--- Functions dealing with metatables and tables merging.
--
-- @module gear.meta
-- @copyright 2022 The DoubleFourteen Code Forge
-- @author Lorenzo Cogotti

local meta = {}


--- Test whether 'obj' is an instance of a given class 'cls'.
function meta.isinstance(obj, cls)
    repeat
        local m = getmetatable(obj)
        if m == cls then return true end

        obj = m
    until obj == nil

    return false
end

--- Merge table 'from' into table 'to'.
--
-- For every field in 'from', copy it to destination
-- table 'to', whenever the same field is nil in that table.
--
-- The same process is applied recursively to sub-tables.
function meta.mergetable(to, from)
    for k,v in pairs(from) do
        if to[k] == nil then
            to[k] = type(v) == 'table' and meta.mergetable({}, v) or v
        end
    end

    return to
end

--- Table deep copy.
--
-- Copy table 'obj', cloning any sub-table.
-- Handles cyclic references.
--
-- @tparam table obj object to be copied
-- @tparam[opt={}] table copied known copied sub-object table
-- @treturn table newly created clone of 'obj'
function meta.deepcopy(obj, copied)
    copied = copied or {}

    local r = {}

    copied[obj] = r

    for k,v in pairs(obj) do
        if type(v) == 'table' then
            local t = copied[v] or meta.deepcopy(v, copied)

            copied[v] = t  -- NOP if object was already copied
            v = t
        end

        r[k] = v
    end

    return r
end

return meta