#include "RichTextBox.hpp"
#include "TextStyleModifier.hpp"
#include <limits>
#include <modules/skparagraph/include/DartTypes.h>
#include <modules/skparagraph/include/Metrics.h>
#include <modules/skparagraph/src/TextLine.h>
#include <modules/skunicode/include/SkUnicode.h>
#include <modules/skunicode/include/SkUnicode_icu.h>
#include <modules/skparagraph/src/ParagraphBuilderImpl.h>
#include <modules/skparagraph/src/ParagraphImpl.h>
#include <Helpers/MathExtras.hpp>
#include <src/base/SkUTF.h>
#include <cereal/types/string.hpp>

void RichTextBox::RichTextData::Paragraph::save(cereal::PortableBinaryOutputArchive& a) const {
    a(text);
    a(static_cast<uint32_t>(tStyles.size()));
    for(auto& [pos, styles] : tStyles) {
        a(pos, static_cast<uint16_t>(styles.size()));
        for(auto& [styleType, style] : styles)
            a(static_cast<uint16_t>(styleType), *style);
    }
}

void RichTextBox::RichTextData::Paragraph::load(cereal::PortableBinaryInputArchive& a) {
    a(text);
    uint32_t styleCount;
    a(styleCount);
    tStyles.clear();
    for(uint32_t i = 0; i < styleCount; i++) {
        uint32_t pos;
        uint16_t styleCountAtPos;
        a(pos, styleCountAtPos);
        TextModAtPosContainer& mods = tStyles[pos];
        for(uint16_t j = 0; j < styleCountAtPos; j++) {
            uint16_t styleType;
            a(styleType);
            std::shared_ptr<TextStyleModifier> modifier = TextStyleModifier::allocate_modifier(static_cast<TextStyleModifier::ModifierType>(styleType));
            a(*modifier);
            mods.emplace(static_cast<TextStyleModifier::ModifierType>(styleType), modifier);
        }
    }
}

bool RichTextBox::TextPosition::operator<(const RichTextBox::TextPosition& o) const {
    return (this->fParagraphIndex < o.fParagraphIndex) || (this->fParagraphIndex == o.fParagraphIndex && this->fTextByteIndex < o.fTextByteIndex);
}

RichTextBox::RichTextBox() {
    paragraphs.emplace_back();
}

void RichTextBox::process_key_input(Cursor& cur, InputKey in, bool ctrl, bool shift) {
    bool moved = false;

    switch(in) {
        case InputKey::LEFT:
            cur.pos = cur.selectionBeginPos = move(ctrl ? Movement::LEFT_WORD : Movement::LEFT, cur.pos, nullptr, true);
            moved = true;
            break;
        case InputKey::RIGHT:
            cur.pos = cur.selectionBeginPos = move(ctrl ? Movement::RIGHT_WORD : Movement::RIGHT, cur.pos, nullptr, true);
            moved = true;
            break;
        case InputKey::UP:
            cur.pos = cur.selectionBeginPos = move(Movement::UP, cur.pos, &cur.previousX);
            moved = true;
            break;
        case InputKey::DOWN:
            cur.pos = cur.selectionBeginPos = move(Movement::DOWN, cur.pos, &cur.previousX);
            moved = true;
            break;
        case InputKey::HOME:
            cur.pos = cur.selectionBeginPos = move(Movement::HOME, cur.pos);
            moved = true;
            break;
        case InputKey::END:
            cur.pos = cur.selectionBeginPos = move(Movement::END, cur.pos);
            moved = true;
            break;
        case InputKey::BACKSPACE:
            if(cur.selectionBeginPos != cur.selectionEndPos)
                cur.selectionEndPos = cur.selectionBeginPos = cur.pos = remove(cur.selectionBeginPos, cur.selectionEndPos);
            else
                cur.selectionEndPos = cur.selectionBeginPos = cur.pos = remove(cur.pos, move(ctrl ? Movement::LEFT_WORD : Movement::LEFT, cur.pos));
            break;
        case InputKey::DELETE:
            if(cur.selectionBeginPos != cur.selectionEndPos)
                cur.selectionEndPos = cur.selectionBeginPos = cur.pos = remove(cur.selectionBeginPos, cur.selectionEndPos);
            else
                cur.selectionEndPos = cur.selectionBeginPos = cur.pos = remove(cur.pos, move(ctrl ? Movement::RIGHT_WORD : Movement::RIGHT, cur.pos));
            break;
        case InputKey::ENTER:
            process_text_input(cur, "\n");
            break;
        case InputKey::TAB: 
            process_text_input(cur, "\t");
            break;
        case InputKey::SELECT_ALL:
            cur.selectionBeginPos = {0, 0};
            cur.pos = cur.selectionEndPos = {paragraphs.back().text.size(), paragraphs.size() - 1};
            break;
    }

