// pathfinder/renderer/src/scene.rs
//
// Copyright © 2019 The Pathfinder Project 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.

//! The vector scene to be rendered.

use crate::builder::SceneBuilder;
use crate::concurrent::executor::Executor;
use crate::gpu::options::RendererLevel;
use crate::gpu::renderer::Renderer;
use crate::gpu_data::RenderCommand;
use crate::options::{BuildOptions, PreparedBuildOptions};
use crate::options::{PreparedRenderTransform, RenderCommandListener};
use crate::paint::{MergedPaletteInfo, Paint, PaintId, PaintInfo, Palette};
use pathfinder_content::effects::BlendMode;
use pathfinder_content::fill::FillRule;
use pathfinder_content::outline::Outline;
use pathfinder_content::render_target::RenderTargetId;
use pathfinder_geometry::rect::RectF;
use pathfinder_geometry::transform2d::Transform2F;
use pathfinder_geometry::vector::{Vector2I, vec2f};
use pathfinder_gpu::Device;
use std::mem;
use std::ops::Range;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::{Arc, Mutex};
use std::u64;

static NEXT_SCENE_ID: AtomicUsize = AtomicUsize::new(0);

/// The vector scene to be rendered.
#[derive(Clone)]
pub struct Scene {
    display_list: Vec<DisplayItem>,
    draw_paths: Vec<DrawPath>,
    clip_paths: Vec<ClipPath>,
    palette: Palette,
    bounds: RectF,
    view_box: RectF,
    id: SceneId,
    epoch: SceneEpoch,
}

/// A globally-unique identifier for the scene.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct SceneId(pub u32);

impl Scene {
    /// Creates a new empty scene.
    #[inline]
    pub fn new() -> Scene {
        let scene_id = SceneId(NEXT_SCENE_ID.fetch_add(1, Ordering::Relaxed) as u32);
        Scene {
            display_list: vec![],
            draw_paths: vec![],
            clip_paths: vec![],
            palette: Palette::new(scene_id),
            bounds: RectF::default(),
            view_box: RectF::default(),
            id: scene_id,
            epoch: SceneEpoch::new(0, 1),
        }
    }

    /// Adds a path to the scene, to be drawn on top of all previously-added paths.
    ///
    /// If a render target is on the stack (see `push_render_target()`), the path goes to the
    /// render target. Otherwise, it goes to the main output.
    ///
    /// Returns an ID which can later be used to retrieve the path via `get_draw_path()`.
    pub fn push_draw_path(&mut self, draw_path: DrawPath) -> DrawPathId {
        let draw_path_index = DrawPathId(self.draw_paths.len() as u32);
        self.draw_paths.push(draw_path);
        self.push_draw_path_with_index(draw_path_index);
        draw_path_index
    }

    fn push_draw_path_with_index(&mut self, draw_path_id: DrawPathId) {
        let new_path_bounds = self.draw_paths[draw_path_id.0 as usize].outline.bounds();
        self.bounds = self.bounds.union_rect(new_path_bounds);

        let end_path_id = DrawPathId(draw_path_id.0 + 1);
        match self.display_list.last_mut() {
            Some(DisplayItem::DrawPaths(ref mut range)) => range.end = end_path_id,
            _ => self.display_list.push(DisplayItem::DrawPaths(draw_path_id..end_path_id)),
        }

        self.epoch.next();
    }

    /// Defines a clip path. Returns an ID that can be used to later clip draw paths.
    pub fn push_clip_path(&mut self, clip_path: ClipPath) -> ClipPathId {
        self.bounds = self.bounds.union_rect(clip_path.outline.bounds());
        let clip_path_id = ClipPathId(self.clip_paths.len() as u32);
        self.clip_paths.push(clip_path);
        self.epoch.next();
        clip_path_id
    }

    /// Directs subsequent draw paths to draw to the given render target instead of the output.
    ///
    /// Render targets form a stack. All `push_draw_path()` commands go to the render target at the
    /// top of the stack.
    pub fn push_render_target(&mut self, render_target: RenderTarget) -> RenderTargetId {
        let render_target_id = self.palette.push_render_target(render_target);
        self.display_list.push(DisplayItem::PushRenderTarget(render_target_id));
        self.epoch.next();
        render_target_id
    }

