extern crate alloc;

use alloc::vec::Vec;

use crate::math::{Vec3, Vec3Ext, VEC3_ZERO};
use crate::pxl8::*;
use crate::voxel::VoxelWorld;
use crate::world::World;

pub type Entity = pxl8_sim_entity;

const ALIVE: u32 = PXL8_SIM_FLAG_ALIVE;
const PLAYER: u32 = PXL8_SIM_FLAG_PLAYER;

const MAX_ENTITIES: usize = 1024;

impl Default for Entity {
    fn default() -> Self {
        Self {
            pos: VEC3_ZERO,
            vel: VEC3_ZERO,
            yaw: 0.0,
            pitch: 0.0,
            flags: 0,
            kind: 0,
            _pad: 0,
        }
    }
}

pub struct Simulation {
    pub entities: Vec<Entity>,
    pub free_list: Vec<u32>,
    pub player: Option<u32>,
    pub tick: u64,
    pub time: f32,
    pub voxels: VoxelWorld,
    pub world: World,
}

impl Simulation {
    pub fn new() -> Self {
        let mut entities = Vec::with_capacity(MAX_ENTITIES);
        entities.resize(MAX_ENTITIES, Entity::default());

        let mut free_list = Vec::with_capacity(MAX_ENTITIES);
        for i in (0..MAX_ENTITIES).rev() {
            free_list.push(i as u32);
        }

        Self {
            entities,
            free_list,
            player: None,
            tick: 0,
            time: 0.0,
            voxels: VoxelWorld::new(12345),
            world: World::new(12345),
        }
    }

    pub fn spawn(&mut self) -> Option<u32> {
        let idx = self.free_list.pop()?;
        self.entities[idx as usize] = Entity {
            flags: ALIVE,
            ..Default::default()
        };
        Some(idx)
    }

    pub fn despawn(&mut self, id: u32) {
        if (id as usize) < self.entities.len() {
            self.entities[id as usize].flags = 0;
            self.free_list.push(id);
        }
    }

    pub fn spawn_player(&mut self, x: f32, y: f32, z: f32) -> u32 {
        let id = self.spawn().unwrap_or(0);
        let ent = &mut self.entities[id as usize];
        ent.flags = ALIVE | PLAYER;
        ent.pos = Vec3::new(x, y, z);
        self.player = Some(id);

        self.voxels.load_chunks_around(ent.pos, 2);

        id
    }

    pub fn teleport_player(&mut self, x: f32, y: f32, z: f32) {
        if let Some(id) = self.player {
            let ent = &mut self.entities[id as usize];
            ent.pos = Vec3::new(x, y, z);
        }
    }

    pub fn step(&mut self, inputs: &[pxl8_input_msg], dt: f32) {
        self.tick += 1;
        self.time += dt;

        for input in inputs {
            self.move_player(input, dt);
        }

        self.integrate(dt);
    }

    fn make_sim_world(&self, pos: Vec3) -> pxl8_sim_world {
        if let Some(chunk) = self.world.active() {
            if let Some(bsp) = chunk.as_bsp() {
                return pxl8_sim_world {
                    bsp: bsp.as_c_bsp(),
                    vxl: core::ptr::null(),
                    vxl_cx: 0,
                    vxl_cy: 0,
                    vxl_cz: 0,
                };
            }
        }

        let cx = VoxelWorld::world_to_chunk(pos.x);
        let cy = VoxelWorld::world_to_chunk(pos.y);
        let cz = VoxelWorld::world_to_chunk(pos.z);

        if let Some(chunk) = self.voxels.get_chunk(cx, cy, cz) {
            pxl8_sim_world {
                bsp: core::ptr::null(),
                vxl: chunk.chunk as *const _,
                vxl_cx: cx,
                vxl_cy: cy,
                vxl_cz: cz,
            }
        } else {
            pxl8_sim_world {
                bsp: core::ptr::null(),
                vxl: core::ptr::null(),
                vxl_cx: 0,
                vxl_cy: 0,
                vxl_cz: 0,
            }
        }
    }

    fn integrate(&mut self, dt: f32) {
        for i in 0..self.entities.len() {
            let ent = &self.entities[i];
            if ent.flags & ALIVE == 0 || ent.flags & PLAYER != 0 {
                continue;
            }

            let world = self.make_sim_world(ent.pos);
            let ent = &mut self.entities[i];
            unsafe {
                pxl8_sim_integrate(ent, &world, dt);
            }
        }
    }

    fn move_player(&mut self, input: &pxl8_input_msg, dt: f32) {
        let Some(id) = self.player else { return };
        let ent = &self.entities[id as usize];
        if ent.flags & ALIVE == 0 {
            return;
        }

        let world = self.make_sim_world(ent.pos);
        let ent = &mut self.entities[id as usize];
        unsafe {
            pxl8_sim_move_player(ent, input, &world, dt);
        }
    }

    pub fn generate_snapshot<F>(&self, _player_id: u64, mut writer: F)
    where
        F: FnMut(&pxl8_entity_state),
    {
        for (i, ent) in self.entities.iter().enumerate() {
            if ent.flags & ALIVE == 0 {
                continue;
            }

            let mut state = pxl8_entity_state {
                entity_id: i as u64,
                userdata: [0u8; 56],
            };

            let bytes = &mut state.userdata;
            bytes[0..4].copy_from_slice(&ent.pos.x.to_be_bytes());
            bytes[4..8].copy_from_slice(&ent.pos.y.to_be_bytes());
            bytes[8..12].copy_from_slice(&ent.pos.z.to_be_bytes());
            bytes[12..16].copy_from_slice(&ent.yaw.to_be_bytes());
            bytes[16..20].copy_from_slice(&ent.pitch.to_be_bytes());
            bytes[20..24].copy_from_slice(&ent.vel.x.to_be_bytes());
            bytes[24..28].copy_from_slice(&ent.vel.y.to_be_bytes());
            bytes[28..32].copy_from_slice(&ent.vel.z.to_be_bytes());
            bytes[32..36].copy_from_slice(&ent.flags.to_be_bytes());
            bytes[36..38].copy_from_slice(&ent.kind.to_be_bytes());

            writer(&state);
        }
    }

    pub fn entity_count(&self) -> usize {
        self.entities.iter().filter(|e| e.flags & ALIVE != 0).count()
    }

    pub fn get_player_position(&self, player_id: u64) -> Option<(f32, f32, f32)> {
        let idx = player_id as usize;
        if idx < self.entities.len() {
            let ent = &self.entities[idx];
            if ent.flags & ALIVE != 0 && ent.flags & PLAYER != 0 {
                return Some((ent.pos.x, ent.pos.y, ent.pos.z));
            }
        }
        None
    }
}

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