#include "grammer.h"

#include <algorithm>

using namespace Gram;

void Compiler::clear() {
 nodes.clear();
 root_node_id = 0;

 tokens_used = 0;
}

std::string Compiler::GetTypeOfNode(index_t node_id) const
{
 return nodes[node_id].type;
}

bool Compiler::IsRootNode(index_t node_id) const
{
 auto node& {nodes[node_id]};
 return node.parent_node_id == node.node_id;
}

void Compiler::Validate() const
{
 // A program is non empty
 if (nodes.size() == 0)
  throw std::runtime_error("");

 // Consistency check for nodes
 if (root_node_id >= nodes.size())
  throw std::runtime_error("Bad root node: "s + std::to_string(root_node_id) + " vs. "s + std::to_string(nodes.size()));
 
 // Start symbol on top
 if (GetTypeOfNode(root_node_id) != Top)
  throw std::runtime_error("Root node not start symbol!");

 // All nodes filled
 for (const auto& node: nodes) {
  if (node.child_ids.size() != bnf[node.type][node.variant].size())
   throw std::runtime_error("Node not filled: "s + node.type + "["s + std::to_string(node.variant) + "]"s);
 }
}

void Compiler::DumpTree()
{
 std::cout << "=== Tree =====================================" << std::endl;
 for (const auto& i : nodes) {
  std::cout << i.type << std::endl;
 }
}

bool Compiler::RootIsStartSymbol() const
{
 return GetTypeOfNode(root_node_id) == Top;
}

namespace {

bool ChildIdIsToken(int32_t child_id)
{
 return child_i < 0;
}

index_t TokenIdFromChildId(int32_t child_id)
{
 return index_t(-child_id) - 1;
}

int32_t ChildIdFromTokenId(index_t token_id)
{
 return -1 - int32_t(token_id);
}

} // namespace

bool Compiler::AllTokensUsed() const
{
 return tokens_used == tokens.size();
}

bool Compiler::treeIsComplete() const
{
 return RootIsStartSymbol() && AllTokensUsed();
}

std::vector<std::string>& Compiler::getNodeExpectedChilds(node_id)
{
 std::string& type = nodes[node_id].type;
 index_t& variant = nodes[node_id].variant;
 return bnf[type][variant];
}

// returns true if all childs are filled, recursively. Else false with to_fill as hint to node to fill
bool Compiler::subTreeIsComplete(index_t node_id, index_t& to_fill)
{
 for (const auto& i : nodes[node_id].child_ids) {
  if (!ChildIdIsToken(i)) { // consider subtrees
   if (!subTreeIsComplete(i, to_fill))
    return false; // found incomplete subtree -> return it!
  }
 }

 if (nodes[node_id].child_ids.size() < getNodeExpectedChilds(node_id).size()) {
  to_fill = node_id;
  return false;
 }

 return true;
}

size_t Compiler::CommonPrefix(const std::vector<Token>& tokens, const std::vector<std::string>& types)
{
 auto [tokens_it, types_it] = std::mismatch(tokens.begin(), tokens.end(), types.begin(), types.end(), [](const Token& token, const std::string& s){ return token.type == s; });
 return types_it - types.begin(); // a distance, 0 on no match
}

void Compiler::AddFirstNode()
{
 root_node_id = 0;

 const std::string& child_type = tokens[0].type;
 auto it = ReverseBNF.find(child_type);
 if (it == ReverseBNF.end())
  throw std::runtime_error("Type not found: "s + child_type + " ("s + tokens[0].value + ")"s);

 std::set<std::string>& alternatives_set {it->second};

 std::string node_type;
 index_t node_variant;
 std::deque<std::pair<std::string, index_t>> alternatives; // only for valid elements from alternatives_set
 std::vector<index_t> child_ids;

 for (const auto& type : alternatives_set) {
  const auto& variants{bnf[type]};
  for (int i = 0; i < variants.size(); i++) {
   const std::vector<std::string> & variant{variants[i]};
   size_t common{};
   if ((common = CommonPrefix(tokens, variant)) > 0) { // match a common prefix
    if (node_type == "") { // no match yet
     node_type = type;
     node_variant = i;
     for (int token_id = 0; token_id < common; token_id++)
      child_ids.push_back(ChildIdFromTokenId(token_id));
    } else
     alternatives.emplace_back(type, i);
   }
  }
 }

 if (node_type == "") // no matching type found
  throw std::runtime_error("No matching first node found.");

 nodes.emplace_back({0, 0, node_type, node_variant, alternatives, child_ids});

 tokens_used = child_ids.size();
}

bool Compiler::AddRootNode()
{
 if (nodes.size() == 0) {
  AddFirstNode();
 } else {
  const std::string& child_type = nodes[root_node_id].type; // starting at old root
  auto it = ReverseBNF.find(child_type);
  if (it == ReverseBNF.end()) // this one doesn't have a parent, maybe a start symbol to discard?
   return false;

  index_t old_root_node_id {root_node_id};
  index_t new_root_node_id {nodes.size()};
  nodes[root_node_id].parent_node_id = new_root_node_id;

  std::set<std::string>& alternatives_set {it->second};

  std::string node_type;
  index_t node_variant;
  std::deque<std::pair<std::string, index_t>> alternatives; // only for valid elements from alternatives_set
  std::vector<index_t> child_ids{1, old_root_node_id};

  for (const auto& type : alternatives_set) {
   const auto& variants{bnf[type]};
   for (int i = 0; i < variants.size(); i++) {
    const std::vector<std::string> & variant{variants[i]};
    if (child_type == variant[0]) {
     if (node_type == "") {
      node_type = type;
      node_variant = i;
     } else
      alternatives.emplace_back(type, i); // duplicates possible: variants of same type
    }
   }
  }

  if (node_type == "") // no matching type found (maybe backtrack possible?)
   return false;

