use std::path::PathBuf;
use std::sync::Arc;
use std::os::unix::io::RawFd;
use std::path::Path;
use std::ffi::OsStr;
use std::collections::HashMap;
use std::hash::BuildHasher;

use anyhow::{bail, format_err, Error};
use serde_json::Value;
use tokio::signal::unix::{signal, SignalKind};
use nix::unistd::{fork, ForkResult, pipe};
use futures::select;
use futures::future::FutureExt;
use futures::stream::{StreamExt, TryStreamExt};

use proxmox::{sortable, identity};
use proxmox::api::{ApiHandler, ApiMethod, RpcEnvironment, schema::*, cli::*};


use proxmox_backup::tools;
use proxmox_backup::backup::{
    load_and_decrypt_key,
    CryptConfig,
    IndexFile,
    BackupDir,
    BackupGroup,
    BufferedDynamicReader,
    AsyncIndexReader,
};

use proxmox_backup::client::*;

use crate::{
    REPO_URL_SCHEMA,
    extract_repository_from_value,
    complete_pxar_archive_name,
    complete_img_archive_name,
    complete_group_or_snapshot,
    complete_repository,
    record_repository,
    connect,
    api_datastore_latest_snapshot,
    BufferedDynamicReadAt,
};

#[sortable]
const API_METHOD_MOUNT: ApiMethod = ApiMethod::new(
    &ApiHandler::Sync(&mount),
    &ObjectSchema::new(
        "Mount pxar archive.",
        &sorted!([
            ("snapshot", false, &StringSchema::new("Group/Snapshot path.").schema()),
            ("archive-name", false, &StringSchema::new("Backup archive name.").schema()),
            ("target", false, &StringSchema::new("Target directory path.").schema()),
            ("repository", true, &REPO_URL_SCHEMA),
            ("keyfile", true, &StringSchema::new("Path to encryption key.").schema()),
            ("verbose", true, &BooleanSchema::new("Verbose output and stay in foreground.").default(false).schema()),
        ]),
    )
);

#[sortable]
const API_METHOD_MAP: ApiMethod = ApiMethod::new(
    &ApiHandler::Sync(&mount),
    &ObjectSchema::new(
        "Map a drive image from a VM backup to a local loopback device. Use 'unmap' to undo.
WARNING: Only do this with *trusted* backups!",
        &sorted!([
            ("snapshot", false, &StringSchema::new("Group/Snapshot path.").schema()),
            ("archive-name", false, &StringSchema::new("Backup archive name.").schema()),
            ("repository", true, &REPO_URL_SCHEMA),
            ("keyfile", true, &StringSchema::new("Path to encryption key.").schema()),
            ("verbose", true, &BooleanSchema::new("Verbose output and stay in foreground.").default(false).schema()),
        ]),
    )
);

#[sortable]
const API_METHOD_UNMAP: ApiMethod = ApiMethod::new(
    &ApiHandler::Sync(&unmap),
    &ObjectSchema::new(
        "Unmap a loop device mapped with 'map' and release all resources.",
        &sorted!([
            ("name", true, &StringSchema::new(
                concat!("Archive name, path to loopdev (/dev/loopX) or loop device number. ",
                        "Omit to list all current mappings and force cleaning up leftover instances.")
            ).schema()),
        ]),
    )
);

pub fn mount_cmd_def() -> CliCommand {

    CliCommand::new(&API_METHOD_MOUNT)
        .arg_param(&["snapshot", "archive-name", "target"])
        .completion_cb("repository", complete_repository)
        .completion_cb("snapshot", complete_group_or_snapshot)
        .completion_cb("archive-name", complete_pxar_archive_name)
        .completion_cb("target", tools::complete_file_name)
}

pub fn map_cmd_def() -> CliCommand {

    CliCommand::new(&API_METHOD_MAP)
        .arg_param(&["snapshot", "archive-name"])
        .completion_cb("repository", complete_repository)
        .completion_cb("snapshot", complete_group_or_snapshot)
        .completion_cb("archive-name", complete_img_archive_name)
}

pub fn unmap_cmd_def() -> CliCommand {

    CliCommand::new(&API_METHOD_UNMAP)
        .arg_param(&["name"])
        .completion_cb("name", complete_mapping_names)
}

