# -*- coding: utf-8 -*-
"""
Created on Mon Feb 19 17:59:31 2018

@author: noordam
"""

import math

epsilon =1e-17
#==============================================================================
# compute the intersection between a line and a circle 
#==============================================================================
def computeCircleLineIntersection(xA,yA,xB, yB, xC, yC, r):
    
    # compute the euclidean distance between A and B
    lAB =math.sqrt((xB-xA)**2.0+(yB-yA)**2.0);
    
    # compute the direction vector D from A to B
    dX = (xB - xA) /lAB;
    dY = (yB - yA) /lAB;
    
    # Now the line equation is x = Dx*t + Ax, y = Dy*t + Ay with 0 <= t <= 1.
    # compute the value t of the closest point to the circle center (Cx, Cy)
    t = dX*(xC -xA) + dY*(yC-yA);
    
    # This is the projection of C on the line from A to B.
    # compute the coordinates of the point E on line and closest to C
    xE = t*dX+xA;
    yE = t*dY + yA;
    
    # compute the euclidean distance from E to C
    lEC = math.sqrt((xE-xC)**2.0+(yE-yC)**2.0);
    
    # test if the line intersects the circle
    if lEC < r:
        # compute distance from t to circle intersection point
        dt = math.sqrt( r**2.0 - lEC**2.0)
    
        # compute first intersection point
       # xF = (t-dt)*dX + xA
       # yF = (t-dt)*dY + yA
    
        # compute second intersection point
        xG = (t+dt)*dX + xA
        yG = (t+dt)*dY + yA
      #  print xF
      #  print yF
        if xG> xA and xG<=xB:
            return(xG,yG)
        else:
            return False
    
    # else test if the line is tangent to circle
    elif( lEC == r ):
       # tangent point to circle is E
        print ("only 1 intersection")
        return False
    else:
        # line doesn't touch circle
        print ("no intersections")
        return False
#==============================================================================
#  get the part of the surface line on which x is located 
#==============================================================================
def GetNearestLineAtX(x,xCoordsSurfaceLine,yCoordsSurfaceLine):
    ii =0;
    if x>=xCoordsSurfaceLine[len(xCoordsSurfaceLine)-1]:
        return False
        
    xLinePoint1=0.0;
    while x> xCoordsSurfaceLine[ii] and ii<len(xCoordsSurfaceLine):
        xLinePoint1=xCoordsSurfaceLine[ii]
        ii =ii+1;
    xLinePoint1
    yLinePoint1 = yCoordsSurfaceLine[ii-1];
    
    xLinePoint2 = xCoordsSurfaceLine[ii];
    yLinePoint2 = yCoordsSurfaceLine[ii];
   
    coordIndexPoint1   = ii-1;
        
    return [xLinePoint1,xLinePoint2],  [yLinePoint1,yLinePoint2], coordIndexPoint1          

#==============================================================================
# get the y coordinate at a given x on a line
#==============================================================================
def GetYatX(x,xCoordsLine,yCoordsLine):
    x1 = xCoordsLine[0]
    x2 = xCoordsLine[1]

    y1 = yCoordsLine[0]  
    y2 = yCoordsLine[1]    
    
    t = (x - x1)/(x2 - x1)
    
    y = y1+ (y2-y1)*t
    return y
     
#==============================================================================
#      find the indexes of points of an existing line within a specified range
#==============================================================================
def FindIndexesInRange(xStart,xEnd,xCoordsSurfaceLine,lineType):
    ii=0

    indexesInRange = [];  
    if lineType=="surfaceLine":
        while xEnd>xCoordsSurfaceLine[ii] and ii<len(xCoordsSurfaceLine):
            if xCoordsSurfaceLine[ii]>=xStart-epsilon:
                indexesInRange.extend([ii])
            ii=ii+1;
    else:
        while ii<len(xCoordsSurfaceLine):
            if xCoordsSurfaceLine[ii]>=xStart-epsilon and xEnd>xCoordsSurfaceLine[ii]:
                indexesInRange.extend([ii])
            ii=ii+1;
    
    
    return indexesInRange