// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.

use deno_core::error::AnyError;
use deno_core::parking_lot::Mutex;
use deno_core::parking_lot::MutexGuard;
use deno_core::task::spawn_blocking;
use deno_runtime::deno_webstorage::rusqlite;
use deno_runtime::deno_webstorage::rusqlite::Connection;
use deno_runtime::deno_webstorage::rusqlite::OptionalExtension;
use deno_runtime::deno_webstorage::rusqlite::Params;
use once_cell::sync::OnceCell;
use std::path::PathBuf;
use std::sync::Arc;

/// What should the cache should do on failure?
#[derive(Default)]
pub enum CacheFailure {
  /// Return errors if failure mode otherwise unspecified.
  #[default]
  Error,
  /// Create an in-memory cache that is not persistent.
  InMemory,
  /// Create a blackhole cache that ignores writes and returns empty reads.
  Blackhole,
}

/// Configuration SQL and other parameters for a [`CacheDB`].
pub struct CacheDBConfiguration {
  /// SQL to run for a new database.
  pub table_initializer: &'static str,
  /// SQL to run when the version from [`crate::version::deno()`] changes.
  pub on_version_change: &'static str,
  /// Prepared statements to pre-heat while initializing the database.
  pub preheat_queries: &'static [&'static str],
  /// What the cache should do on failure.
  pub on_failure: CacheFailure,
}

impl CacheDBConfiguration {
  fn create_combined_sql(&self) -> String {
    format!(
      "
      PRAGMA journal_mode=TRUNCATE;
      PRAGMA synchronous=NORMAL;
      PRAGMA temp_store=memory;
      PRAGMA page_size=4096;
      PRAGMA mmap_size=6000000;
      PRAGMA optimize;

      CREATE TABLE IF NOT EXISTS info (
        key TEXT PRIMARY KEY,
        value TEXT NOT NULL
      );

      {}
    ",
      self.table_initializer
    )
  }
}

enum ConnectionState {
  Connected(Connection),
  Blackhole,
  Error(Arc<AnyError>),
}

/// A cache database that eagerly initializes itself off-thread, preventing initialization operations
/// from blocking the main thread.
#[derive(Clone)]
pub struct CacheDB {
  // TODO(mmastrac): We can probably simplify our thread-safe implementation here
  conn: Arc<Mutex<OnceCell<ConnectionState>>>,
  path: Option<PathBuf>,
  config: &'static CacheDBConfiguration,
  version: &'static str,
}

impl Drop for CacheDB {
  fn drop(&mut self) {
    // No need to clean up an in-memory cache in an way -- just drop and go.
    let path = match self.path.take() {
      Some(path) => path,
      _ => return,
    };

    // If Deno is panicking, tokio is sometimes gone before we have a chance to shutdown. In
    // that case, we just allow the drop to happen as expected.
    if tokio::runtime::Handle::try_current().is_err() {
      return;
    }

    // For on-disk caches, see if we're the last holder of the Arc.
    let arc = std::mem::take(&mut self.conn);
    if let Ok(inner) = Arc::try_unwrap(arc) {
      // Hand off SQLite connection to another thread to do the surprisingly expensive cleanup
      let inner = inner.into_inner().into_inner();
      if let Some(conn) = inner {
        spawn_blocking(move || {
          drop(conn);
          log::trace!(
            "Cleaned up SQLite connection at {}",
            path.to_string_lossy()
          );
        });
      }
    }
  }
}

impl CacheDB {
  #[cfg(test)]
  pub fn in_memory(
    config: &'static CacheDBConfiguration,
    version: &'static str,
  ) -> Self {
    CacheDB {
      conn: Arc::new(Mutex::new(OnceCell::new())),
      path: None,
      config,
      version,
    }
  }

  pub fn from_path(
    config: &'static CacheDBConfiguration,
    path: PathBuf,
    version: &'static str,
  ) -> Self {
    log::debug!("Opening cache {}...", path.to_string_lossy());
    let new = Self {
      conn: Arc::new(Mutex::new(OnceCell::new())),
      path: Some(path),
      config,
      version,
    };

    new.spawn_eager_init_thread();
    new
  }

  /// Useful for testing: re-create this cache DB with a different current version.
  #[cfg(test)]
  pub(crate) fn recreate_with_version(mut self, version: &'static str) -> Self {
    // By taking the lock, we know there are no initialization threads alive
    drop(self.conn.lock());

    let arc = std::mem::take(&mut self.conn);
    let conn = match Arc::try_unwrap(arc) {
      Err(_) => panic!("Failed to unwrap connection"),
      Ok(conn) => match conn.into_inner().into_inner() {
        Some(ConnectionState::Connected(conn)) => conn,
        _ => panic!("Connection had failed and cannot be unwrapped"),
      },
    };