    if(moved && !shift)
        cur.selectionEndPos = cur.selectionBeginPos;

    if(in != InputKey::UP && in != InputKey::DOWN)
        cur.previousX = std::nullopt;
}

void RichTextBox::process_mouse_left_button(Cursor& cur, const Vector2f& pos, bool clicked, bool held, bool shift) {
    if(clicked || held) {
        rebuild();

        cur.pos = get_text_pos_closest_to_point(pos);
        cur.selectionBeginPos = cur.pos;
        if(clicked && !shift)
            cur.selectionEndPos = cur.selectionBeginPos;
        cur.previousX = std::nullopt;
    }
}

std::string RichTextBox::process_copy(Cursor& cur) {
    return get_text_between(cur.selectionBeginPos, cur.selectionEndPos);
}

std::string RichTextBox::process_cut(Cursor& cur) {
    std::string toRet = process_copy(cur);
    if(cur.selectionBeginPos != cur.selectionEndPos) {
        cur.selectionEndPos = cur.selectionBeginPos = cur.pos = remove(cur.selectionBeginPos, cur.selectionEndPos);
        cur.previousX = std::nullopt;
    }
    return toRet;
}

void RichTextBox::process_text_input(Cursor& cur, const std::string& in) {
    if(!in.empty()) {
        if(cur.selectionBeginPos != cur.selectionEndPos)
            cur.selectionEndPos = cur.selectionBeginPos = cur.pos = remove(cur.selectionBeginPos, cur.selectionEndPos);
        cur.selectionEndPos = cur.selectionBeginPos = cur.pos = insert(cur.pos, in);
        cur.previousX = std::nullopt;
    }
}

size_t RichTextBox::count_grapheme(const std::string& text) {
    auto u = SkUnicodes::ICU::Make();
    auto breakIterator = u->makeBreakIterator(SkUnicode::BreakType::kGraphemes);
    breakIterator->setText(text.c_str(), text.size());
    size_t count = 0;
    while(!breakIterator->isDone()) {
        breakIterator->next();
        count++;
    }
    return count - 1;
}

size_t RichTextBox::next_grapheme(const std::string& text, size_t textBytePos) {
    if(textBytePos == text.size())
        return text.size();
    auto u = SkUnicodes::ICU::Make();
    auto breakIterator = u->makeBreakIterator(SkUnicode::BreakType::kGraphemes);
    breakIterator->setText(text.c_str() + textBytePos, text.size() - textBytePos);
    size_t count = breakIterator->next();
    return count + textBytePos;
}

size_t RichTextBox::prev_grapheme(const std::string& text, size_t textBytePos) {
    if(textBytePos == 0)
        return 0;
    auto u = SkUnicodes::ICU::Make();
    auto breakIterator = u->makeBreakIterator(SkUnicode::BreakType::kGraphemes);
    breakIterator->setText(text.c_str(), text.size());
    size_t toRet = 0;
    for(;;) {
        size_t potentialNext = breakIterator->next();
        if(potentialNext >= textBytePos)
            return toRet;
        toRet = potentialNext;
    }
}

