Reconsider the internals of the filter engine ## Background / User story There are a bunch of issue with the filterStorage and filterEnginer we currently have: - Issue adblockpluscore#381 show it is harder to implement as we don't properly handle having duplicate filters - Downloadable filter list are immutable - The implementation of issue adblockpluscore#407 and adblockpluscore#419 makes for an awkward API, including limitations like not being able to add metadata to filters that don't have metadata. (see webext-sdk!291) ### Manifest v3 Manifest V3 brings a set of extra requirements: - Split between URL filters (DNR) & content filters. - DNR static filters are immutable, updates are provided separately. - Dynamic DNR rules are in one single ruleset on the browser side, so we need a mechanism to associate them. ## What to change ### Proposal Subscriptions in MV3 are no longer a single data set, because URL filter are now DNR. - `DownloadableSubscription` - They are associated to a ruleset ID - the core doesn't know DNR but the ID is a string the SDK can use. (MV3) - They have a list of dynamic DNR rules. We need to store these to be able to enable / disable (MV3) - Their content is immutable, unless it's the synchronization process (all) - [ ] Issue adblockpluscore#449 - `CustomFiltersSubscription` replace the `SpecialSubscription`. (all) - They can have metadata. (all) - They might have a list of dynamic DNR rules (MV3) for custom URL filters. The whole rules must be stored. - The core will need to have the index of subscriptions to be able to locate them by `url` or `mv2-url`. - `Subscription.fromURL()` should sort this out. In Manifest V3 we don't have blocking URL filters. - [ ] filterEngine will be instantiated in a `mv3` mode. This is necessary has the core doesn't have access to the webextension API. - [ ] Isseu adblockpluscore#450 - The `CombinedMatcher` should only contain CSP and POPUP filters. #### Operations (example) - enable/disable subscription in EWE: - get subscription from filter engine (using the ID) - enable/disable subscription - get ruleset ID. - enable/disable ruleset (webext) - get dynamic rules - enable/disable the dynamic rules. This is done by adding or removing the rules (webext). ### Question - [ ] how do we handle duplicate filters ? - [ ] how to we handle immutability ? ## Hints for testing TBD