use crossbeam_channel::Receiver;
use hashbrown::HashMap;
use log::info;
use nalgebra::Vector3;
use rapier3d::prelude::{
    vector, ActiveEvents, BroadPhase, CCDSolver, ChannelEventCollector, ColliderBuilder,
    ColliderHandle, ColliderSet, CollisionEvent, ImpulseJointSet, IntegrationParameters,
    IslandManager, MultibodyJointSet, NarrowPhase, PhysicsHooks, PhysicsPipeline,
    RigidBody as RapierBody, RigidBodyBuilder as RapierBodyBuilder,
    RigidBodyHandle as RapierBodyHandle, RigidBodySet as RapierBodySet,
};
use specs::Entity;

use crate::{approx_equals, BlockRotation, Vec3, VoxelAccess};

use super::{registry::Registry, WorldConfig};

mod aabb;
mod raycast;
mod rigidbody;
mod sweep;

pub use aabb::*;
pub use raycast::*;
pub use rigidbody::*;
pub use sweep::*;

pub struct Physics {
    body_set: RapierBodySet,
    collider_set: ColliderSet,
    pipeline: PhysicsPipeline,
    integration_options: IntegrationParameters,
    island_manager: IslandManager,
    broad_phase: BroadPhase,
    narrow_phase: NarrowPhase,
    impulse_joint_set: ImpulseJointSet,
    multibody_joint_set: MultibodyJointSet,
    ccd_solver: CCDSolver,
    collision_recv: Receiver<CollisionEvent>,
    event_handler: ChannelEventCollector,
    gravity: Vector3<f32>,
    pub entity_to_handlers: HashMap<Entity, (ColliderHandle, RapierBodyHandle)>,
}

impl Physics {
    pub fn new() -> Self {
        let (collision_send, collision_recv) = crossbeam_channel::unbounded();
        let (contact_force_send, _) = crossbeam_channel::unbounded();
        let event_handler = ChannelEventCollector::new(collision_send, contact_force_send);

        Self {
            collision_recv,
            body_set: RapierBodySet::default(),
            broad_phase: BroadPhase::default(),
            ccd_solver: CCDSolver::default(),
            collider_set: ColliderSet::default(),
            impulse_joint_set: ImpulseJointSet::default(),
            integration_options: IntegrationParameters::default(),
            island_manager: IslandManager::default(),
            multibody_joint_set: MultibodyJointSet::default(),
            narrow_phase: NarrowPhase::default(),
            pipeline: PhysicsPipeline::default(),
            event_handler,
            gravity: vector![0.0, 0.0, 0.0],
            entity_to_handlers: HashMap::new(),
        }
    }

    pub fn step(&mut self, dt: f32) -> Vec<CollisionEvent> {
        self.integration_options.dt = dt;

        let physics_hooks = ();

        self.pipeline.step(
            &self.gravity,
            &self.integration_options,
            &mut self.island_manager,
            &mut self.broad_phase,
            &mut self.narrow_phase,
            &mut self.body_set,
            &mut self.collider_set,
            &mut self.impulse_joint_set,
            &mut self.multibody_joint_set,
            &mut self.ccd_solver,
            None,
            &physics_hooks,
            &self.event_handler,
        );

        let mut collisions = vec![];

        while let Ok(collision_event) = self.collision_recv.try_recv() {
            // Handle the collision event.
            collisions.push(collision_event);
        }

        collisions
    }

    pub fn register(&mut self, body: &RigidBody) -> (RapierBodyHandle, ColliderHandle) {
        let Vec3(px, py, pz) = body.get_position();

        let rapier_body = RapierBodyBuilder::dynamic()
            .additional_mass(body.mass)
            .translation(vector![px, py, pz])
            .gravity_scale(0.0)
            .lock_rotations()
            .build();
        let mut collider = ColliderBuilder::capsule_y(
            body.aabb.height() / 2.0,
            (body.aabb.width() / 2.0).min(body.aabb.depth() / 2.0),
        )
        .build();

        collider.set_active_events(ActiveEvents::COLLISION_EVENTS);

        let body_handle = self.body_set.insert(rapier_body);
        let collider_handle =
            self.collider_set
                .insert_with_parent(collider, body_handle.clone(), &mut self.body_set);

