Add support for live typing 3 dashes

When using oldschool or inverted dashes,
there is handling of turning both 2 and 3 dashes
into different characters.
When someone types 2 dashes in,
they are swapped out for another character.

This commit introduces handling of *that* character,
plus another dash,
to be seen as if they are 3 dashes.

Closes GH-13.

lib/index.js

@@ -13,8 +13,8 @@
  *   Position of `node` in `parent`.
  * @param {Parents} parent
  *   Parent of `node`.
- * @returns {undefined}
- *   Nothing.
+ * @returns {boolean | undefined | void}
+ *   Whether to remove the node (`true`); or not (otherwise).
  *
  * @typedef Options
  *   Configuration.
@@ -144,7 +144,12 @@ export default function retextSmartypants(options) {
         (node.type === 'PunctuationNode' || node.type === 'SymbolNode')
       ) {
         while (++index < methods.length) {
-          methods[index](state, node, position, parent)
+          const result = methods[index](state, node, position, parent)
+          if (result === true) {
+            console.log('drop', node)
+            parent.children.splice(position, 1)
+            return position
+          }
         }
       }
     })
@@ -195,7 +200,19 @@ function dashesDefault(_, node) {
  *
  * @type {Method}
  */
-function dashesInverted(_, node) {
+function dashesInverted(_, node, index, parent) {
+  const next = parent.children[index + 1]
+
+  if (
+    node.value === '—' &&
+    next &&
+    next.type === 'PunctuationNode' &&
+    next.value === '-'
+  ) {
+    next.value = '–'
+    return true
+  }
+
   if (node.value === '---') {
     node.value = '–'
   } else if (node.value === '--') {
@@ -208,7 +225,19 @@ function dashesInverted(_, node) {
  *
  * @type {Method}
  */
-function dashesOldschool(_, node) {
+function dashesOldschool(_, node, index, parent) {
+  const next = parent.children[index + 1]
+
+  if (
+    node.value === '–' &&
+    next &&
+    next.type === 'PunctuationNode' &&
+    next.value === '-'
+  ) {
+    next.value = '—'
+    return true
+  }
+
   if (node.value === '---') {
     node.value = '—'
   } else if (node.value === '--') {

test.js

@@ -305,6 +305,19 @@ test('En- and em-dashes', async function (t) {
         )
       }
     )
+
+    await t.test(
+      'should turn an en dash + dash into an em-dash',
+      async function () {
+        assert.equal(
+          retext()
+            .use(retextSmartypants, {dashes: 'oldschool'})
+            .processSync('Alfred–-')
+            .toString(),
+          'Alfred—'
+        )
+      }
+    )
   })
 
   await t.test('inverted', async function (t) {
@@ -321,6 +334,19 @@ test('En- and em-dashes', async function (t) {
         )
       }
     )
+
+    await t.test(
+      'should turn an em dash + dash into an en-dash',
+      async function () {
+        assert.equal(
+          retext()
+            .use(retextSmartypants, {dashes: 'inverted'})
+            .processSync('Alfred—-')
+            .toString(),
+          'Alfred–'
+        )
+      }
+    )
   })
 })