RichTextBox::TextPosition RichTextBox::get_text_pos_from_byte_pos(const std::string& text, size_t textBytePos) {
    TextPosition toRet{0, 0};
    for(size_t i = 0; i < textBytePos; i++) {
        char c = text[i];
        if(c == '\n') {
            toRet.fTextByteIndex = 0;
            toRet.fParagraphIndex++;
        }
        else
            toRet.fTextByteIndex++;
    }
    return toRet;
}

size_t RichTextBox::get_byte_pos_from_text_pos(TextPosition textPos) {
    size_t toRet = 0;
    for(size_t pIndex = 0; pIndex < textPos.fParagraphIndex; pIndex++)
        toRet += paragraphs[pIndex].text.size() + 1; // Add 1 byte for newline
    toRet += textPos.fTextByteIndex;
    return toRet;
}

RichTextBox::TextPosition RichTextBox::get_text_pos_closest_to_point(Vector2f point) {
    rebuild();

    skia::textlayout::Paragraph::GlyphClusterInfo glyphInfo;

    size_t pIndex = 0;

    for(; pIndex < (paragraphs.size() - 1) && point.y() > paragraphs[pIndex].p->getHeight(); pIndex++)
        point.y() -= paragraphs[pIndex].p->getHeight();

    ParagraphData& pData = paragraphs[pIndex];

    bool foundGlyph = pData.p->getClosestGlyphClusterAt(point.x(), point.y(), &glyphInfo);
    if(foundGlyph) {
        TextPosition toRet = {0, pIndex};
        toRet.fTextByteIndex = glyphInfo.fClusterTextRange.start;

        if(glyphInfo.fGlyphClusterPosition == skia::textlayout::TextDirection::kLtr) {
            if(std::abs(glyphInfo.fBounds.right() - point.x()) < std::abs(glyphInfo.fBounds.left() - point.x()))
                toRet.fTextByteIndex = next_grapheme(pData.text, toRet.fTextByteIndex);
        }
        else {
            if(std::abs(glyphInfo.fBounds.left() - point.x()) < std::abs(glyphInfo.fBounds.right() - point.x()))
                toRet.fTextByteIndex = next_grapheme(pData.text, toRet.fTextByteIndex);
        }

        // Space at the end of a line will bring the cursor to the next line, check if the cursor moved to the next line
        if(toRet.fTextByteIndex != pData.text.size()) {
            skia::textlayout::LineMetrics lineMetrics;
            int lineNumber = pData.p->getLineNumberAt(toRet.fTextByteIndex);
            if(lineNumber > 0) {
                bool lineMetricsFound = pData.p->getLineMetricsAt(lineNumber, &lineMetrics);
                if(lineMetricsFound) {
                    float top = lineMetrics.fBaseline - lineMetrics.fAscent;
                    if(point.y() < top)
                        toRet.fTextByteIndex = prev_grapheme(pData.text, toRet.fTextByteIndex);
                }
            }
        }

        return toRet;
    }
    else
        return TextPosition{0, pIndex};
}

RichTextBox::RichTextData RichTextBox::get_rich_text_data() {
    RichTextData toRet;
    for(auto& p : paragraphs) {
        toRet.paragraphs.emplace_back();
        toRet.paragraphs.back().text = p.text;
        toRet.paragraphs.back().tStyles = p.tStyles;
    }
    return toRet;
}

void RichTextBox::clear_text() {
    paragraphs.clear();
    paragraphs.emplace_back();
}

void RichTextBox::set_string(const std::string& str) {
    clear_text();
    insert({0, 0}, str);
}

void RichTextBox::set_rich_text_data(const RichTextData& richText) {
    paragraphs.clear();
    for(auto& p : richText.paragraphs) {
        paragraphs.emplace_back();
        paragraphs.back().text = p.text;
        paragraphs.back().tStyles = p.tStyles;
    }
    if(richText.paragraphs.empty())
        paragraphs.emplace_back();
    needsRebuild = true;
}

std::string RichTextBox::get_string() {
    return get_text_between({0, 0}, move(RichTextBox::Movement::END, {0, 0}));
}

std::string RichTextBox::get_text_between(TextPosition p1, TextPosition p2) {
    p1 = move(Movement::NOWHERE, p1);
    p2 = move(Movement::NOWHERE, p2);

    if(p1 == p2)
        return "";

