use super::common::GearId;

use std::{

    any::TypeId,

    fmt::{Debug, Error, Formatter},

    io::Write,

    mem::{size_of, MaybeUninit},

    num::NonZeroU16,

    ptr::{copy_nonoverlapping, null_mut, NonNull},

    slice,

};

pub trait TypeTuple: Sized {

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

    unsafe fn iter<F: FnMut(GearId, 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 get_types(types: &mut Vec<TypeId>) {

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

            }

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

                for i in 0..count {

                }

            }

        }

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

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

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

            }

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

                for i in 0..count {

                }

            }

        }

    }

}

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],

    element_sizes: Box<[u16]>,

}

impl Unpin for DataBlock {}

impl Debug for DataBlock {

    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {

        write!(

            f,

            "Block ({}/{}) {{\n",

            self.elements_count, self.max_elements

        )?;

        write!(f, "\tIDs: [")?;

        let id_slice = unsafe {

            slice::from_raw_parts(

                self.data.as_ptr() as *const GearId,

                self.elements_count as usize,

            )

        };

        for gear_id in id_slice {

            write!(f, "{}, ", gear_id)?;

        }

        write!(f, "]\n")?;

        for type_index in 0..self.element_sizes.len() {

            if let Some(ptr) = self.component_blocks[type_index] {

                write!(f, "\tC{}: [", type_index)?;

                let slice = unsafe {

                    slice::from_raw_parts(

                        ptr.as_ptr(),

                        (self.elements_count * self.element_sizes[type_index]) as usize,

                    )

                };

                for byte in slice {

                    write!(f, "{}, ", byte)?;

                }

                write!(f, "]\n")?;

            }

        }

        write!(f, "}}\n")

    }

}

impl DataBlock {

    fn new(mask: u64, element_sizes: &[u16]) -> 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 + size_of::<GearId>())) as u16;

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

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

        let mut blocks = [None; 64];

        let mut offset = size_of::<GearId>() * max_elements as usize;

        for i in 0..element_sizes.len() {

            if mask & (1 << i as u64) != 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,

            element_sizes: Box::from(element_sizes),

        }

    }

    fn gear_ids(&self) -> &[GearId] {

        unsafe {

            slice::from_raw_parts(

                self.data.as_ptr() as *const GearId,

                self.max_elements as usize,

            )

        }

    }

    fn gear_ids_mut(&mut self) -> &mut [GearId] {

        unsafe {

            slice::from_raw_parts_mut(

                self.data.as_mut_ptr() as *mut GearId,

                self.max_elements as usize,

            )

        }

    }

    fn is_full(&self) -> bool {

        self.elements_count == self.max_elements

    }

}

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

struct LookupEntry {

    index: Option<NonZeroU16>,

    block_index: u16,

}

impl LookupEntry {

    fn new(block_index: u16, index: u16) -> Self {

        Self {

            index: unsafe { Some(NonZeroU16::new_unchecked(index + 1)) },

            block_index,

        }

    }

}

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, src_block_index: u16, src_index: u16, dest_block_index: u16) {

        debug_assert!(src_block_index != dest_block_index);

        let src_mask = self.block_masks[src_block_index as usize];

        let dest_mask = self.block_masks[dest_block_index as usize];

        debug_assert!(src_mask & dest_mask == src_mask);

        let src_block = &self.blocks[src_block_index as usize];

        let dest_block = &self.blocks[dest_block_index as usize];

        debug_assert!(src_index < src_block.elements_count);

        debug_assert!(!dest_block.is_full());

        let dest_index = dest_block.elements_count;

        for i in 0..self.types.len() {

            if src_mask & (1 << i as u64) != 0 {

                let size = self.element_sizes[i];

                let src_ptr = src_block.component_blocks[i].unwrap().as_ptr();

                let dest_ptr = dest_block.component_blocks[i].unwrap().as_ptr();

                unsafe {

                    copy_nonoverlapping(

                        src_ptr.add((src_index * size) as usize),

                        dest_ptr.add((dest_index * size) as usize),

                        size as usize,

                    );

                    if src_index < src_block.elements_count - 1 {

                        copy_nonoverlapping(

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

                            src_ptr.add((size * src_index) as usize),

                            size as usize,

                        );

