--[[
    A module providing:
     - Relative and absolute movement
     - Refuelling support
     -
]]--


--[[
    dig:    Digs a space before moving forward. NOTE: Dig is highly inefficient for moving backwards.
    tunnel: Ensures to dig space above and below for players.
    direct: UNIMPLEMENTED - Take straight line to location.
]]--

local self = {}

self.mode = {dig = true, tunnel = true, direct = false}

self.dirPreference = {"x","y","z"}
pos = vector.new(0,0,0)
-- heading = 0: +x
-- heading = 1: +y
heading = 0

function self.getHeading()
    return heading
end
function getPos()
    return pos
end

function self.faceDir(dir)
    self.turn(dir - heading)
end

function self.zeroHeading(heading)
    local oldHeading = heading
    heading = 0
    return oldHeading
end

function self.turn(dir)
    dir = dir % 4
    if dir == 3 then
        turtle.turnRight()
    else
        for i = 1,dir do
            turtle.turnRight()
        end
    end
    heading = (heading + dir) % 4
end

function forward()
    if self.mode.dig then
        turtle.dig()
    end
    if turtle.forward() then
        if self.mode.tunnel then
            turtle.digUp()
            turtle.digDown()
        end
        return true
    else
        return false
    end
end

function up()
    if self.mode.dig then
        turtle.digUp()
    end
    return turtle.up()
end

function down()
    if self.mode.dig then
        turtle.digDown()
    end
    return turtle.down()
end

function self.moveForward(n)
    n = n or 1
    local dist = 0
    local oldHeading = heading

    -- Face backwards and move forward.
    if n < 0 then
        self.turn(2)
        n = -n
    end

    for i = 1,n do
        -- Takes care of direction and sign.
        if forward() then
            if heading % 2 == 0 then
                pos.x = pos.x + heading - 1 -- heading = 0 or 2
            else
                pos.y = pos.y + heading - 2 -- heading = 1 or 3
            end
            dist = dist + 1
        else
            return dist
        end
    end
    face(oldHeading)
end

function self.moveVert(n)
    n = n or 1
    local dist = 0
    if n > 0 then
        for i = 1,n do

            if up() then
                pos.z = pos.z + 1
                dist = dist + 1
            else
                return dist
            end
        end
    else
        for i = 1,-n do
            if down() then
                pos.z = pos.z - 1
                dist = dist - 1
            else
                return dist
            end
        end
    end
end

function self.moveTo(vect)
    oldHeading = heading
    for dir = 1,#self.dirPreference do
        if self.dirPreference[dir] == "x" then
            self.faceDir(0)
            self.moveForward(vect.x)
        elseif self.dirPreference[dir] == "y" then
            self.faceDir(1)
            self.moveForward(vect.y)
        elseif self.dirPreference[dir] == "z" then
            self.moveVert(vect.z)
        else
            print("Error! self.dirPreference is corrupted")
            os.exit()
        end
    end
    self.faceDir(oldHeading)
end



return self