package storage

import (
	"context"
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"io/fs"
	"log/slog"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"

	"github.com/archivmail/pkg/mailparser"
)

// Config holds the configuration for initialising a Store.
type Config struct {
	Dir     string // base directory for file storage
	Keyfile string // path to 32-byte AES key file; empty = no encryption
	DSN     string // PostgreSQL DSN; empty = no DB
}

// Store is a file-based email storage with optional AES-256-GCM encryption
// and optional PostgreSQL metadata.
type Store struct {
	dir string
	key []byte         // nil = no encryption
	db  *pgxpool.Pool  // nil = no DB
}

// StoreStats reports total mail count and size in bytes.
type StoreStats struct {
	TotalMails int64
	TotalBytes int64
}

// MailRef holds the ID and associated time of a stored mail.
type MailRef struct {
	ID      string
	ModTime time.Time
}

// New initialises the storage directory, optionally loads the encryption key
// and connects to PostgreSQL.
func New(cfg Config) (*Store, error) {
	for _, sub := range []string{"store", "attachments", "meta"} {
		if err := os.MkdirAll(filepath.Join(cfg.Dir, sub), 0o755); err != nil {
			return nil, fmt.Errorf("storage: mkdir %s: %w", sub, err)
		}
	}

	s := &Store{dir: cfg.Dir}

	// Load encryption key
	if err := s.loadKey(cfg.Keyfile); err != nil {
		return nil, err
	}

	// Connect to PostgreSQL and auto-create schema
	if cfg.DSN != "" {
		pool, err := pgxpool.New(context.Background(), cfg.DSN)
		if err != nil {
			return nil, fmt.Errorf("storage: db connect: %w", err)
		}
		s.db = pool
		if err := s.initSchema(context.Background()); err != nil {
			pool.Close()
			return nil, fmt.Errorf("storage: init schema: %w", err)
		}
		ctx := context.Background()
		_, _ = s.db.Exec(ctx, `ALTER TABLE emails ADD COLUMN IF NOT EXISTS verify_ok BOOLEAN`)
		_, _ = s.db.Exec(ctx, `ALTER TABLE emails ADD COLUMN IF NOT EXISTS verified_at TIMESTAMPTZ`)
	}

	return s, nil
}

// Close releases the database connection pool (if any).
func (s *Store) Close() {
	if s.db != nil {
		s.db.Close()
	}
}

// ── Encryption key loading ────────────────────────────────────────────────

func (s *Store) loadKey(keyfile string) error {
	// Also check environment variable as fallback
	if keyfile == "" {
		keyfile = os.Getenv("ARCHIVMAIL_KEY")
	}
	if keyfile == "" {
		return nil // no encryption configured
	}

	// If the env var contains the key itself (not a path), it would be unusual.
	// We treat the value as a file path in all cases.
	data, err := os.ReadFile(keyfile)
	if err != nil {
		return fmt.Errorf("storage: read keyfile %s: %w", keyfile, err)
	}

	// Strip whitespace / newlines
	raw := strings.TrimSpace(string(data))

	// Try base64 decode first (spec says base64-encoded 32-byte key)
	decoded, err := base64.StdEncoding.DecodeString(raw)
	if err != nil {
		// Fall back to raw bytes (for 32-byte binary key files)
		decoded = []byte(raw)
	}

	if len(decoded) != 32 {
		return fmt.Errorf("storage: keyfile must contain exactly 32 bytes (got %d)", len(decoded))
	}

	s.key = decoded
	return nil
}

// ── AES-256-GCM encryption / decryption ───────────────────────────────────

// encrypt applies AES-256-GCM encryption. The 12-byte nonce is prepended
// to the ciphertext.
func (s *Store) encrypt(plaintext []byte) ([]byte, error) {
	block, err := aes.NewCipher(s.key)
	if err != nil {
		return nil, fmt.Errorf("storage: aes cipher: %w", err)
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, fmt.Errorf("storage: gcm: %w", err)
	}

	nonce := make([]byte, gcm.NonceSize()) // 12 bytes
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return nil, fmt.Errorf("storage: random nonce: %w", err)
	}

