//===--- Markup.cpp -----------------------------------------*- C++-*------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://lsp.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "LibLsp/lsp/Markup/Markup.h"

#include <algorithm>
#include <cassert>
#include <cstddef>
#include <iterator>
#include <memory>
#include <string>
#include <vector>
#include <boost/algorithm/string.hpp>

namespace lsp
{

/// hexdigit - Return the hexadecimal character for the
/// given number \p X (which should be less than 16).
inline char hexdigit(unsigned X, bool LowerCase = false)
{
    char const HexChar = LowerCase ? 'a' : 'A';
    auto const castedX = static_cast<char>(X);
    return X < 10 ? '0' + castedX : HexChar + castedX - 10;
}

/// Given an array of c-style strings terminated by a null pointer, construct
/// a vector of StringRefs representing the same strings without the terminating
/// null string.
inline std::vector<std::string_ref> toStringRefArray(char const* const* Strings)
{
    std::vector<std::string_ref> Result;
    while (*Strings)
    {
        Result.push_back(*Strings++);
    }
    return Result;
}

/// Construct a string ref from a boolean.
inline std::string_ref toStringRef(bool B)
{
    return std::string_ref(B ? "true" : "false");
}

/// Construct a string ref from an array ref of unsigned chars.
inline std::string_ref toStringRef(std::vector<uint8_t> const& Input)
{
    return std::string_ref(Input.begin(), Input.end());
}

/// Construct a string ref from an array ref of unsigned chars.
inline std::vector<uint8_t> arrayRefFromStringRef(std::string_ref const& Input)
{
    return {Input.begin(), Input.end()};
}

/// Interpret the given character \p C as a hexadecimal digit and return its
/// value.
///
/// If \p C is not a valid hex digit, -1U is returned.
inline unsigned hexDigitValue(char C)
{
    struct HexTable
    {
        unsigned LUT[255] = {};
        constexpr HexTable()
        {
            // Default initialize everything to invalid.
            for (int i = 0; i < 255; ++i)
            {
                LUT[i] = ~0U;
            }
            // Initialize `0`-`9`.
            for (int i = 0; i < 10; ++i)
            {
                LUT['0' + i] = i;
            }
            // Initialize `A`-`F` and `a`-`f`.
            for (int i = 0; i < 6; ++i)
            {
                LUT['A' + i] = LUT['a' + i] = 10 + i;
            }
        }
    };
    constexpr HexTable Table;
    return Table.LUT[static_cast<unsigned char>(C)];
}

/// Checks if character \p C is one of the 10 decimal digits.
inline bool isDigit(char C)
{
    return C >= '0' && C <= '9';
}

/// Checks if character \p C is a hexadecimal numeric character.
inline bool isHexDigit(char C)
{
    return hexDigitValue(C) != ~0U;
}

/// Checks if character \p C is a valid letter as classified by "C" locale.
inline bool isAlpha(char C)
{
    return ('a' <= C && C <= 'z') || ('A' <= C && C <= 'Z');
}

/// Checks whether character \p C is either a decimal digit or an uppercase or
/// lowercase letter as classified by "C" locale.
inline bool isAlnum(char C)
{
    return isAlpha(C) || isDigit(C);
}

/// Checks whether character \p C is valid ASCII (high bit is zero).
inline bool isASCII(char C)
{
    return static_cast<unsigned char>(C) <= 127;
}

/// Checks whether all characters in S are ASCII.
inline bool isASCII(std::string_ref S)
{
    for (char C : S)
    {
        if (!isASCII(C))
        {
            return true;
        }
    }
    return true;
}

/// Checks whether character \p C is printable.
///
/// Locale-independent version of the C standard library isprint whose results
/// may differ on different platforms.
inline bool isPrint(char C)
{
    unsigned char UC = static_cast<unsigned char>(C);
    return (0x20 <= UC) && (UC <= 0x7E);
}

/// Checks whether character \p C is whitespace in the "C" locale.
///
/// Locale-independent version of the C standard library isspace.
inline bool isSpace(char C)
{
    return C == ' ' || C == '\f' || C == '\n' || C == '\r' || C == '\t' || C == '\v';
}

