/*
 * Copyright (C) 2004-2020 ZNC, see the NOTICE file for details.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef ZNCSTRING_H
#define ZNCSTRING_H

#include <znc/zncconfig.h>
#include <map>
#include <set>
#include <string>
#include <vector>
#include <sstream>
#include <sys/types.h>
#include <initializer_list>

#define _SQL(s) CString("'" + CString(s).Escape_n(CString::ESQL) + "'")
#define _URL(s) CString(s).Escape_n(CString::EURL)
#define _HTML(s) CString(s).Escape_n(CString::EHTML)
#define _NAMEDFMT(s) CString(s).Escape_n(CString::ENAMEDFMT)

class CString;
class MCString;

typedef std::set<CString> SCString;
typedef std::vector<CString> VCString;
typedef std::vector<std::pair<CString, CString>> VPair;

static const unsigned char XX = 0xff;
static const unsigned char base64_table[256] = {
    XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX,
    XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX,
    XX, XX, XX, XX, XX, 62, XX, XX, XX, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60,
    61, XX, XX, XX, XX, XX, XX, XX, 0,  1,  2,  3,  4,  5,  6,  7,  8,  9,  10,
    11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, XX, XX, XX, XX,
    XX, XX, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42,
    43, 44, 45, 46, 47, 48, 49, 50, 51, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX,
    XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX,
    XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX,
    XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX,
    XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX,
    XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX,
    XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX, XX,
    XX, XX, XX, XX, XX, XX, XX, XX, XX,
};

enum class CaseSensitivity { CaseInsensitive, CaseSensitive };

/**
 * @brief String class that is used inside ZNC.
 *
 * All strings that are used in ZNC and its modules should use instances of this
 * class. It provides helpful functions for parsing input like Token() and
 * Split().
 */
class CString : public std::string {
  public:
    typedef enum {
        EASCII,
        EURL,
        EHTML,
        ESQL,
        ENAMEDFMT,
        EDEBUG,
        EMSGTAG,
        EHEXCOLON,
    } EEscape;

    static const CaseSensitivity CaseSensitive = CaseSensitivity::CaseSensitive;
    static const CaseSensitivity CaseInsensitive =
        CaseSensitivity::CaseInsensitive;

    explicit CString(bool b) : std::string(b ? "true" : "false") {}
    explicit CString(char c);
    explicit CString(unsigned char c);
    explicit CString(short i);
    explicit CString(unsigned short i);
    explicit CString(int i);
    explicit CString(unsigned int i);
    explicit CString(long i);
    explicit CString(unsigned long i);
    explicit CString(long long i);
    explicit CString(unsigned long long i);
    explicit CString(double i, int precision = 2);
    explicit CString(float i, int precision = 2);

    CString() : std::string() {}
    CString(const char* c) : std::string(c) {}
    CString(const char* c, size_t l) : std::string(c, l) {}
    CString(const std::string& s) : std::string(s) {}
    CString(size_t n, char c) : std::string(n, c) {}
    CString(std::initializer_list<char> list) : std::string(list) {}
    ~CString() {}

    /**
     * Casts a CString to another type.  Implemented via std::stringstream, you use this
     * for any class that has an operator<<(std::ostream, YourClass).
     * @param target The object to cast into. If the cast fails, its state is unspecified.
     * @return True if the cast succeeds, and false if it fails.
     */
    template <typename T>
    bool Convert(T* target) const {
        std::stringstream ss(*this);
        ss >> *target;
        return (bool)ss;  // we don't care why it failed, only whether it failed
    }

    /**
     * Joins a collection of objects together, using 'this' as a delimiter.
     * You can pass either pointers to arrays, or iterators to collections.
     * @param i_begin An iterator pointing to the beginning of a group of objects.
     * @param i_end An iterator pointing past the end of a group of objects.
     * @return The joined string
     */
    template <typename Iterator>
    CString Join(Iterator i_start, const Iterator& i_end) const {
        if (i_start == i_end) return CString("");
        std::ostringstream output;
        output << *i_start;
        while (true) {
            ++i_start;
            if (i_start == i_end) return CString(output.str());
            output << *this;
            output << *i_start;
        }
    }

