#23 - support for sorting by metadata

- added support for grouping items by the presence of specified metadata
  - new keyword `metadata:` introduced for that purpose in lexer
  - if metadata field name is omitted, the default `sort-index-value` is used
- on top of the above, added support for sorting by the value of the specified metadata
- unit tests of sorting spec processor extended accordingly

src/custom-sort/custom-sort-types.ts

@@ -1,3 +1,5 @@
+import {Plugin} from "obsidian";
+
 export enum CustomSortGroupType {
 	Outsiders, // Not belonging to any of other groups
 	MatchAll, // like a wildard *, used in connection with foldersOnly or filesOnly. The difference between the MatchAll and Outsiders is
@@ -5,6 +7,7 @@ export enum CustomSortGroupType {
 	ExactPrefix,						  // ... while the Outsiders captures items which didn't match any of other defined groups
 	ExactSuffix,
 	ExactHeadAndTail, // Like W...n or Un...ed, which is shorter variant of typing the entire title
+	HasMetadataField  // Notes (or folder's notes) containing a specific metadata field
 }
 
 export enum CustomSortOrder {
@@ -18,6 +21,7 @@ export enum CustomSortOrder {
 	byCreatedTimeAdvanced,
 	byCreatedTimeReverse,
 	byCreatedTimeReverseAdvanced,
+	byMetadataField,
 	standardObsidian,  // Let the folder sorting be in hands of Obsidian, whatever user selected in the UI
 	default = alphabetical
 }
@@ -44,7 +48,8 @@ export interface CustomSortGroup {
 	secondaryOrder?: CustomSortOrder
 	filesOnly?: boolean
 	matchFilenameWithExt?: boolean
-	foldersOnly?: boolean,
+	foldersOnly?: boolean
+	metadataFieldName?: string
 }
 
 export interface CustomSortSpec {
@@ -55,4 +60,5 @@ export interface CustomSortSpec {
 	outsidersFilesGroupIdx?: number
 	outsidersFoldersGroupIdx?: number
 	itemsToHide?: Set<string>
+	plugin?: Plugin                     // to hand over the access to App instance to the sorting engine
 }

src/custom-sort/custom-sort.ts

@@ -1,4 +1,4 @@
-import {requireApiVersion, TAbstractFile, TFile, TFolder} from 'obsidian';
+import {MetadataCache, requireApiVersion, TAbstractFile, TFile, TFolder} from 'obsidian';
 import {CustomSortGroup, CustomSortGroupType, CustomSortOrder, CustomSortSpec} from "./custom-sort-types";
 import {isDefined} from "../utils/utils";
 
@@ -33,6 +33,7 @@ let Sorters: { [key in CustomSortOrder]: SorterFn } = {
 	[CustomSortOrder.byCreatedTimeAdvanced]: (a: FolderItemForSorting, b: FolderItemForSorting) => a.ctimeNewest - b.ctimeNewest,
 	[CustomSortOrder.byCreatedTimeReverse]: (a: FolderItemForSorting, b: FolderItemForSorting) => (a.isFolder && b.isFolder) ? Collator(a.sortString, b.sortString) : (b.ctimeOldest - a.ctimeOldest),
 	[CustomSortOrder.byCreatedTimeReverseAdvanced]: (a: FolderItemForSorting, b: FolderItemForSorting) => b.ctimeOldest - a.ctimeOldest,
+	[CustomSortOrder.byMetadataField]: (a: FolderItemForSorting, b: FolderItemForSorting) => Collator(a.sortString, b.sortString),
 
 	// This is a fallback entry which should not be used - the plugin code should refrain from custom sorting at all
 	[CustomSortOrder.standardObsidian]: (a: FolderItemForSorting, b: FolderItemForSorting) => Collator(a.sortString, b.sortString),
@@ -70,6 +71,7 @@ export const determineSortingGroup = function (entry: TFile | TFolder, spec: Cus
 	let groupIdx: number
 	let determined: boolean = false
 	let matchedGroup: string | null | undefined
+	let sortString: string | undefined
 	const aFolder: boolean = isFolder(entry)
 	const aFile: boolean = !aFolder
 	const entryAsTFile: TFile = entry as TFile
@@ -144,10 +146,24 @@ export const determineSortingGroup = function (entry: TFile | TFolder, spec: Cus
 						matchedGroup = group.regexSpec?.normalizerFn(match[1]);
 					}
 				}
-				break;
+				break
+			case CustomSortGroupType.HasMetadataField:
+				if (group.metadataFieldName) {
+					const mCache: MetadataCache | undefined = spec.plugin?.app.metadataCache
+					if (mCache) {
+						// For folders - scan metadata of 'folder note'
+						const notePathToScan: string = aFile ? entry.path : `${entry.path}/${entry.name}.md`
+						const metadataValue: string | undefined = mCache.getCache(notePathToScan)?.frontmatter?.[group.metadataFieldName]
+						if (metadataValue) {
+							determined = true
+							sortString = metadataValue
+						}
+					}
+				}
+				break
 			case CustomSortGroupType.MatchAll:
 				determined = true;
-				break;
+				break
 		}
 		if (determined) {
 			break;
@@ -171,7 +187,7 @@ export const determineSortingGroup = function (entry: TFile | TFolder, spec: Cus
 	return {
 		// idx of the matched group or idx of Outsiders group or the largest index (= groups count+1)
 		groupIdx: determinedGroupIdx,
-		sortString: matchedGroup ? (matchedGroup + '//' + entry.name) : entry.name,
+		sortString: sortString ?? (matchedGroup ? (matchedGroup + '//' + entry.name) : entry.name),
 		matchGroup: matchedGroup ?? undefined,
 		isFolder: aFolder,
 		folder: aFolder ? (entry as TFolder) : undefined,
@@ -255,7 +271,7 @@ export const folderSort = function (sortingSpec: CustomSortSpec, order: string[]
 			return itemForSorting
 		})
 
