use crossbeam::channel::{Receiver, Sender};
use rand::Rng;
use redis::{Commands, RedisResult};
use serde::{Deserialize, Serialize};
use std::{sync::mpsc, time::Duration};

pub enum TaskReceiverBackend<I, O> {
    Local(Receiver<JobOrder<I, O>>),
    Union(ValkeyJobDispatcher<I, O>),
}

impl<I: Serialize + for<'a> Deserialize<'a>, O: Serialize + for<'a> Deserialize<'a>>
    TaskReceiverBackend<I, O>
{
    pub fn recv(&self) -> Result<JobOrder<I, O>, String> {
        match self {
            TaskReceiverBackend::Local(receiver) => receiver.recv().map_err(|x| x.to_string()),
            TaskReceiverBackend::Union(valkey_job_dispatcher) => valkey_job_dispatcher.recv(),
        }
    }
}

pub struct ValkeyTopicSubscriber<O> {
    output: std::marker::PhantomData<O>,
    topic: String,
    client: redis::Client,
}

impl<O: for<'a> Deserialize<'a>> ValkeyTopicSubscriber<O> {
    pub fn new(channel: &str) -> Self {
        let client =
            redis::Client::open(std::env::var("VALKEY_URL").expect("No $VALKEY_URL variable set"))
                .expect("Invalid Redis URL");
        Self {
            output: std::marker::PhantomData,
            topic: channel.to_string(),
            client: client,
        }
    }

    pub fn recv(&self) -> Option<O> {
        let mut con = self
            .client
            .get_connection()
            .expect("Failed to connect to Redis");

        let result: RedisResult<Vec<String>> = con.blpop(&self.topic, 0.0);

        match result {
            Ok(msg) => {
                let msg = msg.iter().nth(1).unwrap();

                Some(serde_json::from_str(&msg).unwrap())
            }
            Err(_) => None,
        }
    }

    pub fn recv_timeout(&self, timeout: std::time::Duration) -> Option<O> {
        let mut con = self
            .client
            .get_connection()
            .expect("Failed to connect to Redis");

        let result: RedisResult<Vec<String>> = con.blpop(&self.topic, timeout.as_secs_f64());

        match result {
            Ok(msg) => {
                let msg = msg.iter().nth(1).unwrap();

                Some(serde_json::from_str(&msg).unwrap())
            }
            Err(_) => None,
        }
    }
}

#[derive(Clone)]
pub struct ValkeyJobDispatcher<I, O> {
    input: std::marker::PhantomData<I>,
    output: std::marker::PhantomData<O>,
    topic: String,
    client: redis::Client,
    local: bool,
}

impl<I: Serialize + for<'a> Deserialize<'a>, O: Serialize + for<'a> Deserialize<'a>>
    ValkeyJobDispatcher<I, O>
{
    // Creates a new job dispatcher for the given topic.
    pub fn new_topic(topic: &str, local: bool) -> Self {
        let client =
            redis::Client::open(std::env::var("VALKEY_URL").expect("No $VALKEY_URL variable set"))
                .expect("Invalid Redis URL");
        ValkeyJobDispatcher {
            input: std::marker::PhantomData,
            output: std::marker::PhantomData,
            topic: topic.to_string(),
            client,
            local,
        }
    }

    // todo : real pub sub
    pub fn recv(&self) -> Result<JobOrder<I, O>, String> {
        let mut con = self
            .client
            .get_connection()
            .expect("Failed to connect to Redis");

        let result: RedisResult<Vec<String>> = con.blpop(&self.topic, 0.0);

        match result {
            Ok(msg) => {
                let msg = msg.iter().nth(1).unwrap();

                if let serde_json::Value::Object(task) = serde_json::from_str(&msg).unwrap() {
                    let channel_id = task.get("task").unwrap().as_str().unwrap().to_string();
                    let params = task.get("params").unwrap();
                    Ok(JobOrder::new(
                        serde_json::from_value(params.clone()).unwrap(),
                        move |res| {
                            // send back to channel
                            let _: () = con
                                .rpush(
                                    &channel_id,
                                    serde_json::to_string(&serde_json::to_value(&res).unwrap())
                                        .unwrap(),
                                )
                                .expect("Failed to send job");
                        },
                    ))
                } else {
                    Err(String::new())
                }
            }
            Err(e) => {
                log::error!("Valkey error: {e:?}");
                Err(e.to_string())
            }
        }
    }
}

