docs: Add documentation for custom filter functions

README.md

@@ -14,13 +14,12 @@ The list uses the default `NSTableView` styles, so it'll look right at home on B
 
 ## Usage
 
-This module strives for taking care of its components's memory wherever possible. This means you do not need to keep a reference to the window or its controller around. **Both will be freed when the action has been completed.**
+This module strives for taking care of its components's memory wherever possible. This means you do not need to keep a reference to window or its controller around. **Both will be freed when action has been completed.**
 
 ### When all possible items are known
 
 This is useful if you want to filter e.g. a limited collection of files, like "Recent Files", or to display a list of known macros.
 
-
 ```swift
 import FloatingFilter
 
@@ -32,12 +31,151 @@ let items = [
     Item(identifier: "custom-ID_123", title: "Show downloaded data")
 ]
 
-
 FloatingFilterModule.showFilterWindow(items: items) { selectedItems in
     print("Selected:", selectedItems.map { $0.title })
 }
 ```
 
+### Custom Filter Functions
+
+Since version 0.8.0, you can provide a custom filter function instead of using the built-in fuzzy matching. The default implementation performs fuzzy string matching, scoring, filtering below a threshold, and sorting.
+
+A custom filter function has the following type:
+
+```swift
+typealias ItemFilter = (_ needle: String, _ haystack: [Item]) -> [Item]
+```
+
+- `needle`: The search string typed by the user
+- `haystack`: The complete list of items to filter
+- Returns: A filtered and sorted array of matching items
+
+#### Example 1: Exact Match Filter
+
+```swift
+import FloatingFilter
+
+func exactMatchFilter(needle: String, haystack: [Item]) -> [Item] {
+    guard !needle.isEmpty else { return haystack }
+
+    return haystack.filter { item in
+        item.title.localizedCaseInsensitiveContains(needle)
+    }
+}
+
+let items = [
+    Item(identifier: 1, title: "Create new widget"),
+    Item(identifier: 2, title: "Open last document"),
+    Item(identifier: 3, title: "Show downloaded data")
+]
+
+FloatingFilterModule.showFilterWindow(
+    items: items,
+    filter: exactMatchFilter
+) { selectedItems in
+    print("Selected:", selectedItems.map { $0.title })
+}
+```
+
+#### Example 2: Prefix Match Filter
+
+```swift
+func prefixMatchFilter(needle: String, haystack: [Item]) -> [Item] {
+    guard !needle.isEmpty else { return haystack }
+
+    let lowercaseNeedle = needle.localizedLowercase
+    return haystack.filter { item in
+        item.title.localizedLowercase.hasPrefix(lowercaseNeedle)
+    }
+}
+
+FloatingFilterModule.showFilterWindow(
+    items: items,
+    filter: prefixMatchFilter
+) { selectedItems in
+    print("Selected:", selectedItems.map { $0.title })
+}
+```
+
+#### Example 3: Custom Scoring with FuzzyFind
+
+If you want to use the [FuzzyFind](https://github.com/truizlop/FuzzyFind) library instead of the built-in fuzzy matcher:
+
+```swift
+import FloatingFilter
+import FuzzyFind
+
+func fuzzyFindFilter(needle: String, haystack: [Item]) -> [Item] {
+    guard !needle.isEmpty else { return haystack }
+
+    let matcher = FuzzyFind(matcher: FuzzyMatcher.init)
+    return matcher.match(needle, in: haystack)
+        .sorted(by: { $0.score > $1.score })
+        .map { $0.item }
+}
+
+FloatingFilterModule.showFilterWindow(
+    items: items,
+    filter: fuzzyFindFilter
+) { selectedItems in
+    print("Selected:", selectedItems.map { $0.title })
+}
+```
+
+#### Example 4: Filter with Custom Sorting
+
+```swift
+func filterByDate(needle: String, haystack: [Item]) -> [Item] {
+    // Combine your custom filter logic with any sorting you need
+    let filtered = haystack.filter { item in
+        item.title.localizedCaseInsensitiveContains(needle)
+    }
+
+    // Sort by identifier (assuming it's a timestamp)
+    return filtered.sorted { item1, item2 in
+        if let date1 = item1.identifier as? Int,
+           let date2 = item2.identifier as? Int {
+            return date1 > date2  // Newest first
+        }
+        return false
+    }
+}
+
+FloatingFilterModule.showFilterWindow(
+    items: items,
+    filter: filterByDate
+) { selectedItems in
+    print("Selected:", selectedItems.map { $0.title })
+}
+```
+
+#### Default Fuzzy Filter
+
+If you want to use the built-in fuzzy matching with custom parameters:
+
+```swift
+let customFilter = FloatingFilterModule.defaultFuzzyFilter(
+    fuzziness: 0.2,  // Lower = more strict matching
+    threshold: 0.5   // Higher = fewer matches shown
+)
+
+FloatingFilterModule.showFilterWindow(
+    items: items,
+    filter: customFilter
+) { selectedItems in
+    print("Selected:", selectedItems.map { $0.title })
+}
+```
+
+**Filter Parameters:**
+
+- `fuzziness` (default: 0.3): How "fuzzy" the matching should be
+  - Lower values (0.0-0.2): More strict, exact-ish matches
+  - Higher values (0.4-0.5): More permissive, allow typos
+- `threshold` (default: 0.4): Minimum score required to include a match
+  - Lower values (0.2-0.3): More results shown
+  - Higher values (0.5-0.6): Fewer, higher-quality results
+
 
 ## Installation