use once_cell::sync::Lazy;
use std::collections::HashSet;
use std::io::Read;
use std::iter::Iterator;
use std::time::{Duration, SystemTime};
use u_lib::utils::SharedStorage;
use uuid::Uuid;

type Data = Box<dyn Read + Send + Sync>;

/// This struct holds uids of various readable objects (files, streams, etc...)
/// with timeout and permissions for any uids to read data
struct MappedData {
    //ids that allowed to read the data
    for_ids: HashSet<Uuid>,
    created: SystemTime,
    timeout: Duration,
    data: Data,
}

impl MappedData {
    pub fn new(
        ids: impl Iterator<Item = Uuid>,
        data: impl Read + Send + Sync + 'static,
        timeout: Duration,
    ) -> Self {
        MappedData {
            for_ids: ids.collect(),
            created: SystemTime::now(),
            timeout,
            data: Box::new(data),
        }
    }
}

static MAPPER: Lazy<SharedStorage<Uuid, MappedData>> = SharedStorage::new();

pub struct Mapper;

impl Mapper {
    fn remove_overdue() {
        MAPPER
            .lock()
            .retain(|_, v| v.created.elapsed().unwrap() < v.timeout);
    }

    pub fn get(item_uid: Uuid, getter_uid: Uuid) -> Option<Data> {
        Self::remove_overdue();
        let allowed_ids = MAPPER.lock().get(&item_uid)?.for_ids;
        if allowed_ids.contains(&getter_uid) {
            MAPPER.lock().remove(&item_uid).map(|d| d.data)
        } else {
            None
        }
    }

    pub fn set(
        for_ids: impl Iterator<Item = Uuid>,
        data: impl Read + Send + Sync + 'static,
        timeout: Option<Duration>,
    ) -> Uuid {
        Self::remove_overdue();
        let uid = Uuid::new_v4();
        let timeout = timeout.unwrap_or(Duration::from_secs(60));
        let mapped = MappedData::new(for_ids, data, timeout);
        MAPPER.lock().insert(uid, mapped);
        uid
    }
}

// init:
// fill index struct with files allowed to download (probably auto-refresh index on file adding)
// hashmap<stripped_hash_of_file_name, PathBuf>
// download:
// 1) agent sends download_request with hash of wanted file
// 2) handler checks if this agent is allowed to dl file
// 3) if all ok, create in entry in mapper and return its uid and hashsum to agent
// 4) agent downloads file by uid, uid destructed after that