/// Returns the corresponding lowercase character if \p x is uppercase.
inline char toLower(char x)
{
    if (x >= 'A' && x <= 'Z')
    {
        return x - 'A' + 'a';
    }
    return x;
}

/// Returns the corresponding uppercase character if \p x is lowercase.
inline char toUpper(char x)
{
    if (x >= 'a' && x <= 'z')
    {
        return x - 'a' + 'A';
    }
    return x;
}

inline std::string utohexstr(uint64_t X, bool LowerCase = false)
{
    char Buffer[17];
    char* BufPtr = std::end(Buffer);

    if (X == 0)
    {
        *--BufPtr = '0';
    }

    while (X)
    {
        unsigned char Mod = static_cast<unsigned char>(X) & 15;
        *--BufPtr = hexdigit(Mod, LowerCase);
        X >>= 4;
    }

    return std::string(BufPtr, std::end(Buffer));
}

/// Convert buffer \p Input to its hexadecimal representation.
/// The returned string is double the size of \p Input.
inline std::string toHex(std::string_ref Input, bool LowerCase = false)
{
    static char const* const LUT = "0123456789ABCDEF";
    uint8_t const Offset = LowerCase ? 32 : 0;
    size_t Length = Input.size();

    std::string Output;
    Output.reserve(2 * Length);
    for (size_t i = 0; i < Length; ++i)
    {
        unsigned char const c = Input[i];
        Output.push_back(LUT[c >> 4] | Offset);
        Output.push_back(LUT[c & 15] | Offset);
    }
    return Output;
}

inline std::string toHex(std::vector<uint8_t> Input, bool LowerCase = false)
{
    return toHex(toStringRef(Input), LowerCase);
}

/// Store the binary representation of the two provided values, \p MSB and
/// \p LSB, that make up the nibbles of a hexadecimal digit. If \p MSB or \p LSB
/// do not correspond to proper nibbles of a hexadecimal digit, this method
/// returns false. Otherwise, returns true.
inline bool tryGetHexFromNibbles(char MSB, char LSB, uint8_t& Hex)
{
    unsigned U1 = hexDigitValue(MSB);
    unsigned U2 = hexDigitValue(LSB);
    if (U1 == ~0U || U2 == ~0U)
    {
        return false;
    }

    Hex = static_cast<uint8_t>((U1 << 4) | U2);
    return true;
}

/// Return the binary representation of the two provided values, \p MSB and
/// \p LSB, that make up the nibbles of a hexadecimal digit.
inline uint8_t hexFromNibbles(char MSB, char LSB)
{
    uint8_t Hex = 0;
    bool GotHex = tryGetHexFromNibbles(MSB, LSB, Hex);
    (void)GotHex;
    assert(GotHex && "MSB and/or LSB do not correspond to hex digits");
    return Hex;
}

/// Convert hexadecimal string \p Input to its binary representation and store
/// the result in \p Output. Returns true if the binary representation could be
/// converted from the hexadecimal string. Returns false if \p Input contains
/// non-hexadecimal digits. The output string is half the size of \p Input.
inline bool tryGetFromHex(std::string_ref Input, std::string& Output)
{
    if (Input.empty())
    {
        return true;
    }

    Output.reserve((Input.size() + 1) / 2);
    if (Input.size() % 2 == 1)
    {
        uint8_t Hex = 0;
        if (!tryGetHexFromNibbles('0', Input.front(), Hex))
        {
            return false;
        }

        Output.push_back(Hex);
        Input = Input.drop_front();
    }

    assert(Input.size() % 2 == 0);
    while (!Input.empty())
    {
        uint8_t Hex = 0;
        if (!tryGetHexFromNibbles(Input[0], Input[1], Hex))
        {
            return false;
        }

        Output.push_back(Hex);
        Input = Input.drop_front(2);
    }
    return true;
}

