// Package database provides the local SQLite index for Vaultik backup operations.
// The database tracks files, chunks, and their associations with blobs.
//
// Blobs in Vaultik are the final storage units uploaded to S3. Each blob is a
// large (up to 10GB) file containing many compressed and encrypted chunks from
// multiple source files. Blobs are content-addressed, meaning their filename
// is derived from their SHA256 hash after compression and encryption.
//
// The database does not support migrations. If the schema changes, delete
// the local database and perform a full backup to recreate it.
package database

import (
	"context"
	"database/sql"
	_ "embed"
	"fmt"
	"os"
	"strings"

	"git.eeqj.de/sneak/vaultik/internal/log"
	_ "modernc.org/sqlite"
)

//go:embed schema.sql
var schemaSQL string

// DB represents the Vaultik local index database connection.
// It uses SQLite to track file metadata, content-defined chunks, and blob associations.
// The database enables incremental backups by detecting changed files and
// supports deduplication by tracking which chunks are already stored in blobs.
// Write operations are synchronized through a mutex to ensure thread safety.
type DB struct {
	conn *sql.DB
	path string
}

// New creates a new database connection at the specified path.
// It creates the schema if needed and configures SQLite with WAL mode for
// better concurrency. SQLite handles crash recovery automatically when
// opening a database with journal/WAL files present.
// The path parameter can be a file path for persistent storage or ":memory:"
// for an in-memory database (useful for testing).
func New(ctx context.Context, path string) (*DB, error) {
	log.Debug("Opening database connection", "path", path)

	// Note: We do NOT delete journal/WAL files before opening.
	// SQLite handles crash recovery automatically when the database is opened.
	// Deleting these files would corrupt the database after an unclean shutdown.

	// First attempt with standard WAL mode
	log.Debug("Attempting to open database with WAL mode", "path", path)
	conn, err := sql.Open(
		"sqlite",
		path+"?_journal_mode=WAL&_synchronous=NORMAL&_busy_timeout=10000&_locking_mode=NORMAL&_foreign_keys=ON",
	)
	if err == nil {
		// Set connection pool settings
		// SQLite can handle multiple readers but only one writer at a time.
		// Setting MaxOpenConns to 1 ensures all writes are serialized through
		// a single connection, preventing SQLITE_BUSY errors.
		conn.SetMaxOpenConns(1)
		conn.SetMaxIdleConns(1)

		if err := conn.PingContext(ctx); err == nil {
			// Success on first try
			log.Debug("Database opened successfully with WAL mode", "path", path)

			// Enable foreign keys explicitly
			if _, err := conn.ExecContext(ctx, "PRAGMA foreign_keys = ON"); err != nil {
				log.Warn("Failed to enable foreign keys", "error", err)
			}

			db := &DB{conn: conn, path: path}
			if err := db.createSchema(ctx); err != nil {
				_ = conn.Close()
				return nil, fmt.Errorf("creating schema: %w", err)
			}
			return db, nil
		}
		log.Debug("Failed to ping database, closing connection", "path", path, "error", err)
		_ = conn.Close()
	}

	// If first attempt failed, try with TRUNCATE mode to clear any locks
	log.Info(
		"Database appears locked, attempting recovery with TRUNCATE mode",
		"path", path,
	)
	conn, err = sql.Open(
		"sqlite",
		path+"?_journal_mode=TRUNCATE&_synchronous=NORMAL&_busy_timeout=10000&_foreign_keys=ON",
	)
	if err != nil {
		return nil, fmt.Errorf("opening database in recovery mode: %w", err)
	}

	// Set connection pool settings
	// SQLite can handle multiple readers but only one writer at a time.
	// Setting MaxOpenConns to 1 ensures all writes are serialized through
	// a single connection, preventing SQLITE_BUSY errors.
	conn.SetMaxOpenConns(1)
	conn.SetMaxIdleConns(1)

	if err := conn.PingContext(ctx); err != nil {
		log.Debug("Failed to ping database in recovery mode, closing", "path", path, "error", err)
		_ = conn.Close()
		return nil, fmt.Errorf(
			"database still locked after recovery attempt: %w",
			err,
		)
	}

	log.Debug("Database opened in TRUNCATE mode", "path", path)

