/*
 * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibWeb/Layout/BreakNode.h>
#include <LibWeb/Layout/InlineFormattingContext.h>
#include <LibWeb/Layout/InlineLevelIterator.h>
#include <LibWeb/Layout/InlineNode.h>
#include <LibWeb/Layout/ListItemMarkerBox.h>
#include <LibWeb/Layout/ReplacedBox.h>

namespace Web::Layout {

InlineLevelIterator::InlineLevelIterator(Layout::InlineFormattingContext& inline_formatting_context, Layout::LayoutState& layout_state, Layout::BlockContainer const& container, LayoutMode layout_mode)
    : m_inline_formatting_context(inline_formatting_context)
    , m_layout_state(layout_state)
    , m_container(container)
    , m_container_state(layout_state.get(container))
    , m_next_node(container.first_child())
    , m_layout_mode(layout_mode)
{
    skip_to_next();
}

void InlineLevelIterator::enter_node_with_box_model_metrics(Layout::NodeWithStyleAndBoxModelMetrics const& node)
{
    if (!m_extra_leading_metrics.has_value())
        m_extra_leading_metrics = ExtraBoxMetrics {};

    // FIXME: It's really weird that *this* is where we assign box model metrics for these layout nodes..

    auto& used_values = m_layout_state.get_mutable(node);
    auto const& computed_values = node.computed_values();

    used_values.margin_left = computed_values.margin().left().to_px(node, m_container_state.content_width());
    used_values.border_left = computed_values.border_left().width;
    used_values.padding_left = computed_values.padding().left().to_px(node, m_container_state.content_width());

    m_extra_leading_metrics->margin += used_values.margin_left;
    m_extra_leading_metrics->border += used_values.border_left;
    m_extra_leading_metrics->padding += used_values.padding_left;

    // Now's our chance to resolve the inset properties for this node.
    m_inline_formatting_context.compute_inset(node);

    m_box_model_node_stack.append(node);
}

void InlineLevelIterator::exit_node_with_box_model_metrics()
{
    if (!m_extra_trailing_metrics.has_value())
        m_extra_trailing_metrics = ExtraBoxMetrics {};

    auto& node = m_box_model_node_stack.last();
    auto& used_values = m_layout_state.get_mutable(node);
    auto const& computed_values = node->computed_values();

    used_values.margin_right = computed_values.margin().right().to_px(node, m_container_state.content_width());
    used_values.border_right = computed_values.border_right().width;
    used_values.padding_right = computed_values.padding().right().to_px(node, m_container_state.content_width());

    m_extra_trailing_metrics->margin += used_values.margin_right;
    m_extra_trailing_metrics->border += used_values.border_right;
    m_extra_trailing_metrics->padding += used_values.padding_right;

    m_box_model_node_stack.take_last();
}

// This is similar to Layout::Node::next_in_pre_order() but will not descend into inline-block nodes.
Layout::Node const* InlineLevelIterator::next_inline_node_in_pre_order(Layout::Node const& current, Layout::Node const* stay_within)
{
    if (current.first_child()
        && current.first_child()->display().is_inline_outside()
        && current.display().is_flow_inside()
        && !current.is_replaced_box()) {
        if (!current.is_box() || !static_cast<Box const&>(current).is_out_of_flow(m_inline_formatting_context))
            return current.first_child();
    }

    Layout::Node const* node = &current;
    Layout::Node const* next = nullptr;
    while (!(next = node->next_sibling())) {
        node = node->parent();

        // If node is the last node on the "box model node stack", pop it off.
        if (!m_box_model_node_stack.is_empty()
            && m_box_model_node_stack.last() == node) {
            exit_node_with_box_model_metrics();
        }
        if (!node || node == stay_within)
            return nullptr;
    }

