+local function find_next(type, filename, go_back_in_time)
+ local multiplier = 1
+ if go_back_in_time then
+ multiplier = -1
+ end
+
+ local pattern = patterns[type]
+ local year, second_match, day = filename:match(pattern)
+ year = tonumber(year)
+
+ -- Depending on context, second_match is either month, week, or season.
+ if second_match then
+ second_match = tonumber(second_match)
+ end
+
+ if day then
+ day = tonumber(day)
+ end
+
+ local next = nil
+
+ if type == 'daily' and year and second_match and day then
+ next = os.date(templates.daily, os.time({
+ year = year,
+ month = second_match,
+ day = day
+ }) + multiplier * 24 * 60 * 60)
+ elseif type == 'weekly' and year and second_match then
+ -- According to ISO, the first week is the one that contains january 4
+ local first_day_of_the_week = os.time({year = year, month = 1, day = 4})
+ if multiplier < 0 then
+ second_match = second_match - 2
+ end
+ next = os.date(templates.weekly, first_day_of_the_week + second_match * 7 * 24 * 60 * 60)
+ elseif type == 'monthly' and year and second_match then
+ next = os.date(templates.monthly, os.time({
+ year = year,
+ month = second_match + multiplier,
+ day = 1
+ }))
+ elseif type == 'seasonal' and year and second_match then
+ if multiplier > 0 and second_match == 4 then
+ year = year + 1
+ end
+ if multiplier < 0 and second_match == 1 then
+ year = year - 1
+ end
+ if multiplier > 0 then
+ second_match = (second_match % 4) + 1
+ else
+ second_match = (second_match + 2) % 4 + 1
+ end
+ next = year .. '-s' .. second_match
+ elseif type == 'yearly' and year then
+ next = os.date(templates.yearly, os.time({
+ year = year + multiplier,
+ month = 1,
+ day = 1
+ }))
+ end
+
+ if next then
+ Notes['open_' .. type](next)
+ end
+end
+