fn complete_mapping_names<S: BuildHasher>(_arg: &str, _param: &HashMap<String, String, S>)
    -> Vec<String>
{
    match tools::fuse_loop::find_all_mappings() {
        Ok(mappings) => mappings
            .filter_map(|(name, _)| {
                tools::systemd::unescape_unit(&name).ok()
            }).collect(),
        Err(_) => Vec::new()
    }
}

fn mount(
    param: Value,
    _info: &ApiMethod,
    _rpcenv: &mut dyn RpcEnvironment,
) -> Result<Value, Error> {

    let verbose = param["verbose"].as_bool().unwrap_or(false);
    if verbose {
        // This will stay in foreground with debug output enabled as None is
        // passed for the RawFd.
        return proxmox_backup::tools::runtime::main(mount_do(param, None));
    }

    // Process should be deamonized.
    // Make sure to fork before the async runtime is instantiated to avoid troubles.
    let pipe = pipe()?;
    match unsafe { fork() } {
        Ok(ForkResult::Parent { .. }) => {
            nix::unistd::close(pipe.1).unwrap();
            // Blocks the parent process until we are ready to go in the child
            let _res = nix::unistd::read(pipe.0, &mut [0]).unwrap();
            Ok(Value::Null)
        }
        Ok(ForkResult::Child) => {
            nix::unistd::close(pipe.0).unwrap();
            nix::unistd::setsid().unwrap();
            proxmox_backup::tools::runtime::main(mount_do(param, Some(pipe.1)))
        }
        Err(_) => bail!("failed to daemonize process"),
    }
}

async fn mount_do(param: Value, pipe: Option<RawFd>) -> Result<Value, Error> {
    let repo = extract_repository_from_value(&param)?;
    let archive_name = tools::required_string_param(&param, "archive-name")?;
    let client = connect(&repo)?;

    let target = param["target"].as_str();

    record_repository(&repo);

    let path = tools::required_string_param(&param, "snapshot")?;
    let (backup_type, backup_id, backup_time) = if path.matches('/').count() == 1 {
        let group: BackupGroup = path.parse()?;
        api_datastore_latest_snapshot(&client, repo.store(), group).await?
    } else {
        let snapshot: BackupDir = path.parse()?;
        (snapshot.group().backup_type().to_owned(), snapshot.group().backup_id().to_owned(), snapshot.backup_time())
    };

    let keyfile = param["keyfile"].as_str().map(PathBuf::from);
    let crypt_config = match keyfile {
        None => None,
        Some(path) => {
            let (key, _, _) = load_and_decrypt_key(&path, &crate::key::get_encryption_key_password)?;
            Some(Arc::new(CryptConfig::new(key)?))
        }
    };

    let server_archive_name = if archive_name.ends_with(".pxar") {
        if let None = target {
            bail!("use the 'mount' command to mount pxar archives");
        }
        format!("{}.didx", archive_name)
    } else if archive_name.ends_with(".img") {
        if let Some(_) = target {
            bail!("use the 'map' command to map drive images");
        }
        format!("{}.fidx", archive_name)
    } else {
        bail!("Can only mount/map pxar archives and drive images.");
    };

    let client = BackupReader::start(
        client,
        crypt_config.clone(),
        repo.store(),
        &backup_type,
        &backup_id,
        backup_time,
        true,
    ).await?;

    let (manifest, _) = client.download_manifest().await?;

    let file_info = manifest.lookup_file_info(&server_archive_name)?;

    let daemonize = || -> Result<(), Error> {
        if let Some(pipe) = pipe {
            nix::unistd::chdir(Path::new("/")).unwrap();
            // Finish creation of daemon by redirecting filedescriptors.
            let nullfd = nix::fcntl::open(
                "/dev/null",
                nix::fcntl::OFlag::O_RDWR,
                nix::sys::stat::Mode::empty(),
            ).unwrap();
            nix::unistd::dup2(nullfd, 0).unwrap();
            nix::unistd::dup2(nullfd, 1).unwrap();
            nix::unistd::dup2(nullfd, 2).unwrap();
            if nullfd > 2 {
                nix::unistd::close(nullfd).unwrap();
            }
            // Signal the parent process that we are done with the setup and it can
            // terminate.
            nix::unistd::write(pipe, &[0u8])?;
            nix::unistd::close(pipe).unwrap();
        }

        Ok(())
    };

    let options = OsStr::new("ro,default_permissions");