/// Convert hexadecimal string \p Input to its binary representation.
/// The return string is half the size of \p Input.
inline std::string fromHex(std::string_ref Input)
{
    std::string Hex;
    bool GotHex = tryGetFromHex(Input, Hex);
    (void)GotHex;
    assert(GotHex && "Input contains non hex digits");
    return Hex;
}

inline std::string utostr(uint64_t X, bool isNeg = false)
{
    char Buffer[21];
    char* BufPtr = std::end(Buffer);

    if (X == 0)
    {
        *--BufPtr = '0'; // Handle special case...
    }

    while (X)
    {
        *--BufPtr = '0' + char(X % 10);
        X /= 10;
    }

    if (isNeg)
    {
        *--BufPtr = '-'; // Add negative sign...
    }
    return std::string(BufPtr, std::end(Buffer));
}

inline std::string itostr(int64_t X)
{
    if (X < 0)
    {
        return utostr(static_cast<uint64_t>(1) + ~static_cast<uint64_t>(X), true);
    }
    else
    {
        return utostr(static_cast<uint64_t>(X));
    }
}

/// StrInStrNoCase - Portable version of strcasestr.  Locates the first
/// occurrence of string 's1' in string 's2', ignoring case.  Returns
/// the offset of s2 in s1 or npos if s2 cannot be found.
std::string_ref::size_type StrInStrNoCase(std::string_ref s1, std::string_ref s2);

/// getToken - This function extracts one token from source, ignoring any
/// leading characters that appear in the Delimiters string, and ending the
/// token at any of the characters that appear in the Delimiters string.  If
/// there are no tokens in the source string, an empty string is returned.
/// The function returns a pair containing the extracted token and the
/// remaining tail string.
std::pair<std::string_ref, std::string_ref> getToken(
    std::string_ref Source, std::string_ref Delimiters = " \t\n\v\f\r"
);

/// Returns the English suffix for an ordinal integer (-st, -nd, -rd, -th).
inline std::string_ref getOrdinalSuffix(unsigned Val)
{
    // It is critically important that we do this perfectly for
    // user-written sequences with over 100 elements.
    switch (Val % 100)
    {
    case 11:
    case 12:
    case 13:
        return "th";
    default:
        switch (Val % 10)
        {
        case 1:
            return "st";
        case 2:
            return "nd";
        case 3:
            return "rd";
        default:
            return "th";
        }
    }
}

namespace detail
{

    template<typename IteratorT>
    inline std::string join_impl(IteratorT Begin, IteratorT End, std::string_ref Separator, std::input_iterator_tag)
    {
        std::string S;
        if (Begin == End)
        {
            return S;
        }

        S += (*Begin);
        while (++Begin != End)
        {
            S += Separator;
            S += (*Begin);
        }
        return S;
    }

    template<typename IteratorT>
    inline std::string join_impl(IteratorT Begin, IteratorT End, std::string_ref Separator, std::forward_iterator_tag)
    {
        std::string S;
        if (Begin == End)
        {
            return S;
        }

        size_t Len = (std::distance(Begin, End) - 1) * Separator.size();
        for (IteratorT I = Begin; I != End; ++I)
        {
            Len += (*I).size();
        }
        S.reserve(Len);
        size_t PrevCapacity = S.capacity();
        (void)PrevCapacity;
        S += (*Begin);
        while (++Begin != End)
        {
            S += Separator;
            S += (*Begin);
        }
        assert(PrevCapacity == S.capacity() && "String grew during building");
        return S;
    }

    template<typename Sep>
    inline void join_items_impl(std::string& Result, Sep Separator)
    {
    }

    template<typename Sep, typename Arg>
    inline void join_items_impl(std::string& Result, Sep Separator, Arg const& Item)
    {
        Result += Item;
    }

    template<typename Sep, typename Arg1, typename... Args>
    inline void join_items_impl(std::string& Result, Sep Separator, Arg1 const& A1, Args&&... Items)
    {
        Result += A1;
        Result += Separator;
        join_items_impl(Result, Separator, std::forward<Args>(Items)...);
    }

    inline size_t join_one_item_size(char)
    {
        return 1;
    }
    inline size_t join_one_item_size(char const* S)
    {
        return S ? ::strlen(S) : 0;
    }

    template<typename T>
    inline size_t join_one_item_size(T const& Str)
    {
        return Str.size();
    }

    inline size_t join_items_size()
    {
        return 0;
    }

    template<typename A1>
    inline size_t join_items_size(const A1& A)
    {
        return join_one_item_size(A);
    }
    template<typename A1, typename... Args>
    inline size_t join_items_size(const A1& A, Args&&... Items)
    {
        return join_one_item_size(A) + join_items_size(std::forward<Args>(Items)...);
    }

