feat: add learning data fetching utilities

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: sounmind

utils/learningData.js

@@ -0,0 +1,162 @@
+/**
+ * Learning data fetching utilities for DaleStudy GitHub App
+ */
+
+/**
+ * Fetches problem-categories.json from the repo root via GitHub API.
+ * Returns parsed JSON object, or null if the file is not found (404).
+ * Throws on other errors.
+ *
+ * @param {string} repoOwner
+ * @param {string} repoName
+ * @param {string} appToken
+ * @returns {Promise<object|null>}
+ */
+export async function fetchProblemCategories(repoOwner, repoName, appToken) {
+  const url = `https://api.github.com/repos/${repoOwner}/${repoName}/contents/problem-categories.json`;
+
+  const response = await fetch(url, {
+    headers: {
+      Authorization: `Bearer ${appToken}`,
+      Accept: "application/vnd.github.raw+json",
+      "User-Agent": "DaleStudy-GitHub-App",
+    },
+  });
+
+  if (response.status === 404) {
+    return null;
+  }
+
+  if (!response.ok) {
+    throw new Error(
+      `Failed to fetch problem-categories.json: ${response.status} ${response.statusText}`
+    );
+  }
+
+  return await response.json();
+}
+
+/**
+ * Fetches the full repo file tree and returns a deduplicated array of problem
+ * names that have a solution file submitted by the given username.
+ *
+ * Matches files of the form: {problem-name}/{username}.{ext}
+ *
+ * @param {string} repoOwner
+ * @param {string} repoName
+ * @param {string} username
+ * @param {string} appToken
+ * @returns {Promise<string[]>}
+ */
+export async function fetchUserSolutions(
+  repoOwner,
+  repoName,
+  username,
+  appToken
+) {
+  const url = `https://api.github.com/repos/${repoOwner}/${repoName}/git/trees/main?recursive=1`;
+
+  const response = await fetch(url, {
+    headers: {
+      Authorization: `Bearer ${appToken}`,
+      Accept: "application/vnd.github+json",
+      "User-Agent": "DaleStudy-GitHub-App",
+    },
+  });
+
+  if (!response.ok) {
+    throw new Error(
+      `Failed to fetch repo tree: ${response.status} ${response.statusText}`
+    );
+  }
+
+  const data = await response.json();
+
+  // Pattern: {problem-name}/{username}.{ext}
+  // The path must have exactly two segments and the filename must be username.ext
+  const usernamePattern = new RegExp(
+    `^([^/]+)/${escapeRegExp(username)}\\.[^/]+$`
+  );
+
+  const problemNames = new Set();
+
+  for (const item of data.tree) {
+    if (item.type !== "blob") continue;
+
+    const match = item.path.match(usernamePattern);
+    if (match) {
+      problemNames.add(match[1]);
+    }
+  }
+
+  return Array.from(problemNames);
+}
+
+/**
+ * Fetches the files changed in a PR and returns those that match
+ * {problem-name}/{username}.{ext} and are added or modified.
+ *
+ * @param {string} repoOwner
+ * @param {string} repoName
+ * @param {number} prNumber
+ * @param {string} username
+ * @param {string} appToken
+ * @returns {Promise<Array<{ problemName: string, filename: string, rawUrl: string }>>}
+ */
+export async function fetchPRSubmissions(
+  repoOwner,
+  repoName,
+  prNumber,
+  username,
+  appToken
+) {
+  const url = `https://api.github.com/repos/${repoOwner}/${repoName}/pulls/${prNumber}/files?per_page=100`;
+
+  const response = await fetch(url, {
+    headers: {
+      Authorization: `Bearer ${appToken}`,
+      Accept: "application/vnd.github+json",
+      "User-Agent": "DaleStudy-GitHub-App",
+    },
+  });
+
+  if (!response.ok) {
+    throw new Error(
+      `Failed to fetch PR files: ${response.status} ${response.statusText}`
+    );
+  }
+
+  const files = await response.json();
+
+  // Pattern: {problem-name}/{username}.{ext}
+  const usernamePattern = new RegExp(
+    `^([^/]+)/${escapeRegExp(username)}\\.[^/]+$`
+  );
+
+  const results = [];
+
+  for (const file of files) {
+    if (file.status !== "added" && file.status !== "modified") continue;
+
+    const match = file.filename.match(usernamePattern);
+    if (match) {
+      results.push({
+        problemName: match[1],
+        filename: file.filename,
+        rawUrl: file.raw_url,
+      });
+    }
+  }
+
+  return results;
+}
+
+/**
+ * Escapes special regex characters in a string.
+ *
+ * @param {string} str
+ * @returns {string}
+ */
+function escapeRegExp(str) {
+  return str.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+}