impl<I: Serialize + for<'a> Deserialize<'a>, O: for<'a> Deserialize<'a> + Serialize>
    JobDispatch<I, O> for ValkeyJobDispatcher<I, O>
{
    // Sends a job to the Redis topic (publishes a message).
    fn send(&self, param: I) -> O {
        let mut con = self
            .client
            .get_connection()
            .expect("Failed to connect to Redis");

        // Pushing the job to the topic in Redis
        let channel_id = uuid::Uuid::new_v4().to_string();
        let _: () = con
            .rpush(
                &self.topic,
                serde_json::to_string(&serde_json::json!({
                    "task": channel_id,
                    "params": &param
                }))
                .unwrap(),
            )
            .expect("Failed to send job");

        ValkeyTopicSubscriber::new(&channel_id).recv().unwrap()
    }

    // Sends a job asynchronously (non-blocking).
    fn send_async(&self, param: I) -> JobResult<O> {
        let mut con = self
            .client
            .get_connection()
            .expect("Failed to connect to Redis");

        // Pushing the job to the topic in Redis
        let channel_id = uuid::Uuid::new_v4().to_string();
        let _: () = con
            .rpush(
                &self.topic,
                serde_json::to_string(&serde_json::json!({
                    "task": channel_id,
                    "params": &param
                }))
                .unwrap(),
            )
            .expect("Failed to send job");

        JobResult(ReceiverBackend::Valkey(ValkeyTopicSubscriber::new(
            &channel_id,
        )))
    }

    // Tries to send a job, returning None if unsuccessful.
    fn try_send(&self, param: I) -> Option<O> {
        let res = self.send_async(param);
        res.wait_try()
    }
}

#[derive(Clone)]
/// A generic job dispatcher struct that allows sending jobs of type `I` and receiving results of type `O` using message passing.
pub struct JobDispatcher<I: Send + 'static, O: Send + 'static> {
    sender: Sender<JobOrder<I, O>>,
}

pub enum ReceiverBackend<O> {
    Local(std::sync::mpsc::Receiver<O>),
    Valkey(ValkeyTopicSubscriber<O>),
}

impl<O: for<'a> Deserialize<'a>> ReceiverBackend<O> {
    pub fn recv(&self) -> Option<O> {
        match self {
            ReceiverBackend::Local(receiver) => receiver.recv().ok(),
            ReceiverBackend::Valkey(valkey) => valkey.recv(),
        }
    }

    pub fn recv_timeout(&self) -> Option<O> {
        match self {
            ReceiverBackend::Local(receiver) => {
                receiver.recv_timeout(Duration::from_millis(300)).ok()
            }
            ReceiverBackend::Valkey(valkey_topic_subscriber) => {
                valkey_topic_subscriber.recv_timeout(Duration::from_millis(300))
            }
        }
    }
}

pub struct JobResult<O>(ReceiverBackend<O>);

impl<O: for<'a> Deserialize<'a>> JobResult<O> {
    /// Wait for the Result of a Job.
    pub fn wait(self) -> O {
        self.0.recv().unwrap()
    }

    pub fn wait_try(self) -> Option<O> {
        self.0.recv()
    }

    pub fn wait_timeout(&self) -> Option<O> {
        self.0.recv_timeout()
    }
}

impl<I: Send + 'static, O: Send + 'static> JobDispatcher<I, O> {
    /// Creates a new instance of `JobDispatcher` and returns a tuple that contains it and a receiver end for `JobOrder`s.
    /// # Example:
    /// ```
    /// use jobdispatcher::*;
    /// // Create job dispatcher
    /// let (dispatcher, recv) = JobDispatcher::<i32, i32>::new();
    ///
    /// // Worker Thread
    /// std::thread::spawn(move || {
    ///     for job in recv {
    ///         let result = job.param + 1;
    ///         job.done(result);
    ///     }
    /// });
    ///    
    /// // Usage
    /// let result = dispatcher.send(3);
    /// assert_eq!(result, 4);
    /// ```
    #[must_use]
    pub fn new() -> (Self, Receiver<JobOrder<I, O>>) {
        let (sender, receiver) = crossbeam::channel::bounded(8092);