    /**
     * Compare this string caselessly to some other string.
     * @param s The string to compare to.
     * @param uLen The number of characters to compare.
     * @return An integer less than, equal to, or greater than zero if this
     *         string smaller, equal.... to the given string.
     */
    int CaseCmp(const CString& s,
                CString::size_type uLen = CString::npos) const;
    /**
     * Compare this string case sensitively to some other string.
     * @param s The string to compare to.
     * @param uLen The number of characters to compare.
     * @return An integer less than, equal to, or greater than zero if this
     *         string smaller, equal.... to the given string.
     */
    int StrCmp(const CString& s, CString::size_type uLen = CString::npos) const;
    /**
     * Check if this string is equal to some other string.
     * @param s The string to compare to.
     * @param cs CaseSensitive if you want the comparison to be case
     *                       sensitive, CaseInsensitive (default) otherwise.
     * @return True if the strings are equal.
     */
    bool Equals(const CString& s, CaseSensitivity cs = CaseInsensitive) const;
    /**
     * @deprecated
     */
    bool Equals(const CString& s, bool bCaseSensitive,
                CString::size_type uLen = CString::npos) const;
    /**
     * Do a wildcard comparison between two strings.
     * For example, the following returns true:
     * <code>WildCmp("*!?bar@foo", "I_am!~bar@foo");</code>
     * @param sWild The wildcards used for the comparison.
     * @param sString The string that is used for comparing.
     * @param cs CaseSensitive (default) if you want the comparison
     *           to be case sensitive, CaseInsensitive otherwise.
     * @todo Make cs CaseInsensitive by default.
     * @return true if the wildcard matches.
     */
    static bool WildCmp(const CString& sWild, const CString& sString,
                        CaseSensitivity cs = CaseSensitive);
    /**
     * Do a wild compare on this string.
     * @param sWild The wildcards used to for the comparison.
     * @param cs CaseSensitive (default) if you want the comparison
     *           to be case sensitive, CaseInsensitive otherwise.
     * @todo Make cs CaseInsensitive by default.
     * @return The result of <code>this->WildCmp(sWild, *this);</code>.
     */
    bool WildCmp(const CString& sWild,
                 CaseSensitivity cs = CaseSensitive) const;

    /**
     * Turn all characters in this string into their upper-case equivalent.
     * @returns A reference to *this.
     */
    CString& MakeUpper();
    /**
     * Turn all characters in this string into their lower-case equivalent.
     * @returns A reference to *this.
     */
    CString& MakeLower();
    /**
     * Return a copy of this string with all characters turned into
     * upper-case.
     * @return The new string.
     */
    CString AsUpper() const;
    /**
     * Return a copy of this string with all characters turned into
     * lower-case.
     * @return The new string.
     */
    CString AsLower() const;

    static EEscape ToEscape(const CString& sEsc);
    CString Escape_n(EEscape eFrom, EEscape eTo) const;
    CString Escape_n(EEscape eTo) const;
    CString& Escape(EEscape eFrom, EEscape eTo);
    CString& Escape(EEscape eTo);

    /** Replace all occurrences in a string.
     *
     * You can specify a "safe zone" via sLeft and sRight. Anything inside
     * of such a zone will not be replaced. This does not do recursion, so
     * e.g. with <code>Replace("(a()a)", "a", "b", "(", ")", true)</code>
     * you would get "a(b)" as result. The second opening brace and the
     * second closing brace would not be seen as a delimitered and thus
     * wouldn't be removed. The first a is inside a "safe zone" and thus is
     * left alone, too.
     *
     * @param sStr The string to do the replacing on. This will also contain
     *             the result when this function returns.
     * @param sReplace The string that should be replaced.
     * @param sWith The replacement to use.
     * @param sLeft The string that marks the begin of the "safe zone".
     * @param sRight The string that marks the end of the "safe zone".
     * @param bRemoveDelims If this is true, all matches for sLeft and
     *                      sRight are removed.
     * @returns The number of replacements done.
     */
    static unsigned int Replace(CString& sStr, const CString& sReplace,
                                const CString& sWith, const CString& sLeft = "",
                                const CString& sRight = "",
                                bool bRemoveDelims = false);

