class Point{
  public float x;
  public float y;
  public Point(float nx,float ny){
    x = nx;
    y = ny;
  } 
}

class Line{
  //every line is a list of connected points
  public ArrayList listOfPoints; 
  public color c;
  public boolean selected;
  public Line(){
    listOfPoints = new ArrayList();
    selected = false;
    //Every line is given a random color with low alpha so that
    //1) you can tell them apart and 2) the selected onces will be more visible when selected
    c = color(random(255),random(255),random(255),100);
  }

  public void drawLine(){
    // A line needs two points to be a line....
    if(listOfPoints.size() >=2){
      if(selected){
        stroke(255,0,0,255);//full red
      }
      else{
        stroke(c);
      }  
      beginShape();
      for(int i = 0; i<listOfPoints.size();i++){
        Point currentPoint =  (Point)listOfPoints.get(i);
        vertex(currentPoint.x,currentPoint.y);
      }
      endShape();
    } 
  }

  public void addPointToLine(float x,float y){
    //Note: there is no sorting going on, so every point will be connected to the previously added point
    listOfPoints.add(new Point(x,y));
  }
}

ArrayList lines;
float selectionStartX;
float selectionStartY;
void setup(){
  size(800,800);
  background(255);
  lines = new ArrayList();
  noFill();
  smooth();
  //Create 10 lines with 10 random points
  //this should give you an idea of how lines are created
  for(int l = 0;l<10;l++){
    Line temp = new Line();
    for(int p = 0;p<10;p++){
      temp.addPointToLine(random(width),random(height));
    } 
    lines.add(temp);
  }

}

void draw(){
  background(255);
  //if the mouse is pressed then we want to draw a selection rectangle
  if(mousePressed){
    stroke(0);
    rect(selectionStartX,selectionStartY,mouseX-selectionStartX,mouseY-selectionStartY);
  }

  for(int i = 0;i<lines.size();i++){
    Line currentLine = (Line)lines.get(i);
    currentLine.drawLine(); 
  }
}

void mousePressed(){
  selectionStartX = mouseX;
  selectionStartY = mouseY;
}

void mouseReleased(){
  //Run the line select code
  //The cordinates that are passed to the function must be top-left x&y and bottom right x&y
  //So we need to take care of the senario where there mouse is draged in a direction that isn't right-down
  if(mouseX <selectionStartX && mouseY < selectionStartY){
    selectLines(mouseX,mouseY,selectionStartX,selectionStartY);
  }else if(mouseX <selectionStartX){
     selectLines(mouseX,selectionStartY,selectionStartX,mouseY);
  }else if(mouseY < selectionStartY){
    selectLines(selectionStartX,mouseY,mouseX,selectionStartY);
  }else{
    selectLines(selectionStartX,selectionStartY,mouseX,mouseY);
  }
}

void selectLines(float x1,float y1,float x2,float y2){
  for(int l = 0; l < lines.size();l++){
    Line currentLine = (Line)lines.get(l);
    currentLine.selected = false; //reset every line
    for(int p = 0; p< currentLine.listOfPoints.size()-1;p++){
      //a line need two points to be a line! also becouse we are doing .get(p+1) we are stopping the iteration at .size()-1;
      Point currentPoint = (Point)currentLine.listOfPoints.get(p);
      Point nextPoint = (Point)currentLine.listOfPoints.get(p+1);
      if(lineRectangleIntersect(currentPoint.x,currentPoint.y,nextPoint.x,nextPoint.y,x1,y1,x2,y2)){
        currentLine.selected = true;
        //the line is selected - no need to keep looking at it's remaining points so we BREAK!
        break; 
      }
    }
  }
}

// As it turns out i didn't know how to do line-text collision detection (only knew how to do point-rect) so here's REAS code on how to do it,
//slighly modified though :D
// Code from REAS:
// http://www.openprocessing.org/portal/?userID=54

boolean lineRectangleIntersect(float x1, float y1, float  x2, float y2,
float rx1, float ry1, float rx2, float ry2) {

  float topIntersection;
  float bottomIntersection;
  float topPoint;
  float bottomPoint;
  // Calculate m and c for the equation for the line (y = mx+c)
  float m = (y2-y1) / (x2-x1);
  float c = y1 -(m*x1);
  // If the line is going up from right to left then the top intersect point is on the left
  if(m > 0) {
    topIntersection = (m*rx1  + c);
    bottomIntersection = (m*(rx2)  + c);
  }
  // Otherwise it's on the right
  else {
    topIntersection = (m*(rx2)  + c);
    bottomIntersection = (m*rx1  + c);
  }
  // Work out the top and bottom extents for the triangle
  if(y1 < y2) {
    topPoint = y1;
    bottomPoint = y2;
  } 
  else {
    topPoint = y2;
    bottomPoint = y1;
  }
  float topOverlap;
  float botOverlap;
  // Calculate the overlap between those two bounds
  topOverlap = topIntersection > topPoint ? topIntersection : topPoint;
  botOverlap = bottomIntersection < bottomPoint ? bottomIntersection : bottomPoint;

  return (topOverlap<botOverlap) && (!((botOverlap<ry1) || (topOverlap>ry2)));

}