refactor: Extract FilterInstructionsBasedField class to reduce more repetition (#818)

* refactor: Extract class FilterInstructionsBasedField

The fields that are implemented using FilterInstructions
have a lot of duplicated code.

This commit starts to eliminate that duplication by introducing
a partial implementation of Field called FilterInstructionsBasedField.

Not the best of names, but it is an implementation detail.

* refactor: Reimplement RecurringField using FilterInstructionsBasedField

* refactor: Reimplement StatusField using FilterInstructionsBasedField

* chore: Tidy up unnecessary remnant comment.

Author: claremacrae

src/Query/Filter/ExcludeSubItemsField.ts

@@ -1,13 +1,9 @@
-import { Field } from './Field';
-import type { FilterOrErrorMessage } from './Filter';
-import { FilterInstructions } from './FilterInstructions';
+import { FilterInstructionsBasedField } from './FilterInstructionsBasedField';
 
 /**
  * Implements 'exclude sub-items' filter
  */
-export class ExcludeSubItemsField extends Field {
-    private readonly _filters = new FilterInstructions();
-
+export class ExcludeSubItemsField extends FilterInstructionsBasedField {
     constructor() {
         super();
 
@@ -17,19 +13,7 @@ export class ExcludeSubItemsField extends Field {
         );
     }
 
-    public canCreateFilterForLine(line: string): boolean {
-        return this._filters.canCreateFilterForLine(line);
-    }
-
-    public createFilterOrErrorMessage(line: string): FilterOrErrorMessage {
-        return this._filters.createFilterOrErrorMessage(line);
-    }
-
     protected fieldName(): string {
         return 'exclude';
     }
-
-    protected filterRegexp(): RegExp | null {
-        return null;
-    }
 }

src/Query/Filter/FilterInstructionsBasedField.ts

@@ -0,0 +1,25 @@
+import { Field } from './Field';
+import { FilterInstructions } from './FilterInstructions';
+import type { FilterOrErrorMessage } from './Filter';
+
+/**
+ * This class is an implementation for implements of {@link Field}
+ *
+ * The named of the class is weak. It is based solely on the fact that the
+ * class is entirely implemented via the {@link FilterInstructions} class.
+ */
+export abstract class FilterInstructionsBasedField extends Field {
+    protected readonly _filters = new FilterInstructions();
+
+    public canCreateFilterForLine(line: string): boolean {
+        return this._filters.canCreateFilterForLine(line);
+    }
+
+    public createFilterOrErrorMessage(line: string): FilterOrErrorMessage {
+        return this._filters.createFilterOrErrorMessage(line);
+    }
+
+    protected filterRegexp(): RegExp | null {
+        return null;
+    }
+}

src/Query/Filter/RecurringField.ts

@@ -1,10 +1,6 @@
-import { Field } from './Field';
-import type { FilterOrErrorMessage } from './Filter';
-import { FilterInstructions } from './FilterInstructions';
-
-export class RecurringField extends Field {
-    private readonly _filters = new FilterInstructions();
+import { FilterInstructionsBasedField } from './FilterInstructionsBasedField';
 
+export class RecurringField extends FilterInstructionsBasedField {
     constructor() {
         super();
         this._filters.add('is recurring', (task) => task.recurrence !== null);
@@ -14,19 +10,7 @@ export class RecurringField extends Field {
         );
     }
 
-    public canCreateFilterForLine(line: string): boolean {
-        return this._filters.canCreateFilterForLine(line);
-    }
-
-    public createFilterOrErrorMessage(line: string): FilterOrErrorMessage {
-        return this._filters.createFilterOrErrorMessage(line);
-    }
-
     protected fieldName(): string {
         return 'recurring';
     }
-
-    protected filterRegexp(): RegExp | null {
-        return null;
-    }
 }

src/Query/Filter/StatusField.ts

@@ -1,11 +1,7 @@
 import { Status, Task } from '../../Task';
-import { Field } from './Field';
-import type { FilterOrErrorMessage } from './Filter';
-import { FilterInstructions } from './FilterInstructions';
-
-export class StatusField extends Field {
-    private readonly _filters = new FilterInstructions();
+import { FilterInstructionsBasedField } from './FilterInstructionsBasedField';
 
+export class StatusField extends FilterInstructionsBasedField {
     constructor() {
         super();
 
@@ -16,19 +12,7 @@ export class StatusField extends Field {
         );
     }
 
-    public canCreateFilterForLine(line: string): boolean {
-        return this._filters.canCreateFilterForLine(line);
-    }
-
-    public createFilterOrErrorMessage(line: string): FilterOrErrorMessage {
-        return this._filters.createFilterOrErrorMessage(line);
-    }
-
     protected fieldName(): string {
         return 'status';
     }
-
-    protected filterRegexp(): RegExp | null {
-        return null;
-    }
 }

tests/Query/Filter/ExcludeSubItemsField.test.ts

@@ -1,5 +1,3 @@
-// 'exclude sub-items'
-
 import { testTaskFilter } from '../../TestingTools/FilterTestHelpers';
 import { fromLine } from '../../TestHelpers';
 import { ExcludeSubItemsField } from '../../../src/Query/Filter/ExcludeSubItemsField';