use serde::{Deserialize, Serialize};

/// The role of a participant in a chat conversation.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub enum ChatRole {
    /// Message sent by the human user
    User,
    /// Message generated by the AI assistant
    Assistant,
    /// System-level instruction (not displayed in UI)
    System,
}

/// Namespace for grouping chat sessions in the sidebar.
///
/// Sessions are visually separated in the chat sidebar by namespace,
/// with `News` sessions appearing under a dedicated "News Chats" header.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, Default)]
pub enum ChatNamespace {
    /// General user-initiated chat conversations.
    #[default]
    General,
    /// Chats originating from news article follow-ups on the dashboard.
    News,
}

/// The type of file attached to a chat message.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub enum AttachmentKind {
    /// Image file (png, jpg, webp, etc.)
    Image,
    /// Document file (pdf, docx, txt, etc.)
    Document,
    /// Source code file
    Code,
}

/// A file attachment on a chat message.
///
/// # Fields
///
/// * `name` - Original filename
/// * `kind` - Type of attachment for rendering
/// * `size_bytes` - File size in bytes
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct Attachment {
    pub name: String,
    pub kind: AttachmentKind,
    pub size_bytes: u64,
}

/// A persisted chat session stored in MongoDB.
///
/// Messages are stored separately in the `chat_messages` collection
/// and loaded on demand when the user opens a session.
///
/// # Fields
///
/// * `id` - MongoDB document ID (hex string)
/// * `user_sub` - Keycloak subject ID (session owner)
/// * `title` - Display title (auto-generated or user-renamed)
/// * `namespace` - Grouping for sidebar sections
/// * `provider` - LLM provider used (e.g. "ollama", "openai")
/// * `model` - Model ID used (e.g. "llama3.1:8b")
/// * `created_at` - ISO 8601 creation timestamp
/// * `updated_at` - ISO 8601 last-activity timestamp
/// * `article_url` - Source article URL (for News namespace sessions)
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct ChatSession {
    #[serde(default, alias = "_id", skip_serializing_if = "String::is_empty")]
    pub id: String,
    pub user_sub: String,
    pub title: String,
    #[serde(default)]
    pub namespace: ChatNamespace,
    pub provider: String,
    pub model: String,
    pub created_at: String,
    pub updated_at: String,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub article_url: Option<String>,
}

/// A single persisted message within a chat session.
///
/// Stored in the `chat_messages` MongoDB collection, linked to a
/// `ChatSession` via `session_id`.
///
/// # Fields
///
/// * `id` - MongoDB document ID (hex string)
/// * `session_id` - Foreign key to `ChatSession.id`
/// * `role` - Who sent this message
/// * `content` - Message text content (may contain markdown)
/// * `attachments` - File attachments (Phase 2, currently empty)
/// * `timestamp` - ISO 8601 timestamp
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct ChatMessage {
    #[serde(default, alias = "_id", skip_serializing_if = "String::is_empty")]
    pub id: String,
    pub session_id: String,
    pub role: ChatRole,
    pub content: String,
    #[serde(default)]
    pub attachments: Vec<Attachment>,
    pub timestamp: String,
}