Initial module setup

modules/fts-client/src/main/scala/docspell/ftsclient/FtsBasicResult.scala

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+package docspell.ftsclient
+
+import cats.data.NonEmptyList
+import cats.implicits._
+import docspell.common._
+
+import FtsBasicResult.AttachmentMatch
+
+final case class FtsBasicResult(item: Ident, attachments: NonEmptyList[AttachmentMatch]) {
+
+  def score: Double =
+    attachments.map(_.score).toList.max
+}
+
+object FtsBasicResult {
+
+  case class AttachmentMatch(id: Ident, score: Double)
+
+}

modules/fts-client/src/main/scala/docspell/ftsclient/FtsClient.scala

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+package docspell.ftsclient
+
+import fs2.Stream
+
+/** The fts client is the interface for docspell to a fulltext search
+  * engine.
+  *
+  * It defines all operations required for integration into docspell.
+  * It uses data structures and terms of docspell. Implementation
+  * modules need to translate it to the engine that provides the
+  * features.
+  */
+trait FtsClient[F[_]] {
+
+  def searchBasic(q: FtsQuery): Stream[F, FtsBasicResult]
+
+  def indexData(data: TextData): F[Unit]
+}

modules/fts-client/src/main/scala/docspell/ftsclient/FtsQuery.scala

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+package docspell.ftsclient
+
+import docspell.common._
+
+/** A fulltext query.
+  *
+  * The query itself is a raw string. Each implementation may
+  * interpret it according to the system in use.
+  */
+final case class FtsQuery(q: String, collective: Ident, limit: Int, offset: Int)

modules/fts-client/src/main/scala/docspell/ftsclient/TextData.scala

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+package docspell.ftsclient
+
+import docspell.common._
+
+final case class TextData(item: Ident, attachment: Ident, collective: Ident, text: String)

modules/fts-solr/src/main/scala/docspell/ftssolr/SolrFtsClient.scala

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+package docspell.ftssolr
+
+import fs2.Stream
+import docspell.ftsclient._
+
+final class SolrFtsClient[F[_]] extends FtsClient[F] {
+
+  def searchBasic(q: FtsQuery): Stream[F, FtsBasicResult] =
+    ???
+  def indexData(data: TextData): F[Unit] =
+    ???
+}

modules/microsite/docs/dev/adr/0014_fulltext_search_engine.md

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+---
+layout: docs
+title: Fulltext Search Engine
+---
+
+# Choose a Fulltext Search Engine
+
+It should be possible to search the contents of all documents.
+
+## Context and Problem Statement
+
+To allow searching the documents contents efficiently, a separate
+index is necessary. The "defacto standard" for fulltext search on the
+JVM is something backed by [Lucene](https://lucene.apache.org).
+Another option is to use a RDBMS that supports fulltext search.
+
+This adds another component to the mix, which increases the complexity
+of the setup and the software. Since docspell works great without this
+feature, it shouldn't have a huge impact on the application, i.e. if
+the fulltext search component is down or broken, docspell should still
+work (just the fulltext search is then not working).
+
+## Considered Options
+
+* [Apache SOLR](https://lucene.apache.org/solr)
+* [ElasticSearch](https://www.elastic.co/elasticsearch/)
+* [PostgreSQL](https://www.postgresql.org/docs/12/textsearch.html)
+* All of them or a subset
+
+## Decision Outcome
+
+If docspell is running on PostgreSQL, it would be the best option to
+also use it for fulltext search. But I don't want to lock the database
+to PostgreSQL *only* because of the fulltext search feature. This
+would be a too large impact on the whole application.
+
+ElasticSearch and Apache SOLR are quite similiar in features. SOLR is
+part of Lucene and therefore lives in the Apache ecosystem. I would
+choose this over ElasticSearch, which is backed by a company (the oss
+version is released under the Apache License, afaiu). Regarding
+features, both are great.
+
+The last option (supporting all) is interesting, since it would enable
+to use PostgreSQL for fulltext search, when already using PostgreSQL
+as the database for docspell.
+
+So in a first step, identify what docspell needs from a fulltext
+search component and create this interface and an implementation for
+Apache SOLR. This enables all users to use the fulltext search
+feature. As a later step, an implementation based on PostgreSQL could
+be provided, too.

modules/microsite/docs/dev/adr/0015_fulltext_search_design.md

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+---
+layout: docs
+title: Fulltext Search Design
+---
+
+# How to integrate Fulltext Search
+
+
+
+## Context and Problem Statement
+
+
+## Considered Options
+
+
+## Decision Outcome