///////////////////////////////////////////////////////////////////////////////
// PredPreySim2.pde - Processing program to simulate predator-prey cycles
//    (Skeleton with data and starting point for the simulation loop)
// Your job: Implement the Lotka-Volterra equations where indicated!
// (c) 2013 Marie desJardins

///////////////////////////////////////////////////////////////////////////////
// Variable declarations and initializations

int prey=80;             // initial number of predators
int predators=40;        // initial number of predators
float b_prey=2.0;        // birth rate of prey
float d_prey=0.001;      // death rate of prey
float b_pred=0.005;      // birth rate of predators
float d_pred=0.6;        // death rate of predators

int time=0;              // time starts at zero
int max_cycles=200;       // maximum number of time steps to simulate
int max_pred=5000;       // limit on the number pf predators 
int max_prey=5000;       // limit on the number of prey
int new_prey;            // temp variable for new prey population each cycle
int new_predators;       // temp variable for new predator population each cycle

int height = 500;        // height of display region for graph
int width = 2000;        // width of display region for graph
int border = 30;         // additional border space on all four sides of graph

float graph_x = border +  (width * time / max_cycles);
// initial x position (for t=0)
float prey_graph_y = border + height - (height * prey / max_prey);
// initial y position for prey graph 
float pred_graph_y = border + height - (height * predators / max_pred);
// initial y position for predator graph 
float prev_graph_x;      // temp variable for previous x position in graph
float prev_pred_graph_y; // temp variable for previous y position of predator line
float prev_prey_graph_y; // temp variable for previous y position of prey line
color pred_color = color (255, 0, 0);    // predator line is red
color prey_color = color(0, 0, 255);     // prey line is blue

PrintWriter output = createWriter ("outfile.csv");     // open file for recording data


///////////////////////////////////////////////////////////////////////////////
// Program

// Initialize output file and display
size (width + 2*border, height + 2*border);

// Simulation loop
while (time < max_cycles) {
  time = time+1;

  // Update number of prey and predators using L-V equations and temp variables
  new_prey = floor (prey + (b_prey * prey) - (d_prey * prey * predators));
  new_predators = floor (predators + (b_pred * predators * prey) - (d_pred * predators));

  // Make sure prey and predators are in the range [1, max_prey]
  new_prey = min (max_prey, max (1, new_prey));
  new_predators = min (max_pred, max (1, new_predators));

  // Update counts
  prey = new_prey;
  predators = new_predators;

  // Save previous graph positions for line drawing
  prev_graph_x = graph_x;
  prev_prey_graph_y = prey_graph_y;
  prev_pred_graph_y = pred_graph_y;
  
  // YOUR CODE GOES BELOW HERE!  IT SHOULD COMPUTE GRAPH_X,
  // PREY_GRAPH_Y, AND PRED_GRAPH_Y, THEN USE PRED_COLOR AND
  // PREY_COLOR AS FILL COLORS TO DRAW A LINE FOR PREDATORS
  // AND A LINE FOR PREY
}