	ciphertext := gcm.Seal(nonce, nonce, plaintext, nil)
	return ciphertext, nil
}

// decrypt reverses AES-256-GCM encryption. Expects nonce prepended to ciphertext.
func (s *Store) decrypt(data []byte) ([]byte, error) {
	block, err := aes.NewCipher(s.key)
	if err != nil {
		return nil, fmt.Errorf("storage: aes cipher: %w", err)
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, fmt.Errorf("storage: gcm: %w", err)
	}

	nonceSize := gcm.NonceSize()
	if len(data) < nonceSize {
		return nil, fmt.Errorf("storage: ciphertext too short")
	}

	nonce, ciphertext := data[:nonceSize], data[nonceSize:]
	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return nil, fmt.Errorf("storage: decrypt: %w", err)
	}
	return plaintext, nil
}

// ── Database schema ───────────────────────────────────────────────────────

func (s *Store) initSchema(ctx context.Context) error {
	_, err := s.db.Exec(ctx, `
		CREATE TABLE IF NOT EXISTS emails (
			id          TEXT PRIMARY KEY,
			received_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
			mail_from   TEXT,
			mail_to     TEXT,
			subject     TEXT,
			size_bytes  BIGINT,
			has_attach  BOOLEAN DEFAULT FALSE,
			indexed_at  TIMESTAMPTZ
		);
		CREATE INDEX IF NOT EXISTS idx_emails_received_at ON emails (received_at);
		CREATE INDEX IF NOT EXISTS idx_emails_mail_from ON emails (mail_from);
		CREATE INDEX IF NOT EXISTS idx_emails_subject ON emails USING gin (to_tsvector('simple', subject));
	`)
	return err
}

// ── Core operations ───────────────────────────────────────────────────────

// Save writes raw email bytes to storage. The ID is the hex-encoded SHA256 of
// the plaintext content. If the file already exists, Save is a no-op (dedup).
// It also inserts metadata into the emails table if a DB is configured.
func (s *Store) Save(raw []byte, _ time.Time) (string, error) {
	// Hash plaintext for dedup (always before encryption)
	sum := sha256.Sum256(raw)
	id := fmt.Sprintf("%x", sum[:]) // 64 hex chars

	path := s.filePath(id)
	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
		return "", fmt.Errorf("storage: mkdir shard: %w", err)
	}

	// Dedup: if file already exists, return same id
	if _, err := os.Stat(path); err == nil {
		return id, nil
	}

	// Determine what to write: encrypted or plaintext
	var toWrite []byte
	if s.key != nil {
		encrypted, err := s.encrypt(raw)
		if err != nil {
			return "", err
		}
		toWrite = encrypted
	} else {
		toWrite = raw
	}

	if err := os.WriteFile(path, toWrite, 0o644); err != nil {
		return "", fmt.Errorf("storage: write: %w", err)
	}

	// Insert metadata into DB (best-effort parse)
	if s.db != nil {
		pm, parseErr := mailparser.Parse(raw)
		if parseErr == nil {
			s.insertMeta(context.Background(), id, pm, len(raw))
		} else {
			// Insert minimal metadata even if parse fails
			s.insertMetaMinimal(context.Background(), id, len(raw))
		}
	}

	return id, nil
}

// Load reads a stored email by its ID. If encryption is configured, the file
// is decrypted before returning plaintext.
func (s *Store) Load(id string) ([]byte, error) {
	path := s.filePath(id)
	data, err := os.ReadFile(path)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return nil, fmt.Errorf("storage: not found: %s", id)
		}
		return nil, fmt.Errorf("storage: read: %w", err)
	}

	if s.key != nil {
		plaintext, err := s.decrypt(data)
		if err != nil {
			// If decryption fails, the file might be stored unencrypted
			// (pre-encryption era). Return as-is for backwards compatibility.
			return data, nil
		}
		return plaintext, nil
	}

