use crate::data::{Arena, Coarena, ComponentSet, ComponentSetMut};
use crate::dynamics::joint::MultibodyLink;
use crate::dynamics::{
    IslandManager, JointData, Multibody, MultibodyJoint, RigidBodyActivation, RigidBodyHandle,
    RigidBodyIds, RigidBodyType,
};
use crate::geometry::{InteractionGraph, RigidBodyGraphIndex};
use crate::parry::partitioning::IndexedData;
use std::ops::Index;

/// The unique handle of an multibody_joint added to a `MultibodyJointSet`.
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
#[repr(transparent)]
pub struct MultibodyJointHandle(pub crate::data::arena::Index);

/// The temporary index of a multibody added to a `MultibodyJointSet`.
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
#[repr(transparent)]
pub struct MultibodyIndex(pub crate::data::arena::Index);

impl MultibodyJointHandle {
    /// Converts this handle into its (index, generation) components.
    pub fn into_raw_parts(self) -> (u32, u32) {
        self.0.into_raw_parts()
    }

    /// Reconstructs an handle from its (index, generation) components.
    pub fn from_raw_parts(id: u32, generation: u32) -> Self {
        Self(crate::data::arena::Index::from_raw_parts(id, generation))
    }

    /// An always-invalid rigid-body handle.
    pub fn invalid() -> Self {
        Self(crate::data::arena::Index::from_raw_parts(
            crate::INVALID_U32,
            crate::INVALID_U32,
        ))
    }
}

impl Default for MultibodyJointHandle {
    fn default() -> Self {
        Self::invalid()
    }
}

impl IndexedData for MultibodyJointHandle {
    fn default() -> Self {
        Self(IndexedData::default())
    }
    fn index(&self) -> usize {
        self.0.index()
    }
}

#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub struct MultibodyJointLink {
    pub graph_id: RigidBodyGraphIndex,
    pub multibody: MultibodyIndex,
    pub id: usize,
}

impl Default for MultibodyJointLink {
    fn default() -> Self {
        Self {
            graph_id: RigidBodyGraphIndex::new(crate::INVALID_U32),
            multibody: MultibodyIndex(crate::data::arena::Index::from_raw_parts(
                crate::INVALID_U32,
                crate::INVALID_U32,
            )),
            id: 0,
        }
    }
}

/// A set of rigid bodies that can be handled by a physics pipeline.
pub struct MultibodyJointSet {
    pub(crate) multibodies: Arena<Multibody>, // NOTE: a Slab would be sufficient.
    pub(crate) rb2mb: Coarena<MultibodyJointLink>,
    // NOTE: this is mostly for the island extraction. So perhaps we won’t need
    //       that any more in the future when we improve our island builder.
    pub(crate) connectivity_graph: InteractionGraph<RigidBodyHandle, ()>,
}

impl MultibodyJointSet {
    /// Create a new empty set of multibodies.
    pub fn new() -> Self {
        Self {
            multibodies: Arena::new(),
            rb2mb: Coarena::new(),
            connectivity_graph: InteractionGraph::new(),
        }
    }

    pub fn iter(&self) -> impl Iterator<Item = (MultibodyJointHandle, &Multibody, &MultibodyLink)> {
        self.rb2mb
            .iter()
            .filter(|(_, link)| link.id > 0) // The first link of a rigid-body hasn’t been added by the user.
            .map(|(h, link)| {
                let mb = &self.multibodies[link.multibody.0];
                (MultibodyJointHandle(h), mb, mb.link(link.id).unwrap())
            })
    }

    /// Inserts a new multibody_joint into this set.
    pub fn insert(
        &mut self,
        body1: RigidBodyHandle,
        body2: RigidBodyHandle,
        data: impl Into<JointData>,
    ) -> Option<MultibodyJointHandle> {
        let data = data.into();
        let link1 = self.rb2mb.get(body1.0).copied().unwrap_or_else(|| {
            let mb_handle = self.multibodies.insert(Multibody::with_root(body1));
            MultibodyJointLink {
                graph_id: self.connectivity_graph.graph.add_node(body1),
                multibody: MultibodyIndex(mb_handle),
                id: 0,
            }
        });

