use clap::Parser;
use futures_util::StreamExt;
use std::sync::Arc;
use tokio::io::AsyncBufReadExt;
use tokio::sync::RwLock;
use tokio::sync::mpsc;
use tokio_util::io::StreamReader;

#[derive(Parser)]
#[command(name = "mcp-memory-stub", author, version, about = "Antigravity MCP Memory Stub / Proxy", long_about = None)]
struct Cli {
    /// Target URL for the stub to proxy messages to
    #[arg(long, default_value = "http://localhost:3000")]
    target: String,
    /// Optional command to execute if the target server is unreachable
    #[arg(long)]
    wake_cmd: Option<String>,
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let cli = Cli::parse();
    let rt = tokio::runtime::Runtime::new()?;
    rt.block_on(async {
        let (msg_tx, mut msg_rx) = mpsc::channel::<String>(100);
        let (shutdown_tx, mut shutdown_rx) = mpsc::channel::<()>(1);

        tokio::task::spawn_blocking(move || {
            let stdin = std::io::stdin();
            let mut handle = stdin.lock();
            let mut buffer = String::new();
            while let Ok(bytes) = std::io::BufRead::read_line(&mut handle, &mut buffer) {
                if bytes == 0 {
                    break;
                }
                let _ = msg_tx.blocking_send(buffer.clone());
                buffer.clear();
            }
            let _ = shutdown_tx.blocking_send(());
        });

        let target_url = cli.target;
        let post_url = Arc::new(RwLock::new(String::new()));
        let post_url_clone = Arc::clone(&post_url);

        let client = reqwest::Client::builder().build()?;

        tokio::spawn(async move {
            while let Some(msg) = msg_rx.recv().await {
                let mut attempts = 0;
                loop {
                    let url = post_url_clone.read().await.clone();
                    if !url.is_empty() {
                        let res = client
                            .post(&url)
                            .header("Accept", "application/json, text/event-stream")
                            .header("Content-Type", "application/json")
                            .body(msg.clone())
                            .send()
                            .await;

                        if let Ok(resp) = res { if resp.status().is_success() { break; } }
                    }
                    tokio::time::sleep(tokio::time::Duration::from_millis(10)).await;
                    attempts += 1;
                    if attempts % 10 == 0 {
                        eprintln!("[PROXY] Waiting for server to accept messages...");
                    }
                }
            }
        });

        let wake_cmd = cli.wake_cmd;
        loop {
            if shutdown_rx.try_recv().is_ok() {
                break;
            }

            let sse_url = format!("{}/sse", target_url);
            let client = reqwest::Client::builder().build()?;

            match client
                .get(&sse_url)
                .header("Accept", "text/event-stream")
                .send()
                .await
            {
                Ok(resp) => {
                    if resp.status() == reqwest::StatusCode::GONE {
                        eprintln!("[PROXY] Target gone, exiting.");
                        break;
                    }

                    let stream = resp.bytes_stream().map(|res| {
                        res.map_err(std::io::Error::other)
                    });
                    let mut reader = tokio::io::BufReader::new(StreamReader::new(stream));
                    let mut line = String::new();
                    let mut is_message = false;
                    let mut is_endpoint = false;

                    loop {
                        tokio::select! {
                            _ = shutdown_rx.recv() => {
                                return Ok(()); // Stdin closed, exit entirely
                            }
                            res = reader.read_line(&mut line) => {
                                match res {
                                    Ok(bytes) => {
                                        if bytes == 0 { break; }
                                        let trimmed = line.trim();
                                        if trimmed.starts_with("event: message") {
                                            is_message = true;
                                            is_endpoint = false;
                                        } else if trimmed.starts_with("event: endpoint") {
                                            is_endpoint = true;
                                            is_message = false;
                                        } else if let Some(stripped) = trimmed.strip_prefix("data: ") {
                                            if is_message {
                                                println!("{}", stripped);
                                                is_message = false;
                                            } else if is_endpoint {
                                                let mut p = post_url.write().await;
                                                *p = format!("{}{}", target_url, stripped);
                                                is_endpoint = false;
                                            }
                                        }
                                        line.clear();
                                    }
                                    Err(_) => break,
                                }
                            }
                        }
                    }
                    *post_url.write().await = String::new();
                    tokio::time::sleep(tokio::time::Duration::from_millis(10)).await;
                }
                Err(_) => {
                    if let Some(ref cmd) = wake_cmd {
                        let parts: Vec<&str> = cmd.split_whitespace().collect();
                        if !parts.is_empty() {
                            let _ = std::process::Command::new(parts[0])
                                .args(&parts[1..])
                                .spawn();
                        }
                    }
                    tokio::time::sleep(tokio::time::Duration::from_secs(1)).await;
                }
            }
        }
        Ok(())
    })
}