        (body_handle, collider_handle)
    }

    pub fn unregister(&mut self, body_handle: &RapierBodyHandle, collider_handle: &ColliderHandle) {
        self.collider_set.remove(
            collider_handle.to_owned(),
            &mut self.island_manager,
            &mut self.body_set,
            false,
        );
        self.body_set.remove(
            body_handle.to_owned(),
            &mut self.island_manager,
            &mut self.collider_set,
            &mut self.impulse_joint_set,
            &mut self.multibody_joint_set,
            true,
        );
    }

    pub fn get(&self, body_handle: &RapierBodyHandle) -> &RapierBody {
        &self.body_set[body_handle.to_owned()]
    }

    pub fn get_mut(&mut self, body_handle: &RapierBodyHandle) -> &mut RapierBody {
        &mut self.body_set[body_handle.to_owned()]
    }

    pub fn move_rapier_body(&mut self, body_handle: &RapierBodyHandle, position: &Vec3<f32>) {
        let body = self.get_mut(body_handle);
        let &Vec3(px, py, pz) = position;

        body.set_translation(vector![px, py, pz], false);
        body.set_linvel(vector![0.0, 0.0, 0.0], false);
        body.set_angvel(vector![0.0, 0.0, 0.0], false);
        body.reset_forces(false);
        body.reset_torques(false);
    }

    pub fn iterate_body(
        body: &mut RigidBody,
        dt: f32,
        space: &dyn VoxelAccess,
        registry: &Registry,
        config: &WorldConfig,
    ) {
        if approx_equals(dt, 0.0) {
            return;
        }

        let gravity_mag_sq =
            config.gravity[0].powf(2.0) + config.gravity[1].powf(2.0) + config.gravity[2].powf(2.0);
        let no_gravity = approx_equals(0.0, gravity_mag_sq);

        // Reset the flags.
        body.collision = None;
        body.stepped = false;

        // treat bodies with <= 0 mass as static
        if body.mass <= 0.0 {
            body.velocity.set(0.0, 0.0, 0.0);
            body.forces.set(0.0, 0.0, 0.0);
            body.impulses.set(0.0, 0.0, 0.0);
            return;
        }

        // skip bodies if static or no velocity/forces/impulses
        let local_no_grav = no_gravity || approx_equals(body.gravity_multiplier, 0.0);
        let is_body_asleep =
            Physics::is_body_asleep(space, registry, config, body, dt, local_no_grav);
        if is_body_asleep {
            return;
        }
        body.sleep_frame_count -= 1;

        let old_resting = body.resting.clone();

        // Check if under water, if so apply buoyancy and drag forces
        Physics::apply_fluid_forces(space, registry, config, body);

        // semi-implicit Euler integration

        // a = f/m + gravity * gravity_multiplier
        let a = body
            .forces
            .scale(1.0 / body.mass)
            .scale_and_add(&Vec3::from(&config.gravity), body.gravity_multiplier);

        // dv = i/m + a*dt
        // v1 = v0 + dv
        let dv = body.impulses.scale(1.0 / body.mass);
        let dv = dv.scale_and_add(&a, dt);
        body.velocity = body.velocity.add(&dv);

        // apply friction based on change in velocity this frame
        if !approx_equals(body.friction, 0.0) {
            Physics::apply_friction_by_axis(0, body, &dv);
            Physics::apply_friction_by_axis(1, body, &dv);
            Physics::apply_friction_by_axis(2, body, &dv);
        }

        // linear air or fluid friction - effectively v *= drag;
        // body settings override global settings
        let mut drag = if body.air_drag >= 0.0 {
            body.air_drag
        } else {
            config.air_drag
        };
        if body.in_fluid {
            drag = if body.fluid_drag >= 0.0 {
                body.fluid_drag
            } else {
                config.fluid_drag
            };
            drag *= 1.0 - (1.0 - body.ratio_in_fluid).powi(2);
        }
        let mult = (1.0 - (drag * dt) / body.mass).max(0.0);
        body.velocity = body.velocity.scale(mult);

        // x1-x0 = v1*dt
        let dx = body.velocity.scale(dt);

        // clear forces and impulses for next timestep
        body.forces.set(0.0, 0.0, 0.0);
        body.impulses.set(0.0, 0.0, 0.0);

        // cache old position for use in autostepping
        let tmp_box = if body.auto_step {
            Some(body.aabb.clone())
        } else {
            None
        };

        // sweeps aabb along dx and accounts for collisions
        Physics::process_collisions(space, registry, &mut body.aabb, &dx, &mut body.resting);

