#include <boost/algorithm/string.hpp>

#include "gmock/gmock.h"
#include "gtest/gtest.h"

#include <deque>
#include <map>
#include <memory>
#include <string>
#include <utility>
#include <vector>

using namespace std::string_literals;

using BNF = std::map<std::string, std::vector<std::vector<std::string>>>;
using Terminals = std::set<std::string>;
using ProgramNode = std::deque<std::string>;
using PathElement = std::pair<std::string, size_t>; // Name, Index

std::vector<std::string> split(std::string s)
{
 std::vector<std::string> result;
 boost::algorithm::split(result, s, boost::algorithm::is_any_of(s), boost::algorithm::token_compress_on);
 while (result.size() > 0 && result.back() == ""s)
  result.pop_back();
 return result;
}

std::vector<PathElement> GetPath(std::string Token, BNF ReverseBNF, std::string Top, Terminals terminals = {}, std::vector<PathElement> PreviousPath = {})
{
 throw std::runtime_error("Compile error");
 return {}; // TODO
}

auto Reverse(BNF bnf){
 std::map<std::string, std::set<std::string>> result;

 for (const auto& [from, to] : bnf) {
  for (const auto& list : to) {
   for (const auto& element : list) {
    auto i{result.find(element)};
    if (i != result.end()) // already present
     i->second.insert(from);
    else // new element
     result.emplace(element, std::set{from});
   }
  }
 }

 return result;
}

using index_t = size_t;

struct TreeNode {
 index_t parent;
 std::vector<index_t> childs; // fill char by char
 std::vector<std::string> child_names; // fill always
 std::string name;
};

class Tree {
private:
 std::map<index_t, TreeNode> nodes; // index 0 = non existing; index starting at 1
 index_t node_num{};
 index_t root{};
 index_t last{};

public:
 bool Valid(const std::string& Top) const {
  // A token is non empty
  if (node_num == 0)
   return false;

  // Start symbol on top
  auto rootNode{nodes.find(root)};
  if (rootNode == nodes.end())
   throw std::runtime_error("Node not found: "s + std::to_string(root));
  
  if (rootNode->second.name != Top)
   return false;

  // All nodes filled (implies all leaves are terminal)
  for (const auto& [index, node]: nodes) {
   if (node.childs.size() < node.child_names.size())
    return false; // node not filled
  }

  return true;
 }

 bool AddFirstNode(char c, const BNF& bnf, const std::map<std::string, std::set<std::string>>& reverseBNF) {
  node_num ++;
  root = node_num;
  last = node_num;
  std::string node_name(1, char(c));

  auto reverseRule{reverseBNF.find(node_name)};
  if (reverseRule == reverseBNF.end())
   throw std::runtime_error("Reverse rule not found: "s + node_name);

  std::vector<std::string> children; // default: no children for terminal
  auto rule{bnf.find(node_name)};
  if (rule != bnf.end()) { // multiple variants!
   bool hit{false};
   for (const auto& i : rule->second) {
    if (i.size() > 0 && i[0] == node_name) {
     if (hit)
      throw std::runtime_error("Multiple matching rules found for "s + node_name);
     children = i;
     hit = true;
    }
   }
   if (!hit)
    throw std::runtime_error("No matching rule found for "s + node_name);
  }

  nodes.emplace(root, TreeNode{0, std::vector<index_t>{}, children, node_name});
  return true;
 }

 // try to add character to tree
 bool Add(char c, const BNF& bnf, const std::map<std::string, std::set<std::string>>& reverseBNF) {
  if (nodes.empty()) { // first node
   return AddFirstNode(c, bnf, reverseBNF);
  } else { // at least one character is already present
   // Traverse tree until partially filled node found
   // or new node can be added
   index_t current_index{last};

   while (current_index != 0) {
    TreeNode& node {nodes[current_index]};
    if (node.childs.size() < node.child_names.size()) { // partially filled node
     throw std::runtime_error("TODO: partially filled node");
    }
    current_index = node.parent;
   }
   throw std::runtime_error("TODO: need to add node");

  }
  return false;
 }

 // add path to start symbol
 void Resolve(const BNF& bnf, const std::map<std::string, std::set<std::string>>& reverseBNF) {
  if (nodes.empty()) // only handle non-empty trees
   return;

  while (true) {
   std::string& old_root_name { nodes[root].name }; // current root node name

   auto parents {reverseBNF.find(old_root_name)};
   if (parents != reverseBNF.end()) { // parents in bnf available
    bool hit{false};
    for (auto& parent : parents->second) {
     for (const auto& list : bnf.at(parent)) {
      if (list.size() == 1 && list[0] == old_root_name) {
       if (!hit) {
        const std::string& new_root_name {parent};
        // Add new TreeNode in the direction to root:
        // New root with 1 child (old root)
        nodes.emplace(++node_num,
                     TreeNode{0, // parent
                              std::vector<index_t>{root}, // child indices
                              std::vector<std::string>{old_root_name}, // child names
                              new_root_name // name
                     });
        nodes[root].parent = node_num;
        root = node_num;
        // this->last stays
        hit = true;
       } else
        throw std::runtime_error("Error: Multiple resolve nodes for "s + old_root_name);
      }
     }
    }
    if (!hit)
     break;
   } else
    break;
  }
 }

};

class Lexer
{

private:
 const BNF &bnf;
 const std::string& Top;

 std::map<std::string, std::set<std::string>> ReverseBNF;

