/*!
A generic symbol table implementation supporting `O(1)` `clone`, `push`, and `pop` operations which can be shared between threads.

For a faster implementation which is limited to a single thread only, see the `hayami-im-rc` crate.
*/
#![deny(missing_docs, unsafe_code, missing_debug_implementations)]

use ahash::RandomState;
use im::HashMap;
use std::borrow::Borrow;
use std::fmt::{self, Debug, Formatter};
use std::hash::Hash;
use std::hash::{BuildHasher, Hasher};

pub use symbolmap_trait::{MutSymbolMap, SymbolMap, SymbolStack};

/// The `Arc` in use
///
/// Supports `elysees` (default) or `std`
#[cfg(feature = "elysees")]
#[allow(unused)]
type Arc<T> = elysees::Arc<T>;
#[cfg(not(feature = "elysees"))]
#[allow(unused)]
type Arc<T> = std::sync::Arc<T>;

/**
A symbol table implementation supporting snapshots, i.e. an `O(1)` cloning operation.
*/
pub struct SymbolTable<K: Hash + Eq, V, S: BuildHasher = RandomState> {
    /// This layer of the symbol table
    symbols: HashMap<K, V, S>,
    /// The depth of this symbol table
    depth: usize,
    /// A link to the previous layer's table, forming a singly-linked list
    prev: Option<Arc<SymbolTable<K, V, S>>>,
}

impl<K: Hash + Eq, V, S: BuildHasher + Default> Default for SymbolTable<K, V, S> {
    #[inline]
    fn default() -> SymbolTable<K, V, S> {
        SymbolTable {
            symbols: HashMap::default(),
            depth: 0,
            prev: None,
        }
    }
}

impl<K: Hash + Eq, V> SymbolTable<K, V> {
    /// Create a new, empty symbol table
    #[inline]
    pub fn new() -> SymbolTable<K, V> {
        Self::default()
    }
}

impl<K: Hash + Eq, V, S: BuildHasher> SymbolTable<K, V, S> {
    /// Get a reference to the table's BuildHasher
    #[inline]
    pub fn hasher(&self) -> &std::sync::Arc<S> {
        self.symbols.hasher()
    }
    /// Construct an empty hash map using the provided hasher.
    #[inline]
    pub fn with_hasher<RS>(hasher: RS) -> SymbolTable<K, V, S>
    where
        std::sync::Arc<S>: From<RS>,
    {
        SymbolTable {
            symbols: HashMap::with_hasher(hasher),
            depth: 0,
            prev: None,
        }
    }
}

impl<K: Hash + Eq, V: PartialEq, S: BuildHasher> PartialEq for SymbolTable<K, V, S> {
    #[inline]
    fn eq(&self, other: &Self) -> bool {
        //TODO: think about comparing previous tables...
        self.depth == other.depth && self.symbols == other.symbols && self.prev == other.prev
    }
}

impl<K: Hash + Eq, V: Eq, S: BuildHasher> Eq for SymbolTable<K, V, S> {}

impl<K: Hash + Eq, V: Hash, S: BuildHasher> Hash for SymbolTable<K, V, S> {
    fn hash<H: Hasher>(&self, hasher: &mut H) {
        //TODO: think about hashing previous tables...
        self.symbols.hash(hasher);
        self.depth.hash(hasher);
        self.prev.hash(hasher);
    }
}

impl<K: Hash + Eq + Debug, V: Debug, S: BuildHasher> Debug for SymbolTable<K, V, S> {
    #[inline]
    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
        fmt.debug_struct("SymbolTable")
            .field("symbols", &self.symbols)
            .field("depth", &self.depth)
            .field("prev", &self.prev)
            .finish()
    }
}

impl<K: Hash + Eq, V, S: BuildHasher> SymbolTable<K, V, S> {
    /// Get an `Arc` to the previous layer's table, if there is any
    #[inline]
    pub fn get_prev(&self) -> Option<&Arc<SymbolTable<K, V, S>>> {
        self.prev.as_ref()
    }
}

impl<K: Hash + Eq + Clone, V: Clone, S: BuildHasher> Clone for SymbolTable<K, V, S> {
    #[inline]
    fn clone(&self) -> SymbolTable<K, V, S> {
        SymbolTable {
            symbols: self.symbols.clone(),
            depth: self.depth,
            prev: self.prev.clone(),
        }
    }
}

impl<K: Hash + Eq + Clone, V: Clone, S: BuildHasher> SymbolTable<K, V, S> {
    /// Get a new symbol table extending this one
    #[inline]
    pub fn extend(self) -> SymbolTable<K, V, S> {
        let symbols = self.symbols.clone();
        let depth = self.depth + 1;
        SymbolTable {
            symbols,
            depth,
            prev: Some(Arc::new(self)),
        }
    }
}

impl<K: Hash + Eq + Clone, V: Clone, S: BuildHasher> SymbolMap<K> for SymbolTable<K, V, S> {
    type Value = V;
    #[inline]
    fn insert(&mut self, key: K, value: Self::Value) {
        self.symbols.insert(key, value);
    }
    #[inline]
    fn get<Q>(&self, key: &Q) -> Option<&Self::Value>
    where
        Q: ?Sized + Hash + Eq,
        K: Borrow<Q>,
    {
        self.symbols.get(key)
    }
    #[inline]
    fn contains_key<Q>(&self, key: &Q) -> bool
    where
        Q: ?Sized + Hash + Eq,
        K: Borrow<Q>,
    {
        self.symbols.contains_key(key)
    }
    #[inline]
    fn is_empty(&self) -> bool {
        self.symbols.is_empty()
    }
    #[inline]
    fn try_get_mut<Q>(&mut self, key: &Q) -> Option<&mut Self::Value>
    where
        Q: ?Sized + Hash + Eq,
        K: Borrow<Q>,
    {
        self.symbols.get_mut(key)
    }
    #[inline]
    fn push(&mut self) {
        self.prev = Some(Arc::new((*self).clone()));
        self.depth += 1;
    }
    #[inline]
    fn pop(&mut self) {
        if let Some(prev) = self.prev.as_deref() {
            *self = (*prev).clone();
        }
    }
    #[inline]
    fn depth(&self) -> usize {
        self.depth
    }
}

impl<K: Hash + Eq + Clone, V: Clone, S: BuildHasher> MutSymbolMap<K> for SymbolTable<K, V, S> {}

impl<K: Hash + Eq + Clone, V: Clone, S: BuildHasher> SymbolStack<K> for SymbolTable<K, V, S> {
    #[inline]
    fn prev(&self) -> Option<&Self> {
        self.prev.as_deref()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use symbolmap_trait::testing;
    #[test]
    fn basic_symbol_table_test() {
        testing::basic_symbol_table_test(&mut SymbolTable::new())
    }
}