pub mod join;
pub mod thrust;

const FUEL_REGEN_RATE: f32 = 5.0;

use crate::shared::attachment::{Joint, JointOf, Joints, PartInShip, Peer, SnapOf, SnapOfJoint};
use crate::shared::ecs::{DragAction, DragRequestEvent, Part, Player, PlayerStorage};
use crate::server::damping::ModuleJointDamping;
use crate::server::system_sets::PlayerInputSet;
use crate::prelude::*;
use crate::shared::world_config::WorldConfigResource;
use std::f64::consts::PI;
use crate::client::components::Me;

pub fn player_management_plugin(app: &mut App) {
    app.add_systems(
        Update,
        (
            join::handle_pending_players,
            join::handle_new_players,
            magic_fuel_regen,
            dragging,
        )
            .in_set(PlayerInputSet),
    );
    app.add_systems(Update, complete_partial_disconnects);
    app.add_systems(FixedUpdate, complete_partial_disconnects);
}

#[derive(Component)]
struct PartiallyDisconnected;

/// Partial Disconnects are created when a part is disconnected to indicate that a disconnect has started.
/// Disconnects cannot be completed until the next tick, after relevant Peer relationships have been removed.
/// This system does this by performing a flood search to determine if the 'partial-disconnected' parts still have
/// a valid path to hearty; if they do not, they are removed from the ship.
fn complete_partial_disconnects(
    partial_disconnected_parts: Query<Entity, With<PartiallyDisconnected>>,
    mut q_joints: Query<&Joints>,
    mut q_maybe_peer: Query<Option<&Peer>>,
    mut q_joint_of_part: Query<&JointOf>,
    mut q_is_hearty: Query<Option<&Player>>,
    dc_q_joints: Query<(&Joint, &JointOf, &Transform, Option<&Peer>, Entity)>,
    dc_q_only_joints: Query<&Joints>,

    mut commands: Commands,
) {
    for partially_disconnected_part in &partial_disconnected_parts {

        trace!(?partially_disconnected_part, "completing partial disconnect from previous tick");
        commands.entity(partially_disconnected_part).remove::<PartiallyDisconnected>();

        // is it still connected to hearty?
        let mut search_visited_joints = vec![];
        let connected = is_connected_to_hearty(
            partially_disconnected_part,
            q_joints.reborrow(),
            q_maybe_peer.reborrow(),
            q_joint_of_part.reborrow(),
            q_is_hearty.reborrow(),
            &mut search_visited_joints,
        );
        if connected {
            // great, leave them alone
            continue;
        }
        debug!("partial detach DFS: visited {} joints => not connected", search_visited_joints.len());
        // this part cannot reach hearty; propagate the disconnection

        let mut disconnect_queue = vec![];
        commands.entity(partially_disconnected_part).remove::<PartInShip>(); // they're no longer in the ship, remove them from the meta
        propagate_disconnect(
            (partially_disconnected_part, if let Ok(j) = q_joints.get(partially_disconnected_part) { j } else {
                warn!(?partially_disconnected_part, "part does not have a Joints? this should be impossible...");
                continue;
            }),
            &dc_q_joints,
            &dc_q_only_joints,
            &mut disconnect_queue,
            commands.reborrow()
        );
        commands.entity(partially_disconnected_part).remove::<PartiallyDisconnected>();
    }
}

/// Determine if a part is connected to hearty by performing a depth-first search.
/// TODO: This can be very slow on large ships- the path propagation model will be significantly faster
/// TODO: Ask core for an explanation of what the path propagation model is if you want to implement this
fn is_connected_to_hearty(
    part: Entity,

    mut q_joints: Query<&Joints>,
    mut q_maybe_peer: Query<Option<&Peer>>,
    mut q_joint_of_part: Query<&JointOf>,
    mut q_is_hearty: Query<Option<&Player>>,

    visited_joints: &mut Vec<Entity>,
) -> bool {
    // Are we hearty?
    if let Ok(Some(_)) = q_is_hearty.get(part) {
        debug!("partial detach DFS: visited {} joints => we are hearty! @ {:?}", visited_joints.len(), part);
        return true;
    }

    // Get the joints of this entity
    let Ok(our_joints) = q_joints.get(part).cloned() else {
        warn!("part does not have a Joints? this should be impossible...");
        return false;
    };

    // Iterate over each joint:
    // if it's Hearty: great! we're connected
    // if it's another part: recurse to it
    // if it's not connected: lame, move on
    'to_next_joint: for joint in &**our_joints {
        // mark that we've visited this joint, so we don't come back to it later
        visited_joints.push(*joint);

