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// Copyright 2017 The gltf Library Developers
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use std::slice;
use {accessor, json};

use {Gltf, Loaded, Node};

/// Joints and matrices defining a skin.
#[derive(Clone, Debug)]
pub struct Skin<'a> {
    /// The parent `Gltf` struct.
    gltf: &'a Gltf,

    /// The corresponding JSON index.
    index: usize,

    /// The corresponding JSON struct.
    json: &'a json::skin::Skin,
}

/// An `Iterator` that visits the inverse bind matrices of a `Skin`.
#[derive(Clone, Debug)]
pub struct InverseBindMatrices<'a>(accessor::Iter<'a, [[f32; 4]; 4]>);

/// An `Iterator` that visits the joints of a `Skin`.
#[derive(Clone, Debug)]
pub struct Joints<'a> {
    /// The parent `Gltf` struct.
    gltf: &'a Gltf,

    /// The internal node index iterIterator.
    iter: slice::Iter<'a, json::Index<json::scene::Node>>,
}

impl<'a> Skin<'a> {
    /// Constructs a `Skin`.
    pub(crate) fn new(gltf: &'a Gltf, index: usize, json: &'a json::skin::Skin) -> Self {
        Self {
            gltf: gltf,
            index: index,
            json: json,
        }
    }

    /// Returns the internal JSON index.
    pub fn index(&self) -> usize {
        self.index
    }

    /// Returns the internal JSON item.
    pub fn as_json(&self) ->  &json::skin::Skin {
        self.json
    }

    /// Optional application specific data.
    pub fn extras(&self) -> &json::Extras {
        &self.json.extras
    }

    /// Returns an `Iterator` that visits the skeleton nodes used as joints in
    /// this skin.
    pub fn joints(&self) -> Joints<'a> {
        Joints {
            gltf: self.gltf,
            iter: self.json.joints.iter(),
        }
    }

    /// Optional user-defined name for this object.
    #[cfg(feature = "names")]
    pub fn name(&self) -> Option<&str> {
        self.json.name.as_ref().map(String::as_str)
    }

    /// Returns the node used as the skeleton root. When `None`, joints
    /// transforms resolve to scene root.
    pub fn skeleton(&self) -> Option<Node<'a>> {
        self.json.skeleton.as_ref().map(|index| {
            self.gltf.nodes().nth(index.value()).unwrap()
        })
    }
}

impl<'a> Loaded<'a, Skin<'a>> {
    /// Returns an `Iterator` that visits the 4x4 inverse-bind matrices. When
    /// `None`, each matrix is assumed to be the 4x4 identity matrix which implies
    /// that the inverse-bind matrices were pre-applied.
    pub fn inverse_bind_matrices(&self) -> Option<InverseBindMatrices<'a>> {
        self.json.inverse_bind_matrices
            .as_ref()
            .map(|index| {
                let accessor = self.gltf
                    .accessors()
                    .nth(index.value())
                    .unwrap()
                    .loaded(self.source);
                unsafe {
                    InverseBindMatrices(accessor.iter())
                }
            })
    }

    /// Returns an `Iterator` that visits the skeleton nodes used as joints in
    /// this skin.
    pub fn joints(&self) -> Loaded<'a, Joints<'a>> {
        Loaded {
            item: self.item.joints(),
            source: self.source,
        }
    }

    /// Returns the node used as the skeleton root. When `None`, joints
    /// transforms resolve to scene root.
    pub fn skeleton(&self) -> Option<Loaded<'a, Node<'a>>> {
        self.item
            .skeleton()
            .map(|item| {
                Loaded {
                    item,
                    source: self.source,
                }
            })
    }
}

impl<'a> Iterator for InverseBindMatrices<'a> {
    type Item = [[f32; 4]; 4];
    fn next(&mut self) -> Option<Self::Item> {
        self.0.next()
    }
}

impl<'a> Iterator for Joints<'a>  {
    type Item = Node<'a>;
    fn next(&mut self) -> Option<Self::Item> {
        self.iter
            .next()
            .map(|index| self.gltf.nodes().nth(index.value()).unwrap())
    }
}

impl<'a> Iterator for Loaded<'a, Joints<'a>>  {
    type Item = Loaded<'a, Node<'a>>;
    fn next(&mut self) -> Option<Self::Item> {
        self.item
            .next()
            .map(|item| {
                Loaded {
                    item,
                    source: self.source,
                }
            })
    }
}