feat: watch command execute on successful build

src/commands/build.ts

@@ -7,10 +7,12 @@ import assert from 'node:assert';
 import defaultEsbuild from '../utilities/defaultEsbuildConfig';
 import { require } from '../utilities/require';
 import { pathExists, pathExistsSync } from 'find-up';
-import { mkdir, writeFile, readFile } from 'fs/promises';
+import { mkdir, writeFile } from 'fs/promises';
 import * as Preprocessor from '../utilities/preprocessor';
 import { bold, magentaBright } from 'colorette';
 import { parseTsConfig } from '../utilities/parseTsconfig';
+import { execa, type ExecaChildProcess } from 'execa';
+import { InvalidArgumentError } from 'commander';
 
 const VALID_EXTENSIONS = ['.ts', '.js' ];
 
@@ -49,39 +51,107 @@ type BuildOptions = {
      */
     sourcemap?: boolean;
 
+    watch?: {
+        /**
+         * command to run.
+         * defaults to your package
+         * manager's start command.
+         */
+        command?: string;
+    }
+
 };
 
 const CommandHandlerPlugin = (buildConfig: Partial<BuildOptions>, ambientFilePath: string, sernTsConfigPath: string) => {
     return {
-        name: "commandhandler",
+        name: "commandHandler",
         setup(build) {
 
             const options = build.initialOptions
             const defVersion = () => JSON.stringify(require(p.resolve('package.json')).version);
+            // should fix a type error
             options.define = { 
-                ...buildConfig.define ?? {},
+                ...(buildConfig.define ?? {}),
                 __DEV__: `${buildConfig.mode === 'development'}`,
                 __PROD__: `${buildConfig.mode === 'production'}`,
                 __VERSION__: `${buildConfig.defineVersion ? `${defVersion()}` : 'undefined'}`
-            } ?? {} 
+            }
             Preprocessor.writeTsConfig(buildConfig.format!, sernTsConfigPath, writeFile);
             Preprocessor.writeAmbientFile(ambientFilePath, options.define!, writeFile);
 
         }
     } as esbuild.Plugin
 }
-const resolveBuildConfig = (path: string|undefined, language: string) => {
-    if(language === 'javascript') {
+const CommandOnEndPlugin = (watching: boolean, watchCommand?: string) => {
+    // for some reason it runs the command twice on first build
+    let isFirstBuild = true;
+    let currentProcess: ExecaChildProcess | null = null;
+    let restartTimeout: NodeJS.Timeout | null = null;
+    return {
+        name: 'watchRunCommand',
+        setup(build: esbuild.PluginBuild) {
+            build.onEnd(async (result) => {
+                if (!watching || result.errors.length !== 0) return;
+                if (isFirstBuild === true) {
+                    isFirstBuild = false;
+                    return;
+                }
+                if (watchCommand === '') {
+                    console.log('[watch] no command provided, skipping');
+                    return;
+                }
+
+                if (currentProcess) {
+                    console.log('[watch] stopping previous process...');
+                    currentProcess.cancel()
+                    currentProcess = null;
+                }
+
+                const cmd = watchCommand || (() => {
+                    if (pathExistsSync('package-lock.json')) return 'npm start';
+                    if (pathExistsSync('yarn.lock')) return 'yarn start';
+                    if (pathExistsSync('pnpm-lock.yaml')) return 'pnpm start';
+                    if (pathExistsSync('bun.lockb')) return 'bun start';
+                    if (pathExistsSync('bun.lock')) return 'bun start';
+
+                    throw new Error('[watch] default package manager start command not found');
+                })();
+
+                // Clear any pending restart
+                if (restartTimeout) clearTimeout(restartTimeout);
+
+                console.log('[watch] debouncing command for 1.5 seconds...');
+
+                // Set new debounced timeout
+                restartTimeout = setTimeout(() => {
+                    console.log(`[watch] running command: ${cmd}`);
+                    currentProcess = execa(cmd, { stdio: 'inherit', shell: true });
+                    currentProcess.catch(error => {
+                        if (error.isCanceled) return;
+                        console.error(`[watch] command execution error: ${error.message}`);
+                    });
+                }, 1500);
+            });
+        }
+    } as esbuild.Plugin;
+};
+const resolveBuildConfig = (path: string | undefined, language: string) => {
+    if (language === 'javascript') {
         return path ?? 'jsconfig.json'
     }
     return path ?? 'tsconfig.json'
 }
 
