1 files changed, 49 insertions, 0 deletions
diff --git a/src/content/repositories/HintKeyRepository.ts b/src/content/repositories/HintKeyRepository.ts
new file mode 100644
index 0000000..342b003
--- /dev/null
+++ b/src/content/repositories/HintKeyRepository.ts
@@ -0,0 +1,49 @@
+export default interface HintKeyRepository {
+  reset(charset: string): void;
+
+  produce(): string;
+}
+
+const current: {
+  charset: string;
+  counter: number[];
+} = {
+  charset: "",
+  counter: [],
+};
+
+export class HintKeyRepositoryImpl implements HintKeyRepository {
+  reset(charset: string): void {
+    if (charset.length === 0) {
+      throw new TypeError("charset is empty");
+    }
+    current.charset = charset;
+    current.counter = [];
+  }
+
+  produce(): string {
+    if (current.charset === "") {
+      throw new Error("charset is not set");
+    }
+    this.increment();
+
+    return current.counter.map((x) => current.charset[x]).join("");
+  }
+
+  private increment(): void {
+    const max = current.charset.length - 1;
+    if (current.counter.every((x) => x === max)) {
+      current.counter = new Array(current.counter.length + 1).fill(0);
+      return;
+    }
+
+    current.counter.reverse();
+    const len = current.charset.length;
+    let num = current.counter.reduce((x, y, index) => x + y * len ** index) + 1;
+    for (let i = 0; i < current.counter.length; ++i) {
+      current.counter[i] = num % len;
+      num = ~~(num / len);
+    }
+    current.counter.reverse();
+  }
+}