---
-- Gets the relative direction of a source hex to a target hex.
-- Useful to determine in which direction a unit should be facing
-- (from the source) to look at another unit (at the target).
--
-- NOTE: This initial implementation only handles southwest and
-- southeast. The C++ code handling these calculations isn't exposed
-- to Lua yet, but direction.lua provides an attempt at translating
-- it.
--
-- [store_direction]
--     from_x,from_y= ...
--     to_x,to_y= ...
--     variable="direction"
-- [/store_direction]
--
-- Or:
--
-- [store_direction]
--     [from]
--         ... SLF ...
--     [/from]
--     [to]
--         ... SLF ...
--     [/to]
--     variable="direction"
-- [/store_direction]
---
function wesnoth.wml_actions.store_direction(cfg)
    local from_slf = helper.get_child(cfg, "from")
    local to_slf = helper.get_child(cfg, "to")

    local a = { x = cfg.from_x, y = cfg.from_y }
    local b = { x = cfg.to_x  , y = cfg.to_y   }

    if from_slf then
        a.x = wesnoth.get_locations(from_slf)[1][1]
        a.y = wesnoth.get_locations(from_slf)[1][2]
    end
    if to_slf then
        b.x = wesnoth.get_locations(to_slf)[1][1]
        b.y = wesnoth.get_locations(to_slf)[1][2]
    end

    if not a.x or not a.y or not b.x or not b.y then
        helper.wml_error "[store_direction] missing coordinate!"
    end

    local variable = cfg.variable or "direction"

    -- local facing = loc_relative_direction(b, a) or "sw"
    -- wesnoth.set_variable(variable, facing)

    if a.x < b.x then
        wesnoth.set_variable(variable, "se")
    else
        wesnoth.set_variable(variable, "sw")
    end
end