use std::collections::HashMap;
use std::sync::Arc;

use clap::Parser;
use tokio::io::{BufReader, BufWriter};
use tokio::net::{TcpListener, TcpStream};
use tokio::sync::{Mutex, RwLock};

use minisql::interpreter::{Response, State};
use parser::parse_and_validate;
use proto::handshake::errors::ServerHandshakeError;
use proto::handshake::request::HandshakeRequest;
use proto::handshake::response::HandshakeResponse;
use proto::handshake::server::do_server_handshake;
use proto::message::frontend::FrontendMessage;
use proto::reader::frontend::FrontendProtoReader;
use proto::reader::protoreader::ProtoReader;
use proto::writer::backend::BackendProtoWriter;
use proto::writer::protowriter::{ProtoFlush, ProtoWriter};

use crate::cancellation::ResetCancelToken;
use crate::config::Configuration;
use crate::proto_wrapper::{CompleteStatus, ServerProto};

mod config;
mod proto_wrapper;
mod cancellation;

type TokenStore = Arc<Mutex<HashMap<(i32, i32), ResetCancelToken>>>;
type SharedDbState = Arc<RwLock<State>>;

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let config = Configuration::parse();

    let state = Arc::new(RwLock::new(State::new()));
    let tokens = Arc::new(Mutex::new(HashMap::<(i32, i32), ResetCancelToken>::new()));

    let addr = config.get_socket_address();
    let listener = TcpListener::bind(&addr).await?;
    println!("Server started at {addr}");

    loop {
        let state = state.clone();
        let tokens = tokens.clone();

        let (socket, _) = listener.accept().await?;
        println!("New client connected: {}", socket.peer_addr()?);
        tokio::spawn(async move {
            let reason = handle_stream(socket, state, tokens).await;
            println!("Client disconnected: {reason:?}");
        });
    }
}

async fn handle_stream(mut stream: TcpStream, state: SharedDbState, tokens: TokenStore) -> anyhow::Result<()> {
    let (reader, writer) = stream.split();
    let mut writer = ProtoWriter::new(BufWriter::new(writer));
    let mut reader = ProtoReader::new(BufReader::new(reader), 1024);

    // Create a token with random PID and key
    let (pid, key, token) = create_token(&tokens).await?;

    //  Handle handshake
    let response = HandshakeResponse::new("minisql", pid, key);
    let request = do_server_handshake(&mut writer, &mut reader, response).await;

    let result = match request {
        Ok(req) => handle_connection(&mut reader, &mut writer, req, state, token).await,
        Err(ServerHandshakeError::IsCancelRequest(cancel)) => handle_cancellation(cancel.pid, cancel.secret, &tokens).await,
        Err(e) => Err(anyhow::anyhow!("Error during handshake: {:?}", e)),
    };

    // Release cancellation token
    let mut tokens = tokens.lock().await;
    tokens.remove(&(pid, key));

    result
}

fn random_pid_key() -> (i32, i32) {
    let pid = rand::random::<i32>();
    let key = rand::random::<i32>();
    (pid, key)
}

async fn create_token(tokens: &TokenStore) -> anyhow::Result<(i32, i32, ResetCancelToken)> {
    let token = ResetCancelToken::new();
    let mut tokens = tokens.lock().await;
    loop {
        let pid_key = random_pid_key();
        if !tokens.contains_key(&pid_key) {
            tokens.insert(pid_key, token.clone());

            let (pid, key) = pid_key;
            return Ok((pid, key, token));
        }
    }
}

async fn handle_cancellation(pid: i32, key: i32, tokens: &TokenStore) -> anyhow::Result<()> {
    println!("Cancel request, PID: {}, Key: {}", pid, key);

    let tokens = tokens.lock().await;
    let token = tokens.get(&(pid, key));
    match token {
        Some(t) => t.cancel(),
        None => return Err(anyhow::anyhow!("Invalid PID and Key cancel combination")),
    }

    Ok(())
}

async fn handle_connection<R, W>(reader: &mut R, writer: &mut W, request: HandshakeRequest, state: SharedDbState, token: ResetCancelToken) -> anyhow::Result<()>
where
    R: FrontendProtoReader + Send,
    W: BackendProtoWriter + ProtoFlush + Send,
{
    println!("Client connected: {:?}", request);

    loop {
        let next: FrontendMessage = reader.read_proto().await?;

        match next {
            FrontendMessage::Terminate => {
                break;
            }
            FrontendMessage::Query(data) => {
                let result = handle_query(writer, &state, data.query.into(), &token).await;
                match result {
                    Ok(_) => {}
                    Err(e) => {
                        writer.write_error_message(&e.to_string()).await?
                    }
                }
                writer.write_ready_for_query().await?;
            }
        }
        writer.flush().await?;
    }

    Ok(())
}

async fn handle_query<W>(writer: &mut W, state: &SharedDbState, query: String, token: &ResetCancelToken) -> anyhow::Result<()>
where
    W: BackendProtoWriter + ProtoFlush + Send,
{
    let operation = {
        let state = state.read().await;
        let db_schema = state.db_schema();
        parse_and_validate(query, &db_schema)?
    };

    let mut state = state.write().await;
    let response = state.interpret(operation)?;

    match response {
        Response::Deleted(i) => writer.write_command_complete(CompleteStatus::Delete(i)).await?,
        Response::Inserted => writer.write_command_complete(CompleteStatus::Insert { oid: 0, rows: 1 }).await?,
        Response::Selected(schema, mut rows) => {
            match rows.next() {
                Some(row) => {
                    writer.write_table_header(&schema, &row).await?;
                    writer.write_table_row(&row).await?;

                    let mut sent_rows = 1;
                    for row in rows {
                        sent_rows += 1;
                        writer.write_table_row(&row).await?;
                        if token.is_canceled() {
                            token.reset();
                            break;
                        }
                    }

                    writer.write_command_complete(CompleteStatus::Select(sent_rows)).await?;
                }
                _ => {
                    writer.write_command_complete(CompleteStatus::Select(0)).await?;
                }
            }
        }
        _ => {}
    }

    Ok(())
}