    TextPosition start = std::min(p1, p2);
    TextPosition end = std::max(p1, p2);

    std::string toRet;

    for(size_t pIndex = start.fParagraphIndex; pIndex <= end.fParagraphIndex; pIndex++) {
        size_t textIndexStart = pIndex == start.fParagraphIndex ? start.fTextByteIndex : 0;
        size_t textIndexEnd = pIndex == end.fParagraphIndex ? end.fTextByteIndex : paragraphs[pIndex].text.size();
        toRet += paragraphs[pIndex].text.substr(textIndexStart, textIndexEnd - textIndexStart);
        if(pIndex != end.fParagraphIndex)
            toRet += '\n';
    }

    return toRet;
}

void RichTextBox::set_initial_text_style_modifier(const std::shared_ptr<TextStyleModifier>& modifier) {
    std::shared_ptr<TextStyleModifier>& modToSet = paragraphs.back().tStyles[0][modifier->get_type()];
    needsRebuild |= ((modToSet == nullptr) || (!modifier->equivalent(*modToSet)));
    modToSet = modifier;
}

void RichTextBox::set_text_style_modifier_between(TextPosition p1, TextPosition p2, const std::shared_ptr<TextStyleModifier>& modifier) {
    needsRebuild = true;
}

RichTextBox::TextPosition RichTextBox::move(Movement movement, TextPosition pos, std::optional<float>* previousX, bool flipDependingOnTextDirection) {
    if(pos.fParagraphIndex >= paragraphs.size()) {
        pos.fParagraphIndex = paragraphs.size() - 1;
        pos.fTextByteIndex = paragraphs[pos.fParagraphIndex].text.size();
    }

    if(pos.fTextByteIndex >= paragraphs[pos.fParagraphIndex].text.size())
        pos.fTextByteIndex = paragraphs[pos.fParagraphIndex].text.size();

    if(movement != Movement::NOWHERE && movement != Movement::HOME && movement != Movement::END) {
        rebuild();
        if(flipDependingOnTextDirection && paragraphs[pos.fParagraphIndex].pStyle.getTextDirection() == skia::textlayout::TextDirection::kRtl) {
            if(movement == Movement::LEFT)
                movement = Movement::RIGHT;
            else if(movement == Movement::RIGHT)
                movement = Movement::LEFT;
            else if(movement == Movement::LEFT_WORD)
                movement = Movement::RIGHT_WORD;
            else if(movement == Movement::RIGHT_WORD)
                movement = Movement::LEFT_WORD;
        }
    }

    switch (movement) {
        case Movement::NOWHERE:
            break;
        case Movement::LEFT: {
            if(pos.fTextByteIndex == 0) {
                if(pos.fParagraphIndex != 0) {
                    pos.fParagraphIndex--;
                    pos.fTextByteIndex = paragraphs[pos.fParagraphIndex].text.size();
                }
            }
            else
                pos.fTextByteIndex = prev_grapheme(paragraphs[pos.fParagraphIndex].text, pos.fTextByteIndex);
            break;
        }
        case Movement::RIGHT: {
            if(pos.fTextByteIndex == paragraphs[pos.fParagraphIndex].text.size()) {
                if(pos.fParagraphIndex != paragraphs.size() - 1) {
                    pos.fParagraphIndex++;
                    pos.fTextByteIndex = 0;
                }
            }
            else
                pos.fTextByteIndex = next_grapheme(paragraphs[pos.fParagraphIndex].text, pos.fTextByteIndex);
            break;
        }
        case Movement::UP: {
            assert(previousX != nullptr);

