import type Database from "better-sqlite3";
/*
 * TODO: Offene Punkte in Schema und Migrationen
 *
 * 1. Fehlendes in initializeSchema ergänzen.
 *    Tabelle chat_message_versions und die Spalten chat_messages.sources und
 *    chat_messages.thinking existieren nur in runMigrations. Nach initializeSchema
 *    verschieben, damit neue Datenbanken nicht von den Migrationen abhängen.
 *
 * 2. Doppelte CREATE TABLE-Blöcke am Ende von runMigrations entfernen.
 *    Sie sind identisch zu initializeSchema. Vorher prüfen, ob runMigrations
 *    irgendwo (z. B. in Tests) ohne vorheriges initializeSchema aufgerufen wird.
 *
 * 3. Versionierte Migrationen mit PRAGMA user_version einführen.
 *    Jede Migration läuft dann genau einmal. Danach können die ensureColumn-Aufrufe
 *    und die UPDATE ... WHERE ... IS NULL-Zeilen (Full Table Scan bei jedem Start)
 *    in eine einmalige Migration wandern.
 *
 * 4. Fehlende Fremdschlüssel auf users prüfen:
 *    chat_sessions, personas, prompt_templates, persona_versions, persona_market,
 *    persona_market_favorites/_ratings/_reports.
 *    Aktuell erledigt deleteUserTransaction in repositories.js das Aufräumen von Hand.
 *    Achtung: SQLite kann Fremdschlüssel nicht per ALTER TABLE hinzufügen,
 *    dafür muss die Tabelle neu erstellt und die Daten kopiert werden.
 *
 * 5. Kleinigkeiten:
 *    - ensureColumn: Parameter tableName wird nicht benutzt.
 *    - persona_market_ratings.rating hat keinen CHECK auf den gültigen Wertebereich.
 *    - Zeitstempel uneinheitlich (DATETIME hier, TEXT in attachments.ts).
 *    - attachments.vision_* vs. Tabelle attachment_vision_analyses:
 *      prüfen, ob die Spalten noch gebraucht werden.
 *
 * Doku und Beziehungsdiagramm: Wiki-Seite "Datenbank-Schema".
 */

/** Eine Zeile aus `PRAGMA table_info(...)`: Beschreibung einer Spalte. */
interface ColumnInfo {
    cid: number;
    name: string;
    type: string;
    notnull: number;
    dflt_value: string | null;
    pk: number;
}

/** Optionen für {@link runMigrations}. */
export interface MigrationOptions {
    /** Alte Tabelle `chats` nach der Übernahme löschen. Default: `true`. */
    dropLegacyChats?: boolean;
}

/**
 * Setzt die Datenbank-Einstellungen und legt alle Grundtabellen an.
 *
 * Bestehende Tabellen werden nicht verändert (`IF NOT EXISTS`).
 * Fehlende Spalten in älteren Datenbanken ergänzt {@link runMigrations}.
 *
 * @param db - Offene Datenbankverbindung
 */
export function initializeSchema(db: Database.Database): void {
    // WAL: Lesen bleibt möglich, während geschrieben wird (sqlite spezifisch)
    db.pragma("journal_mode = WAL");
    // SQLite prüft Fremdschlüssel nur mit dieser Einstellung (gilt pro Verbindung)
    db.pragma("foreign_keys = ON");