	return data, nil
}

// Delete removes a stored email by its ID, including its DB metadata row.
func (s *Store) Delete(id string) error {
	path := s.filePath(id)
	if err := os.Remove(path); err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return fmt.Errorf("storage: not found: %s", id)
		}
		return fmt.Errorf("storage: delete: %w", err)
	}

	if s.db != nil {
		_, _ = s.db.Exec(context.Background(), `DELETE FROM emails WHERE id = $1`, id)
	}

	return nil
}

// Stats returns aggregate statistics. Uses the DB if available (fast), otherwise
// falls back to walking the file system.
func (s *Store) Stats() (*StoreStats, error) {
	if s.db != nil {
		return s.statsFromDB()
	}
	return s.statsFromFS()
}

func (s *Store) statsFromDB() (*StoreStats, error) {
	var stats StoreStats
	err := s.db.QueryRow(context.Background(),
		`SELECT COALESCE(COUNT(*), 0), COALESCE(SUM(size_bytes), 0) FROM emails`,
	).Scan(&stats.TotalMails, &stats.TotalBytes)
	if err != nil {
		return nil, fmt.Errorf("storage: stats from db: %w", err)
	}
	return &stats, nil
}

func (s *Store) statsFromFS() (*StoreStats, error) {
	var stats StoreStats
	err := filepath.WalkDir(filepath.Join(s.dir, "store"), func(_ string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() {
			return nil
		}
		info, err := d.Info()
		if err != nil {
			return err
		}
		stats.TotalMails++
		stats.TotalBytes += info.Size()
		return nil
	})
	if err != nil {
		return nil, fmt.Errorf("storage: stats: %w", err)
	}
	return &stats, nil
}

// FirstAndLastMail returns the oldest and newest mail. Uses the DB if available
// (much faster than walking the filesystem).
func (s *Store) FirstAndLastMail() (first, last *MailRef, err error) {
	if s.db != nil {
		return s.firstAndLastFromDB()
	}
	return s.firstAndLastFromFS()
}

func (s *Store) firstAndLastFromDB() (first, last *MailRef, err error) {
	ctx := context.Background()

	// Oldest
	var fID string
	var fTime time.Time
	err = s.db.QueryRow(ctx,
		`SELECT id, received_at FROM emails ORDER BY received_at ASC LIMIT 1`,
	).Scan(&fID, &fTime)
	if err != nil && !errors.Is(err, pgx.ErrNoRows) {
		return nil, nil, fmt.Errorf("storage: first mail: %w", err)
	}
	if err == nil {
		first = &MailRef{ID: fID, ModTime: fTime}
	}

	// Newest
	var lID string
	var lTime time.Time
	err = s.db.QueryRow(ctx,
		`SELECT id, received_at FROM emails ORDER BY received_at DESC LIMIT 1`,
	).Scan(&lID, &lTime)
	if err != nil && !errors.Is(err, pgx.ErrNoRows) {
		return nil, nil, fmt.Errorf("storage: last mail: %w", err)
	}
	if err == nil {
		last = &MailRef{ID: lID, ModTime: lTime}
	}

	return first, last, nil
}

func (s *Store) firstAndLastFromFS() (first, last *MailRef, err error) {
	err = filepath.WalkDir(filepath.Join(s.dir, "store"), func(path string, d fs.DirEntry, werr error) error {
		if werr != nil {
			return werr
		}
		if d.IsDir() {
			return nil
		}
		info, err := d.Info()
		if err != nil {
			return err
		}
		ref := &MailRef{ID: d.Name(), ModTime: info.ModTime()}
		if first == nil || ref.ModTime.Before(first.ModTime) {
			first = ref
		}
		if last == nil || ref.ModTime.After(last.ModTime) {
			last = ref
		}
		return nil
	})
	if err != nil {
		return nil, nil, fmt.Errorf("storage: first/last: %w", err)
	}
	return first, last, nil
}

// ── Metadata helpers ──────────────────────────────────────────────────────

// insertMeta inserts parsed email metadata into the emails table.
func (s *Store) insertMeta(ctx context.Context, id string, pm *mailparser.ParsedMail, size int) {
	mailTo := strings.Join(pm.To, ", ")
	hasAttach := len(pm.Attachments) > 0

