//! Compaction: replacing the document with a snapshot in a new epoch.
//!
//! * `snapshot`: deterministic snapshot build (step 3).
//! * `records`: the replicated compaction records under `_continuum/compactions/<id>`.
//! * `coordinator`: proposal, settle period and decision on the node that was asked.
//! * `switch`: switching this node to a committed epoch (worker).
//! * `catchup`: fetching a newer epoch from a peer (late, new or failed nodes).
//! * `delta`: replaying this node's changes since the base into the new epoch.
//! * `local`: per-node in-memory state (prebuilt snapshots, switch status, archive).
//! * `api`: `/admin/compaction(s)` handlers.
//!
//! The rest of the node is reached exclusively through [`Host`], so this module never
//! depends on `AppState`, peers or sync internals.

mod api;
mod catchup;
mod coordinator;
mod delta;
mod local;
mod records;
pub(crate) mod snapshot;
mod switch;

pub(crate) use catchup::{receive_snapshot_reply, serve_snapshot};
pub(crate) use local::Compaction;
pub(crate) use switch::run_worker;

use std::future::Future;
use std::sync::Arc;
use std::time::Duration;

use automerge::AutoCommit;
use axum::{
    routing::{get, post},
    Router,
};
use tokio::sync::broadcast;

use crate::replica::Epoch;
use crate::sync::ChangeSet;
use crate::transport::ParsedMessage;

/// What compaction needs from the node. Implemented by `AppState`.
///
/// Used generically (`H: Host`), never as `dyn Host`, so the generic methods are fine.
pub(crate) trait Host: Clone + Send + Sync + 'static {
    /// This node's in-memory compaction state.
    fn compaction(&self) -> &Compaction;

    /// This node's peer ID.
    fn node_id(&self) -> String;

    /// The epoch of the local replica.
    fn current_epoch(&self) -> Epoch;

    /// Lower bound and default basis for the settle period.
    fn dormant_after(&self) -> Duration;

    fn is_node_ready(&self) -> impl Future<Output = bool> + Send;

    /// Known (not forgotten) peers.
    fn peer_summaries(&self) -> impl Future<Output = Vec<PeerSummary>> + Send;

    /// True if `peer` completed the handshake as a member of our cluster.
    fn is_cluster_member(&self, peer: &str) -> impl Future<Output = bool> + Send;

    /// Sends a message to a peer over the transport.
    fn send_message(
        &self,
        peer: &str,
        message: ParsedMessage,
    ) -> impl Future<Output = anyhow::Result<()>> + Send;

    /// Store paths touched by each published document change.
    fn subscribe_changes(&self) -> broadcast::Receiver<Arc<ChangeSet>>;

    /// Reads the document on the blocking pool.
    fn read_doc<T, F>(&self, f: F) -> impl Future<Output = T> + Send
    where
        F: FnOnce(&AutoCommit) -> T + Send + 'static,
        T: Send + 'static;

    /// Mutable access to the document without publishing a change (e.g. forks).
    fn update_doc<T, F>(&self, f: F) -> impl Future<Output = T> + Send
    where
        F: FnOnce(&mut AutoCommit) -> T + Send + 'static,
        T: Send + 'static;

    /// One committed change (rolled back on error), published and replicated.
    fn commit_doc<T, E, F>(&self, f: F) -> impl Future<Output = Result<T, E>> + Send
    where
        F: FnOnce(&mut AutoCommit) -> Result<T, E> + Send + 'static,
        T: Send + 'static,
        E: Send + 'static;

    /// Replaces the document and its epoch atomically. Under the write lock, `f` gets
    /// the live document and returns the new one. Afterwards the node resets every
    /// peer's sync state and publishes the change. Returns the old document.
    fn switch_epoch<E, F>(
        &self,
        epoch: Epoch,
        f: F,
    ) -> impl Future<Output = Result<AutoCommit, E>> + Send
    where
        F: FnOnce(&mut AutoCommit) -> Result<AutoCommit, E> + Send + 'static,
        E: Send + 'static;
}

#[derive(Clone, Debug)]
pub(crate) struct PeerSummary {
    pub(crate) id: String,
    /// Not dormant.
    pub(crate) active: bool,
    /// Handshake completed.
    pub(crate) established: bool,
    /// The epoch the peer last advertised.
    pub(crate) epoch: Option<Epoch>,
}

/// Admin routes. Merged into the authenticated part of the node's router.
pub(crate) fn router<H: Host>() -> Router<H> {
    Router::new()
        .route(
            "/admin/compaction",
            post(api::start::<H>).delete(api::abort_current::<H>),
        )
        .route("/admin/compactions", get(api::list::<H>))
        .route(
            "/admin/compactions/{id}",
            get(api::get::<H>).delete(api::abort::<H>),
        )
        .route("/admin/epochs", get(api::epochs::<H>))
}