//! Thread participant membership — maps to `message_thread_participant` table.
//!
//! Tracks which users are part of a thread. A user becomes a participant when
//! they reply in a thread, get @mentioned, or are explicitly added.
//! Without this table, `message_thread.participants_count` is un-verifiable.

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

/// A user participating in a thread.
///
/// Maps to the `message_thread_participant` table. Users become participants
/// when they reply, get @mentioned, or are explicitly added.
#[derive(Debug, Clone, Serialize, Deserialize, sqlx::FromRow)]
pub struct MessageThreadParticipant {
    pub id: Uuid,
    pub thread_id: Uuid,
    pub user_id: Uuid,
    /// How the user joined the thread.
    pub joined_reason: Option<String>,
    pub last_read_message_id: Option<Uuid>,
    pub last_read_at: Option<DateTime<Utc>>,
    pub joined_at: DateTime<Utc>,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default)]
#[serde(rename_all = "snake_case")]
pub enum JoinReason {
    /// User sent a reply in the thread.
    #[default]
    Reply,
    /// User was @mentioned in a thread message.
    Mentioned,
    /// User was explicitly added by another participant.
    Added,
    /// User joined the thread themselves.
    Joined,
}

impl JoinReason {
    pub fn as_str(&self) -> &'static str {
        match self {
            Self::Reply => "reply",
            Self::Mentioned => "mentioned",
            Self::Added => "added",
            Self::Joined => "joined",
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_participant_serialize() {
        let p = MessageThreadParticipant {
            id: Uuid::now_v7(),
            thread_id: Uuid::now_v7(),
            user_id: Uuid::now_v7(),
            joined_reason: Some(JoinReason::Reply.as_str().into()),
            last_read_message_id: None,
            last_read_at: None,
            joined_at: Utc::now(),
        };

        let json = serde_json::to_value(&p).unwrap();
        assert_eq!(json["joined_reason"], "reply");
    }
}