use std::{
    io::{BufWriter, Write},
    path::PathBuf,
};

use anyhow::Result;
use futures_util::StreamExt;
use kordophone::APIInterface;
use thiserror::Error;

use kordophone_db::database::Database;

use crate::daemon::events::Event as DaemonEvent;
use crate::daemon::events::Reply;
use crate::daemon::models::Attachment;
use crate::daemon::Daemon;

use std::sync::Arc;
use tokio::sync::mpsc::{Receiver, Sender};
use tokio::sync::Mutex;

use tokio::pin;

mod target {
    pub static ATTACHMENTS: &str = "attachments";
}

#[derive(Debug)]
pub enum AttachmentStoreEvent {
    // Get the attachment info for a given attachment guid.
    // Args: attachment guid, reply channel.
    GetAttachmentInfo(String, Reply<Attachment>),

    // Queue a download for a given attachment guid.
    // Args:
    // - attachment guid
    // - preview: whether to download the preview (true) or full attachment (false)
    QueueDownloadAttachment(String, bool),
}

#[derive(Debug, Error)]
enum AttachmentStoreError {
    #[error("attachment has already been downloaded")]
    AttachmentAlreadyDownloaded,

    #[error("temporary file already exists, assuming download is in progress")]
    DownloadAlreadyInProgress,

    #[error("Client error: {0}")]
    APIClientError(String),
}

#[derive(Debug, Clone)]
struct DownloadRequest {
    guid: String,
    preview: bool,
}

pub struct AttachmentStore {
    store_path: PathBuf,
    database: Arc<Mutex<Database>>,
    daemon_event_sink: Sender<DaemonEvent>,

    event_source: Receiver<AttachmentStoreEvent>,
    event_sink: Option<Sender<AttachmentStoreEvent>>,
}

impl AttachmentStore {
    pub fn get_default_store_path() -> PathBuf {
        let data_dir = Daemon::get_data_dir().expect("Unable to get data path");
        data_dir.join("attachments")
    }

    pub fn new(
        database: Arc<Mutex<Database>>,
        daemon_event_sink: Sender<DaemonEvent>,
    ) -> AttachmentStore {
        let store_path = Self::get_default_store_path();
        log::info!(target: target::ATTACHMENTS, "Attachment store path: {}", store_path.display());

        // Create the attachment store if it doesn't exist
        std::fs::create_dir_all(&store_path)
            .expect("Wasn't able to create the attachment store path");

        let (event_sink, event_source) = tokio::sync::mpsc::channel(100);

        AttachmentStore {
            store_path: store_path,
            database: database,
            daemon_event_sink: daemon_event_sink,
            event_source: event_source,
            event_sink: Some(event_sink),
        }
    }

    pub fn get_event_sink(&mut self) -> Sender<AttachmentStoreEvent> {
        self.event_sink.take().unwrap()
    }

    fn get_attachment(&self, guid: &String) -> Attachment {
        Self::get_attachment_impl(&self.store_path, guid)
    }

    pub fn get_attachment_impl(store_path: &PathBuf, guid: &String) -> Attachment {
        let base_path = store_path.join(guid);
        Attachment {
            guid: guid.to_owned(),
            base_path: base_path,
            metadata: None,
        }
    }

    async fn download_attachment_impl(
        store_path: &PathBuf,
        database: &mut Arc<Mutex<Database>>,
        daemon_event_sink: &Sender<DaemonEvent>,
        guid: &String, 
        preview: bool
    ) -> Result<()> {
        let attachment = Self::get_attachment_impl(store_path, guid);
        
        if attachment.is_downloaded(preview) {
            log::info!(target: target::ATTACHMENTS, "Attachment already downloaded: {}", attachment.guid);
            return Err(AttachmentStoreError::AttachmentAlreadyDownloaded.into());
        }

        let temporary_path = attachment.get_path_for_preview_scratch(preview, true);
        if std::fs::exists(&temporary_path).unwrap_or(false) {
            log::info!(target: target::ATTACHMENTS, "Temporary file already exists: {}, assuming download is in progress", temporary_path.display());
            return Err(AttachmentStoreError::DownloadAlreadyInProgress.into());
        }

        log::info!(target: target::ATTACHMENTS, "Starting download for attachment: {}", attachment.guid);

        let file = std::fs::File::create(&temporary_path)?;
        let mut writer = BufWriter::new(&file);
        let mut client = Daemon::get_client_impl(database).await?;
        let mut stream = client
            .fetch_attachment_data(&attachment.guid, preview)
            .await
            .map_err(|e| AttachmentStoreError::APIClientError(format!("{:?}", e)))?;

        log::trace!(target: target::ATTACHMENTS, "Writing attachment {:?} data to temporary file {:?}", &attachment.guid, &temporary_path);
        while let Some(Ok(data)) = stream.next().await {
            writer.write(data.as_ref())?;
        }
        
        // Flush and sync the temporary file before moving
        writer.flush()?;
        file.sync_all()?;

        // Atomically move the temporary file to the final location
        std::fs::rename(&temporary_path, &attachment.get_path_for_preview_scratch(preview, false))?;

        log::info!(target: target::ATTACHMENTS, "Completed download for attachment: {}", attachment.guid);

        // Send a signal to the daemon that the attachment has been downloaded.
        let event = DaemonEvent::AttachmentDownloaded(attachment.guid.clone());
        daemon_event_sink.send(event).await.unwrap();

        Ok(())
    }

    pub async fn run(&mut self) {
        loop {
            tokio::select! {
                Some(event) = self.event_source.recv() => {
                    log::debug!(target: target::ATTACHMENTS, "Received attachment store event: {:?}", event);

                    match event {
                        AttachmentStoreEvent::QueueDownloadAttachment(guid, preview) => {
                            let attachment = self.get_attachment(&guid);
                            if !attachment.is_downloaded(preview) {
                                let store_path = self.store_path.clone();
                                let mut database = self.database.clone();
                                let daemon_event_sink = self.daemon_event_sink.clone();
                                let _guid = guid.clone();

                                // Spawn a new task here so we don't block incoming queue events. 
                                tokio::spawn(async move {
                                    let result = Self::download_attachment_impl(
                                        &store_path,
                                        &mut database,
                                        &daemon_event_sink,
                                        &_guid,
                                        preview,
                                    ).await;

                                    if let Err(e) = result {
                                        log::error!(target: target::ATTACHMENTS, "Error downloading attachment {}: {}", &_guid, e);
                                    }
                                });

                                log::debug!(target: target::ATTACHMENTS, "Queued download for attachment: {}", &guid);
                            } else {
                                log::info!(target: target::ATTACHMENTS, "Attachment already downloaded: {}", guid);
                            }
                        }

                        AttachmentStoreEvent::GetAttachmentInfo(guid, reply) => {
                            let attachment = self.get_attachment(&guid);
                            reply.send(attachment).unwrap();
                        }
                    }
                }
            }
        }
    }
}