-	// Finally, for advanced sorting by modified date, for some of the folders the modified date has to be determined
+	// Finally, for advanced sorting by modified date, for some folders the modified date has to be determined
 	determineFolderDatesIfNeeded(folderItems, sortingSpec, sortingGroupsCardinality)
 
 	folderItems.sort(function (itA: FolderItemForSorting, itB: FolderItemForSorting) {

src/custom-sort/sorting-spec-processor.spec.ts

@@ -24,6 +24,12 @@ target-folder: tricky folder
 /  
 /:  
 
+:::: tricky folder 2
+/: metadata:
+ > modified
+metadata: Pages 
+ > a-z
+
 :::: Conceptual model
 /: Entities
 %
@@ -71,6 +77,12 @@ target-folder: tricky folder
 /folders  
 /:files  
 
+target-folder: tricky folder 2
+/:files metadata:
+ > modified
+% metadata: Pages 
+ > a-z
+
 :::: Conceptual model
 /:files Entities
 %
@@ -142,6 +154,25 @@ const expectedSortSpecsExampleA: { [key: string]: CustomSortSpec } = {
 		outsidersFoldersGroupIdx: 0,
 		targetFoldersPaths: ['tricky folder']
 	},
+	"tricky folder 2": {
+		groups: [{
+			filesOnly: true,
+			metadataFieldName: 'sort-index-value',
+			order: CustomSortOrder.byModifiedTimeReverse,
+			type: CustomSortGroupType.HasMetadataField
+		}, {
+			metadataFieldName: 'Pages',
+			order: CustomSortOrder.alphabeticalReverse,
+			type: CustomSortGroupType.HasMetadataField
+		}, {
+			order: CustomSortOrder.alphabetical,
+			type: CustomSortGroupType.Outsiders
+		}],
+		outsidersGroupIdx: 2,
+		targetFoldersPaths: [
+			'tricky folder 2'
+		]
+	},
 	"Conceptual model": {
 		groups: [{
 			exactText: "Entities",

src/custom-sort/sorting-spec-processor.ts

@@ -173,6 +173,10 @@ const AnyTypeGroupLexeme: string = '%'  // See % as a combination of / and :
 const HideItemShortLexeme: string = '--%'  // See % as a combination of / and :
 const HideItemVerboseLexeme: string = '/--hide:'
 
+const MetadataFieldIndicatorLexeme: string = 'metadata:'
+
+const DEFAULT_METADATA_FIELD_FOR_SORTING: string = 'sort-index-value'
+
 const CommentPrefix: string = '//'
 
 interface SortingGroupType {
@@ -380,6 +384,12 @@ const stripWildcardPatternSuffix = (path: string): [path: string, priority: numb
 	]
 }
 
+// Simplistic
+const extractIdentifier = (text: string, defaultResult?: string): string | undefined => {
+	const identifier: string = text.trim().split(' ')?.[0]?.trim()
+	return identifier ? identifier : defaultResult
+}
+
 const ADJACENCY_ERROR: string = "Numerical sorting symbol must not be directly adjacent to a wildcard because of potential performance problem. An additional explicit separator helps in such case."
 
 export class SortingSpecProcessor {
@@ -925,14 +935,29 @@ export class SortingSpecProcessor {
 					matchFilenameWithExt: spec.matchFilenameWithExt  // Doesn't make sense for matching, yet for multi-match
 				}               									    // theoretically could match the sorting of matched files
 			} else {
-				// For non-three dots single text line assume exact match group
+				// prototyping - only detect the presence of metadata: lexem
+				if (theOnly.startsWith(MetadataFieldIndicatorLexeme)) {
+					const metadataFieldName: string | undefined = extractIdentifier(
+						theOnly.substring(MetadataFieldIndicatorLexeme.length),
+						DEFAULT_METADATA_FIELD_FOR_SORTING
+					)
 					return {
-					type: CustomSortGroupType.ExactName,
-					exactText: spec.arraySpec[0],
+						type: CustomSortGroupType.HasMetadataField,
+						metadataFieldName: metadataFieldName,
 						filesOnly: spec.filesOnly,
 						foldersOnly: spec.foldersOnly,
 						matchFilenameWithExt: spec.matchFilenameWithExt
 					}
+				} else {
+					// For non-three dots single text line assume exact match group
+					return {
+						type: CustomSortGroupType.ExactName,
+						exactText: theOnly,
+						filesOnly: spec.filesOnly,
+						foldersOnly: spec.foldersOnly,
+						matchFilenameWithExt: spec.matchFilenameWithExt
+					}
+				}
 			}
 		}
 		if (spec.arraySpec?.length === 2) {

src/main.ts

@@ -292,6 +292,7 @@ export default class CustomSortPlugin extends Plugin {
 							}
 						}
 						if (sortSpec) {
+							sortSpec.plugin = plugin
 							return folderSort.call(this, sortSpec, ...args);
 						} else {
 							return old.call(this, ...args);