docs/advanced-ts.md

@@ -2,40 +2,65 @@
 
 ## Edit Provenance
 
-Track which changes came from where using `reconcileWithHistory`:
+Track which changes came from where using `reconcileWithHistory`. The result's
+`history` field is typed as `SpanWithHistory[]`, and each span's `history` is a
+`History` string-literal union.
 
-```javascript
-const result = reconcileWithHistory(
-  'Hello world',
-  'Hello beautiful world',
-  'Hi world'
-);
+```typescript
+import { reconcileWithHistory, type History, type SpanWithHistory } from 'reconcile-text';
 
-console.log(result.text);    // "Hi beautiful world"
-console.log(result.history); /*
-[
-  {
-    "text": "Hello",
-    "history": "RemovedFromRight"
-  },
-  {
-    "text": "Hi",
-    "history": "AddedFromRight"
-  },
-  {
-    "text": " beautiful",
-    "history": "AddedFromLeft"
-  },
-  {
-    "text": " ",
-    "history": "Unchanged"
-  },
-  {
-    "text": "world",
-    "history": "Unchanged"
+const result = reconcileWithHistory('Hello world', 'Hello beautiful world', 'Hi world');
+
+console.log(result.text); // "Hi beautiful world"
+
+const history: SpanWithHistory[] = result.history;
+console.log(history);
+// [
+//   { text: "Hello", history: "RemovedFromRight" },
+//   { text: "Hi", history: "AddedFromRight" },
+//   { text: " beautiful", history: "AddedFromLeft" },
+//   { text: " ", history: "Unchanged" },
+//   { text: "world", history: "Unchanged" },
+// ]
+
+const classByHistory = {
+  Unchanged: 'merge-unchanged',
+  AddedFromLeft: 'merge-added-left',
+  AddedFromRight: 'merge-added-right',
+  RemovedFromLeft: 'merge-removed-left',
+  RemovedFromRight: 'merge-removed-right',
+} satisfies Record<History, string>;
+```
+
+Using `satisfies Record<History, string>` keeps the object literal's values
+narrow while forcing every history case to be handled. If a future version adds
+another `History` value, TypeScript will point at this mapping.
+
+For control flow, use the same union as an exhaustiveness check:
+
+```typescript
+import type { History } from 'reconcile-text';
+
+function historyLabel(history: History): string {
+  switch (history) {
+    case 'Unchanged':
+      return 'unchanged';
+    case 'AddedFromLeft':
+      return 'added by left';
+    case 'AddedFromRight':
+      return 'added by right';
+    case 'RemovedFromLeft':
+      return 'removed from left';
+    case 'RemovedFromRight':
+      return 'removed from right';
+    default:
+      return assertNever(history);
   }
-]
-*/
+}
+
+function assertNever(value: never): never {
+  throw new Error(`Unhandled history value: ${value}`);
+}
 ```
 
 ## Tokenisation Strategies
@@ -45,26 +70,162 @@ console.log(result.history); /*
 - **Word tokeniser** (`"Word"`) - Splits on word boundaries (recommended for prose)
 - **Character tokeniser** (`"Character"`) - Individual characters (fine-grained control)
 - **Line tokeniser** (`"Line"`) - Line-by-line (similar to `git merge` or more precisely [`git merge-file`](https://git-scm.com/docs/git-merge-file))
+- **Markdown tokeniser** (`"Markdown"`) - Splits on Markdown structural boundaries (headings, list items, paragraphs)
+
+```typescript
+import { reconcile, type BuiltinTokenizer } from 'reconcile-text';
+
+const tokenizers = [
+  'Word',
+  'Character',
+  'Line',
+  'Markdown',
+] as const satisfies readonly BuiltinTokenizer[];
+
+const result = reconcile('abc', 'axc', 'abyc', 'Character');
+console.log(result.text); // "axyc"
+
+for (const tokenizer of tokenizers) {
+  const merged = reconcile(
+    '# Title\n\n- old item\n',
+    '# Title\n\n- old item\n- left item\n',
+    '# New title\n\n- old item\n',
+    tokenizer
+  );
+
+  console.log(tokenizer, merged.text);
+}
+```
 
 ## Cursor Tracking
 
-`reconcile-text` automatically tracks cursor positions through merges, which is useful for collaborative editors. Selections can be tracked by providing them as a pair of cursors.
+`reconcile-text` automatically tracks cursor positions through merges, which is
