// SPDX-License-Identifier: GPL-3.0-or-later
// SPDX-FileCopyrightText: 2025 ai-ad4 and the FreePDFEditor contributors
//
// Roundtrip — the core of Spike A. Given a PDF on disk, open it with QPDF,
// ask QPDF to write it back to a fresh file with the same structure, and
// report whether the round-trip is byte-identical. Per the plan §14 step 4:
//
//   "Spike A: QPDF-based open → parse content streams → re-emit verbatim → save.
//    Measure byte-identical round-trip rate over 500 corpus files. Target ≥ 99%."
//
// The "parse content streams" step is what later spikes build on; here we walk
// every page's content stream(s) through QPDF's stream decoder/encoder and
// verify the object graph is structurally preserved, which is the precondition
// for the surgical re-emission in §4.4 to be lossless.

#ifndef FREEPDFEDITOR_SPIKE_A_ROUNDTRIP_H
#define FREEPDFEDITOR_SPIKE_A_ROUNDTRIP_H

#include <cstddef>
#include <filesystem>
#include <string>

namespace freepdfeditor::spike::a {

enum class Outcome {
    ByteIdentical,   // input == output byte-for-byte
    StructurallySame, // QPDF wrote a different byte stream with identical semantics
    Failed,          // could not open / could not write
};

struct FileResult {
    Outcome outcome;
    std::size_t pages = 0;
    std::string error;     // populated when outcome == Failed
};

// Round-trip `input` through QPDF, writing to `output`. `output` must not
// already exist. Walks every page's content stream(s) via
// qpdf_objecthandle to prove the parse path is exercised, then writes the
// document back preserving object order.
FileResult roundtrip(const std::filesystem::path& input,
                     const std::filesystem::path& output);

} // namespace freepdfeditor::spike::a

#endif // FREEPDFEDITOR_SPIKE_A_ROUNDTRIP_H