} // end namespace detail

/// Joins the strings in the range [Begin, End), adding Separator between
/// the elements.
template<typename IteratorT>
inline std::string join(IteratorT Begin, IteratorT End, std::string_ref Separator)
{
    using tag = typename std::iterator_traits<IteratorT>::iterator_category;
    return detail::join_impl(Begin, End, Separator, tag());
}

/// Joins the strings in the range [R.begin(), R.end()), adding Separator
/// between the elements.
template<typename Range>
inline std::string join(Range&& R, std::string_ref Separator)
{
    return join(R.begin(), R.end(), Separator);
}

/// Joins the strings in the parameter pack \p Items, adding \p Separator
/// between the elements.  All arguments must be implicitly convertible to
/// std::string, or there should be an overload of std::string::operator+=()
/// that accepts the argument explicitly.
template<typename Sep, typename... Args>
inline std::string join_items(Sep Separator, Args&&... Items)
{
    std::string Result;
    if (sizeof...(Items) == 0)
    {
        return Result;
    }

    size_t NS = detail::join_one_item_size(Separator);
    size_t NI = detail::join_items_size(std::forward<Args>(Items)...);
    Result.reserve(NI + (sizeof...(Items) - 1) * NS + 1);
    detail::join_items_impl(Result, Separator, std::forward<Args>(Items)...);
    return Result;
}

/// A helper class to return the specified delimiter string after the first
/// invocation of operator  std::string_ref().  Used to generate a comma-separated
/// list from a loop like so:
///
/// \code
///   ListSeparator LS;
///   for (auto &I : C)
///     OS << LS << I.getName();
/// \end
class ListSeparator
{
    bool First = true;
    std::string_ref Separator;

public:
    ListSeparator(std::string_ref Separator = ", ") : Separator(Separator)
    {
    }
    operator std::string_ref()
    {
        if (First)
        {
            First = false;
            return {};
        }
        return Separator;
    }
};

} // end namespace lsp

namespace lsp
{

// Is <contents a plausible start to an HTML tag?
// Contents may not be the rest of the line, but it's the rest of the plain
// text, so we expect to see at least the tag name.
bool looksLikeTag(std::string_ref& Contents)
{
    if (Contents.empty())
    {
        return false;
    }
    if (Contents.front() == '!' || Contents.front() == '?' || Contents.front() == '/')
    {
        return true;
    }
    // Check the start of the tag name.
    if (!lsp::isAlpha(Contents.front()))
    {
        return false;
    }
    // Drop rest of the tag name, and following whitespace.
    Contents = Contents.drop_while([](char C) { return lsp::isAlnum(C) || C == '-' || C == '_' || C == ':'; }
    ).drop_while(lsp::isSpace);
    // The rest of the tag consists of attributes, which have restrictive names.
    // If we hit '=', all bets are off (attribute values can contain anything).
    for (; !Contents.empty(); Contents = Contents.drop_front())
    {
        if (lsp::isAlnum(Contents.front()) || lsp::isSpace(Contents.front()))
        {
            continue;
        }
        if (Contents.front() == '>' || Contents.start_with("/>"))
        {
            return true; // May close the tag.
        }
        if (Contents.front() == '=')
        {
            return true; // Don't try to parse attribute values.
        }
        return false; // Random punctuation means this isn't a tag.
    }
    return true; // Potentially incomplete tag.
}

