--This code is an exact, unmodified copy of that from the official Lua docs: https://lua-users.org/wiki/SortedIteration

local sortingFunction = nil

function __genOrderedIndex( t )
    local orderedIndex = {}
    for key in pairs(t) do
        table.insert( orderedIndex, key )
    end

    table.sort( orderedIndex, sortingFunction )
    return orderedIndex
end

function orderedNext(t, state)
    -- Equivalent of the next function, but returns the keys in the alphabetic
    -- order. We use a temporary ordered key table that is stored in the
    -- table being iterated.

    --print("orderedNext: state = "..tostring(state) )
    if state == nil then
        -- the first time, generate the index
        t.__orderedIndex = __genOrderedIndex( t )
        key = t.__orderedIndex[1]
        return key, t[key]
    end
    -- fetch the next value
    key = nil
    for i = 1,table.getn(t.__orderedIndex) do
        if t.__orderedIndex[i] == state then
            key = t.__orderedIndex[i+1]
        end
    end

    if key then
        return key, t[key]
    end

    -- no more value to return, cleanup
    t.__orderedIndex = nil
    return
end

function orderedPairs(t, sortingFunction2)
    sortingFunction = sortingFunction2
    -- Equivalent of the pairs() function on tables. Allows to iterate
    -- in order
    return orderedNext, t, nil
end