use crate::accounts_index::IndexValue;
use crate::bucket_map_holder_stats::BucketMapHolderStats;
use crate::waitable_condvar::WaitableCondvar;
use std::fmt::Debug;
use std::sync::Mutex;

// will eventually hold the bucket map
pub struct BucketMapHolder<T: IndexValue> {
    pub stats: BucketMapHolderStats,

    // used by bg processing to know when any bucket has become dirty
    pub wait_dirty_bucket: WaitableCondvar,
    next_bucket_to_flush: Mutex<usize>,
    bins: usize,
    _phantom: std::marker::PhantomData<T>,
}

impl<T: IndexValue> Debug for BucketMapHolder<T> {
    fn fmt(&self, _f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        Ok(())
    }
}

#[allow(clippy::mutex_atomic)]
impl<T: IndexValue> BucketMapHolder<T> {
    pub fn new(bins: usize) -> Self {
        Self {
            stats: BucketMapHolderStats::default(),
            wait_dirty_bucket: WaitableCondvar::default(),
            next_bucket_to_flush: Mutex::new(0),
            bins,
            _phantom: std::marker::PhantomData::<T>::default(),
        }
    }

    // get the next bucket to flush, with the idea that the previous bucket
    // is perhaps being flushed by another thread already.
    pub fn next_bucket_to_flush(&self) -> usize {
        // could be lock-free as an optimization
        // wrapping is tricky
        let mut lock = self.next_bucket_to_flush.lock().unwrap();
        let result = *lock;
        *lock = (result + 1) % self.bins;
        result
    }
}

#[cfg(test)]
pub mod tests {
    use super::*;
    use rayon::prelude::*;
    use std::sync::atomic::{AtomicUsize, Ordering};

    #[test]
    fn test_next_bucket_to_flush() {
        solana_logger::setup();
        let bins = 4;
        let test = BucketMapHolder::<u64>::new(bins);
        let visited = (0..bins)
            .into_iter()
            .map(|_| AtomicUsize::default())
            .collect::<Vec<_>>();
        let iterations = bins * 30;
        let threads = bins * 4;
        let expected = threads * iterations / bins;

        (0..threads).into_par_iter().for_each(|_| {
            (0..iterations).into_iter().for_each(|_| {
                let bin = test.next_bucket_to_flush();
                visited[bin].fetch_add(1, Ordering::Relaxed);
            });
        });
        visited.iter().enumerate().for_each(|(bin, visited)| {
            assert_eq!(visited.load(Ordering::Relaxed), expected, "bin: {}", bin)
        });
    }
}