selection_delegate.hpp

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// Copyright Take Vos 2021.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
 
#include "../label.hpp"
#include <memory>
#include <functional>
#include <vector>
 
namespace hi { inline namespace v1 {
 
class selection_delegate {
public:
    using notifier_type = notifier<>;
    using callback_token = notifier_type::callback_token;
    using callback_proto = notifier_type::callback_proto;
 
    virtual ~selection_delegate() = default;
 
    virtual void init(widget& sender) noexcept {}
 
    virtual void deinit(widget& sender) noexcept {}
 
    virtual void set_selected(widget& sender, ssize_t index) noexcept {};
 
    virtual std::pair<std::vector<label>, ssize_t> options_and_selected(widget const& sender) const noexcept
    {
        return {{}, -1};
    }
 
    callback_token
    subscribe(forward_of<callback_proto> auto&& callback, callback_flags flags = callback_flags::synchronous) noexcept
    {
        return _notifier.subscribe(hi_forward(callback), flags);
    }
 
protected:
    notifier_type _notifier;
};
 
template<typename T>
class default_selection_delegate : public selection_delegate {
public:
    using value_type = T;
    using option_type = std::pair<value_type, label>;
    using options_type = std::vector<option_type>;
 
    observer<value_type> value;
    observer<options_type> options;
    observer<value_type> off_value;
 
    default_selection_delegate(
        forward_of<observer<value_type>> auto&& value,
        forward_of<observer<options_type>> auto&& options,
        forward_of<observer<value_type>> auto&& off_value) noexcept :
        value(hi_forward(value)), options(hi_forward(options)), off_value(hi_forward(off_value))
    {
        // clang-format off
        _value_cbt = this->value.subscribe([&](auto...){ this->_notifier(); });
        _options_cbt = this->options.subscribe([&](auto...){ this->_notifier(); });
        _off_value_cbt = this->off_value.subscribe([&](auto...){ this->_notifier(); });
        // clang-format on
    }
 
    default_selection_delegate(
        forward_of<observer<value_type>> auto&& value,
        forward_of<observer<options_type>> auto&& options) noexcept :
        default_selection_delegate(hi_forward(value), hi_forward(options), value_type{})
    {
    }
 
    void set_selected(widget& sender, ptrdiff_t index) noexcept override
    {
        if (index == -1 || index >= std::ssize(*options)) {
            value = *off_value;
        } else {
            value = (*options)[index].first;
        }
    }
 
    std::pair<std::vector<label>, ptrdiff_t> options_and_selected(widget const& sender) const noexcept override
    {
        auto labels = std::vector<label>{};
        labels.reserve(options->size());
 
        auto index = 0_z;
        auto selected_index = -1_z;
        for (auto&& option : *options) {
            if (*value == option.first) {
                selected_index = index;
            }
            labels.push_back(option.second);
            ++index;
        }
 
        return {std::move(labels), selected_index};
    }
 
private:
    typename decltype(value)::callback_token _value_cbt;
    typename decltype(options)::callback_token _options_cbt;
    typename decltype(off_value)::callback_token _off_value_cbt;
};
 
[[nodiscard]] std::shared_ptr<selection_delegate>
    make_default_selection_delegate(auto&& value, auto&& options, auto&&...off_value) noexcept
    requires(sizeof...(off_value) <= 1) and
    requires
{
    default_selection_delegate<observer_decay_t<decltype(value)>>{
        hi_forward(value), hi_forward(options), hi_forward(off_value)...};
}
{
    return std::make_shared<default_selection_delegate<observer_decay_t<decltype(value)>>>(
        hi_forward(value), hi_forward(options), hi_forward(off_value)...);
}
 
}} // namespace hi::v1