// SPDX-License-Identifier: MIT
// SPDX-FileCopyrightText: 2026 Martino Ferrari

#include "export.hpp"

#include <algorithm>
#include <bit>
#include <cerrno>
#include <cstdio>
#include <cstring>

namespace udpscope {
namespace {

// The writers memcpy `f64`/`f32` straight out and label them `<f8`/`<f4`, so a
// big-endian host would produce a file whose bytes contradict its own dtype. There is no
// such host in this app's reach and a byte-swapping path nobody runs is a path nobody
// tests, so the assumption is stated instead of handled.
static_assert(std::endian::native == std::endian::little,
              "the .npy writer labels its fields little-endian and does not swap");

/// A column label a reader can use: NumPy rejects duplicate field names outright, and a
/// quote or a brace in one would break the header dict it is spelled into. Signal names
/// come from the stream, so neither is this app's to promise.
std::string sanitise(const std::string& name) {
  std::string out;
  out.reserve(name.size());
  for (const char ch : name) {
    const bool ok = (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') ||
                    (ch >= '0' && ch <= '9') || ch == '_';
    out.push_back(ok ? ch : '_');
  }
  if (out.empty()) out = "col";
  return out;
}

/// The final labels: sanitised, and de-duplicated against each other *and* against the
/// two time columns, with a `_2`, `_3` suffix. Two elements of one vector signal can
/// easily sanitise to the same string.
std::vector<std::string> column_labels(const ExportTable& table) {
  std::vector<std::string> taken{"time", "stream_time"};
  std::vector<std::string> out;
  out.reserve(table.columns.size());
  for (const ExportTable::Column& col : table.columns) {
    const std::string base = sanitise(col.name);
    std::string label = base;
    for (int n = 2; std::find(taken.begin(), taken.end(), label) != taken.end(); ++n) {
      label = base + "_" + std::to_string(n);
    }
    taken.push_back(label);
    out.push_back(std::move(label));
  }
  return out;
}

struct File {
  explicit File(const std::string& path) : f(std::fopen(path.c_str(), "wb")) {}
  ~File() {
    if (f != nullptr) std::fclose(f);
  }
  File(const File&) = delete;
  File& operator=(const File&) = delete;
  std::FILE* f = nullptr;
};

bool opened(const File& out, const std::string& path, std::string& error) {
  if (out.f != nullptr) return true;
  error = "cannot write '" + path + "': " + std::strerror(errno);
  return false;
}

}  // namespace

ExportTable collect_export(ScopeModel& model, RowSet& rows) {
  ExportTable table;
  const RowSet::Row& r0 = rows.row(0);
  if (r0.plot == nullptr) return table;
  const plot::Range view = r0.plot->x_range(r0.axis_x);

  // Which channels: every bound slot on a visible row, de-duplicated, then sorted. A
  // signal dropped on two rows is one column, and channel order is the signal list's
  // order, so the columns read in the same order as the panel.
  std::vector<int> chans;
  for (int i = 0; i < rows.row_count(); ++i) {
    for (int s = 0; s < RowSet::kSlotsPerRow; ++s) {
      const int c = rows.channel_of(i, s);
      if (c >= 0 && std::find(chans.begin(), chans.end(), c) == chans.end()) {
        chans.push_back(c);
      }
    }
  }
  std::sort(chans.begin(), chans.end());
  if (chans.empty()) return table;

  const std::vector<ChannelInfo>& infos = model.channels();
  const auto name_of = [&](int c) {
    return static_cast<std::size_t>(c) < infos.size() ? infos[static_cast<std::size_t>(c)].name
                                                     : std::string("ch") + std::to_string(c);
  };

