build(aio): truncate API overview parameters at one line

aio/tools/transforms/angular-base-package/rendering/truncateCode.js

@@ -0,0 +1,49 @@
+module.exports = function() {
+  return {
+    name: 'truncateCode',
+    process: function(str, lines) {
+      if (lines === undefined) return str;
+
+      const parts = str && str.split && str.split(/\r?\n/);
+      if (parts && parts.length > lines) {
+        return balance(parts[0] + '...', ['{', '(', '['], ['}', ')', ']']);
+      } else {
+        return str;
+      }
+    }
+  };
+};
+
+/**
+ * Try to balance the brackets by adding closers on to the end of a string
+ * for every bracket that is left open.
+ * The chars at each index in the openers and closers should match (i.e openers = ['{', '('], closers = ['}', ')'])
+ *
+ * @param {string} str The string to balance
+ * @param {string[]} openers an array of chars that open a bracket
+ * @param {string[]} closers an array of chars that close a brack
+ * @returns the balanced string
+ */
+function balance(str, openers, closers) {
+  const stack = [];
+
+  // Add each open bracket to the stack, removing them when there is a matching closer
+  str.split('').forEach(function(char) {
+    const closerIndex = closers.indexOf(char);
+    if (closerIndex !== -1 && stack[stack.length-1] === closerIndex) {
+      stack.pop();
+    } else {
+      const openerIndex = openers.indexOf(char);
+      if (openerIndex !== -1) {
+        stack.push(openerIndex);
+      }
+    }
+  });
+
+  // Now the stack should contain all the unclosed brackets
+  while(stack.length) {
+    str += closers[stack.pop()];
+  }
+
+  return str;
+}