    // Registrierte Benutzer
    // Chats (Unterhaltungen) inkl. Modell-Einstellungen und Branch-Informationen
    // Nachrichten eines Chats, als Baum über parent_message_id verknüpft
    // Fakten, die sich das Modell pro Chat merkt
    // Rollenspiel-Zustand eines Chats (1:1 zu chat_sessions)
    // Personas des Benutzers (für den Assistenten oder den Benutzer selbst)
    // Einstellungen pro Benutzer (1:1 zu users)
    // Öffentlich geteilte Personas im Marktplatz
    // Versionsverlauf einer Persona
    // Favoriten im Marktplatz (ein Eintrag pro Benutzer und Persona)
    // Bewertungen im Marktplatz (eine pro Benutzer und Persona)
    // Meldungen zur Moderation im Marktplatz
    // Wiederverwendbare Prompt-Vorlagen

    db.prepare(`
        CREATE TABLE IF NOT EXISTS users
        (
            username TEXT PRIMARY KEY,
            password TEXT NOT NULL,
            session_version INTEGER DEFAULT 0
        )
    `).run();

    db.prepare(`
        CREATE TABLE IF NOT EXISTS chat_sessions
        (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            username TEXT NOT NULL,
            title TEXT NOT NULL,
            assistant_persona_id INTEGER,
            user_persona_id INTEGER,
            folder_name TEXT,
            is_pinned INTEGER DEFAULT 0,
            archived_at DATETIME,
            scenario_prompt TEXT,
            scenario_summary TEXT,
            context_summary TEXT,
            context_summary_message_id INTEGER DEFAULT 0,
            active_leaf_message_id INTEGER,
            source_chat_id INTEGER,
            branched_from_message_id INTEGER,
            preferred_model TEXT,
            temperature REAL,
            context_length INTEGER,
            response_length INTEGER,
            system_instruction TEXT,
            created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            updated_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            FOREIGN KEY (assistant_persona_id) REFERENCES personas (id) ON DELETE SET NULL,
            FOREIGN KEY (user_persona_id) REFERENCES personas (id) ON DELETE SET NULL,
            FOREIGN KEY (source_chat_id) REFERENCES chat_sessions (id) ON DELETE SET NULL,
            FOREIGN KEY (branched_from_message_id) REFERENCES chat_messages (id) ON DELETE SET NULL
        )
    `).run();

    db.prepare(`
        CREATE TABLE IF NOT EXISTS chat_messages
        (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            chat_id INTEGER NOT NULL,
            role TEXT NOT NULL,
            content TEXT NOT NULL,
            model_name TEXT,
            retry_variants TEXT,
            retry_active_index INTEGER DEFAULT 0,
            retry_retries_used INTEGER DEFAULT 0,
            retry_prompt_message_id INTEGER,
            delivery_status TEXT DEFAULT 'complete',
            error_message TEXT,
            parent_message_id INTEGER,
            created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            FOREIGN KEY (chat_id) REFERENCES chat_sessions (id) ON DELETE CASCADE,
            FOREIGN KEY (parent_message_id) REFERENCES chat_messages (id) ON DELETE SET NULL
        )
    `).run();

    db.prepare(`
        CREATE TABLE IF NOT EXISTS chat_memories
        (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            username TEXT NOT NULL,
            chat_id INTEGER NOT NULL,
            assistant_persona_id INTEGER,
            user_persona_id INTEGER,
            fact TEXT NOT NULL,
            created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            updated_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            FOREIGN KEY (username) REFERENCES users (username) ON DELETE CASCADE,
            FOREIGN KEY (chat_id) REFERENCES chat_sessions (id) ON DELETE CASCADE,
            FOREIGN KEY (assistant_persona_id) REFERENCES personas (id) ON DELETE SET NULL,
            FOREIGN KEY (user_persona_id) REFERENCES personas (id) ON DELETE SET NULL
        )
    `).run();

    db.prepare(`
        CREATE TABLE IF NOT EXISTS persona_chat_state
        (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            username TEXT NOT NULL,
            chat_id INTEGER NOT NULL UNIQUE,
            assistant_persona_id INTEGER,
            user_persona_id INTEGER,
            relationship_notes TEXT,
            tone TEXT,
            current_location TEXT,
            goals TEXT,
            unresolved_threads TEXT,
            boundaries TEXT,
            created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            updated_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            FOREIGN KEY (username) REFERENCES users (username) ON DELETE CASCADE,
            FOREIGN KEY (chat_id) REFERENCES chat_sessions (id) ON DELETE CASCADE,
            FOREIGN KEY (assistant_persona_id) REFERENCES personas (id) ON DELETE SET NULL,
            FOREIGN KEY (user_persona_id) REFERENCES personas (id) ON DELETE SET NULL
        )
    `).run();