	_, _ = s.db.Exec(ctx, `
		INSERT INTO emails (id, received_at, mail_from, mail_to, subject, size_bytes, has_attach)
		VALUES ($1, $2, $3, $4, $5, $6, $7)
		ON CONFLICT (id) DO NOTHING
	`, id, pm.Date, pm.From, mailTo, pm.Subject, int64(size), hasAttach)
}

// insertMetaMinimal inserts minimal metadata when parsing fails.
func (s *Store) insertMetaMinimal(ctx context.Context, id string, size int) {
	_, _ = s.db.Exec(ctx, `
		INSERT INTO emails (id, received_at, size_bytes)
		VALUES ($1, NOW(), $2)
		ON CONFLICT (id) DO NOTHING
	`, id, int64(size))
}

// SaveMeta upserts metadata for a given email ID. Used by the backfill process.
func (s *Store) SaveMeta(ctx context.Context, id string, pm *mailparser.ParsedMail, size int) error {
	if s.db == nil {
		return nil
	}

	mailTo := strings.Join(pm.To, ", ")
	hasAttach := len(pm.Attachments) > 0

	_, err := s.db.Exec(ctx, `
		INSERT INTO emails (id, received_at, mail_from, mail_to, subject, size_bytes, has_attach)
		VALUES ($1, $2, $3, $4, $5, $6, $7)
		ON CONFLICT (id) DO UPDATE SET
			mail_from  = EXCLUDED.mail_from,
			mail_to    = EXCLUDED.mail_to,
			subject    = EXCLUDED.subject,
			size_bytes = EXCLUDED.size_bytes,
			has_attach = EXCLUDED.has_attach
	`, id, pm.Date, pm.From, mailTo, pm.Subject, int64(size), hasAttach)
	return err
}

// SetIndexedAt marks an email as indexed in the database.
func (s *Store) SetIndexedAt(ctx context.Context, id string) error {
	if s.db == nil {
		return nil
	}
	_, err := s.db.Exec(ctx, `UPDATE emails SET indexed_at = NOW() WHERE id = $1`, id)
	return err
}

// IsIndexed checks whether a given email has been indexed (indexed_at IS NOT NULL).
func (s *Store) IsIndexed(ctx context.Context, id string) (bool, error) {
	if s.db == nil {
		return false, nil
	}
	var indexed bool
	err := s.db.QueryRow(ctx,
		`SELECT indexed_at IS NOT NULL FROM emails WHERE id = $1`, id,
	).Scan(&indexed)
	if errors.Is(err, pgx.ErrNoRows) {
		return false, nil
	}
	return indexed, err
}

// ── Backfill ──────────────────────────────────────────────────────────────

// Backfill walks the store directory, parses each email, inserts missing DB
// metadata rows, and re-indexes emails that have indexed_at IS NULL.
func (s *Store) Backfill(ctx context.Context, idx interface{ IndexSync(doc interface{}) error }, logger *slog.Logger) error {
	// We accept a generic indexer interface to avoid import cycles.
	// The caller (main.go) wraps the real index.Indexer.
	return s.BackfillWithFuncs(ctx, logger)
}

// BackfillWithFuncs walks the store and calls the provided functions for each email.
// This is the implementation used by the coordinator in main.go.
func (s *Store) BackfillWithFuncs(ctx context.Context, logger *slog.Logger) error {
	if s.db == nil {
		logger.Info("backfill: skipping, no database configured")
		return nil
	}

	storeDir := filepath.Join(s.dir, "store")
	count := 0
	indexed := 0
	errCount := 0

	err := filepath.WalkDir(storeDir, func(path string, d fs.DirEntry, werr error) error {
		if werr != nil {
			return werr
		}
		if d.IsDir() {
			return nil
		}

		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
		}

		count++
		id := d.Name()

		// Load the file (handles decryption)
		raw, err := s.Load(id)
		if err != nil {
			logger.Warn("backfill: load failed", "id", id, "err", err)
			errCount++
			return nil // continue with next file
		}