        (Self { sender: sender }, receiver)
    }
}

impl<I: Send + 'static, O: Send + 'static> JobDispatch<I, O> for JobDispatcher<I, O> {
    /// Sends a job of type `T` to the job dispatcher and waits for its result of type `V`.
    /// Returns the result of the job once it has been processed.
    /// # Panics
    /// This function panics when the `JobOrder` struct gets out of scope without returning a finished result.
    /// Additionally if the internal `Mutex` is poisoned, this function will panic as well.
    fn send(&self, param: I) -> O {
        let (tx, rx) = mpsc::channel();
        let job_order = JobOrder::new(param, move |ret| {
            tx.send(ret).unwrap();
        });
        self.sender.send(job_order).unwrap();
        rx.recv().unwrap()
    }

    fn send_async(&self, param: I) -> JobResult<O> {
        let (tx, rx) = mpsc::channel();
        let job_order = JobOrder::new(param, move |ret| {
            tx.send(ret).unwrap();
        });
        self.sender.send(job_order).unwrap();
        JobResult(ReceiverBackend::Local(rx))
    }

    /// Sends a job of type `T` to the job dispatcher and waits for its result of type `V`.
    /// Returns `Some(V)` when the job returns an result, `None` if somehow nothing was returned or the internal `Mutex` is poisoned.
    fn try_send(&self, param: I) -> Option<O> {
        let (tx, rx) = mpsc::channel();
        let job_order = JobOrder::new(param, move |ret| {
            tx.send(ret).unwrap();
        });
        self.sender.send(job_order).ok()?;
        rx.recv().ok()
    }
}

pub trait JobDispatch<I, O> {
    fn send(&self, param: I) -> O;
    fn send_async(&self, param: I) -> JobResult<O>;
    fn try_send(&self, param: I) -> Option<O>;
}

/// A struct that represents a job order that encapsulates a job of type `I` and its result of type `O`, along with a callback function that will send the result back to the job origin.
pub struct JobOrder<I, O> {
    /// The job parameter of type `T`.
    pub param: I,
    callback: Box<dyn FnOnce(O) + Send>,
}

impl<I, O> JobOrder<I, O> {
    /// Creates a new `JobOrder` instance with the specified job parameter `param` of type `I` and a callback function that takes the job result of type `O` as an argument.
    #[must_use]
    fn new(param: I, callback: impl FnOnce(O) + Send + 'static) -> Self {
        Self {
            param,
            callback: Box::new(callback),
        }
    }

    /// Send the result of the `JobOrder` back to it's origin
    pub fn done(self, val: O) {
        (self.callback)(val);
    }
}

pub enum Dispatcher<I: Send + 'static, O: Send + 'static> {
    Local(JobDispatcher<I, O>),
    Union(ValkeyJobDispatcher<I, O>),
}

impl<
    I: Serialize + for<'a> Deserialize<'a> + Send + 'static,
    O: Serialize + for<'a> Deserialize<'a> + Send + 'static,
> Dispatcher<I, O>
{
    pub fn is_local(&self) -> bool {
        match self {
            Dispatcher::Local(_) => true,
            Dispatcher::Union(valkey_job_dispatcher) => valkey_job_dispatcher.local,
        }
    }

    fn send(&self, param: I) -> O {
        match self {
            Dispatcher::Local(job_dispatcher) => job_dispatcher.send(param),
            Dispatcher::Union(valkey_job_dispatcher) => valkey_job_dispatcher.send(param),
        }
    }

    fn send_async(&self, param: I) -> JobResult<O> {
        match self {
            Dispatcher::Local(job_dispatcher) => job_dispatcher.send_async(param),
            Dispatcher::Union(valkey_job_dispatcher) => valkey_job_dispatcher.send_async(param),
        }
    }
}

