This is just a small "pet project" I did to learn a little bit about the go programming language.
The program, when called, reads data on the current/last known figures about the "Pegel Köln", measuring water level and temperature of the river Rhine in Cologne. It then does - depending on a few rules - do a little post on Mastodon.
The level and temperature data is received from a public service of PEGELONLINE, leveraging their REST API.
The actual executable is called "kpg" (KoelnPegelGo) and requires next to it a file with environment information, mainly to be able to post on Mastodon:
SERVER=https://social.cologne # the Mastodon server to post to
CLIENT_ID=<snip> # client id on that server
CLIENT_SECRET=<snip> # client secret needed to post
ACCESS_TOKEN=<snip> # access token to post
When called, the client reads historic data, decides whether to post on Mastodon or not and then updates two files: .kpg_history (storing the results of the last successful call to the REST API) and .kpg_last (storing the date and time of the last successful post to Mastodon).
If a post is made to Mastodon is decided based on quite a number of criteria - and of course these are evaluated only, if the call to the API was successful at all. These criteria do also depend on a number of predefined "thresholds" officially defined by the City of Cologne.
GLW: "GLW" (gleichwertiger Wasserstand) (139cm)MARK_01: "Hochwassermarke 1" (620cm)MARK_02: "Hochwassermarke 2" (830cm)KATA_01: "Rheinufertunnel läuft voll (1000cm)KATA_02: "Altstadt überflutet" (1130cm)
The algorithm then decides as follows:
- Check, whether current (water) level is above
KATA_02, if yes: post, no matter what time it is - Else: check, whether current (water) level is above
KATA_01, if yes: post, if it is a full half-hour and the last post has been done at least 30 minutes before - Else: check, whether current (water) level is above
MARK_02, if yes: post, if it is a full hour and the last post has been done at least 60 minutes before - Else: check, whether current (water) level is above
MARK_01, if yes: post, if it is an even hour and the last post has been done at least 120 minutes before - Else: post, if current time is a full "4-hour" and the last post has been done at least 240 minutes before
I.e., in normal conditions (no specific thresholds are reached), the program does post only all 4 hours (midnight, 4am, 8am, 12pm, 4pm, 8pm).
The actual text that is posted depends on the difference to the last known measurement (with 5cm and 10cm differences - these thresholds are a bit arbitray and derived from BAFG).
Code is split across a couple of files:
| File | Content |
|---|---|
kpg.go |
Main program |
core.go |
Routines to fetch data, do all checks and calculations and prepare text to post |
environment.go |
Routines to read configuration file kpg.env |
history.go |
Routines to read/write and use historic data (see file .kpg_history) |
mastopost.go |
Routine to post to Mastodon |
wsv/wsv.go |
Routines to call PEGELONLINE API |
elwis/elwis.go |
Draft routines to retrieve prognosis data - not tests and not in use yet |
*_test.go |
Some small unit tests |
During development, you might set the environment variable KPG_TEST to some value to avoid posting to Mastodon but print the post to stdout instead.
Please note: I am not a professional developer, I am new to the go language and this is just a pet project. There is little documentation in the code, there is no error handling (except writing to stdout) and many things can be made better, I guess. But it was fun, and I got a couple of followers on Mastodon. 😉
Originally, the program fetched and then posted water level as well as water temperature. However, in August 2024, the API started not to deliver the temperature any more. So the posting style changed. We log the temperature, however, to understand if it returns some day.
MIT License, Copyright (c) 2023 Jonas Rathert - see file LICENSE.txt