package store

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"

	_ "modernc.org/sqlite"
)

const schemaVersion = 6

var ErrNotFound = errors.New("store: not found")

// Store owns the SQLite connection used by the process.
type Store struct {
	db *sql.DB
}

type Admin struct {
	ID           int64
	Username     string
	PasswordHash []byte
	CreatedAt    time.Time
	UpdatedAt    time.Time
}

type Session struct {
	TokenHash []byte
	CSRFHash  []byte
	ExpiresAt time.Time
	CreatedAt time.Time
	Admin     Admin
}

// Open creates the parent directory, opens SQLite, applies safety pragmas and
// runs the built-in schema migration.
func Open(ctx context.Context, path string) (*Store, error) {
	if err := prepareDatabasePath(path); err != nil {
		return nil, err
	}

	db, err := sql.Open("sqlite", path)
	if err != nil {
		return nil, fmt.Errorf("open sqlite: %w", err)
	}
	db.SetMaxOpenConns(1)
	db.SetMaxIdleConns(1)

	closeOnError := func(err error) (*Store, error) {
		_ = db.Close()
		return nil, err
	}

	if err := db.PingContext(ctx); err != nil {
		return closeOnError(fmt.Errorf("ping sqlite: %w", err))
	}
	for _, pragma := range []string{
		"PRAGMA foreign_keys = ON",
		"PRAGMA busy_timeout = 5000",
		"PRAGMA journal_mode = WAL",
	} {
		if _, err := db.ExecContext(ctx, pragma); err != nil {
			return closeOnError(fmt.Errorf("%s: %w", pragma, err))
		}
	}
	if err := migrate(ctx, db); err != nil {
		return closeOnError(err)
	}
	if isFilesystemPath(path) {
		if err := os.Chmod(path, 0o600); err != nil {
			return closeOnError(fmt.Errorf("secure sqlite file: %w", err))
		}
	}
	return &Store{db: db}, nil
}

func prepareDatabasePath(path string) error {
	if !isFilesystemPath(path) {
		return nil
	}
	parent := filepath.Dir(path)
	if parent == "." {
		return nil
	}
	if err := os.MkdirAll(parent, 0o750); err != nil {
		return fmt.Errorf("create sqlite directory: %w", err)
	}
	return nil
}

func isFilesystemPath(path string) bool {
	return path != ":memory:" && !strings.HasPrefix(path, "file:")
}

func migrate(ctx context.Context, db *sql.DB) error {
	var version int
	if err := db.QueryRowContext(ctx, "PRAGMA user_version").Scan(&version); err != nil {
		return fmt.Errorf("read sqlite schema version: %w", err)
	}
	if version > schemaVersion {
		return fmt.Errorf("sqlite schema version %d is newer than supported version %d", version, schemaVersion)
	}
	if version == schemaVersion {
		return nil
	}

	for nextVersion := version + 1; nextVersion <= schemaVersion; nextVersion++ {
		tx, err := db.BeginTx(ctx, nil)
		if err != nil {
			return fmt.Errorf("begin sqlite migration %d: %w", nextVersion, err)
		}
		for _, statement := range migrationStatements(nextVersion) {
			if _, err := tx.ExecContext(ctx, statement); err != nil {
				_ = tx.Rollback()
				return fmt.Errorf("apply sqlite migration %d: %w", nextVersion, err)
			}
		}
		if _, err := tx.ExecContext(
			ctx,
			fmt.Sprintf("PRAGMA user_version = %d", nextVersion),
		); err != nil {
			_ = tx.Rollback()
			return fmt.Errorf("record sqlite migration %d: %w", nextVersion, err)
		}
		if err := tx.Commit(); err != nil {
			return fmt.Errorf("commit sqlite migration %d: %w", nextVersion, err)
		}
	}
	return nil
}

func (s *Store) Close() error {
	return s.db.Close()
}

func (s *Store) Ready(ctx context.Context) error {
	if err := s.db.PingContext(ctx); err != nil {
		return err
	}
	var one int
	if err := s.db.QueryRowContext(ctx, "SELECT 1").Scan(&one); err != nil {
		return err
	}
	if one != 1 {
		return errors.New("sqlite readiness query returned an unexpected value")
	}
	return nil
}

func (s *Store) CurrentAdmin(ctx context.Context) (Admin, error) {
	return scanAdmin(s.db.QueryRowContext(ctx, `
		SELECT id, username, password_hash, created_at, updated_at
		FROM admins
		WHERE id = 1
	`))
}

func (s *Store) AdminByUsername(ctx context.Context, username string) (Admin, error) {
	return scanAdmin(s.db.QueryRowContext(ctx, `
		SELECT id, username, password_hash, created_at, updated_at
		FROM admins
		WHERE username = ?
	`, username))
}

type rowScanner interface {
	Scan(dest ...any) error
}

func scanAdmin(row rowScanner) (Admin, error) {
	var admin Admin
	var createdAt int64
	var updatedAt int64
	err := row.Scan(
		&admin.ID,
		&admin.Username,
		&admin.PasswordHash,
		&createdAt,
		&updatedAt,
	)
	if errors.Is(err, sql.ErrNoRows) {
		return Admin{}, ErrNotFound
	}
	if err != nil {
		return Admin{}, err
	}
	admin.CreatedAt = time.Unix(createdAt, 0).UTC()
	admin.UpdatedAt = time.Unix(updatedAt, 0).UTC()
	return admin, nil
}

