package main

import (
	"database/sql"
	"embed"
	"encoding/json"
	"fmt"
	"io/fs"
	"log"
	"net/http"
	"os"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/google/uuid"
	_ "github.com/mattn/go-sqlite3"
)

//go:embed frontend/dist
var staticFiles embed.FS

// ==== Models ====

type Checklist struct {
	UUID string `json:"uuid"`
	Name string `json:"name"`
}

type ChecklistItem struct {
	ID        int        `json:"id"`
	Content   string     `json:"content"`
	Checked   bool       `json:"checked"`
	ParentID  *int       `json:"parent_id"`
	LockedBy  *string    `json:"locked_by,omitempty"`
	LockUntil *time.Time `json:"lock_until,omitempty"`
	Checklist string     `json:"checklist_uuid"`
}

type ItemLock struct {
	LockedBy      string
	Expires       time.Time
	ChecklistUUID string
}

// ==== Globals ====
var (
	db              *sql.DB
	sseClients      = make(map[string]map[chan string]bool) // checklist uuid → set of client channels
	sseClientsMutex sync.Mutex
	itemLocks       = make(map[int]*ItemLock) // item ID → lock
	itemLocksMutex  sync.Mutex
)

// ==== Database ====

func setupDatabase() error {
	var err error
	db, err = sql.Open("sqlite3", "data/checklists.db")
	if err != nil {
		return err
	}
	queries := []string{
		`CREATE TABLE IF NOT EXISTS checklists (
			uuid TEXT PRIMARY KEY,
			name TEXT NOT NULL
		);`,
		`CREATE TABLE IF NOT EXISTS items (
			id INTEGER PRIMARY KEY AUTOINCREMENT,
			content TEXT NOT NULL,
			checked INTEGER NOT NULL,
			parent_id INTEGER,
			checklist_uuid TEXT NOT NULL,
			FOREIGN KEY(parent_id) REFERENCES items(id),
			FOREIGN KEY(checklist_uuid) REFERENCES checklists(uuid)
		);`,
	}
	for _, q := range queries {
		if _, err := db.Exec(q); err != nil {
			return err
		}
	}
	return nil
}

func loadChecklistName(uuid string) (string, error) {
	rows, err := db.Query(
		`SELECT name FROM checklists WHERE uuid = ?`,
		uuid)
	if err != nil {
		return "", err
	}
	defer rows.Close()
	if rows.Next() {
		var name string
		err = rows.Scan(&name)
		if err != nil {
			return "", err
		}
		return name, nil
	}
	return "", fmt.Errorf("not found")
}

func loadChecklistItems(uuid string) ([]ChecklistItem, error) {
	rows, err := db.Query(
		`SELECT id, content, checked, parent_id FROM items WHERE checklist_uuid = ?`,
		uuid)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var items []ChecklistItem
	for rows.Next() {
		var it ChecklistItem
		var checked int
		var parentID sql.NullInt64
		err = rows.Scan(&it.ID, &it.Content, &checked, &parentID)
		if err != nil {
			return nil, err
		}
		it.Checked = checked != 0
		if parentID.Valid {
			v := int(parentID.Int64)
			it.ParentID = &v
		}
		it.Checklist = uuid

		// Attach lock info if present
		itemLocksMutex.Lock()
		if lock, ok := itemLocks[it.ID]; ok && lock.Expires.After(time.Now()) {
			it.LockedBy = &lock.LockedBy
			t := lock.Expires
			it.LockUntil = &t
		}
		itemLocksMutex.Unlock()

		items = append(items, it)
	}
	return items, nil
}

func addChecklist(name string) (string, error) {
	uuidStr := uuid.New().String()
	_, err := db.Exec(`INSERT INTO checklists (uuid, name) VALUES (?, ?)`, uuidStr, name)
	return uuidStr, err
}