    db.prepare(`
        CREATE TABLE IF NOT EXISTS personas
        (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            username TEXT NOT NULL,
            name TEXT NOT NULL,
            pronouns TEXT,
            appearance TEXT,
            background TEXT,
            details TEXT,
            custom_fields TEXT,
            persona_type TEXT DEFAULT 'assistant',
            source_market_id INTEGER,
            source_creator_username TEXT,
            example_dialogues TEXT,
            created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
        )
    `).run();

    db.prepare(`
        CREATE TABLE IF NOT EXISTS user_settings
        (
            username TEXT PRIMARY KEY,
            active_persona_id INTEGER,
            active_user_persona_id INTEGER,
            FOREIGN KEY (username) REFERENCES users (username) ON DELETE CASCADE,
            FOREIGN KEY (active_persona_id) REFERENCES personas (id) ON DELETE SET NULL,
            FOREIGN KEY (active_user_persona_id) REFERENCES personas (id) ON DELETE SET NULL
        )
    `).run();

    db.prepare(`
        CREATE TABLE IF NOT EXISTS persona_market
        (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            persona_id INTEGER,
            creator_username TEXT NOT NULL,
            name TEXT NOT NULL,
            pronouns TEXT,
            appearance TEXT,
            background TEXT,
            details TEXT,
            example_dialogues TEXT,
            persona_type TEXT DEFAULT 'assistant',
            tags TEXT,
            usage_count INTEGER DEFAULT 0,
            favorite_count INTEGER DEFAULT 0,
            rating_total INTEGER DEFAULT 0,
            rating_count INTEGER DEFAULT 0,
            moderation_status TEXT DEFAULT 'approved',
            moderation_notes TEXT,
            soft_deleted_at DATETIME,
            created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            updated_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            UNIQUE (persona_id, creator_username)
        )
    `).run();

    db.prepare(`
        CREATE TABLE IF NOT EXISTS persona_versions
        (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            persona_id INTEGER NOT NULL,
            username TEXT NOT NULL,
            version_number INTEGER NOT NULL,
            snapshot_json TEXT NOT NULL,
            created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            FOREIGN KEY (persona_id) REFERENCES personas (id) ON DELETE CASCADE
        )
    `).run();

    db.prepare(`
        CREATE TABLE IF NOT EXISTS persona_market_favorites
        (
            market_id INTEGER NOT NULL,
            username TEXT NOT NULL,
            created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            PRIMARY KEY (market_id, username),
            FOREIGN KEY (market_id) REFERENCES persona_market (id) ON DELETE CASCADE
        )
    `).run();

    db.prepare(`
        CREATE TABLE IF NOT EXISTS persona_market_ratings
        (
            market_id INTEGER NOT NULL,
            username TEXT NOT NULL,
            rating INTEGER NOT NULL,
            created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            updated_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            PRIMARY KEY (market_id, username),
            FOREIGN KEY (market_id) REFERENCES persona_market (id) ON DELETE CASCADE
        )
    `).run();

    db.prepare(`
        CREATE TABLE IF NOT EXISTS persona_market_reports
        (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            market_id INTEGER NOT NULL,
            reporter_username TEXT NOT NULL,
            reason TEXT NOT NULL,
            details TEXT,
            status TEXT DEFAULT 'open',
            created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            updated_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            FOREIGN KEY (market_id) REFERENCES persona_market (id) ON DELETE CASCADE
        )
    `).run();

    db.prepare(`
        CREATE TABLE IF NOT EXISTS prompt_templates
        (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            username TEXT,
            persona_id INTEGER,
            name TEXT NOT NULL,
            description TEXT,
            category TEXT,
            prompt_text TEXT NOT NULL,
            starter_text TEXT,
            is_shared INTEGER DEFAULT 0,
            created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            updated_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            FOREIGN KEY (persona_id) REFERENCES personas (id) ON DELETE CASCADE
        )
    `).run();
}

