//! 画布Agent对话领域模型。
//!
//! 本 crate 只描述会话元数据、消息与附件的纯领域事实与规则；
//! LLM、SSE、OSS 读写和 SpacetimeDB 写表均留在外层 adapter。

use serde::{Deserialize, Serialize};
#[cfg(feature = "spacetime-types")]
use spacetimedb::SpacetimeType;

pub const EDITOR_AGENT_CONVERSATION_ID_PREFIX: &str = "editor-agent-conv-";
pub const EDITOR_AGENT_MESSAGE_ID_PREFIX: &str = "editor-agent-message-";
/// 会话消息 OSS 对象目录前缀，完整键见 [`editor_agent_messages_object_key`]。
pub const EDITOR_AGENT_MESSAGES_OBJECT_PREFIX: &str = "editor-agent/";
/// 单条消息附件上限（超出由前端拦截、后端兜底拒绝）。
pub const EDITOR_AGENT_MAX_ATTACHMENTS: usize = 9;
/// 会话标题取首条用户消息的前 N 个字符。
pub const EDITOR_AGENT_TITLE_MAX_CHARS: usize = 20;
/// 新会话默认标题。
pub const EDITOR_AGENT_DEFAULT_CONVERSATION_TITLE: &str = "新对话";

/// 会话元数据快照：SpacetimeDB 表只存这些字段，消息正文整体存 OSS。
#[cfg_attr(feature = "spacetime-types", derive(SpacetimeType))]
#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
pub struct EditorAgentConversationSnapshot {
    pub conversation_id: String,
    pub project_id: String,
    pub owner_user_id: String,
    pub title: String,
    pub messages_object_key: String,
    pub deleted: bool,
    pub created_at_micros: i64,
    pub updated_at_micros: i64,
}

/// 会话消息 OSS 对象键：`editor-agent/{conversationId}.json`，会话粒度整体读写。
pub fn editor_agent_messages_object_key(conversation_id: &str) -> String {
    format!("{EDITOR_AGENT_MESSAGES_OBJECT_PREFIX}{conversation_id}.json")
}

/// 从首条用户消息推导会话标题：去掉首尾空白与换行后截取前 N 个字符；
/// 空文本退回默认标题，供尚未发送消息的新会话使用。
pub fn derive_conversation_title(first_message_text: &str) -> String {
    let normalized: String = first_message_text
        .chars()
        .map(|c| if c == '\n' || c == '\r' { ' ' } else { c })
        .collect::<String>()
        .split_whitespace()
        .collect::<Vec<_>>()
        .join(" ");
    if normalized.is_empty() {
        return EDITOR_AGENT_DEFAULT_CONVERSATION_TITLE.to_string();
    }
    normalized
        .chars()
        .take(EDITOR_AGENT_TITLE_MAX_CHARS)
        .collect()
}