    // If node is the last node on the "box model node stack", pop it off.
    if (!m_box_model_node_stack.is_empty()
        && m_box_model_node_stack.last() == node) {
        exit_node_with_box_model_metrics();
    }

    return next;
}

void InlineLevelIterator::compute_next()
{
    if (m_next_node == nullptr)
        return;
    do {
        m_next_node = next_inline_node_in_pre_order(*m_next_node, m_container);
    } while (m_next_node && (!m_next_node->is_inline() && !m_next_node->is_out_of_flow(m_inline_formatting_context)));
}

void InlineLevelIterator::skip_to_next()
{
    if (m_next_node
        && is<Layout::NodeWithStyleAndBoxModelMetrics>(*m_next_node)
        && m_next_node->display().is_flow_inside()
        && !m_next_node->is_out_of_flow(m_inline_formatting_context)
        && !m_next_node->is_replaced_box())
        enter_node_with_box_model_metrics(static_cast<Layout::NodeWithStyleAndBoxModelMetrics const&>(*m_next_node));

    m_current_node = m_next_node;
    compute_next();
}

Optional<InlineLevelIterator::Item> InlineLevelIterator::next()
{
    if (m_lookahead_items.is_empty())
        return next_without_lookahead();
    return m_lookahead_items.dequeue();
}

CSSPixels InlineLevelIterator::next_non_whitespace_sequence_width()
{
    CSSPixels next_width = 0;
    for (;;) {
        auto next_item_opt = next_without_lookahead();
        if (!next_item_opt.has_value())
            break;
        m_lookahead_items.enqueue(next_item_opt.release_value());
        auto& next_item = m_lookahead_items.tail();
        if (next_item.type == InlineLevelIterator::Item::Type::ForcedBreak)
            break;
        if (next_item.node->computed_values().white_space() != CSS::WhiteSpace::Nowrap) {
            if (next_item.type != InlineLevelIterator::Item::Type::Text)
                break;
            if (next_item.is_collapsible_whitespace)
                break;
            auto& next_text_node = verify_cast<Layout::TextNode>(*(next_item.node));
            auto next_view = next_text_node.text_for_rendering().substring_view(next_item.offset_in_node, next_item.length_in_node);
            if (next_view.is_whitespace())
                break;
        }
        next_width += next_item.border_box_width();
    }
    return next_width;
}

Optional<InlineLevelIterator::Item> InlineLevelIterator::next_without_lookahead()
{
    if (!m_current_node)
        return {};

    if (is<Layout::TextNode>(*m_current_node)) {
        auto& text_node = static_cast<Layout::TextNode const&>(*m_current_node);

        if (!m_text_node_context.has_value())
            enter_text_node(text_node);

        auto chunk_opt = m_text_node_context->next_chunk;
        if (!chunk_opt.has_value()) {
            m_text_node_context = {};
            skip_to_next();
            return next_without_lookahead();
        }

        m_text_node_context->next_chunk = m_text_node_context->chunk_iterator.next();
        if (!m_text_node_context->next_chunk.has_value())
            m_text_node_context->is_last_chunk = true;

        auto& chunk = chunk_opt.value();

        if (m_text_node_context->do_respect_linebreaks && chunk.has_breaking_newline) {
            return Item {
                .type = Item::Type::ForcedBreak,
            };
        }

        CSSPixels chunk_width;

        if (m_text_node_context->is_last_chunk)
            chunk_width = CSSPixels::nearest_value_for(text_node.font().width(chunk.view));
        else
            chunk_width = CSSPixels::nearest_value_for(text_node.font().width(chunk.view) + text_node.font().glyph_spacing());

        // NOTE: We never consider `content: ""` to be collapsible whitespace.
        bool is_generated_empty_string = text_node.is_generated() && chunk.length == 0;

        Item item {
            .type = Item::Type::Text,
            .node = &text_node,
            .offset_in_node = chunk.start,
            .length_in_node = chunk.length,
            .width = chunk_width,
            .is_collapsible_whitespace = m_text_node_context->do_collapse && chunk.is_all_whitespace && !is_generated_empty_string,
        };

        add_extra_box_model_metrics_to_item(item, m_text_node_context->is_first_chunk, m_text_node_context->is_last_chunk);
        return item;
    }

    if (m_current_node->is_absolutely_positioned()) {
        auto& node = *m_current_node;
        skip_to_next();
        return Item {
            .type = Item::Type::AbsolutelyPositionedElement,
            .node = &node,
        };
    }

