// Copyright 2024 RustFS Team
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use std::{
    collections::{HashMap, HashSet},
    ops::{Deref, DerefMut},
    ptr,
    sync::Arc,
};

use arc_swap::{ArcSwap, AsRaw, Guard};
use rustfs_policy::{
    auth::UserIdentity,
    policy::{Args, PolicyDoc},
};
use time::OffsetDateTime;
use tracing::warn;

use crate::store::{GroupInfo, MappedPolicy};

pub struct Cache {
    pub policy_docs: ArcSwap<CacheEntity<PolicyDoc>>,
    pub users: ArcSwap<CacheEntity<UserIdentity>>,
    pub user_policies: ArcSwap<CacheEntity<MappedPolicy>>,
    pub sts_accounts: ArcSwap<CacheEntity<UserIdentity>>,
    pub sts_policies: ArcSwap<CacheEntity<MappedPolicy>>,
    pub groups: ArcSwap<CacheEntity<GroupInfo>>,
    pub user_group_memberships: ArcSwap<CacheEntity<HashSet<String>>>,
    pub group_policies: ArcSwap<CacheEntity<MappedPolicy>>,
}

impl Default for Cache {
    fn default() -> Self {
        Self {
            policy_docs: ArcSwap::new(Arc::new(CacheEntity::default())),
            users: ArcSwap::new(Arc::new(CacheEntity::default())),
            user_policies: ArcSwap::new(Arc::new(CacheEntity::default())),
            sts_accounts: ArcSwap::new(Arc::new(CacheEntity::default())),
            sts_policies: ArcSwap::new(Arc::new(CacheEntity::default())),
            groups: ArcSwap::new(Arc::new(CacheEntity::default())),
            user_group_memberships: ArcSwap::new(Arc::new(CacheEntity::default())),
            group_policies: ArcSwap::new(Arc::new(CacheEntity::default())),
        }
    }
}

impl Cache {
    pub fn ptr_eq<Base, A, B>(a: A, b: B) -> bool
    where
        A: AsRaw<Base>,
        B: AsRaw<Base>,
    {
        let a = a.as_raw();
        let b = b.as_raw();
        ptr::eq(a, b)
    }

    fn exec<T: Clone>(target: &ArcSwap<CacheEntity<T>>, t: OffsetDateTime, mut op: impl FnMut(&mut CacheEntity<T>)) {
        let mut cur = target.load();
        loop {
            // If the current update time is later than the execution time,
            // the background task is loaded and the current operation does not need to be performed.
            if cur.load_time >= t {
                return;
            }

            let mut new = CacheEntity::clone(&cur);
            op(&mut new);

            // Replace content with CAS atoms
            let prev = target.compare_and_swap(&*cur, Arc::new(new));
            let swapped = Self::ptr_eq(&*cur, &*prev);
            if swapped {
                return;
            } else {
                cur = prev;
            }
        }
    }

    pub fn add_or_update<T: Clone>(target: &ArcSwap<CacheEntity<T>>, key: &str, value: &T, t: OffsetDateTime) {
        Self::exec(target, t, |map: &mut CacheEntity<T>| {
            map.insert(key.to_string(), value.clone());
        })
    }

    pub fn delete<T: Clone>(target: &ArcSwap<CacheEntity<T>>, key: &str, t: OffsetDateTime) {
        Self::exec(target, t, |map: &mut CacheEntity<T>| {
            map.remove(key);
        })
    }

    pub fn build_user_group_memberships(&self) {
        let groups = self.groups.load();
        let mut user_group_memberships = HashMap::new();
        for (group_name, group) in groups.iter() {
            for user_name in &group.members {
                user_group_memberships
                    .entry(user_name.clone())
                    .or_insert_with(HashSet::new)
                    .insert(group_name.clone());
            }
        }
        self.user_group_memberships
            .store(Arc::new(CacheEntity::new(user_group_memberships)));
    }
}

impl CacheInner {
    #[inline]
    pub fn get_user(&self, user_name: &str) -> Option<&UserIdentity> {
        self.users.get(user_name).or_else(|| self.sts_accounts.get(user_name))
    }

    // fn get_policy(&self, _name: &str, _groups: &[String]) -> crate::Result<Vec<Policy>> {
    //     todo!()
    // }

    // /// Return Ok(Some(parent_name)) when the user is temporary.
    // /// Return Ok(None) for non-temporary users.
    // fn is_temp_user(&self, user_name: &str) -> crate::Result<Option<&str>> {
    //     let user = self
    //         .get_user(user_name)
    //         .ok_or_else(|| Error::NoSuchUser(user_name.to_owned()))?;

    //     if user.credentials.is_temp() {
    //         Ok(Some(&user.credentials.parent_user))
    //     } else {
    //         Ok(None)
    //     }
    // }

    // /// Return Ok(Some(parent_name)) when the user is a temporary identity.
    // /// Return Ok(None) when the user is not temporary.
    // fn is_service_account(&self, user_name: &str) -> crate::Result<Option<&str>> {
    //     let user = self
    //         .get_user(user_name)
    //         .ok_or_else(|| Error::NoSuchUser(user_name.to_owned()))?;

    //     if user.credentials.is_service_account() {
    //         Ok(Some(&user.credentials.parent_user))
    //     } else {
    //         Ok(None)
    //     }
    // }

    // todo
    pub fn is_allowed_sts(&self, _args: &Args, _parent: &str) -> bool {
        warn!("policy cache STS check path is not implemented");
        false
    }

