import { HttpClient } from '@angular/common/http'
import { Injectable, inject } from '@angular/core'
import {
  QueryClient,
  mutationOptions,
  queryOptions,
} from '@tanstack/angular-query-experimental'

import { lastValueFrom } from 'rxjs'

@Injectable({
  providedIn: 'root',
})
export class TasksService {
  readonly #queryClient = inject(QueryClient) // Manages query state and caching
  readonly #http = inject(HttpClient) // Handles HTTP requests

  /**
   * Fetches all tasks from the API.
   * Returns an observable containing an array of task strings.
   */
  allTasks = (intervalMs: number) =>
    queryOptions({
      queryKey: ['tasks'],
      queryFn: () => {
        return lastValueFrom(this.#http.get<Array<string>>('/api/tasks'))
      },
      refetchInterval: intervalMs,
    })

  /**
   * Creates a mutation for adding a task.
   * On success, invalidates and refetches the "tasks" query cache to update the task list.
   */
  addTask() {
    return mutationOptions({
      mutationFn: (task: string) =>
        lastValueFrom(this.#http.post('/api/tasks', task)),
      mutationKey: ['tasks'],
      onSuccess: () => {
        this.#queryClient.invalidateQueries({ queryKey: ['tasks'] })
      },
    })
  }

  /**
   * Creates a mutation for clearing all tasks.
   * On success, invalidates and refetches the "tasks" query cache to ensure consistency.
   */
  clearAllTasks() {
    return mutationOptions({
      mutationFn: () => lastValueFrom(this.#http.delete('/api/tasks')),
      mutationKey: ['clearTasks'],
      onSuccess: () => {
        this.#queryClient.invalidateQueries({ queryKey: ['tasks'] })
      },
    })
  }
}