use crate::axes::{Axis, Operation};
use indexmap::{Equivalent, IndexMap};
use ndarray::{ArrayD, SliceInfoElem};
use std::any::Any;
use std::fmt::{Debug, Formatter};
use std::hash::{Hash, Hasher};
use std::path::{Path, PathBuf};
use std::sync::{Arc, Mutex, OnceLock};

use crate::readers::Frame;

/// maximum number of frames held in the cache
const DEFAULT_FRAME_CACHE_SIZE: usize = 128;

/// maximum number of materialized arrays held in the cache
const DEFAULT_ARRAY_CACHE_SIZE: usize = 32;

/// identity of the reader a frame was read from
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub(crate) struct ReaderKey {
    pub(crate) name: String,
    pub(crate) path: PathBuf,
    pub(crate) series: usize,
    pub(crate) position: usize,
}

/// borrowed view of [`ReaderKey`] for cache lookups without allocation.
/// hashes byte-identically to [`ReaderKey`] (str/String and Path/PathBuf hash
/// the same), so it only matches the same reader identity.
#[derive(Debug, PartialEq, Eq)]
pub(crate) struct ReaderKeyRef<'a> {
    pub(crate) name: &'a str,
    pub(crate) path: &'a Path,
    pub(crate) series: usize,
    pub(crate) position: usize,
}

impl Hash for ReaderKeyRef<'_> {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.name.hash(state);
        self.path.hash(state);
        self.series.hash(state);
        self.position.hash(state);
    }
}

impl Equivalent<ReaderKey> for ReaderKeyRef<'_> {
    fn equivalent(&self, key: &ReaderKey) -> bool {
        self.name == key.name
            && self.path == key.path.as_path()
            && self.series == key.series
            && self.position == key.position
    }
}

impl ReaderKeyRef<'_> {
    pub(crate) fn to_owned(&self) -> ReaderKey {
        ReaderKey {
            name: self.name.to_string(),
            path: self.path.to_path_buf(),
            series: self.series,
            position: self.position,
        }
    }
}

pub(crate) type FrameKey = (ReaderKey, usize, usize, usize);

/// borrowed view of [`FrameKey`] for cache lookups without allocation.
#[derive(Debug, PartialEq, Eq)]
pub(crate) struct FrameKeyRef<'a> {
    pub(crate) reader: ReaderKeyRef<'a>,
    pub(crate) c: usize,
    pub(crate) z: usize,
    pub(crate) t: usize,
}

impl Hash for FrameKeyRef<'_> {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.reader.hash(state);
        self.c.hash(state);
        self.z.hash(state);
        self.t.hash(state);
    }
}

impl Equivalent<FrameKey> for FrameKeyRef<'_> {
    fn equivalent(&self, key: &FrameKey) -> bool {
        let (rk, c, z, t) = key;
        self.reader.equivalent(rk) && self.c == *c && self.z == *z && self.t == *t
    }
}

impl FrameKeyRef<'_> {
    pub(crate) fn to_owned(&self) -> FrameKey {
        (self.reader.to_owned(), self.c, self.z, self.t)
    }
}

/// identity of a materialized array in the process-wide cache
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub(crate) struct ArrayKey {
    pub(crate) reader: ReaderKey,
    pub(crate) dtype: &'static str,
    pub(crate) slice: Vec<SliceInfoElem>,
    pub(crate) axes: Vec<Axis>,
    pub(crate) operations: Vec<(Axis, Operation)>,
}

/// borrowed view of [`ArrayKey`] for cache lookups without allocation.
#[derive(Debug, PartialEq, Eq)]
pub(crate) struct ArrayKeyRef<'a> {
    pub(crate) reader: ReaderKeyRef<'a>,
    pub(crate) dtype: &'static str,
    pub(crate) slice: &'a [SliceInfoElem],
    pub(crate) axes: &'a [Axis],
    pub(crate) operations: &'a IndexMap<Axis, Operation>,
}

impl Hash for ArrayKeyRef<'_> {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.reader.hash(state);
        self.dtype.hash(state);
        self.slice.hash(state);
        self.axes.hash(state);
        self.operations.len().hash(state);
        for (ax, op) in self.operations.iter() {
            ax.hash(state);
            op.hash(state);
        }
    }
}

impl Equivalent<ArrayKey> for ArrayKeyRef<'_> {
    fn equivalent(&self, key: &ArrayKey) -> bool {
        self.reader.equivalent(&key.reader)
            && self.dtype == key.dtype
            && self.slice == key.slice
            && self.axes == key.axes
            && self.operations.len() == key.operations.len()
            && self
                .operations
                .iter()
                .zip(&key.operations)
                .all(|((ax, op), (key_ax, key_op))| ax == key_ax && op == key_op)
    }
}

impl ArrayKeyRef<'_> {
    pub(crate) fn to_owned(&self) -> ArrayKey {
        ArrayKey {
            reader: self.reader.to_owned(),
            dtype: self.dtype,
            slice: self.slice.to_vec(),
            axes: self.axes.to_vec(),
            operations: self
                .operations
                .iter()
                .map(|(ax, op)| (*ax, op.clone()))
                .collect(),
        }
    }
}

