refactor: Config persistence architecture

The architecture in the main process is split into 3 main parts:
* services: interfaces for services are injected into the stores through
  the MainEnv interface (for testability)
* services/impl: electron-specific implementations of services
* stores: the actions of the stores can invoke (asynchronous) services

3 files changed, 176 insertions, 0 deletions

diff --git a/packages/main/src/services/ConfigPersistence.ts b/packages/main/src/services/ConfigPersistence.ts
new file mode 100644
index 0000000..f9a82de
--- /dev/null
+++ b/packages/main/src/services/ConfigPersistence.ts
@@ -0,0 +1,36 @@
+/*
+ * Copyright (C)  2021-2022 Kristóf Marussy <kristof@marussy.com>
+ *
+ * This file is part of Sophie.
+ *
+ * Sophie is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { IDisposer } from 'mobx-state-tree';
+import ms from 'ms';
+
+import type { ConfigSnapshotOut } from '../stores/Config';
+
+export const CONFIG_DEBOUNCE_TIME: number = ms('1s');
+
+export type ReadConfigResult = { found: true; data: unknown; } | { found: false; };
+
+export interface ConfigPersistence {
+  readConfig(): Promise<ReadConfigResult>;
+
+  writeConfig(configSnapshot: ConfigSnapshotOut): Promise<Date>;
+
+  watchConfig(callback: (mtime: Date) => Promise<void>): IDisposer;
+}
diff --git a/packages/main/src/services/MainEnv.ts b/packages/main/src/services/MainEnv.ts
new file mode 100644
index 0000000..23ee9a1
--- /dev/null
+++ b/packages/main/src/services/MainEnv.ts
@@ -0,0 +1,38 @@
+/*
+ * Copyright (C)  2021-2022 Kristóf Marussy <kristof@marussy.com>
+ *
+ * This file is part of Sophie.
+ *
+ * Sophie is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { IAnyStateTreeNode, getEnv as getAnyEnv } from 'mobx-state-tree';
+
+import type { ConfigPersistence } from './ConfigPersistence';
+
+export interface MainEnv {
+  configPersistence: ConfigPersistence;
+}
+
+/**
+ * Gets a well-typed environment from `model`.
+ *
+ * Only useable inside state trees created by `createAndConnectRootStore`.
+ *
+ * @param model The state tree node.
+ */
+export function getEnv(model: IAnyStateTreeNode): MainEnv {
+  return getAnyEnv<MainEnv>(model);
+}
diff --git a/packages/main/src/services/impl/ConfigPersistenceImpl.ts b/packages/main/src/services/impl/ConfigPersistenceImpl.ts
new file mode 100644
index 0000000..097ab74
--- /dev/null
+++ b/packages/main/src/services/impl/ConfigPersistenceImpl.ts
@@ -0,0 +1,102 @@
+/*
+ * Copyright (C)  2021-2022 Kristóf Marussy <kristof@marussy.com>
+ *
+ * This file is part of Sophie.
+ *
+ * Sophie is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { watch } from 'fs';
+import { readFile, stat, writeFile } from 'fs/promises';
+import JSON5 from 'json5';
+import { throttle } from 'lodash';
+import { IDisposer } from 'mobx-state-tree';
+import { join } from 'path';
+
+import { CONFIG_DEBOUNCE_TIME, ConfigPersistence, ReadConfigResult } from '../ConfigPersistence';
+import type { ConfigSnapshotOut } from  '../../stores/Config';
+
+export class ConfigPersistenceImpl implements ConfigPersistence {
+  readonly #userDataDir: string;
+
+  readonly #configFileName: string;
+
+  readonly #configFilePath: string;
+
+  constructor(
+    userDataDir: string,
+    configFileName: string,
+  ) {
+    this.#userDataDir = userDataDir;
+    this.#configFileName = configFileName;
+    this.#configFilePath = join(this.#userDataDir, this.#configFileName);
+  }
+
+  async readConfig(): Promise<ReadConfigResult> {
+    let configStr;
+    try {
+      configStr = await readFile(this.#configFilePath, 'utf8');
+    } catch (err) {
+      if ((err as NodeJS.ErrnoException).code === 'ENOENT') {
+        return { found: false };
+      }
+      throw err;
+    }
+    return {
+      found: true,
+      data: JSON5.parse(configStr),
+    };
+  }
+
+  async writeConfig(configSnapshot: ConfigSnapshotOut): Promise<Date> {
+    const configJson = JSON5.stringify(configSnapshot, {
+      space: 2,
+    });
+    await writeFile(this.#configFilePath, configJson, 'utf8');
+    const { mtime } = await stat(this.#configFilePath);
+    return mtime;
+  }
+
+  watchConfig(callback: (mtime: Date) => Promise<void>): IDisposer {
+    const configChanged = throttle(async () => {
+      let mtime: Date;
+      try {
+        const stats = await stat(this.#configFilePath);
+        mtime = stats.mtime;
+      } catch (err) {
+        if ((err as NodeJS.ErrnoException).code === 'ENOENT') {
+          return;
+        }
+        throw err;
+      }
+      return callback(mtime);
+    }, CONFIG_DEBOUNCE_TIME);
+
+    const watcher = watch(this.#userDataDir, {
+      persistent: false,
+    });
+
+    watcher.on('change', (eventType, filename) => {
+      if (eventType === 'change'
+        && (filename === this.#configFileName || filename === null)) {
+        configChanged()?.catch((err) => {
+          console.log('Unhandled error while listening for config changes', err);
+        });
+      }
+    });
+
+    return () => watcher.close();
+  }
+}