local math_abs, math_sign
    = math.abs, math.sign
local minetest, vector, include
    = minetest, vector, include

local rotate = include("rotate")

local utility = {}

-- Default selection boxes for a node that doesn't have one them explicitly.
local DEFAULT_SELECTION_BOX = { min = vector.new(-0.5, -0.5, -0.5),
                                max = vector.new( 0.5,  0.5,  0.5) }

-- Gets the active `selection_box` for the specified `node` which
-- has a `paramtype2` of `facedir`, based on its `param2` value.
local function get_node_active_selection_box(node)
    local def = minetest.registered_nodes[node.name]
    local box = def.selection_box and def.selection_box.fixed
    -- No need to rotate the default selection box.
    if not box then return DEFAULT_SELECTION_BOX end
    -- If node definition specifies multiple selection boxes, just pick the first (for now).
    if type(box[1]) == "table" then box = box[1] end
    -- Transform the `{ x1, y1, z1, x2, y2, z2 }` box to a `{ min, max }` one.
    box = { min = vector.new(box[1], box[2], box[3]),
            max = vector.new(box[4], box[5], box[6]) }
    -- Rotate the box to face `facedir`.
    rotate.rotate_box_by_facedir(box, node.param2)
    return box
end

-- Finds the closest edge of the node the player is looking at as
-- a vector pointing away from the center, and the distance to it.
local function find_closest_edge(node, pointed_thing)
    -- For this math to work, we assume that selection box is centered.
    local max = get_node_active_selection_box(node).max
    -- Point relative to the collision box we're pointing at.
    local point = pointed_thing.intersection_point - pointed_thing.under

    -- Find the edge we're closest to.
    local vec = vector.zero()
    if math_abs(point.y / point.x) > max.x / max.y then
        vec.y = math_sign(point.y)
        if math_abs(point.z / point.x) > max.x / max.z
            then vec.z = math_sign(point.z)
            else vec.x = math_sign(point.x)
        end
    else
        vec.x = math_sign(point.x)
        if math_abs(point.z / point.y) > max.y / max.z
            then vec.z = math_sign(point.z)
            else vec.y = math_sign(point.y)
        end
    end

    local d = 1
    local v = max - point:multiply(vec):apply(math_abs)
    local EPSILON = tonumber("1.19e-07")
    if math_abs(v.x) > EPSILON and v.x < d then d = v.x end
    if math_abs(v.y) > EPSILON and v.y < d then d = v.y end
    if math_abs(v.z) > EPSILON and v.z < d then d = v.z end

    return vec, d
end
utility.find_closest_edge = find_closest_edge

return utility