use super::common::GearId;

use std::{

    any::TypeId,

    mem::{size_of, MaybeUninit},

    num::NonZeroU16,

    ptr::{copy_nonoverlapping, null_mut, NonNull},

    slice,

};

pub trait TypeTuple: Sized {

    fn len() -> usize;

    fn get_types(dest: &mut Vec<TypeId>);

    unsafe fn iter<F: FnMut(Self)>(slices: &[*mut u8], count: usize, mut f: F);

}

macro_rules! type_tuple_impl {

    ($($n: literal: $t: ident),+) => {

        impl<$($t: 'static),+> TypeTuple for ($(&$t),+,) {

            fn len() -> usize {

                [$({TypeId::of::<$t>(); 1}),+].iter().sum()

            }

            fn get_types(types: &mut Vec<TypeId>) {

                $(types.push(TypeId::of::<$t>()));+

            }

                for i in 0..count {

                    unsafe {

                        f(($(&*(*slices.get_unchecked($n) as *mut $t).add(i)),+,));

                    }

                }

            }

        }

        impl<$($t: 'static),+> TypeTuple for ($(&mut $t),+,) {

            fn len() -> usize {

                [$({TypeId::of::<$t>(); 1}),+].iter().sum()

            }

            fn get_types(types: &mut Vec<TypeId>) {

                $(types.push(TypeId::of::<$t>()));+

            }

                for i in 0..count {

                    unsafe {

                        f(($(&mut *(*slices.get_unchecked($n) as *mut $t).add(i)),+,));

                    }

                }

            }

        }

    }

}

type_tuple_impl!(0: A);

type_tuple_impl!(0: A, 1: B);

type_tuple_impl!(0: A, 1: B, 2: C);

type_tuple_impl!(0: A, 1: B, 2: C, 3: D);

type_tuple_impl!(0: A, 1: B, 2: C, 3: D, 4: E);

const BLOCK_SIZE: usize = 32768;

struct DataBlock {

    max_elements: u16,

    elements_count: u16,

    data: Box<[u8; BLOCK_SIZE]>,

    component_blocks: [Option<NonNull<u8>>; 64],

}

impl Unpin for DataBlock {}

impl DataBlock {

    fn new(mask: u64, element_sizes: &[u16; 64]) -> Self {

        let total_size: u16 = element_sizes

            .iter()

            .enumerate()

            .filter(|(i, _)| mask & (1 << *i as u64) != 0)

            .map(|(_, size)| *size)

            .sum();

        let max_elements = (BLOCK_SIZE / total_size as usize) as u16;

        let mut data: Box<[u8; BLOCK_SIZE]> =

            Box::new(unsafe { MaybeUninit::uninit().assume_init() });

        let mut blocks = [None; 64];

        let mut offset = 0;

        for i in 0..64 {

            if mask & (1 << i) != 0 {

                blocks[i] = Some(NonNull::new(data[offset..].as_mut_ptr()).unwrap());

                offset += element_sizes[i] as usize * max_elements as usize;

            }

        }

        Self {

            elements_count: 0,

            max_elements,

            data,

            component_blocks: blocks,

        }

    }

    fn is_full(&self) -> bool {

        self.elements_count == self.max_elements

    }

}

#[derive(Clone, Copy, Debug, Default)]

pub struct LookupEntry {

    index: Option<NonZeroU16>,

    block_index: u16,

}

pub struct GearDataManager {

    types: Vec<TypeId>,

    blocks: Vec<DataBlock>,

    block_masks: Vec<u64>,

    element_sizes: Box<[u16; 64]>,

    lookup: Box<[LookupEntry]>,

}

impl GearDataManager {

    pub fn new() -> Self {

        Self {

            types: vec![],

            blocks: vec![],

            block_masks: vec![],

            element_sizes: Box::new([0; 64]),

            lookup: vec![LookupEntry::default(); u16::max_value() as usize].into_boxed_slice(),

        }

    }

    #[inline]

    fn get_type_index<T: 'static>(&self) -> Option<usize> {

        let type_id = TypeId::of::<T>();

        self.types.iter().position(|id| *id == type_id)

    }

    fn move_between_blocks(&mut self, from_block_index: u16, from_index: u16, to_block_index: u16) {

        debug_assert!(from_block_index != to_block_index);

        let source_mask = self.block_masks[from_block_index as usize];

        let destination_mask = self.block_masks[to_block_index as usize];

        debug_assert!(source_mask & destination_mask == source_mask);

        let source = &self.blocks[from_block_index as usize];

        let destination = &self.blocks[to_block_index as usize];

        debug_assert!(from_index < source.elements_count);

        debug_assert!(!destination.is_full());

        for i in 0..64 {

            if source_mask & 1 << i != 0 {

                unsafe {

                    copy_nonoverlapping(

                        source.component_blocks[i].unwrap().as_ptr(),

                        destination.component_blocks[i].unwrap().as_ptr(),

                        self.element_sizes[i] as usize,

                    );

                }

            }

        }

        self.blocks[from_block_index as usize].elements_count -= 1;

        self.blocks[to_block_index as usize].elements_count += 1;

    }

    fn add_to_block<T: Clone>(&mut self, block_index: u16, value: &T) {

        debug_assert!(self.block_masks[block_index as usize].count_ones() == 1);

        let block = &mut self.blocks[block_index as usize];

        debug_assert!(block.elements_count < block.max_elements);

        unsafe {

            let slice = slice::from_raw_parts_mut(

                block.data.as_mut_ptr() as *mut T,

                block.max_elements as usize,

            );

