use board::Board;
use evaluate::PosValue;
use static_assertions::const_assert_eq;
use std::collections::{HashMap};
use log::info;
use zobrist;

use crate::movegen::{SimpleMove};
use crate::zobrist::Hash;

#[derive(Clone, PartialEq)]
pub enum EntryType {
    Value,
    LowerBound,
    UpperBound,
    NoBound
}

#[derive(Clone)]
pub struct CacheEntry {
    pub entry_type: EntryType,  // 1 byte
    pub halfmove_age: u8,       // 1 byte
    pub mov: SimpleMove,        // 2 bytes
    pub value_and_depth: i32,   // 4 bytes
}
const_assert_eq!(std::mem::size_of::<CacheEntry>(), 8);

impl CacheEntry {
    pub fn null() -> Self {
        CacheEntry { entry_type: EntryType::Value, halfmove_age: 0, mov: SimpleMove { from: 0, to: 0 }, value_and_depth: 0 }
    }

    pub fn new_value(depth: u8, halfmove_age: u8, mov: SimpleMove, value: PosValue) -> Self {
        CacheEntry {
            entry_type: EntryType::Value,
            halfmove_age,
            mov,
            value_and_depth: (value << 8) | (depth as i32),
        }
    }

    pub fn new_upper(depth: u8, halfmove_age: u8, mov: SimpleMove, value: PosValue) -> Self {
        CacheEntry {
            entry_type: EntryType::UpperBound,
            halfmove_age,
            mov,
            value_and_depth: (value << 8) | (depth as i32),
        }
    }

    pub fn new_lower(depth: u8, halfmove_age: u8, mov: SimpleMove, value: PosValue) -> Self {
        CacheEntry {
            entry_type: EntryType::LowerBound,
            halfmove_age,
            mov,
            value_and_depth: (value << 8) | (depth as i32),
        }
    }
    
    pub fn value(&self) -> PosValue {
        self.value_and_depth >> 8
    }

    pub fn depth(&self) -> u8 {
        (self.value_and_depth & 0xFF) as u8
    }
}

struct Bucket {
    hashes: [Hash; 4],
    entries: [CacheEntry; 4],
}

const_assert_eq!(std::mem::size_of::<Bucket>(), 64);

pub struct Cache {
    table: Vec<Bucket>,
}

#[derive(Clone)]
pub struct RepetitionTable {
    hashmap: HashMap<zobrist::Hash, i32>,
}

impl Cache {
    pub fn new_in_megabytes(mbytes: usize) -> Self {
        Self::new(mbytes * 1024 * 1024 / std::mem::size_of::<Bucket>())
    }

    pub fn new(length: usize) -> Self {
        let c = Cache {
            table: unsafe {
                let layout = std::alloc::Layout::array::<Bucket>(length).unwrap();
                let allayout = layout.align_to(64).unwrap();
                let ptr = std::alloc::alloc(allayout);
                Vec::from_raw_parts(ptr.cast(), length, length)
            },
        };
        c
    }

    fn get_index(&self, hash: zobrist::Hash) -> usize {
        (hash % (self.table.len() as u64)) as usize
    }

    pub fn lookup<'a>(&'a self, board: &Board) -> Option<&'a CacheEntry> {
        if board.zobrist.is_none() {
            info!("invalid zobrist");
        }
        let hash = board.zobrist.as_ref().unwrap().1;
        let index = self.get_index(hash);

        let bucket = &self.table[index];
        for i in 0..bucket.hashes.len() {
            if bucket.hashes[i] == hash {
                return Some(&bucket.entries[i]);
            }
        }
        return None;
    }

    fn should_replace(old_hash: Hash, old_ce: &CacheEntry, new_hash: Hash, new: &CacheEntry) -> bool {
        if old_hash == 0 {
            return true;
        }

        // different positions
        if old_hash != new_hash {
            if old_ce.halfmove_age < new.halfmove_age {
                return true;
            }
            if old_ce.entry_type == EntryType::Value {
                return false;
            }
            if old_ce.depth() <= new.depth() {
                return true;
            }
        }

        if new.depth() >= old_ce.depth() {
            return true;
        }

        return false;
    }
    
    pub fn cache(&mut self, game_pos: &Board, ce: CacheEntry) {
        if game_pos.zobrist.is_none() {
            info!("invalid zobrist");
        }

        let hash = game_pos.zobrist.as_ref().unwrap().1;
        let index = self.get_index(hash);

        let bucket = &mut self.table[index];


        for i in 0..bucket.hashes.len() {
            if bucket.hashes[i] == hash {
                if bucket.entries[i].depth() <= ce.depth() {
                    bucket.entries[i] = ce;
                }
                return;
            }
        }

        for i in 0..bucket.hashes.len() {
            if Self::should_replace(bucket.hashes[i], &bucket.entries[i], hash, &ce) {
                bucket.hashes[i] = hash;
                bucket.entries[i] = ce;
                break;
            }
        }
    }

    pub fn fullness_permill(&self) -> usize {
        let mut permill = 0;
        for i in 0..25 {
            permill += 10 * self.table[i].hashes.iter().filter(|h| **h != 0).count();
        }
        permill
    }

    pub fn clear(&mut self) {
        for bucket in &mut self.table {
            bucket.hashes = [0; 4];
        }
    }
}


impl RepetitionTable {
    pub fn new() -> Self {
        RepetitionTable {
            hashmap: HashMap::with_capacity(64)
        }
    }

    pub fn clear(&mut self) {
        self.hashmap.clear();
    }

    pub fn lookup(&self, hash: zobrist::Hash) -> i32 {
        *self.hashmap.get(&hash).unwrap_or(&0)
    }

    pub fn increment(&mut self, hash: zobrist::Hash) -> i32 {
        if let Some(entry) = self.hashmap.get_mut(&hash) {
            *entry += 1;
            *entry
        }
        else {
            self.hashmap.insert(hash, 1);
            1
        }
    }

    pub fn decrement(&mut self, hash: zobrist::Hash) {
        if let Some(entry) = self.hashmap.get_mut(&hash) {
            *entry -= 1;
            if *entry == 0 {
                self.hashmap.remove(&hash);
            }
        }
    }
}