    Self::initialize_connection(self.config, &conn, version).unwrap();

    let cell = OnceCell::new();
    _ = cell.set(ConnectionState::Connected(conn));
    Self {
      conn: Arc::new(Mutex::new(cell)),
      path: self.path.clone(),
      config: self.config,
      version,
    }
  }

  fn spawn_eager_init_thread(&self) {
    let clone = self.clone();
    debug_assert!(tokio::runtime::Handle::try_current().is_ok());
    spawn_blocking(move || {
      let lock = clone.conn.lock();
      clone.initialize(&lock);
    });
  }

  /// Open the connection in memory or on disk.
  fn actually_open_connection(
    &self,
    path: &Option<PathBuf>,
  ) -> Result<Connection, rusqlite::Error> {
    match path {
      // This should never fail unless something is very wrong
      None => Connection::open_in_memory(),
      Some(path) => Connection::open(path),
    }
  }

  /// Attempt to initialize that connection.
  fn initialize_connection(
    config: &CacheDBConfiguration,
    conn: &Connection,
    version: &str,
  ) -> Result<(), AnyError> {
    let sql = config.create_combined_sql();
    conn.execute_batch(&sql)?;

    // Check the version
    let existing_version = conn
      .query_row(
        "SELECT value FROM info WHERE key='CLI_VERSION' LIMIT 1",
        [],
        |row| row.get::<_, String>(0),
      )
      .optional()?
      .unwrap_or_default();

    // If Deno has been upgraded, run the SQL to update the version
    if existing_version != version {
      conn.execute_batch(config.on_version_change)?;
      let mut stmt = conn
        .prepare("INSERT OR REPLACE INTO info (key, value) VALUES (?1, ?2)")?;
      stmt.execute(["CLI_VERSION", version])?;
    }

    // Preheat any prepared queries
    for preheat in config.preheat_queries {
      drop(conn.prepare_cached(preheat)?);
    }
    Ok(())
  }

  /// Open and initialize a connection.
  fn open_connection_and_init(
    &self,
    path: &Option<PathBuf>,
  ) -> Result<Connection, AnyError> {
    let conn = self.actually_open_connection(path)?;
    Self::initialize_connection(self.config, &conn, self.version)?;
    Ok(conn)
  }

  /// This function represents the policy for dealing with corrupted cache files. We try fairly aggressively
  /// to repair the situation, and if we can't, we prefer to log noisily and continue with in-memory caches.
  fn open_connection(&self) -> Result<ConnectionState, AnyError> {
    // Success on first try? We hope that this is the case.
    let err = match self.open_connection_and_init(&self.path) {
      Ok(conn) => return Ok(ConnectionState::Connected(conn)),
      Err(err) => err,
    };

    if self.path.is_none() {
      // If an in-memory DB fails, that's game over
      log::error!("Failed to initialize in-memory cache database.");
      return Err(err);
    }

    let path = self.path.as_ref().unwrap();

    // There are rare times in the tests when we can't initialize a cache DB the first time, but it succeeds the second time, so
    // we don't log these at a debug level.
    log::trace!(
      "Could not initialize cache database '{}', retrying... ({err:?})",
      path.to_string_lossy(),
    );

    // Try a second time
    let err = match self.open_connection_and_init(&self.path) {
      Ok(conn) => return Ok(ConnectionState::Connected(conn)),
      Err(err) => err,
    };

    // Failed, try deleting it
    log::warn!(
      "Could not initialize cache database '{}', deleting and retrying... ({err:?})",
      path.to_string_lossy()
    );
    if std::fs::remove_file(path).is_ok() {
      // Try a third time if we successfully deleted it
      let res = self.open_connection_and_init(&self.path);
      if let Ok(conn) = res {
        return Ok(ConnectionState::Connected(conn));
      };
    }

    match self.config.on_failure {
      CacheFailure::InMemory => {
        log::error!(
          "Failed to open cache file '{}', opening in-memory cache.",
          path.to_string_lossy()
        );
        Ok(ConnectionState::Connected(
          self.open_connection_and_init(&None)?,
        ))
      }
      CacheFailure::Blackhole => {
        log::error!(
          "Failed to open cache file '{}', performance may be degraded.",
          path.to_string_lossy()
        );
        Ok(ConnectionState::Blackhole)
      }
      CacheFailure::Error => {
        log::error!(
          "Failed to open cache file '{}', expect further errors.",
          path.to_string_lossy()
        );
        Err(err)
      }
    }
  }

  fn initialize<'a>(
    &self,
    lock: &'a MutexGuard<OnceCell<ConnectionState>>,
  ) -> &'a ConnectionState {
    lock.get_or_init(|| match self.open_connection() {
      Ok(conn) => conn,
      Err(e) => ConnectionState::Error(e.into()),
    })
  }

  pub fn with_connection<T: Default>(
    &self,
    f: impl FnOnce(&Connection) -> Result<T, AnyError>,
  ) -> Result<T, AnyError> {
    let lock = self.conn.lock();
    let conn = self.initialize(&lock);

    match conn {
      ConnectionState::Blackhole => {
        // Cache is a blackhole - nothing in or out.
        Ok(T::default())
      }
      ConnectionState::Error(e) => {
        // This isn't ideal because we lose the original underlying error
        let err = AnyError::msg(e.clone().to_string());
        Err(err)
      }
      ConnectionState::Connected(conn) => f(conn),
    }
  }

