CompletionProxyModel.h

// SPDX-FileCopyrightText: 2021 Nheko Contributors
//
// SPDX-License-Identifier: GPL-3.0-or-later

#pragma once

// Class for showing a limited amount of completions at a time

#include <QAbstractProxyModel>

template<typename Key, typename Value>
struct trie
{
        std::vector<Value> values;
        std::map<Key, trie> next;

        void insert(const QVector<Key> &keys, const Value &v)
        {
                auto t = this;
                for (const auto k : keys) {
                        t = &t->next[k];
                }

                t->values.push_back(v);
        }

        std::vector<Value> valuesAndSubvalues(size_t limit = -1) const
        {
                std::vector<Value> ret;
                if (limit < 200)
                        ret.reserve(limit);

                for (const auto &v : values) {
                        if (ret.size() >= limit)
                                return ret;
                        else
                                ret.push_back(v);
                }

                for (const auto &[k, t] : next) {
                        (void)k;
                        if (ret.size() >= limit)
                                return ret;
                        else {
                                auto temp = t.valuesAndSubvalues(limit - ret.size());
                                for (auto &&v : temp) {
                                        if (ret.size() >= limit)
                                                return ret;

                                        if (std::find(ret.begin(), ret.end(), v) == ret.end()) {
                                                ret.push_back(std::move(v));
                                        }
                                }
                        }
                }

                return ret;
        }

        std::vector<Value> search(const QVector<Key> &keys, //< TODO(Nico): replace this with a span
                                  size_t result_count_limit,
                                  size_t max_edit_distance_ = 2) const
        {
                std::vector<Value> ret;
                if (!result_count_limit)
                        return ret;

                if (keys.isEmpty())
                        return valuesAndSubvalues(result_count_limit);

                auto append = [&ret, result_count_limit](std::vector<Value> &&in) {
                        for (auto &&v : in) {
                                if (ret.size() >= result_count_limit)
                                        return;

                                if (std::find(ret.begin(), ret.end(), v) == ret.end()) {
                                        ret.push_back(std::move(v));
                                }
                        }
                };

                auto limit = [&ret, result_count_limit] {
                        return std::min(result_count_limit, (result_count_limit - ret.size()) * 2);
                };

                // Try first exact matches, then with maximum errors
                for (size_t max_edit_distance = 0;
                     max_edit_distance <= max_edit_distance_ && ret.size() < result_count_limit;
                     max_edit_distance += 1) {
                        if (max_edit_distance && ret.size() < result_count_limit) {
                                max_edit_distance -= 1;

                                // swap chars case
                                if (keys.size() >= 2) {
                                        auto t = this;
                                        for (int i = 1; i >= 0; i--) {
                                                if (auto e = t->next.find(keys[i]);
                                                    e != t->next.end()) {
                                                        t = &e->second;
                                                } else {
                                                        t = nullptr;
                                                        break;
                                                }
                                        }

                                        if (t) {
                                                append(t->search(
                                                  keys.mid(2), limit(), max_edit_distance));
                                        }
                                }

                                // insert case
                                for (const auto &[k, t] : this->next) {
                                        if (k == keys[0])
                                                continue;
                                        if (ret.size() >= limit())
                                                break;

                                        // insert
                                        append(t.search(keys, limit(), max_edit_distance));
                                }

                                // delete character case
                                append(this->search(keys.mid(1), limit(), max_edit_distance));

                                // substitute case
                                for (const auto &[k, t] : this->next) {
                                        if (k == keys[0])
                                                continue;
                                        if (ret.size() >= limit())
                                                break;

                                        // substitute
                                        append(t.search(keys.mid(1), limit(), max_edit_distance));
                                }

                                max_edit_distance += 1;
                        }

                        if (auto e = this->next.find(keys[0]); e != this->next.end()) {
                                append(e->second.search(keys.mid(1), limit(), max_edit_distance));
                        }
                }

                return ret;
        }
};

class CompletionProxyModel : public QAbstractProxyModel
{
        Q_OBJECT
        Q_PROPERTY(
          QString searchString READ searchString WRITE setSearchString NOTIFY newSearchString)
public:
        CompletionProxyModel(QAbstractItemModel *model,
                             int max_mistakes       = 2,
                             size_t max_completions = 7,
                             QObject *parent        = nullptr);

        void invalidate();

        QHash<int, QByteArray> roleNames() const override;
        int rowCount(const QModelIndex &parent = QModelIndex()) const override;
        int columnCount(const QModelIndex &) const override;

        QModelIndex mapFromSource(const QModelIndex &sourceIndex) const override;
        QModelIndex mapToSource(const QModelIndex &proxyIndex) const override;

        QModelIndex index(int row,
                          int column,
                          const QModelIndex &parent = QModelIndex()) const override;
        QModelIndex parent(const QModelIndex &) const override;

public slots:
        QVariant completionAt(int i) const;

        void setSearchString(QString s);
        QString searchString() const { return searchString_; }

signals:
        void newSearchString(QString);

private:
        QString searchString_;
        trie<uint, int> trie_;
        std::vector<int> mapping;
        int maxMistakes_;
        size_t max_completions_;
};