/**
 * Copyright (c) 2019 Razeware LLC
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * Notwithstanding the foregoing, you may not use, copy, modify, merge, publish,
 * distribute, sublicense, create a derivative work, and/or sell copies of the
 * Software in any work that is designed, intended, or marketed for pedagogical or
 * instructional purposes related to programming, coding, application development,
 * or information technology.  Permission for such use, copying, modification,
 * merger, publication, distribution, sublicensing, creation of derivative works,
 * or sale is expressly withheld.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

import MetalKit

struct Particle {
  var startPosition: float2
  var position: float2
  var direction: Float
  var speed: Float
  var color: float4
  var age: Float
  var life: Float
  var size: Float
  var scale: Float = 1.0
  var startScale: Float = 1.0
  var endScale: Float = 1.0
}

struct ParticleDescriptor {
  var position: float2 = [0, 0]
  var positionXRange: ClosedRange<Float> = 0...0
  var positionYRange: ClosedRange<Float> = 0...0
  var direction: Float = 0
  var directionRange: ClosedRange<Float> = 0...0
  var speed: Float = 0
  var speedRange: ClosedRange<Float> = 0...0
  var pointSize: Float = 80
  var pointSizeRange: ClosedRange<Float> = 0...0
  var startScale: Float = 0
  var startScaleRange: ClosedRange<Float> = 1...1
  var endScale: Float = 0
  var endScaleRange: ClosedRange<Float>?
  var life: Float = 0
  var lifeRange: ClosedRange<Float> = 1...1
  var color: float4 = [0, 0, 0, 1]
}

class Emitter {
  var position: float2 = [0, 0]
  var currentParticles = 0
  var particleCount: Int = 0 {
    didSet {
      let bufferSize = MemoryLayout<Particle>.stride * particleCount
      particleBuffer = Renderer.device.makeBuffer(length: bufferSize)!
    }
  }
  var birthRate = 0
  var birthDelay = 0 {
    didSet {
      birthTimer = birthDelay
    }
  }
  private var birthTimer = 0
  
  var particleTexture: MTLTexture!
  var particleBuffer: MTLBuffer?
  
  var particleDescriptor: ParticleDescriptor?
  
  func emit() {
    if currentParticles >= particleCount {
      return
    }
    guard let particleBuffer = particleBuffer,
      let pd = particleDescriptor else {
      return
    }
    birthTimer += 1
    if birthTimer < birthDelay {
      return
    }
    birthTimer = 0
    var pointer = particleBuffer.contents().bindMemory(to: Particle.self,
                                                       capacity: particleCount)
    pointer = pointer.advanced(by: currentParticles)
    for _ in 0..<birthRate {
      let positionX = pd.position.x + .random(in: pd.positionXRange)
      let positionY = pd.position.y + .random(in: pd.positionYRange)
      pointer.pointee.position = [positionX, positionY]
      pointer.pointee.startPosition = pointer.pointee.position
      pointer.pointee.size = pd.pointSize + .random(in: pd.pointSizeRange)
      pointer.pointee.direction = pd.direction + .random(in: pd.directionRange)
      pointer.pointee.speed = pd.speed + .random(in: pd.speedRange)
      pointer.pointee.scale = pd.startScale + .random(in: pd.startScaleRange)
      pointer.pointee.startScale = pointer.pointee.scale
      if let range = pd.endScaleRange {
        pointer.pointee.endScale = pd.endScale + .random(in: range)
      } else {
        pointer.pointee.endScale = pointer.pointee.startScale
      }
      
      pointer.pointee.age = 0
      pointer.pointee.life = pd.life + .random(in: pd.lifeRange)
      pointer.pointee.color = pd.color
      pointer = pointer.advanced(by: 1)
    }
    currentParticles += birthRate
  }
  
  static func loadTexture(imageName: String) -> MTLTexture? {
    let textureLoader = MTKTextureLoader(device: Renderer.device)
    var texture: MTLTexture?
    let textureLoaderOptions: [MTKTextureLoader.Option : Any]
    textureLoaderOptions = [.origin: MTKTextureLoader.Origin.bottomLeft, .SRGB: false]
    do {
      let fileExtension: String? = URL(fileURLWithPath: imageName).pathExtension.count == 0 ? "png" : nil
      if let url: URL = Bundle.main.url(forResource: imageName, withExtension: fileExtension) {
        texture = try textureLoader.newTexture(URL: url, options: textureLoaderOptions)
      } else {
        print("Failed to load \(imageName)")
      }
    } catch let error {
      print(error.localizedDescription)
    }
    return texture
  }
}