/* This file is part of DarkFi (https://dark.fi)
 *
 * Copyright (C) 2020-2026 Dyne.org foundation
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

use std::{
    collections::HashSet,
    path::{Path, PathBuf},
    process::exit,
    sync::{
        atomic::{AtomicBool, Ordering},
        Arc,
    },
};

use arg::Args;
use async_trait::async_trait;
use darkfi::{
    blockchain::BlockInfo,
    rpc::{
        client::RpcClient,
        jsonrpc::{ErrorCode, JsonError, JsonRequest, JsonResult},
        server::{listen_and_serve, RequestHandler},
        settings::RpcSettings,
    },
    system::{msleep, CondVar, Publisher, PublisherPtr, StoppableTask, StoppableTaskPtr},
    util::{encoding::base64, path::expand_path},
    verbose, Error, Result, ANSI_LOGO,
};
use darkfi_serial::deserialize_async;
use smol::{
    future,
    lock::{Mutex, MutexGuard},
    Executor,
};
use tapes::{TapeOpenOptions, Tapes};
use tinyjson::JsonValue;
use tracing::{debug, error, info, warn};
use url::Url;

/// Database interfaces
mod db;
use db::{DifficultyIndex, TapesDatabase};
/// JSON-RPC server methods
mod rpc;

const ABOUT: &str =
    concat!("explorer ", env!("CARGO_PKG_VERSION"), '\n', env!("CARGO_PKG_DESCRIPTION"));

const USAGE: &str = r#"
Usage: explorer [OPTIONS]

Options:
  -e <endpoint>  darkfid JSON-RPC endpoint (default: tcp://127.0.0.1:18345)
  -d <path>      Path to database (default: ~/.local/share/darkfi/explorer/db)
  -r <height>    Revert database to <height>
  -h             Show this help
"#;

fn usage() {
    print!("{ANSI_LOGO}{ABOUT}\n{USAGE}");
}

pub struct Explorer {
    synced: AtomicBool,
    synced_notifier: Arc<CondVar>,
    _sled_db: sled::Db,
    header_indices: sled::Tree,
    tx_indices: sled::Tree,
    contracts: sled::Tree,
    stats: sled::Tree,

    tapes_db: Tapes,
    _tapes_options: TapeOpenOptions,
    database: TapesDatabase,

    rpc_sub: StoppableTaskPtr,
    rpc_sub_handler: StoppableTaskPtr,
    blocks_publisher: PublisherPtr<JsonResult>,

    rpc_connections: Mutex<HashSet<StoppableTaskPtr>>,
}

struct RpcHandler;

#[async_trait]
impl RequestHandler<RpcHandler> for Explorer {
    async fn handle_request(&self, req: JsonRequest) -> JsonResult {
        debug!(target: "explorer::rpc", "--> {}", req.stringify().unwrap());

        match req.method.as_str() {
            "current_difficulty" => self.rpc_current_difficulty(req.id, req.params).await,
            "current_height" => self.rpc_current_height(req.id, req.params).await,
            "latest_blocks" => self.rpc_latest_blocks(req.id, req.params).await,
            "get_block" => self.rpc_get_block(req.id, req.params).await,
            "get_tx" => self.rpc_get_tx(req.id, req.params).await,
            "search" => self.rpc_search(req.id, req.params).await,
            "get_hashrate" => self.rpc_get_hashrate(req.id, req.params).await,
            "get_contract" => self.rpc_get_contract(req.id, req.params).await,
            "list_contracts" => self.rpc_list_contracts(req.id, req.params).await,
            "contract_count" => self.rpc_contract_count(req.id, req.params).await,
            "get_stats" => self.rpc_get_stats(req.id, req.params).await,
            _ => JsonError::new(ErrorCode::MethodNotFound, None, req.id).into(),
        }
    }

    async fn connections_mut(&self) -> MutexGuard<'life0, HashSet<StoppableTaskPtr>> {
        self.rpc_connections.lock().await
    }
}