            int lineNumber = paragraphs[pos.fParagraphIndex].p->getLineNumberAt(pos.fTextByteIndex == paragraphs[pos.fParagraphIndex].text.size() ? prev_grapheme(paragraphs[pos.fParagraphIndex].text, pos.fTextByteIndex) : pos.fTextByteIndex);
            if(lineNumber <= 0 && pos.fParagraphIndex == 0) {
                pos.fTextByteIndex = 0;
                if(previousX != nullptr)
                    *previousX = get_cursor_rect(pos).centerX();
            }
            else {
                if(lineNumber <= 0 && paragraphs[pos.fParagraphIndex - 1].text.empty()) {
                    if(previousX != nullptr && !previousX->has_value())
                        *previousX = get_cursor_rect(pos).centerX();
                    pos = TextPosition{0, pos.fParagraphIndex - 1};
                }
                else {
                    skia::textlayout::LineMetrics prevLineMetrics;
                    SkRect cursorRect = get_cursor_rect(pos);
                    if(lineNumber <= 0) {
                        pos.fParagraphIndex--;
                        lineNumber = paragraphs[pos.fParagraphIndex].p->lineNumber();
                    }
                    paragraphs[pos.fParagraphIndex].p->getLineMetricsAt(lineNumber - 1, &prevLineMetrics);
                    Vector2f pointToCheck = {(previousX != nullptr && previousX->has_value()) ? previousX->value() : cursorRect.centerX(), prevLineMetrics.fBaseline + paragraphs[pos.fParagraphIndex].heightOffset};
                    pos = get_text_pos_closest_to_point(pointToCheck);

                    if(previousX != nullptr && !previousX->has_value())
                        *previousX = pointToCheck.x();
                }
            }
            break;
        }
        case Movement::DOWN: {
            assert(previousX != nullptr);

            int lineNumber = paragraphs[pos.fParagraphIndex].p->getLineNumberAt(pos.fTextByteIndex);
            if((lineNumber == -1 || lineNumber == static_cast<int>(paragraphs[pos.fParagraphIndex].p->lineNumber() - 1)) && pos.fParagraphIndex == (paragraphs.size() - 1)) {
                pos.fTextByteIndex = paragraphs[pos.fParagraphIndex].text.size();
                if(previousX != nullptr)
                    *previousX = get_cursor_rect(pos).centerX();
            }
            else {
                if((lineNumber == -1 || lineNumber == static_cast<int>(paragraphs[pos.fParagraphIndex].p->lineNumber() - 1)) && paragraphs[pos.fParagraphIndex + 1].text.empty()) {
                    if(previousX != nullptr && !previousX->has_value())
                        *previousX = get_cursor_rect(pos).centerX();
                    pos = TextPosition{0, pos.fParagraphIndex + 1};
                }
                else {
                    skia::textlayout::LineMetrics nextLineMetrics;
                    SkRect cursorRect = get_cursor_rect(pos);
                    if(lineNumber == -1 || lineNumber == static_cast<int>(paragraphs[pos.fParagraphIndex].p->lineNumber() - 1)) {
                        pos.fParagraphIndex++;
                        lineNumber = -1;
                    }
                    paragraphs[pos.fParagraphIndex].p->getLineMetricsAt(lineNumber + 1, &nextLineMetrics);
                    Vector2f pointToCheck = {(previousX != nullptr && previousX->has_value()) ? previousX->value() : cursorRect.centerX(), nextLineMetrics.fBaseline + paragraphs[pos.fParagraphIndex].heightOffset};
                    pos = get_text_pos_closest_to_point(pointToCheck);

                    if(previousX != nullptr && !previousX->has_value())
                        *previousX = pointToCheck.x();
                }
            }
            break;
        }
        case Movement::LEFT_WORD: {
            if(pos == TextPosition{0, 0})
                break;

            std::string fullText = get_string();
            size_t bytePosInFullText = get_byte_pos_from_text_pos(pos);

            auto u = SkUnicodes::ICU::Make();