pub struct JobMultiplexer<I: Send + 'static, O: Send + 'static> {
    dispatchers: Vec<Dispatcher<I, O>>,
}

fn get_random_item<T>(list: &[T]) -> Option<&T> {
    if list.is_empty() {
        return None;
    }
    let mut rng = rand::rng();
    let index = rng.random_range(0..list.len());
    list.get(index)
}

impl<
    I: Serialize + for<'a> Deserialize<'a> + Send + 'static,
    O: Serialize + for<'a> Deserialize<'a> + Send + 'static,
> JobMultiplexer<I, O>
{
    pub fn from(dispatchers: Vec<Dispatcher<I, O>>) -> Self {
        Self { dispatchers }
    }

    pub fn send(&self, param: I) -> O {
        let d = get_random_item(&self.dispatchers).unwrap();
        d.send(param)
    }

    pub fn send_async(&self, param: I) -> JobResult<O> {
        let d = get_random_item(&self.dispatchers).unwrap();
        d.send_async(param)
    }
}

impl<
    I: Clone + Serialize + for<'a> Deserialize<'a> + Send + 'static,
    O: Serialize + for<'a> Deserialize<'a> + Send + 'static,
> JobMultiplexer<I, O>
{
    pub fn send_all(&self, param: I) {
        for d in &self.dispatchers {
            if d.is_local() {
                let _ = d.send(param.clone());
            }
        }
    }
}

/// Iterator which returns ready results from a `Vec<JobResult<O>>.
///
/// This Iterator waits for each `JobResult<O>` with a timeout and yields a result once it finds one finished `JobResult<O>`.
///
/// # Example
/// ```ignore
/// // Started Tasks which are pending
/// let pending_tasks = vec![...];
///
/// for task in pending_tasks {
///     // blocks and waits for the first `JobResult<_>` even though the next ones in the `Vec<_>` could be finished and processed already.
///     let result = task.wait();
///     // ...
/// }
///
/// // With the Iterator
///
/// for value in PendingTaskIterator(pending_tasks) {
///     // You can immidiatelly start processing the first finished result
///     // ...
/// }
/// ```
pub struct PendingTaskIterator<O>(pub Vec<JobResult<O>>);

impl<O: for<'a> Deserialize<'a>> Iterator for PendingTaskIterator<O> {
    type Item = O;

    fn next(&mut self) -> Option<Self::Item> {
        if self.0.is_empty() {
            return None;
        }

        loop {
            for (i, task) in self.0.iter().enumerate() {
                if let Some(res) = task.wait_timeout() {
                    self.0.remove(i);
                    return Some(res);
                }
            }
        }
    }
}

/// Iterator which returns ready results from a `Vec<JobResult<O>> along with a label.
///
/// Compared to a normal `PendingTaskIterator<O>` this Iterator takes a `Vec<(L, JobResult<I, O>)>`.
/// You can use the variable `L` for an associated label to correlate results to their origins.
///
/// This Iterator waits for each `JobResult<O>` with a timeout and yields a result once it finds one finished `JobResult<O>`.
///
/// # Example
/// ```ignore
/// // Started Tasks which are pending
/// let pending_tasks = vec![...];
///
/// for task in pending_tasks {
///     // blocks and waits for the first `JobResult<_>` even though the next ones in the `Vec<_>` could be finished and processed already.
///     let result = task.wait();
///     // ...
/// }
///
/// // With the Iterator
///
/// for value in LabelPendingTaskIterator(pending_tasks) {
///     // You can immidiatelly start processing the first finished result
///     // ...
/// }
/// ```
pub struct LabelPendingTaskIterator<L, O>(pub Vec<(L, JobResult<O>)>);

impl<L: Clone, O: for<'a> Deserialize<'a>> Iterator for LabelPendingTaskIterator<L, O> {
    type Item = (L, O);

    fn next(&mut self) -> Option<Self::Item> {
        if self.0.is_empty() {
            return None;
        }

        loop {
            for (i, task) in self.0.iter().enumerate() {
                let result = &task.1;
                let label = task.0.clone();
                if let Some(res) = result.wait_timeout() {
                    self.0.remove(i);
                    return Some((label, res));
                }
            }
        }
    }
}