    /// Removes the most-recently-pushed render target from the top of the stack.
    ///
    /// After calling this method, drawing will go to the previous render target. If no render
    /// targets remain on the stack, drawing goes to the main output.
    pub fn pop_render_target(&mut self) {
        self.display_list.push(DisplayItem::PopRenderTarget);
    }

    /// Adds all elements in a scene to this one.
    ///
    /// This includes draw paths, clip paths, render targets, and paints.
    pub fn append_scene(&mut self, scene: Scene) {
        let MergedPaletteInfo {
            render_target_mapping,
            paint_mapping,
        } = self.palette.append_palette(scene.palette);

        // Merge clip paths.
        let mut clip_path_mapping = Vec::with_capacity(scene.clip_paths.len());
        for clip_path in scene.clip_paths {
            clip_path_mapping.push(self.clip_paths.len());
            self.clip_paths.push(clip_path);
        }

        // Merge draw paths.
        let mut draw_path_mapping = Vec::with_capacity(scene.draw_paths.len());
        for draw_path in scene.draw_paths {
            draw_path_mapping.push(self.draw_paths.len() as u32);
            self.draw_paths.push(DrawPath {
                outline: draw_path.outline,
                paint: paint_mapping[&draw_path.paint],
                clip_path: draw_path.clip_path.map(|clip_path_id| {
                    ClipPathId(clip_path_mapping[clip_path_id.0 as usize] as u32)
                }),
                fill_rule: draw_path.fill_rule,
                blend_mode: draw_path.blend_mode,
                name: draw_path.name,
            });
        }

        // Merge display items.
        for display_item in scene.display_list {
            match display_item {
                DisplayItem::PushRenderTarget(old_render_target_id) => {
                    let new_render_target_id = render_target_mapping[&old_render_target_id];
                    self.display_list.push(DisplayItem::PushRenderTarget(new_render_target_id));
                }
                DisplayItem::PopRenderTarget => {
                    self.display_list.push(DisplayItem::PopRenderTarget);
                }
                DisplayItem::DrawPaths(range) => {
                    for old_path_index in (range.start.0 as usize)..(range.end.0 as usize) {
                        let old_draw_path_id = DrawPathId(draw_path_mapping[old_path_index]);
                        self.push_draw_path_with_index(old_draw_path_id);
                    }
                }
            }
        }

        // Bump epoch.
        self.epoch.next();
    }

    #[inline]
    pub(crate) fn build_paint_info(&mut self, render_transform: Transform2F) -> PaintInfo {
        self.palette.build_paint_info(render_transform)
    }

    /// Defines a new paint, which specifies how paths are to be filled or stroked. Returns a paint
    /// ID that can be later specified alongside draw paths.
    #[allow(clippy::trivially_copy_pass_by_ref)]
    pub fn push_paint(&mut self, paint: &Paint) -> PaintId {
        let paint_id = self.palette.push_paint(paint);
        self.epoch.next();
        paint_id
    }

    /// Returns a rectangle that should enclose all objects in the scene.
    ///
    /// FIXME(pcwalton): Is this really needed?
    #[inline]
    pub fn bounds(&self) -> RectF {
        self.bounds
    }

    /// Sets a rectangle that should enclose all objects in the scene.
    ///
    /// FIXME(pcwalton): Is this really needed?
    #[inline]
    pub fn set_bounds(&mut self, new_bounds: RectF) {
        self.bounds = new_bounds;
        self.epoch.next();
    }

    /// Returns the view box, which defines the visible portion of the scene.
    #[inline]
    pub fn view_box(&self) -> RectF {
        self.view_box
    }

    /// Changes the view box, which defines the visible portion of the scene.
    #[inline]
    pub fn set_view_box(&mut self, new_view_box: RectF) {
        self.view_box = new_view_box;
        self.epoch.next();
    }

    #[allow(deprecated)]
    pub(crate) fn apply_render_options(&self,
                                       original_outline: &Outline,
                                       options: &PreparedBuildOptions)
                                       -> Outline {
        let mut outline;
        match options.transform {
            PreparedRenderTransform::Perspective {
                ref perspective,
                ref clip_polygon,
                ..
            } => {
                if original_outline.is_outside_polygon(clip_polygon) {
                    outline = Outline::new();
                } else {
                    outline = (*original_outline).clone();
                    outline.close_all_contours();
                    outline.clip_against_polygon(clip_polygon);
                    outline.apply_perspective(perspective);