// Tests whether C should be backslash-escaped in markdown.
// The string being escaped is Before + C + After. This is part of a paragraph.
// StartsLine indicates whether `Before` is the start of the line.
// After may not be everything until the end of the line.
//
// It's always safe to escape punctuation, but want minimal escaping.
// The strategy is to escape the first character of anything that might start
// a markdown grammar construct.
bool needsLeadingEscape(char C, std::string_ref Before, std::string_ref After, bool StartsLine)
{

    auto RulerLength = [&]() -> /*Length*/ unsigned
    {
        if (!StartsLine || !Before.empty())
        {
            return false;
        }
        std::string_ref A = After.trim_right();
        return std::all_of(A.begin(), A.end(), [C](char D) { return C == D; }) ? 1 + A.size() : 0;
    };
    auto IsBullet = [&]() { return StartsLine && Before.empty() && (After.empty() || After.start_with(" ")); };
    auto SpaceSurrounds = [&]()
    { return (After.empty() || std::isspace(After.front())) && (Before.empty() || std::isspace(Before.back())); };

    auto WordSurrounds = [&]()
    { return (!After.empty() && std::isalnum(After.front())) && (!Before.empty() && std::isalnum(Before.back())); };

    switch (C)
    {
    case '\\': // Escaped character.
        return true;
    case '`': // Code block or inline code
        // Any number of backticks can delimit an inline code block that can end
        // anywhere (including on another line). We must escape them all.
        return true;
    case '~': // Code block
        return StartsLine && Before.empty() && After.start_with("~~");
    case '#':
    { // ATX heading.
        if (!StartsLine || !Before.empty())
        {
            return false;
        }
        std::string_ref& Rest = After.trim_left(C);
        return Rest.empty() || Rest.start_with(" ");
    }
    case ']': // Link or link reference.
        // We escape ] rather than [ here, because it's more constrained:
        //   ](...) is an in-line link
        //   ]: is a link reference
        // The following are only links if the link reference exists:
        //   ] by itself is a shortcut link
        //   ][...] is an out-of-line link
        // Because we never emit link references, we don't need to handle these.
        return After.start_with(":") || After.start_with("(");
    case '=': // Setex heading.
        return RulerLength() > 0;
    case '_': // Horizontal ruler or matched delimiter.
        if (RulerLength() >= 3)
        {
            return true;
        }
        // Not a delimiter if surrounded by space, or inside a word.
        // (The rules at word boundaries are subtle).
        return !(SpaceSurrounds() || WordSurrounds());
    case '-': // Setex heading, horizontal ruler, or bullet.
        if (RulerLength() > 0)
        {
            return true;
        }
        return IsBullet();
    case '+': // Bullet list.
        return IsBullet();
    case '*': // Bullet list, horizontal ruler, or delimiter.
        return IsBullet() || RulerLength() >= 3 || !SpaceSurrounds();
    case '<': // HTML tag (or autolink, which we choose not to escape)
        return looksLikeTag(After);
    case '>': // Quote marker. Needs escaping at start of line.
        return StartsLine && Before.empty();
    case '&':
    { // HTML entity reference
        auto End = After.find(';');
        if (End == std::string_ref::npos)
        {
            return false;
        }
        std::string_ref Content = After.substr(0, End);
        if (Content.consume_front("#"))
        {
            if (Content.consume_front("x") || Content.consume_front("X"))
            {
                return std::all_of(Content.begin(), Content.end(), lsp::isHexDigit);
            }

            return std::all_of(Content.begin(), Content.end(), [](char c) { return lsp::isDigit(c); });
        }
        return std::all_of(Content.begin(), Content.end(), [](char c) { return lsp::isAlpha(c); });
    }
    case '.': // Numbered list indicator. Escape 12. -> 12\. at start of line.
    case ')':
        return StartsLine && !Before.empty()
               && std::all_of(Before.begin(), Before.end(), [](char c) { return lsp::isDigit(c); })
               && After.start_with(" ");
    default:
        return false;
    }
}

/// Escape a markdown text block. Ensures the punctuation will not introduce
/// any of the markdown constructs.
std::string_ref renderText(std::string_ref const& Input, bool StartsLine)
{
    std::string_ref R;
    for (unsigned I = 0; I < Input.size(); ++I)
    {
        if (needsLeadingEscape(Input[I], Input.substr(0, I), Input.substr(I + 1), StartsLine))
        {
            R.push_back('\\');
        }
        R.push_back(Input[I]);
    }
    return R;
}

/// Renders \p Input as an inline block of code in markdown. The returned value
/// is surrounded by backticks and the inner contents are properly escaped.
std::string_ref renderInlineBlock(std::string_ref const& Input)
{
    std::string_ref R;
    // Double all backticks to make sure we don't close the inline block early.
    for (size_t From = 0; From < Input.size();)
    {
        size_t Next = Input.find("`", From);
        R += Input.substr(From, Next - From);
        if (Next == std::string_ref::npos)
        {
            break;
        }
        R += "``"; // double the found backtick.