 export async function build(options: Record<string, any>) {
+    //console.log(options)
     if (!options.supressWarnings) {
         console.info(`${magentaBright('EXPERIMENTAL')}: This API has not been stabilized. add -W or --suppress-warnings flag to suppress`);
     }
-    console.log(options)
+    // if watch was not enabled and watchCommand is present
+    if(!options.watch && options.watchCommand) {
+        throw new InvalidArgumentError("enable watch to use --watch-command")
+    }
+
     const sernConfig = await getConfig();
     let buildConfig: BuildOptions; 
     const buildConfigPath = p.resolve(options.project ?? 'sern.build.js');
@@ -94,22 +164,34 @@ export async function build(options: Record<string, any>) {
         sourcemap: options.sourceMaps,
         tsconfig: resolveBuildConfig(options.tsconfig, sernConfig.language),
         env: options.env ?? '.env',
-        include: []
+        include: [],
+        watch: {
+            command: options.watchCommand
+        }
     };
+
+    // merging configuration with sern.build.js, if exists buildConfigPath 
     if (pathExistsSync(buildConfigPath)) {
-        //throwable, buildConfigPath may not exist
-        buildConfig = { ...defaultBuildConfig, ...(await import('file:///' + buildConfigPath)).default };
+        let fileConfig; 
+        try { fileConfig=await import('file:///' + buildConfigPath).then(r=>r.default) }
+        catch(e) { 
+            console.error("Could not find buildConfigPath")
+            throw e;
+        }
+        //throwable, buildConfigPath may not exist, todo, merge
+        buildConfig = { ...defaultBuildConfig, ...fileConfig };
     } else {
         buildConfig = defaultBuildConfig;
         console.log('No build config found, defaulting');
     }
+
     configDotenv({ path: buildConfig.env  });
 
     if (process.env.NODE_ENV) {
         buildConfig.mode = process.env.NODE_ENV as 'production' | 'development';
         console.log(magentaBright('NODE_ENV:'), 'Found NODE_ENV variable, setting `mode` to this.');
     }
-    assert(buildConfig.mode === 'development' || buildConfig.mode === 'production', 'Mode is not `production` or `development`');
+    assert(buildConfig.mode === 'development' || buildConfig.mode === 'production', 'NODE_ENV is not `production` or `development`');
     try {
         let config = await parseTsConfig(buildConfig.tsconfig!);
         config?.extends && console.warn("Extend the generated tsconfig")
@@ -130,7 +212,7 @@ export async function build(options: Record<string, any>) {
     console.log(' ', magentaBright('sourceMaps'), buildConfig.sourcemap);
 
     const sernDir = p.resolve('.sern'),
-          [ambientFilePath, sernTsConfigPath, genDir] = 
+          [ambientFilePath, sernTsConfigPath, genDir] = // resolves the file paths in the .sern dir
           ['ambient.d.ts', 'tsconfig.json', 'generated'].map(f => p.resolve(sernDir, f));
 
     if (!(await pathExists(genDir))) {
@@ -146,14 +228,17 @@ export async function build(options: Record<string, any>) {
     //https://esbuild.github.io/content-types/#tsconfig-json
     const ctx = await esbuild.context({
         entryPoints,
-        plugins: [CommandHandlerPlugin(buildConfig, ambientFilePath, sernTsConfigPath)],
+        plugins: [
+            CommandHandlerPlugin(buildConfig, ambientFilePath, sernTsConfigPath),
+            CommandOnEndPlugin(options.watch, buildConfig.watch?.command)
+        ],
         sourcemap: buildConfig.sourcemap,
         ...defaultEsbuild(buildConfig.format!, buildConfig.tsconfig),
         dropLabels: [buildConfig.mode === 'production' ? '__DEV__' : '__PROD__', ...buildConfig.dropLabels!],
     });
 
     await ctx.rebuild()
-    if(options.watch) {
+    if (options.watch) {
         await ctx.watch()
     } else {
         await ctx.dispose()

src/index.ts

@@ -58,6 +58,7 @@ program
     .option('-f --format [fmt]', 'The module system of your application. `cjs` or `esm`', 'esm')
     .option('-m --mode [mode]', 'the mode for sern to build in. `production` or `development`', 'development')
     .option('-w --watch')
+    .option('--watch-command [cmd]', 'the command for sern to watch. if watch is not enabled, an error is thrown', '')
     .option('-W --suppress-warnings', 'suppress experimental warning')
     .option('-p --project [filePath]', 'build with the provided sern.build file')
     .option('-e --env', 'path to .env file')