#include <XCEngine/UI/Text/UITextInputController.h>

#include <XCEngine/Input/InputTypes.h>
#include <XCEngine/UI/Text/UITextEditing.h>

#include <algorithm>

namespace XCEngine {
namespace UI {
namespace Text {

namespace {

using XCEngine::Input::KeyCode;

} // namespace

void ClampCaret(UITextInputState& state) {
    state.caret = (std::min)(state.caret, state.value.size());
}

bool InsertCharacter(UITextInputState& state, std::uint32_t character) {
    if (character < 32u || character == 127u) {
        return false;
    }

    std::string encoded = {};
    AppendUtf8Codepoint(encoded, character);
    if (encoded.empty()) {
        return false;
    }

    ClampCaret(state);
    state.value.insert(state.caret, encoded);
    state.caret += encoded.size();
    return true;
}

UITextInputEditResult HandleKeyDown(
    UITextInputState& state,
    std::int32_t keyCode,
    const UIInputModifiers& modifiers,
    const UITextInputOptions& options) {
    ClampCaret(state);

    UITextInputEditResult result = {};

    if (keyCode == static_cast<std::int32_t>(KeyCode::Backspace)) {
        result.handled = true;
        if (state.caret > 0u) {
            const std::size_t previousCaret = RetreatUtf8Offset(state.value, state.caret);
            state.value.erase(previousCaret, state.caret - previousCaret);
            state.caret = previousCaret;
            result.valueChanged = true;
        }
        return result;
    }

    if (keyCode == static_cast<std::int32_t>(KeyCode::Delete)) {
        result.handled = true;
        if (state.caret < state.value.size()) {
            const std::size_t nextCaret = AdvanceUtf8Offset(state.value, state.caret);
            state.value.erase(state.caret, nextCaret - state.caret);
            result.valueChanged = true;
        }
        return result;
    }

    if (keyCode == static_cast<std::int32_t>(KeyCode::Left)) {
        result.handled = true;
        state.caret = RetreatUtf8Offset(state.value, state.caret);
        return result;
    }

    if (keyCode == static_cast<std::int32_t>(KeyCode::Right)) {
        result.handled = true;
        state.caret = AdvanceUtf8Offset(state.value, state.caret);
        return result;
    }

    if (keyCode == static_cast<std::int32_t>(KeyCode::Up) && options.multiline) {
        result.handled = true;
        state.caret = MoveCaretVertically(state.value, state.caret, -1);
        return result;
    }

    if (keyCode == static_cast<std::int32_t>(KeyCode::Down) && options.multiline) {
        result.handled = true;
        state.caret = MoveCaretVertically(state.value, state.caret, 1);
        return result;
    }

    if (keyCode == static_cast<std::int32_t>(KeyCode::Home)) {
        result.handled = true;
        state.caret = options.multiline
            ? FindLineStartOffset(state.value, state.caret)
            : 0u;
        return result;
    }

    if (keyCode == static_cast<std::int32_t>(KeyCode::End)) {
        result.handled = true;
        state.caret = options.multiline
            ? FindLineEndOffset(state.value, state.caret)
            : state.value.size();
        return result;
    }

    if (keyCode == static_cast<std::int32_t>(KeyCode::Enter)) {
        result.handled = true;
        if (options.multiline) {
            state.value.insert(state.caret, "\n");
            ++state.caret;
            result.valueChanged = true;
        } else {
            result.submitRequested = true;
        }
        return result;
    }

    if (keyCode == static_cast<std::int32_t>(KeyCode::Tab) &&
        options.multiline &&
        !modifiers.control &&
        !modifiers.alt &&
        !modifiers.super) {
        result.handled = true;

        if (modifiers.shift) {
            const std::size_t lineStart = FindLineStartOffset(state.value, state.caret);
            std::size_t removed = 0u;
            while (removed < options.tabWidth &&
                lineStart + removed < state.value.size() &&
                state.value[lineStart + removed] == ' ') {
                ++removed;
            }

            if (removed > 0u) {
                state.value.erase(lineStart, removed);
                state.caret = state.caret >= lineStart + removed ? state.caret - removed : lineStart;
                result.valueChanged = true;
            }
        } else {
            state.value.insert(state.caret, std::string(options.tabWidth, ' '));
            state.caret += options.tabWidth;
            result.valueChanged = true;
        }

        return result;
    }

    return result;
}

} // namespace Text
} // namespace UI
} // namespace XCEngine