Add ability to navigate to date

src/App.tsx

@@ -1,6 +1,6 @@
-import React from 'react';
+import React, {FormEvent} from 'react';
 import {Calendar} from './Calendar';
-import {frSupportedYear, gregorianJDN, jdnFrench, Month} from './dates';
+import {endGregorian, frSupportedYear, gregorianJDN, jdnFrench, Month, startGregorian} from './dates';
 
 type YearMonth = {
     year: number;
@@ -21,6 +21,9 @@ function parseURL(): YearMonth | null {
 
 type AppState = YearMonth & {
     todayJDN: number,
+    goYear: string,
+    goMonth: string,
+    goDay: string,
 };
 
 class App extends React.Component<{}, AppState> {
@@ -35,6 +38,9 @@ class App extends React.Component<{}, AppState> {
         this.state = {
             ...(parseURL() || {year, month}),
             todayJDN,
+            goYear: today.getFullYear().toString(),
+            goMonth: (today.getMonth() + 1).toString(),
+            goDay: today.getDate().toString(),
         };
         this.updateURL();
         this.updateStateFromURL = this.updateStateFromURL.bind(this);
@@ -60,6 +66,36 @@ class App extends React.Component<{}, AppState> {
         }
     }
 
+    changeField(field: keyof AppState, event: any) {
+        const change: Partial<AppState> = {};
+        change[field] = event.target.value;
+        this.setState(change);
+    }
+
+    validYear() {
+        return /^-?\d+$/.test(this.state.goYear) && startGregorian.getFullYear() <= +this.state.goYear &&
+            +this.state.goYear <= endGregorian.getFullYear();
+    }
+
+    validMonth() {
+        return /^\d+$/.test(this.state.goMonth) && 1 <= +this.state.goMonth && +this.state.goMonth <= 12;
+    }
+
+    validDay() {
+        return /^\d+$/.test(this.state.goDay) && 1 <= +this.state.goDay && +this.state.goDay <= 31;
+    }
+
+    goToGregorian(event: FormEvent) {
+        event.preventDefault();
+
+        if (!this.validYear() || !this.validMonth() || !this.validDay())
+            return;
+
+        const jdn = gregorianJDN(+this.state.goYear, +this.state.goMonth, +this.state.goDay);
+        const {year, month} = jdnFrench(jdn);
+        this.setState({year, month});
+    }
+
     setState(state: any, callback?: () => void) {
         super.setState(state, () => {
             this.updateURL();
@@ -68,11 +104,30 @@ class App extends React.Component<{}, AppState> {
     }
 
     render() {
-        return <Calendar
+        return <>
+            <Calendar
                 year={this.state.year} month={this.state.month} todayJDN={this.state.todayJDN}
                 onSwitch={(year, month) => {
-                this.setState({year, month})
-            }}/>;
+                    this.setState({year, month});
+                }}/>
+
+            <div className="navigate">
+                <h4>Go to a date</h4>
+                <form className="input-group" onSubmit={this.goToGregorian.bind(this)}>
+                    <span className="input-group-text">Gregorian<span className="hide-small">&nbsp;Date</span></span>
+                    <input type="number" className={`form-control go-year ${this.validYear() ? '' : 'is-invalid'}`}
+                           onChange={this.changeField.bind(this, 'goYear')} value={this.state.goYear}
+                           min={startGregorian.getFullYear()} max={endGregorian.getFullYear()}/>
+                    <input type="number" className={`form-control go-month ${this.validMonth() ? '' : 'is-invalid'}`}
+                           onChange={this.changeField.bind(this, 'goMonth')} value={this.state.goMonth}
+                           min={1} max={12}/>
+                    <input type="number" className={`form-control go-day ${this.validDay() ? '' : 'is-invalid'}`}
+                           onChange={this.changeField.bind(this, 'goDay')} value={this.state.goDay}
+                           min={1} max={31}/>
+                    <button type="submit" className="form-control btn btn-primary go-button">Go</button>
+                </form>
+            </div>
+        </>;
     }
 }
 

src/dates.ts

@@ -107,6 +107,9 @@ export function jdnGregorian(jdn: number): Date {
     return new Date(year, month - 1, day);
 }
 
+export const startGregorian = jdnGregorian(startJD);
+export const endGregorian = jdnGregorian(frJDN(endYear, 13, frIsLeap(endYear) ? 6: 5));
+
 export function jdnFrench(jdn: number): FrenchDate {
     let lo = 0;
     let hi = leaps.length;

src/index.scss

@@ -6,6 +6,7 @@
 @import 'bootstrap/scss/transitions';
 @import 'bootstrap/scss/type';
 @import 'bootstrap/scss/card';
+@import 'bootstrap/scss/forms';
 @import './consts';
 
 body {
@@ -34,6 +35,30 @@ nav.navbar {
   }
 }
 
+@include media-breakpoint-down(sm) {
+  .hide-small {
+    display: none;
+  }
+}
+
+.navigate {
+  max-width: $calendar-width;
+  margin-top: $spacer;
+  @include make-container();
+
+  .go-year {
+    max-width: 7em;
+  }
+
+  .go-month, .go-day {
+    max-width: 5em;
+  }
+
+  .go-button {
+    max-width: 3em;
+  }
+}
+
 .main {
   max-width: $calendar-width;
   margin-top: $spacer;