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frontend-web/src/open-canvas/api/rewrite.ts

@@ -0,0 +1,108 @@
+import { apiFetch } from "@/core/api/fetch-client";
+import { env } from "@/env";
+
+const BASE = (env.NEXT_PUBLIC_BACKEND_BASE_URL as string | undefined) ?? "http://localhost:8001";
+
+export type RewriteAction = "polish" | "expand" | "shorten" | "tone";
+export type RewriteTone =
+  | "professional"
+  | "casual"
+  | "readable"
+  | "academic"
+  | "expressive";
+
+export interface RewriteRequest {
+  threadId: string;
+  selection: { from: number; to: number; text: string };
+  action: RewriteAction;
+  tone?: RewriteTone;
+  modelName?: string;
+  surroundingContext?: { before?: string; after?: string };
+  customInstruction?: string;
+  followUpInstruction?: string;
+  previousResult?: string;
+}
+
+export type RewriteStreamEvent =
+  | { type: "thinking"; chunk: string }
+  | { type: "text"; chunk: string }
+  | { type: "done" }
+  | { type: "error"; message: string };
+
+// ── SSE parser ────────────────────────────────────────────────────────────────
+
+async function* parseSse(body: ReadableStream<Uint8Array>): AsyncGenerator<{ event: string; data: string }> {
+  const reader = body.getReader();
+  const decoder = new TextDecoder();
+  let buffer = "";
+  let currentEvent = "";
+
+  try {
+    while (true) {
+      const { done, value } = await reader.read();
+      if (done) break;
+      buffer += decoder.decode(value, { stream: true });
+
+      const lines = buffer.split("\n");
+      buffer = lines.pop() ?? "";
+
+      for (const line of lines) {
+        const trimmed = line.trimEnd();
+        if (trimmed.startsWith("event: ")) {
+          currentEvent = trimmed.slice(7);
+        } else if (trimmed.startsWith("data: ")) {
+          yield { event: currentEvent, data: trimmed.slice(6) };
+          currentEvent = "";
+        }
+        // empty line resets event field (SSE spec)
+        else if (trimmed === "") {
+          currentEvent = "";
+        }
+      }
+    }
+  } finally {
+    reader.releaseLock();
+  }
+}
+
+// ── Streaming entry point ─────────────────────────────────────────────────────
+
+export async function* streamRewrite(
+  req: RewriteRequest,
+  signal?: AbortSignal,
+): AsyncGenerator<RewriteStreamEvent> {
+  const res = await apiFetch(`${BASE}/api/writing/rewrite`, {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify(req),
+    signal,
+  });
+
+  if (!res.ok) {
+    const body = await res.json().catch(() => ({})) as Record<string, unknown>;
+    const msg = (body?.detail as string | undefined) ?? (body?.message as string | undefined) ?? `HTTP ${res.status}`;
+    throw new Error(msg);
+  }
+
+  if (!res.body) throw new Error("No response body");
+
+  for await (const { event, data } of parseSse(res.body)) {
+    if (signal?.aborted) return;
+    try {
+      const parsed = JSON.parse(data) as Record<string, unknown>;
+      if (event === "thinking") {
+        yield { type: "thinking", chunk: parsed.chunk as string };
+      } else if (event === "text") {
+        yield { type: "text", chunk: parsed.chunk as string };
+      } else if (event === "done") {
+        yield { type: "done" };
+        return;
+      } else if (event === "error") {
+        yield { type: "error", message: parsed.message as string };
+        return;
+      }
+    } catch {
+      // skip malformed frame
+    }
+  }
+}