            size_t byteIndexToRet = 0;

            auto breakIterator = u->makeBreakIterator(SkUnicode::BreakType::kWords);
            breakIterator->setText(fullText.c_str(), fullText.size());

            while(!breakIterator->isDone()) {
                size_t nextByteIndex = breakIterator->next();
                if(nextByteIndex >= bytePosInFullText)
                    return get_text_pos_from_byte_pos(fullText, byteIndexToRet);

                const char* tPtr = fullText.c_str() + nextByteIndex;
                SkUnichar u = SkUTF::NextUTF8(&tPtr, fullText.c_str() + fullText.size());
                if(!SkUnicodes::ICU::Make()->isWhitespace(u))
                    byteIndexToRet = nextByteIndex;
            }
            break;
        }
        case Movement::RIGHT_WORD: {
            TextPosition endPos = move(Movement::END, {0, 0});
            if(pos == endPos)
                break;

            std::string fullText = get_string();
            size_t bytePosInFullText = get_byte_pos_from_text_pos(pos);

            auto u = SkUnicodes::ICU::Make();
            auto breakIterator = u->makeBreakIterator(SkUnicode::BreakType::kWords);

            breakIterator->setText(fullText.c_str() + bytePosInFullText, fullText.size() - bytePosInFullText);

            while(!breakIterator->isDone()) {
                size_t p = breakIterator->next() + bytePosInFullText;
                if(p == fullText.size())
                    return get_text_pos_from_byte_pos(fullText, p);
                const char* tPtr = fullText.c_str() + p;
                SkUnichar u = SkUTF::NextUTF8(&tPtr, fullText.c_str() + fullText.size());
                if(!SkUnicodes::ICU::Make()->isWhitespace(u))
                    return get_text_pos_from_byte_pos(fullText, p);
            }

            break;
        }
        case Movement::HOME:
            pos.fTextByteIndex = 0;
            pos.fParagraphIndex = 0;
            break;
        case Movement::END:
            pos.fTextByteIndex = paragraphs.back().text.size();
            pos.fParagraphIndex = paragraphs.size() - 1;
            break;
    }
    return pos;

}

void RichTextBox::set_width(float newWidth) {
    if(width != newWidth) {
        width = newWidth;
        needsRebuild = true;
    }
}

void RichTextBox::set_allow_newlines(bool allow) {
    newlinesAllowed = allow;
}

void RichTextBox::set_font_collection(const sk_sp<skia::textlayout::FontCollection>& fC) {
    if(fontCollection != fC) {
        fontCollection = fC;
        needsRebuild = true;
    }
}

void RichTextBox::rebuild() {
    if(needsRebuild) {
        float heightOffset = 0.0f;
        skia::textlayout::TextStyle tStyle;

        for(ParagraphData& pData : paragraphs) {
            pData.pStyle.setTextAlign(skia::textlayout::TextAlign::kLeft);
            pData.pStyle.setTextDirection(skia::textlayout::TextDirection::kLtr);
            skia::textlayout::ParagraphBuilderImpl a(pData.pStyle, fontCollection, SkUnicodes::ICU::Make());

            size_t startPos = 0;
            for(auto& [pos, tStylesAtPos] : pData.tStyles) {
                if(pos > pData.text.size())
                    break;

                for(auto& [styleType, styleMod] : tStylesAtPos)
                    styleMod->modify_text_style(tStyle);
                if(startPos != pos) {
                    a.pushStyle(tStyle);
                    a.addText(pData.text.c_str() + startPos, pos - startPos);
                    a.pop();
                }
                startPos = pos;
            }

            if(startPos < pData.text.size()) {
                a.pushStyle(tStyle);
                a.addText(pData.text.c_str() + startPos, pData.text.size() - startPos);
                a.pop();
            }

            pData.p = a.Build();
            pData.p->layout(width);
            pData.heightOffset = heightOffset;
            heightOffset += pData.p->getHeight();
        }
        needsRebuild = false;
    }
}

void RichTextBox::set_tab_space_width(unsigned newTabWidth) {
    tabWidth = newTabWidth;
}

