package auth

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"sync"
)

type UserStore struct {
	Path string
	Mu   sync.Mutex
}

type userRecord struct {
	Username string     `json:"username"`
	Password string     `json:"passwordHash"`
	Home     string     `json:"home"`
	Enabled  *bool      `json:"enabled,omitempty"`
	Rules    []userRule `json:"rules,omitempty"`
}

type userRule struct {
	Dir          string `json:"dir"`
	Mask         string `json:"mask"`
	Deny         bool   `json:"deny,omitempty"`
	ChildrenOnly bool   `json:"childrenOnly,omitempty"`
}

var validUsername = regexp.MustCompile("^[A-Za-z0-9][A-Za-z0-9._-]{0,31}$")

func ValidateUsername(username string) error {
	if !validUsername.MatchString(username) {
		return fmt.Errorf("invalid username")
	}
	return nil
}

func unsafeUserPath(p string) bool {
	p = strings.ReplaceAll(p, "\\", "/")
	return p == ".." || strings.HasPrefix(p, "../") || strings.Contains(p, "/../") || strings.HasPrefix(p, "/")
}

func (u *UserStore) Load(m *Manager, homeRoot string) error {
	if u.Path == "" {
		return nil
	}
	data, err := os.ReadFile(u.Path)
	if os.IsNotExist(err) {
		return nil
	}
	if err != nil {
		return err
	}
	var records []userRecord
	if err := json.Unmarshal(data, &records); err != nil {
		return fmt.Errorf("invalid user store: %w", err)
	}
	for _, rec := range records {
		if err := ValidateUsername(rec.Username); err != nil || rec.Password == "" {
			continue
		}
		if _, exists := m.Accounts[rec.Username]; exists {
			continue
		}
		home := filepath.ToSlash(strings.Trim(strings.TrimSpace(rec.Home), "/"))
		if home == "" {
			home = filepath.ToSlash(filepath.Join(homeRoot, rec.Username))
		}
		enabled := true
		if rec.Enabled != nil {
			enabled = *rec.Enabled
		}
		a := &Account{Username: rec.Username, PasswordHash: rec.Password, Mask: None, Home: home, Enabled: enabled}
		if len(rec.Rules) == 0 {
			a.Rules = append(a.Rules, PathRule{Dir: home, Mask: Read | Write | Delete})
		} else {
			for _, rr := range rec.Rules {
				dir := strings.Trim(strings.ReplaceAll(rr.Dir, "\\", "/"), "/")
				if dir == "" || unsafeUserPath(dir) {
					continue
				}
				a.Rules = append(a.Rules, PathRule{Dir: dir, Mask: ParseMask(rr.Mask), Deny: rr.Deny, ChildrenOnly: rr.ChildrenOnly})
			}
		}
		m.Accounts[rec.Username] = a
	}
	return nil
}

func (u *UserStore) Save(m *Manager) error {
	if u.Path == "" {
		return nil
	}
	u.Mu.Lock()
	defer u.Mu.Unlock()
	records := make([]userRecord, 0)
	for _, a := range m.Accounts {
		if a.PasswordHash == "" || a.Home == "" || a.Admin {
			continue
		}
		rec := userRecord{Username: a.Username, Password: a.PasswordHash, Home: a.Home, Enabled: &a.Enabled}
		for _, rr := range a.Rules {
			rec.Rules = append(rec.Rules, userRule{Dir: rr.Dir, Mask: maskString(rr.Mask), Deny: rr.Deny, ChildrenOnly: rr.ChildrenOnly})
		}
		records = append(records, rec)
	}
	data, err := json.MarshalIndent(records, "", "  ")
	if err != nil {
		return err
	}
	if dir := filepath.Dir(u.Path); dir != "." {
		if err := os.MkdirAll(dir, 0700); err != nil {
			return err
		}
	}
	tmp := u.Path + ".tmp"
	if err := os.WriteFile(tmp, data, 0600); err != nil {
		return err
	}
	return os.Rename(tmp, u.Path)
}

func (u *UserStore) Add(m *Manager, username, password, home string) (*Account, error) {
	if err := ValidateUsername(username); err != nil {
		return nil, err
	}
	if strings.TrimSpace(password) == "" {
		return nil, fmt.Errorf("password required")
	}
	if _, ok := m.Accounts[username]; ok {
		return nil, fmt.Errorf("user already exists")
	}
	home = strings.Trim(home, "/")
	a := &Account{Username: username, PasswordHash: PasswordHash(password), Mask: None, Home: home, Enabled: true}
	a.Rules = append(a.Rules, PathRule{Dir: home, Mask: Read | Write | Delete})
	m.Accounts[username] = a
	return a, u.Save(m)
}

func maskString(p PermMask) string {
	var b strings.Builder
	if p.HasRead() {
		b.WriteByte('r')
	}
	if p.HasWrite() {
		b.WriteByte('w')
	}
	if p.HasDelete() {
		b.WriteByte('d')
	}
	return b.String()
}

func (u *UserStore) Update(m *Manager, username, password string, enabled *bool, rules []PathRule) error {
	a, ok := m.Accounts[username]
	if !ok || a.PasswordHash == "" || a.Admin {
		return fmt.Errorf("managed user not found")
	}
	if strings.TrimSpace(password) != "" {
		a.PasswordHash = PasswordHash(password)
		a.Password = ""
	}
	if enabled != nil {
		a.Enabled = *enabled
	}
	if rules != nil {
		a.Rules = rules
	}
	return u.Save(m)
}

func (u *UserStore) UpdatePassword(m *Manager, username, password string) error {
	if strings.TrimSpace(password) == "" {
		return fmt.Errorf("password required")
	}
	a, ok := m.Accounts[username]
	if !ok || a.PasswordHash == "" {
		return fmt.Errorf("managed user not found")
	}
	a.PasswordHash = PasswordHash(password)
	a.Password = ""
	return u.Save(m)
}

func (u *UserStore) Delete(m *Manager, username string) error {
	a, ok := m.Accounts[username]
	if !ok || a.Admin || a.PasswordHash == "" {
		return fmt.Errorf("managed user not found")
	}
	delete(m.Accounts, username)
	return u.Save(m)
}