local math, ipairs, tostring
    = math, ipairs, tostring

local minetest, vector, include
    = minetest, vector, include

local function debug_tell(...)
    local text = ""
    for _, v in ipairs({...}) do text = text .. tostring(v) end
    minetest.chat_send_all(text)
end

local AXIS_LOOKUP = {
    vector.new( 0,  1,  0), -- +Y
    vector.new( 0,  0,  1), -- +Z
    vector.new( 0,  0, -1), -- -Z
    vector.new( 1,  0,  0), -- +X
    vector.new(-1,  0,  0), -- -X
    vector.new( 0, -1,  0), -- -Y
}

local function unit_vector_to_axis_index(vec)
    if     vec.y ==  1 then if vec.x == 0 and vec.z == 0 then return 1 end
    elseif vec.z ==  1 then if vec.x == 0 and vec.y == 0 then return 2 end
    elseif vec.z == -1 then if vec.x == 0 and vec.y == 0 then return 3 end
    elseif vec.x ==  1 then if vec.y == 0 and vec.z == 0 then return 4 end
    elseif vec.x == -1 then if vec.y == 0 and vec.z == 0 then return 5 end
    elseif vec.y == -1 then if vec.x == 0 and vec.z == 0 then return 6 end
    end
    error("Not a unit vector")
end

local FACEDIR_LOOKUP = {}
for up_index, up in ipairs(AXIS_LOOKUP) do
    FACEDIR_LOOKUP[up_index] = {}
    for rot = 0, 3 do
        local facedir = (up_index - 1) * 4 + rot
        local back = minetest.facedir_to_dir(facedir)
        local back_index = unit_vector_to_axis_index(back)
        FACEDIR_LOOKUP[up_index][back_index] = facedir
    end
end

minetest.register_on_punchnode(function(pos, node, puncher, pointed_thing)
    local def = minetest.registered_nodes[node.name]
    if def.paramtype2 == "facedir" and pointed_thing.above and pointed_thing.under then
        local facedir = node.param2
        -- Vector that points away from the punched face.
        local punched_face = vector.subtract(pointed_thing.above, pointed_thing.under)

        local up   = AXIS_LOOKUP[1 + math.floor(facedir / 4)]
        local back = minetest.facedir_to_dir(facedir)

        up   = up:rotate_around_axis(punched_face, math.rad(-90)):round()
        back = back:rotate_around_axis(punched_face, math.rad(-90)):round()

        local up_index   = unit_vector_to_axis_index(up)
        local back_index = unit_vector_to_axis_index(back)

        facedir = FACEDIR_LOOKUP[up_index][back_index]
        if facedir == nil then minetest.chat_send_all("Could not look up facedir") end
        node.param2 = facedir
        minetest.set_node(pos, node)
    end
end)