;;; my-uptime.el --- calculates uptime for SLOs

;;; Commentary:

;; Calculate how much downtime is allowed for different period of time
;; based on a given SLO.

;;; Code:

(defconst my-uptime/buffer-name "*slo-calculator*")

(defconst my-uptime/seconds-per-hour 3600
  "Number of seconds in an hour.")
(defconst my-uptime/seconds-per-day (* my-uptime/seconds-per-hour 24)
  "Number of seconds in a day.")
(defconst my-uptime/seconds-per-week (* my-uptime/seconds-per-day 7)
  "Number of seconds in a week.")
(defconst my-uptime/seconds-per-month (* my-uptime/seconds-per-day 30)
  "Number of seconds in a month.")
(defconst my-uptime/seconds-per-quarter (* my-uptime/seconds-per-month 3)
  "Number of seconds in a quarter.")
(defconst my-uptime/seconds-per-year (* my-uptime/seconds-per-month 12)
  "Number of seconds in a year.")

(defun my/uptime-is (slo)
  "Return the amount of allowed downtime for a given SLO."
  (interactive "nSLO:")
  (let* ((slo (cond ((< slo 0) 0)
                    ((> slo 100) 100)
                    (t slo)))
         (allowed (/ (- (* 100 100) (* slo 100.0)) (* 100 100))))
    (my/uptime--message allowed slo)))

(defun my/uptime--message (seconds slo)
  "Insert buffer text with allowed downtime based on SECONDS (derived from SLO)."
  (let ((inhibit-read-only t)
	(buffer-undo-list t))
    (pop-to-buffer my-uptime/buffer-name)
    (erase-buffer)
    (insert (format "calculated allowed downtime for %s%% availability.\n" slo))
    (insert
     (format "daily:     %s\n" (format-seconds "%H %M %S" (seconds-to-time (* my-uptime/seconds-per-day seconds)))))
    (insert
     (format "weekly:    %s\n" (format-seconds "%H %M %S" (seconds-to-time (* my-uptime/seconds-per-week seconds)))))
    (insert
     (format "monthly:   %s\n" (format-seconds "%D %H %M %S" (seconds-to-time (* my-uptime/seconds-per-month seconds)))))
    (insert
     (format "quarterly: %s\n" (format-seconds "%D %H %M %S" (seconds-to-time (* my-uptime/seconds-per-quarter seconds)))))
    (insert
     (format "yearly:    %s\n" (format-seconds "%D %H %M %S" (seconds-to-time (* my-uptime/seconds-per-year seconds))))))
  (special-mode))

(provide 'my-uptime)

;;; my-uptime.el ends here