/// process-wide LRU cache of frames, shared between all views and threads
static GLOBAL_FRAME_CACHE: OnceLock<FrameCache> = OnceLock::new();

/// thread-safe LRU cache of frames read from the underlying reader
pub(crate) struct FrameCache {
    inner: Mutex<FrameCacheInner>,
}

struct FrameCacheInner {
    map: IndexMap<FrameKey, Arc<Frame>>,
    capacity: usize,
}

impl Default for FrameCache {
    fn default() -> Self {
        Self::new(DEFAULT_FRAME_CACHE_SIZE)
    }
}

impl FrameCache {
    pub(crate) fn new(capacity: usize) -> Self {
        Self {
            inner: Mutex::new(FrameCacheInner {
                map: IndexMap::with_capacity(capacity),
                capacity,
            }),
        }
    }

    pub(crate) fn global() -> &'static FrameCache {
        GLOBAL_FRAME_CACHE.get_or_init(FrameCache::default)
    }

    pub(crate) fn capacity(&self) -> usize {
        self.inner.lock().unwrap().capacity
    }

    pub(crate) fn set_capacity(&self, capacity: usize) {
        let mut inner = self.inner.lock().unwrap();
        inner.capacity = capacity;
        while inner.map.len() > inner.capacity {
            inner.map.shift_remove_index(0);
        }
    }

    pub(crate) fn get<Q>(&self, key: &Q) -> Option<Arc<Frame>>
    where
        Q: ?Sized + Hash + Equivalent<FrameKey>,
    {
        let mut inner = self.inner.lock().unwrap();
        if let Some(idx) = inner.map.get_index_of(key) {
            let (key, frame) = inner.map.shift_remove_index(idx).unwrap();
            inner.map.insert(key, frame.clone());
            Some(frame)
        } else {
            None
        }
    }

    pub(crate) fn insert(&self, key: FrameKey, frame: Arc<Frame>) {
        let mut inner = self.inner.lock().unwrap();
        inner.map.insert(key, frame);
        while inner.map.len() > inner.capacity {
            inner.map.shift_remove_index(0);
        }
    }

    #[cfg(test)]
    pub(crate) fn len(&self) -> usize {
        self.inner.lock().unwrap().map.len()
    }
}

impl Debug for FrameCache {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("FrameCache").finish_non_exhaustive()
    }
}

/// process-wide LRU cache of materialized arrays, shared between all views and threads
static GLOBAL_ARRAY_CACHE: OnceLock<ArrayCache> = OnceLock::new();

/// thread-safe LRU cache of materialized arrays produced by `as_array_dyn`
pub(crate) struct ArrayCache {
    inner: Mutex<ArrayCacheInner>,
}

struct ArrayCacheInner {
    map: IndexMap<ArrayKey, Arc<dyn Any + Send + Sync>>,
    capacity: usize,
}

impl Default for ArrayCache {
    fn default() -> Self {
        Self::new(DEFAULT_ARRAY_CACHE_SIZE)
    }
}

impl ArrayCache {
    pub(crate) fn new(capacity: usize) -> Self {
        Self {
            inner: Mutex::new(ArrayCacheInner {
                map: IndexMap::with_capacity(capacity),
                capacity,
            }),
        }
    }

    pub(crate) fn global() -> &'static ArrayCache {
        GLOBAL_ARRAY_CACHE.get_or_init(ArrayCache::default)
    }

    pub(crate) fn capacity(&self) -> usize {
        self.inner.lock().unwrap().capacity
    }

    pub(crate) fn set_capacity(&self, capacity: usize) {
        let mut inner = self.inner.lock().unwrap();
        inner.capacity = capacity;
        while inner.map.len() > inner.capacity {
            inner.map.shift_remove_index(0);
        }
    }

    pub(crate) fn get<T, Q>(&self, key: &Q) -> Option<Arc<ArrayD<T>>>
    where
        Q: ?Sized + Hash + Equivalent<ArrayKey>,
        T: Any + Send + Sync,
    {
        let mut inner = self.inner.lock().unwrap();
        if let Some(idx) = inner.map.get_index_of(key) {
            let (key, array) = inner.map.shift_remove_index(idx).unwrap();
            inner.map.insert(key, array.clone());
            array.downcast::<ArrayD<T>>().ok()
        } else {
            None
        }
    }

    pub(crate) fn insert<T: Any + Send + Sync>(&self, key: ArrayKey, array: ArrayD<T>) {
        let mut inner = self.inner.lock().unwrap();
        inner.map.insert(key, Arc::new(array));
        while inner.map.len() > inner.capacity {
            inner.map.shift_remove_index(0);
        }
    }

    #[cfg(test)]
    pub(crate) fn len(&self) -> usize {
        self.inner.lock().unwrap().map.len()
    }
}

impl Debug for ArrayCache {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("ArrayCache").finish_non_exhaustive()
    }
}