  // What the rows bind to is what gets exported, which is the same branch `RowSet::bind()`
  // takes: the frozen event in trigger mode, the live ring otherwise. Reading the ring
  // while an event is on screen would export data the user cannot see.
  std::shared_ptr<const EventSnapshot> snap = model.event();
  if (model.trigger_enabled() && snap != nullptr) {
    // The snapshot is immutable and already index-aligned, so the visible window is two
    // binary searches over its stamps and the same index range for every channel.
    const std::vector<f32>& st = snap->stamps;
    const auto lo = std::lower_bound(st.begin(), st.end(), static_cast<f32>(view.min));
    const auto hi = std::upper_bound(st.begin(), st.end(), static_cast<f32>(view.max));
    if (hi <= lo) return table;
    const std::size_t first = static_cast<std::size_t>(lo - st.begin());
    const std::size_t n = static_cast<std::size_t>(hi - lo);
    // The event's x = 0 is the edge, so the stream clock has to be added back for the
    // second column -- the one case where the visible x is not the stream's own.
    const f64 edge = model.trigger_time().load(std::memory_order_relaxed);

    table.time.resize(n);
    table.stream_time.resize(n);
    for (std::size_t i = 0; i < n; ++i) {
      table.time[i] = static_cast<f64>(st[first + i]);
      table.stream_time[i] = edge + table.time[i];
    }
    for (const int c : chans) {
      const std::size_t ch = static_cast<std::size_t>(c);
      if (ch >= snap->values.size()) continue;
      const std::vector<f32>& src = snap->values[ch];
      if (src.size() < first + n) continue;
      table.columns.push_back({name_of(c), std::vector<f32>(src.begin() + static_cast<std::ptrdiff_t>(first),
                                                            src.begin() + static_cast<std::ptrdiff_t>(first + n))});
    }
    return table;
  }

  // Live: one absolute index range over the shared time ring, used for every channel --
  // `live_window_locked()` is the same cut a latch makes, so an export and a capture of
  // the same window hold the same samples. The lock is against a structural change
  // dropping the rings under the copy, which is what the UI thread has to fear here.
  std::lock_guard<std::mutex> lock(model.mutex());
  // The axis reads `display_epoch + stamp`, so the window has to be put back on the
  // stream's clock before the ring is searched. It is 0 in live mode, but reading it is
  // what keeps this correct rather than merely true today.
  const f64 epoch = model.display_epoch();
  u64 first = 0, last = 0;
  model.live_window_locked(view.min - epoch, view.max - epoch, first, last);
  const u64 n = last - first;
  if (n == 0) return table;

  BufferStore& store = model.live();
  std::vector<f32> stamps(static_cast<std::size_t>(n));
  store.time().copy_from(first, n, stamps.data());
  table.time.resize(static_cast<std::size_t>(n));
  table.stream_time.resize(static_cast<std::size_t>(n));
  for (std::size_t i = 0; i < stamps.size(); ++i) {
    table.stream_time[i] = static_cast<f64>(stamps[i]);
    table.time[i] = epoch + table.stream_time[i];
  }
  for (const int c : chans) {
    const std::size_t ch = static_cast<std::size_t>(c);
    if (ch >= model.channel_count()) continue;
    std::vector<f32> values(static_cast<std::size_t>(n));
    store.values(ch).copy_from(first, n, values.data());
    table.columns.push_back({name_of(c), std::move(values)});
  }
  return table;
}

bool write_npy(const std::string& path, const ExportTable& table, std::string& error) {
  if (table.empty()) {
    error = "nothing to export: no signal is plotted in the visible range";
    return false;
  }
  const std::vector<std::string> labels = column_labels(table);

