message-store: add Category class

message-store/category.js

@@ -0,0 +1,24 @@
+const { AssertionError } = require('assert')
+const { StreamName } = require('./stream-name')
+
+exports.createCategory = (category) => {
+  const commandStreamName = (id, extra = {}) => {
+    if (id === null || id === undefined) {
+      throw new AssertionError({
+        message: 'ID is required to create a command stream name',
+        actual: id,
+        stackStartFn: commandStreamName
+      })
+    }
+
+    const types = extra.types || []
+    if (extra.type) {
+      types.unshift(extra.type)
+    }
+    types.unshift('command')
+
+    return StreamName.create(category, id, { types })
+  }
+
+  return { commandStreamName }
+}

message-store/index.js

@@ -1,4 +1,5 @@
 module.exports = {
+  ...require('./category'),
   ...require('./examples'),
   ...require('./expected-version-error'),
   ...require('./stream-name')

message-store/test/category.test.js

@@ -0,0 +1,73 @@
+const { AssertionError } = require('assert')
+const { createCategory } = require('../category')
+
+const A_CATEGORY = 'SomeCategory'
+const AN_ENTITY_ID = 'abc123'
+
+const catchError = (fn) => {
+  try {
+    fn()
+  } catch (error) {
+    return error
+  }
+}
+
+describe('category', () => {
+  describe('commandStreamName', () => {
+    describe('given no types specified', () => {
+      it('adds "command" type to stream name', () => {
+        const category = createCategory(A_CATEGORY)
+
+        const streamName = category.commandStreamName(AN_ENTITY_ID)
+
+        expect(streamName).toBe('SomeCategory:command-abc123')
+      })
+    })
+
+    describe('given types specified', () => {
+      it('adds "command" and the specified types to stream name', () => {
+        const category = createCategory(A_CATEGORY)
+
+        const types = ['other', 'thang']
+        const streamName = category.commandStreamName(AN_ENTITY_ID, { types })
+
+        expect(streamName).toBe('SomeCategory:command+other+thang-abc123')
+      })
+    })
+
+    describe('given a type is specified', () => {
+      it('adds "command" and the specified type to stream name', () => {
+        const category = createCategory(A_CATEGORY)
+
+        const type = 'other'
+        const streamName = category.commandStreamName(AN_ENTITY_ID, { type })
+
+        expect(streamName).toBe('SomeCategory:command+other-abc123')
+      })
+    })
+
+    describe('when id is null', () => {
+      it('throws an error', () => {
+        const category = createCategory(A_CATEGORY)
+
+        const error = catchError(() => category.commandStreamName(null))
+
+        expect(error).toBeDefined()
+        expect(error).toBeInstanceOf(AssertionError)
+        expect(error.message).toBe('ID is required to create a command stream name')
+      })
+    })
+
+    describe('when id is undefined', () => {
+      it('throws an error', () => {
+        const category = createCategory(A_CATEGORY)
+
+        const error = catchError(() => category.commandStreamName())
+
+        expect(error).toBeDefined()
+        expect(error).toBeInstanceOf(AssertionError)
+        expect(error.message).toBe('ID is required to create a command stream name')
+      })
+    })
+  })
+})