feat(validations): add validateOptions module

src/index.js

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+import { validateOptions } from './lib/validate-options';
+
+export default validateOptions;

src/lib/validate-options.js

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+import Ajv from 'ajv';
+
+const validateOptions = (schema, data) => {
+  // This mutates the original data with defaults!
+  const ajv = new Ajv({
+    useDefaults: true,
+    errorDataPath: 'property',
+  });
+  const isValid = ajv.validate(schema, data);
+
+  return {
+    isValid,
+    error: ajv.errors && ajv.errorsText(),
+  };
+};
+
+export default validateOptions;

src/lib/validate-options.test.js

@@ -0,0 +1,129 @@
+import assert from 'assert';
+import validateOptions from './validate-options';
+
+const generateProperties = (entry) => {
+  const ret = {};
+
+  Object.keys(entry).forEach((e) => {
+    ret[e] = {
+      type: ['array', 'string'],
+      items: {
+        type: 'string',
+      },
+    };
+  });
+
+  return ret;
+};
+
+const parsePaths = (entry) => {
+  const ret = {
+    type: ['array', 'object'],
+  };
+
+  if (entry instanceof Object) {
+    ret.additionalProperties = false;
+    ret.properties = generateProperties(entry);
+  } else {
+    ret.items = {
+      type: 'string',
+    };
+  }
+
+  return ret;
+};
+
+const testSchema = ({ entry } = {}) => {
+  return {
+    $schema: 'http://json-schema.org/draft-04/schema#',
+    additionalProperties: false,
+    type: 'object',
+    properties: {
+      styleExtensions: {
+        type: 'array',
+        items: {
+          type: 'string',
+        },
+        default: ['.css'],
+      },
+      minimize: {
+        type: 'boolean',
+      },
+      moduleExtensions: {
+        type: 'array',
+        items: {
+          type: 'string',
+        },
+      },
+      paths: parsePaths(entry),
+      purifyOptions: {
+        type: 'object',
+        properties: {},
+      },
+      verbose: {
+        type: 'boolean',
+      },
+    },
+    required: [
+      'paths',
+    ],
+  };
+};
+
+describe('Validate options', () => {
+  it('fails without a schema and data', () => {
+    assert.throws(
+      () => {
+        validateOptions();
+      },
+      Error,
+    );
+  });
+
+  it('fails with empty data', () => {
+    const result = validateOptions(testSchema());
+
+    assert.ok(!result.isValid);
+    assert.ok(result.error);
+  });
+
+  it('does not fail if paths are provided', () => {
+    const result = validateOptions(testSchema(), { paths: ['./foo'] });
+
+    assert.ok(result.isValid);
+    assert.ok(!result.error);
+  });
+
+  it('does not allow arbitrary properties', () => {
+    const result = validateOptions(testSchema(), { paths: ['./foo'], foobar: ['./foo'] });
+
+    assert.ok(!result.isValid);
+    assert.ok(result.error);
+  });
+
+  it('styleExtensions have defaults', () => {
+    const paths = ['./foo'];
+    const data = { paths };
+
+    const result = validateOptions(testSchema(), data);
+
+    assert.deepEqual(data, { paths, styleExtensions: ['.css'] });
+    assert.ok(!result.error);
+  });
+
+  it('fails without matching path keys', () => {
+    const data = {
+      paths: {
+        a: './foo',
+      },
+    };
+
+    const result = validateOptions(testSchema({
+      entry: {
+        b: './bar',
+      },
+    }), data);
+
+    assert.ok(result.error);
+  });
+});