From f1c920e0003238a8f319fd29cd7aea068fd4f231 Mon Sep 17 00:00:00 2001
From: Shin'ya Ueoka <ueokande@i-beam.org>
Date: Thu, 17 Aug 2017 22:33:46 +0900
Subject: add HintKeyProducer

---
 src/content/hint-key-producer.js | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 src/content/hint-key-producer.js

(limited to 'src')

diff --git a/src/content/hint-key-producer.js b/src/content/hint-key-producer.js
new file mode 100644
index 0000000..8064afb
--- /dev/null
+++ b/src/content/hint-key-producer.js
@@ -0,0 +1,33 @@
+export default class HintKeyProducer {
+  constructor(charset) {
+    if (charset.length === 0) {
+      throw new TypeError('charset is empty');
+    }
+
+    this.charset = charset;
+    this.counter = [];
+  }
+
+  produce() {
+    this.increment();
+
+    return this.counter.map((x) => this.charset[x]).join('');
+  }
+
+  increment() {
+    let max = this.charset.length - 1;
+    if (this.counter.every((x) => x == max)) {
+      this.counter = new Array(this.counter.length + 1).fill(0);
+      return;
+    }
+
+    this.counter.reverse();
+    let len = this.charset.length;
+    let num = this.counter.reduce((x,y,index) => x + y * (len ** index)) + 1;
+    for (let i = 0; i < this.counter.length; ++i) {
+      this.counter[i] = num % len;
+      num = ~~(num / len);
+    }
+    this.counter.reverse();
+  }
+}
-- 
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