function yl_announcements.list()
    if next(yl_announcements.data) ~= nil then
        return true, yl_announcements.data
    end
    return false, {}
end

function yl_announcements.get(announcement_id)

    -- Check announcement_id
    if (type(announcement_id) ~= "number") then
        return false, "Announcement ID is not a number"
    end
    if (announcement_id <= 0) then
        return false, "Announcement ID cannot be zero or negative"
    end

    local success, data = yl_announcements.list()
    if ((success == true) and (data[announcement_id] ~= nil)) then
        return true, table.copy(data[announcement_id])
    end
    return nil
end

function yl_announcements.set(message, frequency, runtime, owner)

    -- Check message
    if (type(message) ~= "string") then return false, "message not a string" end

    -- Check frequency
    if (type(frequency) ~= "number") then
        return false, "frequency not a number"
    end
    if (frequency <= 0) then
        return false, "Frequency cannot be zero or negative"
    end

    -- Check runtime
    if (type(runtime) ~= "number") then return false, "Runtime not a number" end
    if (runtime <= 0) then return false, "Runtime cannot be zero or negative" end

    -- Check owner
    if (type(owner) ~= "string") then return false, "Owner not a string" end
    if (owner == "") then return false, "Owner cannot be empty" end

    local index = 1
    while yl_announcements.data[index] ~= nil do index = index + 1 end

    local content = {
        id = index,
        creation_date = os.time(),
        message = message,
        frequency = frequency,
        runtime = runtime,
        owner = owner
    }

    yl_announcements.data[index] = content

    local success = yl_announcements.save_json(tostring(index) .. ".json",
                                               content)

    if (success == true) then return true, index end
    return false, "Could not store announcement"
end

-- /announcement_add message$frequency in seconds$runtime in seconds
function yl_announcements.formspec(announcement_id)

    -- Check announcement_id
    if (type(announcement_id) ~= "number") then
        return false, "Announcement ID is not a number"
    end
    if (announcement_id <= 0) then
        return false, "Announcement ID cannot be zero or negative"
    end

    local success, announcement = yl_announcements.get(announcement_id)
    core.log("action", "announcement = " .. dump(announcement))
    if ((success == false) or (announcement == nil)) then
        return false, "No announcement"
    end

    local m = announcement.message or "message"
    local f = announcement.frequency or "frequency"
    local r = announcement.runtime or "runtime"

    local c = "/announcement_add " .. m .. "$" .. f .. "$" .. r
    local content = minetest.formspec_escape(c .. "\n\n" .. dump(announcement))
    local formspec = "formspec_version[6]" .. "size[16,4]" ..
                         "button_exit[15.4,0.1;0.5,0.5;X;X]" ..
                         "textarea[0.05,0.05;15.3,3.9;;;" .. content .. "]"
    return true, formspec
end

function yl_announcements.delete(announcement_id)

    -- Check announcement_id
    if (type(announcement_id) ~= "number") then
        return false, "Announcement ID is not a number"
    end
    if (announcement_id <= 0) then
        return false, "Announcement ID cannot be zero or negative"
    end

    local success, data = yl_announcements.list()

    if ((success == false) or (data == nil)) then
        return false, "Could not retrieve list"
    end
    if ((success == true) and (data[announcement_id] == nil)) then
        return false, "Could not retrieve announcement"
    end

    local announcement = table.copy(data[announcement_id]) or
                             "No data available"

    if (announcement ~= nil) then
        data[announcement_id] = nil
        local success_f, err = yl_announcements.remove_file(announcement_id ..
                                                                ".json")
        if (success_f == nil) then return false, err end
        success = true
    end

    if (success ~= true) then
        announcement = "Could not find announcement with id " ..
                           dump(announcement_id)
    end
    return success, announcement
end

function yl_announcements.say(announcement_id, target)

    -- Check announcement_id
    if (type(announcement_id) ~= "number") then
        return false, "Announcement ID is not a number"
    end
    if (announcement_id <= 0) then
        return false, "Announcement ID cannot be zero or negative"
    end

    -- No check for target, it is optional

    local success = false

    local announcement = yl_announcements.data[announcement_id]

    if (announcement ~= nil) then
        local color = yl_announcements.settings.colour
        local message = announcement.message
        local content = minetest.colorize(color, message)

        if ((target == "*") or (target == nil)) then
            minetest.chat_send_all(content)
        else
            minetest.chat_send_player(target, content)
        end
        success = true
    end

    if (success ~= true) then
        announcement = "Could not find announcement with id " ..
                           dump(announcement_id)
    end
    return success, announcement
end