                    // TODO(pcwalton): Support subpixel AA in 3D.
                }
            }
            _ => {
                // TODO(pcwalton): Short circuit.
                outline = (*original_outline).clone();
                outline.close_all_contours();
                if options.transform.is_2d() || options.subpixel_aa_enabled {
                    let mut transform = match options.transform {
                        PreparedRenderTransform::Transform2D(transform) => transform,
                        PreparedRenderTransform::None => Transform2F::default(),
                        PreparedRenderTransform::Perspective { .. } => unreachable!(),
                    };
                    if options.subpixel_aa_enabled {
                        transform *= Transform2F::from_scale(vec2f(3.0, 1.0))
                    }
                    outline.transform(&transform);
                }
            }
        }

        if !options.dilation.is_zero() {
            outline.dilate(options.dilation);
        }

        outline
    }

    #[inline]
    pub(crate) fn effective_view_box(&self, render_options: &PreparedBuildOptions) -> RectF {
        if render_options.subpixel_aa_enabled {
            self.view_box * vec2f(3.0, 1.0)
        } else {
            self.view_box
        }
    }

    /// Builds render commands necessary to render the scene and sends them to the `SceneSink`.
    ///
    /// The given executor will be used to prepare these commands. Typically, this will be a
    /// `SequentialExecutor` to prepare commands on a single thread or `RayonExecutor` to prepare
    /// commands in parallel across multiple threads.
    #[inline]
    pub fn build<'a, 'b, E>(&mut self,
                            options: BuildOptions,
                            sink: &'b mut SceneSink<'a>,
                            executor: &E)
                            where E: Executor {
        let prepared_options = options.prepare(self.bounds);
        SceneBuilder::new(self, &prepared_options, sink).build(executor)
    }

    #[inline]
    pub(crate) fn display_list(&self) -> &[DisplayItem] {
        &self.display_list
    }

    #[inline]
    pub(crate) fn draw_paths(&self) -> &[DrawPath] {
        &self.draw_paths
    }

    #[inline]
    pub(crate) fn clip_paths(&self) -> &[ClipPath] {
        &self.clip_paths
    }

    /// Returns the number of draw paths in this scene.
    #[inline]
    pub fn draw_path_count(&self) -> u32 {
        self.draw_paths.len() as u32
    }

    /// Returns the draw path with the given ID.
    #[inline]
    pub fn get_draw_path(&self, draw_path_id: DrawPathId) -> &DrawPath {
        &self.draw_paths[draw_path_id.0 as usize]
    }

    /// Returns the clip path with the given ID.
    #[inline]
    pub fn get_clip_path(&self, clip_path_id: ClipPathId) -> &ClipPath {
        &self.clip_paths[clip_path_id.0 as usize]
    }

    /// Returns the paint with the given ID.
    #[inline]
    pub fn get_paint(&self, paint_id: PaintId) -> &Paint {
        self.palette.paints.get(paint_id.0 as usize).expect("No paint with that ID!")
    }

    /// Returns the globally-unique ID of the scene.
    #[inline]
    pub fn id(&self) -> SceneId {
        self.id
    }

    #[inline]
    pub(crate) fn epoch(&self) -> SceneEpoch {
        self.epoch
    }

    /// A convenience method to build a scene and accumulate commands into a vector.
    pub fn build_into_vector<D, E>(&mut self,
                                   renderer: &mut Renderer<D>,
                                   build_options: BuildOptions,
                                   executor: E)
                                   -> Vec<RenderCommand>
                                   where D: Device, E: Executor {
        let commands = Arc::new(Mutex::new(vec![]));
        let commands_for_listener = commands.clone();
        let listener = RenderCommandListener::new(Box::new(move |command| {
            commands_for_listener.lock().unwrap().push(command)
        }));
        let mut sink = SceneSink::new(listener, renderer.mode().level);
        self.build(build_options, &mut sink, &executor);
        let mut commands = commands.lock().unwrap();
        mem::replace(&mut *commands, vec![])
    }

    /// A convenience method to build a scene and send the resulting commands to the given
    /// renderer.
    pub fn build_and_render<D, E>(&mut self,
                                  renderer: &mut Renderer<D>,
                                  build_options: BuildOptions,
                                  executor: E)
                                  where D: Device, E: Executor {
        let commands = self.build_into_vector(renderer, build_options, executor);
        renderer.begin_scene();
        commands.into_iter().for_each(|command| renderer.render_command(&command));
        renderer.end_scene();
    }
}

