// Copyright 2016 The G3N Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package renderer

import (
	"github.com/g3n/engine/camera"
	"github.com/g3n/engine/core"
	"github.com/g3n/engine/gls"
	"github.com/g3n/engine/graphic"
	"github.com/g3n/engine/gui"
	"github.com/g3n/engine/light"
	"github.com/g3n/engine/math32"
	"sort"
)

// Renderer renders a scene containing 3D objects and/or 2D GUI elements.
type Renderer struct {
	Shaman                      // Embedded shader manager
	gs          *gls.GLS        // Reference to OpenGL state
	rinfo       core.RenderInfo // Preallocated Render info
	specs       ShaderSpecs     // Preallocated Shader specs
	sortObjects bool            // Flag indicating whether objects should be sorted before rendering
	stats       Stats           // Renderer statistics

	// Populated each frame
	rgraphics    []*graphic.Graphic         // Array of rendered graphics
	cgraphics    []*graphic.Graphic         // Array of culled graphics
	grmatsOpaque []*graphic.GraphicMaterial // Array of rendered opaque graphic materials for scene
	grmatsTransp []*graphic.GraphicMaterial // Array of rendered transparent graphic materials for scene
	grmatsGui    []*graphic.GraphicMaterial // Array of rendered GUI graphic materials for scene
	ipanels      []gui.IPanel               // Array of all top rendered IPanels (panels which are not children of other IPanels)
	ambLights    []*light.Ambient           // Array of ambient lights for last scene
	dirLights    []*light.Directional       // Array of directional lights for last scene
	pointLights  []*light.Point             // Array of point
	spotLights   []*light.Spot              // Array of spot lights for the scene
	others       []core.INode               // Other nodes (audio, players, etc)
}

// Stats describes how many object types were rendered.
// It is cleared at the start of each render.
type Stats struct {
	Graphics int // Number of graphic objects rendered
	Lights   int // Number of lights rendered
	Panels   int // Number of Gui panels rendered
	Others   int // Number of other objects rendered
}

// NewRenderer creates and returns a pointer to a new Renderer.
func NewRenderer(gs *gls.GLS) *Renderer {

	r := new(Renderer)
	r.gs = gs
	r.Shaman.Init(gs)
	r.sortObjects = true

	r.ambLights = make([]*light.Ambient, 0)
	r.dirLights = make([]*light.Directional, 0)
	r.pointLights = make([]*light.Point, 0)
	r.spotLights = make([]*light.Spot, 0)
	r.others = make([]core.INode, 0)
	r.rgraphics = make([]*graphic.Graphic, 0)
	r.cgraphics = make([]*graphic.Graphic, 0)
	r.grmatsOpaque = make([]*graphic.GraphicMaterial, 0)
	r.grmatsTransp = make([]*graphic.GraphicMaterial, 0)
	r.ipanels = make([]gui.IPanel, 0)

	return r
}

// Stats returns a copy of the statistics for the last frame.
// Should be called after the frame was rendered.
func (r *Renderer) Stats() Stats {

	return r.stats
}

// SetObjectSorting sets whether objects will be sorted before rendering.
func (r *Renderer) SetObjectSorting(sort bool) {

	r.sortObjects = sort
}

// ObjectSorting returns whether objects will be sorted before rendering.
func (r *Renderer) ObjectSorting() bool {

	return r.sortObjects
}

// Render renders the specified scene using the specified camera. Returns an an error.
func (r *Renderer) Render(scene core.INode, cam camera.ICamera) error {

	// Updates world matrices of all scene nodes
	scene.UpdateMatrixWorld()

	// Build RenderInfo
	cam.ViewMatrix(&r.rinfo.ViewMatrix)
	cam.ProjMatrix(&r.rinfo.ProjMatrix)

	// Clear stats and scene arrays
	r.stats = Stats{}
	r.ambLights = r.ambLights[0:0]
	r.dirLights = r.dirLights[0:0]
	r.pointLights = r.pointLights[0:0]
	r.spotLights = r.spotLights[0:0]
	r.others = r.others[0:0]
	r.rgraphics = r.rgraphics[0:0]
	r.cgraphics = r.cgraphics[0:0]
	r.grmatsOpaque = r.grmatsOpaque[0:0]
	r.grmatsTransp = r.grmatsTransp[0:0]
	r.ipanels = r.ipanels[0:0]