            *slice.get_unchecked_mut(block.elements_count as usize) = value.clone();

        };

        block.elements_count += 1;

    }

    fn remove_from_block(&mut self, block_index: u16, index: u16) {

        let block = &mut self.blocks[block_index as usize];

        debug_assert!(index < block.elements_count);

        for (i, size) in self.element_sizes.iter().cloned().enumerate() {

            if index < block.elements_count - 1 {

                if let Some(ptr) = block.component_blocks[i] {

                    unsafe {

                        copy_nonoverlapping(

                            ptr.as_ptr()

                                .add((size * (block.elements_count - 1)) as usize),

                            ptr.as_ptr().add((size * index) as usize),

                            size as usize,

                        );

                    }

                }

            }

        }

        block.elements_count -= 1;

    }

    #[inline]

    fn ensure_block(&mut self, mask: u64) -> u16 {

        if let Some(index) = self

            .block_masks

            .iter()

            .enumerate()

            .position(|(i, m)| *m == mask && !self.blocks[i].is_full())

        {

            index as u16

        } else {

            self.blocks.push(DataBlock::new(mask, &self.element_sizes));

            self.block_masks.push(mask);

            (self.blocks.len() - 1) as u16

        }

    }

    pub fn add<T: Clone + 'static>(&mut self, gear_id: GearId, value: &T) {

        if let Some(type_index) = self.get_type_index::<T>() {

            let type_bit = 1 << type_index as u64;

            let entry = self.lookup[gear_id.get() as usize - 1];

            if let Some(index) = entry.index {

                let mask = self.block_masks[entry.block_index as usize];

                let new_mask = mask | type_bit;

                if new_mask != mask {

                    let dest_block_index = self.ensure_block(new_mask);

                    self.move_between_blocks(entry.block_index, index.get() - 1, dest_block_index);

                }

            } else {

                let dest_block_index = self.ensure_block(type_bit);

                self.add_to_block(dest_block_index, value);

            }

        } else {

            panic!("Unregistered type")

        }

    }

    pub fn remove<T: 'static>(&mut self, gear_id: GearId) {

        if let Some(type_index) = self.get_type_index::<T>() {

            let entry = self.lookup[gear_id.get() as usize - 1];

            if let Some(index) = entry.index {

                let destination_mask =

                    self.block_masks[entry.block_index as usize] & !(1 << type_index as u64);

                if destination_mask == 0 {

                    self.remove_all(gear_id)

                } else {

                    let destination_block_index = self.ensure_block(destination_mask);

                    self.move_between_blocks(

                        entry.block_index,

                        index.get() - 1,

                        destination_block_index,

                    );

                }

            }

        } else {

            panic!("Unregistered type")

        }

    }

    pub fn remove_all(&mut self, gear_id: GearId) {

        let entry = self.lookup[gear_id.get() as usize - 1];

        if let Some(index) = entry.index {

            self.remove_from_block(entry.block_index, index.get() - 1);

        }

    }

    pub fn register<T: 'static>(&mut self) {

        debug_assert!(!std::mem::needs_drop::<T>());

        debug_assert!(self.types.len() <= 64);

        debug_assert!(size_of::<T>() <= u16::max_value() as usize);

        let id = TypeId::of::<T>();

        if !self.types.contains(&id) {

            self.element_sizes[self.types.len()] = size_of::<T>() as u16;

            self.types.push(id);

        }

    }

    pub fn iter<T: TypeTuple + 'static, F: FnMut(T)>(&self, mut f: F) {

        let mut arg_types = Vec::with_capacity(64);

        T::get_types(&mut arg_types);

        let mut type_indices = vec![-1i8; arg_types.len()];

        let mut selector = 0u64;

        for (arg_index, type_id) in arg_types.iter().enumerate() {

            match self.types.iter().position(|t| t == type_id) {

                Some(i) if selector & 1 << i as u64 != 0 => panic!("Duplicate type"),

                Some(i) => {

                    type_indices[arg_index] = i as i8;

                    selector &= 1 << i as u64;

                }

                None => panic!("Unregistered type"),

            }

        }

        let mut slices = vec![null_mut(); arg_types.len()];

        for (block_index, mask) in self.block_masks.iter().enumerate() {

            if mask & selector == selector {

                let block = &self.blocks[block_index];

                for (arg_index, type_index) in type_indices.iter().cloned().enumerate() {

                    slices[arg_index as usize] = block.component_blocks[type_index as usize]

                        .unwrap()

                        .as_ptr()

                }

                unsafe {

                    T::iter(&slices[..], block.elements_count as usize, |x| f(x));

                }

            }

        }

    }

}

#[cfg(test)]

mod test {

    use super::{super::common::GearId, GearDataManager};

    #[derive(Clone)]

    struct Datum {

        value: u32,

    }

    #[test]

    fn single_component_iteration() {

        let mut manager = GearDataManager::new();

        manager.register::<Datum>();

        for i in 1..=5 {

            manager.add(GearId::new(i as u16).unwrap(), &Datum { value: i });

        }

        let mut sum = 0;

        manager.iter(|(d,): (&Datum,)| sum += d.value);

        assert_eq!(sum, 15);

        manager.iter(|(d,): (&mut Datum,)| d.value += 1);

        manager.iter(|(d,): (&Datum,)| sum += d.value);

        assert_eq!(sum, 35);

    }

}