        // if autostep, and on ground, run collisions again with stepped up aabb
        if body.auto_step {
            let mut tmp_box = tmp_box.unwrap();
            Physics::try_auto_stepping(space, registry, body, &mut tmp_box, &dx);
        }

        let mut impacts: Vec3<f32> = Vec3::default();

        // collision impacts. body.resting shows which axes had collisions
        for i in 0..3 {
            impacts[i] = 0.0;
            if body.resting[i] != 0 {
                // count impact only if wasn't collided last frame
                if old_resting[i] == 0 {
                    impacts[i] = -body.velocity[i];
                }
                body.velocity[i] = 0.0;
            }
        }

        let mag = impacts.len();
        if mag > 0.001 {
            // epsilon
            // send collision event - allow player to optionally change
            // body's restitution depending on what terrain it hit
            // event argument is impulse J = m * dv
            impacts = impacts.scale(body.mass);
            body.collision = Some(impacts.clone().to_arr());

            // bounce depending on restitution and min_bounce_impulse
            if body.restitution > 0.0 && mag > config.min_bounce_impulse {
                impacts = impacts.scale(body.restitution);
                body.apply_impulse(impacts.0, impacts.1, impacts.2);
            }
        }

        // sleep check
        let vsq = body.velocity.len().powi(2);
        if vsq > 1e-5 {
            body.mark_active()
        }
    }

    pub fn is_body_asleep(
        space: &dyn VoxelAccess,
        registry: &Registry,
        config: &WorldConfig,
        body: &mut RigidBody,
        dt: f32,
        no_gravity: bool,
    ) -> bool {
        if body.sleep_frame_count > 0 {
            return false;
        }

        // without gravity bodies stay asleep until a force/impulse wakes them up
        if no_gravity {
            return true;
        }

        // otherwise check body is resting against something
        // i.e. sweep along by distance d = 1/2 g*t^2
        // and check there's still collision
        let g_mult = 0.5 * dt * dt * body.gravity_multiplier;

        let sleep_vec = Vec3(
            config.gravity[0] * g_mult,
            config.gravity[1] * g_mult,
            config.gravity[2] * g_mult,
        );

        let mut is_resting = false;

        sweep(
            space,
            registry,
            &mut body.aabb,
            &sleep_vec,
            &mut |_, _, _, _| {
                is_resting = true;
                true
            },
            false,
            10,
        );

        is_resting
    }

    fn apply_fluid_forces(
        space: &dyn VoxelAccess,
        registry: &Registry,
        config: &WorldConfig,
        body: &mut RigidBody,
    ) {
        let aabb = &body.aabb;
        let cx = aabb.min_x.floor() as i32;
        let cz = aabb.min_z.floor() as i32;
        let y0 = aabb.min_y.floor() as i32;
        let y1 = aabb.max_y.floor() as i32;

        let test_fluid = |vx: i32, vy: i32, vz: i32| -> bool {
            let id = space.get_voxel(vx, vy, vz);
            let block = registry.get_block_by_id(id);
            block.is_fluid
        };

        if !test_fluid(cx, y0, cz) {
            body.in_fluid = false;
            body.ratio_in_fluid = 0.0;
            return;
        }

        // body is in fluid - find out how much body is submerged
        let mut submerged = 1;
        let mut cy = y0 + 1;

        while cy <= y1 && test_fluid(cx, cy, cz) {
            submerged += 1;
            cy += 1;
        }

        let fluid_level = y0 + submerged;
        let height_in_fluid = fluid_level as f32 - aabb.min_y;
        let mut ratio_in_fluid = height_in_fluid / (aabb.max_y - aabb.min_y);
        if ratio_in_fluid > 1.0 {
            ratio_in_fluid = 1.0;
        }
        let vol = aabb.width() * aabb.height() * aabb.depth();
        let displaced = vol * ratio_in_fluid;

        // buoyant force = -gravity * fluid_density * volume_displaced
        let scalar = config.fluid_density * displaced;
        body.apply_force(
            config.gravity[0] * scalar,
            config.gravity[1] * scalar,
            config.gravity[2] * scalar,
        );
    }

    fn apply_friction_by_axis(axis: usize, body: &mut RigidBody, dvel: &Vec3<f32>) {
        // friction applies only if moving into a touched surface
        let rest_dir = body.resting[axis];
        let v_normal = dvel[axis];
        if rest_dir == 0 || rest_dir as f32 * v_normal <= 0.0 {
            return;
        }