	// Prepare for frustum culling
	var proj math32.Matrix4
	proj.MultiplyMatrices(&r.rinfo.ProjMatrix, &r.rinfo.ViewMatrix)
	frustum := math32.NewFrustumFromMatrix(&proj)

	// Classify scene and all scene nodes, culling renderable IGraphics which are fully outside of the camera frustum
	r.classifyAndCull(scene, frustum)
	//log.Debug("Rendered/Culled: %v/%v", len(r.grmats), len(r.cgrmats))

	// Set light counts in shader specs
	r.specs.AmbientLightsMax = len(r.ambLights)
	r.specs.DirLightsMax = len(r.dirLights)
	r.specs.PointLightsMax = len(r.pointLights)
	r.specs.SpotLightsMax = len(r.spotLights)

	// Pre-calculate MV and MVP matrices and compile lists of opaque and transparent graphic materials
	for _, gr := range r.rgraphics {
		// Calculate MV and MVP matrices for all non-GUI graphics to be rendered
		gr.CalculateMatrices(r.gs, &r.rinfo)
		// Append all graphic materials of this graphic to lists of graphic materials to be rendered
		materials := gr.Materials()
		for i := range materials {
			if materials[i].IMaterial().GetMaterial().Transparent() {
				r.grmatsTransp = append(r.grmatsTransp, &materials[i])
			} else {
				r.grmatsOpaque = append(r.grmatsOpaque, &materials[i])
			}
		}
	}

	// TODO: If both GraphicMaterials belong to same Graphic we might want to keep their relative order...

	// Z-sort graphic materials (opaque front-to-back and transparent back-to-front)
	if r.sortObjects {
		zSort(r.grmatsOpaque, false) // Sort opaque graphics front to back
		zSort(r.grmatsTransp, true)  // Sort transparent graphics back to front
	}

	// Render GUI elements first
	for i := len(r.ipanels) - 1; i > -1; i-- {
		err := r.renderPanel(r.ipanels[i])
		if err != nil {
			return err
		}
	}

	// Render opaque objects (already sorted front to back)
	for _, grmat := range r.grmatsOpaque {
		err := r.renderGraphicMaterial(grmat)
		if err != nil {
			return err
		}
	}

	// Render transparent objects (already sorted back to front)
	for _, grmat := range r.grmatsTransp {
		err := r.renderGraphicMaterial(grmat)
		if err != nil {
			return err
		}
	}

	// Render other nodes (audio players, etc)
	for _, inode := range r.others {
		inode.Render(r.gs)
		r.stats.Others++
	}

	return nil
}

// classifyAndCull classifies the provided INode and all of its descendents.
// It ignores (culls) renderable IGraphics which are fully outside of the specified frustum.
func (r *Renderer) classifyAndCull(inode core.INode, frustum *math32.Frustum) {

	classifyChildren := true
	// Ignore invisible nodes and their descendants
	if !inode.Visible() {
		return
	}
	// If node is an IPanel append it to appropriate list
	if ipan, ok := inode.(gui.IPanel); ok {
		r.ipanels = append(r.ipanels, ipan)
		classifyChildren = false // Don't classify children since they must be IPanels
		// Check if node is an IGraphic
	} else if igr, ok := inode.(graphic.IGraphic); ok {
		if igr.Renderable() {
			gr := igr.GetGraphic()
			// Frustum culling
			if igr.Cullable() {
				mw := gr.MatrixWorld()
				geom := igr.GetGeometry()
				bb := geom.BoundingBox()
				bb.ApplyMatrix4(&mw)
				if frustum.IntersectsBox(&bb) {
					// Append graphic to list of graphics to be rendered
					r.rgraphics = append(r.rgraphics, gr)
				} else {
					// Append graphic to list of culled graphics
					r.cgraphics = append(r.cgraphics, gr)
				}
			} else {
				// Append graphic to list of graphics to be rendered
				r.rgraphics = append(r.rgraphics, gr)
			}
		}
		// Node is not a Graphic
	} else {
		// Check if node is a Light
		if il, ok := inode.(light.ILight); ok {
			switch l := il.(type) {
			case *light.Ambient:
				r.ambLights = append(r.ambLights, l)
			case *light.Directional:
				r.dirLights = append(r.dirLights, l)
			case *light.Point:
				r.pointLights = append(r.pointLights, l)
			case *light.Spot:
				r.spotLights = append(r.spotLights, l)
			default:
				panic("Invalid light type")
			}
			// Other nodes
		} else {
			r.others = append(r.others, inode)
		}
	}
	// Classify children (if not an IPanel)
	if classifyChildren {
		for _, ichild := range inode.Children() {
			r.classifyAndCull(ichild, frustum)
		}
	}
}

