--- Helper module for performing a deep copy.
-- @module lqc.helpers.deep_copy
-- @alias deep_copy
local pairs = pairs
local type = type
local setmetatable = setmetatable
local getmetatable = getmetatable

--- Deep copies an object recursively (including (nested) tables, metatables,
--  circular references, ...)
-- Heavily based on http://stackoverflow.com/questions/640642/how-do-you-copy-a-lua-table-by-value
-- @param obj Object to be copied
-- @param seen Table of previously seen objects (for handling circular references), default nil
-- @return deep copy of obj
local function deep_copy(obj, seen)
    -- handle number, string, boolean, ...
    if type(obj) ~= 'table' then
        return obj
    end

    seen = seen or {}
    if seen[obj] then
        return seen[obj]
    end -- handle circular references

    -- handle table
    local result = {}
    seen[obj] = result

    for key, value in pairs(obj) do
        result[deep_copy(key, seen)] = deep_copy(value, seen)
    end

    -- handle metatable
    return setmetatable(result, deep_copy(getmetatable(obj), seen))
end

return deep_copy