#![allow(
    clippy::cast_possible_truncation,
    clippy::cast_sign_loss,
    clippy::cast_precision_loss,
    clippy::cast_possible_wrap
)]
//! In-memory conversation state: message history plus the system prompt and
//! model parameters used to drive the LLM.
use serde::{Deserialize, Serialize};

use super::message::{ChatMessage, Role};

/// A single conversation's message history and generation settings.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Conversation {
    pub messages: Vec<ChatMessage>,
    pub system_prompt: String,
    pub session_id: String,
    pub model: String,
    pub max_tokens: Option<u32>,
    pub temperature: Option<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: None,
            temperature: None,
        }
    }

    /// Append a message to the conversation history.
    pub fn push(&mut self, msg: 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, 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<ChatMessage> {
        let mut msgs = Vec::with_capacity(self.messages.len() + 1);
        msgs.push(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()
    }

    /// Returns `true` if the conversation has no messages.
    pub fn is_empty(&self) -> bool {
        self.messages.is_empty()
    }

    /// Persist the conversation to a JSON file at the given base directory.
    ///
    /// Flow: compute path from `session_id` → ensure directory exists →
    /// serialize to pretty JSON → write-then-rename with fsync.
    ///
    /// Return: `Ok(())` on success, or an `io::Error` from any step.
    pub fn save_conversation(&self, base_dir: &std::path::Path) -> std::io::Result<()> {
        let dir = base_dir.join("sessions").join(&self.session_id);
        std::fs::create_dir_all(&dir)?;
        let path = dir.join("conversation.json");
        let data = serde_json::to_string_pretty(self)?;
        let tmp = dir.join("conversation.json.tmp");
        std::fs::write(&tmp, data)?;
        let f = std::fs::File::open(&tmp)?;
        f.sync_all()?;
        std::fs::rename(&tmp, path)?;
        let _ = std::fs::File::open(&dir).and_then(|d| d.sync_all());
        Ok(())
    }

    /// Load a conversation from a JSON file for the given session id.
    ///
    /// Flow: read `<base_dir>/sessions/<session_id>/conversation.json` →
    /// JSON-parse.
    ///
    /// Return: the parsed `Conversation`, or an `io::Error` if the file is
    /// missing or malformed.
    pub fn load_conversation(
        session_id: &str,
        base_dir: &std::path::Path,
    ) -> std::io::Result<Self> {
        let path = base_dir
            .join("sessions")
            .join(session_id)
            .join("conversation.json");
        let data = std::fs::read_to_string(path)?;
        let conv: Conversation = serde_json::from_str(&data)?;
        Ok(conv)
    }
}