feat(exercises): add solution for 30_task_scheduler (#125)

Author: sidharth-chauhan

internal/exercises/solutions/103_task_scheduler/task_scheduler.go

@@ -0,0 +1,112 @@
+package task_scheduler
+
+import (
+	"fmt"
+	"time"
+)
+
+// Task represents a scheduled job.
+type Task struct {
+	ID        int
+	Name      string
+	Scheduled time.Time
+	Execute   func()
+}
+
+// SchedulerError is a typed error returned by scheduler operations.
+type SchedulerError struct {
+	Code    int
+	Message string
+}
+
+func (e *SchedulerError) Error() string {
+	return fmt.Sprintf("code=%d: %s", e.Code, e.Message)
+}
+
+// TaskScheduler holds scheduled tasks and next ID.
+type TaskScheduler struct {
+	tasks  []*Task
+	nextID int
+}
+
+// NewTaskScheduler initializes and returns a TaskScheduler.
+func NewTaskScheduler() *TaskScheduler {
+	return &TaskScheduler{
+		tasks:  make([]*Task, 0),
+		nextID: 1,
+	}
+}
+
+// AddTask validates input and appends a new task with auto-increment ID.
+// Returns the created Task and nil error on success.
+// If name is empty returns SchedulerError with Code 1.
+func (ts *TaskScheduler) AddTask(name string, scheduled time.Time, execFn func()) (*Task, *SchedulerError) {
+	if name == "" {
+		return nil, &SchedulerError{
+			Code:    1,
+			Message: "task name cannot be empty",
+		}
+	}
+	task := &Task{
+		ID:        ts.nextID,
+		Name:      name,
+		Scheduled: scheduled,
+		Execute:   execFn,
+	}
+	ts.tasks = append(ts.tasks, task)
+	ts.nextID++
+	return task, nil
+}
+
+// GetTask finds a task by ID. If not found returns SchedulerError with Code 2.
+func (ts *TaskScheduler) GetTask(id int) (*Task, *SchedulerError) {
+	for _, t := range ts.tasks {
+		if t.ID == id {
+			return t, nil
+		}
+	}
+	return nil, &SchedulerError{
+		Code:    2,
+		Message: "task not found",
+	}
+}
+
+// TaskIterator iterates over tasks in insertion order.
+type TaskIterator struct {
+	scheduler    *TaskScheduler
+	currentIndex int
+}
+
+// Iterator returns a new TaskIterator for the scheduler.
+func (ts *TaskScheduler) Iterator() *TaskIterator {
+	return &TaskIterator{
+		scheduler:    ts,
+		currentIndex: 0,
+	}
+}
+
+// Next returns the next task and true if available, otherwise nil,false.
+func (it *TaskIterator) Next() (*Task, bool) {
+	if it.scheduler == nil {
+		return nil, false
+	}
+	if it.currentIndex >= len(it.scheduler.tasks) {
+		return nil, false
+	}
+	t := it.scheduler.tasks[it.currentIndex]
+	it.currentIndex++
+	return t, true
+}
+
+// RunScheduledTasks executes tasks whose Scheduled time is <= now.
+// This implementation calls task.Execute synchronously in the current goroutine.
+func (ts *TaskScheduler) RunScheduledTasks() {
+	now := time.Now()
+	for _, t := range ts.tasks {
+		if !t.Scheduled.After(now) {
+			if t.Execute != nil {
+				t.Execute()
+			}
+		}
+	}
+}