 // to be called on token end
 void FinalizeCandidates(std::deque<Tree>& candidates, std::string& token, std::vector<std::string>& result)
 {
  if (candidates.empty()) { // skip
   if (!token.empty())
    throw std::runtime_error("Expected empty token, got "s + token);
  } else { // check candidates
   bool valid{false};
   for (auto& ct : candidates) {
    ct.Resolve(bnf, ReverseBNF);
    if (ct.Valid(Top)) {
     if (valid)
      throw std::runtime_error("Found ambiguous token "s + token);
     result.push_back(token);
     token.clear();
     valid = true;
    }
   }
   if (!valid)
    throw std::runtime_error("Invalid token: "s + token);

   candidates.clear();
  }
 }

 void AddCandidate(char c, std::deque<Tree>& candidates) {
  // new candidate: starting with c
  auto element {ReverseBNF.find(std::string(1, c))};
  if (element != ReverseBNF.end()) {
   Tree newTree;
   if (newTree.Add(c, bnf, ReverseBNF))
    candidates.push_back(newTree);
  }
 }

public:
 Lexer(const BNF& bnf, const std::string& Top): bnf(bnf), Top(Top), ReverseBNF{Reverse(bnf)}
 {
 }

 std::vector<std::string> Lex(const std::string& s)
 {
  std::vector<std::string> result;
  std::string token;

  std::string Whitespace{"\t \n\r"};
  std::deque<Tree> candidates;

  for (size_t pos{0}; pos < s.size(); pos++) {
   char c{s[pos]};
   std::cout << "Char: |" << c << "|" << std::endl;
   if (Whitespace.find(c) != std::string::npos) { // found whitespace character
    // evaluate token up to now and skip whitespace
    FinalizeCandidates(candidates, token, result);
   } else { // no whitespace: try to add to tree
    std::deque<index_t> EraseList;
    int i = 0;
    for (auto ct = candidates.begin(); ct != candidates.end(); ct++, i++) {
     if (!ct->Add(c, bnf, ReverseBNF)) { // either add char or delete candidate
      // push to front to get reversed order
      EraseList.push_front(i); // no candidate anymore
     }
    }
    
    if (token.empty()) {
     AddCandidate(c, candidates);
    } else if (candidates.size() - EraseList.size() > 0) { // added to some candidates: Erase invalidated ones
     for (const auto& i : EraseList)
      candidates.erase(candidates.begin() + i);
    } else { // no candidates left: new tree
     FinalizeCandidates(candidates, token, result);
     AddCandidate(c, candidates);
    }
    token.push_back(c);
   }
  }

  // Final evaluation of last token
  FinalizeCandidates(candidates, token, result);

  return result;
 }

};

ProgramNode Compile(std::vector<std::string> Tokens, std::string Top, BNF bnf, Terminals terminals)
{
 BNF ReverseBNF;//{ Reverse(bnf)};

 if (Tokens.size()){
  std::string Token = Tokens[0];
  auto Path = GetPath(Token, ReverseBNF, Top, terminals);
  if (Path.size()) {
   size_t Index{1};
   while (Index < Tokens.size()) {
    Path = GetPath(Token, ReverseBNF, Top, terminals, Path);
    Index++;
   }
  } else
   throw std::runtime_error("Invalid token: "s + Token);
 } else
  throw std::runtime_error("No tokens!");

 return {};
}

class Test: public ::testing::Test {
protected:
 Test(){}
 ~Test() override {}
};

TEST_F(Test, BNF) {
 std::string LexTop{"preprocessing-token"};
 BNF LexBNF{
  {"preprocessing-token", {{"identifier"},
                           {"preprocessing-op-or-punc"},
                           {"pp-number"}}},

  {"identifier", {{"identifier-nondigit"},
                  {"identifier", "identifier-nondigit"},
                  {"identifier", "digit"}}},
  {"digit", {{"0"}, {"1"}, {"2"}, {"3"}, {"4"}, {"5"}, {"6"}, {"7"}, {"8"}, {"9"} }},
  {"identifier-nondigit",
    {{"a"}, {"b"}, {"c"}, {"d"}, {"e"}, {"f"}, {"g"}, {"h"}, {"i"}, {"j"}, {"k"}, {"l"}, {"m"},
     {"n"}, {"o"}, {"p"}, {"q"}, {"r"}, {"s"}, {"t"}, {"u"}, {"v"}, {"w"}, {"x"}, {"y"}, {"z"},
     {"A"}, {"B"}, {"C"}, {"D"}, {"E"}, {"F"}, {"G"}, {"H"}, {"I"}, {"J"}, {"K"}, {"L"}, {"M"},
     {"N"}, {"O"}, {"P"}, {"Q"}, {"R"}, {"S"}, {"T"}, {"U"}, {"V"}, {"W"}, {"X"}, {"Y"}, {"Z"}, {"_"}}},
  {"preprocessing-op-or-punc", {{";"},
                                {"="}}},
  {"pp-number", {{"digit"},
                 {"pp-number", "digit"}}}
 };

 std::string Top{"program"};
 BNF bnf{
  {"program", {{"statement-list"}}},
  {"statement-list", {{"statement", "statement-list"},
                      {}, }},
  {"statement", {{"assigmnent", ";"}}},
  {"assignment", {{"identifier", "=", "identifier"}}}
 };

 std::set<std::string> Terminals{"identifier", "=", ";"};

 std::string Code{"a = bc ; c = 123 ; esd = Ff ; 1 = XYZ"};

 Lexer lexer(LexBNF, LexTop);
 auto tokens = lexer.Lex(Code);
#if 1
 for (const auto& i: tokens) {
  std::cout << i << std::endl;
 }
#endif
 //auto Program = Compile(tokens, Top, bnf, Terminals);
}

int main(int argc, char* argv[]) {
 ::testing::InitGoogleMock(&argc, argv);
 return RUN_ALL_TESTS();
}