Computercraft position class

function dirToNum(d)
    assert(type(d) == "string", "Expected string, got " .. type(d))
    d = d:lower()

    if d == "north" then
        return 0
    elseif d == "east" then
        return 1
    elseif d == "south" then
        return 2
    elseif d == "west" then
        return 3
    else
        error('"' .. d .. '"' .. " is an unrecognized direction")
    end
end

function numToDir(n)
    assert(type(n) == "number", "Expected number, got " .. type(n))
    n = n % 4

    if n == 0 then
        return "north"
    elseif n == 1 then
        return "east"
    elseif n == 2 then
        return "south"
    elseif n == 3 then
        return "west"
    end
end

function getUpVector()
    return new(0, 1, 0)
end

function getDownVector()
    return new(0, -1, 0)
end

function getNorthVector()
    return new(0, 0, -1, 0)
end

function getSouthVector()
    return new(0, 0, 1, 2)
end

function getWestVector()
    return new(-1, 0, 0, 3)
end

function getEastVector()
    return new(1, 0, 0, 1)
end

local pos = {}
pos.__index = pos

function new(x, y, z, dir)
    if type(dir) == "string" then
        dir = dirToNum(dir)
    end
    local t = {
        ["x"] = x or 0,
        ["y"] = y or 0,
        ["z"] = z or 0,
        ["dir"] = dir or 0
    }
    t.dir = t.dir % 4

    setmetatable(t, pos)
    return t
end

function fromGPS(loadDir)
    if not loadDir then loadDir = false end
    local coords = {gps.locate()}

    assert(coords ~= nil, "Cannot load pos from GPS. There is no modem. ")

    local t = new(coords[1], coords[2], coords[3])
    if loadDir then
        if not turtle.forward() then
            repeat until not turtle.dig()
            if not turtle.forward() then error("must be able to go forward to load dir!") end
        end

        local newCoords = {gps.locate()}
        local newT = new(newCoords[1], newCoords[2], newCoords[3])
        local changeInCoords = newT - t;

        turtle.back()

        if changeInCoords == new(0, 0, -1) then
            t:set(nil, nil, nil, "north")
        elseif changeInCoords == new(1, 0, 0) then
            t:set(nil, nil, nil, "east")
        elseif changeInCoords == new(0, 0, 1) then
            t:set(nil, nil, nil, "south")
        elseif changeInCoords == new(-1, 0, 0) then
            t:set(nil, nil, nil, "west")
        end
    end
    return t
end

function isPos(t)
    return getmetatable(t) == pos
end

function pos:set(x, y, z, dir)
    if isPos(x) then
        self.x = x.x
        self.y = x.y
        self.z = x.z
        self.dir = x.dir
    else
        self.x = x or self.x
        self.y = y or self.y
        self.z = z or self.z
        if type(dir) == "number" then
            self.dir = dir % 4
        elseif type(dir) == "string" then
            self.dir = dirToNum(dir)
        end
    end
end

function pos:clone()
    return new(self.x, self.y, self.z, self.dir)
end

function pos:replace(newPos, keepDir)
    assert(isPos(newPos), "Cannot replace pos with non-pos")
    if not keepDir then keepDir = false end

    self.x = newPos.x
    self.y = newPos.y
    self.z = newPos.z

    if not keepDir then self.dir = newPos.dir end

    return self
end

function pos:change()

end

function pos:getForwardVector()
    if self.dir == 0 then
        return new(0, 0, -1, 0)
    elseif self.dir == 1 then
        return new(1, 0, 0, 1)
    elseif self.dir == 2 then
        return new(0, 0, 1, 2)
    elseif self.dir == 3 then
        return new(-1, 0, 0, 3)
    end
end

function pos:getBackwardVector()
    return self:getForwardVector() * -1
end

function pos:getLeftVector()
    if self.dir == 0 then
        return new(-1, 0, 0, 3)
    elseif self.dir == 1 then
        return new(0, 0, -1, 0)
    elseif self.dir == 2 then
        return new(1, 0, 0, 1)
    elseif self.dir == 3 then
        return new(0, 0, 1, 2)
    end
end

function pos:getRightVector()
    return self:getLeftVector() * -1
end

function pos.__add(a,b)
    assert(isPos(a) and isPos(b), "Can't add pos to non-pos")
    return new(a.x + b.x, a.y + b.y, a.z + b.z, a.dir)
end

function pos.__sub(a,b)
    assert(isPos(a) and isPos(b), "Can't sub pos from non-pos")
    return new(a.x - b.x, a.y - b.y, a.z - b.z, a.dir)
end

function pos.__mul(a,b)
    if isPos(a) and type(b) == "number" then
        return new(a.x * b, a.y * b, a.z * b)
    elseif isPos(b) and type(a) == "number" then
        return new(b.x * a, b.y * a, b.z * a)
    else
        error("expected pos and number")
    end
end

function pos.__div(a,b)
    assert(isPos(a) and type(b) == "number", "Cannot divide pos by non-number")

    return new(a.x / b, a.y / b, a.z / b)
end

function pos.__eq(a,b)
    assert(isPos(a) and isPos(b), "Can't compare pos with non-pos")
    return a.x == b.x and a.y == b.y and a.z == b.z
end