os.loadAPI("file")
[["move" API]]

fuelSlot = 0
defaultSlot = 0
minFuel = 0
x = 0
y = 0
z = 0
dirx = 0
dirz = 0

function register(slot, default, fuel, facex, facez)
    if not start() then
        fuelSlot = slot
        defaultSlot = default
        minFuel = fuel
        dirx = facex
        dirz = facez
    end
end

function start()
    vars = file.read("movement")

    if vars == {} then
        return false
    end

    fuelSlot = vars["fuelSlot"]
    defaultSlot = vars["defaultSlot"]
    minFuel = vars["minFuel"]
    x = vars["x"]
    y = vars["y"]
    z = vars["z"]
    dirx = vars["dirx"]
    dirz = vars["dirz"]

    return true
end

function write()
    file.write("movement", {["fuelSlot"]=fuelSlot,
                            ["defaultSlot"]=defaultSlot,
                            ["minFuel"]=minFuel,
                            ["x"]=x,
                            ["y"]=y,
                            ["z"]=z,
                            ["dirx"]=dirx,
                            ["dirz"]=dirz})
end

function move_(direction)
    if direction=="forward" then
        x += dirx
        z += dirz
    elseif direction=="back" then
        x -= dirx
        z -= dirz
    elseif direction=="up" then
        y += 1
    elseif direction=="down" then
        y -= 1
    else
        failed("MOVEDIR")
    end
    write()
end

function turn(direction)
    if direction=="right" then
        if dirx == 0 then
            dirx = dirz*-1
            dirz = 0
        else
            dirz = dirx
            dirx = 0
        end
    elseif direction=="left" then
        if dirx == 0 then
            dirx = dirz
            dirz = 0
        else
            dirz = dirx*-1
            dirx = 0
        end
    else
        failed("TURNDIR")
    end
    write()
end

function refuel()
    if turtle.getFuelLevel() < minFuel then
        turtle.select(fuelSlot)
        if not turtle.refuel(1) then
            failed("FUEL")
        end
        turtle.select(defaultSlot)
    end
end

function failed(message)
    print("Failed with error : " .. message)
    write()
    shell.exit()
end

function dig()
    if not turtle.dig() then
        failed("DIG")
    end
end

function digUp()
    if not turtle.digUp() then
        failed("DIGUP")
    end
end

function digDown()
    if not turtle.digDown() then
        failed("DIGDN")
    end
end

function rt()
    turtle.turnRight()
    turn("right")
end

function lt()
    turtle.turnLeft()
    turn("left")
end

function fwd()
    refuel()
    while not turtle.forward() do
        dig()
    end
    move_("forward")
end

function back()
    refuel()
    while not turtle.back() do
        rt()
        rt()
        dig()
        rt()
        rt()
    end
    move_("back")
end

function up()
    refuel()
    while not turtle.up() do
        digUp()
    end
    move_("up")
end

function down()
    refuel()
    while not turtle.down() do
        digDown()
    end
    move_("down")
end

function seekdir(seek, dir):
    if dir=="x" then
        if dirx ~= seek then
            if dirz == seek then
                lt()
            elseif dirx == seek*-1 then
                rt()
                rt()
            else
                rt()
            end
        end
    elseif dir=="z" then
        if dirz ~= seekz then
            if dirx == seekz then
                rt()
            elseif dirz == seekz*-1 then
                lt()
                lt()
            else
                lt()
            end
        end
    else
        failed("SEEKDIR")
    end

function seekcoords(seekx, seeky, seekz, seekdirx, seekdirz)
    toxd = x - seekx
    tox = toxd / math.abs(toxd)

    toyd = y - seeky
    toy = toyd / math.abs(toyd)

    tozd = z - seekz
    toz = tozd / math.abs(tozd)

    seekdir(tox, "x")

    for i=1,toxd do
        fwd()
    end

    seekdir(toz, "z")

    for i=1,tozd do
        fwd()
    end

    seekdir(seekdirx, "x")
    seekdir(seekdirz, "z")

    for i=1,toyd do
        if toy > 0 then
            up()
        elseif toy < 0 then
            down()
        end
    end
end

function getx()
    return x
end

function gety()
    return y
end

function getz()
    return z
end

function getfacex()
    return dirx
end

function getfacez()
    return dirz
end