[GitHub] kristw commented on a change in pull request #5785: Handle "ambiguous durations"

[GitBox <gi...@apache.org>]

kristw commented on a change in pull request #5785: Handle "ambiguous durations"
URL: https://github.com/apache/incubator-superset/pull/5785#discussion_r214381190
 
 

 ##########
 File path: superset/assets/src/modules/time.js
 ##########
 @@ -1,38 +1,155 @@
 import parseIsoDuration from 'parse-iso-duration';
 
 
+export class IsoDuration {
+  /*
+   * Class that handles ambiguous durations like `P1M` or `P1Y`.
+   */
+
+  constructor(isoDuration) {
+    this.isoDuration = isoDuration;
+
+    // special cases not handled by parse-iso-duration
+    this.pattern = /P(\d+)(M|Y)/;
+
+    this.addTo = this.addTo.bind(this);
+    this.subtractFrom = this.subtractFrom.bind(this);
+    this.operateOn = this.operateOn.bind(this);
+    this.truncate = this.truncate.bind(this);
+    this.explode = this.explode.bind(this);
+  }
+
+  addTo(timestamp) {
+    const op = (a, b) => a + b;
+    return this.operateOn(op, timestamp);
+  }
+
+  subtractFrom(timestamp) {
+    const op = (a, b) => a - b;
+    return this.operateOn(op, timestamp);
+  }
+
+  operateOn(op, timestamp) {
+    try {
+      return op(timestamp, parseIsoDuration(this.isoDuration));
+    } catch (error) {
+      const match = this.pattern.exec(this.isoDuration);
+      if (match === null) {
+        throw error;
+      }
+      const n = parseInt(match[1], 10);  // how many months or years
+
+      const date = new Date(timestamp);
+      let year = date.getFullYear();
+      let month = date.getMonth();
+
+      if (match[2] === 'M') {
+        year = op(year, Math.floor(n / 12));
+        month = op(month, (n % 12));
+        if (month < 0 || month > 11) {
+          month = op(month, -12);
+          year = op(year, 1);
+        }
+      } else if (match[2] === 'Y') {
+        year = op(year, n);
+      } else {
+        throw error;  // should never happen
+      }
+      date.setFullYear(year);
+      date.setMonth(month);
+      return date.getTime();
+    }
+  }
+
+  explode(timestamp) {
+    // Return year, month, day, hour, minute, second, millisecond
+    const date = new Date(timestamp);
+    return [
+      date.getFullYear(),
+      date.getMonth() + 1,  // fuck Javascript
+      date.getDate(),
+      date.getHours(),
+      date.getMinutes(),
+      date.getSeconds(),
+      date.getMilliseconds(),
+    ];
+  }
+
+  truncate(timestamp) {
+    /*
+     * Truncate timestamp down to duration resolution.
+     *
+     *  > const duration = new IsoDuration('PT2H');  // 2 hours
+     *  > const date = new Date('2018-01-01 23:37:00').getTime();
+     *  > new Date(duration.truncate(date));
+     *  Mon Jan 01 2018 22:00:00 GMT
+     */
+    const lowerBound = this.subtractFrom(timestamp);
+    const explodedTimestamp = this.explode(timestamp);
+    const explodedLowerBound = this.explode(lowerBound);
+    let foundDifference = false;
+    const args = [];
+    const first = [1, 1, 1, 0, 0, 0, 0];
+    for (let i = 0; i < explodedTimestamp.length; i++) {
 
 Review comment:
   Avoid naming the variable `args` as it is usually used for the entire function `arguments`.
   
   Can also simplify the code
   
   ```
   const dateParts = explodedTimestamp.map((part, i) => 
     (explodedLowerBound[i] !== part) ? first[i] : part
   );
   return Date.UTC(...dateParts)
   ```

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