RichTextBox::TextPosition RichTextBox::insert(TextPosition pos, std::string_view textToInsert) {
    pos = move(Movement::NOWHERE, pos);

    for(char c : textToInsert) {
        if(c == '\n') {
            if(newlinesAllowed) {
                paragraphs.insert(paragraphs.begin() + pos.fParagraphIndex + 1, ParagraphData{});
                paragraphs[pos.fParagraphIndex + 1].text = paragraphs[pos.fParagraphIndex].text.substr(pos.fTextByteIndex, paragraphs[pos.fParagraphIndex].text.size() - pos.fTextByteIndex);
                paragraphs[pos.fParagraphIndex].text.erase(pos.fTextByteIndex, paragraphs[pos.fParagraphIndex].text.size() - pos.fTextByteIndex);
                pos.fParagraphIndex++;
                pos.fTextByteIndex = 0;
            }
        }
        else if(c == '\t') {
            paragraphs[pos.fParagraphIndex].text.insert(pos.fTextByteIndex, std::string(tabWidth, ' '));
            pos.fTextByteIndex += tabWidth;
        }
        else {
            paragraphs[pos.fParagraphIndex].text.insert(paragraphs[pos.fParagraphIndex].text.begin() + pos.fTextByteIndex, c);
            pos.fTextByteIndex++;
        }
    }

    needsRebuild = true;
    return pos;
}

RichTextBox::TextPosition RichTextBox::remove(TextPosition p1, TextPosition p2) {
    p1 = move(Movement::NOWHERE, p1);
    p2 = move(Movement::NOWHERE, p2);

    TextPosition start = std::min(p1, p2);
    TextPosition end = std::max(p1, p2);
    if(start == end || start.fParagraphIndex == paragraphs.size())
        return start;
    if(start.fParagraphIndex == end.fParagraphIndex) {
        assert(end.fTextByteIndex > start.fTextByteIndex);
        paragraphs[start.fParagraphIndex].text.erase(start.fTextByteIndex, end.fTextByteIndex - start.fTextByteIndex);
    }
    else {
        assert(end.fParagraphIndex < paragraphs.size());
        auto& paragraph = paragraphs[start.fParagraphIndex];
        paragraph.text.erase(start.fTextByteIndex, paragraph.text.size() - start.fTextByteIndex);
        paragraph.text.insert(start.fTextByteIndex, paragraphs[end.fParagraphIndex].text.substr(end.fTextByteIndex));
        paragraphs.erase(paragraphs.begin() + start.fParagraphIndex + 1, paragraphs.begin() + end.fParagraphIndex + 1);
    }
    needsRebuild = true;
    return start;
}

SkRect RichTextBox::get_cursor_rect(TextPosition pos) {
    pos = move(Movement::NOWHERE, pos);

    SkPoint topPoint;
    float height;

    const ParagraphData& pData = paragraphs[pos.fParagraphIndex];
    if(pData.text.empty()) {
        bool isAlignLeft = (pData.pStyle.getTextAlign() == skia::textlayout::TextAlign::kLeft) || (pData.pStyle.getTextAlign() == skia::textlayout::TextAlign::kJustify && pData.pStyle.getTextDirection() == skia::textlayout::TextDirection::kLtr);
        topPoint = {isAlignLeft ? 0.0f : pData.p->getMaxWidth(), pData.heightOffset};
        height = pData.p->getHeight();
    }
    else {
        if(pos.fTextByteIndex == pData.text.size()) {
            skia::textlayout::Paragraph::GlyphClusterInfo glyphInfo;
            bool exists = pData.p->getGlyphClusterAt(prev_grapheme(pData.text, pos.fTextByteIndex), &glyphInfo);
            if(exists) {
                bool isLtr = glyphInfo.fGlyphClusterPosition == skia::textlayout::TextDirection::kLtr;
                topPoint = (isLtr ? glyphInfo.fBounds.TR() : glyphInfo.fBounds.TL()) + SkPoint{0.0f, pData.heightOffset};
                height = glyphInfo.fBounds.height();
            }
            else {
                topPoint = {0.0f, pData.heightOffset};
                height = 0.0f;
            }
        }
        else {
            skia::textlayout::Paragraph::GlyphClusterInfo glyphInfo;
            bool exists = pData.p->getGlyphClusterAt(pos.fTextByteIndex, &glyphInfo);
            if(exists) {
                bool isLtr = glyphInfo.fGlyphClusterPosition == skia::textlayout::TextDirection::kLtr;
                topPoint = (isLtr ? glyphInfo.fBounds.TL() : glyphInfo.fBounds.TR()) + SkPoint{0.0f, pData.heightOffset};
                height = glyphInfo.fBounds.height();
            }
            else {
                topPoint = {0.0f, pData.heightOffset};
                height = 0.0f;
            }
        }
    }