                    }

                }

            }

        }

        let src_block = &mut self.blocks[src_block_index as usize];

        let gear_id = src_block.gear_ids()[src_index as usize];

        if src_index < src_block.elements_count - 1 {

            let relocated_index = src_block.elements_count as usize - 1;

            let gear_ids = src_block.gear_ids_mut();

            let relocated_id = gear_ids[relocated_index];

            gear_ids[src_index as usize] = relocated_id;

            self.lookup[relocated_id.get() as usize - 1] =

                LookupEntry::new(src_block_index, src_index);

        }

        src_block.elements_count -= 1;

        let dest_block = &mut self.blocks[dest_block_index as usize];

        let dest_index = dest_block.elements_count;

        dest_block.gear_ids_mut()[dest_index as usize] = gear_id;

        self.lookup[gear_id.get() as usize - 1] = LookupEntry::new(dest_block_index, dest_index);

        dest_block.elements_count += 1;

    }

    fn add_to_block<T: Clone>(&mut self, gear_id: GearId, 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.component_blocks[0].unwrap().as_ptr() as *mut T,

                block.max_elements as usize,

            );

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

        };

        let index = block.elements_count;

        self.lookup[gear_id.get() as usize - 1] = LookupEntry::new(block_index, index);

        block.gear_ids_mut()[index as usize] = gear_id;

        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,

                        );

                    }

                }

            }

        }

        self.lookup[block.gear_ids()[index as usize].get() as usize - 1] = LookupEntry::default();

        if index < block.elements_count - 1 {

            let relocated_index = block.elements_count as usize - 1;

            let gear_ids = block.gear_ids_mut();

            gear_ids[index as usize] = gear_ids[relocated_index];

            self.lookup[gear_ids[relocated_index].get() as usize - 1] =

                LookupEntry::new(block_index, index);

        }

        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[0..self.types.len()],

            ));

            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(gear_id, 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 dest_mask =

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

                if dest_mask == 0 {

                    self.remove_all(gear_id)

                } else {

                    let dest_block_index = self.ensure_block(dest_mask);

                    self.move_between_blocks(entry.block_index, index.get() - 1, dest_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)>(&mut self, mut f: F) {

        self.iter_id(|_, x| f(x));

    }

    pub fn iter_id<T: TypeTuple + 'static, F: FnMut(GearId, T)>(&mut 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() + 1];

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

            if mask & selector == selector {

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

                slices[0] = block.data.as_mut_ptr();

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

                    slices[arg_index as usize + 1] = block.component_blocks[type_index as usize]

                        .unwrap()

                        .as_ptr()

                }

                unsafe {

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

                }

            }

        }

    }

}

#[cfg(test)]

mod test {

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

    #[derive(Clone)]

    struct Datum {

        value: u32,

    }

    #[derive(Clone)]

    struct Tag {

        nothing: u8,

    }

    #[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);

    }

    #[test]

    fn multiple_component_iteration() {

        let mut manager = GearDataManager::new();

        manager.register::<Datum>();

        manager.register::<Tag>();

        for i in 1..=10 {

            let gear_id = GearId::new(i as u16).unwrap();

            manager.add(gear_id, &Datum { value: i });

        }

        for i in 1..=10 {

            let gear_id = GearId::new(i as u16).unwrap();

            if i & 1 == 0 {

                manager.add(GearId::new(i as u16).unwrap(), &Tag { nothing: 0 });

            }

        }

        let mut sum = 0;

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

        assert_eq!(sum, 55);

        let mut tag_sum1 = 0;

        let mut tag_sum2 = 0;

        manager.iter(|(d, _): (&Datum, &Tag)| tag_sum1 += d.value);

        manager.iter(|(_, d): (&Tag, &Datum)| tag_sum2 += d.value);

        assert_eq!(tag_sum1, 30);

        assert_eq!(tag_sum2, tag_sum1);

    }

}