  #[cfg(test)]
  pub fn ensure_connected(&self) -> Result<(), AnyError> {
    self.with_connection(|_| Ok(()))
  }

  pub fn execute(
    &self,
    sql: &'static str,
    params: impl Params,
  ) -> Result<usize, AnyError> {
    self.with_connection(|conn| {
      let mut stmt = conn.prepare_cached(sql)?;
      let res = stmt.execute(params)?;
      Ok(res)
    })
  }

  pub fn exists(
    &self,
    sql: &'static str,
    params: impl Params,
  ) -> Result<bool, AnyError> {
    self.with_connection(|conn| {
      let mut stmt = conn.prepare_cached(sql)?;
      let res = stmt.exists(params)?;
      Ok(res)
    })
  }

  /// Query a row from the database with a mapping function.
  pub fn query_row<T, F>(
    &self,
    sql: &'static str,
    params: impl Params,
    f: F,
  ) -> Result<Option<T>, AnyError>
  where
    F: FnOnce(&rusqlite::Row<'_>) -> Result<T, AnyError>,
  {
    let res = self.with_connection(|conn| {
      let mut stmt = conn.prepare_cached(sql)?;
      let mut rows = stmt.query(params)?;
      if let Some(row) = rows.next()? {
        let res = f(row)?;
        Ok(Some(res))
      } else {
        Ok(None)
      }
    })?;
    Ok(res)
  }
}

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

  static TEST_DB: CacheDBConfiguration = CacheDBConfiguration {
    table_initializer: "create table if not exists test(value TEXT);",
    on_version_change: "delete from test;",
    preheat_queries: &[],
    on_failure: CacheFailure::InMemory,
  };

  static TEST_DB_BLACKHOLE: CacheDBConfiguration = CacheDBConfiguration {
    table_initializer: "create table if not exists test(value TEXT);",
    on_version_change: "delete from test;",
    preheat_queries: &[],
    on_failure: CacheFailure::Blackhole,
  };

  static TEST_DB_ERROR: CacheDBConfiguration = CacheDBConfiguration {
    table_initializer: "create table if not exists test(value TEXT);",
    on_version_change: "delete from test;",
    preheat_queries: &[],
    on_failure: CacheFailure::Error,
  };

  static BAD_SQL_TEST_DB: CacheDBConfiguration = CacheDBConfiguration {
    table_initializer: "bad sql;",
    on_version_change: "delete from test;",
    preheat_queries: &[],
    on_failure: CacheFailure::InMemory,
  };

  static FAILURE_PATH: &str = "/tmp/this/doesnt/exist/so/will/always/fail";

  #[tokio::test]
  async fn simple_database() {
    let db = CacheDB::in_memory(&TEST_DB, "1.0");
    db.ensure_connected()
      .expect("Failed to initialize in-memory database");

    db.execute("insert into test values (?1)", [1]).unwrap();
    let res = db
      .query_row("select * from test", [], |row| {
        Ok(row.get::<_, String>(0).unwrap())
      })
      .unwrap();
    assert_eq!(Some("1".into()), res);
  }

  #[tokio::test]
  async fn bad_sql() {
    let db = CacheDB::in_memory(&BAD_SQL_TEST_DB, "1.0");
    db.ensure_connected()
      .expect_err("Expected to fail, but succeeded");
  }

  #[tokio::test]
  async fn failure_mode_in_memory() {
    let db = CacheDB::from_path(&TEST_DB, FAILURE_PATH.into(), "1.0");
    db.ensure_connected()
      .expect("Should have created a database");

    db.execute("insert into test values (?1)", [1]).unwrap();
    let res = db
      .query_row("select * from test", [], |row| {
        Ok(row.get::<_, String>(0).unwrap())
      })
      .unwrap();
    assert_eq!(Some("1".into()), res);
  }

  #[tokio::test]
  async fn failure_mode_blackhole() {
    let db = CacheDB::from_path(&TEST_DB_BLACKHOLE, FAILURE_PATH.into(), "1.0");
    db.ensure_connected()
      .expect("Should have created a database");

    db.execute("insert into test values (?1)", [1]).unwrap();
    let res = db
      .query_row("select * from test", [], |row| {
        Ok(row.get::<_, String>(0).unwrap())
      })
      .unwrap();
    assert_eq!(None, res);
  }

  #[tokio::test]
  async fn failure_mode_error() {
    let db = CacheDB::from_path(&TEST_DB_ERROR, FAILURE_PATH.into(), "1.0");
    db.ensure_connected().expect_err("Should have failed");

    db.execute("insert into test values (?1)", [1])
      .expect_err("Should have failed");
    db.query_row("select * from test", [], |row| {
      Ok(row.get::<_, String>(0).unwrap())
    })
    .expect_err("Should have failed");
  }
}