--- Computes a "temporary" value into a property
-- Example: You cant to give an actor a boost to life_regen, but you do not want it to be permanent<br/>
-- You cannot simply increase life_regen, so you use this method which will increase it AND
-- store the increase. it will return an "increase id" that can be passed to removeTemporaryValue()
-- to remove the effect.
-- @param prop the property to affect.  This can be either a string or a table of strings, the latter allowing nested properties to be modified.
-- @param v the value to add.  This should either be a number or a table of properties and numbers.
-- @param noupdate if true the actual property is not changed and needs to be changed by the caller
-- @return an id that can be passed to removeTemporaryValue() to delete this value
function _M:addTemporaryValue(prop, v, noupdate)
    if not self.compute_vals then self.compute_vals = {n=0} end

    local t = self.compute_vals
    local id = t.n + 1
    while t[id] ~= nil do id = id + 1 end
    t[id] = v
    t.n = id

    -- Find the base, one removed from the last prop
    local initial_base, initial_prop
    if type(prop) == "table" then
        initial_base = self
        local idx = 1
        while idx < #prop do
            initial_base = initial_base[prop[idx]]
            idx = idx + 1
        end
        initial_prop = prop[idx]
    else
        initial_base = self
        initial_prop = prop
    end

    -- The recursive enclosure
    local recursive
    recursive = function(base, prop, v)
        if type(v) == "number" then
            -- Simple addition
            base[prop] = (base[prop] or 0) + v
            self:onTemporaryValueChange(prop, nil, v)
            print("addTmpVal", base.name or base, prop, v, " :=: ", #t, id)
        elseif type(v) == "table" then
            print("addTmpValTable", base.name or base, base[prop])
            for k, e in pairs(v) do
                base[prop] = base[prop] or {}
                recursive(base[prop], k, e)
            end
        else
            error("unsupported temporary value type: "..type(v).." :=: "..v)
        end
    end

    -- Update the base prop
    if not noupdate then
        recursive(initial_base, initial_prop, v)
    end

    return id
end

--- Removes a temporary value, see addTemporaryValue()
-- @param prop the property to affect
-- @param id the id of the increase to delete
-- @param noupdate if true the actual property is not changed and needs to be changed by the caller
function _M:removeTemporaryValue(prop, id, noupdate)
    local oldval = self.compute_vals[id]
    print("removeTempVal", prop, oldval, " :=: ", id)
    self.compute_vals[id] = nil

    -- Find the base, one removed from the last prop
    local initial_base, initial_prop
    if type(prop) == "table" then
        initial_base = self
        local idx = 1
        while idx < #prop do
            initial_base = initial_base[prop[idx]]
            idx = idx + 1
        end
        initial_prop = prop[idx]
    else
        initial_base = self
        initial_prop = prop
    end

    -- The recursive enclosure
    local recursive
    recursive = function(base, prop, v)
        if type(v) == "number" then
            -- Simple addition
            base[prop] = base[prop] - v
            self:onTemporaryValueChange(prop, nil, v)
            print("removeTmpVal", base.name or base, prop, v)
        elseif type(v) == "table" then
            print("removeTmpValTable", base.name or base, base[prop])
            for k, e in pairs(v) do
                recursive(base[prop], k, e)
            end
        else
            error("unsupported temporary value type: "..type(v).." :=: "..v)
        end
    end

    -- Update the base prop
    if not noupdate then
        recursive(initial_base, initial_prop, oldval)
    end
end