feat(chat): add local-first conversation workspace

chat/lib/incremental-markdown-cache.ts

@@ -0,0 +1,79 @@
+import {splitStreamingMarkdown} from "./streaming-markdown";
+
+export type IncrementalMarkdownBlock<T> = T & {
+  source: string;
+  type: string;
+  index: number;
+  stable: boolean;
+};
+
+export type IncrementalMarkdownResult<T> = {
+  blocks: Array<IncrementalMarkdownBlock<T>>;
+  parsed: number;
+  reused: number;
+};
+
+type IncrementalMarkdownState<T> = {
+  stableSource: string;
+  stableBlocks: Array<IncrementalMarkdownBlock<T>>;
+  nextIndex: number;
+};
+
+export class IncrementalMarkdownCache<T> {
+  private readonly states = new Map<string, IncrementalMarkdownState<T>>();
+
+  render(
+    messageId: string,
+    value: string,
+    renderBlock: (source: string, type: string, index: number, stable: boolean) => T,
+    onSplit?: (durationMs: number) => void,
+    complete = false
+  ): IncrementalMarkdownResult<T> {
+    let state = this.states.get(messageId);
+    if (!state || !value.startsWith(state.stableSource)) {
+      state = {stableSource: "", stableBlocks: [], nextIndex: 0};
+      this.states.set(messageId, state);
+    }
+    if (value === state.stableSource) return {blocks: state.stableBlocks, parsed: 0, reused: state.stableBlocks.length};
+
+    const tail = value.slice(state.stableSource.length);
+    const startedAt = performance.now();
+    const split = splitStreamingMarkdown(tail, complete);
+    onSplit?.(performance.now() - startedAt);
+    const renderedTail = split.blocks.map((block, offset) => ({
+      ...renderBlock(block.source, block.type, state!.nextIndex + offset, block.stable),
+      source: block.source,
+      type: block.type,
+      index: state!.nextIndex + offset,
+      stable: block.stable
+    }));
+    const newlyStable = renderedTail.filter((_block, index) => split.blocks[index].end <= split.stableOffset);
+    const previouslyStableCount = state.stableBlocks.length;
+    if (split.stableOffset > 0) {
+      state.stableSource += tail.slice(0, split.stableOffset);
+      state.stableBlocks.push(...newlyStable);
+      state.nextIndex += newlyStable.length;
+    }
+    return {
+      blocks: [...state.stableBlocks.slice(0, state.stableBlocks.length - newlyStable.length), ...renderedTail],
+      parsed: renderedTail.length,
+      reused: previouslyStableCount
+    };
+  }
+
+  delete(messageId: string) {
+    this.states.delete(messageId);
+  }
+
+  move(fromMessageId: string, toMessageId: string) {
+    if (fromMessageId === toMessageId) return;
+    const state = this.states.get(fromMessageId);
+    if (!state) return;
+    this.states.set(toMessageId, state);
+    this.states.delete(fromMessageId);
+  }
+
+  has(messageId: string) {
+    return this.states.has(messageId);
+  }
+}