lakehouse/crates/queryd/src/service.rs

use arrow::array::RecordBatch;
use arrow::json::writer::{JsonArray, Writer as JsonWriter};
use axum::{
    Json, Router,
    extract::{Path, Query, State},
    http::StatusCode,
    response::IntoResponse,
    routing::{get, post},
};
use serde::{Deserialize, Serialize};

use crate::cache::CacheStats;
use crate::context::QueryEngine;
use crate::delta;
use crate::paged::ResultStore;

#[derive(Clone)]
pub struct QueryState {
    pub engine: QueryEngine,
    pub result_store: ResultStore,
}

pub fn router(engine: QueryEngine) -> Router {
    let state = QueryState {
        engine: engine.clone(),
        result_store: ResultStore::new(100, 50), // 100 rows/page, keep 50 results
    };
    Router::new()
        .route("/health", get(health))
        .route("/sql", post(execute_query))
        .route("/paged", post(paged_query))
        .route("/page/{query_id}/{page}", get(get_page))
        .route("/cache/pin", post(pin_dataset))
        .route("/cache/evict", post(evict_dataset))
        .route("/cache/stats", get(cache_stats))
        .route("/compact", post(compact_dataset))
        .with_state(state)
}

async fn health() -> &'static str {
    "queryd ok"
}

// --- SQL Query ---

#[derive(Deserialize)]
struct QueryRequest {
    sql: String,
}

#[derive(Serialize)]
struct QueryResponse {
    columns: Vec<ColumnInfo>,
    rows: serde_json::Value,
    row_count: usize,
}

#[derive(Serialize)]
struct ColumnInfo {
    name: String,
    data_type: String,
}

fn batches_to_json(batches: &[RecordBatch]) -> Result<serde_json::Value, String> {
    let mut buf = Vec::new();
    let mut writer = JsonWriter::<_, JsonArray>::new(&mut buf);
    for batch in batches {
        writer.write(batch).map_err(|e| format!("JSON write error: {e}"))?;
    }
    writer.finish().map_err(|e| format!("JSON finish error: {e}"))?;
    drop(writer);
    serde_json::from_slice(&buf).map_err(|e| format!("JSON parse error: {e}"))
}

async fn execute_query(
    State(state): State<QueryState>,
    Json(req): Json<QueryRequest>,
) -> impl IntoResponse {
    tracing::info!("executing query: {}", req.sql);

    match state.engine.query(&req.sql).await {
        Ok(batches) => {
            if batches.is_empty() {
                return Ok(Json(QueryResponse {
                    columns: vec![],
                    rows: serde_json::Value::Array(vec![]),
                    row_count: 0,
                }));
            }

            let schema = batches[0].schema();
            let columns: Vec<ColumnInfo> = schema.fields().iter().map(|f| ColumnInfo {
                name: f.name().clone(),
                data_type: f.data_type().to_string(),
            }).collect();

            let rows = batches_to_json(&batches)
                .map_err(|e| (StatusCode::INTERNAL_SERVER_ERROR, e))?;

            let row_count = rows.as_array().map(|a| a.len()).unwrap_or(0);

            Ok(Json(QueryResponse {
                columns,
                rows,
                row_count,
            }))
        }
        Err(e) => Err((StatusCode::BAD_REQUEST, e)),
    }
}

// --- Paged Queries (large result sets) ---

async fn paged_query(
    State(state): State<QueryState>,
    Json(req): Json<QueryRequest>,
) -> impl IntoResponse {
    tracing::info!("paged query: {}", req.sql);
    match state.result_store.execute_and_store(&state.engine, &req.sql).await {
        Ok(handle) => Ok(Json(handle)),
        Err(e) => Err((StatusCode::BAD_REQUEST, e)),
    }
}

#[derive(Deserialize)]
struct PageQuery {
    size: Option<usize>,
}

async fn get_page(
    State(state): State<QueryState>,
    Path((query_id, page)): Path<(String, usize)>,
    Query(q): Query<PageQuery>,
) -> impl IntoResponse {
    match state.result_store.get_page(&query_id, page, q.size).await {
        Ok(result) => Ok(Json(result)),
        Err(e) => Err((StatusCode::NOT_FOUND, e)),
    }
}

// --- Cache Management ---

#[derive(Deserialize)]
struct CacheRequest {
    dataset: String,
}

async fn pin_dataset(
    State(state): State<QueryState>,
    Json(req): Json<CacheRequest>,
) -> impl IntoResponse {
    match state.engine.pin_dataset(&req.dataset).await {
        Ok(()) => Ok((StatusCode::OK, format!("pinned: {}", req.dataset))),
        Err(e) => Err((StatusCode::INTERNAL_SERVER_ERROR, e)),
    }
}

async fn evict_dataset(
    State(state): State<QueryState>,
    Json(req): Json<CacheRequest>,
) -> impl IntoResponse {
    if state.engine.cache().evict(&req.dataset).await {
        (StatusCode::OK, format!("evicted: {}", req.dataset))
    } else {
        (StatusCode::NOT_FOUND, format!("not cached: {}", req.dataset))
    }
}

async fn cache_stats(State(state): State<QueryState>) -> impl IntoResponse {
    let stats = state.engine.cache().stats().await;
    Json(stats)
}

// --- Compaction ---

#[derive(Deserialize)]
struct CompactRequest {
    dataset: String,
    base_key: String,
    primary_key: Option<String>,
}

async fn compact_dataset(
    State(state): State<QueryState>,
    Json(req): Json<CompactRequest>,
) -> impl IntoResponse {
    // Phase E: pull tombstones for this dataset and let compact physically
    // drop those rows. After a successful rewrite, clear the tombstone log
    // — the rows are gone from disk, the tombstones have done their job.
    let tombstones = state
        .engine
        .catalog()
        .list_tombstones(&req.dataset)
        .await
        .unwrap_or_default();

    match delta::compact(
        state.engine.store(),
        &req.dataset,
        &req.base_key,
        req.primary_key.as_deref(),
        &tombstones,
    ).await {
        Ok(result) => {
            if result.rows_dropped_by_tombstones > 0 {
                if let Err(e) = state.engine.catalog().tombstones().clear(&req.dataset).await {
                    tracing::warn!("post-compact tombstone clear failed: {e}");
                }
            }
            Ok(Json(result))
        }
        Err(e) => Err((StatusCode::INTERNAL_SERVER_ERROR, e)),
    }
}