Refactor AddTaskHandler and AddTaskToTaskwarrior to improve maintainability and performance

[its-me-abhishek]

Description
The current task creation pipeline (from AddTaskHandler to AddTaskToTaskwarrior) suffers from high memory overhead, unnecessary CLI/DB calls, and a brittle function signature. This refactor targets performance bottlenecks and improves maintainability by consolidating data structures.

Changes Required:

1. Optimize Request Parsing

   • Replace io.ReadAll and json.Unmarshal with json.NewDecoder.
   • Reason: json.NewDecoder streams the request body directly, which is more memory-efficient than reading the entire body into a byte slice before parsing.

2. Check dependencies only when they're not null

existingTasks, err := tw.FetchTasksFromTaskwarrior(email, encryptionSecret, origin, uuid)
		if err != nil {
			if err := utils.ValidateDependencies(depends, ""); err != nil {
				http.Error(w, fmt.Sprintf("Invalid dependencies: %v", err), http.StatusBadRequest)
				return
			}
		} else {
			taskDeps := make([]utils.TaskDependency, len(existingTasks))
			for i, task := range existingTasks {
				taskDeps[i] = utils.TaskDependency{
					UUID:    task.UUID,
					Depends: task.Depends,
					Status:  task.Status,
				}
			}

			if err := utils.ValidateCircularDependencies(depends, "", taskDeps); err != nil {
				http.Error(w, fmt.Sprintf("Invalid dependencies: %v", err), http.StatusBadRequest)
				return
			}
		}

This can prevent the unnecessary fetching of tasks. Which will then reduce the overall response time.

// Only fetch and validate if dependencies exist
if len(requestBody.Depends) > 0 {
    existingTasks, err := tw.FetchTasksFromTaskwarrior(requestBody.Email, ...)
    // ... validation logic
}

3. Parameter Bloat: The function signature currently takes 15 arguments.
   • Fix: Change the signature to accept a models.AddTaskRequestBody. Can use this inside the AddTasktoTW as well as the handler.
   • Exception: dueDateStr should be passed as a second argument since it requires pre-processing/formatting before being sent to the TW CLI.
   • Quite similar to func AddTaskToTaskwarrior(req models.AddTaskRequestBody, dueDateStr string)
   • An alternative could be to compute this dueDateStr directly inside the AddTaskToTaskwarrior function. Making the handler cleaner

Acceptance Criteria

• Handler uses json.NewDecoder.
• Task fetching is skipped if Depends is empty.
• AddTaskToTaskwarrior signature is consolidated.
• Log output is detailed enough to reconstruct a failure without a debugger.
• 100% test coverage on the new logic paths in AddTaskHandler.
• The code is manually reviewed and relevant comments are present inside the code-review.

[Rustix69]

@its-me-abhishek I am picking this issue will raise the PR tommorow EOD.

My Approach :

1. Use json.NewDecoder(r.Body).Decode(&requestBody) instead of io.ReadAll + json.Unmarshal
   More memory efficient streaming parse
2. Add conditional check: Only fetch tasks if len(requestBody.Depends) > 0
   Skips unnecessary Taskwarrior calls when no dependencies exist
3. Change AddTaskToTaskwarrior signature from 15 params to (req models.AddTaskRequestBody, dueDateStr string)
   Consolidates parameters into single struct for cleaner code