(core) move home server into core

Summary: This moves enough server material into core to run a home server.  The data engine is not yet incorporated (though in manual testing it works when ported).

Test Plan: existing tests pass

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2552

app/common/NumberFormat.ts

@@ -0,0 +1,76 @@
+/**
+ * Here are the most relevant formats we want to support.
+ *   -1234.56     Plain
+ *   -1,234.56    Number (with separators)
+ *   12.34%       Percent
+ *   1.23E3       Scientific
+ *   $(1,234.56)  Accounting
+ *   (1,234.56)   Financial
+ *   -$1,234.56   Currency
+ *
+ * We implement a button-based UI, using one selector button to choose mode:
+ *    none  = NumMode undefined (plain number, no thousand separators)
+ *    `$`   = NumMode 'currency'
+ *    `,`   = NumMode 'decimal' (plain number, with thousand separators)
+ *    `%`   = NumMode 'percent'
+ *    `Exp` = NumMode 'scientific'
+ * A second toggle button is `(-)` for Sign, to use parentheses rather than "-" for negative
+ * numbers. It is Ignored and disabled when mode is 'scientific'.
+ */
+
+import {clamp} from 'app/common/gutil';
+
+// Options for number formatting.
+export type NumMode = 'currency' | 'decimal' | 'percent' | 'scientific';
+export type NumSign = 'parens';
+
+// TODO: In the future, locale should be a value associated with the document or the user.
+const defaultLocale = 'en-US';
+
+// TODO: The currency to use for currency formatting could be made configurable.
+const defaultCurrency = 'USD';
+
+export interface NumberFormatOptions {
+  numMode?: NumMode;
+  numSign?: NumSign;
+  decimals?: number;      // aka minimum fraction digits
+  maxDecimals?: number;
+}
+
+export function buildNumberFormat(options: NumberFormatOptions): Intl.NumberFormat {
+  const nfOptions: Intl.NumberFormatOptions = parseNumMode(options.numMode);
+
+  // numSign is implemented outside of Intl.NumberFormat since the latter's similar 'currencySign'
+  // option is not well-supported, and doesn't apply to non-currency formats.
+
+  if (options.decimals !== undefined) {
+    // Should be at least 0
+    nfOptions.minimumFractionDigits = clamp(Number(options.decimals), 0, 20);
+  }
+
+  // maximumFractionDigits must not be less than the minimum, so we need to know the minimum
+  // implied by numMode.
+  const tmp = new Intl.NumberFormat(defaultLocale, nfOptions).resolvedOptions();
+
+  if (options.maxDecimals !== undefined) {
+    // Should be at least 0 and at least minimumFractionDigits.
+    nfOptions.maximumFractionDigits = clamp(Number(options.maxDecimals), tmp.minimumFractionDigits || 0, 20);
+  } else if (!options.numMode) {
+    // For the default format, keep max digits at 10 as we had before.
+    nfOptions.maximumFractionDigits = clamp(10, tmp.minimumFractionDigits || 0, 20);
+  }
+
+  return new Intl.NumberFormat(defaultLocale, nfOptions);
+}
+
+function parseNumMode(numMode?: NumMode): Intl.NumberFormatOptions {
+  switch (numMode) {
+    case 'currency': return {style: 'currency', currency: defaultCurrency};
+    case 'decimal': return {useGrouping: true};
+    case 'percent': return {style: 'percent'};
+    // TODO 'notation' option (and therefore numMode 'scientific') works on recent Firefox and
+    // Chrome, not on Safari or Node 10.
+    case 'scientific': return {notation: 'scientific'} as Intl.NumberFormatOptions;
+    default: return {useGrouping: false};
+  }
+}