use std::collections::{HashMap, HashSet};
use std::{io};
use std::convert::TryFrom;
use std::fs::File;
use std::future::Future;
use std::path::{PathBuf};
use std::io::{BufReader, BufWriter, ErrorKind, Read, Write};
use std::sync::Arc;
use std::time::Duration;
use anyhow::anyhow;
use futures::{StreamExt, TryStreamExt};
use kuchiki::iter::NodeIterator;
use serde_json::to_writer;
use tokio::net::TcpStream;
use tokio_rustls::client::TlsStream;
use tokio_rustls::rustls::{ClientConfig, RootCertStore};
use tokio_rustls::rustls::pki_types::ServerName;
use crate::config::Config;
use crate::{add_email};
use tokio::task;
use tokio::time::sleep;

#[cfg(not(target_os = "wasi"))]
use async_imap::{Client, Session};
#[cfg(not(target_os = "wasi"))]
use async_imap::extensions::idle::IdleResponse::NewData;

#[cfg(target_os = "wasi")]
use async_imap_wasi::{Client, Session};
#[cfg(target_os = "wasi")]
use async_imap_wasi::extensions::idle::IdleResponse::NewData;

/// create TLS connect with the IMAP server
pub async fn connect_to_imap() -> anyhow::Result<Client<TlsStream<TcpStream>>>{
    let mut root_cert_store = RootCertStore::empty();
    root_cert_store.extend(webpki_roots::TLS_SERVER_ROOTS.iter().cloned());
    let config = ClientConfig::builder()
        .with_root_certificates(root_cert_store)
        .with_no_client_auth();
    let connector = tokio_rustls::TlsConnector::from(Arc::new(config));
    let dnsname = ServerName::try_from(Config::global().imap_domain.clone()).unwrap();

    let stream = TcpStream::connect(format!("{}:{}", Config::global().imap_domain.clone(), Config::global().imap_port.clone())).await?;
    let stream = connector.connect(dnsname, stream).await?;
    
    #[cfg(not(target_os = "wasi"))]
    let client = async_imap::Client::new(stream);
    #[cfg(target_os = "wasi")]
    let client = async_imap_wasi::Client::new(stream);
    
    Ok(client)
}

/// download all emails from the server and persist them
pub async fn download_email_from_imap() -> anyhow::Result<Vec<(u32, PathBuf)>>{
    let mut client = connect_to_imap().await?;
    let mut session_result = client.login(Config::global().username.clone(), Config::global().password.clone()).await;
    let mut session = match session_result {
        Ok(session) => {session}
        Err(_) => {return Err(anyhow!("Unable to login to IMAP server"))}
    };
    
    let mut stored_paths: Vec<(u32, PathBuf)> = vec![];
    match list_imap_folders(&mut session).await { 
        Ok(folders) => {
            for folder in folders {
                println!("Start downloading {}", folder.clone());
                let new_paths = match fetch_and_store_emails(&mut session, folder.clone()).await {
                    Ok(paths) => {
                        println!("Emails fetched and stored successfully for {}.", folder);
                        paths
                    },
                    Err(err) => {
                        eprintln!("Error during email fetching and storing: {}", err);
                        vec![]
                    }
                };
                stored_paths.extend(new_paths);
            }
        } 
        Err(_) => {return Err(anyhow!("Unable to retrieve folders from IMAP server"))}
    }
    
    // Logout from the IMAP session
    session.logout().await.expect("Unable to logout");

    Ok(stored_paths)
}

/// return Vec with all mailboxes
pub async fn list_imap_folders(session: &mut Session<TlsStream<TcpStream>>) -> anyhow::Result<Vec<String>> {
    let mut folders: Vec<String> = vec![];
    let mut folders_stream = session.list(None, Some("*")).await?;
    while let Some(folder_result) = folders_stream.next().await {
        match folder_result {
            Ok(folder) => {
                folders.push(folder.name().to_string())
            }
            Err(_) => {}
        }
    }
    Ok(folders)
}

/// download all emails from one mailbox 
pub async fn fetch_and_store_emails(session: &mut Session<TlsStream<TcpStream>>, list: String) -> anyhow::Result<Vec<(u32, PathBuf)>> {
    session.select(list.clone()).await?;

