filter: add new time_delta filter

[Akasurde]

SUMMARY

• Calculate datetime string based upon time delta
  provided by user

Signed-off-by: Abhijeet Kasurde [email protected]

ISSUE TYPE

• Feature Pull Request

[ansibullbot]

cc @resmo
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[resmo]

nice

[russoz]

Whilst I appreciate the idea very much, the name time_delta made me think two dates would be given and the difference/delta between them would be calculated. Maybe something like time_add_delta ? Update: or even time_add?

Additionally, I think forcing this to use string representation is limiting. We can have datetime objects and time delta objects, as shown in:
https://docs.ansible.com/ansible/latest/playbook_guide/playbooks_filters.html#handling-dates-and-times)

Therefore, I reckon it would be interesting to:

• allow datetime objects to be passed (through the pipe operator), forsaking the need to specify a format
• allow time delta objects to be passed as parameters instead of forcing users to specify days, weeks or whatever.

I mean those in addition to the current code, which is clearly quite useful.

WDYT?

[felixfontein]

Thanks for your contribution! I agree with @russoz that the name should be adjusted; I was thinking as well that this filter allows to compute the difference between two timestamps, and not to modify a timestamp.

[felixfontein]

I think this should be validated to be a string.

[felixfontein]

It would be good to validate the above to be integers if supplied as options. Also you should check whether kwargs has more arguments than the ones we use (and fail if there are more).

[felixfontein]

Shouldn't date_format be used to format the timestamp?

[VannTen]

A few thought on this:
Ansible has the to_datetime builtin filter which can produces datetime object, which you can use to obtain a timedelta object:

---
- gather_facts: no
  hosts: localhost
  connection: local
  vars:
    date1: '00:00'
    date2: '01:00'
    fmt: '%H:%M'
    timedelta: "{{ (date2 | to_datetime(fmt)) - (date1 | to_datetime(fmt)) }}" # this is coerced to string, you can't "store" your timedelta
  tasks:
    - debug:
        var: now() + ((date2 | to_datetime(fmt)) - (date1 | to_datetime(fmt)))

IMO, instead of a filter applying a computed timedelta on a datetime, it would be better to have a way to directly construct a timedelta. This allows more things, like comparing timedeltas, doing arithemic on it etc

(example usecase: checking if remaining validity time of a certificate is greater than 20% of it's total duration, that sort of thing)

I don't think there is a way to add jinja functions as extension (is there ?), but maybe a filter passing a dict to the timedelta constructor would do it.
That would change the example above to :

---
- gather_facts: no
  hosts: localhost
  connection: local
  tasks:
    - debug:
        var: "now() + ({'hours': 1} | community.general.timedelta)" # NOT IMPLEMENTED