func addItem(uuid, content string, parentID *int) (ChecklistItem, error) {
	res, err := db.Exec(`INSERT INTO items (content, checked, parent_id, checklist_uuid) VALUES (?, 0, ?, ?)`,
		content, parentID, uuid)
	if err != nil {
		return ChecklistItem{}, err
	}
	id, _ := res.LastInsertId()
	return ChecklistItem{
		ID:        int(id),
		Content:   content,
		Checked:   false,
		ParentID:  parentID,
		Checklist: uuid,
	}, nil
}

func updateItem(uuid string, id int, content *string, checked *bool, parentID *int) (ChecklistItem, error) {
	q := "UPDATE items SET "
	args := []interface{}{}
	set := []string{}
	if content != nil {
		set = append(set, "content = ?")
		args = append(args, *content)
	}
	if checked != nil {
		set = append(set, "checked = ?")
		if *checked {
			args = append(args, 1)
		} else {
			args = append(args, 0)
		}
	}
	if parentID != nil {
		set = append(set, "parent_id = ?")
		args = append(args, *parentID)
	}
	q += strings.Join(set, ", ") + " WHERE id = ? AND checklist_uuid = ?"
	args = append(args, id, uuid)
	_, err := db.Exec(q, args...)
	if err != nil {
		return ChecklistItem{}, err
	}
	// Return updated item
	rows, err := db.Query(
		`SELECT id, content, checked, parent_id FROM items WHERE id = ? AND checklist_uuid = ?`, id, uuid)
	if err != nil {
		return ChecklistItem{}, err
	}
	defer rows.Close()
	if rows.Next() {
		var it ChecklistItem
		var checkedInt int
		var parentID sql.NullInt64
		err = rows.Scan(&it.ID, &it.Content, &checkedInt, &parentID)
		if err != nil {
			return ChecklistItem{}, err
		}
		it.Checked = checkedInt != 0
		if parentID.Valid {
			v := int(parentID.Int64)
			it.ParentID = &v
		}
		it.Checklist = uuid
		return it, nil
	}
	return ChecklistItem{}, fmt.Errorf("not found")
}

func deleteItem(uuid string, id int) error {
	_, err := db.Exec(`DELETE FROM items WHERE id = ? AND checklist_uuid = ?`, id, uuid)
	return err
}

// ==== SSE Broadcast Logic ====

func broadcast(uuid string, msg interface{}) {
	js, _ := json.Marshal(msg)
	sseClientsMutex.Lock()
	for ch := range sseClients[uuid] {
		select {
		case ch <- string(js):
		default:
			// skip if channel is full (consider logging in prod!)
		}
	}
	sseClientsMutex.Unlock()
}

// ==== HTTP Handlers ====

func handleGetItems(w http.ResponseWriter, r *http.Request) {
	uuid := strings.TrimPrefix(r.URL.Path, "/api/checklists/")
	uuid = uuid[:36]
	items, err := loadChecklistItems(uuid)
	if err != nil {
		http.Error(w, "Failed to load items", 500)
		return
	}
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(map[string]interface{}{
		"success": true,
		"message": "Items loaded successfully",
		"items":   items,
	})
}

func handleCreateChecklist(w http.ResponseWriter, r *http.Request) {
	type Req struct {
		Name string `json:"name"`
	}
	var req Req
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil || strings.TrimSpace(req.Name) == "" {
		http.Error(w, "Missing name", 400)
		return
	}
	uuid, err := addChecklist(req.Name)
	if err != nil {
		http.Error(w, "Failed to create checklist", 500)
		return
	}
	w.Header().Set("Content-Type", "application/json")
	resp := map[string]interface{}{
		"success": true,
		"message": "Checklist created successfully",
		"uuid":    uuid,
	}
	json.NewEncoder(w).Encode(resp)
}

func handleAddItem(w http.ResponseWriter, r *http.Request) {
	uuid := strings.TrimPrefix(r.URL.Path, "/api/checklists/")
	uuid = uuid[:36]
	type Req struct {
		Content  string `json:"content"`
		ParentID *int   `json:"parent_id"`
	}
	var req Req
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil || strings.TrimSpace(req.Content) == "" {
		http.Error(w, "Missing content", 400)
		return
	}
	item, err := addItem(uuid, req.Content, req.ParentID)
	if err != nil {
		http.Error(w, "Failed to add item", 500)
		return
	}
	// broadcast
	broadcast(uuid, map[string]interface{}{"type": "item_added", "item": item})
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(201)
	json.NewEncoder(w).Encode(map[string]interface{}{
		"success": true,
		"message": "Item added successfully",
		"item":    item,
	})
}

