use anyhow::{Result, Context};
use tokio::io::{AsyncReadExt, AsyncWriteExt};
use tokio::net::TcpStream;
use tracing::debug;

/// RCON packet types
const PACKET_LOGIN: i32 = 3;
const PACKET_COMMAND: i32 = 2;
const PACKET_RESPONSE: i32 = 0;

/// A minimal Source RCON client.
pub struct RconClient {
    stream: TcpStream,
    request_id: i32,
}

impl RconClient {
    /// Connect to an RCON server and authenticate.
    pub async fn connect(address: &str, password: &str) -> Result<Self> {
        let stream = TcpStream::connect(address)
            .await
            .context("Failed to connect to RCON")?;

        let mut client = Self {
            stream,
            request_id: 0,
        };

        // Authenticate
        let response = client.send_packet(PACKET_LOGIN, password).await?;
        if response.id == -1 {
            anyhow::bail!("RCON authentication failed");
        }

        debug!(address = %address, "RCON connected and authenticated");
        Ok(client)
    }

    /// Send a command and return the response body.
    pub async fn command(&mut self, cmd: &str) -> Result<String> {
        let response = self.send_packet(PACKET_COMMAND, cmd).await?;
        Ok(response.body)
    }

    async fn send_packet(&mut self, packet_type: i32, body: &str) -> Result<RconPacket> {
        self.request_id += 1;
        let id = self.request_id;

        let body_bytes = body.as_bytes();
        let length = 4 + 4 + body_bytes.len() + 2; // id + type + body + 2 null bytes

        // Write packet
        self.stream.write_i32_le(length as i32).await?;
        self.stream.write_i32_le(id).await?;
        self.stream.write_i32_le(packet_type).await?;
        self.stream.write_all(body_bytes).await?;
        self.stream.write_all(&[0, 0]).await?; // two null terminators
        self.stream.flush().await?;

        // Read response
        let resp_length = self.stream.read_i32_le().await?;
        let resp_id = self.stream.read_i32_le().await?;
        let resp_type = self.stream.read_i32_le().await?;

        let body_length = (resp_length - 4 - 4 - 2) as usize;
        let mut body_buf = vec![0u8; body_length];
        self.stream.read_exact(&mut body_buf).await?;

        // Read two null terminators
        let mut null_buf = [0u8; 2];
        self.stream.read_exact(&mut null_buf).await?;

        let response_body = String::from_utf8_lossy(&body_buf).to_string();

        Ok(RconPacket {
            id: resp_id,
            packet_type: resp_type,
            body: response_body,
        })
    }
}

struct RconPacket {
    id: i32,
    packet_type: i32,
    body: String,
}