    /** Replace all occurrences in the current string.
     * @see CString::Replace
     * @param sReplace The string to look for.
     * @param sWith The replacement to use.
     * @param sLeft The delimiter at the beginning of a safe zone.
     * @param sRight The delimiter at the end of a safe zone.
     * @param bRemoveDelims If true, all matching delimiters are removed.
     * @return The result of the replacing. The current string is left
     *         unchanged.
     */
    CString Replace_n(const CString& sReplace, const CString& sWith,
                      const CString& sLeft = "", const CString& sRight = "",
                      bool bRemoveDelims = false) const;
    /** Replace all occurrences in the current string.
     * @see CString::Replace
     * @param sReplace The string to look for.
     * @param sWith The replacement to use.
     * @param sLeft The delimiter at the beginning of a safe zone.
     * @param sRight The delimiter at the end of a safe zone.
     * @param bRemoveDelims If true, all matching delimiters are removed.
     * @returns The number of replacements done.
     */
    unsigned int Replace(const CString& sReplace, const CString& sWith,
                         const CString& sLeft = "", const CString& sRight = "",
                         bool bRemoveDelims = false);
    /** Ellipsize the current string.
     * For example, ellipsizing "Hello, I'm Bob" to the length 9 would
     * result in "Hello,...".
     * @param uLen The length to ellipsize to.
     * @return The ellipsized string.
     */
    CString Ellipsize(unsigned int uLen) const;
    /** Return the left part of the string.
     * @param uCount The number of characters to keep.
     * @return The resulting string.
     */
    CString Left(size_type uCount) const;
    /** Return the right part of the string.
     * @param uCount The number of characters to keep.
     * @return The resulting string.
     */
    CString Right(size_type uCount) const;

    /** Get the first line of this string.
     * @return The first line of text.
     */
    CString FirstLine() const { return Token(0, false, "\n"); }

    /** Get a token out of this string. For example in the string "a bc d  e",
     *  each of "a", "bc", "d" and "e" are tokens.
     * @param uPos The number of the token you are interested. The first
     *             token has a position of 0.
     * @param bRest If false, only the token you asked for is returned. Else
     *              you get the substring starting from the beginning of
     *              your token.
     * @param sSep Seperator between tokens.
     * @param bAllowEmpty If this is true, empty tokens are allowed. In the
     *                    example from above this means that there is a
     *                    token "" before the "e" token.
     * @return The token you asked for and, if bRest is true, everything
     *         after it.
     * @see Split() if you need a string split into all of its tokens.
     */
    CString Token(size_t uPos, bool bRest = false, const CString& sSep = " ",
                  bool bAllowEmpty = false) const;

    /** Get a token out of this string. This function behaves much like the
     *  other Token() function in this class. The extra arguments are
     *  handled similarly to Split().
     */
    CString Token(size_t uPos, bool bRest, const CString& sSep,
                  bool bAllowEmpty, const CString& sLeft, const CString& sRight,
                  bool bTrimQuotes = true) const;

    size_type URLSplit(MCString& msRet) const;
    size_type OptionSplit(MCString& msRet, bool bUpperKeys = false) const;
    size_type QuoteSplit(VCString& vsRet) const;

    /** Split up this string into tokens.
     * Via sLeft and sRight you can define "markers" like with Replace().
     * Anything in such a marked section is treated as a single token. All
     * occurrences of sDelim in such a block are ignored.
     * @param sDelim Delimiter between tokens.
     * @param vsRet Vector for returning the result.
     * @param bAllowEmpty Do empty tokens count as a valid token?
     * @param sLeft Left delimiter like with Replace().
     * @param sRight Right delimiter like with Replace().
     * @param bTrimQuotes Should sLeft and sRight be removed from the token
     *                    they mark?
     * @param bTrimWhiteSpace If this is true, CString::Trim() is called on
     *                        each token.
     * @return The number of tokens found.
     */
    size_type Split(const CString& sDelim, VCString& vsRet,
                    bool bAllowEmpty = true, const CString& sLeft = "",
                    const CString& sRight = "", bool bTrimQuotes = true,
                    bool bTrimWhiteSpace = false) const;

    /** Split up this string into tokens.
     * This function is identical to the other CString::Split(), except that
     * the result is returned as a SCString instead of a VCString.
     */
    size_type Split(const CString& sDelim, SCString& ssRet,
                    bool bAllowEmpty = true, const CString& sLeft = "",
                    const CString& sRight = "", bool bTrimQuotes = true,
                    bool bTrimWhiteSpace = false) const;

