TL;DR : I updated the module README.md https://github.com/folio-org/mod-licenses with info on how mod-licenses supports the scenarios in this use case. Happy to talk about the extended support needed to get mod-licenses to store links to things. Not a massive task IMO

Search for licenses by doing a http GET to /licenses/licenses.

This endpoint supports the filters= query parameter as per mod-agreements. Any property in the license domain (https://github.com/folio-org/mod-licenses/blob/master/service/grails-app/domain/org/olf/licenses/License.groovy) model can be used, for example

curl --header "X-Okapi-Tenant: diku" "http://localhost:9130/licenses/licenses?filters=name%3dtest&stats=true"

will search for a license name starting with test. Looking at the domain model, you will see that License extends Taggable

License also extends CustomProperties

Create a license by posting to that URL endpoint also

curl -sSL -H 'Accept:application/json' -H 'Content-Type: application/json' -H 'X-OKAPI-TENANT: diku' -XPOST "$TARGET/licenses/licenses" -d '
{
"name": "Academic Rights Press/Test Consortium/InteLex Collections - Perpetual Purchase Agreementi 2",
"description": "This is a test licenses",
"customProperties": {
"licenseEndAdvanceNoticeRequired": ["Yes"]
}
}
'

Linking to licenses

Licenses does not currently store links to any other objects (For example, agreements points in to licenses, not vice-versa) - so we would expect people wanting to refer to a license to find the license and then refer to it's .id property ( a UUID).

We could however add an arbitrary references list to licenses that allow links to anything else in the folio system like this
License.links [ { linkToType:'eholdings.package', linkToId:'ID-OF-EHOLDINGS-PACKAGE' },... ]

We would need to schedule that work however, please shout if you want us to do this. It's not currently the way links to licenses are organised tho.

Ability to link to attached license

Obviously, if you store the UUID of the license, you just link to /licenses/licenses/UUID - that works today

If you want to have references to external systems, as the suggestion above, you would use the query api to find all licenses attached, that would look something like this:

curl --header "X-Okapi-Tenant: diku" "http://localhost:9130/licenses/licenses?filters=links.linkToType=eholdings.package&filters=links.linkToId=ID-TO-LINK&stats=true"

This would work automatically once the domain model above was set up.

Ability to return the number of licenses

using the query endpoint curl --header "X-Okapi-Tenant: diku" "http://localhost:9130/licenses/licenses with &stats=true returns the number of licenses in the system (As you are implicitly doing a search for *). You can filter by license status values, or query the refdata endpoint to get refdata value lists.

Current mod-license clients would do this by nulling out the UUID in their own store, so is no business of license.

In the world were we enable licenses to have outbound links, PUTting

links : [ { id:UUID-OF-LINK, _delete:trie } ] to /licenses/licenses/{UUID_OF_LICENSE}

would cause the license link to be deleted. This would work automatically, once the domain model for links was established.