        // does this joint have a peer?
        let maybe_peer = q_maybe_peer.get(*joint).expect("cannot fail");

        if let Some(peer_info) = maybe_peer {
            // we have a peer! figure out what it's connected to...
            let other_parts_joint = peer_info.peer_joint_entity_id;
            // have we visited this joint already?
            if visited_joints.contains(&other_parts_joint) {
                // if so, move on
                continue 'to_next_joint;
            }
            // we have not, find it's parent part
            let other_part = q_joint_of_part.get(other_parts_joint).expect("joint is missing JointOf").0;
            // is this part Hearty?
            let maybe_is_hearty = q_is_hearty.get(other_part).expect("cannot fail");
            if maybe_is_hearty.is_some() {
                // yay! found hearty
                debug!("partial detach DFS: visited {} joints => found hearty @ {:?}", visited_joints.len(), other_part);
                debug!("-> via {:?}", part);
                return true;
            }
            // not hearty, but can the other part reach hearty?
            let other_connected = is_connected_to_hearty(
                other_part,
                q_joints.reborrow(),
                q_maybe_peer.reborrow(),
                q_joint_of_part.reborrow(),
                q_is_hearty.reborrow(),
                visited_joints,
            );
            if other_connected {
                debug!("-> via {:?}", part);
                return true;
            }

        }
    }

    false
}



fn propagate_disconnect(
    (entity, joints): (Entity, &Joints),
    q_joints: &Query<(&Joint, &JointOf, &Transform, Option<&Peer>, Entity)>,
    q_only_joints: &Query<&Joints>,
    processed_peers: &mut Vec<Entity>,
    mut commands: Commands,
) {
    //trace!(?entity, ?joints, ?processed_peers, "recursive disconnect");
    // loop the joints in the entity
    for joint in joints.iter() {
        // now we have the entity "joint"
        let Ok((_, _, _, peer, _)) = q_joints.get(joint) else {
            continue;
        };
        // don't want to double process a joint
        if processed_peers.contains(&joint) { continue; }

        // we have the peer that holds the physics joint
        let Some(peer) = peer else { continue; };
        commands.entity(joint).remove::<Peer>();
        processed_peers.push(joint);

        let mut physics_joint = commands.entity(peer.physics_joint);
        // the physics joint shouldnt exist anymore
        physics_joint.despawn();

        // delete the other side's peer that exists for some reason
        let Ok((_, other_joint_of, _, _, _)) = q_joints.get(peer.peer_joint_entity_id) else {
            continue;
        };
        commands.entity(peer.peer_joint_entity_id).remove::<Peer>();

        let Ok(_) = q_only_joints.get(other_joint_of.0) else {
            continue
        };
        //commands.entity(other_joint_of.0).remove::<PartInShip>();

        if !processed_peers.contains(&peer.peer_joint_entity_id) {
            propagate_disconnect((other_joint_of.0, joints), q_joints,
                q_only_joints, processed_peers, commands.reborrow());
        }

        processed_peers.push(peer.peer_joint_entity_id);
    }
    // recursive disconnect part
    //commands.entity(entity).remove::<PartInShip>();
    commands.entity(entity).insert(PartiallyDisconnected);
}

fn dragging(
    mut events: MessageReader<DragRequestEvent>,
    me: Query<Entity, With<Me>>,
    mut parts: Query<
        (
            &mut Transform,
            Option<&PartInShip>,
            Entity,
            &mut LinearVelocity,
            &Joints,
            &mut AngularVelocity,
            &Part,
        ),
        Without<Joint>,
    >,
    snaps: Query<(&SnapOf, &SnapOfJoint)>,
    joints: Query<(&Joint, &JointOf, &Transform, Option<&Peer>, Entity)>,
    q_joints: Query<&Joints>,
    world_config: Res<WorldConfigResource>,
    mut commands: Commands,
) {
    let Some(world_config) = &world_config.config else {
        return;
    };
    let Ok(player_hearty_entity) = me.single() else { return };

    for event in events.read() {
        debug!(?event, "got drag request event");

        let teleport_to_translation;
        let teleport_to_rotation;
        let mut new_linvel = None;
        let mut new_angvel = None;

        match &event.action {
            DragAction::Attach { snap_target, peer_snap } => {
                let Ok((target_snap_part, target_snap_joint)) = snaps.get(*snap_target) else {
                    continue;
                };
                let Ok((source_snap_part, source_snap_joint)) = snaps.get(*peer_snap) else {
                    continue;
                };

                let Ok((target_jt, target_jt_of, target_jt_xform, target_jt_peer, target_jt_id)) = joints.get(target_snap_joint.0) else {
                    continue;
                };
                let Ok((source_jt, source_jt_of, _source_jt_xform, source_jt_peer, source_jt_id)) = joints.get(source_snap_joint.0) else {
                    continue;
                };