    // Create directories for maildir
    std::fs::create_dir_all(Config::global().maildir.clone().join(list.clone()).join("new"))
        .expect(&*("Unable to create 'new' directory in ".to_owned() + &*list.clone()));
    std::fs::create_dir_all(Config::global().maildir.clone().join(list.clone()).join("cur"))
        .expect(&*("Unable to create 'cur' directory in ".to_owned() + &*list.clone()));
    std::fs::create_dir_all(Config::global().maildir.clone().join(list.clone()).join("tmp"))
        .expect(&*("Unable to create 'tmp' directory in ".to_owned() + &*list.clone()));

    let uids_path = Config::global().maildir.clone().join(".uids.json");

    let uids_server = session.uid_search("ALL").await.unwrap();
    let uids_local = read_local_uids(uids_path.clone()).unwrap();
    let mut stored_paths: Vec<(u32, PathBuf)> = vec![];

    for uid in uids_server {
        if let Some(uids) = uids_local.get(&list) {
            if uids.contains(&uid.to_string()) {
                continue;
            }
        }

        let mut messages_stream = session.uid_fetch(uid.to_string(), "(UID BODY[])").await?;
        let mut message = None;
        while let Some(message_result) = messages_stream.next().await {
            match message_result {
                Ok(message_ok) => {
                    message = Some(message_ok);
                }
                Err(_) => {
                    return Err(anyhow!("Unable to retrieve message"));
                }
            }
        }

        if let Some(msg) = &message {
            if let Some(body) = msg.body() {
                let mail_file = store(Config::global().maildir.clone().join(list.clone()), uid.clone().to_string(), "new".to_string(), body, "");
                match mail_file {
                    Ok(file) => stored_paths.push((uid.to_string().parse().unwrap(), file)),
                    Err(e) => eprintln!("Failed to store email: {}", e),
                }
            } else {
                eprintln!("Failed to retrieve email body");
            }

            if let Some(uid) = msg.uid {
                update_local_uids(uid.to_string(), list.clone(), uids_path.clone())
                    .expect("Cannot write uid to .uids.json");
            }

            println!("Downloaded message with UID {}", uid.to_string());
        } else {
            return Err(anyhow!("No message found with the given UID"));
        }
    }

    Ok(stored_paths)
}

/// read uids that have been already downloaded
fn read_local_uids(uids_path: PathBuf) -> anyhow::Result<HashMap<String, HashSet<String>>> {
    let file = match File::open(&uids_path) {
        Ok(file) => file,
        Err(_) => return Ok(HashMap::new()), // Propagate other errors
    };

    let mut reader = BufReader::new(file);
    let mut content = String::new();
    reader.read_to_string(&mut content)?;

    if content.trim().is_empty() {
        // Return an empty HashMap if the file is empty
        return Ok(HashMap::new());
    }

    // Deserialize the JSON into a temporary structure
    let data: HashMap<String, Vec<String>> = match serde_json::from_str(&content) {
        Ok(data) => data,
        Err(e) => return Err(anyhow!("Error deserializing local uids")), // Handle JSON parsing errors
    };

    // Convert Vec<String> to HashSet<String>
    let mut result: HashMap<String, HashSet<String>> = HashMap::new();
    for (key, value) in data {
        result.insert(key, value.into_iter().collect());
    }

    Ok(result)
}

/// add uid to the local list of downloaded uids
fn update_local_uids(uid: String, list: String, uids_path: PathBuf) -> anyhow::Result<()> {
    let file = std::fs::OpenOptions::new()
        .write(true)
        .create(true)
        .open(uids_path.clone())?;

    let mut data = read_local_uids(uids_path.clone())?;

    data.entry(list)
        .or_insert_with(HashSet::new)
        .insert(uid);

    let writer = BufWriter::new(file);

    // Convert HashSet<String> back to Vec<String> for serialization
    let mut temp_data: HashMap<String, Vec<String>> = HashMap::new();
    for (key, value) in data {
        temp_data.insert(key.clone(), value.iter().cloned().collect());
    }

    // Serialize the data back to JSON and write to file
    to_writer(writer, &temp_data)?;
    
    Ok(())
}

/// delete single message remotely by uid (marks deleted and deletes from the server at the same time)
pub async fn delete_email_by_uid(list: String, uid: u32) -> anyhow::Result<()>{
    // TODO split to mark_deleted() and expunge()
    let mut client = connect_to_imap().await?;
    let mut session_result = client.login(Config::global().username.clone(), Config::global().password.clone()).await;
    let mut session = match session_result {
        Ok(session) => {session}
        Err(_) => {return Err(anyhow!("Unable to login to IMAP server"))}
    };
    
    session.select(list.clone()).await?;
    let updates_stream = session.store(format!("{}", uid), "+FLAGS (\\Deleted)").await?;
    let _updates: Vec<_> = updates_stream.try_collect().await?;
    let _stream = session.expunge().await?;
    drop(_stream);
    session.logout().await?;
    Ok(())
}

/// create a folder remotely
pub async fn create_folder(name: String) -> anyhow::Result<()>{
    let mut client = connect_to_imap().await?;
    let mut session_result = client.login(Config::global().username.clone(), Config::global().password.clone()).await;
    let mut session = match session_result {
        Ok(session) => {session}
        Err(_) => {return Err(anyhow!("Unable to login to IMAP server"))}
    };
    session.create(name.clone()).await?;
    session.logout().await?;
    Ok(())
}