func handleUpdateItem(w http.ResponseWriter, r *http.Request) {
	parts := strings.Split(r.URL.Path, "/")
	uuid := parts[3]
	id := 0
	fmt.Sscanf(parts[5], "%d", &id)
	type Req struct {
		Content  *string `json:"content"`
		Checked  *bool   `json:"checked"`
		ParentID *int    `json:"parent_id"`
	}
	var req Req
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		http.Error(w, "Bad body", 400)
		return
	}
	item, err := updateItem(uuid, id, req.Content, req.Checked, req.ParentID)
	if err != nil {
		http.Error(w, "Not found", 404)
		return
	}
	broadcast(uuid, map[string]interface{}{"type": "item_updated", "item": item})
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(map[string]interface{}{
		"success": true,
		"message": "Item updated successfully",
		"item":    item,
	})
}

func handleDeleteItem(w http.ResponseWriter, r *http.Request) {
	parts := strings.Split(r.URL.Path, "/")
	uuid := parts[3]
	id := 0
	fmt.Sscanf(parts[5], "%d", &id)
	if err := deleteItem(uuid, id); err != nil {
		http.Error(w, "Delete failed", 500)
		return
	}
	broadcast(uuid, map[string]interface{}{"type": "item_deleted", "id": id})
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(map[string]interface{}{
		"success": true,
		"message": "Item deleted successfully",
		"id":      id,
	})
}

func handleLockItem(w http.ResponseWriter, r *http.Request) {
	parts := strings.Split(r.URL.Path, "/")
	uuid := parts[3]
	id := 0
	fmt.Sscanf(parts[5], "%d", &id)
	type Req struct {
		User string `json:"user"`
	}
	var req Req
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil || strings.TrimSpace(req.User) == "" {
		http.Error(w, "Missing user", 400)
		return
	}
	expiry := time.Now().Add(15 * time.Second) // e.g. 30 sec lock

	itemLocksMutex.Lock()
	itemLocks[id] = &ItemLock{LockedBy: req.User, Expires: expiry, ChecklistUUID: uuid}
	itemLocksMutex.Unlock()

	// Broadcast lock
	broadcast(uuid, map[string]interface{}{"type": "item_locked", "id": id, "locked_by": req.User, "expires": expiry})
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(map[string]interface{}{
		"success":   true,
		"message":   "Item locked successfully",
		"id":        id,
		"locked_by": req.User,
		"expires":   expiry,
	})
}

func lockExpiryDaemon() {
	for {
		time.Sleep(1 * time.Second)
		now := time.Now()

		// Collect expired locks first
		var expiredLocks []struct {
			id   int
			uuid string
		}

		itemLocksMutex.Lock()
		for id, lock := range itemLocks {
			if lock.Expires.Before(now) {
				expiredLocks = append(expiredLocks, struct {
					id   int
					uuid string
				}{id: id, uuid: lock.ChecklistUUID})
				delete(itemLocks, id)
			}
		}
		itemLocksMutex.Unlock()

		// Broadcast unlock events after releasing the mutex
		for _, expired := range expiredLocks {
			broadcast(expired.uuid, map[string]interface{}{
				"type": "item_unlocked",
				"id":   expired.id,
			})
		}
	}
}

func handleSSE(w http.ResponseWriter, r *http.Request) {
	uuid := strings.TrimPrefix(r.URL.Path, "/api/checklists/")
	uuid = uuid[:36]

	flusher, ok := w.(http.Flusher)
	if !ok {
		http.Error(w, "Streaming unsupported", http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "text/event-stream")
	w.Header().Set("Cache-Control", "no-cache")
	w.Header().Set("Connection", "keep-alive")

	ch := make(chan string, 20)
	// Register client
	sseClientsMutex.Lock()
	if sseClients[uuid] == nil {
		sseClients[uuid] = make(map[chan string]bool)
	}
	sseClients[uuid][ch] = true
	sseClientsMutex.Unlock()
	defer func() {
		sseClientsMutex.Lock()
		delete(sseClients[uuid], ch)
		sseClientsMutex.Unlock()
		close(ch)
	}()