impl Explorer {
    fn new(sled_path: &Path, tapes_db_path: &Path, tapes_path: &Path) -> Result<Self> {
        info!(target: "explorer::new", "Opening sled trees");
        let sled_db = sled::open(sled_path)?;
        let header_indices = sled_db.open_tree("header_indices")?;
        let tx_indices = sled_db.open_tree("tx_indices")?;
        let contracts = sled_db.open_tree("contracts")?;
        let stats = sled_db.open_tree("stats")?;

        info!(target: "explorer::new", "Opening tapes");
        std::fs::create_dir_all(tapes_db_path)?;
        std::fs::create_dir_all(tapes_path)?;
        let tapes_db = Tapes::open(tapes_db_path)?;
        let tapes_options =
            TapeOpenOptions { top_cache_size: 64 * 1024, dir: tapes_path.to_path_buf() };

        let database = Self::open_tapes(&tapes_db, &tapes_options)?;

        Ok(Self {
            synced: AtomicBool::new(false),
            synced_notifier: Arc::new(CondVar::new()),
            _sled_db: sled_db,
            header_indices,
            tx_indices,
            contracts,
            stats,
            tapes_db,
            _tapes_options: tapes_options,
            database,
            rpc_sub: StoppableTask::new(),
            rpc_sub_handler: StoppableTask::new(),
            blocks_publisher: Publisher::new(),
            rpc_connections: Mutex::new(HashSet::new()),
        })
    }

    async fn handle_block_sub(&self, rpc_endpoint: Url, ex: Arc<Executor<'_>>) -> Result<()> {
        info!(
            target: "explorer::handle_block_sub",
            "Started block subscription, waiting until blockchain is synced",
        );
        let block_subscription = self.blocks_publisher.clone().subscribe().await;
        self.synced_notifier.wait().await;
        info!(
            target: "explorer::handle_block_sub",
            "Blockchain synced, now waiting for new blocks...",
        );

        loop {
            // Handle the new block. We get a JsonResult, so also handle
            // any errors that might arise.
            let block_notification = block_subscription.receive().await;
            info!(target: "explorer::handle_block_sub", "Got new block notification!");

            match block_notification {
                JsonResult::Notification(notification) => {
                    for param in notification.params.get::<Vec<JsonValue>>().unwrap() {
                        // Deserialize base64 block
                        let block_bytes = base64::decode(param.get::<String>().unwrap()).unwrap();
                        let block: BlockInfo = deserialize_async(&block_bytes).await.unwrap();
                        let incoming_height = block.header.height as u64;

                        info!(target: "explorer::handle_block_sub", "Height {}", incoming_height);

                        // Check if we need to reorg or sync
                        let current_height = self.get_height().ok().flatten().unwrap_or(0);

                        if incoming_height > current_height + 1 {
                            // Sync needed: we have at least one missing block
                            info!(
                                target: "explorer::handle_block_sub",
                                "Sync needed! Incoming height {} > current_height {}.",
                                incoming_height, current_height,
                            );
                            self.synced.store(false, Ordering::SeqCst);
                            self.sync_blockchain(
                                rpc_endpoint.clone(),
                                current_height + 1,
                                incoming_height - 1,
                                ex.clone(),
                            )
                            .await?;
                            self.synced.store(true, Ordering::SeqCst);
                            info!(
                                target: "explorer::handle_block_sub",
                                "Synced to height {}", incoming_height - 1,
                            );
                        }

                        if incoming_height <= current_height {
                            // Reorg needed: incoming block is at or before our current height
                            let blocks_to_revert = current_height - incoming_height + 1;
                            info!(
                                target: "explorer::handle_block_sub",
                                "Reorg detected! Incoming height {} <= current height {}. Reverting {} blocks.",
                                incoming_height, current_height, blocks_to_revert
                            );

                            if let Err(e) = self.revert_to_height(incoming_height - 1).await {
                                error!(
                                    target: "explorer::handle_block_sub",
                                    "Failed to revert blocks during reorg: {e}",
                                );
                                // Exit from this task if there's an error.
                                // It'll let us inspect the db and what happened.
                                return Err(e.into())
                            }
                        }

                        // Get difficulty
                        let rpc_client =
                            RpcClient::new(rpc_endpoint.clone(), ex.clone()).await.unwrap();