/// rename a folder remotely
pub async fn rename_folder(name: String, new_name: String) -> anyhow::Result<()>{
    let mut client = connect_to_imap().await?;
    let mut session_result = client.login(Config::global().username.clone(), Config::global().password.clone()).await;
    let mut session = match session_result {
        Ok(session) => {session}
        Err(_) => {return Err(anyhow!("Unable to login to IMAP server"))}
    };
    session.rename(name.clone(), new_name.clone()).await?;
    session.logout().await?;
    Ok(())
}

/// delete a folder remotely
pub async fn delete_folder(name: String) -> anyhow::Result<()>{
    let mut client = connect_to_imap().await?;
    let mut session_result = client.login(Config::global().username.clone(), Config::global().password.clone()).await;
    let mut session = match session_result {
        Ok(session) => {session}
        Err(_) => {return Err(anyhow!("Unable to login to IMAP server"))}
    };
    session.delete(name.clone()).await?;
    session.logout().await?;
    Ok(())
}

/// run a async task to monitor any changes in the mailbox 
pub async fn check_for_updates(mailbox: String) -> anyhow::Result<()> {
    task::spawn(async move {
        let mut client = match connect_to_imap().await {
            Ok(client) => client,
            Err(e) => {
                return Err::<(), anyhow::Error>(anyhow!("Failed to connect to IMAP"));
            }
        };

        let session_result = client
            .login(Config::global().username.clone(), Config::global().password.clone())
            .await;

        let mut session = match session_result {
            Ok(session) => session,
            Err(_) => return Err(anyhow!("Unable to login to IMAP server")),
        };

        session.select(mailbox.clone()).await?;

        loop {
            let mut idle = session.idle();
            idle.init().await.unwrap();
            let (idle_wait, interrupt) = idle.wait();
            let idle_handle = task::spawn(async move {
                println!("IDLE: waiting for 30s"); // TODO remove debug prints
                sleep(Duration::from_secs(30)).await;
                println!("IDLE: waited 30 secs, now interrupting idle");
                drop(interrupt);
            });

            match idle_wait.await.unwrap() {
                // TODO add more cases like delete, move...
                NewData(data) => {
                    // TODO do not update all emails (IMAP returns * {number} RECENT) and do it only for one mailbox
                    let new_paths = download_email_from_imap().await.expect("Cannot download new emails");
                    for (uid, path) in new_paths.clone() {
                        match add_email(path.clone(), uid.clone()){
                            Ok(_) => {}
                            Err(_) => {println!("Error adding email from {:?}", path.clone())}
                        };
                    }
                }
                reason => {
                    println!("IDLE failed {:?}", reason);
                }
            }

            // Ensure the idle handle is dropped before the next loop iteration
            idle_handle.await.unwrap();

            // Reassign session to prevent ownership issues in the next loop iteration
            session = idle.done().await.unwrap();
        }
    });

    Ok(())
}

/// saves a raw email properly
fn store(path: PathBuf, uid: String, subfolder: String, data: &[u8], info: &str) -> io::Result<PathBuf> {
    // loop when conflicting filenames occur, as described at
    // http://www.courier-mta.org/maildir.html
    // this assumes that pid and hostname don't change.
    let mut tmppath = path.clone();
    tmppath.push("tmp");

    let mut file;
    loop {

        tmppath.push(format!("email_{uid}"));

        match std::fs::OpenOptions::new()
            .write(true)
            .create_new(true)
            .open(&tmppath)
        {
            Ok(f) => {
                file = f;
                break;
            }
            Err(err) => {
                if err.kind() != ErrorKind::AlreadyExists {
                    return Err(err.into());
                }
                tmppath.pop();
            }
        }
    }

    /// At this point, `file` is our new file at `tmppath`.
    /// If we leave the scope of this function prior to
    /// successfully writing the file to its final location,
    /// we need to ensure that we remove the temporary file.
    /// This struct takes care of that detail.
    struct UnlinkOnError {
        path_to_unlink: Option<PathBuf>,
    }

    impl Drop for UnlinkOnError {
        fn drop(&mut self) {
            if let Some(path) = self.path_to_unlink.take() {
                // Best effort to remove it
                std::fs::remove_file(path).ok();
            }
        }
    }

    // Ensure that we remove the temporary file on failure
    let mut unlink_guard = UnlinkOnError {
        path_to_unlink: Some(tmppath.clone()),
    };

    file.write_all(data)?;
    file.sync_all()?;

    let mut newpath = path.clone();
    newpath.push(subfolder);


    let id = format!("email_{uid}");
    newpath.push(format!("{}{}", id, info));

    std::fs::rename(&tmppath, &newpath)?;
    unlink_guard.path_to_unlink.take();
    Ok(newpath)
}