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use std::future::Future;
use std::sync::Arc;
use tokio::sync::{mpsc, Mutex};
use tokio::task::{JoinSet, LocalSet};

use crate::shard::InternalJoinSetResult;
use crate::{ServiceData, UpstreamError};

struct DataCommitGuard<'a, Key: Send + 'static, Data: ServiceData> {
    key: Option<Key>,
    internal_join_set: &'a mut JoinSet<InternalJoinSetResult<Key, Data>>,
}
#[must_use = "the data commit request must be resolved or rejected, otherwise the operation will be considered aborted."]
pub struct DataCommitRequest<'a, Key: Send + 'static, Data: ServiceData> {
    data: &'a mut Data,
    commit_guard: DataCommitGuard<'a, Key, Data>,
}

impl<'a, Key: Send, Data: ServiceData> DataCommitRequest<'a, Key, Data> {
    pub(crate) fn new(
        key: Key,
        data: &'a mut Data,
        internal_join_set: &'a mut JoinSet<InternalJoinSetResult<Key, Data>>,
    ) -> Self {
        Self {
            commit_guard: DataCommitGuard {
                key: Some(key),
                internal_join_set,
            },
            data,
        }
    }

    pub fn data_mut(&mut self) -> &mut Data {
        self.data
    }

    pub fn data(&self) -> &Data {
        self.data
    }

    pub fn key(&self) -> &Key {
        self.commit_guard.key()
    }

    pub fn into_processing(self) -> ProcessingDataCommitRequest<'a, Key, Data> {
        ProcessingDataCommitRequest {
            drop_guard: self.commit_guard,
        }
    }

    pub fn resolve(self) {
        self.into_processing().resolve();
    }

    pub fn reject<E: Into<UpstreamError>>(self, error: E) {
        self.into_processing().reject(error);
    }
}

impl<'a, Key: Send + 'static, Data: ServiceData> DataCommitRequest<'a, Key, Data> {
    pub fn spawn<F: Future<Output = Result<(), UpstreamError>> + Send + 'static>(self, fut: F) {
        self.into_processing().spawn(fut);
    }
}

impl<'a, Key: Send, Data: ServiceData + Clone> DataCommitRequest<'a, Key, Data> {
    pub fn into_owned(self) -> OwnedDataCommitRequest<'a, Key, Data> {
        OwnedDataCommitRequest {
            data: self.data.clone(),
            commit_guard: self.commit_guard,
        }
    }
}

#[must_use = "the data commit request must be resolved or rejected, otherwise the operation will be considered aborted."]
pub struct OwnedDataCommitRequest<'a, Key: Send + 'static, Data: ServiceData> {
    data: Data,
    commit_guard: DataCommitGuard<'a, Key, Data>,
}

impl<'a, Key: Send, Data: ServiceData> OwnedDataCommitRequest<'a, Key, Data> {
    pub fn into_inner(self) -> (Data, ProcessingDataCommitRequest<'a, Key, Data>) {
        (
            self.data,
            ProcessingDataCommitRequest {
                drop_guard: self.commit_guard,
            },
        )
    }

    pub fn data(&self) -> &Data {
        &self.data
    }

    pub fn resolve(self) {
        self.commit_guard.resolve();
    }

    pub fn reject<E: Into<UpstreamError>>(self, error: E) {
        self.commit_guard.reject(error);
    }
}

impl<'a, Key: Send + 'static, Data: ServiceData> OwnedDataCommitRequest<'a, Key, Data> {
    pub fn spawn<
        R: Future<Output = Result<(), UpstreamError>> + Send + 'static,
        F: FnOnce(&Key, Data) -> R + Send + 'static,
    >(
        mut self,
        func: F,
    ) {
        let key = self.commit_guard.take_key();
        self.commit_guard.internal_join_set.spawn(async move {
            let fut = (func)(&key, self.data);
            match fut.await {
                Ok(()) => InternalJoinSetResult::DataCommitResult(key, Ok(())),
                Err(err) => InternalJoinSetResult::DataCommitResult(key, Err(err)),
            }
        });
    }
}

#[must_use = "the data commit request must be resolved or rejected, otherwise the operation will be considered aborted."]
pub struct ProcessingDataCommitRequest<'a, Key: Send + 'static, Data: ServiceData> {
    drop_guard: DataCommitGuard<'a, Key, Data>,
}

impl<'a, Key: Send, Data: ServiceData> ProcessingDataCommitRequest<'a, Key, Data> {
    pub fn resolve(self) {
        self.drop_guard.resolve();
    }

    pub fn reject<E: Into<UpstreamError>>(self, error: E) {
        self.drop_guard.reject(error);
    }
}

impl<'a, Key: Send + 'static, Data: ServiceData> ProcessingDataCommitRequest<'a, Key, Data> {
    pub fn spawn<F: Future<Output = Result<(), UpstreamError>> + Send + 'static>(mut self, fut: F) {
        let key = self.drop_guard.take_key();
        self.drop_guard.internal_join_set.spawn(async move {
            match fut.await {
                Ok(()) => InternalJoinSetResult::DataCommitResult(key, Ok(())),
                Err(err) => InternalJoinSetResult::DataCommitResult(key, Err(err)),
            }
        });
    }
}

impl<'a, Key: Send, Data: ServiceData> DataCommitGuard<'a, Key, Data> {
    fn key(&self) -> &Key {
        self.key.as_ref().unwrap()
    }

    fn take_key(&mut self) -> Key {
        self.key
            .take()
            .expect("invariant: key must be present, unless dropped.")
    }

    fn emit_result_async(&mut self, result: InternalJoinSetResult<Key, Data>) {
        self.internal_join_set.spawn(async move { result });
    }

    fn resolve(mut self) {
        let key = self.take_key();
        self.emit_result_async(InternalJoinSetResult::DataCommitResult(key, Ok(())));
    }

    fn reject<E: Into<UpstreamError>>(mut self, error: E) {
        let key = self.take_key();
        self.emit_result_async(InternalJoinSetResult::DataCommitResult(
            key,
            Err(error.into()),
        ));
    }
}

impl<Key: Send, Data: ServiceData> Drop for DataCommitGuard<'_, Key, Data> {
    fn drop(&mut self) {
        if let Some(key) = self.key.take() {
            self.emit_result_async(InternalJoinSetResult::DataCommitResult(
                key,
                Err(UpstreamError::OperationAborted),
            ));
        }
    }
}