use std::collections::HashMap;
use std::io::ErrorKind;
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::persistence::state_to_file;
use crate::proto_wrapper::{CompleteStatus, ServerProto};

mod config;
mod proto_wrapper;
mod cancellation;
mod persistence;

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 config = Arc::new(config);

    let state = Arc::new(RwLock::new(get_state(&config).await?));
    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 config = config.clone();
        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, config).await;
            println!("Client disconnected: {reason:?}");
        });
    }
}

async fn get_state(config: &Configuration) -> anyhow::Result<State> {
    let result = persistence::state_from_file(config.get_file_path()).await;
    match result {
        Err(ref e) if e.kind() == ErrorKind::NotFound => {
            println!("WARNING: No DB state file found, creating new one");
            Ok(State::new())
        }
        Err(e) => {
            Err(e)?
        }
        Ok(state) => {
            Ok(state)
        }
    }
}

async fn handle_stream(mut stream: TcpStream, state: SharedDbState, tokens: TokenStore, config: Arc<Configuration>) -> 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, config).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, config: Arc<Configuration>) -> 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, &config).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, config: &Arc<Configuration>) -> anyhow::Result<()>
    where
        W: BackendProtoWriter + ProtoFlush + Send,
{
    //  Make sure token is reset before next query
    token.reset();

    let operation = {
        let state = state.read().await;
        let db_schema = state.db_schema();
        parse_and_validate(query, &db_schema)?
    };

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

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

    if need_write {
        let state = state.read().await;
        state_to_file(&state, &config.get_file_path()).await?;
    }

    Ok(())
}