  // now add! 
  root_node_id = new_root_node_id;
  nodes.emplace_back({root_node_id, root_node_id, node_type, node_variant, alternatives, child_ids});
  // keep tokens_used as is
 }

 return true;
}

void Compiler::RemoveLastNode()
{
 TreeNode& node {nodes.back()};
 index_t node_id = node.node_id;
 
 if (node_id == root_node_id) { // No parent -> remove root
  if (node.child_ids().empty()) { // No children -> now empty
   clear();
  } else if (node.child_ids().size() == 1) { // One child: removing possible
   root_node_id = node.child_ids()[0];
   nodes.pop_back();
  } else
   throw std::runtime_error("Backtrack not possible: Root not empty"); // ICE
 } else if (node.child_ids().empty()) { // No children -> remove leaf
  // We have a parent, otherwise we would have taken previous branch
  TreeNode& parent {nodes[node.parent_node_id]};
  if (parent.child_ids().empty() || parent.child_ids().last() != node_id)
   throw std::runtime_error("Backtrack: Bad child nodes"); // ICE
  parent.childs_ids().pop_back();
  nodes.pop_back();
 } else { // In the middle
  throw std::runtime_error("Backtrack in the middle of the tree."); // ICE
 }
}

// Change type of last node according to alternatives
void Compiler::ChangeNodeType()
{
 TreeNode& node {nodes.back()};
 index_t node_id = node.node_id;

 if (node.alternatives.empty())
  throw std::runtime_error("No alternatives found during Backtrack"); // ICE

 auto& [type, variant] {node.alternatives.front()};

 node.type = type;
 node.variant = variant;

 node.alternatives.pop_front();
}

// throws if no further track back is possible: compile error
void Compiler::TrackBack()
{
 // Search backwards for alternatives: last node with alternatives (variant or alt. token)
 while (!nodes.empty() && nodes.last().alternatives.empty()) {
  RemoveLastNode();
 }

 if (nodes.empty()) {
  throw std::runtime_error("Compile error: Invalid program.");
 }

 ChangeNodeType();
}

// return shortest path with variants
// via first-entry-in-bnf-rule
// excluding lower (already exists)
// including upper (already determined to be included)

// breadth-first search
std::map<std::string, std::string> Compiler::traverse(lower, upper)
{
 std::map<std::string, std::string> visited; // node, child
 std::deque<std::pair<std::string, std::string>> todo{{lower, ""}}; // node, child
 
 while (!todo.empty()) {
  auto& [current_node, current_child] = todo.front();
  todo.pop_front();

  if (!visited[current_node]) {
   auto parents_it {reverseBNF.find(current_node)};

   if (parents_it != reverseBNF.end()) {
    auto& parents {parents_it->second};
    
    visited[current_node] = current_child;
    
    std::for_each(parents.begin(), parents.end(), [&](const auto&x) {todo.emplace_back(x, current_node);});
   }
  }
 }
 
 return visited;
}

// returns list from lower (excluding) to upper (including)
// returns empty list on fail
std::vector<std::string> Compiler::GetPath(std::string upper, std::string lower)
{
 std::vector<std::string> result;

 // traverse bnf from lower to upper
 std::map<std::string, std::string> visited {traverse(lower, upper)};
 
 auto current {upper};
 while (current != lower) {
  auto& child = visited[current];

  result.push_back(current);

  current = child;
 }
 return result;
}

index_t Compiler::AddNode(const std::string& name, const std::string& child_type, index_t parent_index)
{
 TreeNode& parent {nodes[parent_index]};
 index_t index = nodes.size();
 parent.child_ids.push_back(index);

 index_t variant;
 std::deque<std::string> alternatives;

 const auto& lists { bnf[parent.type] };
 for (int i = 0; i < lists.size(); i++) { // variants
  if (lists[i].size() > 0 && lists[i][0] == child_type)
   variant = i;
 }

 nodes.emplace_back({parent_index, index, child_type, variant, alternatives, {}});
 //root stays, tokens_used stays

 return index;
}

void Compiler::AddPath(const std::vector<std::string>& path, index_t current_index)
{
 for (int i = path.size() - 1; i > 0; i--) {
  std::string child_name = path[i - 1];
  current_index = AddNode(path[i], child_name, current_index);
 }

 nodes.back().child_ids.emplace_back(ChildIdFromTokenId(tokens_used));
 tokens_used++;
}

bool Compiler::FillTree()
{
 if (nodes.size() == 0) // ignore empty tree, successfully
  return true;

 index_t to_fill;

 while (!subTreeIsComplete(root_node_id, to_fill)) {
  auto& node {nodes[to_fill]};
  auto list = GetPath(bnf[node.type][node.variant][node.child_ids.size()], tokens[tokens_used]);
  if (list.size() > 0) {
   AddPath(list, to_fill);
   return true;
  } else {
   return false;
  }
 }
}

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

Tree Compiler::compile(std::vector<Token> Tokens)
{
 clear();
 tokens = Tokens;

 if (tokens.size() == 0)
  throw std::runtime_error("No tokens!");

 while (!treeIsComplete()) {
  if (!FillTree())
   TrackBack();
  else if (!AddRootNode())
   TrackBack();
  else if (!FillTree())
   TrackBack();
 }

 Validate();

 return tree;
}