#pragma once

#include <QAbstractListModel>
#include <QHash>
#include <QJsonArray>
#include <QJsonObject>
#include <QString>
#include <QVector>
#include <QtQmlIntegration>

class QNetworkAccessManager;
class QNetworkReply;
class QTimer;

namespace PhpQml::Bridge {

class MercureClient;

/// QAbstractListModel that mirrors a `#[BridgeResource]` collection from
/// the backend. Loads via HTTP GET, then keeps in sync via Mercure SSE.
///
/// The role names are derived dynamically from the first row's JSON keys,
/// plus an internal `pending` role used by optimistic mutations
/// (PLAN.md §5 *Optimistic updates*).
///
/// Phase 2 implements diff application (upsert / delete / replace) and
/// version-gap detection. Cursor pagination is wired but the default
/// "fetch everything" behaviour is fine for small collections; bigger
/// resources should set `pageSize` and call `fetchMore()` from the view.
class ReactiveListModel : public QAbstractListModel
{
    Q_OBJECT
    QML_ELEMENT

    Q_PROPERTY(QString baseUrl   READ baseUrl   WRITE setBaseUrl   NOTIFY baseUrlChanged)
    Q_PROPERTY(QString token     READ token     WRITE setToken     NOTIFY tokenChanged)
    Q_PROPERTY(QString source    READ source    WRITE setSource    NOTIFY sourceChanged)
    Q_PROPERTY(QString topic     READ topic     WRITE setTopic     NOTIFY topicChanged)
    Q_PROPERTY(bool    ready     READ ready                        NOTIFY readyChanged)
    Q_PROPERTY(QString error     READ error                        NOTIFY errorChanged)

public:
    explicit ReactiveListModel(QObject* parent = nullptr);
    ~ReactiveListModel() override;

    // QAbstractListModel
    int rowCount(const QModelIndex& parent = QModelIndex()) const override;
    QVariant data(const QModelIndex& index, int role) const override;
    QHash<int, QByteArray> roleNames() const override;

    QString baseUrl() const { return m_baseUrl; }
    void setBaseUrl(const QString& v);

    QString token() const { return m_token; }
    void setToken(const QString& v);

    QString source() const { return m_source; }
    void setSource(const QString& v);

    QString topic() const { return m_topic; }
    void setTopic(const QString& v);

    bool ready() const noexcept { return m_ready; }
    QString error() const { return m_error; }

    /// Triggers a re-fetch from `source`. Useful for manual refresh and
    /// after a Mercure version gap has been detected.
    Q_INVOKABLE void refresh();

    /// Optimistically apply a local change and POST/PATCH/DELETE the
    /// matching command. The model marks the row `pending` until the
    /// matching Mercure echo arrives (correlation-key matched). On HTTP
    /// 4xx/5xx or timeout, rolls back and emits `commandFailed` /
    /// `commandTimedOut`.
    ///
    /// @param method one of "POST", "PATCH", "DELETE"
    /// @param path   absolute path on the backend, e.g. "/api/todos/42"
    /// @param body   QVariantMap to JSON-encode (or QVariant{} for none)
    /// @param optimistic local mutation to apply immediately:
    ///                   {"op":"upsert"|"delete", "id":..., "data":{...}}
    Q_INVOKABLE void invoke(const QString& method,
                            const QString& path,
                            const QVariant& body,
                            const QVariantMap& optimistic);

signals:
    void baseUrlChanged();
    void tokenChanged();
    void sourceChanged();
    void topicChanged();
    void readyChanged();
    void errorChanged();

    void commandSucceeded(const QString& correlationKey, const QVariant& response);
    void commandFailed(const QString& correlationKey, int status, const QVariant& problem);
    void commandTimedOut(const QString& correlationKey);

private slots:
    void onFetchFinished();
    void onMercureUpdate(const QString& data, const QString& id);
    void onCommandReplyFinished();

private:
    void rewireMercure();
    void setReady(bool r);
    void setError(const QString& e);

    void fetchInitial();
    QByteArray buildIdempotencyKey() const;
    void applyEnvelope(const QJsonObject& envelope);
    void applyOptimisticDiff(const QVariantMap& diff, const QByteArray& key);
    void rollbackOptimistic(const QByteArray& key);

    int findIndexById(const QString& id) const;
    QHash<int, QByteArray> deriveRoleNames(const QJsonObject& sample) const;
    void resetRolesFromSample(const QJsonObject& sample);
    QVariant roleValue(const QJsonObject& row, int role) const;

    QString m_baseUrl;
    QString m_token;
    QString m_source;
    QString m_topic;
    bool    m_ready = false;
    QString m_error;

    QNetworkAccessManager* m_nam     = nullptr;
    QNetworkReply*         m_pending = nullptr;
    MercureClient*         m_mercure = nullptr;

    QVector<QJsonObject> m_rows;
    QHash<QString, int>  m_idToIndex;
    QHash<int, QByteArray> m_roles;
    int                  m_pendingRole = -1;  // assigned when roles built

    int m_lastVersion = 0;

    /// In-flight optimistic mutations keyed by Idempotency-Key.
    /// Stored: { backupRow (or sentinel), action ("upsert"/"delete"), id }.
    struct InFlight {
        QString    id;
        QString    op;            // "upsert" or "delete"
        bool       hadRow = false;
        QJsonObject backupRow;    // pre-mutation snapshot for rollback
    };
    QHash<QByteArray, InFlight> m_inFlight;

    QHash<QNetworkReply*, QByteArray> m_replyToKey;

    /// commandTimedOut fires this many ms after the request goes out
    /// without a Mercure echo (PLAN.md §5).
    static constexpr int kEchoTimeoutMs = 10000;
    QHash<QByteArray, QTimer*> m_echoTimers;
};

} // namespace PhpQml::Bridge