local nodecore, vector, math_round
    = nodecore, vector, math.round

local TAU = math.pi * 2 -- The real circle constant.
local QUARTER_CIRCLE = TAU / 4

local LABEL_ROTATION_HINT = "rotation hint"
local LABEL_AXIS_HINT     = "axis hint"

local TEX_ROTATE_FACE   = "nc_extended_rotating_hud_rotate_face.png"
local TEX_ROTATE_EDGE   = "nc_extended_rotating_hud_rotate_edge.png"
local TEX_ROTATION_AXIS = "nc_extended_rotating_hud_rotation_axis.png"


local hud = {}

function hud.update_player_hud(player, state)
    local rotation_texture = nil
    local axis_texture     = nil

    local mode = state and state.mode
    if mode == "face" then
        local tex = TEX_ROTATE_FACE
        if state.invert then tex = tex .. "^[transformFX" end
        rotation_texture = tex

    elseif mode == "edge" then
        local tex = TEX_ROTATE_EDGE
        if state.invert then tex = tex .. "^[transformFX" end

        local face = state.face -- Face looked at.
        local edge = state.edge -- Face, edge or corner looked at.
        local axis = state.axis -- Actual axis of rotation.
        local look = player:get_look_dir() -- Player look vector.

        -- Transform a vertical face to an equivalent horizontal one,
        -- to make the following comparisons work in either case.
        if state.face.y ~= 0 then
            local player_yaw     = math_round(player:get_look_horizontal() / QUARTER_CIRCLE) * QUARTER_CIRCLE
            local playing_facing = vector.new(0, 0, 1):rotate_around_axis(vector.new(0, 1, 0), player_yaw)
            local rotation_axis  = face:cross(playing_facing)

            face = face:rotate_around_axis(rotation_axis, QUARTER_CIRCLE)
            edge = edge:rotate_around_axis(rotation_axis, QUARTER_CIRCLE)
            axis = axis:rotate_around_axis(rotation_axis, QUARTER_CIRCLE)
            look = look:rotate_around_axis(rotation_axis, QUARTER_CIRCLE)
        end

        if edge.y == 0 then -- Looking at left or right edge.
            if axis.y > 0
                then tex = tex .. "^[transformFX"    -- left
                else                                 -- right
            end
            -- Flip side the arrow is on depending on look vector.
            if look.y < 0 then tex = tex .. "^[transformFY" end
            -- Vertical axis rotation texture.
            axis_texture = TEX_ROTATION_AXIS

        else                -- Looking at top or bottom edge.
            if edge.y > 0
                then tex = tex .. "^[transformR90"   -- top
                else tex = tex .. "^[transformFXR90" -- bottom
            end
            -- Flip side the arrow is on depending on look vector.
            if face:cross(look).y < 0 then tex = tex .. "^[transformFX" end
            -- Horizontal axis rotation texture.
            axis_texture = TEX_ROTATION_AXIS .. "^[transformR270"
        end

        rotation_texture = tex

    elseif mode == "corner" then
        -- TODO: Handle corners.
    end

    local function crosshair_hud_element(label, texture)
        if texture then return {
            label = label,
            hud_elem_type = "image",
            text = texture .. "^[opacity:" .. 192,
            position  = { x = 0.5, y = 0.5 },
            offset    = { x = 0, y = 0 },
            alignment = { x = 0, y = 0 },
            scale     = { x = 1, y = 1 },
            quick = true,
        } else return {
            label = label,
            ttl   = 0,
        } end
    end

    -- Actually update the HUD elements.
    nodecore.hud_set(player, crosshair_hud_element(LABEL_ROTATION_HINT, rotation_texture))
    nodecore.hud_set(player, crosshair_hud_element(LABEL_AXIS_HINT, axis_texture))
end

return hud