Add a feature to retrieve the default branch to the web installer

because GitHub made the breaking change about the default branch.
Now we cannot use any fixed branch name for our purpose.

Author: kmyk

.verify-helper/docs/static/installer.ja.md

@@ -9,6 +9,7 @@
 1.  <form>
         <label>競プロライブラリの GitHub のレポジトリの URL を右の textbox に入力: </label>
         <input type="text" id="input" placeholder="https://github.com/beet-aizu/library" value="https://github.com/beet-aizu/library" size="48">
+        (ブランチ: <input type="text" id="input-branch" placeholder="master" value="master" size="12">)
     </form>
 
 1.  ページ <a id="output" target="_blank"></a> を開き、下の方にある緑の `Commit new file` ボタンを押す

.verify-helper/docs/static/installer.js

@@ -13,6 +13,7 @@ data["example.test.cpp"] = (function () {
 })();
 
 const input = document.getElementById("input");
+const inputBranch = document.getElementById("input-branch");
 const output = document.getElementById("output");
 const output2 = document.getElementById("output2");
 const output3 = document.getElementById("output3");
@@ -27,22 +28,36 @@ const output11 = document.getElementById("output11");
 const output12 = document.getElementById("output12");
 const output13 = document.getElementById("output13");
 
-function update() {
+function retrieveDefaultBranch() {
+    const found = input.value.match(/\/github.com\/([^\/]+)\/([^\/]+)/);
+    if (!found) return;
+    const url = "https://api.github.com/repos/" + found[1] + "/" + found[2];
+    const req = new XMLHttpRequest();
+    req.open("GET", url, false);
+    req.send();
+    const resp = JSON.parse(req.responseText);
+    if (resp['default_branch']) {
+        inputBranch.value = resp['default_branch'];
+    }
+}
+
+function updateLinks() {
     const found = input.value.match(/\/github.com\/([^\/]+)\/([^\/]+)/);
     if (found) {
         const url = input.value.replace(/\/$/, "");
         const ghpages = "https://" + found[1] + ".github.io/" + found[2] + "/";
+        const branch = inputBranch.value;
 
         // adding verify.yml
         const filename = ".github%2Fworkflows%2Fverify.yml"
         const value = encodeURIComponent(data["verify.yml"].replace("git+https://github.com/online-judge-tools/verification-helper.git@master", "online-judge-verify-helper"));
-        output.href = url + "/new/master?filename=" + filename + "&value=" + value;
+        output.href = url + "/new/" + branch + "?filename=" + filename + "&value=" + value;
         output.textContent = url + "&value=...";
 
         // adding example.text.cpp
         const filename2 = "example.test.cpp";
         const value2 = encodeURIComponent(data["example.test.cpp"]);
-        output2.href = url + "/new/master?filename=" + filename2 + "&value=" + value2;
+        output2.href = url + "/new/" + branch + "?filename=" + filename2 + "&value=" + value2;
 
         // links to GitHub Actions
         output3.href = input.value.replace(/\/$/, "") + "/actions";
@@ -66,6 +81,14 @@ function update() {
         output13.href = url + "/commits/gh-pages";
     }
 }
+
+function update() {
+    retrieveDefaultBranch();
+    updateLinks();
+}
+
 input.addEventListener('change', update);
 input.addEventListener('keyup', update);
-update();
+inputBranch.addEventListener('change', updateLinks);
+inputBranch.addEventListener('keyup', updateLinks);
+updateLinks();

.verify-helper/docs/static/installer.md

@@ -9,6 +9,7 @@ Steps:
 1.  <form>
         <label>Input the URL of the library repository in the textbox on the right: </label>
         <input type="text" id="input" placeholder="https://github.com/beet-aizu/library" value="https://github.com/beet-aizu/library" size="48">
+        (branch: <input type="text" id="input-branch" placeholder="master" value="master" size="12">)
     </form>
 
 1.  Open <a id="output" target="_blank"></a> and click the green `Commit new file` button.