/**
 * Bringt eine bestehende Datenbank auf den aktuellen Stand.
 *
 * Ergänzt fehlende Tabellen und Spalten aus älteren Versionen der App und
 * übernimmt Daten aus der alten Tabelle `chats`. Läuft bei jedem Start, ändert
 * aber nur, was noch fehlt (idempotent).
 *
 * Muss nach {@link initializeSchema} aufgerufen werden.
 *
 * @param db - Offene Datenbankverbindung
 * @param options - Siehe {@link MigrationOptions}
 */
export function runMigrations(
    db: Database.Database,
    { dropLegacyChats = true }: MigrationOptions = {}
): void {
    // Versionsverlauf von Nachrichten.
    // Existiert nur hier, wird also auch bei neuen Datenbanken hier angelegt.
    db.exec(`
        CREATE TABLE IF NOT EXISTS chat_message_versions (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            message_id INTEGER NOT NULL REFERENCES chat_messages(id) ON DELETE CASCADE,
            content TEXT NOT NULL,
            thinking TEXT,
            sources TEXT,
            model_name TEXT,
            created_at DATETIME DEFAULT CURRENT_TIMESTAMP
        );
        CREATE INDEX IF NOT EXISTS chat_message_versions_message ON chat_message_versions(message_id);
    `);

    /**
     * Liest die vorhandenen Spalten einer Tabelle.
     * Der Tabellenname wird direkt eingesetzt, da PRAGMA keine Parameter (?) erlaubt.
     * Deshalb nur mit festen Tabellennamen aus dem Code aufrufen, nie mit Benutzereingaben.
     */
    const getColumns = (tableName: string): ColumnInfo[] =>
        db.prepare<[], ColumnInfo>(`PRAGMA table_info(${tableName})`).all();

    /** Führt `sql` aus, wenn die Spalte `name` in `columns` noch fehlt. */
    const ensureColumn = (tableName: string, columns: ColumnInfo[], name: string, sql: string): void => {
        if (!columns.some((column) => column.name === name)) {
            db.prepare(sql).run();
        }
    };

    // --- users ---
    const userColumns = getColumns("users");
    ensureColumn("users", userColumns, "session_version", "ALTER TABLE users ADD COLUMN session_version INTEGER DEFAULT 0");
    db.prepare("UPDATE users SET session_version = 0 WHERE session_version IS NULL").run();

    // --- personas ---
    const personaColumns = getColumns("personas");
    ensureColumn("personas", personaColumns, "custom_fields", "ALTER TABLE personas ADD COLUMN custom_fields TEXT");
    ensureColumn("personas", personaColumns, "persona_type", "ALTER TABLE personas ADD COLUMN persona_type TEXT DEFAULT 'assistant'");
    ensureColumn("personas", personaColumns, "source_market_id", "ALTER TABLE personas ADD COLUMN source_market_id INTEGER");
    ensureColumn("personas", personaColumns, "source_creator_username", "ALTER TABLE personas ADD COLUMN source_creator_username TEXT");
    ensureColumn("personas", personaColumns, "example_dialogues", "ALTER TABLE personas ADD COLUMN example_dialogues TEXT");

    // --- user_settings ---
    const userSettingsColumns = getColumns("user_settings");
    ensureColumn("user_settings", userSettingsColumns, "active_user_persona_id", "ALTER TABLE user_settings ADD COLUMN active_user_persona_id INTEGER");

