package customerauth

import (
	"context"
	"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")

// Credentials is the email→credential index the auth server depends on. It is
// satisfied by the file-backed CredentialStore (single-instance / dev) and by
// RedisCredentialStore (shared, horizontally scalable). All methods normalize
// the email key internally.
type Credentials interface {
	// Get returns the record for email and whether it exists. A backing-store
	// failure is reported as "not found" so callers fail closed.
	Get(ctx context.Context, email string) (Record, bool)
	// Register adds a new credential, returning ErrEmailExists if taken.
	Register(ctx context.Context, email string, profileID uint64, hash, createdAt string) error
	// MarkVerified records email verification. The bool reports whether the
	// email was known; an unknown email is not an error (avoids enumeration).
	MarkVerified(ctx context.Context, email, verifiedAt string) (bool, error)
	// UpdateHash replaces the password hash. The bool reports whether the email
	// was known; an unknown email is not an error.
	UpdateHash(ctx context.Context, email, hash string) (bool, error)
	// Delete removes a credential record by email. The bool reports whether the email
	// was known.
	Delete(ctx context.Context, email string) (bool, error)
}

// 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"`
	VerifiedAt string `json:"verifiedAt,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. The ctx is accepted
// for interface parity with the Redis store; the file store ignores it.
func (s *CredentialStore) Get(_ context.Context, 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(_ context.Context, 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()
}

// MarkVerified records that email completed email verification and persists the
// store. It is a no-op if already verified. The bool reports whether the email
// was known; an unknown email is not an error (callers avoid leaking which
// emails exist).
func (s *CredentialStore) MarkVerified(_ context.Context, email, verifiedAt string) (bool, error) {
	key := NormalizeEmail(email)
	s.mu.Lock()
	defer s.mu.Unlock()
	rec, ok := s.byMail[key]
	if !ok {
		return false, nil
	}
	if rec.VerifiedAt != "" {
		return true, nil
	}
	rec.VerifiedAt = verifiedAt
	s.byMail[key] = rec
	return true, s.persistLocked()
}

// UpdateHash replaces the stored password hash for email and persists the store.
// The bool reports whether the email was known; an unknown email is not an error.
func (s *CredentialStore) UpdateHash(_ context.Context, email, hash string) (bool, error) {
	key := NormalizeEmail(email)
	s.mu.Lock()
	defer s.mu.Unlock()
	rec, ok := s.byMail[key]
	if !ok {
		return false, nil
	}
	rec.Hash = hash
	s.byMail[key] = rec
	return true, s.persistLocked()
}

// Delete removes the credential record for email and persists the store.
// The bool reports whether the email was known.
func (s *CredentialStore) Delete(_ context.Context, email string) (bool, error) {
	key := NormalizeEmail(email)
	s.mu.Lock()
	defer s.mu.Unlock()
	if _, ok := s.byMail[key]; !ok {
		return false, nil
	}
	delete(s.byMail, key)
	return true, 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
}