    // todo
    pub fn is_allowed_service_account(&self, _args: &Args, _parent: &str) -> bool {
        warn!("policy cache service account check path is not implemented");
        false
    }

    pub fn is_allowed(&self, _args: Args) -> bool {
        warn!("policy cache is_allowed check path is currently denied by default");
        false
    }

    pub fn policy_db_get(&self, _name: &str, _groups: &[String]) -> Vec<String> {
        warn!("policy cache policy_db_get is not implemented, returning empty policy set");
        vec![]
    }
}

#[derive(Clone)]
pub struct CacheEntity<T> {
    map: HashMap<String, T>,
    /// The time of the reload
    load_time: OffsetDateTime,
}

impl<T> Deref for CacheEntity<T> {
    type Target = HashMap<String, T>;
    fn deref(&self) -> &Self::Target {
        &self.map
    }
}

impl<T> DerefMut for CacheEntity<T> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.map
    }
}

impl<T> CacheEntity<T> {
    pub fn new(map: HashMap<String, T>) -> Self {
        Self {
            map,
            load_time: OffsetDateTime::UNIX_EPOCH,
        }
    }
}

impl<T> Default for CacheEntity<T> {
    fn default() -> Self {
        Self {
            map: HashMap::new(),
            load_time: OffsetDateTime::UNIX_EPOCH,
        }
    }
}

impl<T> CacheEntity<T> {
    pub fn update_load_time(mut self) -> Self {
        self.load_time = OffsetDateTime::now_utc();
        self
    }
}

pub type G<T> = Guard<Arc<CacheEntity<T>>>;

pub struct CacheInner {
    pub policy_docs: G<PolicyDoc>,
    pub users: G<UserIdentity>,
    pub user_policies: G<MappedPolicy>,
    pub sts_accounts: G<UserIdentity>,
    pub sts_policies: G<MappedPolicy>,
    pub groups: G<GroupInfo>,
    pub user_group_memberships: G<HashSet<String>>,
    pub group_policies: G<MappedPolicy>,
}

impl From<&Cache> for CacheInner {
    fn from(value: &Cache) -> Self {
        Self {
            policy_docs: value.policy_docs.load(),
            users: value.users.load(),
            user_policies: value.user_policies.load(),
            sts_accounts: value.sts_accounts.load(),
            sts_policies: value.sts_policies.load(),
            groups: value.groups.load(),
            user_group_memberships: value.user_group_memberships.load(),
            group_policies: value.group_policies.load(),
        }
    }
}

#[cfg(test)]
mod tests {
    use std::sync::Arc;

    use arc_swap::ArcSwap;
    use futures::future::join_all;
    use time::OffsetDateTime;

    use super::CacheEntity;
    use crate::cache::Cache;

    #[tokio::test]
    async fn test_cache_entity_add() {
        let cache = ArcSwap::new(Arc::new(CacheEntity::<usize>::default()));

        let mut f = vec![];

        for (index, key) in (0..100).map(|x| x.to_string()).enumerate() {
            let c = &cache;
            f.push(async move {
                Cache::add_or_update(c, &key, &index, OffsetDateTime::now_utc());
            });
        }
        join_all(f).await;

        let cache = cache.load();
        for (index, key) in (0..100).map(|x| x.to_string()).enumerate() {
            assert_eq!(cache.get(&key), Some(&index));
        }
    }

    #[tokio::test]
    async fn test_cache_entity_update() {
        let cache = ArcSwap::new(Arc::new(CacheEntity::<usize>::default()));

        let mut f = vec![];

        for (index, key) in (0..100).map(|x| x.to_string()).enumerate() {
            let c = &cache;
            f.push(async move {
                Cache::add_or_update(c, &key, &index, OffsetDateTime::now_utc());
            });
        }
        join_all(f).await;

        let cache_load = cache.load();
        for (index, key) in (0..100).map(|x| x.to_string()).enumerate() {
            assert_eq!(cache_load.get(&key), Some(&index));
        }

        let mut f = vec![];

        for (index, key) in (0..100).map(|x| x.to_string()).enumerate() {
            let c = &cache;
            f.push(async move {
                Cache::add_or_update(c, &key, &(index * 1000), OffsetDateTime::now_utc());
            });
        }
        join_all(f).await;

        let cache_load = cache.load();
        for (index, key) in (0..100).map(|x| x.to_string()).enumerate() {
            assert_eq!(cache_load.get(&key), Some(&(index * 1000)));
        }
    }

    #[tokio::test]
    async fn test_cache_entity_delete() {
        let cache = ArcSwap::new(Arc::new(CacheEntity::<usize>::default()));

        let mut f = vec![];

        for (index, key) in (0..100).map(|x| x.to_string()).enumerate() {
            let c = &cache;
            f.push(async move {
                Cache::add_or_update(c, &key, &index, OffsetDateTime::now_utc());
            });
        }
        join_all(f).await;

        let cache_load = cache.load();
        for (index, key) in (0..100).map(|x| x.to_string()).enumerate() {
            assert_eq!(cache_load.get(&key), Some(&index));
        }

        let mut f = vec![];

        for key in (0..100).map(|x| x.to_string()) {
            let c = &cache;
            f.push(async move {
                Cache::delete(c, &key, OffsetDateTime::now_utc());
            });
        }
        join_all(f).await;

        let cache_load = cache.load();
        assert!(cache_load.is_empty());
    }
}