#include "JetParser.h"
#include <cctype>
#include <stdexcept>

namespace jetc {

   bool Parser::starts(const std::string &lit) const {
      return s.compare(pos, lit.size(), lit) == 0;
   }

   bool Parser::isNameChar(char c) {
      return std::isalnum((unsigned char)c) || c == '-' || c == '_';
   }

   void Parser::skipWs() {
      while (!eof() && std::isspace((unsigned char)s[pos])) pos++;
   }

   std::string Parser::readName() {
      size_t start = pos;
      while (!eof() && isNameChar(s[pos])) pos++;
      return s.substr(start, pos - start);
   }

   std::string Parser::peekTagName(size_t at) const {
      size_t p = at + 1;
      size_t start = p;
      while (p < s.size() && isNameChar(s[p])) p++;
      return s.substr(start, p - start);
   }

   bool Parser::matchTagOpen(const std::string &name, size_t at) const {
      if (s.compare(at, 1, "<") != 0) return false;
      size_t p = at + 1;
      size_t nstart = p;
      while (p < s.size() && isNameChar(s[p])) p++;
      if (s.compare(nstart, p - nstart, name) != 0) return false;
      if (p >= s.size()) return false;
      char c = s[p];
      return c == ' ' || c == '>' || c == '/';
   }

   bool Parser::matchTagClose(const std::string &name, size_t at) const {
      std::string closer = "</" + name + ">";
      return s.compare(at, closer.size(), closer) == 0;
   }

   bool Parser::skipOpenTag(size_t &p) const {
      p++; // '<'
      while (p < s.size() && isNameChar(s[p])) p++;
      while (p < s.size()) {
         if (s[p] == '"') {
            p++;
            while (p < s.size() && s[p] != '"') {
               if (s[p] == '\\' && p + 1 < s.size()) p++;
               p++;
            }
            if (p < s.size()) p++;
            continue;
         }
         if (s.compare(p, 2, "/>") == 0) { p += 2; return true; }
         if (s[p] == '>') { p += 1; return false; }
         p++;
      }
      throw std::runtime_error("jetc: unterminated tag near end of input");
   }

   std::map<std::string, std::string> Parser::parseAttrs(bool &hasContainer) {
      std::map<std::string, std::string> attrs;
      while (true) {
         skipWs();
         if (eof()) throw std::runtime_error("jetc: unterminated tag near end of input");
         if (starts("/>")) { pos += 2; hasContainer = false; break; }
         if (starts(">"))  { pos += 1; hasContainer = true;  break; }
         std::string aname = readName();
         if (aname.empty()) throw std::runtime_error("jetc: malformed attribute near offset " + std::to_string(pos));
         if (starts("=\"")) {
            pos += 2;
            std::string val;
            while (!eof() && s[pos] != '"') {
               if (s[pos] == '\\' && pos + 1 < s.size()) { val += s[pos]; val += s[pos + 1]; pos += 2; continue; }
               val += s[pos++];
            }
            if (!eof()) pos++; // closing quote
            attrs[aname] = val;
         }
      }
      return attrs;
   }

   std::pair<size_t, size_t> Parser::scanBody(size_t bodyStart, const std::string &tagName, bool lookForElse) {
      size_t p = bodyStart;
      int depth = 1;
      size_t elsePos = std::string::npos;
      while (p < s.size()) {
         if (matchTagClose(tagName, p)) {
            depth--;
            if (depth == 0) return {p, elsePos};
            p += 3 + tagName.size();
            continue;
         }
         if (lookForElse && depth == 1 && elsePos == std::string::npos && s.compare(p, 6, "<else>") == 0) {
            elsePos = p;
            p += 6;
            continue;
         }
         if (matchTagOpen(tagName, p)) {
            bool selfClosing = skipOpenTag(p);
            if (!selfClosing) depth++;
            continue;
         }
         if (s[p] == '<') {
            if (s.compare(p, 2, "</") == 0) {
               size_t q = p + 2;
               while (q < s.size() && isNameChar(s[q])) q++;
               if (q < s.size() && s[q] == '>') q++;
               p = q;
            } else {
               skipOpenTag(p);
            }
            continue;
         }
         p++;
      }
      throw std::runtime_error("jetc: unterminated <" + tagName + "> - no matching close tag found");
   }

   std::vector<NodePtr> Parser::parseSub(size_t start, size_t end) {
      Parser sub(s.substr(start, end - start));
      return sub.parseNodes();
   }

   NodePtr Parser::parseVar() {
      size_t start = pos;
      pos += 2; // "$[" or "#["
      int depth = 1;
      while (!eof() && depth > 0) {
         if (starts("$[") || starts("#[")) { depth++; pos += 2; continue; }
         if (s[pos] == ']') { depth--; pos++; continue; }
         pos++;
      }
      auto n = std::make_shared<Node>();
      n->kind = NodeKind::VAR;
      n->varText = s.substr(start, pos - start);
      return n;
   }