  // `descr` as a list of (name, format) pairs is a *packed* structured dtype -- NumPy
  // only inserts alignment padding when asked to (`align=True`) -- so the records below
  // are field widths back to back with no gaps.
  std::string descr = "[('time', '<f8'), ('stream_time', '<f8')";
  for (const std::string& label : labels) descr += ", ('" + label + "', '<f4')";
  descr += "]";
  std::string header = "{'descr': " + descr + ", 'fortran_order': False, 'shape': (" +
                       std::to_string(table.rows()) + ",), }";
  // v1.0: a 6-byte magic, 2 version bytes and a 2-byte little-endian header length, and
  // the whole preamble padded so the data starts on a 64-byte boundary.
  constexpr std::size_t kPreamble = 10;
  const std::size_t unpadded = kPreamble + header.size() + 1;
  const std::size_t padded = (unpadded + 63) / 64 * 64;
  header.append(padded - unpadded, ' ');
  header.push_back('\n');
  if (header.size() > 0xFFFFu) {
    error = "too many columns for a v1.0 .npy header";
    return false;
  }

  File out(path);
  if (!opened(out, path, error)) return false;
  const unsigned char len[2] = {static_cast<unsigned char>(header.size() & 0xFFu),
                                static_cast<unsigned char>((header.size() >> 8) & 0xFFu)};
  std::fwrite("\x93NUMPY\x01\x00", 1, 8, out.f);
  std::fwrite(len, 1, 2, out.f);
  std::fwrite(header.data(), 1, header.size(), out.f);

  // One record at a time, into a reused buffer: a column-major staging array would be a
  // second copy of the whole export, which at a full ring is tens of megabytes.
  std::vector<unsigned char> record(2 * sizeof(f64) + table.columns.size() * sizeof(f32));
  for (std::size_t i = 0; i < table.rows(); ++i) {
    std::size_t at = 0;
    std::memcpy(record.data() + at, &table.time[i], sizeof(f64));
    at += sizeof(f64);
    std::memcpy(record.data() + at, &table.stream_time[i], sizeof(f64));
    at += sizeof(f64);
    for (const ExportTable::Column& col : table.columns) {
      const f32 v = i < col.values.size() ? col.values[i] : 0.0f;
      std::memcpy(record.data() + at, &v, sizeof(f32));
      at += sizeof(f32);
    }
    if (std::fwrite(record.data(), 1, record.size(), out.f) != record.size()) {
      error = "short write to '" + path + "': " + std::strerror(errno);
      return false;
    }
  }
  if (std::fflush(out.f) != 0) {
    error = "cannot flush '" + path + "': " + std::strerror(errno);
    return false;
  }
  return true;
}

bool write_csv(const std::string& path, const ExportTable& table, std::string& error) {
  if (table.empty()) {
    error = "nothing to export: no signal is plotted in the visible range";
    return false;
  }
  File out(path);
  if (!opened(out, path, error)) return false;

  const std::vector<std::string> labels = column_labels(table);
  std::string line = "time,stream_time";
  for (const std::string& label : labels) line += "," + label;
  line += "\n";
  std::fwrite(line.data(), 1, line.size(), out.f);

  // `%.17g` for the f64 times and `%.9g` for the f32 values: the shortest widths that
  // round-trip each type exactly. Anything less silently rewrites the samples, which is
  // the one thing an export may not do.
  char buf[64];
  for (std::size_t i = 0; i < table.rows(); ++i) {
    line.clear();
    std::snprintf(buf, sizeof(buf), "%.17g", table.time[i]);
    line += buf;
    std::snprintf(buf, sizeof(buf), "%.17g", table.stream_time[i]);
    line += ",";
    line += buf;
    for (const ExportTable::Column& col : table.columns) {
      std::snprintf(buf, sizeof(buf), "%.9g",
                    double(i < col.values.size() ? col.values[i] : 0.0f));
      line += ",";
      line += buf;
    }
    line += "\n";
    if (std::fwrite(line.data(), 1, line.size(), out.f) != line.size()) {
      error = "short write to '" + path + "': " + std::strerror(errno);
      return false;
    }
  }
  if (std::fflush(out.f) != 0) {
    error = "cannot flush '" + path + "': " + std::strerror(errno);
    return false;
  }
  return true;
}

}  // namespace udpscope