// zSort sorts a list of graphic materials based on the
// user-specified order first then based on their Z position relative to the camera
func zSort(grmats []*graphic.GraphicMaterial, backToFront bool) {

	sort.Slice(grmats, func(i, j int) bool {
		gr1 := grmats[i].IGraphic().GetGraphic()
		gr2 := grmats[j].IGraphic().GetGraphic()
		// Check for user-supplied render order
		rO1 := gr1.RenderOrder()
		rO2 := gr2.RenderOrder()
		if rO1 != rO2 {
			return rO1 < rO2
		}
		mvm1 := gr1.ModelViewMatrix()
		mvm2 := gr2.ModelViewMatrix()
		g1pos := gr1.Position()
		g2pos := gr2.Position()
		g1pos.ApplyMatrix4(mvm1)
		g2pos.ApplyMatrix4(mvm2)
		if backToFront {
			return g1pos.Z < g2pos.Z
		}
		return g1pos.Z > g2pos.Z
	})
}

// renderGraphicMaterial renders the specified graphic material.
func (r *Renderer) renderGraphicMaterial(grmat *graphic.GraphicMaterial) error {

	mat := grmat.IMaterial().GetMaterial()
	geom := grmat.IGraphic().GetGeometry()
	gr := grmat.IGraphic().GetGraphic()

	// Add defines from material, geometry and graphic
	r.specs.Defines = *gls.NewShaderDefines()
	r.specs.Defines.Add(&mat.ShaderDefines)
	r.specs.Defines.Add(&geom.ShaderDefines)
	r.specs.Defines.Add(&gr.ShaderDefines)

	// Set the shader specs for this material and sets shader program
	r.specs.Name = mat.Shader()
	r.specs.ShaderUnique = mat.ShaderUnique()
	r.specs.UseLights = mat.UseLights()
	r.specs.MatTexturesMax = mat.TextureCount()

	// Set active program and apply shader specs
	_, err := r.Shaman.SetProgram(&r.specs)
	if err != nil {
		return err
	}

	// Set up lights (transfer lights' uniforms)
	for idx, l := range r.ambLights {
		l.RenderSetup(r.gs, &r.rinfo, idx)
		r.stats.Lights++
	}
	for idx, l := range r.dirLights {
		l.RenderSetup(r.gs, &r.rinfo, idx)
		r.stats.Lights++
	}
	for idx, l := range r.pointLights {
		l.RenderSetup(r.gs, &r.rinfo, idx)
		r.stats.Lights++
	}
	for idx, l := range r.spotLights {
		l.RenderSetup(r.gs, &r.rinfo, idx)
		r.stats.Lights++
	}

	// Render this graphic material
	grmat.Render(r.gs, &r.rinfo)
	r.stats.Graphics++

	return nil
}

// renderPanel renders the specified panel and all its children
// and then sets the panel as not changed.
func (r *Renderer) renderPanel(ipan gui.IPanel) error {

	if !ipan.Visible() {
		return nil
	}

	// If panel is renderable, render it
	if ipan.Renderable() {
		// Set shader program for the panel's material
		grmat := ipan.GetGraphic().Materials()[0]
		mat := grmat.IMaterial().GetMaterial()
		r.specs.Name = mat.Shader()
		r.specs.ShaderUnique = mat.ShaderUnique()
		_, err := r.Shaman.SetProgram(&r.specs)
		if err != nil {
			return err
		}
		// Render this panel's graphic material
		grmat.Render(r.gs, &r.rinfo)
		r.stats.Panels++
	}

	// Render children panels
	for i := 0; i < len(ipan.Children()); i++ {
		err := r.renderPanel(ipan.Children()[i].(gui.IPanel))
		if err != nil {
			return err
		}
	}

	return nil
}