                // validation: snap ownership must agree with joint ownership
                if target_snap_part.0 != target_jt_of.0 {
                    warn!("drag request: mismatched target entities (potential manipulation?), ignoring");
                    continue;
                }
                if source_snap_part.0 != source_jt_of.0 {
                    warn!("drag request: mismatched source entities (potential manipulation?), ignoring request");
                    continue;
                }

                // do not allow drags where either joint already has a peer (is attached)
                if target_jt_peer.is_some() {
                    warn!("drag request: cannot attach to a joint that already has a peer, ignoring request");
                    continue;
                }
                if source_jt_peer.is_some() {
                    warn!("drag request: dragging from a part that is already attached is currently not supported, ignoring request");
                    continue;
                }

                // getting attached to (hearty)
                let Ok((target_xform, target_in_ship, target_entity, target_linvel, _, target_angvel, _)) = parts.get(target_jt_of.0) else {
                    continue;
                };

                // attached (housing)
                let Ok((_, _, source_entity, _, source_joints, _, _)) = parts.get(source_jt_of.0) else {
                    continue;
                };

                let allowed = target_jt_of.0 == player_hearty_entity
                    || target_in_ship.is_some_and(|u| u.0 == player_hearty_entity);
                if !allowed {
                    warn!("drag request: this player cannot move this part, ignoring request");
                    continue;
                }

                let mut processed = vec![source_jt_id];
                propagate_disconnect(
                    (source_entity, source_joints),
                    &joints,
                    &q_joints,
                    &mut processed,
                    commands.reborrow(),
                );

                // create the physics joint
                let fixed_joint = FixedJoint::new(target_entity, source_entity)
                    .with_local_anchor1(target_jt_xform.translation.xy().into())
                    .with_local_basis1(target_jt.transform.rotation.to_euler(EulerRot::ZYX).0 as f64 + PI
                        - source_jt.transform.rotation.to_euler(EulerRot::ZYX).0 as f64)
                    .with_point_compliance(world_config.part.joint_point_compliance)
                    .with_angle_compliance(world_config.part.joint_angle_compliance);
                let joint_damping = ModuleJointDamping {
                    distance: world_config.part.joint_distance_damping,
                    angular: world_config.part.joint_angular_damping,
                };
                let joint_id = commands.spawn((fixed_joint, joint_damping)).id();

                // create the peering components
                commands.entity(source_jt_id).insert(Peer {
                    peer_joint_entity_id: target_jt_id,
                    physics_joint: joint_id,
                });
                commands.entity(target_jt_id).insert(Peer {
                    peer_joint_entity_id: source_jt_id,
                    physics_joint: joint_id,
                });

                // propagate PartInShip
                let part_in_ship = if target_jt_of.0 == player_hearty_entity {
                    PartInShip(player_hearty_entity)
                } else {
                    PartInShip(target_in_ship.unwrap().0) // unwrap: checked above (during 'allowed' calculation)
                };
                commands.entity(source_entity).insert(part_in_ship);

                let target_position = target_xform.mul_transform(*target_jt_xform);
                teleport_to_translation = target_position.translation.xy();
                teleport_to_rotation = target_position.rotation
                    * source_jt.transform.rotation.inverse()
                    * Quat::from_rotation_z(PI as f32);
                new_linvel = Some(*target_linvel);
                new_angvel = Some(*target_angvel);
            }
            DragAction::Free { position, rotation } => {
                warn!("blindly accepting non-attachment request, someone should change this eventually");
                warn!("dragging already attached entities may cause inconsistent behavior!!");
                let Ok((_, _, free_entity, _, free_joints, _, _)) = parts.get(event.drag_target) else {
                    continue;
                };
                let mut processed = vec![];
                propagate_disconnect(
                    (free_entity, free_joints),
                    &joints,
                    &q_joints,
                    &mut processed,
                    commands.reborrow(),
                );
                teleport_to_translation = *position;
                teleport_to_rotation = *rotation;
            }
        }

        let Ok((mut xform, _, _, mut linvel, _, mut angvel, _)) = parts.get_mut(event.drag_target) else {
            continue;
        };
        xform.translation.x = teleport_to_translation.x;
        xform.translation.y = teleport_to_translation.y;
        xform.rotation = teleport_to_rotation; // client calculates this; no reason to recalculate
        if let Some(vel) = new_linvel {
            *linvel = vel;
        }
        if let Some(vel) = new_angvel {
            *angvel = vel;
        }
    }
}

fn magic_fuel_regen(players: Query<&mut PlayerStorage, With<Player>>, time: Res<Time>) {
    for mut storage in players {
        storage.fuel = (storage.fuel + FUEL_REGEN_RATE * time.delta_secs()).min(storage.fuel_capacity);
    }
}