//! Pure Conversation entity — in-memory message history plus system prompt
//! and LLM generation parameters.
//!
//! # Architecture
//! This is a pure data structure with **no I/O logic**.  Load/save
//! responsibilities live in [`ConversationRepository`](super::repository::ConversationRepository).

#![allow(
    clippy::cast_possible_truncation,
    clippy::cast_sign_loss,
    clippy::cast_precision_loss,
    clippy::cast_possible_wrap
)]

use serde::{Deserialize, Serialize};

/// A single message role / content pair.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub enum Role {
    #[serde(rename = "user")]
    User,
    #[serde(rename = "assistant")]
    Assistant,
    #[serde(rename = "system")]
    System,
    #[serde(rename = "tool")]
    Tool,
}

/// A single message in a conversation.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ChatMessage {
    pub role: Role,
    pub content: Option<String>,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub tool_calls: Option<Vec<serde_json::Value>>,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub tool_call_id: Option<String>,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub name: Option<String>,
}

impl ChatMessage {
    /// Build a user-role message with the given text content.
    pub fn user(content: impl Into<String>) -> Self {
        Self {
            role: Role::User,
            content: Some(content.into()),
            tool_calls: None,
            tool_call_id: None,
            name: None,
        }
    }

    /// Build an assistant-role message with an optional text response.
    pub fn assistant(content: Option<String>) -> Self {
        Self {
            role: Role::Assistant,
            content,
            tool_calls: None,
            tool_call_id: None,
            name: None,
        }
    }

    /// Build a system-role message with the given instruction text.
    pub fn system(content: impl Into<String>) -> Self {
        Self {
            role: Role::System,
            content: Some(content.into()),
            tool_calls: None,
            tool_call_id: None,
            name: None,
        }
    }

    /// Build a tool-role result message referencing a prior tool call.
    pub fn tool(tool_call_id: String, content: String) -> Self {
        Self {
            role: Role::Tool,
            content: Some(content),
            tool_calls: None,
            tool_call_id: Some(tool_call_id),
            name: None,
        }
    }
}

/// 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 {
        Self {
            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.
    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 as the first message.
    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()
    }
}