	// Send full state on connect
	items, err := loadChecklistItems(uuid)
	name, err2 := loadChecklistName(uuid)
	if err == nil && err2 == nil {
		msg, _ := json.Marshal(map[string]interface{}{
			"type":  "full_state",
			"items": items,
		})
		fmt.Fprintf(w, "data: %s\n\n", msg)
		flusher.Flush()
		msg, _ = json.Marshal(map[string]interface{}{
			"type": "checklist_name",
			"name": name,
		})
		fmt.Fprintf(w, "data: %s\n\n", msg)
		flusher.Flush()
	}

	// Forward events
	for {
		select {
		case ev := <-ch:
			fmt.Fprintf(w, "data: %s\n\n", ev)
			flusher.Flush()
		case <-r.Context().Done():
			return
		}
	}
}

// ==== Main + Routing ====

func main() {
	if err := setupDatabase(); err != nil {
		log.Fatalf("DB setup: %v", err)
	}
	go lockExpiryDaemon()

	// Serve static files from embedded filesystem
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		// Check if this is a UUID path (starts with / followed by 36 characters)
		isUUIDPath := len(r.URL.Path) == 37 && r.URL.Path[0] == '/' &&
			!strings.Contains(r.URL.Path[1:], "/")

		if r.URL.Path == "/" || isUUIDPath {
			// Serve index.html at root or for routes with /{uuid}
			content, err := staticFiles.ReadFile("frontend/dist/index.html")
			if err != nil {
				http.Error(w, "Not found", 404)
				return
			}
			w.Header().Set("Content-Type", "text/html")
			w.Write(content)
		} else {
			// Serve other static files from the static/ subdirectory
			subFS, err := fs.Sub(staticFiles, "frontend/dist")
			if err != nil {
				http.Error(w, "Not found", 404)
				return
			}
			http.StripPrefix("/", http.FileServer(http.FS(subFS))).ServeHTTP(w, r)
		}
	})

	http.HandleFunc("/api/checklists", func(w http.ResponseWriter, r *http.Request) {
		if r.Method == "POST" {
			handleCreateChecklist(w, r)
		} else {
			http.NotFound(w, r)
		}
	})

	http.HandleFunc("/api/checklists/", func(w http.ResponseWriter, r *http.Request) {
		path := r.URL.Path
		switch {
		case strings.HasSuffix(path, "/items") && r.Method == "GET":
			handleGetItems(w, r)
		case strings.HasSuffix(path, "/items") && r.Method == "POST":
			handleAddItem(w, r)
		case strings.Contains(path, "/items/") && strings.HasSuffix(path, "/lock") && r.Method == "POST":
			handleLockItem(w, r)
		case strings.Contains(path, "/items/") && r.Method == "PATCH":
			handleUpdateItem(w, r)
		case strings.Contains(path, "/items/") && r.Method == "DELETE":
			handleDeleteItem(w, r)
		case strings.HasSuffix(path, "/sse") && r.Method == "GET":
			handleSSE(w, r)
		default:
			http.NotFound(w, r)
		}
	})

	port := strings.TrimSpace(os.Getenv("PORT"))
	if port == "" {
		port = "8080"
	}
	parsedPort, err := strconv.Atoi(port)
	if err != nil {
		log.Fatalf("Invalid PORT environment variable: %v", err)
	}

	log.Printf("Listening on :%d", parsedPort)
	log.Printf("Frontend available at: http://localhost:%d", parsedPort)
	log.Fatal(http.ListenAndServe(":"+port, nil))
}