catalog-backend/next: add Context

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

plugins/catalog-backend/src/next/Context/BaseContext.ts

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2021 Spotify AB
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { Context, ContextKey } from './types';
+
+/**
+ * A base Context implementation that does not hold any value.
+ */
+export class BaseContext implements Context {
+  getContextValue<T>(key: ContextKey<T>): T {
+    return key.defaultValue;
+  }
+}

plugins/catalog-backend/src/next/Context/ContextWithValue.ts

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2021 Spotify AB
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { BaseContext } from './BaseContext';
+import { Context, ContextKey } from './types';
+
+/**
+ * A Context implementation that holds a single value, optionally extending an existing context.
+ */
+export class ContextWithValue implements Context {
+  static create(key: ContextKey<unknown>, value: unknown, parent?: Context) {
+    return new ContextWithValue(parent ?? new BaseContext(), key, value);
+  }
+
+  private constructor(
+    private readonly parent: Context,
+    private readonly key: ContextKey<unknown>,
+    private readonly value: unknown,
+  ) {}
+
+  getContextValue<T>(key: ContextKey<T>): T {
+    if (this.key === key) {
+      return this.value as T;
+    }
+    return this.parent.getContextValue(key);
+  }
+}

plugins/catalog-backend/src/next/Context/TransactionContext.ts

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2021 Spotify AB
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { Context, ContextKey } from './types';
+import { Knex } from 'knex';
+import { ContextWithValue } from './ContextWithValue';
+
+const transactionContextKey = new ContextKey<Knex.Transaction | undefined>(
+  undefined,
+);
+
+/**
+ * TransactionContext handles the wrapping of a knex transaction in a Context.
+ */
+export class TransactionContext {
+  static create(tx: Knex.Transaction, parent?: Context) {
+    return ContextWithValue.create(transactionContextKey, tx, parent);
+  }
+
+  static getTransaction(context: Context): Knex.Transaction {
+    const transaction = context.getContextValue(transactionContextKey);
+    if (!transaction) {
+      throw new Error(`No transaction available in context`);
+    }
+    return transaction;
+  }
+}

plugins/catalog-backend/src/next/Context/index.ts

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2021 Spotify AB
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export { BaseContext } from './BaseContext';
+export { ContextWithValue } from './ContextWithValue';
+export { TransactionContext } from './TransactionContext';
+export { ContextKey } from './types';
+export type { Context } from './types';

plugins/catalog-backend/src/next/Context/types.ts

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+/*
+ * Copyright 2021 Spotify AB
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export class ContextKey<T> {
+  constructor(readonly defaultValue: T) {}
+}
+
+export interface Context {
+  getContextValue<T>(key: ContextKey<T>): T;
+}