                        let req = JsonRequest::new(
                            "blockchain.get_difficulty",
                            JsonValue::Array(vec![(block.header.height as f64).into()]),
                        );
                        let rep = rpc_client.request(req).await?;
                        rpc_client.stop().await;

                        let params = rep.get::<Vec<JsonValue>>().unwrap();
                        let difficulty = *params[0].get::<f64>().unwrap() as u64;
                        let cumulative = *params[1].get::<f64>().unwrap() as u64;

                        let diff = DifficultyIndex { difficulty, cumulative };

                        self.append_block(&block, &diff).await.unwrap();
                    }
                }
                x => unreachable!("{:?}", x),
            }
        }
    }

    async fn sync_blockchain(
        &self,
        rpc_endpoint: Url,
        from_height: u64,
        to_height: u64,
        ex: Arc<Executor<'_>>,
    ) -> Result<()> {
        if from_height >= to_height {
            return Ok(())
        }

        info!(
            target: "explorer::sync_blockchain",
            "Started blockchain sync from_height={from_height} to_height={to_height}...",
        );
        let rpc_client = Arc::new(RpcClient::new(rpc_endpoint, ex.clone()).await?);

        for height in from_height..=to_height {
            info!(target: "explorer::sync_blockchain", "Requesting block at height {height}");

            // Get block
            let req = JsonRequest::new(
                "blockchain.get_block",
                JsonValue::Array(vec![(height as f64).into()]),
            );
            let rep = rpc_client.request(req).await?;

            let param = rep.get::<String>().unwrap();
            let bytes = base64::decode(param).unwrap();
            let block: BlockInfo = deserialize_async(&bytes).await?;

            // Get difficulty
            let req = JsonRequest::new(
                "blockchain.get_difficulty",
                JsonValue::Array(vec![(height as f64).into()]),
            );
            let rep = rpc_client.request(req).await?;

            let params = rep.get::<Vec<JsonValue>>().unwrap();
            let difficulty = *params[0].get::<f64>().unwrap() as u64;
            let cumulative = *params[1].get::<f64>().unwrap() as u64;

            let diff = DifficultyIndex { difficulty, cumulative };
            self.append_block(&block, &diff).await?;
        }

        rpc_client.stop().await;
        Ok(())
    }
}

async fn realmain(
    rpc_endpoint: Url,
    db_path: PathBuf,
    revert_to: u64,
    ex: Arc<Executor<'static>>,
) -> Result<()> {
    let explorer = Arc::new(Explorer::new(
        &db_path.join("sled_db"),
        &db_path.join("tapes_metadata"),
        &db_path.join("tapes"),
    )?);

    // First we should subscribe to new blocks and queue them to apply
    // after we sync. For this we create a new longterm background task
    // that will handle incoming blocks. It will wait until the blockchain
    // is synced and then proceed to process them.
    let explorer_ = Arc::clone(&explorer);
    let ex_ = ex.clone();
    let rpc_endpoint_ = rpc_endpoint.clone();
    explorer.rpc_sub_handler.clone().start(
        async move { explorer_.handle_block_sub(rpc_endpoint_, ex_).await },
        |_| async {},
        Error::RpcServerStopped,
        ex.clone(),
    );

    // Then we subscribe to darkfid's RPC to get new blocks. We should first
    // fetch the current height, so we know how far to sync. Then any blocks
    // that come after that should be queued in the `blocks_publisher`.
    info!(target: "explorer", "Connecting to darkfid RPC...");
    let rpc_client = loop {
        let Ok(rpc_client) = RpcClient::new(rpc_endpoint.clone(), ex.clone()).await else {
            msleep(500).await;
            continue
        };

        break rpc_client
    };

    let req = JsonRequest::new("blockchain.last_confirmed_block", JsonValue::Array(vec![]));
    let rep = rpc_client.request(req).await?;
    rpc_client.stop().await;
    let params = rep.get::<Vec<JsonValue>>().unwrap();
    let confirmed_height = *params[0].get::<f64>().unwrap() as u64;

