Implement new history instance methods

app/models/return-version.model.js

@@ -50,6 +50,185 @@ class ReturnVersionModel extends BaseModel {
       }
     }
   }
+
+  /**
+   * Modifiers allow us to reuse logic in queries, eg. select the licence and everything to get the licence holder:
+   *
+   * return LicenceModel.query()
+   *   .findById(licenceId)
+   *   .modify('licenceHolder')
+   *
+   * See {@link https://vincit.github.io/objection.js/recipes/modifiers.html | Modifiers} for more details
+   */
+  static get modifiers () {
+    return {
+      /**
+       * history modifier fetches all the records related to determining history properties, for example, created date
+       * and created by, from the record and its NALD mod logs (where they exist)
+       */
+      history (query) {
+        query
+          .withGraphFetched('modLogs')
+          .modifyGraph('modLogs', (builder) => {
+            builder.select([
+              'id',
+              'naldDate',
+              'note',
+              'reasonDescription',
+              'userId'
+            ])
+              .orderBy('externalId', 'asc')
+          })
+          .withGraphFetched('user')
+          .modifyGraph('user', (builder) => {
+            builder.select([
+              'id',
+              'username'
+            ])
+          })
+      }
+    }
+  }
+
+  /**
+   * Determine which user created the 'source' record using history
+   *
+   * > We recommend adding the `history` modifier to your query to support this determination
+   *
+   * NALD has a concept called 'mod log'. When someone creates a new licence, charge, or return version, they can
+   * provide a reason and a note, which is saved as the 'mod log'. Who created the 'mod log' and when is also captured.
+   *
+   * It was intended to record a history of changes to the licence.
+   *
+   * Unfortunately, NALD doesn't enforce it's creation. But as the NALD version records don't capture the who and when,
+   * they are the best 'source' we have to determine this information for imported records.
+   *
+   * If a user record exists for this version then it was created in WRLS and it is the 'source'. It extracts the user
+   * name, for example, `[email protected]`.
+   *
+   * If a user record doesn't exist, it falls back to attempting to extract the user ID from the first mod log
+   * record, for example, `JSMITH`. If one exists it is the 'source'.
+   *
+   * If neither a user nor any mod logs exist it will return `null`.
+   *
+   * @returns the user name of the user that created the 'source' record, else `null` if it cannot be determined
+   */
+  $createdBy () {
+    if (this.user) {
+      return this.user.username
+    }
+
+    const firstModLog = this._firstModLog()
+
+    return firstModLog?.userId ?? null
+  }
+
+  /**
+   * Determine the created at date of the 'source' record using history
+   *
+   * > We recommend adding the `history` modifier to your query to support this determination
+   *
+   * NALD has a concept called 'mod log'. When someone creates a new licence, charge, or return version, they can
+   * provide a reason and a note, which is saved as the 'mod log'. Who created the 'mod log' and when is also captured.
+   *
+   * It was intended to record a history of changes to the licence.
+   *
+   * Unfortunately, NALD doesn't enforce it's creation. But as the NALD version records don't capture the who and when,
+   * they are the best 'source' we have to determine this information for imported records.
+   *
+   * If there are mod logs for this record, it extracts the date from it, for example, `2019-06-02`, and returns it.
+   * Else, it falls back to using the return version's `createdAt` time stamp.
+   *
+   * > The NALD date takes priority, because all records will have a created at date. But in the case of imported
+   * > records this will be when it was imported to WRLS, which can be some time after it was created in NALD.
+   *
+   * @returns the date the 'source' record was created
+   */
+  $createdAt () {
+    const firstModLog = this._firstModLog()
+
+    return firstModLog?.naldDate ?? this.createdAt
+  }
+
+  /**
+   * Determine the notes for the record using its history
+   *
+   * > We recommend adding the `history` modifier to your query to support this determination
+   *
+   * NALD has a concept called 'mod log'. When someone creates a new licence, charge, or return version, they can
+   * provide a reason and a note, which is saved as the 'mod log'. Who created the 'mod log' and when is also captured.
+   *
+   * It was intended to record a history of changes to the licence.
+   *
+   * In NALD a return version can have multiple mod logs, each with their own note. NALD also allows users to enter a
+   * note against each return requirement linked to the return version.
+   *
+   * In WRLS (when we takeover from NALD) only a single note is captured against the return version.
+   *
+   * Till we takeover, the import job for NALD return versions extracts then concatenates the return requirement notes
+   * and saves them the return version's `notes` field.
+   *
+   * In short, for imported records, the mod log notes take precedence then whatever note was generated during import.
+   * Records created directly in WRLS will just have the single note and no mod log records.
+   *
+   * @returns an array of all the notes in ascending date order taken from the record's history
+   */
+  $notes () {
+    const notes = []
+
+    for (const modLog of this.modLogs) {
+      if (modLog.note) {
+        notes.push(modLog.note)
+      }
+    }
+
+    if (this.notes) {
+      notes.push(this.notes)
+    }
+
+    return notes
+  }
+
+  /**
+   * Determine the reason the 'source' record was created using history
+   *
+   * > We recommend adding the `history` modifier to your query to support this determination
+   *
+   * NALD has a concept called 'mod log'. When someone creates a new licence, charge, or return version, they can
+   * provide a reason and a note, which is saved as the 'mod log'. Who created the 'mod log' and when is also captured.
+   *
+   * It was intended to record a history of changes to the licence.
+   *
+   * Unfortunately, NALD doesn't enforce it's creation. But as the NALD version records don't capture the who and when,
+   * they are the best 'source' we have to determine this information for imported records.
+   *
+   * If the record has a reason, either it was created in WRLS or we have mapped the NALD 'source' reason to a WRLS one.
+   * The version record is the 'source'.
+   *
+   * If a reason doesn't exist, it falls back to attempting to extract the reason description from the first mod log
+   * record, for example, `Record Loaded During Migration`. If one exists it is the 'source'.
+   *
+   * If neither 'source' records have a reason then it returns `null`
+   *
+   * @returns the reason the 'source' record was created, else `null` if it cannot be determined
+   */
+  $reason () {
+    if (this.reason) {
+      return this.reason
+    }
+
+    const firstModLog = this._firstModLog()
+
+    return firstModLog?.reasonDescription ?? null
+  }
+
+  _firstModLog () {
+    if (this.modLogs.length > 0) {
+      return this.modLogs[0]
+    }
+
+    return null
+  }
 }
 
 module.exports = ReturnVersionModel