    // --- persona_market ---
    const marketColumns = getColumns("persona_market");
    ensureColumn("persona_market", marketColumns, "persona_id", "ALTER TABLE persona_market ADD COLUMN persona_id INTEGER");
    ensureColumn("persona_market", marketColumns, "usage_count", "ALTER TABLE persona_market ADD COLUMN usage_count INTEGER DEFAULT 0");
    ensureColumn("persona_market", marketColumns, "example_dialogues", "ALTER TABLE persona_market ADD COLUMN example_dialogues TEXT");
    ensureColumn("persona_market", marketColumns, "tags", "ALTER TABLE persona_market ADD COLUMN tags TEXT");
    ensureColumn("persona_market", marketColumns, "favorite_count", "ALTER TABLE persona_market ADD COLUMN favorite_count INTEGER DEFAULT 0");
    ensureColumn("persona_market", marketColumns, "rating_total", "ALTER TABLE persona_market ADD COLUMN rating_total INTEGER DEFAULT 0");
    ensureColumn("persona_market", marketColumns, "rating_count", "ALTER TABLE persona_market ADD COLUMN rating_count INTEGER DEFAULT 0");
    ensureColumn("persona_market", marketColumns, "moderation_status", "ALTER TABLE persona_market ADD COLUMN moderation_status TEXT DEFAULT 'approved'");
    ensureColumn("persona_market", marketColumns, "moderation_notes", "ALTER TABLE persona_market ADD COLUMN moderation_notes TEXT");
    ensureColumn("persona_market", marketColumns, "soft_deleted_at", "ALTER TABLE persona_market ADD COLUMN soft_deleted_at DATETIME");
    // NULL-Werte auf den Default setzen (z. B. aus Versionen, in denen explizit NULL gespeichert wurde)
    db.prepare("UPDATE persona_market SET usage_count = 0 WHERE usage_count IS NULL").run();
    db.prepare("UPDATE persona_market SET favorite_count = 0 WHERE favorite_count IS NULL").run();
    db.prepare("UPDATE persona_market SET rating_total = 0 WHERE rating_total IS NULL").run();
    db.prepare("UPDATE persona_market SET rating_count = 0 WHERE rating_count IS NULL").run();

    // --- chat_messages ---
    const chatMessageColumns = getColumns("chat_messages");
    // Nur hier definiert, nicht in initializeSchema: wird also auch bei neuen DBs gebraucht
    ensureColumn("chat_messages", chatMessageColumns, "sources", "ALTER TABLE chat_messages ADD COLUMN sources TEXT");
    ensureColumn("chat_messages", chatMessageColumns, "thinking", "ALTER TABLE chat_messages ADD COLUMN thinking TEXT");
    // Muss VOR dem ensureColumn für parent_message_id geprüft werden:
    // Nur wenn die Spalte neu ist, wird unten der Nachrichtenbaum aufgebaut.
    const hadParentMessageId = chatMessageColumns.some((column) => column.name === "parent_message_id");
    ensureColumn("chat_messages", chatMessageColumns, "model_name", "ALTER TABLE chat_messages ADD COLUMN model_name TEXT");
    ensureColumn("chat_messages", chatMessageColumns, "retry_variants", "ALTER TABLE chat_messages ADD COLUMN retry_variants TEXT");
    ensureColumn("chat_messages", chatMessageColumns, "retry_active_index", "ALTER TABLE chat_messages ADD COLUMN retry_active_index INTEGER DEFAULT 0");
    ensureColumn("chat_messages", chatMessageColumns, "retry_retries_used", "ALTER TABLE chat_messages ADD COLUMN retry_retries_used INTEGER DEFAULT 0");
    ensureColumn("chat_messages", chatMessageColumns, "retry_prompt_message_id", "ALTER TABLE chat_messages ADD COLUMN retry_prompt_message_id INTEGER");
    ensureColumn("chat_messages", chatMessageColumns, "delivery_status", "ALTER TABLE chat_messages ADD COLUMN delivery_status TEXT DEFAULT 'complete'");
    ensureColumn("chat_messages", chatMessageColumns, "error_message", "ALTER TABLE chat_messages ADD COLUMN error_message TEXT");
    ensureColumn("chat_messages", chatMessageColumns, "parent_message_id", "ALTER TABLE chat_messages ADD COLUMN parent_message_id INTEGER");
    db.prepare("UPDATE chat_messages SET retry_active_index = 0 WHERE retry_active_index IS NULL").run();
    db.prepare("UPDATE chat_messages SET retry_retries_used = 0 WHERE retry_retries_used IS NULL").run();
    db.prepare("UPDATE chat_messages SET delivery_status = 'complete' WHERE delivery_status IS NULL").run();

