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// Copyright Materialize, Inc. and contributors. All rights reserved.
//
// Use of this software is governed by the Business Source License
// included in the LICENSE file.
//
// As of the Change Date specified in that file, in accordance with
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0.

use std::collections::BTreeMap;

use mz_sql::session::user::SYSTEM_USER;
use tracing::{error, info};

use crate::config::SynchronizedParameters;
use crate::session::SessionConfig;
use crate::{AdapterError, Client, SessionClient};

/// A backend client for pushing and pulling [SynchronizedParameters].
///
/// Pulling is required in order to catch concurrent changes before pushing
/// modified values in the [crate::config::system_parameter_sync].
pub struct SystemParameterBackend {
    session_client: SessionClient,
}

impl SystemParameterBackend {
    pub async fn new(client: Client) -> Result<Self, AdapterError> {
        let conn_id = client.new_conn_id()?;
        let session = client.new_session(SessionConfig {
            conn_id,
            user: SYSTEM_USER.name.clone(),
            external_metadata_rx: None,
        });
        let session_client = client.startup(session).await?;
        Ok(Self { session_client })
    }

    /// Push all current values from the given [SynchronizedParameters] that are
    /// marked as modified to the [SystemParameterBackend] and reset their
    /// modified status.
    pub async fn push(&mut self, params: &mut SynchronizedParameters) {
        for param in params.modified() {
            let mut vars = BTreeMap::new();
            vars.insert(param.name.clone(), param.value.clone());
            match self.session_client.set_system_vars(vars).await {
                Ok(()) => {
                    info!(name = param.name, value = param.value, "sync parameter");
                }
                Err(error) => {
                    error!(
                        name = param.name,
                        value = param.value,
                        "cannot update system variable: {}",
                        error
                    );
                }
            }
        }
    }

    /// Pull the current values for all [SynchronizedParameters] from the
    /// [SystemParameterBackend].
    pub async fn pull(&mut self, params: &mut SynchronizedParameters) {
        match self.session_client.get_system_vars().await {
            Ok(vars) => {
                for (name, value) in vars {
                    params.modify(&name, &value);
                }
            }
            Err(error) => {
                error!("cannot execute `SHOW ALL` query: {}", error)
            }
        }
    }
}