local ipairs, unpack
    = ipairs, unpack
local math_min, math_max, math_floor, math_rad
    = math.min, math.max, math.floor, math.rad
local minetest, vector
    = minetest, vector

local rotate = {}

local rotatable_registry = {}

-- Axis lookup table based on how Minetest's `facedir` operates.
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
}

-- Lookup table to find out how to rotate for each `facedir` axis.
local AXIS_ROTATION = {
    nil, -- No rotation.
    { vector.new(1, 0, 0),  90 },
    { vector.new(1, 0, 0), -90 },
    { vector.new(0, 0, 1), -90 },
    { vector.new(0, 0, 1),  90 },
    { vector.new(0, 0, 1), 180 },
}

-- Takes an axis vector and returns its index in the `AXIS_LOOKUP` table.
-- Returns `nil` for any vector that is not a valid axis vector.
local function axis_vector_to_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
    else return nil end
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 = axis_vector_to_index(back)
        FACEDIR_LOOKUP[up_index][back_index] = facedir
    end
end

local function register_rotatable(name, facedir_lookup)
    local def = minetest.registered_nodes[name]
    if not def then error("Unknown node '" .. name .. "'") end
    if def.paramtype2 ~= "facedir" then error("Node '" .. name .. "' must be 'facedir'") end
    rotatable_registry[name] = { lookup = facedir_lookup }
end
rotate.register_rotatable = register_rotatable

-- Returns whether the specified `node` is rotatable by this mod.
local function is_rotatable(node)
    local name = node and node.name or ""
    return not not rotatable_registry[name]
end
rotate.is_rotatable = is_rotatable

-- Fixes facedir for the specified `node` when rotated to `facedir`.
-- * Returns `nil` if the node can't rotate this way.
-- * Returns `facedir` when the node can rotate this way.
-- * Returns another facedir when the node should rotate another equivalent way.
local function fix_rotatable_facedir(node, facedir)
    local name  = node and node.name or ""
    local entry = rotatable_registry[name]
    if not entry then return nil end
    if not entry.lookup then return facedir end
    return entry.lookup[facedir]
end
rotate.fix_rotatable_facedir = fix_rotatable_facedir

-- Returns the specified `facedir` rotated around `axis` by `degrees` counter-clickwise.
local function rotate_facedir(facedir, axis, degrees)
    if degrees % 90 ~= 0 then error("degrees must be divisible by 90") end
    if axis_vector_to_index(axis) == nil then error("axis " .. tostring(axis) .. " is not an axis vector") end

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

    up   = up  :rotate_around_axis(axis, math_rad(degrees)):round()
    back = back:rotate_around_axis(axis, math_rad(degrees)):round()

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

    return FACEDIR_LOOKUP[up_index][back_index]
end
rotate.rotate_facedir = rotate_facedir

-- Rotates the specified default orientation `{ min, max }` box to
-- one matching Minetest's rotation algorithm pointing to `facedir`.
local function rotate_box_by_facedir(box, facedir)
    if facedir == 0 then return end

    local axis_index = math_floor(facedir / 4)
    if axis_index ~= 0 then
        local axis, degrees = unpack(AXIS_ROTATION[1 + axis_index])
        box.min = box.min:rotate_around_axis(axis, math_rad(degrees))
        box.max = box.max:rotate_around_axis(axis, math_rad(degrees))
    end

    local axis_rot = facedir % 4
    if axis_rot ~= 0 then
        local axis = AXIS_LOOKUP[1 + axis_index]
        local degrees = axis_rot * 90
        box.min = box.min:rotate_around_axis(axis, math_rad(degrees))
        box.max = box.max:rotate_around_axis(axis, math_rad(degrees))
    end

    -- Recalculate the proper minimum and maximum bounds, since we just rotated these vectors.
    box.min.x, box.max.x = math_min(box.min.x, box.max.x), math_max(box.min.x, box.max.x)
    box.min.y, box.max.y = math_min(box.min.y, box.max.y), math_max(box.min.y, box.max.y)
    box.min.z, box.max.z = math_min(box.min.z, box.max.z), math_max(box.min.z, box.max.z)
end
rotate.rotate_box_by_facedir = rotate_box_by_facedir

return rotate