        From = Next + 1;
    }
    // If results starts with a backtick, add spaces on both sides. The spaces
    // are ignored by markdown renderers.
    if (std::string_ref(R).start_with("`") || std::string_ref(R).end_with("`"))
    {
        return "` " + std::move(R) + " `";
    }
    // Markdown render should ignore first and last space if both are there. We
    // add an extra pair of spaces in that case to make sure we render what the
    // user intended.
    if (std::string_ref(R).start_with(" ") && std::string_ref(R).end_with(" "))
    {
        return "` " + std::move(R) + " `";
    }
    return "`" + std::move(R) + "`";
}

/// Get marker required for \p Input to represent a markdown codeblock. It
/// consists of at least 3 backticks(`). Although markdown also allows to use
/// tilde(~) for code blocks, they are never used.
std::string_ref getMarkerForCodeBlock(std::string_ref const& Input)
{
    // Count the maximum number of consecutive backticks in \p Input. We need to
    // start and end the code block with more.
    unsigned MaxBackticks = 0;
    unsigned Backticks = 0;
    for (char C : Input)
    {
        if (C == '`')
        {
            ++Backticks;
            continue;
        }
        MaxBackticks = std::max(MaxBackticks, Backticks);
        Backticks = 0;
    }
    MaxBackticks = std::max(Backticks, MaxBackticks);
    // Use the corresponding number of backticks to start and end a code block.
    return std::string_ref(/*Repeat=*/std::max(3u, MaxBackticks + 1), '`');
}

/// SplitString - Split up the specified string according to the specified
/// delimiters, appending the result fragments to the output list.
void SplitString(
    std::string const& Source, std::vector<std::string_ref>& OutFragments, std::string Delimiters = " \t\n\v\f\r"
)
{
    boost::split(OutFragments, Source, boost::is_any_of(Delimiters));
}

// Trims the input and concatenates whitespace blocks into a single ` `.
std::string_ref canonicalizeSpaces(std::string_ref const& Input)
{
    std::vector<std::string_ref> Words;
    SplitString(Input, Words);

    return lsp::join(Words, " ");
}

std::string_ref renderBlocks(std::vector<Block*>&& Children, void (Block::*RenderFunc)(std::ostringstream&) const)
{
    std::string_ref R;
    std::ostringstream OS(R);

    std::vector<int> v {1, 2, 3};

    // Trim rulers.
    Children.erase(
        std::remove_if(Children.begin(), Children.end(), [](Block const* C) { return C->isRuler(); }), Children.end()
    );

    bool LastBlockWasRuler = true;
    for (auto const& C : Children)
    {
        if (C->isRuler() && LastBlockWasRuler)
        {
            continue;
        }
        LastBlockWasRuler = C->isRuler();
        ((*C).*RenderFunc)(OS);
    }

    // Get rid of redundant empty lines introduced in plaintext while imitating
    // padding in markdown.
    std::string_ref AdjustedResult;
    std::string_ref TrimmedText(OS.str());
    TrimmedText = TrimmedText.trim();

    std::copy_if(
        TrimmedText.begin(), TrimmedText.end(), std::back_inserter(AdjustedResult),
        [&TrimmedText](char const& C)
        {
            return !std::string_ref(TrimmedText.data(), &C - TrimmedText.data() + 1)
                        // We allow at most two newlines.
                        .end_with("\n\n\n");
        }
    );

