package handler

import (
	"encoding/json"
	"net/http"
	"time"

	"gitea.kleinsense.nl/DariusKlein/kleinTodo/common"
	"gitea.kleinsense.nl/DariusKlein/kleinTodo/common/jwt"
)

func SyncHandler(w http.ResponseWriter, r *http.Request) {
	// 1. Setup: Auth, Decode, Database Connection
	user, err := jwt.GetVerifiedUser(r)
	if handleError(w, http.StatusUnauthorized, err) {
		return
	}

	var todoList common.TodoList
	if handleError(w, http.StatusBadRequest, json.NewDecoder(r.Body).Decode(&todoList)) {
		return
	}

	store, err := common.GetTodoDataStore()
	if handleError(w, http.StatusInternalServerError, err) {
		return
	}

	// 2. Load Server State
	serverTodos := store.GetTodoMap(user)
	response := common.SyncResponse{
		SyncedTodos:      []common.Todo{},
		MisMatchingTodos: []common.MisMatchingTodo{},
	}

	// 3. Process Client Updates
	for _, clientTodo := range todoList.Todos {

		// Default to "Now"
		if clientTodo.LastModified.IsZero() {
			clientTodo.LastModified = time.Now().UTC()
		}

		serverTodo, exists := serverTodos[clientTodo.Id]

		// New Item (Does not exist on server)
		if !exists {
			if clientTodo.Deleted {
				continue // Ignore deleted items that don't exist
			}

			if handleError(w, http.StatusInternalServerError, clientTodo.Store(store, user)) {
				return
			}
			// Add to map so it gets returned in the "Synced" list
			serverTodos[clientTodo.Id] = clientTodo
			continue
		}

		// Item is deleted (Client wants to delete)
		if clientTodo.Deleted {
			// Only delete if client is newer than server
			if clientTodo.LastModified.After(serverTodo.LastModified) {
				if handleError(w, http.StatusInternalServerError, store.RemoveValueFromBucket(user, clientTodo.Id)) {
					return
				}
				// Remove from map so it is NOT returned in the "Synced" list
				delete(serverTodos, clientTodo.Id)
			}
			continue
		}

		// Item is updated (Item exists and is not deleted) ---
		if serverTodo.IsEqual(clientTodo) {
			continue
		}

		isMergeable := serverTodo.IsEqualIgnoringStatus(clientTodo) && clientTodo.LastModified.After(serverTodo.LastModified)

		if isMergeable {
			if handleError(w, http.StatusInternalServerError, clientTodo.Store(store, user)) {
				return
			}
			serverTodos[clientTodo.Id] = clientTodo
		} else {
			response.MisMatchingTodos = append(response.MisMatchingTodos, common.MisMatchingTodo{
				ServerTodo: serverTodo,
				LocalTodo:  clientTodo,
			})
			delete(serverTodos, clientTodo.Id)
		}
	}

	// Build Final Response
	for _, todo := range serverTodos {
		response.SyncedTodos = append(response.SyncedTodos, todo)
	}

	w.Header().Set("Content-Type", "application/json")
	handleError(w, http.StatusInternalServerError, json.NewEncoder(w).Encode(response))
}