package main

import (
	"encoding/json"
	"log"
	"net/http"
	"strconv"
	"sync"
	"time"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"
	"github.com/go-chi/cors"
)

type Task struct {
	ID          int       `json:"id"`
	Title       string    `json:"title"`
	Description string    `json:"description"`
	Status      string    `json:"status"`
	Priority    string    `json:"priority"`
	CreatedAt   time.Time `json:"createdAt"`
	UpdatedAt   time.Time `json:"updatedAt"`
}

type TaskStore struct {
	mu     sync.RWMutex
	tasks  map[int]Task
	nextID int
}

func NewTaskStore() *TaskStore {
	store := &TaskStore{
		tasks:  make(map[int]Task),
		nextID: 1,
	}
	// Add some sample tasks
	store.Create(Task{Title: "Set up project structure", Description: "Initialize the repository with proper folder structure", Status: "completed", Priority: "high"})
	store.Create(Task{Title: "Implement backend API", Description: "Create REST endpoints for task management", Status: "in_progress", Priority: "high"})
	store.Create(Task{Title: "Build frontend UI", Description: "Design and implement the user interface with Next.js", Status: "pending", Priority: "medium"})
	return store
}

func (s *TaskStore) GetAll() []Task {
	s.mu.RLock()
	defer s.mu.RUnlock()
	tasks := make([]Task, 0, len(s.tasks))
	for _, task := range s.tasks {
		tasks = append(tasks, task)
	}
	return tasks
}

func (s *TaskStore) Get(id int) (Task, bool) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	task, ok := s.tasks[id]
	return task, ok
}

func (s *TaskStore) Create(task Task) Task {
	s.mu.Lock()
	defer s.mu.Unlock()
	task.ID = s.nextID
	task.CreatedAt = time.Now()
	task.UpdatedAt = time.Now()
	if task.Status == "" {
		task.Status = "pending"
	}
	if task.Priority == "" {
		task.Priority = "medium"
	}
	s.tasks[s.nextID] = task
	s.nextID++
	return task
}

func (s *TaskStore) Delete(id int) bool {
	s.mu.Lock()
	defer s.mu.Unlock()
	if _, ok := s.tasks[id]; ok {
		delete(s.tasks, id)
		return true
	}
	return false
}

type APIResponse struct {
	Success bool        `json:"success"`
	Data    interface{} `json:"data,omitempty"`
	Error   string      `json:"error,omitempty"`
}

func main() {
	store := NewTaskStore()
	r := chi.NewRouter()

	// Middleware
	r.Use(middleware.Logger)
	r.Use(middleware.Recoverer)
	r.Use(cors.Handler(cors.Options{
		AllowedOrigins:   []string{"http://localhost:3000", "http://frontend:3000", "*"},
		AllowedMethods:   []string{"GET", "POST", "PUT", "DELETE", "OPTIONS"},
		AllowedHeaders:   []string{"Accept", "Authorization", "Content-Type", "X-CSRF-Token"},
		ExposedHeaders:   []string{"Link"},
		AllowCredentials: true,
		MaxAge:           300,
	}))

	// Health check
	r.Get("/health", func(w http.ResponseWriter, r *http.Request) {
		json.NewEncoder(w).Encode(map[string]string{"status": "ok"})
	})

	// API routes
	r.Route("/api", func(r chi.Router) {
		r.Route("/tasks", func(r chi.Router) {
			r.Get("/", func(w http.ResponseWriter, r *http.Request) {
				w.Header().Set("Content-Type", "application/json")
				tasks := store.GetAll()
				json.NewEncoder(w).Encode(APIResponse{Success: true, Data: tasks})
			})

			r.Post("/", func(w http.ResponseWriter, r *http.Request) {
				w.Header().Set("Content-Type", "application/json")
				var task Task
				if err := json.NewDecoder(r.Body).Decode(&task); err != nil {
					w.WriteHeader(http.StatusBadRequest)
					json.NewEncoder(w).Encode(APIResponse{Success: false, Error: "Invalid request body"})
					return
				}
				if task.Title == "" {
					w.WriteHeader(http.StatusBadRequest)
					json.NewEncoder(w).Encode(APIResponse{Success: false, Error: "Title is required"})
					return
				}
				created := store.Create(task)
				w.WriteHeader(http.StatusCreated)
				json.NewEncoder(w).Encode(APIResponse{Success: true, Data: created})
			})

			r.Get("/{id}", func(w http.ResponseWriter, r *http.Request) {
				w.Header().Set("Content-Type", "application/json")
				idStr := chi.URLParam(r, "id")
				id, err := strconv.Atoi(idStr)
				if err != nil {
					w.WriteHeader(http.StatusBadRequest)
					json.NewEncoder(w).Encode(APIResponse{Success: false, Error: "Invalid task ID"})
					return
				}
				task, ok := store.Get(id)
				if !ok {
					w.WriteHeader(http.StatusNotFound)
					json.NewEncoder(w).Encode(APIResponse{Success: false, Error: "Task not found"})
					return
				}
				json.NewEncoder(w).Encode(APIResponse{Success: true, Data: task})
			})

			r.Delete("/{id}", func(w http.ResponseWriter, r *http.Request) {
				w.Header().Set("Content-Type", "application/json")
				idStr := chi.URLParam(r, "id")
				id, err := strconv.Atoi(idStr)
				if err != nil {
					w.WriteHeader(http.StatusBadRequest)
					json.NewEncoder(w).Encode(APIResponse{Success: false, Error: "Invalid task ID"})
					return
				}
				if !store.Delete(id) {
					w.WriteHeader(http.StatusNotFound)
					json.NewEncoder(w).Encode(APIResponse{Success: false, Error: "Task not found"})
					return
				}
				json.NewEncoder(w).Encode(APIResponse{Success: true, Data: map[string]string{"message": "Task deleted"}})
			})
		})
	})

	log.Println("Backend server starting on :8080")
	log.Fatal(http.ListenAndServe(":8080", r))
}