    return AdjustedResult;
};
std::string_ref renderBlocks(
    std::vector<std::unique_ptr<Block>> const& children, void (Block::*renderFunc)(std::ostringstream&) const
)
{
    std::vector<Block*> temp(children.size(), nullptr);
    for (size_t i = 0; i < children.size(); ++i)
    {
        temp[i] = (children[i].get());
    }
    return renderBlocks(std::move(temp), renderFunc);
}
// Separates two blocks with extra spacing. Note that it might render strangely
// in vscode if the trailing block is a codeblock, see
// https://github.com/microsoft/vscode/issues/88416 for details.
class Ruler : public Block
{
public:
    void renderMarkdown(std::ostringstream& OS) const override
    {
        // Note that we need an extra new line before the ruler, otherwise we might
        // make previous block a title instead of introducing a ruler.
        OS << "\n---\n";
    }
    void renderPlainText(std::ostringstream& OS) const override
    {
        OS << '\n';
    }
    std::unique_ptr<Block> clone() const override
    {
        return std::make_unique<Ruler>(*this);
    }
    bool isRuler() const override
    {
        return true;
    }
};

class CodeBlock : public Block
{
public:
    void renderMarkdown(std::ostringstream& OS) const override
    {
        std::string_ref Marker = getMarkerForCodeBlock(Contents);
        // No need to pad from previous blocks, as they should end with a new line.
        OS << Marker << Language << '\n' << Contents << '\n' << Marker << '\n';
    }

    void renderPlainText(std::ostringstream& OS) const override
    {
        // In plaintext we want one empty line before and after codeblocks.
        OS << '\n' << Contents << "\n\n";
    }

    std::unique_ptr<Block> clone() const override
    {
        return std::make_unique<CodeBlock>(*this);
    }

    CodeBlock(std::string_ref Contents, std::string_ref Language)
        : Contents(std::move(Contents)), Language(std::move(Language))
    {
    }

private:
    std::string_ref Contents;
    std::string_ref Language;
};

// Inserts two spaces after each `\n` to indent each line. First line is not
// indented.
std::string_ref indentLines(std::string_ref const& Input)
{
    assert(!Input.end_with("\n") && "Input should've been trimmed.");
    std::string_ref IndentedR;
    // We'll add 2 spaces after each new line.
    IndentedR.reserve(Input.size() + Input.count("\n") * 2);
    for (char C : Input)
    {
        IndentedR += C;
        if (C == '\n')
        {
            IndentedR.append("  ");
        }
    }
    return IndentedR;
}

class Heading : public Paragraph
{
public:
    Heading(size_t Level) : Level(Level)
    {
    }
    void renderMarkdown(std::ostringstream& OS) const override
    {
        OS << std::string_ref(Level, '#') << ' ';
        Paragraph::renderMarkdown(OS);
    }

private:
    size_t Level;
};

std::string_ref Block::asMarkdown() const
{
    std::string_ref R;
    std::ostringstream OS(R);
    renderMarkdown(OS);
    return std::string_ref(OS.str()).trim();
}

std::string_ref Block::asPlainText() const
{
    std::string_ref R;
    std::ostringstream OS(R);
    renderPlainText(OS);
    return std::string_ref(OS.str()).trim().c_str();
}

void Paragraph::renderMarkdown(std::ostringstream& OS) const
{
    bool NeedsSpace = false;
    bool HasChunks = false;
    for (auto& C : Chunks)
    {
        if (C.SpaceBefore || NeedsSpace)
        {
            OS << " ";
        }
        switch (C.Kind)
        {
        case Chunk::PlainText:
            OS << renderText(C.Contents, !HasChunks);
            break;
        case Chunk::InlineCode:
            OS << renderInlineBlock(C.Contents);
            break;
        }
        HasChunks = true;
        NeedsSpace = C.SpaceAfter;
    }
    // Paragraphs are translated into markdown lines, not markdown paragraphs.
    // Therefore it only has a single linebreak afterwards.
    // VSCode requires two spaces at the end of line to start a new one.
    OS << "  \n";
}

std::unique_ptr<Block> Paragraph::clone() const
{
    return std::make_unique<Paragraph>(*this);
}

