Customize layer assignment problem

[davide-f]

This commit enables to slightly change the layer assignment problem highlighted in #16 ; yet, for simplicity, nodes cannot be moved beyond layers containing their children nodes.
This change enables the creation of this map:

The original plot had nodes 6 at layer 3 and node 8 at layer 4, instead.

[codecov-commenter]

Codecov Report

Merging #16 (f3e03e9) into main (88117f5) will decrease coverage by 0.63%.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##             main      #16      +/-   ##
==========================================
- Coverage   92.72%   92.09%   -0.64%     
==========================================
  Files           4        4              
  Lines         165      177      +12     
==========================================
+ Hits          153      163      +10     
- Misses         12       14       +2     

Impacted Files	Coverage Δ
src/layering.jl	95.91% <87.50%> (-4.09%)	⬇️
src/zarate.jl	90.26% <100.00%> (+0.08%)	⬆️

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[oxinabox]

Sorry again for the delay in reviewing.
This seems really complex.
I think it might be simpler if rather than post-processing the layer_groups
this was implemented via modifying the dists before the layer_groups are constructed.

# basic form that just always does what the user asked for
force_layers!(dists, forced_layers::Dict{Int, Int})
    for (node_id, target_layer) in forced_layers
        dists[node_id] = target_layer
    end
    return dists
end

Which we can fancy up to add the other features.
For example:

force_layers!(graphdists, forced_layers::Dict{Int, Int})
    # must process from end to beginning as otherwise can't move things after to make space
    ordered_forced_layers = sort(collect(forced_layers), by=last; rev=true)
    for (node_id, target_layer) in ordered_forced_layers
        curr_layer = dists[node_id]
        if target_layer < curr_layer
            @warn "Ignored opt_layer_assign for node $node_id; curr layer ($curr_layer) > desired layer ($target_layer)"
        elseif any(dists[child] <= target_layer for child in outneighbors(graph, node_id))
            @warn "Ignored opt_layer_assign for node $node_id; as placing it at $target_layer would place it on same layer, or later than it's children."
        else
            dists[node_id] = target_layer
        end
    end
    return dists
end

[davide-f]

@oxinabox Sorry for my long delay; I added the test case for the additional feature.
Now it should work as suggested including also the testing.
I will merge these changes in the other pull request

[davide-f]

Not sure why codecov fails, however the CI works perfectly
@oxinabox May we fix this "soon" so to close the requests once for all (my bad for the delay...)

[davide-f]

The coverage seems to decrease because there are @Warns that are not tested (clearly...), I think that the code should be fine

[oxinabox]

LGTM
thanks

I will merge after CI finishes

[Warns]

The coverage seems to decrease because there are @Warns that are not tested (clearly...), I think that the code should be fine

I think I was summoned here by mistake ^^