    // Now create the subscription task.
    let explorer_ = Arc::clone(&explorer);
    let ex_ = Arc::clone(&ex);
    let rpc_endpoint_ = rpc_endpoint.clone();
    explorer.rpc_sub.clone().start(
        async move {
            loop {
                let rpc_client = match RpcClient::new(rpc_endpoint_.clone(), ex_.clone()).await {
                    Ok(v) => v,
                    Err(e) => {
                        warn!(target: "explorer::subscribe_blocks", "darkfid RPC connection lost ({e})), retrying...");
                        msleep(500).await;
                        continue
                    }
                };

                info!(target: "explorer::subscribe_blocks", "Connected to darkfid RPC");
                let req = JsonRequest::new("blockchain.subscribe_blocks", JsonValue::Array(vec![]));

                if let Err(e) = rpc_client.subscribe(req, explorer_.blocks_publisher.clone()).await {
                    rpc_client.stop().await;
                    warn!(target: "explorer::subscribe_blocks", "darkfid RPC connection lost ({e}), retrying...");
                    msleep(500).await;
                }
            }
        },
        |_| async {},
        Error::RpcServerStopped,
        ex.clone(),
    );

    // Once the tasks are set up, we'll now perform a manual sync up to
    // the last confirmed height. This will create a new RPC client that
    // is going to request and parse all the necessary blocks, and then
    // apply them to the databases.
    let mut sync_from = explorer.get_height()?.unwrap_or(0);
    if sync_from > 0 {
        // If we're not syncing from genesis, account for it.
        sync_from += 1;
    }

    explorer.sync_blockchain(rpc_endpoint.clone(), sync_from, confirmed_height, ex.clone()).await?;
    explorer.synced.store(true, Ordering::SeqCst);
    explorer.synced_notifier.notify();

    if revert_to > 0 {
        info!("Reverting to {}", revert_to);
        explorer.revert_to_height(revert_to).await?;
    }

    // Start up an RPC server that can be queried for data.
    // This normally serves the data to the Python website frontend.
    info!(target: "explorer", "Starting JSONRPC server");
    let rpc_settings = RpcSettings::default();
    listen_and_serve(rpc_settings, explorer, None, ex.clone()).await?;

    Ok(())
}

fn main() -> Result<()> {
    let mut hflag = false;
    let mut evalue = "tcp://127.0.0.1:18345".to_string();
    let mut dvalue = "~/.local/share/darkfi/explorer/db".to_string();
    let mut rvalue = "0".to_string();
    let mut verbose = 0;

    {
        let mut args = Args::new().with_cb(|args, flag| match flag {
            'e' => evalue = args.eargf().to_string(),
            'd' => dvalue = args.eargf().to_string(),
            'r' => rvalue = args.eargf().to_string(),
            'v' => verbose += 1,
            _ => hflag = true,
        });

        args.parse();
    }

    let revert_to: u64 = rvalue.parse()?;

    if hflag {
        usage();
        exit(1);
    }

    let rpc_endpoint: Url = match evalue.parse() {
        Ok(v) => v,
        Err(e) => {
            println!("Error parsing RPC endpoint: {e}");
            usage();
            exit(1);
        }
    };

    let db_path: PathBuf = match expand_path(&dvalue) {
        Ok(v) => v,
        Err(e) => {
            println!("Error parsing DB path: {e}");
            usage();
            exit(1);
        }
    };

    let ex = Arc::new(Executor::new());
    let (signal, shutdown) = async_channel::unbounded::<()>();

    darkfi::util::logger::setup_logging(verbose, None)?;

    info!(target: "explorer", "RPC Endpoint: {}", evalue);
    info!(target: "explorer", "DB Path: {}", dvalue);
    verbose!(target: "explorer", "Log Level: {}", verbose);

    let (_, result) = easy_parallel::Parallel::new()
        // Run four executor threads
        .each(0..4, |_| future::block_on(ex.run(shutdown.recv())))
        // Run the main future on the current thread
        .finish(|| {
            future::block_on(async {
                realmain(rpc_endpoint, db_path, revert_to, ex.clone()).await?;
                drop(signal);
                Ok::<(), darkfi::Error>(())
            })
        });

    result
}