use std::path::PathBuf;
use std::process::{ExitStatus, Stdio};

use anyhow::{Context, Result};
use tokio::io::{AsyncBufReadExt, AsyncRead, BufReader};
use tokio::process::Command;
use tokio::sync::{mpsc, oneshot};

use super::output::{OutputStream, SessionOutputStore};
use super::store::StateStore;
use super::SessionState;

type DbAck = std::result::Result<(), String>;

enum DbMessage {
    UpdateState {
        state: SessionState,
        ack: oneshot::Sender<DbAck>,
    },
    UpdatePid {
        pid: Option<u32>,
        ack: oneshot::Sender<DbAck>,
    },
    AppendOutputLine {
        stream: OutputStream,
        line: String,
        ack: oneshot::Sender<DbAck>,
    },
}

#[derive(Clone)]
struct DbWriter {
    tx: mpsc::UnboundedSender<DbMessage>,
}

impl DbWriter {
    fn start(db_path: PathBuf, session_id: String) -> Self {
        let (tx, rx) = mpsc::unbounded_channel();
        std::thread::spawn(move || run_db_writer(db_path, session_id, rx));
        Self { tx }
    }

    async fn update_state(&self, state: SessionState) -> Result<()> {
        self.send(|ack| DbMessage::UpdateState { state, ack }).await
    }

    async fn update_pid(&self, pid: Option<u32>) -> Result<()> {
        self.send(|ack| DbMessage::UpdatePid { pid, ack }).await
    }

    async fn append_output_line(&self, stream: OutputStream, line: String) -> Result<()> {
        self.send(|ack| DbMessage::AppendOutputLine { stream, line, ack })
            .await
    }

    async fn send<F>(&self, build: F) -> Result<()>
    where
        F: FnOnce(oneshot::Sender<DbAck>) -> DbMessage,
    {
        let (ack_tx, ack_rx) = oneshot::channel();
        self.tx
            .send(build(ack_tx))
            .map_err(|_| anyhow::anyhow!("DB writer channel closed"))?;

        match ack_rx.await {
            Ok(Ok(())) => Ok(()),
            Ok(Err(error)) => Err(anyhow::anyhow!(error)),
            Err(_) => Err(anyhow::anyhow!("DB writer acknowledgement dropped")),
        }
    }
}

fn run_db_writer(
    db_path: PathBuf,
    session_id: String,
    mut rx: mpsc::UnboundedReceiver<DbMessage>,
) {
    let (opened, open_error) = match StateStore::open(&db_path) {
        Ok(db) => (Some(db), None),
        Err(error) => (None, Some(error.to_string())),
    };

    while let Some(message) = rx.blocking_recv() {
        match message {
            DbMessage::UpdateState { state, ack } => {
                let result = match opened.as_ref() {
                    Some(db) => db.update_state(&session_id, &state).map_err(|error| error.to_string()),
                    None => Err(open_error
                        .clone()
                        .unwrap_or_else(|| "Failed to open state store".to_string())),
                };
                let _ = ack.send(result);
            }
            DbMessage::UpdatePid { pid, ack } => {
                let result = match opened.as_ref() {
                    Some(db) => db.update_pid(&session_id, pid).map_err(|error| error.to_string()),
                    None => Err(open_error
                        .clone()
                        .unwrap_or_else(|| "Failed to open state store".to_string())),
                };
                let _ = ack.send(result);
            }
            DbMessage::AppendOutputLine { stream, line, ack } => {
                let result = match opened.as_ref() {
                    Some(db) => db
                        .append_output_line(&session_id, stream, &line)
                        .map_err(|error| error.to_string()),
                    None => Err(open_error
                        .clone()
                        .unwrap_or_else(|| "Failed to open state store".to_string())),
                };
                let _ = ack.send(result);
            }
        }
    }
}

pub async fn capture_command_output(
    db_path: PathBuf,
    session_id: String,
    mut command: Command,
    output_store: SessionOutputStore,
) -> Result<ExitStatus> {
    let db_writer = DbWriter::start(db_path, session_id.clone());

    let result = async {
        let mut child = command
            .stdout(Stdio::piped())
            .stderr(Stdio::piped())
            .spawn()
            .with_context(|| format!("Failed to start process for session {}", session_id))?;