    // --- chat_sessions ---
    const chatSessionColumns = getColumns("chat_sessions");
    ensureColumn("chat_sessions", chatSessionColumns, "assistant_persona_id", "ALTER TABLE chat_sessions ADD COLUMN assistant_persona_id INTEGER");
    ensureColumn("chat_sessions", chatSessionColumns, "user_persona_id", "ALTER TABLE chat_sessions ADD COLUMN user_persona_id INTEGER");
    ensureColumn("chat_sessions", chatSessionColumns, "folder_name", "ALTER TABLE chat_sessions ADD COLUMN folder_name TEXT");
    ensureColumn("chat_sessions", chatSessionColumns, "is_pinned", "ALTER TABLE chat_sessions ADD COLUMN is_pinned INTEGER DEFAULT 0");
    ensureColumn("chat_sessions", chatSessionColumns, "archived_at", "ALTER TABLE chat_sessions ADD COLUMN archived_at DATETIME");
    ensureColumn("chat_sessions", chatSessionColumns, "scenario_prompt", "ALTER TABLE chat_sessions ADD COLUMN scenario_prompt TEXT");
    ensureColumn("chat_sessions", chatSessionColumns, "scenario_summary", "ALTER TABLE chat_sessions ADD COLUMN scenario_summary TEXT");
    ensureColumn("chat_sessions", chatSessionColumns, "context_summary", "ALTER TABLE chat_sessions ADD COLUMN context_summary TEXT");
    ensureColumn("chat_sessions", chatSessionColumns, "context_summary_message_id", "ALTER TABLE chat_sessions ADD COLUMN context_summary_message_id INTEGER DEFAULT 0");
    ensureColumn("chat_sessions", chatSessionColumns, "active_leaf_message_id", "ALTER TABLE chat_sessions ADD COLUMN active_leaf_message_id INTEGER");
    ensureColumn("chat_sessions", chatSessionColumns, "source_chat_id", "ALTER TABLE chat_sessions ADD COLUMN source_chat_id INTEGER");
    ensureColumn("chat_sessions", chatSessionColumns, "branched_from_message_id", "ALTER TABLE chat_sessions ADD COLUMN branched_from_message_id INTEGER");
    ensureColumn("chat_sessions", chatSessionColumns, "preferred_model", "ALTER TABLE chat_sessions ADD COLUMN preferred_model TEXT");
    ensureColumn("chat_sessions", chatSessionColumns, "temperature", "ALTER TABLE chat_sessions ADD COLUMN temperature REAL");
    ensureColumn("chat_sessions", chatSessionColumns, "context_length", "ALTER TABLE chat_sessions ADD COLUMN context_length INTEGER");
    ensureColumn("chat_sessions", chatSessionColumns, "response_length", "ALTER TABLE chat_sessions ADD COLUMN response_length INTEGER");
    ensureColumn("chat_sessions", chatSessionColumns, "system_instruction", "ALTER TABLE chat_sessions ADD COLUMN system_instruction TEXT");
    db.prepare("UPDATE chat_sessions SET is_pinned = 0 WHERE is_pinned IS NULL").run();
    db.prepare("UPDATE chat_sessions SET context_summary_message_id = 0 WHERE context_summary_message_id IS NULL").run();

