feat(primitives): implement decimal type

packages/primitives/package.json

@@ -20,9 +20,11 @@
     "test": "jest"
   },
   "devDependencies": {
+    "@types/big.js": "^4.0.5",
     "typescript": "^3.2.2"
   },
   "dependencies": {
+    "big.js": "^5.2.2",
     "fp-ts": "^1.12.3",
     "io-ts": "^1.5.2"
   },

packages/primitives/src/decimal.ts

@@ -0,0 +1,59 @@
+/**
+ * Decimal FHIR Primitive Runtime Type
+ */
+
+import { Big } from "big.js";
+import { Type, success, failure } from "io-ts";
+
+/**
+ * Class that wraps big.js to maintain precision, including trailing zeros
+ */
+export class Decimal extends Big {
+  private dp: number;
+  constructor(n) {
+    super(n);
+    this.dp = this.decimalPlaces(n);
+  }
+
+  public toFixed(dp?: number) {
+    return super.toFixed(this.dp);
+  }
+
+  private decimalPlaces(n: string | number) {
+    // Coerce to string
+    const number = String(n);
+    const hasDecimal = number.includes(".");
+    const exponentialForm = number.includes("e");
+    if (hasDecimal) {
+      if (exponentialForm) {
+        const [mantissa, exponent] = number.split(".")[1].split("e");
+        return mantissa.length - parseInt(exponent);
+      } else {
+        return number.split(".")[1].length;
+      }
+    } else {
+      return 0;
+    }
+  }
+}
+
+export class DecimalType extends Type<Decimal, string, unknown> {
+  readonly _tag: "DecimalType" = "DecimalType";
+  constructor() {
+    super(
+      "decimal",
+      (m): m is Decimal => m instanceof Decimal,
+      (m, c) => {
+        try {
+          const decimal = new Decimal(<any>m);
+          return success(decimal);
+        } catch (e) {
+          return failure(m, c);
+        }
+      },
+      a => a.toFixed()
+    );
+  }
+}
+
+export const decimal = new DecimalType();

packages/primitives/src/index.ts

@@ -3,7 +3,17 @@
  */
 
 import { BooleanType, boolean } from "./boolean";
+import { DecimalType, decimal } from "./decimal";
 import { IntegerType, integer } from "./integer";
 import { StringType, string } from "./string";
 
-export { BooleanType, boolean, IntegerType, integer, StringType, string };
+export {
+  boolean,
+  BooleanType,
+  decimal,
+  DecimalType,
+  integer,
+  IntegerType,
+  string,
+  StringType
+};

packages/primitives/test/decimal.test.ts

@@ -0,0 +1,40 @@
+/**
+ * Tests for Decimal Runtime Type
+ */
+
+import { assertSuccess, assertFailure } from "./helpers";
+import { decimal } from "../src";
+import { Decimal } from "../src/decimal";
+
+describe("DecimalType", () => {
+  it("should succeed validating a valid value", () => {
+    const T = decimal;
+    const input = "1.01";
+    const value = new Decimal(input);
+    assertSuccess(T.decode(input));
+    expect(T.decode(input).value).toEqual(value);
+  });
+
+  it("should successfully maintain precision", () => {
+    const T = decimal;
+    expect(T.decode("1.0100").map(T.encode).value).toEqual("1.0100");
+    expect(T.decode(1.01).map(T.encode).value).toEqual("1.01");
+    expect(T.decode("1.01e2").map(T.encode).value).toEqual("101");
+    expect(T.decode("1.0100e2").map(T.encode).value).toEqual("101.00");
+  });
+
+  it("should fail validating an invalid value", () => {
+    const T = decimal;
+    assertFailure(T.decode("abc"), [
+      'Invalid value "abc" supplied to : decimal'
+    ]);
+  });
+
+  it("should type guard", () => {
+    const T = decimal;
+    const value = new Decimal("1.010");
+    expect(T.is(value)).toEqual(true);
+    expect(T.is("b")).toEqual(false);
+    expect(T.is(undefined)).toEqual(false);
+  });
+});

