#include "ChapterXPathReverseMapper.h"

#include <HalStorage.h>
#include <Logging.h>
#include <expat.h>

#include <algorithm>
#include <cstdlib>
#include <string>

#include "ChapterXPathIndexerInternal.h"
#include "ChapterXPathIndexerState.h"

namespace ChapterXPathIndexerInternal {

namespace {

// Reverse mapper: translate KOReader XPath to intra-spine progress.
// Matching preference order is strict and deterministic:
//   exact > exact-no-index > ancestor > ancestor-no-index.
// For /text()[N].M, M is treated as codepoint offset and converted back to
// internal visible-byte progress.

enum class MatchTier : int {
  NONE = 0,
  ANCESTOR_NO_IDX = 1,
  ANCESTOR = 2,
  EXACT_NO_IDX = 3,
  EXACT = 4,
};

struct ReverseState : StackState {
  int spineIndex;
  std::string targetNorm;
  std::string targetNoIndex;

  int targetTextNodeIndex = 0;
  int targetCharOffset = 0;
  bool inParentTextNode = false;
  size_t codepointsInCurrentTextNode = 0;
  int currentTextNodeCount = 0;

  MatchTier bestTier = MatchTier::NONE;
  int bestDepth = -1;
  size_t bestOffset = 0;
  bool bestExact = false;
  const char* bestTierName = nullptr;

  ReverseState(const int spineIndex, const std::string& xpath) : spineIndex(spineIndex) {
    // Parse optional /text()[N].M suffix before normalizing for element matching.
    std::string raw = xpath;
    for (char& c : raw) c = static_cast<char>(std::tolower(static_cast<unsigned char>(c)));
    const std::string tnPat = "/text()[";
    const size_t tnPos = raw.rfind(tnPat);
    if (tnPos != std::string::npos) {
      const size_t numStart = tnPos + tnPat.size();
      size_t numEnd = numStart;
      while (numEnd < raw.size() && std::isdigit(static_cast<unsigned char>(raw[numEnd]))) {
        numEnd++;
      }
      if (numEnd > numStart && numEnd < raw.size() && raw[numEnd] == ']') {
        const long nodeIdx = std::strtol(raw.substr(numStart, numEnd - numStart).c_str(), nullptr, 10);
        if (nodeIdx >= 1) {
          targetTextNodeIndex = static_cast<int>(nodeIdx);
          size_t after = numEnd + 1;
          if (after < raw.size() && raw[after] == '.') {
            after++;
            size_t charEnd = after;
            while (charEnd < raw.size() && std::isdigit(static_cast<unsigned char>(raw[charEnd]))) {
              charEnd++;
            }
            if (charEnd > after) {
              const long charOff = std::strtol(raw.substr(after, charEnd - after).c_str(), nullptr, 10);
              if (charOff >= 0) {
                targetCharOffset = static_cast<int>(charOff);
              }
            }
          }
        }
      }
    }
    targetNorm = normalizeXPath(xpath);
    targetNoIndex = removeIndices(targetNorm);
  }

  void onStartElement(const XML_Char* rawName) {
    inParentTextNode = false;
    pushElement(rawName);
  }

  void onEndElement() {
    // Empty/textless elements can still be a valid anchor location.
    if (!stack.empty() && !stack.back().hasText) {
      checkMatch();
    }
    inParentTextNode = false;
    popElement();
  }

  void onCharData(const XML_Char* text, const int len) {
    if (shouldSkipText(len)) {
      return;
    }

    const size_t visible = countVisibleBytes(text, len);
    const size_t codepoints = countUtf8Codepoints(text, len);

    if (targetTextNodeIndex > 0 && !stack.empty()) {
      const std::string xpath = normalizeXPath(currentXPath(spineIndex));
      if (xpath == targetNorm) {
        stack.back().hasText = true;
        if (!inParentTextNode) {
          inParentTextNode = true;
          currentTextNodeCount++;
          codepointsInCurrentTextNode = 0;
        }
        if (currentTextNodeCount == targetTextNodeIndex && bestTier < MatchTier::EXACT) {
          const size_t charOff = static_cast<size_t>(targetCharOffset);
          if (charOff >= codepointsInCurrentTextNode && charOff <= codepointsInCurrentTextNode + codepoints) {
            const size_t cpInChunk = charOff - codepointsInCurrentTextNode;
            const size_t pos = totalTextBytes + visibleBytesBeforeCodepoint(text, len, cpInChunk);
            bestTier = MatchTier::EXACT;
            bestDepth = pathDepth(xpath);
            bestOffset = pos;
            bestExact = true;
            bestTierName = "text-node-exact";
          }
        }
        codepointsInCurrentTextNode += codepoints;
        totalTextBytes += visible;
        return;
      }
    }