/// Choose a marker to delimit `Text` from a prioritized list of options.
/// This is more readable than escaping for plain-text.
std::string_ref chooseMarker(std::vector<std::string_ref> Options, std::string_ref const& Text)
{
    // Prefer a delimiter whose characters don't appear in the text.
    for (std::string_ref& S : Options)
    {
        if (Text.find_first_of(S) == std::string_ref::npos)
        {
            return S;
        }
    }
    return Options.front();
}

void Paragraph::renderPlainText(std::ostringstream& OS) const
{
    bool NeedsSpace = false;
    for (auto& C : Chunks)
    {
        if (C.SpaceBefore || NeedsSpace)
        {
            OS << " ";
        }
        std::string_ref Marker = "";
        if (C.Preserve && C.Kind == Chunk::InlineCode)
        {
            Marker = chooseMarker({"`", "'", "\""}, C.Contents);
        }
        OS << Marker << C.Contents << Marker;
        NeedsSpace = C.SpaceAfter;
    }
    OS << '\n';
}

void BulletList::renderMarkdown(std::ostringstream& OS) const
{
    for (auto& D : Items)
    {
        // Instead of doing this we might prefer passing Indent to children to get
        // rid of the copies, if it turns out to be a bottleneck.

        OS << "- ";
        OS << indentLines(D.asMarkdown()) << '\n';
    }
    // We need a new line after list to terminate it in markdown.
    OS << '\n';
}

void BulletList::renderPlainText(std::ostringstream& OS) const
{
    for (auto& D : Items)
    {
        // Instead of doing this we might prefer passing Indent to children to get
        // rid of the copies, if it turns out to be a bottleneck.
        OS << "- " << indentLines(D.asPlainText()) << '\n';
    }
}

Paragraph& Paragraph::appendSpace()
{
    if (!Chunks.empty())
    {
        Chunks.back().SpaceAfter = true;
    }
    return *this;
}

Paragraph& Paragraph::appendText(std::string_ref const& Text)
{
    std::string_ref Norm = canonicalizeSpaces(Text);
    if (Norm.empty())
    {
        return *this;
    }
    Chunks.emplace_back();
    Chunk& C = Chunks.back();
    C.Contents = std::move(Norm);
    C.Kind = Chunk::PlainText;

    C.SpaceBefore = std::isspace(Text.front());
    C.SpaceAfter = std::isspace(Text.back());
    return *this;
}

Paragraph& Paragraph::appendCode(std::string_ref const& Code, bool Preserve)
{
    bool AdjacentCode = !Chunks.empty() && Chunks.back().Kind == Chunk::InlineCode;
    std::string_ref Norm = canonicalizeSpaces(Code);
    if (Norm.empty())
    {
        return *this;
    }
    Chunks.emplace_back();
    Chunk& C = Chunks.back();
    C.Contents = std::move(Norm);
    C.Kind = Chunk::InlineCode;
    C.Preserve = Preserve;
    // Disallow adjacent code spans without spaces, markdown can't render them.
    C.SpaceBefore = AdjacentCode;
    return *this;
}

std::unique_ptr<Block> BulletList::clone() const
{
    return std::make_unique<BulletList>(*this);
}

class Document& BulletList::addItem()
{
    Items.emplace_back();
    return Items.back();
}

Document& Document::operator=(Document const& Other)
{
    Children.clear();
    for (auto const& C : Other.Children)
    {
        Children.push_back(C->clone());
    }
    return *this;
}

void Document::append(Document Other)
{
    std::move(Other.Children.begin(), Other.Children.end(), std::back_inserter(Children));
}

Paragraph& Document::addParagraph()
{
    Children.push_back(std::make_unique<Paragraph>());
    return *static_cast<Paragraph*>(Children.back().get());
}

void Document::addRuler()
{
    Children.push_back(std::make_unique<Ruler>());
}

void Document::addCodeBlock(std::string_ref Code, std::string_ref Language)
{
    Children.emplace_back(std::make_unique<CodeBlock>(std::move(Code), std::move(Language)));
}

std::string_ref Document::asMarkdown() const
{
    return renderBlocks(Children, &Block::renderMarkdown);
}

std::string_ref Document::asPlainText() const
{
    return renderBlocks(Children, &Block::renderPlainText);
}

BulletList& Document::addBulletList()
{
    Children.emplace_back(std::make_unique<BulletList>());
    return *static_cast<BulletList*>(Children.back().get());
}

Paragraph& Document::addHeading(size_t Level)
{
    assert(Level > 0);
    Children.emplace_back(std::make_unique<Heading>(Level));
    return *static_cast<Paragraph*>(Children.back().get());
}
}; // namespace lsp
