feat(task): combineEvents

@vates/task/.USAGE.md

@@ -72,3 +72,43 @@ Task.warning(message, data)
 // - progress
 Task.set(property, value)
 ```
+
+### `combineEvents`
+
+Create a consolidated log from individual events.
+
+It can be used directly as an `onProgress` callback:
+
+```js
+import { makeOnProgress } from '@vates/task/combineEvents'
+
+const onProgress = makeOnProgress({
+  // This function is called each time a root task starts.
+  //
+  // It will be called for as many times as there are tasks created with this `onProgress` function.
+  onRootTaskStart(taskLog) {
+    // `taskLog` is an object reflecting the state of this task and all its subtasks,
+    // and will be mutated in real-time to reflect the changes of the task.
+  },
+
+  // This function is called each time a root task ends.
+  onRootTaskEnd(taskLog) {},
+
+  // This function is called each time a root task or a subtask is updated.
+  //
+  // `taskLog.$root` can be used to uncondionally access the root task.
+  onTaskUpdate(taskLog) {},
+})
+
+Task.run({ data: { name: 'my task' }, onProgress }, asyncFn)
+```
+
+It can also be fed event logs directly:
+
+```js
+import { makeOnProgress } from '@vates/task/combineEvents'
+
+const onProgress = makeOnProgress({ onRootTaskStart, onRootTaskEnd, onTaskUpdate })
+
+eventLogs.forEach(onProgress)
+```

@vates/task/README.md

@@ -89,6 +89,46 @@ Task.warning(message, data)
 Task.set(property, value)
 ```
 
+### `combineEvents`
+
+Create a consolidated log from individual events.
+
+It can be used directly as an `onProgress` callback:
+
+```js
+import { makeOnProgress } from '@vates/task/combineEvents'
+
+const onProgress = makeOnProgress({
+  // This function is called each time a root task starts.
+  //
+  // It will be called for as many times as there are tasks created with this `onProgress` function.
+  onRootTaskStart(taskLog) {
+    // `taskLog` is an object reflecting the state of this task and all its subtasks,
+    // and will be mutated in real-time to reflect the changes of the task.
+  },
+
+  // This function is called each time a root task ends.
+  onRootTaskEnd(taskLog) {},
+
+  // This function is called each time a root task or a subtask is updated.
+  //
+  // `taskLog.$root` can be used to uncondionally access the root task.
+  onTaskUpdate(taskLog) {},
+})
+
+Task.run({ data: { name: 'my task' }, onProgress }, asyncFn)
+```
+
+It can also be fed event logs directly:
+
+```js
+import { makeOnProgress } from '@vates/task/combineEvents'
+
+const onProgress = makeOnProgress({ onRootTaskStart, onRootTaskEnd, onTaskUpdate })
+
+eventLogs.forEach(onProgress)
+```
+
 ## Contributions
 
 Contributions are _very_ welcomed, either on the documentation or on

@vates/task/combineEvents.js

@@ -0,0 +1,77 @@
+'use strict'
+
+const assert = require('node:assert').strict
+
+const noop = Function.prototype
+
+function omit(source, keys, target = { __proto__: null }) {
+  for (const key of Object.keys(source)) {
+    if (!keys.has(key)) {
+      target[key] = source[key]
+    }
+  }
+  return target
+}
+
+const IGNORED_START_PROPS = new Set([
+  'end',
+  'infos',
+  'properties',
+  'result',
+  'status',
+  'tasks',
+  'timestamp',
+  'type',
+  'warnings',
+])
+
+exports.makeOnProgress = function ({ onRootTaskEnd = noop, onRootTaskStart = noop, onTaskUpdate = noop }) {
+  const taskLogs = new Map()
+  return function onProgress(event) {
+    const { id, type } = event
+    let taskLog
+    if (type === 'start') {
+      taskLog = omit(event, IGNORED_START_PROPS)
+      taskLog.start = event.timestamp
+      taskLog.status = 'pending'
+      taskLogs.set(id, taskLog)
+
+      const { parentId } = event
+      if (parentId === undefined) {
+        Object.defineProperty(taskLog, '$root', { value: taskLog })
+
+        // start of a root task
+        onRootTaskStart(taskLog)
+      } else {
+        // start of a subtask
+        const parent = taskLogs.get(parentId)
+        assert.notEqual(parent, undefined)
+
+        // inject a (non-enumerable) reference to the parent and the root task
+        Object.defineProperty(taskLog, { $parent: { value: parent }, $root: { value: parent.$root } })
+        ;(parent.tasks ?? (parent.tasks = [])).push(taskLog)
+      }
+    } else {
+      taskLog = taskLogs.get(id)
+      assert.notEqual(taskLog, undefined)
+
+      if (type === 'info' || type === 'warning') {
+        const key = type + 's'
+        const { data, message } = event
+        ;(taskLog[key] ?? (taskLog[key] = [])).push({ data, message })
+      } else if (type === 'property') {
+        ;(taskLog.properties ?? (taskLog.properties = { __proto__: null }))[event.name] = event.value
+      } else if (type === 'end') {
+        taskLog.end = event.timestamp
+        taskLog.result = event.result
+        taskLog.status = event.status
+      }
+
+      if (type === 'end' && taskLog.$root === taskLog) {
+        onRootTaskEnd(taskLog)
+      }
+    }
+
+    onTaskUpdate(taskLog)
+  }
+}

@vates/task/package.json

@@ -19,5 +19,9 @@
   },
   "scripts": {
     "postversion": "npm publish --access public"
+  },
+  "exports": {
+    ".": "./index.js",
+    "./combineEvents": "./combineEvents.js"
   }
 }