feat(dates): introduce dateFormatPlaceholder method

The method will return localized format specifier name:
d -> day; M -> mo.; MMMM -> month and etc

Author: ggkrustev

src/dates.js

@@ -1,3 +1,4 @@
 export { default as formatDate } from './dates/format-date';
 export { default as parseDate } from './dates/parse-date';
-export { default as splitDateFormat } from './dates/split-date-format';
+export { default as splitDateFormat } from './dates/split-date-format';
+export { default as dateFormatPlaceholder } from './dates/date-format-placeholder';

src/dates/date-format-placeholder.js

@@ -0,0 +1,88 @@
+import { localeInfo } from '../cldr';
+
+const dateNameType = function(formatLength) {
+    let nameType;
+    if (formatLength <= 3) {
+        nameType = "short";
+    } else if (formatLength === 4) {
+        nameType = "wide";
+    } else {
+        nameType = "narrow";
+    }
+
+    return nameType;
+};
+
+const dateFieldName = function(formatChar) {
+    switch (formatChar) {
+    case 'd':
+    case 'E':
+        return 'day';
+    case 'M':
+    case 'L':
+        return 'month';
+    case 'y':
+        return 'year';
+    case 'h':
+    case 'H':
+        return 'hour';
+    case 'm':
+        return 'minute';
+    case 's':
+        return 'second';
+    case 'a':
+        return 'dayperiod';
+    case 'x':
+    case 'X':
+    case 'z':
+    case 'Z':
+        return 'zone';
+    case 'G':
+        return 'era';
+    case 'c':
+    case 'e':
+        return 'weekday';
+
+    case 'q':
+    case 'Q':
+        return 'quarter';
+    default:
+        return ''; //XXX: Only milliseconds are not handled here!
+    }
+};
+
+const dateFieldDisplayName = function(info, match, matchLength) {
+    const fieldName = dateFieldName(match);
+    const nameType = dateNameType(matchLength);
+    const fieldNameInfo = info.calendar.dateFields[fieldName];
+
+    return fieldNameInfo[nameType] || fieldNameInfo['wide'];
+};
+
+
+export default function(specifier = "", locale = "en") {
+    const info = localeInfo(locale);
+    return dateFieldDisplayName(info, specifier[0], specifier.length);
+}
+
+/*
+//TODO: export in common file
+import datePattern from './date-pattern';
+
+const dateFormatRegExp = /d{1,2}|E{1,6}|e{1,6}|c{3,6}|c{1}|M{1,5}|L{1,5}|y{1,4}|H{1,2}|h{1,2}|m{1,2}|a{1,5}|s{1,2}|S{1,3}|z{1,4}|Z{1,5}|x{1,5}|X{1,5}|G{1,5}|q{1,5}|Q{1,5}|"[^"]*"|'[^']*'/g;
+
+export default function(format, locale = "en") {
+    const info = localeInfo(locale);
+    const pattern = datePattern(format, info);
+    const formatLength = format.length;
+
+    console.log(pattern);
+
+    return pattern.replace(dateFormatRegExp, function(match) {
+        if (match.includes("'") || match.includes("\"")) {
+            return match.slice(1, formatLength - 1);
+        }
+
+        return dateFieldDisplayName(info, match[0], match.length);
+    });
+}*/

test/dates.js

@@ -1,5 +1,5 @@
 import { load, localeInfo, dateFormatNames } from '../src/cldr';
-import { formatDate, parseDate, splitDateFormat } from '../src/dates';
+import { dateFormatPlaceholder, formatDate, parseDate, splitDateFormat } from '../src/dates';
 import { convertTimeZone } from '../src/dates/time-utils';
 import pad from '../src/common/pad';
 
@@ -24,6 +24,68 @@ function date(year, month, day, hour, minute, second, millisecond) {
     return d;
 }
 
+describe('dateFormatPlaceholder', () => {
+    it('should return placeholder for wide year name', () => {
+        expect(dateFormatPlaceholder("yyyy")).toEqual("year");
+    });
+
+    it('should return placeholder for short year name', () => {
+        expect(dateFormatPlaceholder("y")).toEqual("yr.");
+    });
+
+    it('should return placeholder for wide month name', () => {
+        expect(dateFormatPlaceholder("MMMM")).toEqual("month");
+    });
+
+    it('should return placeholder for short month name', () => {
+        expect(dateFormatPlaceholder("M")).toEqual("mo.");
+    });
+
+    it('should return placeholder for wide day name', () => {
+        expect(dateFormatPlaceholder("EEEE", "bg")).toEqual("ден");
+    });
+
+    it('should return placeholder for short day name', () => {
+        expect(dateFormatPlaceholder("d", "bg")).toEqual("д");
+    });
+
+    it('should return placeholder for short hour name', () => {
+        expect(dateFormatPlaceholder("h")).toEqual("hr.");
+        expect(dateFormatPlaceholder("h", "bg")).toEqual("ч");
+    });
+
+    it('should return placeholder for short minute name', () => {
+        expect(dateFormatPlaceholder("m")).toEqual("min.");
+        expect(dateFormatPlaceholder("m", "bg")).toEqual("мин");
+    });
+
+    it('should return placeholder for short second name', () => {
+        expect(dateFormatPlaceholder("s")).toEqual("sec.");
+        expect(dateFormatPlaceholder("s", "bg")).toEqual("с");
+    });
+
+    it('should return placeholder for day period', () => {
+        expect(dateFormatPlaceholder("a")).toEqual("AM/PM");
+    });
+
+    it('should return placeholder for era', () => {
+        expect(dateFormatPlaceholder("G")).toEqual("era");
+    });
+
+    it('should return placeholder for zone', () => {
+        expect(dateFormatPlaceholder("x")).toEqual("time zone");
+        expect(dateFormatPlaceholder("z")).toEqual("time zone");
+    });
+
+    it('should return placeholder for wide quarter name', () => {
+        expect(dateFormatPlaceholder("QQQQ")).toEqual("quarter");
+    });
+
+    it('should return placeholder for short quarter name', () => {
+        expect(dateFormatPlaceholder("q")).toEqual("qtr.");
+    });
+});
+
 describe('date formatting', () => {
     it('returns value if it is not a date', () => {
         expect(formatDate("foo")).toEqual("foo");