//! In-memory presence store for tracking user online status.
//!
//! This module maintains an in-memory store of user presence states,
//! indexed by (project_id, user_id). Presence is updated via WebSocket
//! messages and is broadcast to relevant project subscribers.
//!
//! Note: This is a per-instance in-memory store. In a multi-node deployment,
//! presence state is not synchronized between nodes. For production use,
//! consider using Redis Sorted Sets with TTL-based idle detection.

use std::time::{Duration, Instant};

use chrono::{DateTime, Utc};
use dashmap::DashMap;
use serde::{Deserialize, Serialize};
use uuid::Uuid;

/// User presence status enum.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, utoipa::ToSchema)]
#[serde(rename_all = "snake_case")]
pub enum PresenceStatus {
    Online,
    Idle,
    Dnd,
    Offline,
}

impl Default for PresenceStatus {
    fn default() -> Self {
        PresenceStatus::Offline
    }
}

/// Presence changed event for broadcasting.
#[derive(Debug, Clone, Serialize, Deserialize, utoipa::ToSchema)]
pub struct PresenceChanged {
    pub user_id: Uuid,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub project_id: Option<Uuid>,
    pub status: PresenceStatus,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub last_seen_at: Option<DateTime<Utc>>,
}

/// Custom status event for broadcasting.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct CustomStatusChanged {
    pub user_id: Uuid,
    pub emoji: Option<String>,
    pub text: Option<String>,
    pub expires_at: Option<DateTime<Utc>>,
}

/// Maximum time before a user is considered "idle" when no heartbeat is received.
pub const IDLE_TIMEOUT: Duration = Duration::from_secs(5 * 60); // 5 minutes

/// Maximum time before a user is considered "offline" when no heartbeat is received.
pub const OFFLINE_TIMEOUT: Duration = Duration::from_secs(10 * 60); // 10 minutes

/// Presence entry for a single user in a project context.
#[derive(Clone, Debug)]
pub struct PresenceEntry {
    pub user_id: Uuid,
    pub project_id: Option<Uuid>,
    pub status: PresenceStatus,
    pub custom_emoji: Option<String>,
    pub custom_text: Option<String>,
    pub custom_expires_at: Option<DateTime<Utc>>,
    pub last_seen_at: Option<DateTime<Utc>>,
    pub last_activity: Instant,
}

impl PresenceEntry {
    pub fn new(user_id: Uuid, project_id: Option<Uuid>, status: PresenceStatus) -> Self {
        Self {
            user_id,
            project_id,
            status,
            custom_emoji: None,
            custom_text: None,
            custom_expires_at: None,
            last_seen_at: Some(Utc::now()),
            last_activity: Instant::now(),
        }
    }

    /// Update the presence status and activity timestamp.
    pub fn update_status(&mut self, status: PresenceStatus) {
        self.status = status;
        self.last_seen_at = Some(Utc::now());
        self.last_activity = Instant::now();
    }

    /// Update custom status (emoji, text, expires_at).
    pub fn update_custom_status(
        &mut self,
        emoji: Option<String>,
        text: Option<String>,
        expires_at: Option<DateTime<Utc>>,
    ) {
        self.custom_emoji = emoji;
        self.custom_text = text;
        self.custom_expires_at = expires_at;
    }

    /// Compute effective status based on last activity.
    /// If user hasn't sent any presence update for a while, they're "idle".
    pub fn effective_status(&self) -> PresenceStatus {
        match self.status {
            PresenceStatus::Online | PresenceStatus::Idle | PresenceStatus::Dnd => {
                let elapsed = self.last_activity.elapsed();
                if elapsed >= OFFLINE_TIMEOUT {
                    PresenceStatus::Offline
                } else if elapsed >= IDLE_TIMEOUT && self.status == PresenceStatus::Online {
                    PresenceStatus::Idle
                } else {
                    self.status
                }
            }
            PresenceStatus::Offline => PresenceStatus::Offline,
        }
    }
}

