Change over-time graphs from line to stacked bar representation

[DL6ER]

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• I have made only one major change in my proposed changes.
• I have commented my proposed changes within the code.
• I have tested my proposed changes, and have included unit tests where possible.
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• I have squashed any insignificant commits. (git rebase)

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What does this PR aim to accomplish?:

Change over-time graphs from line to stacked bar representation. This is much more natural for this kind of data (it is discrete, not continuous!).

   Before

   Now

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Also, improve DB graphs to always generate a meaningful display (always generate about 200 bars). This graph was basically unusable when specifying a larger range than, say, one week.

   Before (this week)

   Now (this week)

   Before (this month)

   Now (this month)

The slight difference seen in the strongest peeks is due to the monotone interpolation of the lines graphs (and wrong!).

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How does this PR accomplish the above?:

Change over-time graphs from line to stacked bar representation. Compute interval based on specified time window.

What documentation changes (if any) are needed to support this PR?:

[DL6ER]

With bar graphs, we do not need to fill gaps (there will simply be gaps for empty days). This change enhances processing speed notably.

[DL6ER]

This variable controls how many lines will be computed. I don't think we need to make it user-defined, however, I put it in a common place so users can still modify it when they deem it appropriate. We could also make it a global variable, users could then modify this value (live) through the developer tools.

[XhmikosR]

I definitely like this change, but I really think we need #1080 and #1079 sorted before any further JS changes

[DL6ER]

The changes in here are of purely functional. We can get them in and cherry-pick them into the PRs that format the code. This seems a logical order because this new code would be formatted in them as well. I don't know if we merge #1079 and #1080 is still a [WIP].

[XhmikosR]

They might be functional but they don't follow the best practices, hence why I suggested the above...

scripts\pi-hole\js\db_graph.js:199:1
  ×  199:1   Avoid using extended native objects                                       no-use-extend-native/no-use-extend-native
  ×  199:1   Date prototype is read only, properties should not be added.              no-extend-native

  scripts\pi-hole\js\index.js:10:20
  ×   10:20  forwardDestinationChart is defined but never used.                        no-unused-vars

(the lines don't match this patch due to the style changes, but it is the date prototype addition and one unused var)

Anyway, as long as the above are sorted, this is fine by me. Generally extending the native objects is bad practice. Many things work but it doesn't mean they are OK to do :)

[DL6ER]

@XhmikosR I have never learned any language by attending a course so I may not know what best practices are or may have learned them from the wrong people (you never know). Which checker did you use to get the reply you're seeing? I'd like to see the same being mentioned by the CI to teach me how to get better. But this might be what you are looking into with #1080

I addressed the mentioned points meanwhile.

[XhmikosR]

@DL6ER yeah that's with #1080 which only misses the CI part and someone to check out my comments

[DL6ER]

Once this is merged, we should update the screenshots shown at https://github.com/pi-hole/AdminLTE/blob/master/README.md

(see also here: https://github.com/pi-hole/graphics/tree/master/Screenshots)

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/query-activity-graphs-changed-to-individual-bars/31297/2