        let stdout = match child.stdout.take() {
            Some(stdout) => stdout,
            None => {
                let _ = child.kill().await;
                let _ = child.wait().await;
                anyhow::bail!("Child stdout was not piped");
            }
        };
        let stderr = match child.stderr.take() {
            Some(stderr) => stderr,
            None => {
                let _ = child.kill().await;
                let _ = child.wait().await;
                anyhow::bail!("Child stderr was not piped");
            }
        };

        let pid = child
            .id()
            .ok_or_else(|| anyhow::anyhow!("Spawned process did not expose a process id"))?;
        db_writer.update_pid(Some(pid)).await?;
        db_writer.update_state(SessionState::Running).await?;

        let stdout_task = tokio::spawn(capture_stream(
            session_id.clone(),
            stdout,
            OutputStream::Stdout,
            output_store.clone(),
            db_writer.clone(),
        ));
        let stderr_task = tokio::spawn(capture_stream(
            session_id.clone(),
            stderr,
            OutputStream::Stderr,
            output_store,
            db_writer.clone(),
        ));

        let status = child.wait().await?;
        stdout_task.await??;
        stderr_task.await??;

        let final_state = if status.success() {
            SessionState::Completed
        } else {
            SessionState::Failed
        };
        db_writer.update_pid(None).await?;
        db_writer.update_state(final_state).await?;

        Ok(status)
    }
    .await;

    if result.is_err() {
        let _ = db_writer.update_pid(None).await;
        let _ = db_writer.update_state(SessionState::Failed).await;
    }

    result
}

async fn capture_stream<R>(
    session_id: String,
    reader: R,
    stream: OutputStream,
    output_store: SessionOutputStore,
    db_writer: DbWriter,
) -> Result<()>
where
    R: AsyncRead + Unpin,
{
    let mut lines = BufReader::new(reader).lines();

    while let Some(line) = lines.next_line().await? {
        db_writer
            .append_output_line(stream, line.clone())
            .await?;
        output_store.push_line(&session_id, stream, line);
    }

    Ok(())
}

#[cfg(test)]
mod tests {
    use std::collections::HashSet;
    use std::env;

    use anyhow::Result;
    use chrono::Utc;
    use tokio::process::Command;
    use uuid::Uuid;

    use super::capture_command_output;
    use crate::session::output::{SessionOutputStore, OUTPUT_BUFFER_LIMIT};
    use crate::session::store::StateStore;
    use crate::session::{Session, SessionMetrics, SessionState};

    #[tokio::test]
    async fn capture_command_output_persists_lines_and_events() -> Result<()> {
        let db_path = env::temp_dir().join(format!("ecc2-runtime-{}.db", Uuid::new_v4()));
        let db = StateStore::open(&db_path)?;
        let session_id = "session-1".to_string();
        let now = Utc::now();

        db.insert_session(&Session {
            id: session_id.clone(),
            task: "stream output".to_string(),
            agent_type: "test".to_string(),
            state: SessionState::Pending,
            pid: None,
            worktree: None,
            created_at: now,
            updated_at: now,
            metrics: SessionMetrics::default(),
        })?;

        let output_store = SessionOutputStore::default();
        let mut rx = output_store.subscribe();
        let mut command = Command::new("/bin/sh");
        command
            .arg("-c")
            .arg("printf 'alpha\\n'; printf 'beta\\n' >&2");

        let status =
            capture_command_output(db_path.clone(), session_id.clone(), command, output_store)
                .await?;

        assert!(status.success());

        let db = StateStore::open(&db_path)?;
        let session = db
            .get_session(&session_id)?
            .expect("session should still exist");
        assert_eq!(session.state, SessionState::Completed);
        assert_eq!(session.pid, None);

        let lines = db.get_output_lines(&session_id, OUTPUT_BUFFER_LIMIT)?;
        let texts: HashSet<_> = lines.iter().map(|line| line.text.as_str()).collect();
        assert_eq!(lines.len(), 2);
        assert!(texts.contains("alpha"));
        assert!(texts.contains("beta"));

        let mut events = Vec::new();
        while let Ok(event) = rx.try_recv() {
            events.push(event.line.text);
        }

        assert_eq!(events.len(), 2);
        assert!(events.iter().any(|line| line == "alpha"));
        assert!(events.iter().any(|line| line == "beta"));

        let _ = std::fs::remove_file(db_path);

        Ok(())
    }
}