        // current vel lateral to friction axis
        let mut lateral_vel = body.velocity.clone();
        lateral_vel[axis] = 0.0;
        let v_curr = lateral_vel.len();
        if approx_equals(v_curr, 0.0) {
            return;
        }

        // treat current change in velocity as the result of a pseudoforce
        //        Fpseudo = m*dv/dt
        // Base friction force on normal component of the pseudoforce
        //        Ff = u * Fnormal
        //        Ff = u * m * dvnormal / dt
        // change in velocity due to friction force
        //        dvF = dt * Ff / m
        //            = dt * (u * m * dvnormal / dt) / m
        //            = u * dvnormal
        let dv_max = (body.friction * v_normal).abs();

        // decrease lateral vel by dv_max (or clamp to zero)
        let scalar = if v_curr > dv_max {
            (v_curr - dv_max) / v_curr
        } else {
            0.0
        };

        body.velocity[(axis + 1) % 3] *= scalar;
        body.velocity[(axis + 2) % 3] *= scalar;
    }

    fn process_collisions(
        space: &dyn VoxelAccess,
        registry: &Registry,
        aabb: &mut AABB,
        velocity: &Vec3<f32>,
        resting: &mut Vec3<i32>,
    ) {
        resting.set(0, 0, 0);

        sweep(
            space,
            registry,
            aabb,
            velocity,
            &mut |_, axis, dir, vec| -> bool {
                resting[axis] = dir;
                vec[axis] = 0.0;
                false
            },
            true,
            10,
        );
    }

    fn try_auto_stepping(
        space: &dyn VoxelAccess,
        registry: &Registry,
        body: &mut RigidBody,
        old_aabb: &mut AABB,
        dx: &Vec3<f32>,
    ) {
        // in the air
        if body.resting[1] >= 0 && !body.in_fluid {
            return;
        }

        // direction movement was blocked before trying a step
        let x_blocked = body.resting[0] != 0;
        let z_blocked = body.resting[2] != 0;
        if !(x_blocked || z_blocked) {
            return;
        }

        // continue auto-stepping only if headed sufficiently into obstruction
        let ratio = (dx[0] / dx[2]).abs();
        let cutoff = 4.0;
        if !x_blocked && ratio > cutoff || !z_blocked && ratio < 1.0 / cutoff {
            return;
        }

        // original target position before being obstructed
        let target_pos = [
            old_aabb.min_x + dx.0,
            old_aabb.min_y + dx.1,
            old_aabb.min_z + dx.2,
        ];

        // move towards the target until the first x/z collision
        sweep(
            space,
            registry,
            &mut body.aabb,
            dx,
            &mut |_, axis, _, vec| {
                if axis == 1 {
                    vec[axis] = 0.0;
                    return false;
                }
                true
            },
            true,
            10,
        );

        let y = body.aabb.min_y;
        // TODO: AUTO_STEPPING HAPPENS HERE
        let y_dist = (y + 1.001).floor() - y;
        let up_vec = Vec3(0.0, y_dist, 0.0);
        let mut collided = false;

        sweep(
            space,
            registry,
            &mut body.aabb,
            &up_vec,
            &mut |_, _, _, _| {
                collided = true;
                true
            },
            true,
            10,
        );

        if collided {
            return;
        }

        // now move in x/z however far was left over before hitting the obstruction
        let mut leftover = Vec3(
            target_pos[0] - old_aabb.min_x,
            target_pos[1] - old_aabb.min_y,
            target_pos[2] - old_aabb.min_z,
        );
        leftover[1] = 0.0;
        let mut tmp_resting = Vec3::default();
        Physics::process_collisions(space, registry, &mut body.aabb, &leftover, &mut tmp_resting);

        // bail if no movement happened in the originally blocked direction
        // if x_blocked && !approx_equals(old_aabb.min_x, target_pos[0]) {
        //     return;
        // }
        // if z_blocked && !approx_equals(old_aabb.min_z, target_pos[2]) {
        //     return;
        // }

        // if the new position is below the old position, then the new position is invalid
        // since we trying to step upwards
        if old_aabb.min_y < body.aabb.min_y {
            return;
        }

        // done, old_box is now at the target auto-stepped position
        body.aabb.copy(old_aabb);
        body.resting[0] = tmp_resting[0];
        body.resting[2] = tmp_resting[2];
        body.stepped = true;
    }
}