yarn.lock

@@ -631,6 +631,11 @@
   resolved "https://registry.yarnpkg.com/@nodelib/fs.stat/-/fs.stat-1.1.3.tgz#2b5a3ab3f918cca48a8c754c08168e3f03eba61b"
   integrity sha512-shAmDyaQC4H92APFoIaVDHCx5bStIocgvbwQyxPRrbUY20V1EYTbSDchWbuwlMG3V17cprZhA6+78JfB+3DTPw==
 
+"@types/big.js@^4.0.5":
+  version "4.0.5"
+  resolved "https://registry.yarnpkg.com/@types/big.js/-/big.js-4.0.5.tgz#62c61697646269e39191f24e55e8272f05f21fc0"
+  integrity sha512-D9KFrAt05FDSqLo7PU9TDHfDgkarlwdkuwFsg7Zm4xl62tTNaz+zN+Tkcdx2wGLBbSMf8BnoMhOVeUGUaJfLKg==
+
 "@types/events@*":
   version "1.2.0"
   resolved "https://registry.yarnpkg.com/@types/events/-/events-1.2.0.tgz#81a6731ce4df43619e5c8c945383b3e62a89ea86"
@@ -1111,6 +1116,11 @@ bcrypt-pbkdf@^1.0.0:
   dependencies:
     tweetnacl "^0.14.3"
 
+big.js@^5.2.2:
+  version "5.2.2"
+  resolved "https://registry.yarnpkg.com/big.js/-/big.js-5.2.2.tgz#65f0af382f578bcdc742bd9c281e9cb2d7768328"
+  integrity sha512-vyL2OymJxmarO8gxMr0mhChsO9QGwhynfuu4+MHTAW6czfq9humCB7rKpUjDd9YUiDPU4mzpyupFSvOClAwbmQ==
+
 bin-links@^1.1.2:
   version "1.1.2"
   resolved "https://registry.yarnpkg.com/bin-links/-/bin-links-1.1.2.tgz#fb74bd54bae6b7befc6c6221f25322ac830d9757"
@@ -2184,6 +2194,13 @@ fb-watchman@^2.0.0:
   dependencies:
     bser "^2.0.0"
 
+"fhir-ts-codegen@file:packages/fhir-ts-codegen":
+  version "0.0.6"
+  dependencies:
+    clime "^0.5.9"
+    glob "^7.1.3"
+    ts-simple-ast "^14.4.2"
+
 figgy-pudding@^3.4.1, figgy-pudding@^3.5.1:
   version "3.5.1"
   resolved "https://registry.yarnpkg.com/figgy-pudding/-/figgy-pudding-3.5.1.tgz#862470112901c727a0e495a80744bd5baa1d6790"
@@ -5997,7 +6014,7 @@ tslint-config-prettier@^1.15.0:
   resolved "https://registry.yarnpkg.com/tslint-config-prettier/-/tslint-config-prettier-1.17.0.tgz#946ed6117f98f3659a65848279156d87628c33dc"
   integrity sha512-NKWNkThwqE4Snn4Cm6SZB7lV5RMDDFsBwz6fWUkTxOKGjMx8ycOHnjIbhn7dZd5XmssW3CwqUjlANR6EhP9YQw==
 
-tslint@^5.11.0, tslint@^5.12.1:
+tslint@^5.11.0:
   version "5.12.1"
   resolved "https://registry.yarnpkg.com/tslint/-/tslint-5.12.1.tgz#8cec9d454cf8a1de9b0a26d7bdbad6de362e52c1"
   integrity sha512-sfodBHOucFg6egff8d1BvuofoOQ/nOeYNfbp7LDlKBcLNrL3lmS5zoiDGyOMdT7YsEXAwWpTdAHwOGOc8eRZAw==