local fin = {}
local radians = 180/math.pi  --> precalculate radians
 
fin.distanceBetween = function ( pos1, pos2 )
         local sqrt = math.sqrt
        if not pos1 or not pos2 then
                return
        end
        if not pos1.x or not pos1.y or not pos2.x or not pos2.y then
                return
        end
        local factor = { x = pos2.x - pos1.x, y = pos2.y - pos1.y }
        return sqrt( ( factor.x * factor.x ) + ( factor.y * factor.y ) )
end
 
 
 
fin.doFollow = function (follower, targetObject, missileSpeed, turnRate, doRotate, runAway)
 
        local missileSpeed = missileSpeed or 8
        local turnRate = turnRate or 0.8
      
        -- get distance between follower and target
        
        local target = targetObject
        
        local distanceX = target.object.x - follower.object.x;
        local distanceY = target.object.y - follower.object.y;
        
        -- get total distance as one number
        local distanceTotal = fin.distanceBetween (follower.object, target.object)
        
        -- calculate how much to move
         local moveDistanceX = turnRate * distanceX / distanceTotal;
         local moveDistanceY = turnRate * distanceY / distanceTotal;
        
        -- increase current speed
        follower.moveX = follower.moveX + moveDistanceX; 
        follower.moveY = follower.moveY + moveDistanceY;
                
        -- get total move distance
        local totalmove = math.sqrt(follower.moveX * follower.moveX + follower.moveY * follower.moveY);
        
        -- apply easing
        follower.moveX = missileSpeed*follower.moveX/totalmove;
        follower.moveY = missileSpeed*follower.moveY/totalmove;
        
        -- move follower (or runner)
        
        if runAway then
                follower.object.x = follower.object.x - follower.moveX;
                follower.object.y = follower.object.y - follower.moveY;
                if doRotate == true then
                  follower.object.rotation = math.atan2(follower.moveY, follower.xMove) * radians;
                end
        else
                follower.object.x = follower.object.x + follower.moveX;
                follower.object.y = follower.object.y + follower.moveY;
                if doRotate == true then
                  follower.object.rotation = (math.atan2(follower.moveY, follower.moveX) * radians)+180;
                end
        end
 
        -- !!!!! you got to check if we hit the target - here or in main game logic !!!!!
 
end
return fin

-- require the module
local  fin = require("fin")
 
-- fin.doFollow (missileDisplayObject,  targetDisplayObject [, missileSpeed, turnRate, doRotate, runAway])
-- example:
 
local obj1 = {}
local obj2 = {}
obj1.object = display.newCircle( 200, 200, 20 ) -- touch object
obj2.object = display.newCircle( 200, 200, 5 ) -- follower object
 
-- you also have to setup initial speed for each follower object
obj2.moveX = 2
obj2.moveY = 2
 
function mainLogic () 
-- in your game logic loop call the function fin.doFollow
-- follower and target must be display object tables!
-- tinker with missileSpeed and turnRate
 
    -- example 1:
    -- obj2 runs away from obj1, rotating
    fin.doFollow (obj2, obj1, 5, 1, true, true) 
 
    -- example 2:
    -- obj2 follows obj1, rotating
    -->  fin.doFollow (obj2, obj1, 5, 1, true, false)
 
end
 
function onTouch( event )
local phase = event.phase
                if "began" == phase or "moved" == phase then
                                obj1.object.x = event.x
                                obj1.object.y = event.y         
                elseif  "cancelled" == phase then
                end
end
 
 Runtime:addEventListener( "enterFrame", mainLogic );
 Runtime:addEventListener( "touch"         , onTouch )