    /** Build a string from a format string, replacing values from a map.
     * The format specification can contain simple named parameters that match
     * keys in the given map. For example in the string "a {b} c", the key "b"
     * is looked up in the map, and inserted for "{b}".
     * @param sFormat The format specification.
     * @param msValues A map of named parameters to their values.
     * @return The string with named parameters replaced.
     */
    static CString NamedFormat(const CString& sFormat,
                               const MCString& msValues);

    /** Produces a random string.
     * @param uLength The length of the resulting string.
     * @return A random string.
     */
    static CString RandomString(unsigned int uLength);

    /** @return The MD5 hash of this string. */
    CString MD5() const;
    /** @return The SHA256 hash of this string. */
    CString SHA256() const;

    /** Treat this string as base64-encoded data and decode it.
     * @param sRet String to which the result of the decode is safed.
     * @return The length of the resulting string.
     */
    unsigned long Base64Decode(CString& sRet) const;
    /** Treat this string as base64-encoded data and decode it.
     *  The result is saved in this CString instance.
     * @return The length of the resulting string.
     */
    unsigned long Base64Decode();
    /** Treat this string as base64-encoded data and decode it.
     * @return The decoded string.
     */
    CString Base64Decode_n() const;
    /** Base64-encode the current string.
     * @param sRet String where the result is saved.
     * @param uWrap A boolean(!?!) that decides if the result should be
     *              wrapped after everywhere 57 characters.
     * @return true unless this code is buggy.
     * @todo WTF @ uWrap.
     * @todo This only returns false if some formula we use was wrong?!
     */
    bool Base64Encode(CString& sRet, unsigned int uWrap = 0) const;
    /** Base64-encode the current string.
     *  This string is overwritten with the result of the encode.
     *  @todo return value and param are as with Base64Encode() from above.
     */
    bool Base64Encode(unsigned int uWrap = 0);
    /** Base64-encode the current string
     * @todo uWrap is as broken as Base64Encode()'s uWrap.
     * @return The encoded string.
     */
    CString Base64Encode_n(unsigned int uWrap = 0) const;

#ifdef HAVE_LIBSSL
    CString Encrypt_n(const CString& sPass, const CString& sIvec = "") const;
    CString Decrypt_n(const CString& sPass, const CString& sIvec = "") const;
    void Encrypt(const CString& sPass, const CString& sIvec = "");
    void Decrypt(const CString& sPass, const CString& sIvec = "");
    void Crypt(const CString& sPass, bool bEncrypt, const CString& sIvec = "");
#endif

    /** Pretty-print a percent value.
     * @param d The percent value. This should be in range 0-100.
     * @return The "pretty" string.
     */
    static CString ToPercent(double d);
    /** Pretty-print a number of bytes.
     * @param d The number of bytes.
     * @return A string describing the number of bytes.
     */
    static CString ToByteStr(unsigned long long d);
    /** Pretty-print a time span.
     * @param s Number of seconds to print.
     * @return A string like "4w 6d 4h 3m 58s".
     */
    static CString ToTimeStr(unsigned long s);

    /** @return True if this string is not "false". */
    bool ToBool() const;
    /** @return The numerical value of this string similar to atoi(). */
    short ToShort() const;
    /** @return The numerical value of this string similar to atoi(). */
    unsigned short ToUShort() const;
    /** @return The numerical value of this string similar to atoi(). */
    int ToInt() const;
    /** @return The numerical value of this string similar to atoi(). */
    long ToLong() const;
    /** @return The numerical value of this string similar to atoi(). */
    unsigned int ToUInt() const;
    /** @return The numerical value of this string similar to atoi(). */
    unsigned long ToULong() const;
    /** @return The numerical value of this string similar to atoi(). */
    unsigned long long ToULongLong() const;
    /** @return The numerical value of this string similar to atoi(). */
    long long ToLongLong() const;
    /** @return The numerical value of this string similar to atoi(). */
    double ToDouble() const;

