.push(msg);
    }

    /// Replace the system prompt and strip any prior `System`-role
    /// messages from history.
    ///
    /// Why: the system prompt is re-injected fresh at request time via
    /// `to_api_messages`, so stale `System` messages in `self.messages`
    /// would be redundant/conflicting if left in place.
    pub fn rebuild_system(&mut self, new_prompt: String) {
        self.system_prompt = new_prompt;
        self.messages.retain(|m| {
            !matches!(m.role, crate::dto::chat::message::Role::System)
        });
    }

    /// Build the message list to send to the LLM API, with the system
    /// prompt prepended.
    ///
    /// Return: a new `Vec` (clone of history) with a synthesized system
    /// message at index 0.
    pub fn to_api_messages(&self) -> Vec<crate::dto::chat::message::ChatMessage> {
        let mut msgs = Vec::with_capacity(self.messages.len() + 1);
        msgs.push(crate::dto::chat::message::ChatMessage::system(&self.system_prompt));
        msgs.extend(self.messages.iter().cloned());
        msgs
    }

    /// Number of messages in the conversation history (excluding the
    /// synthesized system message).
    pub fn len(&self) -> usize {
        self.messages.len()
    }
}