// Copyright (c) 2005-2024 Jay Berkenbilt
//
// This file is part of qpdf.
//
// 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.
//
// Versions of qpdf prior to version 7 were released under the terms of version 2.0 of the Artistic
// License. At your option, you may continue to consider qpdf to be licensed under those terms.
// Please see the manual for additional information.

#ifndef QPDF_INPUTSOURCE_HH
#define QPDF_INPUTSOURCE_HH

#include <qpdf/DLL.h>
#include <qpdf/PointerHolder.hh> // unused -- remove in qpdf 12 (see #785)
#include <qpdf/Types.h>

#include <cstdio>
#include <memory>
#include <string>

// Remember to use QPDF_DLL_CLASS on anything derived from InputSource so it will work with
// dynamic_cast across the shared object boundary.
class QPDF_DLL_CLASS InputSource
{
  public:
    QPDF_DLL
    InputSource()
    {
    }
    QPDF_DLL
    virtual ~InputSource() = default;

    class QPDF_DLL_CLASS Finder
    {
      public:
        QPDF_DLL
        Finder() = default;
        QPDF_DLL
        virtual ~Finder() = default;
        virtual bool check() = 0;
    };

    QPDF_DLL
    void setLastOffset(qpdf_offset_t);
    QPDF_DLL
    qpdf_offset_t getLastOffset() const;
    QPDF_DLL
    std::string readLine(size_t max_line_length);

    // Find first or last occurrence of a sequence of characters starting within the range defined
    // by offset and len such that, when the input source is positioned at the beginning of that
    // sequence, finder.check() returns true. If len is 0, the search proceeds until EOF. If a
    // qualifying pattern is found, these methods return true and leave the input source positioned
    // wherever check() left it at the end of the matching pattern.
    QPDF_DLL
    bool findFirst(char const* start_chars, qpdf_offset_t offset, size_t len, Finder& finder);
    QPDF_DLL
    bool findLast(char const* start_chars, qpdf_offset_t offset, size_t len, Finder& finder);

    virtual qpdf_offset_t findAndSkipNextEOL() = 0;
    virtual std::string const& getName() const = 0;
    virtual qpdf_offset_t tell() = 0;
    virtual void seek(qpdf_offset_t offset, int whence) = 0;
    virtual void rewind() = 0;
    virtual size_t read(char* buffer, size_t length) = 0;

    // Note: you can only unread the character you just read. The specific character is ignored by
    // some implementations, and the implementation doesn't check this. Use of unreadCh is
    // semantically equivalent to seek(-1, SEEK_CUR) but is much more efficient.
    virtual void unreadCh(char ch) = 0;

    // The following methods are for use by QPDFTokenizer
    inline qpdf_offset_t fastTell();
    inline bool fastRead(char&);
    inline void fastUnread(bool);
    inline void loadBuffer();

  protected:
    qpdf_offset_t last_offset{0};

  private:
    class QPDF_DLL_PRIVATE Members
    {
        friend class InputSource;

      public:
        QPDF_DLL
        ~Members() = default;

      private:
        Members() = default;
        Members(Members const&) = delete;
    };

    std::shared_ptr<Members> m;

    // State for fast... methods
    static const qpdf_offset_t buf_size = 128;
    char buffer[buf_size];
    qpdf_offset_t buf_len = 0;
    qpdf_offset_t buf_idx = 0;
    qpdf_offset_t buf_start = 0;
};

inline void
InputSource::loadBuffer()
{
    this->buf_idx = 0;
    this->buf_len = qpdf_offset_t(read(this->buffer, this->buf_size));
    // NB read sets last_offset
    this->buf_start = this->last_offset;
}

inline qpdf_offset_t
InputSource::fastTell()
{
    if (this->buf_len == 0) {
        loadBuffer();
    } else {
        auto curr = tell();
        if (curr < this->buf_start || curr >= (this->buf_start + this->buf_len)) {
            loadBuffer();
        } else {
            this->last_offset = curr;
            this->buf_idx = curr - this->buf_start;
        }
    }
    return this->last_offset;
}

inline bool
InputSource::fastRead(char& ch)
{
    // Before calling fastRead, fastTell must be called to prepare the buffer. Once reading is
    // complete, fastUnread must be called to set the correct file position.
    if (this->buf_idx < this->buf_len) {
        ch = this->buffer[this->buf_idx];
        ++(this->buf_idx);
        ++(this->last_offset);
        return true;

    } else if (this->buf_len == 0) {
        return false;
    } else {
        seek(this->buf_start + this->buf_len, SEEK_SET);
        fastTell();
        return fastRead(ch);
    }
}

inline void
InputSource::fastUnread(bool back)
{
    this->last_offset -= back ? 1 : 0;
    seek(this->last_offset, SEEK_SET);
}

#endif // QPDF_INPUTSOURCE_HH