package authelia

import (
	"crypto/rand"
	"encoding/base64"
	"fmt"
	"os"
	"sort"

	"golang.org/x/crypto/argon2"
	"gopkg.in/yaml.v3"

	"github.com/wild-cloud/wild-central/internal/storage"
)

// User represents an Authelia user account
type User struct {
	Username    string   `json:"username" yaml:"-"`
	Displayname string   `json:"displayname" yaml:"displayname"`
	Password    string   `json:"password,omitempty" yaml:"password"` // argon2id hash (cleartext on create, never returned)
	Email       string   `json:"email,omitempty" yaml:"email,omitempty"`
	Groups      []string `json:"groups,omitempty" yaml:"groups,omitempty"`
	Disabled    bool     `json:"disabled,omitempty" yaml:"disabled,omitempty"`
}

// UserUpdate holds partial updates for a user
type UserUpdate struct {
	Displayname *string  `json:"displayname,omitempty"`
	Password    *string  `json:"password,omitempty"` // cleartext, will be hashed
	Email       *string  `json:"email,omitempty"`
	Groups      []string `json:"groups,omitempty"`
	Disabled    *bool    `json:"disabled,omitempty"`
}

// usersDB is the top-level structure of Authelia's users_database.yml
type usersDB struct {
	Users map[string]*userEntry `yaml:"users"`
}

type userEntry struct {
	Displayname string   `yaml:"displayname"`
	Password    string   `yaml:"password"`
	Email       string   `yaml:"email,omitempty"`
	Groups      []string `yaml:"groups,omitempty"`
	Disabled    bool     `yaml:"disabled,omitempty"`
}

// ListUsers returns all users from the database (passwords omitted)
func (m *Manager) ListUsers() ([]User, error) {
	db, err := m.readUsersDB()
	if err != nil {
		return nil, err
	}

	var users []User
	for name, entry := range db.Users {
		users = append(users, User{
			Username:    name,
			Displayname: entry.Displayname,
			Email:       entry.Email,
			Groups:      entry.Groups,
			Disabled:    entry.Disabled,
		})
	}

	sort.Slice(users, func(i, j int) bool {
		return users[i].Username < users[j].Username
	})
	return users, nil
}

// CreateUser adds a new user with an argon2id-hashed password
func (m *Manager) CreateUser(user User) error {
	if user.Username == "" {
		return fmt.Errorf("username is required")
	}
	if user.Password == "" {
		return fmt.Errorf("password is required")
	}

	lockPath := m.usersDBPath() + ".lock"
	return storage.WithLock(lockPath, func() error {
		db, err := m.readUsersDB()
		if err != nil {
			return err
		}

		if _, exists := db.Users[user.Username]; exists {
			return fmt.Errorf("user %q already exists", user.Username)
		}

		hash, err := hashPassword(user.Password)
		if err != nil {
			return fmt.Errorf("hashing password: %w", err)
		}

		db.Users[user.Username] = &userEntry{
			Displayname: user.Displayname,
			Password:    hash,
			Email:       user.Email,
			Groups:      user.Groups,
			Disabled:    user.Disabled,
		}

		return m.writeUsersDB(db)
	})
}

// UpdateUser applies partial updates to an existing user
func (m *Manager) UpdateUser(username string, updates UserUpdate) error {
	lockPath := m.usersDBPath() + ".lock"
	return storage.WithLock(lockPath, func() error {
		db, err := m.readUsersDB()
		if err != nil {
			return err
		}

		entry, exists := db.Users[username]
		if !exists {
			return fmt.Errorf("user %q not found", username)
		}

		if updates.Displayname != nil {
			entry.Displayname = *updates.Displayname
		}
		if updates.Email != nil {
			entry.Email = *updates.Email
		}
		if updates.Disabled != nil {
			entry.Disabled = *updates.Disabled
		}
		if updates.Groups != nil {
			entry.Groups = updates.Groups
		}
		if updates.Password != nil {
			hash, err := hashPassword(*updates.Password)
			if err != nil {
				return fmt.Errorf("hashing password: %w", err)
			}
			entry.Password = hash
		}

		return m.writeUsersDB(db)
	})
}

// DeleteUser removes a user from the database
func (m *Manager) DeleteUser(username string) error {
	lockPath := m.usersDBPath() + ".lock"
	return storage.WithLock(lockPath, func() error {
		db, err := m.readUsersDB()
		if err != nil {
			return err
		}

		if _, exists := db.Users[username]; !exists {
			return fmt.Errorf("user %q not found", username)
		}

		delete(db.Users, username)
		return m.writeUsersDB(db)
	})
}

// UserCount returns the number of users in the database
func (m *Manager) UserCount() int {
	db, err := m.readUsersDB()
	if err != nil {
		return 0
	}
	return len(db.Users)
}

// EnsureUsersDB creates an empty users database file if one doesn't exist
func (m *Manager) EnsureUsersDB() error {
	if _, err := os.Stat(m.usersDBPath()); err == nil {
		return nil
	}
	db := &usersDB{Users: map[string]*userEntry{}}
	return m.writeUsersDB(db)
}

func (m *Manager) readUsersDB() (*usersDB, error) {
	data, err := os.ReadFile(m.usersDBPath())
	if err != nil {
		if os.IsNotExist(err) {
			return &usersDB{Users: map[string]*userEntry{}}, nil
		}
		return nil, fmt.Errorf("reading users db: %w", err)
	}

	db := &usersDB{Users: map[string]*userEntry{}}
	if err := yaml.Unmarshal(data, db); err != nil {
		return nil, fmt.Errorf("parsing users db: %w", err)
	}
	if db.Users == nil {
		db.Users = map[string]*userEntry{}
	}
	return db, nil
}

func (m *Manager) writeUsersDB(db *usersDB) error {
	data, err := yaml.Marshal(db)
	if err != nil {
		return fmt.Errorf("marshaling users db: %w", err)
	}

	tmpPath := m.usersDBPath() + ".tmp"
	if err := os.WriteFile(tmpPath, data, 0600); err != nil {
		return fmt.Errorf("writing temp users db: %w", err)
	}
	if err := os.Rename(tmpPath, m.usersDBPath()); err != nil {
		os.Remove(tmpPath)
		return fmt.Errorf("installing users db: %w", err)
	}
	return nil
}

// hashPassword creates an argon2id hash in Authelia's expected format.
// Parameters tuned for Raspberry Pi: memory=64MB, iterations=3, parallelism=2.
func hashPassword(password string) (string, error) {
	salt := make([]byte, 16)
	if _, err := rand.Read(salt); err != nil {
		return "", fmt.Errorf("generating salt: %w", err)
	}

	const (
		memory     = 64 * 1024 // 64MB
		iterations = 3
		parallel   = 2
		keyLen     = 32
	)

	hash := argon2.IDKey([]byte(password), salt, iterations, memory, uint8(parallel), keyLen)

	// Authelia expects: $argon2id$v=19$m=65536,t=3,p=2$<base64-salt>$<base64-hash>
	saltB64 := base64.RawStdEncoding.EncodeToString(salt)
	hashB64 := base64.RawStdEncoding.EncodeToString(hash)

	return fmt.Sprintf("$argon2id$v=19$m=%d,t=%d,p=%d$%s$%s",
		memory, iterations, parallel, saltB64, hashB64), nil
}