Add SSE response summary helpers (#466)

Co-authored-by: Gregory Schier <gschier1990@gmail.com>

crates/yaak-sse/summary.ts

@@ -0,0 +1,131 @@
+import { JSONPath } from "jsonpath-plus";
+
+export interface SseSummary {
+  fragmentCount: number;
+  summary: string;
+}
+
+type JSONPathJson = null | boolean | number | string | object | unknown[];
+
+const STANDARD_SSE_FIELD = /^(event|id|retry):/i;
+
+export function candidateJsonPayloadsFromSseText(text: string): string[] {
+  const normalized = text.replace(/\r\n/g, "\n").replace(/\r/g, "\n");
+  const blocks = normalized.split(/\n{2,}/);
+  const candidates: string[] = [];
+
+  for (const block of blocks) {
+    const lines = block.split("\n");
+    const dataLines = lines
+      .map((line) => {
+        const match = /^data:(?: ?)(.*)$/.exec(line);
+        return match?.[1];
+      })
+      .filter((line): line is string => line != null);
+
+    if (dataLines.length > 0) {
+      const payload = dataLines.join("\n").trim();
+      if (payload) {
+        candidates.push(payload);
+      }
+      continue;
+    }
+
+    const trimmedBlock = block.trim();
+    if (!trimmedBlock) {
+      continue;
+    }
+
+    if (isParsableJson(trimmedBlock)) {
+      candidates.push(trimmedBlock);
+      continue;
+    }
+
+    for (const line of lines) {
+      const trimmedLine = line.trim();
+      if (
+        !trimmedLine ||
+        trimmedLine.startsWith(":") ||
+        STANDARD_SSE_FIELD.test(trimmedLine) ||
+        !isParsableJson(trimmedLine)
+      ) {
+        continue;
+      }
+      candidates.push(trimmedLine);
+    }
+  }
+
+  return candidates;
+}
+
+export function computeSseSummary(text: string, keyPath: string): SseSummary {
+  const fragments: string[] = [];
+
+  for (const payload of candidateJsonPayloadsFromSseText(text)) {
+    const fragment = extractSseValueAtPath(payload, keyPath);
+    if (fragment != null) {
+      fragments.push(fragment);
+    }
+  }
+
+  return {
+    fragmentCount: fragments.length,
+    summary: fragments.join(""),
+  };
+}
+
+export function extractSseValueAtPath(payload: string, keyPath: string): string | null {
+  let parsed: unknown;
+  try {
+    parsed = JSON.parse(payload);
+  } catch {
+    return null;
+  }
+
+  const path = keyPath.trim();
+  if (!path) {
+    return null;
+  }
+
+  let result: unknown;
+  try {
+    result = JSONPath({ path, json: parsed as JSONPathJson });
+  } catch {
+    return null;
+  }
+
+  if (Array.isArray(result)) {
+    const fragments = result
+      .map((item) => stringifySummaryValue(item))
+      .filter((item): item is string => item != null);
+    return fragments.length > 0 ? fragments.join("") : null;
+  }
+
+  return stringifySummaryValue(result);
+}
+
+function stringifySummaryValue(value: unknown): string | null {
+  if (value == null) {
+    return null;
+  }
+  if (typeof value === "string") {
+    return value;
+  }
+  if (typeof value === "number" || typeof value === "boolean" || typeof value === "bigint") {
+    return String(value);
+  }
+  try {
+    return JSON.stringify(value);
+  } catch {
+    return null;
+  }
+}
+
+function isParsableJson(value: string): boolean {
+  try {
+    JSON.parse(value);
+    return true;
+  } catch {
+    return false;
+  }
+}