//! Sqlite-backed message broker. Survives `hive-c0re` restart, and taps every
//! send/recv onto a broadcast channel so the dashboard can stream it.

use std::path::Path;
use std::sync::Mutex;
use std::time::{SystemTime, UNIX_EPOCH};

use anyhow::{Context, Result};
use hive_sh4re::Message;
use rusqlite::{Connection, OptionalExtension, params};
use serde::Serialize;
use tokio::sync::broadcast;

const SCHEMA: &str = r"
CREATE TABLE IF NOT EXISTS messages (
    id           INTEGER PRIMARY KEY AUTOINCREMENT,
    sender       TEXT    NOT NULL,
    recipient    TEXT    NOT NULL,
    body         TEXT    NOT NULL,
    sent_at      INTEGER NOT NULL,
    delivered_at INTEGER
);
CREATE INDEX IF NOT EXISTS idx_messages_undelivered
    ON messages (recipient, id) WHERE delivered_at IS NULL;
";

/// Capacity of the live event channel. Slow subscribers (e.g. an idle browser)
/// may drop events past this; we send a `lagged` notice in their stream.
const EVENT_CHANNEL: usize = 256;

#[derive(Debug, Clone, Serialize)]
#[serde(rename_all = "snake_case", tag = "kind")]
pub enum MessageEvent {
    Sent {
        from: String,
        to: String,
        body: String,
        at: i64,
    },
    Delivered {
        from: String,
        to: String,
        body: String,
        at: i64,
    },
}

pub struct Broker {
    conn: Mutex<Connection>,
    events: broadcast::Sender<MessageEvent>,
}

impl Broker {
    pub fn open(path: &Path) -> Result<Self> {
        if let Some(parent) = path.parent() {
            std::fs::create_dir_all(parent)
                .with_context(|| format!("create db parent {}", parent.display()))?;
        }
        let conn = Connection::open(path)
            .with_context(|| format!("open broker db {}", path.display()))?;
        conn.execute_batch(SCHEMA).context("apply broker schema")?;
        let (events, _) = broadcast::channel(EVENT_CHANNEL);
        Ok(Self {
            conn: Mutex::new(conn),
            events,
        })
    }

    pub fn subscribe(&self) -> broadcast::Receiver<MessageEvent> {
        self.events.subscribe()
    }

    pub fn send(&self, message: &Message) -> Result<()> {
        let conn = self.conn.lock().unwrap();
        conn.execute(
            "INSERT INTO messages (sender, recipient, body, sent_at) VALUES (?1, ?2, ?3, ?4)",
            params![message.from, message.to, message.body, now_unix()],
        )?;
        drop(conn);
        let _ = self.events.send(MessageEvent::Sent {
            from: message.from.clone(),
            to: message.to.clone(),
            body: message.body.clone(),
            at: now_unix(),
        });
        Ok(())
    }

    pub fn recv(&self, recipient: &str) -> Result<Option<Message>> {
        let conn = self.conn.lock().unwrap();
        let row: Option<(i64, String, String, String)> = conn
            .query_row(
                "SELECT id, sender, recipient, body
                   FROM messages
                  WHERE recipient = ?1 AND delivered_at IS NULL
                  ORDER BY id ASC
                  LIMIT 1",
                params![recipient],
                |row| Ok((row.get(0)?, row.get(1)?, row.get(2)?, row.get(3)?)),
            )
            .optional()?;
        let Some((id, from, to, body)) = row else {
            return Ok(None);
        };
        conn.execute(
            "UPDATE messages SET delivered_at = ?1 WHERE id = ?2",
            params![now_unix(), id],
        )?;
        drop(conn);
        let _ = self.events.send(MessageEvent::Delivered {
            from: from.clone(),
            to: to.clone(),
            body: body.clone(),
            at: now_unix(),
        });
        Ok(Some(Message { from, to, body }))
    }
}

fn now_unix() -> i64 {
    SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .ok()
        .and_then(|d| i64::try_from(d.as_secs()).ok())
        .unwrap_or(0)
}