    constexpr float CURSOR_WIDTH = 3.0f;

    return SkRect::MakeXYWH(topPoint.x() - CURSOR_WIDTH * 0.5f, topPoint.y(), CURSOR_WIDTH, height);
}

void RichTextBox::rects_between_text_positions_func(TextPosition p1, TextPosition p2, std::function<void(const SkRect& r)> f) {
    p1 = move(Movement::NOWHERE, p1);
    p2 = move(Movement::NOWHERE, p2);

    constexpr float SELECTION_RECT_EXTRA_AREA = 1.0f;

    TextPosition start = std::min(p1, p2);
    TextPosition end = std::max(p1, p2);

    for(size_t p = start.fParagraphIndex; p <= end.fParagraphIndex; p++) {
        size_t tStart = p == start.fParagraphIndex ? start.fTextByteIndex : 0;
        size_t tEnd = p == end.fParagraphIndex ? end.fTextByteIndex : paragraphs[p].text.size();
        ParagraphData& pData = paragraphs[p];
        for(size_t t = tStart; t < tEnd; t++) {
            skia::textlayout::Paragraph::GlyphClusterInfo glyphInfo;
            if(pData.p->getGlyphClusterAt(t, &glyphInfo)) {
                int lineNumber = pData.p->getLineNumberAt(t);
                if(lineNumber == -1)
                    break;
                skia::textlayout::LineMetrics lineMetrics;
                if(pData.p->getLineMetricsAt(lineNumber, &lineMetrics)) {
                    SkRect r = SkRect::MakeLTRB(glyphInfo.fBounds.left() - SELECTION_RECT_EXTRA_AREA, lineMetrics.fBaseline - lineMetrics.fAscent - SELECTION_RECT_EXTRA_AREA + pData.heightOffset, glyphInfo.fBounds.right() + SELECTION_RECT_EXTRA_AREA, lineMetrics.fBaseline + lineMetrics.fDescent + pData.heightOffset + SELECTION_RECT_EXTRA_AREA);
                    f(r);
                }
            }
        }
    }
}

void RichTextBox::paint(SkCanvas* canvas, const PaintOpts& paintOpts) {
    rebuild();

    if(paintOpts.cursor.has_value()) {
        auto& cur = paintOpts.cursor.value();
        SkPaint p{SkColor4f{paintOpts.cursorColor.x(), paintOpts.cursorColor.y(), paintOpts.cursorColor.z(), 1.0f}};
        if(cur.selectionBeginPos != cur.selectionEndPos) {
            canvas->saveLayerAlphaf(nullptr, 0.6f);
            rects_between_text_positions_func(cur.selectionBeginPos, cur.selectionEndPos, [&](const SkRect& rect) {
                canvas->drawRect(rect, p);
            });
            canvas->restore();
        }
        canvas->drawRect(get_cursor_rect(cur.pos), p);
    }

    for(auto& pData : paragraphs)
        pData.p->paint(canvas, 0.0f, pData.heightOffset);
}