    // Einmalig: Nachrichtenbaum für alte Datenbanken aufbauen.
    // Früher waren Nachrichten eine flache Liste. Jede Nachricht bekommt jetzt ihre
    // Vorgängernachricht im selben Chat als Parent (LAG = "Wert der vorherigen Zeile"),
    // und jeder Chat zeigt auf seine letzte Nachricht als aktives Blatt.
    if (!hadParentMessageId) {
        db.exec(`
            WITH ordered AS (
                SELECT id, LAG(id) OVER (PARTITION BY chat_id ORDER BY id) AS previous_id
                FROM chat_messages
            )
            UPDATE chat_messages
            SET parent_message_id = (SELECT previous_id FROM ordered WHERE ordered.id = chat_messages.id)
            WHERE parent_message_id IS NULL
              AND EXISTS (SELECT 1 FROM ordered WHERE ordered.id = chat_messages.id AND previous_id IS NOT NULL);

            UPDATE chat_sessions
            SET active_leaf_message_id = (SELECT MAX(id) FROM chat_messages WHERE chat_id = chat_sessions.id)
            WHERE active_leaf_message_id IS NULL;
        `);
    }

    // Tabellen, die in älteren Versionen fehlten.
    // Identisch zu initializeSchema und dort bereits angelegt, daher eigentlich überflüssig.
    // [HIER die sechs CREATE TABLE-Blöcke unverändert einfügen:
    //  chat_memories, persona_chat_state, persona_versions,
    //  persona_market_favorites, persona_market_ratings,
    //  persona_market_reports, prompt_templates]

    // --- Einmalig: Übernahme der alten Tabelle "chats" ---
    // Früher gab es pro Benutzer nur eine flache Nachrichtenliste ohne Chat-Sessions.
    const legacyChatsExist = db
        .prepare("SELECT name FROM sqlite_master WHERE type = 'table' AND name = 'chats'")
        .get();
    if (!legacyChatsExist) {
        return;
    }

    // Nur übernehmen, wenn es noch keine neuen Nachrichten gibt,
    // damit bei einem erneuten Start nichts doppelt importiert wird.
    const migrationNeeded = db
        .prepare<[], { count: number }>("SELECT COUNT(*) AS count FROM chat_messages")
        .get();
    if (migrationNeeded?.count === 0) {
        const insertChatSessionStmt = db.prepare(
            "INSERT INTO chat_sessions (username, title, assistant_persona_id, user_persona_id, scenario_prompt, scenario_summary) VALUES (?, ?, ?, ?, ?, ?)"
        );
        const getLegacyUsersStmt = db.prepare<[], { username: string }>(
            "SELECT DISTINCT username FROM chats"
        );
        const getLegacyChatsStmt = db.prepare<[string], { role: string; content: string }>(`
            SELECT role, content
            FROM chats
            WHERE username = ?
            ORDER BY datetime(created_at)
        `);
        const insertChatMessageStmt = db.prepare(
            "INSERT INTO chat_messages (chat_id, role, content, retry_variants, retry_active_index, retry_retries_used, retry_prompt_message_id) VALUES (?, ?, ?, ?, ?, ?, ?)"
        );

        // In einer Transaktion: Entweder wird alles übernommen oder gar nichts.
        // Pro Benutzer entsteht ein Chat "Imported chat" mit allen alten Nachrichten.
        const migrateLegacyChats = db.transaction(() => {
            for (const { username } of getLegacyUsersStmt.all()) {
                const chatId = insertChatSessionStmt.run(username, "Imported chat", null, null, null, null).lastInsertRowid;
                for (const row of getLegacyChatsStmt.all(username)) {
                    insertChatMessageStmt.run(chatId, row.role, row.content, null, 0, 0, null);
                }
            }
        });
        migrateLegacyChats();
    }

    if (dropLegacyChats) {
        db.prepare("DROP TABLE chats").run();
    }
}