//! `GET /admin/document`: the local document as Automerge bytes, for backups and as
//! input to an `import` remake.
//!
//! The whole document is saved: history, and protocol data under `_continuum`. Where
//! it came from is in headers: `X-Continuum-Swarm`, `X-Continuum-Epoch`
//! (`<generation>:<id hex>`) and `X-Continuum-Heads` (hex, comma-separated).

use axum::{
    extract::State,
    http::{HeaderName, HeaderValue, StatusCode, header},
    response::{IntoResponse, Response},
};
use tokio::time::Instant;
use tracing::{info, warn};

use crate::state::AppState;

pub(crate) async fn get_document(State(state): State<AppState>) -> Response {
    if !state.is_ready().await {
        return (StatusCode::SERVICE_UNAVAILABLE, "node is not ready\n").into_response();
    }
    let swarm_id = state.swarm_id().await.unwrap_or_default();

    let start = Instant::now();
    let version = crate::swarm::stats::document_version(&state);
    let doc = std::sync::Arc::clone(&state.doc);
    // Both steps take time proportional to the document: off the async threads, and
    // the lock only for the copy.
    let saved = tokio::task::spawn_blocking(move || {
        let (mut copy, epoch) = {
            let replica = doc.blocking_read();
            (replica.doc.clone(), replica.epoch)
        };
        let heads = copy.get_heads();
        (copy.save(), heads, epoch)
    })
    .await;
    let (bytes, heads, epoch) = match saved {
        Ok(saved) => saved,
        Err(error) => {
            warn!(error = %error, "Saving the document for export failed");
            return (StatusCode::INTERNAL_SERVER_ERROR, "saving failed\n").into_response();
        }
    };
    let took = start.elapsed();
    state
        .stats
        .saved_size_measured(bytes.len() as u64, took, version);
    info!(
        bytes = bytes.len(),
        took_ms = took.as_millis() as u64,
        "Exported the document"
    );

    let heads = heads
        .iter()
        .map(|head| head.to_string())
        .collect::<Vec<_>>()
        .join(",");
    let filename = format!(
        "attachment; filename=\"continuum-{swarm_id}-{}.automerge\"",
        epoch.generation
    );
    let mut response = bytes.into_response();
    let headers = response.headers_mut();
    let mut set = |name: HeaderName, value: String| {
        if let Ok(value) = HeaderValue::from_str(&value) {
            headers.insert(name, value);
        }
    };
    set(header::CONTENT_TYPE, "application/octet-stream".to_owned());
    set(header::CONTENT_DISPOSITION, filename);
    set(HeaderName::from_static("x-continuum-swarm"), swarm_id);
    set(
        HeaderName::from_static("x-continuum-epoch"),
        format!("{}:{}", epoch.generation, epoch.id_hex()),
    );
    set(HeaderName::from_static("x-continuum-heads"), heads);
    response
}