    /** Trim this string. All leading/trailing occurrences of characters from
     *  s are removed.
     * @param s A list of characters that should be trimmed.
     * @return true if this string was modified.
     */
    bool Trim(const CString& s = " \t\r\n");
    /** Trim this string. All leading occurrences of characters from s are
     *  removed.
     * @param s A list of characters that should be trimmed.
     * @return true if this string was modified.
     */
    bool TrimLeft(const CString& s = " \t\r\n");
    /** Trim this string. All trailing occurrences of characters from s are
     *  removed.
     * @param s A list of characters that should be trimmed.
     * @return true if this string was modified.
     */
    bool TrimRight(const CString& s = " \t\r\n");
    /** Trim this string. All leading/trailing occurrences of characters from
     *  s are removed. This CString instance is not modified.
     * @param s A list of characters that should be trimmed.
     * @return The trimmed string.
     */
    CString Trim_n(const CString& s = " \t\r\n") const;
    /** Trim this string. All leading occurrences of characters from s are
     *  removed. This CString instance is not modified.
     * @param s A list of characters that should be trimmed.
     * @return The trimmed string.
     */
    CString TrimLeft_n(const CString& s = " \t\r\n") const;
    /** Trim this string. All trailing occurrences of characters from s are
     *  removed. This CString instance is not modified.
     * @param s A list of characters that should be trimmed.
     * @return The trimmed string.
     */
    CString TrimRight_n(const CString& s = " \t\r\n") const;

    /** Trim a given prefix.
     * @param sPrefix The prefix that should be removed.
     * @return True if this string was modified.
     */
    bool TrimPrefix(const CString& sPrefix = ":");
    /** Trim a given suffix.
     * @param sSuffix The suffix that should be removed.
     * @return True if this string was modified.
     */
    bool TrimSuffix(const CString& sSuffix);
    /** Trim a given prefix.
     * @param sPrefix The prefix that should be removed.
     * @return A copy of this string without the prefix.
     */
    CString TrimPrefix_n(const CString& sPrefix = ":") const;
    /** Trim a given suffix.
     * @param sSuffix The suffix that should be removed.
     * @return A copy of this string without the prefix.
     */
    CString TrimSuffix_n(const CString& sSuffix) const;

    /** Find the position of the given substring.
     * @param s The substring to search for.
     * @param cs CaseSensitive if you want the comparison to be case
     *                       sensitive, CaseInsensitive (default) otherwise.
     * @return The position of the substring if found, CString::npos otherwise.
     */
    size_t Find(const CString& s, CaseSensitivity cs = CaseInsensitive) const;
    /** Check whether the string starts with a given prefix.
     * @param sPrefix The prefix.
     * @param cs CaseSensitive if you want the comparison to be case
     *                       sensitive, CaseInsensitive (default) otherwise.
     * @return True if the string starts with prefix, false otherwise.
     */
    bool StartsWith(const CString& sPrefix,
                    CaseSensitivity cs = CaseInsensitive) const;
    /** Check whether the string ends with a given suffix.
     * @param sSuffix The suffix.
     * @param cs CaseSensitive if you want the comparison to be case
     *                       sensitive, CaseInsensitive (default) otherwise.
     * @return True if the string ends with suffix, false otherwise.
     */
    bool EndsWith(const CString& sSuffix,
                  CaseSensitivity cs = CaseInsensitive) const;
    /**
     * Check whether the string contains a given string.
     * @param s The string to search.
     * @param bCaseSensitive Whether the search is case sensitive.
     * @return True if this string contains the other string, falser otherwise.
     */
    bool Contains(const CString& s, CaseSensitivity cs = CaseInsensitive) const;

    /** Remove characters from the beginning of this string.
     * @param uLen The number of characters to remove.
     * @return true if this string was modified.
     */
    bool LeftChomp(size_type uLen = 1);
    /** Remove characters from the end of this string.
     * @param uLen The number of characters to remove.
     * @return true if this string was modified.
     */
    bool RightChomp(size_type uLen = 1);
    /** Remove characters from the beginning of this string.
     * This string object isn't modified.
     * @param uLen The number of characters to remove.
     * @return The result of the conversion.
     */
    CString LeftChomp_n(size_type uLen = 1) const;
    /** Remove characters from the end of this string.
     * This string object isn't modified.
     * @param uLen The number of characters to remove.
     * @return The result of the conversion.
     */
    CString RightChomp_n(size_type uLen = 1) const;
    /** Remove controls characters from this string.
     * Controls characters are color codes, and those in C0 set
     * See https://en.wikipedia.org/wiki/C0_and_C1_control_codes
     * @return The result of the conversion.
     */
    CString& StripControls();
    /** Remove controls characters from this string.
     * Controls characters are color codes, and those in C0 set
     * See https://en.wikipedia.org/wiki/C0_and_C1_control_codes
     * This string object isn't modified.
     * @return The result of the conversion.
     */
    CString StripControls_n() const;

  private:
  protected:
    unsigned char* strnchr(const unsigned char* src, unsigned char c,
                           unsigned int iMaxBytes,
                           unsigned char* pFill = nullptr,
                           unsigned int* piCount = nullptr) const;
};