/// Receives render commands and delivers them to a `RenderCommandListener`.
///
/// Scene sinks wrap render command listeners with cached information about the previous scene.
pub struct SceneSink<'a> {
    pub(crate) listener: RenderCommandListener<'a>,
    pub(crate) renderer_level: RendererLevel,
    pub(crate) last_scene: Option<LastSceneInfo>,
}

pub(crate) struct LastSceneInfo {
    pub(crate) scene_id: SceneId,
    pub(crate) scene_epoch: SceneEpoch,
    pub(crate) draw_segment_ranges: Vec<Range<u32>>,
    pub(crate) clip_segment_ranges: Vec<Range<u32>>,
}

#[derive(Clone, Copy, PartialEq, Debug)]
pub(crate) struct SceneEpoch {
    pub(crate) hi: u64,
    pub(crate) lo: u64,
}

impl SceneEpoch {
    #[inline]
    fn new(hi: u64, lo: u64) -> SceneEpoch {
        SceneEpoch { hi, lo }
    }

    #[inline]
    fn successor(&self) -> SceneEpoch {
        if self.lo == u64::MAX {
            SceneEpoch { hi: self.hi + 1, lo: 0 }
        } else {
            SceneEpoch { hi: self.hi, lo: self.lo + 1 }
        }
    }

    #[inline]
    fn next(&mut self) {
        *self = self.successor();
    }
}

impl<'a> SceneSink<'a> {
    /// Creates a new scene sink from the given render command listener and level.
    #[inline]
    pub fn new(listener: RenderCommandListener<'a>, renderer_level: RendererLevel)
               -> SceneSink<'a> {
        SceneSink { listener, renderer_level, last_scene: None }
    }
}

/// A path drawn to the output or to a render target.
#[derive(Clone, Debug)]
pub struct DrawPath {
    /// The actual vector path outline.
    pub outline: Outline,
    /// The ID of the paint that specifies how to fill the interior of this outline.
    pub paint: PaintId,
    /// The ID of an optional clip path that will be used to clip this path.
    pub clip_path: Option<ClipPathId>,
    /// How to fill this path (winding or even-odd).
    pub fill_rule: FillRule,
    /// How to blend this path with everything below it.
    pub blend_mode: BlendMode,
    /// The name of this path, for debugging.
    ///
    /// Pass the empty string (which does not allocate) if debugging is not needed.
    pub name: String,
}

/// Describes a path that can be used to clip other paths.
#[derive(Clone, Debug)]
pub struct ClipPath {
    /// The actual vector path outline.
    pub outline: Outline,
    /// The ID of another, previously-defined, clip path that clips this one.
    ///
    /// Nested clips can be achieved by clipping clip paths with other clip paths.
    pub clip_path: Option<ClipPathId>,
    /// How to fill this path (winding or even-odd).
    pub fill_rule: FillRule,
    /// The name of this clip path, for debugging.
    ///
    /// Pass the empty string (which does not allocate) if debugging is not needed.
    pub name: String,
}

/// The ID of a draw path, unique to a single scene.
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
pub struct DrawPathId(pub u32);

/// The ID of a clip path, unique to a single scene.
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
pub struct ClipPathId(pub u32);

/// Either a draw path ID or a clip path ID, depending on context.
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
pub struct PathId(pub u32);

/// A raster image target that can be rendered to and later reused as a pattern.
///
/// This can be useful for creating "stamps" or "symbols" that are rendered once and reused. It can
/// also be useful for image effects that require many paths to be processed at once; e.g. opacity
/// applied to a group of paths.
#[derive(Clone, Debug)]
pub struct RenderTarget {
    size: Vector2I,
    name: String,
}

/// High-level drawing commands.
#[derive(Clone, Debug)]
pub enum DisplayItem {
    /// Draws paths to the render target on top of the stack.
    DrawPaths(Range<DrawPathId>),

    /// Pushes a render target onto the top of the stack.
    PushRenderTarget(RenderTargetId),