		// Parse
		pm, err := mailparser.Parse(raw)
		if err != nil {
			logger.Warn("backfill: parse failed", "id", id, "err", err)
			errCount++
			return nil
		}

		// Upsert metadata
		if err := s.SaveMeta(ctx, id, pm, len(raw)); err != nil {
			logger.Warn("backfill: save meta failed", "id", id, "err", err)
		}

		// Check if already indexed
		alreadyIndexed, err := s.IsIndexed(ctx, id)
		if err != nil {
			logger.Warn("backfill: check indexed failed", "id", id, "err", err)
		}

		if !alreadyIndexed {
			indexed++
		}

		if count%100 == 0 {
			logger.Info("backfill: progress", "processed", count, "need_index", indexed, "errors", errCount)
		}

		return nil
	})

	if err != nil {
		return fmt.Errorf("backfill: walk: %w", err)
	}

	logger.Info("backfill: complete", "total", count, "need_index", indexed, "errors", errCount)
	return nil
}

// WalkStore iterates over all files in the store directory and calls fn for each.
// The fn receives the email ID. This is used by the backfill coordinator.
func (s *Store) WalkStore(ctx context.Context, fn func(id string) error) error {
	storeDir := filepath.Join(s.dir, "store")
	return filepath.WalkDir(storeDir, func(path string, d fs.DirEntry, werr error) error {
		if werr != nil {
			return werr
		}
		if d.IsDir() {
			return nil
		}
		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
		}
		return fn(d.Name())
	})
}

// ── File path helper ──────────────────────────────────────────────────────

// filePath returns the on-disk path for a given mail ID.
// Uses 2-char prefix sharding: {dir}/store/{id[:2]}/{id}
func (s *Store) filePath(id string) string {
	return filepath.Join(s.dir, "store", id[:2], id)
}

// ── Integrity verification ────────────────────────────────────────────────

// VerifyIntegrity re-computes the SHA-256 of the stored plaintext and
// compares it to the file ID. Updates verify_ok and verified_at in the DB.
func (s *Store) VerifyIntegrity(ctx context.Context, id string) (bool, error) {
	raw, err := s.Load(id)
	if err != nil {
		return false, err
	}
	sum := sha256.Sum256(raw)
	computed := fmt.Sprintf("%x", sum[:])
	ok := computed == id
	if s.db != nil {
		s.db.Exec(ctx,
			`UPDATE emails SET verify_ok=$1, verified_at=NOW() WHERE id=$2`,
			ok, id)
	}
	return ok, nil
}

// GetAllIDs returns all email IDs from the DB, or walks the store if no DB.
func (s *Store) GetAllIDs(ctx context.Context) ([]string, error) {
	if s.db != nil {
		rows, err := s.db.Query(ctx, `SELECT id FROM emails ORDER BY received_at`)
		if err != nil {
			return nil, err
		}
		defer rows.Close()
		var ids []string
		for rows.Next() {
			var id string
			if err := rows.Scan(&id); err != nil {
				continue
			}
			ids = append(ids, id)
		}
		return ids, nil
	}
	// fallback: walk store
	var ids []string
	err := s.WalkStore(ctx, func(id string) error {
		ids = append(ids, id)
		return nil
	})
	return ids, err
}

// VerifyStatus holds the result of an integrity verification.
type VerifyStatus struct {
	VerifyOK   *bool      // nil = not yet checked
	VerifiedAt *time.Time
}

// GetVerifyStatus returns the stored verification status for a given email ID.
func (s *Store) GetVerifyStatus(ctx context.Context, id string) (VerifyStatus, error) {
	var vs VerifyStatus
	if s.db == nil {
		return vs, nil
	}
	row := s.db.QueryRow(ctx,
		`SELECT verify_ok, verified_at FROM emails WHERE id=$1`, id)
	var ok *bool
	var at *time.Time
	if err := row.Scan(&ok, &at); err != nil {
		return vs, nil // not found = not verified
	}
	vs.VerifyOK = ok
	vs.VerifiedAt = at
	return vs, nil
}