// SetAdmin inserts or replaces the single configured administrator and
// atomically revokes all existing sessions.
func (s *Store) SetAdmin(ctx context.Context, username string, passwordHash []byte) error {
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return fmt.Errorf("begin admin update: %w", err)
	}
	defer tx.Rollback()

	now := time.Now().UTC().Unix()
	_, err = tx.ExecContext(ctx, `
		INSERT INTO admins (id, username, password_hash, created_at, updated_at)
		VALUES (1, ?, ?, ?, ?)
		ON CONFLICT(id) DO UPDATE SET
			username = excluded.username,
			password_hash = excluded.password_hash,
			updated_at = excluded.updated_at
	`, username, passwordHash, now, now)
	if err != nil {
		return fmt.Errorf("set admin: %w", err)
	}
	if _, err := tx.ExecContext(ctx, "DELETE FROM sessions"); err != nil {
		return fmt.Errorf("revoke sessions after admin update: %w", err)
	}
	if err := tx.Commit(); err != nil {
		return fmt.Errorf("commit admin update: %w", err)
	}
	return nil
}

func (s *Store) DeleteAllSessions(ctx context.Context) error {
	if _, err := s.db.ExecContext(ctx, "DELETE FROM sessions"); err != nil {
		return fmt.Errorf("delete all sessions: %w", err)
	}
	return nil
}

func (s *Store) CreateSession(
	ctx context.Context,
	adminID int64,
	tokenHash []byte,
	csrfHash []byte,
	expiresAt time.Time,
) error {
	now := time.Now().UTC().Unix()
	_, err := s.db.ExecContext(ctx, `
		INSERT INTO sessions (token_hash, admin_id, csrf_hash, expires_at, created_at)
		VALUES (?, ?, ?, ?, ?)
	`, tokenHash, adminID, csrfHash, expiresAt.UTC().Unix(), now)
	if err != nil {
		return fmt.Errorf("create session: %w", err)
	}
	return nil
}

func (s *Store) SessionByTokenHash(ctx context.Context, tokenHash []byte) (Session, error) {
	var session Session
	var expiresAt int64
	var createdAt int64
	var adminCreatedAt int64
	var adminUpdatedAt int64
	err := s.db.QueryRowContext(ctx, `
		SELECT
			s.token_hash,
			s.csrf_hash,
			s.expires_at,
			s.created_at,
			a.id,
			a.username,
			a.created_at,
			a.updated_at
		FROM sessions s
		JOIN admins a ON a.id = s.admin_id
		WHERE s.token_hash = ?
	`, tokenHash).Scan(
		&session.TokenHash,
		&session.CSRFHash,
		&expiresAt,
		&createdAt,
		&session.Admin.ID,
		&session.Admin.Username,
		&adminCreatedAt,
		&adminUpdatedAt,
	)
	if errors.Is(err, sql.ErrNoRows) {
		return Session{}, ErrNotFound
	}
	if err != nil {
		return Session{}, err
	}
	session.ExpiresAt = time.Unix(expiresAt, 0).UTC()
	session.CreatedAt = time.Unix(createdAt, 0).UTC()
	session.Admin.CreatedAt = time.Unix(adminCreatedAt, 0).UTC()
	session.Admin.UpdatedAt = time.Unix(adminUpdatedAt, 0).UTC()
	return session, nil
}

func (s *Store) UpdateSessionCSRF(ctx context.Context, tokenHash []byte, csrfHash []byte) error {
	result, err := s.db.ExecContext(ctx, `
		UPDATE sessions
		SET csrf_hash = ?
		WHERE token_hash = ?
	`, csrfHash, tokenHash)
	if err != nil {
		return fmt.Errorf("update session csrf: %w", err)
	}
	affected, err := result.RowsAffected()
	if err != nil {
		return fmt.Errorf("read session update result: %w", err)
	}
	if affected == 0 {
		return ErrNotFound
	}
	return nil
}

func (s *Store) DeleteSession(ctx context.Context, tokenHash []byte) error {
	if _, err := s.db.ExecContext(ctx, "DELETE FROM sessions WHERE token_hash = ?", tokenHash); err != nil {
		return fmt.Errorf("delete session: %w", err)
	}
	return nil
}

func (s *Store) DeleteExpiredSessions(ctx context.Context, now time.Time) error {
	if _, err := s.db.ExecContext(ctx, "DELETE FROM sessions WHERE expires_at <= ?", now.UTC().Unix()); err != nil {
		return fmt.Errorf("delete expired sessions: %w", err)
	}
	return nil
}