/**
 * @brief A dictionary for strings.
 * @todo Replace with "using MCString = std::map<CString, CString>;" in ZNC 2.0
 *
 * This class maps strings to other strings.
 */
class MCString : public std::map<CString, CString> {
  public:
    /** Construct an empty MCString. */
    MCString() : std::map<CString, CString>() {}
    /** Construct a MCString using an initializer list eg. MCString m = { {"key1", "val1"}, {"key2", "val2"} }; */
    MCString(std::initializer_list<std::pair<const CString, CString>> list)
        : std::map<CString, CString>(list) {}
    /** Destruct this MCString. */
    virtual ~MCString() { clear(); }

    /** A static instance of an empty map. */
    static const MCString EmptyMap;

    /** Status codes that can be returned by WriteToDisk() and
     * ReadFromDisk(). */
    enum status_t {
        /// No errors.
        MCS_SUCCESS = 0,
        /// Opening the file failed.
        MCS_EOPEN = 1,
        /// Writing to the file failed.
        MCS_EWRITE = 2,
        /// WriteFilter() failed.
        MCS_EWRITEFIL = 3,
        /// ReadFilter() failed.
        MCS_EREADFIL = 4
    };

    /** Write this map to a file.
     * @param sPath The file name to write to.
     * @param iMode The mode for the file.
     * @return The result of the operation.
     * @see WriteFilter.
     */
    enum status_t WriteToDisk(const CString& sPath, mode_t iMode = 0644) const;
    /** Read a map from a file.
     * @param sPath The file name to read from.
     * @return The result of the operation.
     * @see ReadFilter.
     */
    enum status_t ReadFromDisk(const CString& sPath);

    /** Filter used while writing this map. This function is called by
     * WriteToDisk() for each pair that is going to be written. This
     * function has the chance to modify the data that will be written.
     * @param sKey The key that will be written. Can be modified.
     * @param sValue The value that will be written. Can be modified.
     * @return true unless WriteToDisk() should fail with MCS_EWRITEFIL.
     */
    virtual bool WriteFilter(CString& sKey, CString& sValue) const {
        return true;
    }
    /** Filter used while reading this map. This function is called by
     * ReadFromDisk() for each pair that is beging read. This function has
     * the chance to modify the data that is being read.
     * @param sKey The key that was read. Can be modified.
     * @param sValue The value that was read. Can be modified.
     * @return true unless ReadFromDisk() should fail with MCS_EWRITEFIL.
     */
    virtual bool ReadFilter(CString& sKey, CString& sValue) const {
        return true;
    }

    /** Encode a value so that it can safely be parsed by ReadFromDisk().
     * This is an internal function.
     */
    virtual CString& Encode(CString& sValue) const;
    /** Undo the effects of Encode(). This is an internal function. */
    virtual CString& Decode(CString& sValue) const;
};

namespace std {
template <>
struct hash<CString> : hash<std::string> {};
}

// Make translateable messages easy to write:
// t_f("Foo is {1}")(foo)
class CInlineFormatMessage {
  public:
    explicit CInlineFormatMessage(const CString& sFormat)
        : m_sFormat(sFormat) {}
    explicit CInlineFormatMessage(CString&& sFormat)
        : m_sFormat(std::move(sFormat)) {}

    template <typename... Args>
    CString operator()(const Args&... args) const {
        MCString values;
        apply(values, 1, args...);
        return CString::NamedFormat(m_sFormat, values);
    }

  private:
    template <typename Arg, typename... Rest>
    void apply(MCString& values, int index, const Arg& arg,
               const Rest&... rest) const {
        values[CString(index)] = CString(arg);
        apply(values, index + 1, rest...);
    }

    void apply(MCString& values, int index) const {}

    CString m_sFormat;
};

// For gtest
#ifdef GTEST_FAIL
inline void PrintTo(const CString& s, std::ostream* os) {
    *os << '"' << s.Escape_n(CString::EDEBUG) << '"';
}
#endif

#endif  // !ZNCSTRING_H