        let link2 = self.rb2mb.get(body2.0).copied().unwrap_or_else(|| {
            let mb_handle = self.multibodies.insert(Multibody::with_root(body2));
            MultibodyJointLink {
                graph_id: self.connectivity_graph.graph.add_node(body2),
                multibody: MultibodyIndex(mb_handle),
                id: 0,
            }
        });

        if link1.multibody == link2.multibody || link2.id != 0 {
            // This would introduce an invalid configuration.
            return None;
        }

        self.connectivity_graph
            .graph
            .add_edge(link1.graph_id, link2.graph_id, ());
        self.rb2mb.insert(body1.0, link1);
        self.rb2mb.insert(body2.0, link2);

        let mb2 = self.multibodies.remove(link2.multibody.0).unwrap();
        let multibody1 = &mut self.multibodies[link1.multibody.0];

        for mb_link2 in mb2.links() {
            let link = self.rb2mb.get_mut(mb_link2.rigid_body.0).unwrap();
            link.multibody = link1.multibody;
            link.id += multibody1.num_links();
        }

        multibody1.append(mb2, link1.id, MultibodyJoint::new(data));

        // Because each rigid-body can only have one parent link,
        // we can use the second rigid-body’s handle as the multibody_joint’s
        // handle.
        Some(MultibodyJointHandle(body2.0))
    }

    /// Removes an multibody_joint from this set.
    pub fn remove<Bodies>(
        &mut self,
        handle: MultibodyJointHandle,
        islands: &mut IslandManager,
        bodies: &mut Bodies,
        wake_up: bool,
    ) where
        Bodies: ComponentSetMut<RigidBodyActivation>
            + ComponentSet<RigidBodyType>
            + ComponentSetMut<RigidBodyIds>,
    {
        if let Some(removed) = self.rb2mb.get(handle.0).copied() {
            let multibody = self.multibodies.remove(removed.multibody.0).unwrap();

            // Remove the edge from the connectivity graph.
            if let Some(parent_link) = multibody.link(removed.id).unwrap().parent_id() {
                let parent_rb = multibody.link(parent_link).unwrap().rigid_body;
                self.connectivity_graph.remove_edge(
                    self.rb2mb.get(parent_rb.0).unwrap().graph_id,
                    removed.graph_id,
                );

                if wake_up {
                    islands.wake_up(bodies, RigidBodyHandle(handle.0), true);
                    islands.wake_up(bodies, parent_rb, true);
                }

                // TODO: remove the node if it no longer has any attached edges?

                // Extract the individual sub-trees generated by this removal.
                let multibodies = multibody.remove_link(removed.id, true);

                // Update the rb2mb mapping.
                for multibody in multibodies {
                    if multibody.num_links() == 1 {
                        // We don’t have any multibody_joint attached to this body, remove it.
                        if let Some(other) = self.connectivity_graph.remove_node(removed.graph_id) {
                            self.rb2mb.get_mut(other.0).unwrap().graph_id = removed.graph_id;
                        }
                    } else {
                        let mb_id = self.multibodies.insert(multibody);
                        for link in self.multibodies[mb_id].links() {
                            let ids = self.rb2mb.get_mut(link.rigid_body.0).unwrap();
                            ids.multibody = MultibodyIndex(mb_id);
                            ids.id = link.internal_id;
                        }
                    }
                }
            }
        }
    }

    /// Removes all the multibody_joints from the multibody the given rigid-body is part of.
    pub fn remove_multibody_articulations<Bodies>(
        &mut self,
        handle: RigidBodyHandle,
        islands: &mut IslandManager,
        bodies: &mut Bodies,
        wake_up: bool,
    ) where
        Bodies: ComponentSetMut<RigidBodyActivation>
            + ComponentSet<RigidBodyType>
            + ComponentSetMut<RigidBodyIds>,
    {
        if let Some(removed) = self.rb2mb.get(handle.0).copied() {
            // Remove the multibody.
            let multibody = self.multibodies.remove(removed.multibody.0).unwrap();
            for link in multibody.links() {
                let rb_handle = link.rigid_body;

                if wake_up {
                    islands.wake_up(bodies, rb_handle, true);
                }