    if (isWhitespaceOnly(text, len)) {
      return;
    }

    if (!stack.empty() && !stack.back().hasText) {
      stack.back().hasText = true;
      checkMatch();
    }

    totalTextBytes += visible;
  }

  void checkMatch() {
    const std::string xpath = normalizeXPath(currentXPath(spineIndex));
    const int depth = pathDepth(xpath);

    const bool targetIsTextSelector = targetTextNodeIndex > 0;

    if (xpath == targetNorm) {
      // For /text()[N].M targets, the normalized parent element path is equal to
      // targetNorm. Treat that as an ancestor-level anchor so text-node exact
      // matching can still determine the real intra-node offset.
      if (targetIsTextSelector) {
        tryUpdate(MatchTier::ANCESTOR, depth, "text-parent", false);
      } else {
        tryUpdate(MatchTier::EXACT, depth, "exact", true);
      }
      return;
    }
    if (isAncestorPath(xpath, targetNorm)) {
      tryUpdate(MatchTier::ANCESTOR, depth, "ancestor", false);
      return;
    }

    const std::string xpathNoIdx = removeIndices(xpath);
    if (xpathNoIdx == targetNoIndex) {
      tryUpdate(MatchTier::EXACT_NO_IDX, depth, "index-insensitive", false);
    } else if (isAncestorPath(xpathNoIdx, targetNoIndex)) {
      tryUpdate(MatchTier::ANCESTOR_NO_IDX, depth, "index-insensitive-ancestor", false);
    }
  }

  void tryUpdate(const MatchTier tier, const int depth, const char* tierName, const bool isExact) {
    if (tier > bestTier || (tier == bestTier && depth > bestDepth)) {
      bestTier = tier;
      bestDepth = depth;
      bestOffset = totalTextBytes;
      bestExact = isExact;
      bestTierName = tierName;
    }
  }
};

}  // namespace

bool findProgressForXPathInternal(const std::shared_ptr<Epub>& epub, const int spineIndex, const std::string& xpath,
                                  float& outIntraSpineProgress, bool& outExactMatch) {
  outIntraSpineProgress = 0.0f;
  outExactMatch = false;

  if (xpath.empty()) {
    return false;
  }

  const std::string tmpPath = decompressToTempFile(epub, spineIndex);
  if (tmpPath.empty()) {
    return false;
  }

  ReverseState state(spineIndex, xpath);
  XML_Parser parser = XML_ParserCreate(nullptr);
  if (!parser) {
    Storage.remove(tmpPath.c_str());
    return false;
  }

  XML_SetUserData(parser, &state);
  XML_SetElementHandler(parser, parserStartCb<ReverseState>, parserEndCb<ReverseState>);
  XML_SetCharacterDataHandler(parser, parserCharCb<ReverseState>);
  XML_SetDefaultHandlerExpand(parser, parserDefaultCb<ReverseState>);
  const bool parseOk = runParse(parser, tmpPath);

  if (!parseOk) {
    LOG_ERR("KOX", "XPath parse failed for spine=%d at line %lu: %s", spineIndex, XML_GetCurrentLineNumber(parser),
            XML_ErrorString(XML_GetErrorCode(parser)));
  }
  XML_ParserFree(parser);
  Storage.remove(tmpPath.c_str());

  if (!parseOk || state.bestTier == MatchTier::NONE) {
    LOG_DBG("KOX", "Reverse: spine=%d no match for '%s'", spineIndex, xpath.c_str());
    return false;
  }

  outExactMatch = state.bestExact;
  if (state.totalTextBytes == 0) {
    outIntraSpineProgress = 0.0f;
  } else {
    outIntraSpineProgress = static_cast<float>(state.bestOffset) / static_cast<float>(state.totalTextBytes);
    outIntraSpineProgress = std::max(0.0f, std::min(1.0f, outIntraSpineProgress));
  }

  if (state.targetTextNodeIndex > 0) {
    LOG_DBG("KOX", "Reverse: spine=%d %s match textNode=%d char=%d offset=%zu/%zu -> progress=%.3f for '%s'",
            spineIndex, state.bestTierName, state.targetTextNodeIndex, state.targetCharOffset, state.bestOffset,
            state.totalTextBytes, outIntraSpineProgress, xpath.c_str());
  } else {
    LOG_DBG("KOX", "Reverse: spine=%d %s match offset=%zu/%zu -> progress=%.3f for '%s'", spineIndex,
            state.bestTierName, state.bestOffset, state.totalTextBytes, outIntraSpineProgress, xpath.c_str());
  }
  return true;
}

}  // namespace ChapterXPathIndexerInternal