fix: Improve spanner.date handling of years before 1000AD (#1654)

* fix: Improve spanner.date handling of years before 1000AD

* fix: linting and code comment for date return

src/codec.ts

@@ -92,24 +92,19 @@ export class SpannerDate extends Date {
   }
   /**
    * Returns the date in ISO date format.
-   * `YYYY-[M]M-[D]D`
+   * `YYYY-MM-DD`
    *
    * @returns {string}
    */
   toJSON(): string {
-    const year = this.getFullYear();
-    let month = (this.getMonth() + 1).toString();
-    let date = this.getDate().toString();
-
-    if (month.length === 1) {
-      month = `0${month}`;
-    }
-
-    if (date.length === 1) {
-      date = `0${date}`;
-    }
-
-    return `${year}-${month}-${date}`;
+    const year = this.getFullYear().toString();
+    const month = (this.getMonth() + 1).toString();
+    const date = this.getDate().toString();
+
+    return `${year.padStart(4, '0')}-${month.padStart(2, '0')}-${date.padStart(
+      2,
+      '0'
+    )}`;
   }
 }
 

test/codec.ts

@@ -50,6 +50,13 @@ describe('codec', () => {
         assert.strictEqual(json, '1986-03-22');
       });
 
+      it('should accept dates before 1000AD', () => {
+        const date = new codec.SpannerDate('2-25-985');
+        const json = date.toJSON();
+
+        assert.strictEqual(json, '0985-02-25');
+      });
+
       it('should default to the current local date', () => {
         const date = new codec.SpannerDate();
         const today = new Date();
@@ -118,6 +125,24 @@ describe('codec', () => {
         const json = date.toJSON();
         assert.strictEqual(json, '1999-12-03');
       });
+
+      it('should pad single digit years', () => {
+        (date.getFullYear as sinon.SinonStub).returns(5);
+        const json = date.toJSON();
+        assert.strictEqual(json, '0005-12-31');
+      });
+
+      it('should pad double digit years', () => {
+        (date.getFullYear as sinon.SinonStub).returns(52);
+        const json = date.toJSON();
+        assert.strictEqual(json, '0052-12-31');
+      });
+
+      it('should pad triple digit years', () => {
+        (date.getFullYear as sinon.SinonStub).returns(954);
+        const json = date.toJSON();
+        assert.strictEqual(json, '0954-12-31');
+      });
     });
   });