                // Remove the rigid-body <-> multibody mapping for this link.
                let removed = self.rb2mb.remove(rb_handle.0, Default::default()).unwrap();
                // Remove the node (and all it’s edges) from the connectivity graph.
                if let Some(other) = self.connectivity_graph.remove_node(removed.graph_id) {
                    self.rb2mb.get_mut(other.0).unwrap().graph_id = removed.graph_id;
                }
            }
        }
    }

    pub fn remove_articulations_attached_to_rigid_body<Bodies>(
        &mut self,
        rb_to_remove: RigidBodyHandle,
        islands: &mut IslandManager,
        bodies: &mut Bodies,
    ) where
        Bodies: ComponentSetMut<RigidBodyActivation>
            + ComponentSet<RigidBodyType>
            + ComponentSetMut<RigidBodyIds>,
    {
        // TODO: optimize this.
        if let Some(link_to_remove) = self.rb2mb.get(rb_to_remove.0).copied() {
            let mut articulations_to_remove = vec![];
            for (rb1, rb2, _) in self
                .connectivity_graph
                .interactions_with(link_to_remove.graph_id)
            {
                // There is an multibody_joint that we need to remove between these two bodies.
                // If this is an outbound edge, then the multibody_joint’s handle is equal to the
                // second body handle.
                if rb1 == rb_to_remove {
                    articulations_to_remove.push(MultibodyJointHandle(rb2.0));
                } else {
                    articulations_to_remove.push(MultibodyJointHandle(rb1.0));
                }

                islands.wake_up(bodies, rb1, true);
                islands.wake_up(bodies, rb2, true);
            }

            for articulation_handle in articulations_to_remove {
                self.remove(articulation_handle, islands, bodies, true);
            }
        }
    }

    /// Returns the link of this multibody attached to the given rigid-body.
    ///
    /// Returns `None` if `rb` isn’t part of any rigid-body.
    pub fn rigid_body_link(&self, rb: RigidBodyHandle) -> Option<&MultibodyJointLink> {
        self.rb2mb.get(rb.0)
    }

    /// Gets a reference to a multibody, based on its temporary index.
    pub fn get_multibody(&self, index: MultibodyIndex) -> Option<&Multibody> {
        self.multibodies.get(index.0)
    }

    /// Gets a mutable reference to a multibody, based on its temporary index.
    ///
    /// This method will bypass any modification-detection automatically done by the
    /// `MultibodyJointSet`.
    pub fn get_multibody_mut_internal(&mut self, index: MultibodyIndex) -> Option<&mut Multibody> {
        self.multibodies.get_mut(index.0)
    }

    /// Gets a reference to the multibody identified by its `handle`.
    pub fn get(&self, handle: MultibodyJointHandle) -> Option<(&Multibody, usize)> {
        let link = self.rb2mb.get(handle.0)?;
        let multibody = self.multibodies.get(link.multibody.0)?;
        Some((multibody, link.id))
    }

    /// Gets a mutable reference to the multibody identified by its `handle`.
    pub fn get_mut_internal(
        &mut self,
        handle: MultibodyJointHandle,
    ) -> Option<(&mut Multibody, usize)> {
        let link = self.rb2mb.get(handle.0)?;
        let multibody = self.multibodies.get_mut(link.multibody.0)?;
        Some((multibody, link.id))
    }

    /// Iterate through the handles of all the rigid-bodies attached to this rigid-body
    /// by an multibody_joint.
    pub fn attached_bodies<'a>(
        &'a self,
        body: RigidBodyHandle,
    ) -> impl Iterator<Item = RigidBodyHandle> + 'a {
        self.rb2mb
            .get(body.0)
            .into_iter()
            .flat_map(move |id| self.connectivity_graph.interactions_with(id.graph_id))
            .map(move |inter| crate::utils::select_other((inter.0, inter.1), body))
    }

    /// Iterates through all the multibodies on this set.
    pub fn multibodies(&self) -> impl Iterator<Item = &Multibody> {
        self.multibodies.iter().map(|e| e.1)
    }
}

impl Index<MultibodyIndex> for MultibodyJointSet {
    type Output = Multibody;

    fn index(&self, index: MultibodyIndex) -> &Multibody {
        &self.multibodies[index.0]
    }
}

// impl Index<MultibodyJointHandle> for MultibodyJointSet {
//     type Output = Multibody;
//
//     fn index(&self, index: MultibodyJointHandle) -> &Multibody {
//         &self.multibodies[index.0]
//     }
// }