package customerauth

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

// ErrEmailExists is returned by Register when the (normalized) email is already
// associated with a credential record.
var ErrEmailExists = errors.New("customerauth: email already registered")

// Record is a single stored credential: which profile an email belongs to and
// its password hash. It deliberately does not embed any profile data — the
// profile grain remains the source of truth for that.
type Record struct {
	Email     string `json:"email"`
	ProfileID uint64 `json:"profileId"`
	Hash      string `json:"hash"`
	CreatedAt string `json:"createdAt,omitempty"`
}

// CredentialStore is a small email→credential index persisted to a JSON file.
// It is the email lookup that the event-sourced profile grains intentionally
// lack. Concurrency-safe; writes are atomic (temp file + rename).
type CredentialStore struct {
	mu     sync.RWMutex
	path   string
	byMail map[string]Record // key: normalized email
}

// LoadCredentialStore opens (or initializes) the store backed by path. A
// missing file is treated as an empty store; the file is created on first write.
func LoadCredentialStore(path string) (*CredentialStore, error) {
	s := &CredentialStore{path: path, byMail: make(map[string]Record)}
	data, err := os.ReadFile(path)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return s, nil
		}
		return nil, fmt.Errorf("customerauth: read %s: %w", path, err)
	}
	var records []Record
	if len(data) > 0 {
		if err := json.Unmarshal(data, &records); err != nil {
			return nil, fmt.Errorf("customerauth: parse %s: %w", path, err)
		}
	}
	for _, r := range records {
		s.byMail[NormalizeEmail(r.Email)] = r
	}
	return s, nil
}

// NormalizeEmail lower-cases and trims an email for use as a lookup key.
func NormalizeEmail(email string) string {
	return strings.ToLower(strings.TrimSpace(email))
}

// Get returns the record for email and whether it exists.
func (s *CredentialStore) Get(email string) (Record, bool) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	r, ok := s.byMail[NormalizeEmail(email)]
	return r, ok
}

// Register adds a new credential record and persists the store. It returns
// ErrEmailExists if the email is already taken.
func (s *CredentialStore) Register(email string, profileID uint64, hash, createdAt string) error {
	key := NormalizeEmail(email)
	s.mu.Lock()
	defer s.mu.Unlock()
	if _, exists := s.byMail[key]; exists {
		return ErrEmailExists
	}
	s.byMail[key] = Record{Email: key, ProfileID: profileID, Hash: hash, CreatedAt: createdAt}
	return s.persistLocked()
}

// persistLocked writes the whole store to disk atomically. Caller holds s.mu.
func (s *CredentialStore) persistLocked() error {
	records := make([]Record, 0, len(s.byMail))
	for _, r := range s.byMail {
		records = append(records, r)
	}
	data, err := json.MarshalIndent(records, "", "  ")
	if err != nil {
		return fmt.Errorf("customerauth: marshal store: %w", err)
	}
	if dir := filepath.Dir(s.path); dir != "" {
		if err := os.MkdirAll(dir, 0o755); err != nil {
			return fmt.Errorf("customerauth: mkdir %s: %w", dir, err)
		}
	}
	tmp, err := os.CreateTemp(filepath.Dir(s.path), ".credentials-*.tmp")
	if err != nil {
		return fmt.Errorf("customerauth: temp file: %w", err)
	}
	tmpName := tmp.Name()
	if _, err := tmp.Write(data); err != nil {
		tmp.Close()
		os.Remove(tmpName)
		return fmt.Errorf("customerauth: write temp: %w", err)
	}
	if err := tmp.Close(); err != nil {
		os.Remove(tmpName)
		return fmt.Errorf("customerauth: close temp: %w", err)
	}
	if err := os.Rename(tmpName, s.path); err != nil {
		os.Remove(tmpName)
		return fmt.Errorf("customerauth: rename temp: %w", err)
	}
	return nil
}