+useful for collaborative editors. Selections can be tracked by providing them as
+a pair of cursors.
 
-```javascript
-const result = reconcile(
-  'Hello world',
-  {
-    text: 'Hello beautiful world',
-    cursors: [{ id: 1, position: 6 }], // After "Hello "
-  },
-  {
-    text: 'Hi world',
-    cursors: [{ id: 2, position: 0 }], // At the beginning
-  }
-);
+```typescript
+import { reconcile, type TextWithOptionalCursors } from 'reconcile-text';
+
+const left = {
+  text: 'Hello beautiful world',
+  cursors: [{ id: 1, position: 6 }], // After "Hello "
+} satisfies TextWithOptionalCursors;
+
+const right = {
+  text: 'Hi world',
+  cursors: [{ id: 2, position: 0 }], // At the beginning
+} satisfies TextWithOptionalCursors;
+
+const result = reconcile('Hello world', left, right);
 
 // Result: "Hi beautiful world" with repositioned cursors
-console.log(result.text);    // "Hi beautiful world"
+console.log(result.text); // "Hi beautiful world"
 console.log(result.cursors); // [{ id: 2, position: 0 }, { id: 1, position: 3 }]
 ```
+
 > The `cursors` list is sorted by character position (not IDs).
+
+## Generic Helpers and Inference
+
+The exported merge functions are intentionally small: they merge strings, or
+strings plus cursor metadata. In TypeScript applications, keep domain-specific
+metadata in your own typed wrappers and let inference preserve the surrounding
+shape.
+
+```typescript
+import { reconcile, type BuiltinTokenizer } from 'reconcile-text';
+
+type ReconciledText<T extends { text: string }> = Omit<T, 'text'> & {
+  text: string;
+};
+
+function reconcileDraft<TDraft extends { text: string }>(
+  parent: TDraft,
+  left: TDraft,
+  right: TDraft,
+  tokenizer?: BuiltinTokenizer
+): ReconciledText<TDraft> {
+  return {
+    ...right,
+    text: reconcile(parent.text, left.text, right.text, tokenizer).text,
+  };
+}
+
+interface MarkdownDraft {
+  id: string;
+  text: string;
+  updatedAt: Date;
+}
+
+const parent: MarkdownDraft = {
+  id: 'intro',
+  text: '# Title\n\nOld text\n',
+  updatedAt: new Date('2026-01-01T00:00:00Z'),
+};
+
+const left: MarkdownDraft = {
+  ...parent,
+  text: '# Title\n\nOld text\n\n- left note\n',
+};
+
+const right: MarkdownDraft = {
+  ...parent,
+  text: '# New title\n\nOld text\n',
+};
+
+const merged = reconcileDraft(parent, left, right, 'Markdown');
+// merged is inferred as { id: string; updatedAt: Date; text: string }
+```
+
+Use `satisfies` for configuration objects and cursor payloads when you want
+compile-time checking without widening everything to the library interface.
+
+```typescript
+import type { BuiltinTokenizer, TextWithOptionalCursors } from 'reconcile-text';
+
+const mergeOptions = {
+  tokenizer: 'Markdown',
+  renderDeletedSpans: true,
+} satisfies {
+  tokenizer: BuiltinTokenizer;
+  renderDeletedSpans: boolean;
+};
+
+const documentWithSelection = {
+  text: 'Hello beautiful world',
+  cursors: [
+    { id: 1, position: 6 },
+    { id: 2, position: 15 },
+  ],
+} satisfies TextWithOptionalCursors;
+```
+
+## Compact Diffs
+
+Generate and apply compact diff representations. The TypeScript type is
+`Array<number | string>` for `diff()` and `Array<number | bigint | string>` for
+`undiff()`, because the underlying WebAssembly layer may represent integer
+entries as `bigint`.
+
+```typescript
+import { diff, undiff } from 'reconcile-text';
+
+const original = 'Hello world';
+const changed = 'Hello beautiful world';
+
+// Generate a compact diff
+const changes = diff(original, changed);
+console.log(changes); // [5, " beautiful world"]
+
+// Reconstruct the changed text from the diff
+const reconstructed = undiff(original, changes);
+console.assert(reconstructed === changed);
+```
+
+Diff entries are positive integers (retain N characters), negative integers
+(delete N characters), and strings (insert text).
+
+## Complete Example
+
+For a complete browser example that renders `SpanWithHistory` values and cursor
+selections, see the [example website source](../examples/website/src/index.ts).