    // handle SIGINT and SIGTERM
    let mut interrupt_int = signal(SignalKind::interrupt())?;
    let mut interrupt_term = signal(SignalKind::terminate())?;
    let mut interrupt = futures::future::select(interrupt_int.next(), interrupt_term.next());

    if server_archive_name.ends_with(".didx") {
        let index = client.download_dynamic_index(&manifest, &server_archive_name).await?;
        let most_used = index.find_most_used_chunks(8);
        let chunk_reader = RemoteChunkReader::new(client.clone(), crypt_config, file_info.chunk_crypt_mode(), most_used);
        let reader = BufferedDynamicReader::new(index, chunk_reader);
        let archive_size = reader.archive_size();
        let reader: proxmox_backup::pxar::fuse::Reader =
            Arc::new(BufferedDynamicReadAt::new(reader));
        let decoder = proxmox_backup::pxar::fuse::Accessor::new(reader, archive_size).await?;

        let session = proxmox_backup::pxar::fuse::Session::mount(
            decoder,
            &options,
            false,
            Path::new(target.unwrap()),
        )
        .map_err(|err| format_err!("pxar mount failed: {}", err))?;

        daemonize()?;

        select! {
            res = session.fuse() => res?,
            _ = interrupt => {
                // exit on interrupted
            }
        }
    } else if server_archive_name.ends_with(".fidx") {
        let index = client.download_fixed_index(&manifest, &server_archive_name).await?;
        let size = index.index_bytes();
        let chunk_reader = RemoteChunkReader::new(client.clone(), crypt_config, file_info.chunk_crypt_mode(), HashMap::new());
        let reader = AsyncIndexReader::new(index, chunk_reader);

        let name = &format!("{}:{}/{}", repo.to_string(), path, archive_name);
        let name_escaped = tools::systemd::escape_unit(name, false);

        let mut session = tools::fuse_loop::FuseLoopSession::map_loop(size, reader, &name_escaped, options).await?;
        let loopdev = session.loopdev_path.clone();

        let (st_send, st_recv) = futures::channel::mpsc::channel(1);
        let (mut abort_send, abort_recv) = futures::channel::mpsc::channel(1);
        let mut st_recv = st_recv.fuse();
        let mut session_fut = session.main(st_send, abort_recv).boxed().fuse();

        // poll until loop file is mapped (or errors)
        select! {
            res = session_fut => {
                bail!("FUSE session unexpectedly ended before loop file mapping");
            },
            res = st_recv.try_next() => {
                if let Err(err) = res {
                    // init went wrong, abort now
                    abort_send.try_send(()).map_err(|err|
                        format_err!("error while sending abort signal - {}", err))?;
                    // ignore and keep original error cause
                    let _ = session_fut.await;
                    return Err(err);
                }
            }
        }

        // daemonize only now to be able to print mapped loopdev or startup errors
        println!("Image '{}' mapped on {}", name, loopdev);
        daemonize()?;

        // continue polling until complete or interrupted (which also happens on unmap)
        select! {
            res = session_fut => res?,
            _ = interrupt => {
                // exit on interrupted
                abort_send.try_send(()).map_err(|err|
                    format_err!("error while sending abort signal - {}", err))?;
                session_fut.await?;
            }
        }

        println!("Image unmapped");
    } else {
        bail!("unknown archive file extension (expected .pxar or .img)");
    }

    Ok(Value::Null)
}

fn unmap(
    param: Value,
    _info: &ApiMethod,
    _rpcenv: &mut dyn RpcEnvironment,
) -> Result<Value, Error> {

    let mut name = match param["name"].as_str() {
        Some(name) => name.to_owned(),
        None => {
            tools::fuse_loop::cleanup_unused_run_files(None);
            let mut any = false;
            for (backing, loopdev) in tools::fuse_loop::find_all_mappings()? {
                let name = tools::systemd::unescape_unit(&backing)?;
                println!("{}:\t{}", loopdev.unwrap_or("(unmapped)".to_owned()), name);
                any = true;
            }
            if !any {
                println!("Nothing mapped.");
            }
            return Ok(Value::Null);
        },
    };

    // allow loop device number alone
    if let Ok(num) = name.parse::<u8>() {
        name = format!("/dev/loop{}", num);
    }

    if name.starts_with("/dev/loop") {
        tools::fuse_loop::unmap_loopdev(name)?;
    } else {
        let name = tools::systemd::escape_unit(&name, false);
        tools::fuse_loop::unmap_name(name)?;
    }

    Ok(Value::Null)
}