/// Global presence store - keyed by (project_id, user_id).
/// project_id = None means "global" presence (across all projects).
#[derive(Default, Clone)]
pub struct PresenceStore {
    /// Main presence storage: (project_id, user_id) -> PresenceEntry
    entries: DashMap<(Option<Uuid>, Uuid), PresenceEntry>,
    /// Quick lookup: user_id -> Set of project_ids they're present in
    user_projects: DashMap<Uuid, std::collections::HashSet<Uuid>>,
}

impl PresenceStore {
    pub fn new() -> Self {
        Self {
            entries: DashMap::new(),
            user_projects: DashMap::new(),
        }
    }

    /// Set user presence in a project context.
    pub fn set_presence(
        &self,
        user_id: Uuid,
        project_id: Option<Uuid>,
        status: PresenceStatus,
    ) -> Option<PresenceChanged> {
        let key = (project_id, user_id);
        let now = Utc::now();

        let mut entry = self.entries.entry(key).or_insert_with(|| {
            // Add to user_projects index
            if let Some(pid) = project_id {
                let mut projects = self.user_projects.entry(user_id).or_default();
                projects.insert(pid);
            }
            PresenceEntry::new(user_id, project_id, status)
        });

        let old_status = entry.status;
        entry.update_status(status);

        // Return event if status actually changed
        if old_status != status {
            Some(PresenceChanged {
                user_id,
                project_id,
                status,
                last_seen_at: Some(now),
            })
        } else {
            None
        }
    }

    /// Update custom status for a user.
    pub fn set_custom_status(
        &self,
        user_id: Uuid,
        emoji: Option<String>,
        text: Option<String>,
        expires_at: Option<DateTime<Utc>>,
    ) -> Option<CustomStatusChanged> {
        // Find the primary presence entry (first one found)
        let key = self.entries.iter().find(|e| e.user_id == user_id).map(|e| *e.key());

        if let Some(key) = key {
            if let Some(mut entry) = self.entries.get_mut(&key) {
                entry.update_custom_status(emoji.clone(), text.clone(), expires_at.clone());
                return Some(CustomStatusChanged {
                    user_id,
                    emoji,
                    text,
                    expires_at,
                });
            }
        }
        None
    }

    /// Get presence entry for a user in a specific project.
    pub fn get_presence(&self, user_id: Uuid, project_id: Option<Uuid>) -> Option<PresenceEntry> {
        self.entries.get(&(project_id, user_id)).map(|e| e.clone())
    }

    /// Get all presence entries for a project.
    pub fn get_project_presence(&self, project_id: Uuid) -> Vec<PresenceChanged> {
        self.entries
            .iter()
            .filter(|entry| entry.key().0 == Some(project_id))
            .map(|entry| PresenceChanged {
                user_id: entry.user_id,
                project_id: entry.project_id,
                status: entry.effective_status(),
                last_seen_at: entry.last_seen_at,
            })
            .collect()
    }

    /// Get all online users across all projects.
    pub fn get_all_online(&self) -> Vec<PresenceChanged> {
        self.entries
            .iter()
            .filter(|entry| entry.effective_status() != PresenceStatus::Offline)
            .map(|entry| PresenceChanged {
                user_id: entry.user_id,
                project_id: entry.project_id,
                status: entry.effective_status(),
                last_seen_at: entry.last_seen_at,
            })
            .collect()
    }

    /// Remove user presence when they disconnect.
    pub fn remove_presence(&self, user_id: Uuid, project_id: Option<Uuid>) -> Option<PresenceChanged> {
        let key = (project_id, user_id);
        if let Some((_, entry)) = self.entries.remove(&key) {
            // Remove from user_projects index
            if let Some(pid) = project_id {
                if let Some(mut projects) = self.user_projects.get_mut(&user_id) {
                    projects.remove(&pid);
                    if projects.is_empty() {
                        drop(projects);
                        self.user_projects.remove(&user_id);
                    }
                }
            }
            return Some(PresenceChanged {
                user_id: entry.user_id,
                project_id,
                status: PresenceStatus::Offline,
                last_seen_at: entry.last_seen_at,
            });
        }
        None
    }

    /// Get count of online users in a project.
    pub fn project_online_count(&self, project_id: Uuid) -> usize {
        self.entries
            .iter()
            .filter(|entry| entry.key().0 == Some(project_id) && entry.effective_status() != PresenceStatus::Offline)
            .count()
    }
}