1 files changed, 257 insertions, 0 deletions
diff --git a/src/amounts.ts b/src/amounts.ts
new file mode 100644
index 000000000..a31bec3da
--- /dev/null
+++ b/src/amounts.ts
@@ -0,0 +1,257 @@
+/*
+ This file is part of TALER
+ (C) 2018 GNUnet e.V. and INRIA
+
+ TALER is free software; you can redistribute it and/or modify it under the
+ terms of the GNU General Public License as published by the Free Software
+ Foundation; either version 3, or (at your option) any later version.
+
+ TALER is distributed in the hope that it will be useful, but WITHOUT ANY
+ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License along with
+ TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+
+/**
+ * Types and helper functions for dealing with Taler amounts.
+ */
+
+/**
+ * Imports.
+ */
+import { Checkable } from "./checkable";
+
+/**
+ * Number of fractional units that one value unit represents.
+ */
+export const fractionalBase = 1e8;
+
+/**
+ * Non-negative financial amount.  Fractional values are expressed as multiples
+ * of 1e-8.
+ */
+@Checkable.Class()
+export class AmountJson {
+  /**
+   * Value, must be an integer.
+   */
+  @Checkable.Number
+  readonly value: number;
+
+  /**
+   * Fraction, must be an integer.  Represent 1/1e8 of a unit.
+   */
+  @Checkable.Number
+  readonly fraction: number;
+
+  /**
+   * Currency of the amount.
+   */
+  @Checkable.String
+  readonly currency: string;
+
+  /**
+   * Verify that a value matches the schema of this class and convert it into a
+   * member.
+   */
+  static checked: (obj: any) => AmountJson;
+}
+
+/**
+ * Result of a possibly overflowing operation.
+ */
+export interface Result {
+  /**
+   * Resulting, possibly saturated amount.
+   */
+  amount: AmountJson;
+  /**
+   * Was there an over-/underflow?
+   */
+  saturated: boolean;
+}
+
+/**
+ * Get the largest amount that is safely representable.
+ */
+export function getMaxAmount(currency: string): AmountJson {
+  return {
+    currency,
+    fraction: 2 ** 32,
+    value: Number.MAX_SAFE_INTEGER,
+  };
+}
+
+/**
+ * Get an amount that represents zero units of a currency.
+ */
+export function getZero(currency: string): AmountJson {
+  return {
+    currency,
+    fraction: 0,
+    value: 0,
+  };
+}
+
+/**
+ * Add two amounts.  Return the result and whether
+ * the addition overflowed.  The overflow is always handled
+ * by saturating and never by wrapping.
+ *
+ * Throws when currencies don't match.
+ */
+export function add(first: AmountJson, ...rest: AmountJson[]): Result {
+  const currency = first.currency;
+  let value = first.value + Math.floor(first.fraction / fractionalBase);
+  if (value > Number.MAX_SAFE_INTEGER) {
+    return { amount: getMaxAmount(currency), saturated: true };
+  }
+  let fraction = first.fraction % fractionalBase;
+  for (const x of rest) {
+    if (x.currency !== currency) {
+      throw Error(`Mismatched currency: ${x.currency} and ${currency}`);
+    }
+
+    value = value + x.value + Math.floor((fraction + x.fraction) / fractionalBase);
+    fraction = Math.floor((fraction + x.fraction) % fractionalBase);
+    if (value > Number.MAX_SAFE_INTEGER) {
+      return { amount: getMaxAmount(currency), saturated: true };
+    }
+  }
+  return { amount: { currency, value, fraction }, saturated: false };
+}
+
+/**
+ * Subtract two amounts.  Return the result and whether
+ * the subtraction overflowed.  The overflow is always handled
+ * by saturating and never by wrapping.
+ *
+ * Throws when currencies don't match.
+ */
+export function sub(a: AmountJson, ...rest: AmountJson[]): Result {
+  const currency = a.currency;
+  let value = a.value;
+  let fraction = a.fraction;
+
+  for (const b of rest) {
+    if (b.currency !== currency) {
+      throw Error(`Mismatched currency: ${b.currency} and ${currency}`);
+    }
+    if (fraction < b.fraction) {
+      if (value < 1) {
+        return { amount: { currency, value: 0, fraction: 0 }, saturated: true };
+      }
+      value--;
+      fraction += fractionalBase;
+    }
+    console.assert(fraction >= b.fraction);
+    fraction -= b.fraction;
+    if (value < b.value) {
+      return { amount: { currency, value: 0, fraction: 0 }, saturated: true };
+    }
+    value -= b.value;
+  }
+
+  return { amount: { currency, value, fraction }, saturated: false };
+}
+
+/**
+ * Compare two amounts.  Returns 0 when equal, -1 when a < b
+ * and +1 when a > b.  Throws when currencies don't match.
+ */
+export function cmp(a: AmountJson, b: AmountJson): number {
+  if (a.currency !== b.currency) {
+    throw Error(`Mismatched currency: ${a.currency} and ${b.currency}`);
+  }
+  const av = a.value + Math.floor(a.fraction / fractionalBase);
+  const af = a.fraction % fractionalBase;
+  const bv = b.value + Math.floor(b.fraction / fractionalBase);
+  const bf = b.fraction % fractionalBase;
+  switch (true) {
+    case av < bv:
+      return -1;
+    case av > bv:
+      return 1;
+    case af < bf:
+      return -1;
+    case af > bf:
+      return 1;
+    case af === bf:
+      return 0;
+    default:
+      throw Error("assertion failed");
+  }
+}
+
+/**
+ * Create a copy of an amount.
+ */
+export function copy(a: AmountJson): AmountJson {
+  return {
+    currency: a.currency,
+    fraction: a.fraction,
+    value: a.value,
+  };
+}
+
+/**
+ * Divide an amount.  Throws on division by zero.
+ */
+export function divide(a: AmountJson, n: number): AmountJson {
+  if (n === 0) {
+    throw Error(`Division by 0`);
+  }
+  if (n === 1) {
+    return {value: a.value, fraction: a.fraction, currency: a.currency};
+  }
+  const r = a.value % n;
+  return {
+    currency: a.currency,
+    fraction: Math.floor(((r * fractionalBase) + a.fraction) / n),
+    value: Math.floor(a.value / n),
+  };
+}
+
+/**
+ * Check if an amount is non-zero.
+ */
+export function isNonZero(a: AmountJson): boolean {
+  return a.value > 0 || a.fraction > 0;
+}
+
+/**
+ * Parse an amount like 'EUR:20.5' for 20 Euros and 50 ct.
+ */
+export function parse(s: string): AmountJson|undefined {
+  const res = s.match(/([a-zA-Z0-9_*-]+):([0-9])+([.][0-9]+)?/);
+  if (!res) {
+    return undefined;
+  }
+  return {
+    currency: res[1],
+    fraction: Math.round(fractionalBase * Number.parseFloat(res[3] || "0")),
+    value: Number.parseInt(res[2]),
+  };
+}
+
+/**
+ * Convert the amount to a float.
+ */
+export function toFloat(a: AmountJson): number {
+  return a.value + (a.fraction / fractionalBase);
+}
+
+/**
+ * Convert a float to a Taler amount.
+ * Loss of precision possible.
+ */
+export function fromFloat(floatVal: number, currency: string) {
+  return {
+    currency,
+    fraction: Math.floor((floatVal - Math.floor(floatVal)) * fractionalBase),
+    value: Math.floor(floatVal),
+  };
+}