	// Switch back to WAL mode
	log.Debug("Switching database back to WAL mode", "path", path)
	if _, err := conn.ExecContext(ctx, "PRAGMA journal_mode=WAL"); err != nil {
		log.Warn("Failed to switch back to WAL mode", "path", path, "error", err)
	}

	// Ensure foreign keys are enabled
	if _, err := conn.ExecContext(ctx, "PRAGMA foreign_keys=ON"); err != nil {
		log.Warn("Failed to enable foreign keys", "path", path, "error", err)
	}

	db := &DB{conn: conn, path: path}
	if err := db.createSchema(ctx); err != nil {
		_ = conn.Close()
		return nil, fmt.Errorf("creating schema: %w", err)
	}

	log.Debug("Database connection established successfully", "path", path)
	return db, nil
}

// Close closes the database connection.
// It ensures all pending operations are completed before closing.
// Returns an error if the database connection cannot be closed properly.
func (db *DB) Close() error {
	log.Debug("Closing database connection", "path", db.path)
	if err := db.conn.Close(); err != nil {
		log.Error("Failed to close database", "path", db.path, "error", err)
		return fmt.Errorf("failed to close database: %w", err)
	}
	log.Debug("Database connection closed successfully", "path", db.path)
	return nil
}

// Conn returns the underlying *sql.DB connection.
// This should be used sparingly and primarily for read operations.
// For write operations, prefer using the ExecWithLog method.
func (db *DB) Conn() *sql.DB {
	return db.conn
}

// BeginTx starts a new database transaction with the given options.
// The caller is responsible for committing or rolling back the transaction.
// For write transactions, consider using the Repositories.WithTx method instead,
// which handles locking and rollback automatically.
func (db *DB) BeginTx(
	ctx context.Context,
	opts *sql.TxOptions,
) (*sql.Tx, error) {
	return db.conn.BeginTx(ctx, opts)
}

// Note: LockForWrite and UnlockWrite methods have been removed.
// SQLite handles its own locking internally, so explicit locking is not needed.

// ExecWithLog executes a write query with SQL logging.
// SQLite handles its own locking internally, so we just pass through to ExecContext.
// The query and args parameters follow the same format as sql.DB.ExecContext.
func (db *DB) ExecWithLog(
	ctx context.Context,
	query string,
	args ...interface{},
) (sql.Result, error) {
	LogSQL("Execute", query, args...)
	return db.conn.ExecContext(ctx, query, args...)
}

// QueryRowWithLog executes a query that returns at most one row with SQL logging.
// This is useful for queries that modify data and return values (e.g., INSERT ... RETURNING).
// SQLite handles its own locking internally.
// The query and args parameters follow the same format as sql.DB.QueryRowContext.
func (db *DB) QueryRowWithLog(
	ctx context.Context,
	query string,
	args ...interface{},
) *sql.Row {
	LogSQL("QueryRow", query, args...)
	return db.conn.QueryRowContext(ctx, query, args...)
}

func (db *DB) createSchema(ctx context.Context) error {
	_, err := db.conn.ExecContext(ctx, schemaSQL)
	return err
}

// NewTestDB creates an in-memory SQLite database for testing purposes.
// The database is automatically initialized with the schema and is ready for use.
// Each call creates a new independent database instance.
func NewTestDB() (*DB, error) {
	return New(context.Background(), ":memory:")
}

// repeatPlaceholder generates a string of ", ?" repeated n times for IN clause construction.
// For example, repeatPlaceholder(2) returns ", ?, ?".
func repeatPlaceholder(n int) string {
	if n <= 0 {
		return ""
	}
	return strings.Repeat(", ?", n)
}

// LogSQL logs SQL queries and their arguments when debug mode is enabled.
// Debug mode is activated by setting the GODEBUG environment variable to include "vaultik".
// This is useful for troubleshooting database operations and understanding query patterns.
//
// The operation parameter describes the type of SQL operation (e.g., "Execute", "Query").
// The query parameter is the SQL statement being executed.
// The args parameter contains the query arguments that will be interpolated.
func LogSQL(operation, query string, args ...interface{}) {
	if strings.Contains(os.Getenv("GODEBUG"), "vaultik") {
		log.Debug(
			"SQL "+operation,
			"query",
			strings.TrimSpace(query),
			"args",
			fmt.Sprintf("%v", args),
		)
	}
}