feat: Add String type (#29)

Author: bbernays

.gitignore

@@ -131,3 +131,4 @@ dist
 
 # Editor settings
 .idea
+.vscode

src/scalar/text.test.ts

@@ -0,0 +1,33 @@
+import { DataType } from '@apache-arrow/esnext-esm';
+import test from 'ava';
+
+import { Text } from './text.js';
+
+// eslint-disable-next-line unicorn/no-null
+[null, undefined].forEach((v) => {
+  test(`should set values to empty string when ${v} is passed`, (t) => {
+    const s = new Text(v);
+    t.is(s.value, '');
+    t.is(s.valid, false);
+    t.true(DataType.isUtf8(s.dataType));
+  });
+});
+
+[
+  { value: '', expected: '' },
+  { value: 'test string', expected: 'test string' },
+  { value: String('new string object'), expected: 'new string object' },
+  { value: new Text('new text object'), expected: 'new text object' },
+  { value: new TextEncoder().encode('test'), expected: 'test' },
+].forEach(({ value, expected }, index) => {
+  test(`valid strings: '${value}' (${index})`, (t) => {
+    const s = new Text(value);
+    t.is(s.valid, true);
+    t.is(s.value, expected);
+    t.true(DataType.isUtf8(s.dataType));
+  });
+});
+
+test('should throw when unable to set value', (t) => {
+  t.throws(() => new Text({ value: {} }), { message: "Unable to set '[object Object]' as Text" });
+});

src/scalar/text.ts

@@ -0,0 +1,61 @@
+import { Utf8 as ArrowString } from '@apache-arrow/esnext-esm';
+
+import { Scalar } from './scalar.js';
+import { isInvalid, NULL_VALUE } from './util.js';
+
+export class Text implements Scalar<string> {
+  private _valid = false;
+  private _value = '';
+
+  public constructor(v: unknown) {
+    this.value = v;
+    return this;
+  }
+
+  public get dataType() {
+    return new ArrowString();
+  }
+
+  public get valid(): boolean {
+    return this._valid;
+  }
+
+  public get value(): string {
+    return this._value;
+  }
+
+  public set value(value: unknown) {
+    if (isInvalid(value)) {
+      this._valid = false;
+      return;
+    }
+
+    if (typeof value === 'string') {
+      this._value = value;
+      this._valid = true;
+      return;
+    }
+
+    if (value instanceof Uint8Array) {
+      this._value = new TextDecoder().decode(value);
+      this._valid = true;
+      return;
+    }
+
+    if (typeof value!.toString === 'function' && value!.toString !== Object.prototype.toString) {
+      this._value = value!.toString();
+      this._valid = true;
+      return;
+    }
+
+    throw new Error(`Unable to set '${value}' as Text`);
+  }
+
+  public toString() {
+    if (this._valid) {
+      return this._value.toString();
+    }
+
+    return NULL_VALUE;
+  }
+}