//Title: Line Calculation
//Credit to: Jtgibson
//Contributed by: Jtgibson


//This returns a precise list of turfs in a near-perfect
// line from point A to point B.  The turfs are presented
// in order of distance, so they can be used to follow a
// path.


proc/get_line(atom/A, atom/B)
    var/x_dif = B.x - A.x
    var/y_dif = B.y - A.y

    if(A.z != B.z) return(list())
    if(!A.loc || !B.loc) return(list())

    if(!x_dif && !y_dif) return(list(A.loc)) //prevent divide by zero errors

    if(abs(x_dif) > abs(y_dif)) //horizontal-tending line
        var/y_offset = y_dif/abs(x_dif)

        var/list/line = list()

        for(var/x_offset = 0, abs(x_offset) <= abs(x_dif),)
            var/x_pos = A.x + x_offset
            var/y_pos = A.y + (abs(x_offset)*y_offset)

            var/turf/T = locate(x_pos, y_pos, A.z)
            line += T

            if(x_dif < 0) x_offset--
            else x_offset++

        return(line)

    else if(abs(y_dif) > abs(x_dif)) //vertical-tending line
        var/x_offset = x_dif/abs(y_dif)

        var/list/line = list()

        for(var/y_offset = 0, abs(y_offset) <= abs(y_dif),)
            var/x_pos = A.x + (abs(y_offset)*x_offset)
            var/y_pos = A.y + y_offset

            var/turf/T = locate(x_pos, y_pos, A.z)
            line += T

            if(y_dif < 0) y_offset--
            else y_offset++

        return(line)

    else //diagonal line
        var/x_offset
        var/y_offset
        var/dir = get_dir(A,B)
        if(dir&NORTH) y_offset = 1
        else          y_offset = -1
        if(dir&EAST)  x_offset = 1
        else          x_offset = -1

        var/list/line = list()

        for(var/position = 0, position <= abs(x_dif), position++)
            var/x_pos = A.x + (position*x_offset)
            var/y_pos = A.y + (position*y_offset)

            var/turf/T = locate(x_pos, y_pos, A.z)
            line += T

        return(line)