feat: Add backend for route segments for unfinished detours

[joshlarson]

Asana Ticket: https://app.asana.com/0/1205385723132845/1207449517841757/f

[github-actions]

Coverage of commit b32389e

Summary coverage rate:
  lines......: 93.6% (3257 of 3480 lines)
  functions..: 73.4% (1343 of 1830 functions)
  branches...: no data found

Files changed coverage rate:
                                                                  |Lines       |Functions  |Branches    
  Filename                                                        |Rate     Num|Rate    Num|Rate     Num
  ======================================================================================================
  lib/skate/detours/route_segments.ex                             | 100%      9| 100%     4|    -      0
  lib/skate_web/controllers/detours_controller.ex                 | 100%     32|92.3%    13|    -      0
  lib/skate_web/router.ex                                         |88.9%     63|16.2%   136|    -      0

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[hannahpurcell]

Great! I'm delighted, this was a perfect bite-size of detour logic that helped things come into focus a bit better. ✅ Readable ✅ Logical

[firestack]

question(non-blocking): why specify only here if it includes all keys?

[joshlarson]

I copied it from the other route segments result, but it looks like that also maybe doesn't need only?

I'm kind of new to the world of Jason, so would it be better to just omit the only: section entirely, and have it say 👇?

    @enforce_keys [:before_start_point, :after_start_point]
    @derive {Jason.Encoder}

[firestack]

Given I wrote the first one with @enforce_keys, I'm not really sure why I did that in retrospect, I think just because I'd never used @derive before I was curious and it "seemed" right. I don't think I agree with my decision anymore, but it's not a big deal that it's like this.

(also, dang, I really wanted replying via email to work)

[firestack]

question(non-blocking): I find the overhead of understanding this slightly annoying, could we use Enum.split instead?

Something like this?

Suggested change

	{:ok,
	%__MODULE__.UnfinishedResult{
	before_start_point: Enum.slice(shape, 0..index) ++ [nearest_point],
	after_start_point: [nearest_point] ++ Enum.slice(shape, (index + 1)..-1)
	}}
	[shape_before_start_point, shape_after_start_point] = Enum.split(shape, index)
	{:ok,
	%__MODULE__.UnfinishedResult{
	before_start_point: shape_before_start_point ++ [nearest_point],
	after_start_point: [nearest_point] ++ shape_after_start_point
	}}

[joshlarson]

Oh huh - I assumed that Enum.split/2 would work more similarly to String.split/3, so it didn't even occur to me to do it this way.

But unless I'm missing something, your way is a lot cleaner, both for this and for the other route segments function - will do a follow-up

[firestack]

https://hexdocs.pm/elixir/1.17.0-rc.1/enum-cheat.html has been very helpful for me fwiw.