    /// Pops a render target from the stack.
    PopRenderTarget,
}

impl DrawPath {
    /// Creates a new draw path with the given outline and paint.
    ///
    /// Initially, there is no clip path, the fill rule is set to winding, the blend mode is set to
    /// source-over, and the path has no name.
    #[inline]
    pub fn new(outline: Outline, paint: PaintId) -> DrawPath {
        DrawPath {
            outline,
            paint,
            clip_path: None,
            fill_rule: FillRule::Winding,
            blend_mode: BlendMode::SrcOver,
            name: String::new(),
        }
    }

    /// Returns the outline of this path, which defines its vector commands.
    #[inline]
    pub fn outline(&self) -> &Outline {
        &self.outline
    }

    #[inline]
    pub(crate) fn clip_path(&self) -> Option<ClipPathId> {
        self.clip_path
    }

    /// Sets a previously-defined clip path that will be used to limit the filled region of this
    /// path.
    ///
    /// Clip paths are defined in world space, not relative to the bounds of this path.
    #[inline]
    pub fn set_clip_path(&mut self, new_clip_path: Option<ClipPathId>) {
        self.clip_path = new_clip_path
    }

    #[inline]
    pub(crate) fn paint(&self) -> PaintId {
        self.paint
    }

    #[inline]
    pub(crate) fn fill_rule(&self) -> FillRule {
        self.fill_rule
    }

    /// Sets the fill rule: even-odd or winding.
    #[inline]
    pub fn set_fill_rule(&mut self, new_fill_rule: FillRule) {
        self.fill_rule = new_fill_rule
    }

    #[inline]
    pub(crate) fn blend_mode(&self) -> BlendMode {
        self.blend_mode
    }

    /// Sets the blend mode, which specifies how this path will be composited with content
    /// underneath it.
    #[inline]
    pub fn set_blend_mode(&mut self, new_blend_mode: BlendMode) {
        self.blend_mode = new_blend_mode
    }

    /// Assigns a name to this path, for debugging.
    #[inline]
    pub fn set_name(&mut self, new_name: String) {
        self.name = new_name
    }
}

impl ClipPath {
    /// Creates a new clip path with the given outline.
    ///
    /// Initially, there is no nested clip path, the fill rule is set to winding, and the clip path
    /// has no name.
    #[inline]
    pub fn new(outline: Outline) -> ClipPath {
        ClipPath { outline, clip_path: None, fill_rule: FillRule::Winding, name: String::new() }
    }

    /// Returns the outline of this clip path, which defines its vector commands.
    #[inline]
    pub fn outline(&self) -> &Outline {
        &self.outline
    }

    #[inline]
    pub(crate) fn clip_path(&self) -> Option<ClipPathId> {
        self.clip_path
    }

    /// Sets a nested clip path for this one by ID.
    ///
    /// Draw paths can effectively be clipped by multiple paths by clipping one of the clip paths
    /// with the other, forming a chain of clips.
    #[inline]
    pub fn set_clip_path(&mut self, new_clip_path: Option<ClipPathId>) {
        self.clip_path = new_clip_path
    }

    #[inline]
    pub(crate) fn fill_rule(&self) -> FillRule {
        self.fill_rule
    }

    /// Sets the fill rule for this clip path: even-odd or winding.
    #[inline]
    pub fn set_fill_rule(&mut self, new_fill_rule: FillRule) {
        self.fill_rule = new_fill_rule
    }

    /// Assigns a name to this clip path, for debugging.
    #[inline]
    pub fn set_name(&mut self, new_name: String) {
        self.name = new_name
    }
}

impl RenderTarget {
    /// Declares a new render target of the given device pixel size and with the given name for
    /// debugging.
    ///
    /// Pass the empty string (which does not allocate) if a name is not needed.
    #[inline]
    pub fn new(size: Vector2I, name: String) -> RenderTarget {
        RenderTarget { size, name }
    }

    /// Returns the device pixel size of this render target.
    #[inline]
    pub fn size(&self) -> Vector2I {
        self.size
    }
}

impl DrawPathId {
    #[inline]
    pub(crate) fn to_path_id(self) -> PathId {
        PathId(self.0)
    }
}

impl ClipPathId {
    #[inline]
    pub(crate) fn to_path_id(self) -> PathId {
        PathId(self.0)
    }
}

impl PathId {
    #[inline]
    pub(crate) fn to_clip_path_id(self) -> ClipPathId {
        ClipPathId(self.0)
    }

    #[inline]
    pub(crate) fn to_draw_path_id(self) -> DrawPathId {
        DrawPathId(self.0)
    }
}