    if (m_current_node->is_floating()) {
        auto& node = *m_current_node;
        skip_to_next();
        return Item {
            .type = Item::Type::FloatingElement,
            .node = &node,
        };
    }

    if (is<Layout::BreakNode>(*m_current_node)) {
        auto& node = *m_current_node;
        skip_to_next();
        return Item {
            .type = Item::Type::ForcedBreak,
            .node = &node,
        };
    }

    if (is<Layout::ListItemMarkerBox>(*m_current_node)) {
        skip_to_next();
        return next_without_lookahead();
    }

    if (!is<Layout::Box>(*m_current_node)) {
        skip_to_next();
        return next_without_lookahead();
    }

    if (is<Layout::ReplacedBox>(*m_current_node)) {
        auto& replaced_box = static_cast<Layout::ReplacedBox const&>(*m_current_node);
        // FIXME: This const_cast is gross.
        const_cast<Layout::ReplacedBox&>(replaced_box).prepare_for_replaced_layout();
    }

    auto& box = verify_cast<Layout::Box>(*m_current_node);
    auto& box_state = m_layout_state.get(box);
    m_inline_formatting_context.dimension_box_on_line(box, m_layout_mode);

    skip_to_next();
    auto item = Item {
        .type = Item::Type::Element,
        .node = &box,
        .offset_in_node = 0,
        .length_in_node = 0,
        .width = box_state.content_width(),
        .padding_start = box_state.padding_left,
        .padding_end = box_state.padding_right,
        .border_start = box_state.border_left,
        .border_end = box_state.border_right,
        .margin_start = box_state.margin_left,
        .margin_end = box_state.margin_right,
    };
    add_extra_box_model_metrics_to_item(item, true, true);
    return item;
}

void InlineLevelIterator::enter_text_node(Layout::TextNode const& text_node)
{
    bool do_collapse = true;
    bool do_wrap_lines = true;
    bool do_respect_linebreaks = false;

    if (text_node.computed_values().white_space() == CSS::WhiteSpace::Nowrap) {
        do_collapse = true;
        do_wrap_lines = false;
        do_respect_linebreaks = false;
    } else if (text_node.computed_values().white_space() == CSS::WhiteSpace::Pre) {
        do_collapse = false;
        do_wrap_lines = false;
        do_respect_linebreaks = true;
    } else if (text_node.computed_values().white_space() == CSS::WhiteSpace::PreLine) {
        do_collapse = true;
        do_wrap_lines = true;
        do_respect_linebreaks = true;
    } else if (text_node.computed_values().white_space() == CSS::WhiteSpace::PreWrap) {
        do_collapse = false;
        do_wrap_lines = true;
        do_respect_linebreaks = true;
    }

    if (text_node.dom_node().is_editable() && !text_node.dom_node().is_uninteresting_whitespace_node())
        do_collapse = false;

    m_text_node_context = TextNodeContext {
        .do_collapse = do_collapse,
        .do_wrap_lines = do_wrap_lines,
        .do_respect_linebreaks = do_respect_linebreaks,
        .is_first_chunk = true,
        .is_last_chunk = false,
        .chunk_iterator = TextNode::ChunkIterator { text_node.text_for_rendering(), do_wrap_lines, do_respect_linebreaks },
    };
    m_text_node_context->next_chunk = m_text_node_context->chunk_iterator.next();
}

void InlineLevelIterator::add_extra_box_model_metrics_to_item(Item& item, bool add_leading_metrics, bool add_trailing_metrics)
{
    if (add_leading_metrics && m_extra_leading_metrics.has_value()) {
        item.margin_start += m_extra_leading_metrics->margin;
        item.border_start += m_extra_leading_metrics->border;
        item.padding_start += m_extra_leading_metrics->padding;
        m_extra_leading_metrics = {};
    }

    if (add_trailing_metrics && m_extra_trailing_metrics.has_value()) {
        item.margin_end += m_extra_trailing_metrics->margin;
        item.border_end += m_extra_trailing_metrics->border;
        item.padding_end += m_extra_trailing_metrics->padding;
        m_extra_trailing_metrics = {};
    }
}

}