   NodePtr Parser::parseSet() {
      size_t origStart = pos;
      pos += 4; // "<set"
      bool hasContainer;
      auto attrs = parseAttrs(hasContainer);
      if (hasContainer) {
         // Container-form <set> (value comes from rendering nested content)
         // isn't modeled by this prototype - fall back to full interpretation
         // of the whole tag instead of failing to compile.
         auto span = scanBody(pos, "set", false);
         pos = span.first + 3 + 3; // "</set>"
         auto n = std::make_shared<Node>();
         n->kind = NodeKind::FALLBACK;
         n->rawSpan = s.substr(origStart, pos - origStart);
         return n;
      }
      auto n = std::make_shared<Node>();
      n->kind = NodeKind::SET;
      n->setName = attrs.count("name") ? attrs["name"] : "";
      if (attrs.count("value")) { n->setHasValue = true; n->setValue = attrs["value"]; }
      if (attrs.count("expr"))  { n->setHasExpr = true;  n->setExpr = attrs["expr"]; }
      n->setScope = attrs.count("scope") ? attrs["scope"] : "";
      return n;
   }

   NodePtr Parser::parseIf() {
      pos += 3; // "<if"
      bool hasContainer;
      auto attrs = parseAttrs(hasContainer);
      auto n = std::make_shared<Node>();
      n->kind = NodeKind::IF;
      if (attrs.count("expr")) {
         n->cond.mode = CondMode::EXPR;
         n->cond.expr = attrs["expr"];
      } else {
         n->cond.mode = CondMode::VALUES;
         n->cond.value1 = attrs.count("value1") ? attrs["value1"] : "";
         n->cond.value2 = attrs.count("value2") ? attrs["value2"] : "";
         n->cond.type   = attrs.count("type")   ? attrs["type"]   : "";
      }
      if (hasContainer) {
         auto span = scanBody(pos, "if", true);
         size_t closePos = span.first, elsePos = span.second;
         size_t thenEnd = (elsePos != std::string::npos) ? elsePos : closePos;
         n->thenBody = parseSub(pos, thenEnd);
         if (elsePos != std::string::npos) {
            n->hasElse = true;
            n->elseBody = parseSub(elsePos + 6, closePos);
         }
         pos = closePos + 3 + 2; // "</if>"
      }
      return n;
   }

   NodePtr Parser::parseFor() {
      pos += 4; // "<for"
      bool hasContainer;
      auto attrs = parseAttrs(hasContainer);
      auto n = std::make_shared<Node>();
      n->kind = NodeKind::FOR;
      if (attrs.count("start")) { n->forHasStart = true; n->forStart = attrs["start"]; }
      n->forEnd  = attrs.count("end")  ? attrs["end"]  : "0";
      n->forStep = attrs.count("step") ? attrs["step"] : "1";
      if (attrs.count("name")) { n->forHasName = true; n->forName = attrs["name"]; }
      n->forScope = attrs.count("scope") ? attrs["scope"] : "";
      if (hasContainer) {
         auto span = scanBody(pos, "for", false);
         n->body = parseSub(pos, span.first);
         pos = span.first + 3 + 3; // "</for>"
      }
      return n;
   }

   NodePtr Parser::parseWhile() {
      pos += 6; // "<while"
      bool hasContainer;
      auto attrs = parseAttrs(hasContainer);
      auto n = std::make_shared<Node>();
      n->kind = NodeKind::WHILE;
      if (attrs.count("expr")) {
         n->cond.mode = CondMode::EXPR;
         n->cond.expr = attrs["expr"];
      } else {
         n->cond.mode = CondMode::VALUES;
         n->cond.value1 = attrs.count("value1") ? attrs["value1"] : "";
         n->cond.value2 = attrs.count("value2") ? attrs["value2"] : "";
         n->cond.type   = attrs.count("type")   ? attrs["type"]   : "";
      }
      if (hasContainer) {
         auto span = scanBody(pos, "while", false);
         n->body = parseSub(pos, span.first);
         pos = span.first + 3 + 5; // "</while>"
      }
      return n;
   }

   NodePtr Parser::parseFallback() {
      size_t origStart = pos;
      std::string tagName = peekTagName(pos);
      size_t p = pos;
      bool selfClosing = skipOpenTag(p);
      if (!selfClosing) {
         auto span = scanBody(p, tagName, false);
         p = span.first + 3 + tagName.size();
      }
      pos = p;
      auto n = std::make_shared<Node>();
      n->kind = NodeKind::FALLBACK;
      n->rawSpan = s.substr(origStart, pos - origStart);
      return n;
   }

   std::vector<NodePtr> Parser::parseNodes() {
      std::vector<NodePtr> nodes;
      std::string textBuf;
      auto flush = [&]() {
         if (!textBuf.empty()) {
            auto n = std::make_shared<Node>();
            n->kind = NodeKind::TEXT;
            n->text = textBuf;
            nodes.push_back(n);
            textBuf.clear();
         }
      };
      while (!eof()) {
         if (starts("|>")) {
            flush();
            pos += 2;
            std::string buf;
            while (!eof() && !starts("<|")) buf += s[pos++];
            if (!eof()) pos += 2;
            auto n = std::make_shared<Node>();
            n->kind = NodeKind::TEXT;
            n->text = buf;
            nodes.push_back(n);
            continue;
         }
         if (s[pos] == '<') {
            if (matchTagOpen("set", pos))   { flush(); nodes.push_back(parseSet());   continue; }
            if (matchTagOpen("if", pos))    { flush(); nodes.push_back(parseIf());    continue; }
            if (matchTagOpen("for", pos))   { flush(); nodes.push_back(parseFor());   continue; }
            if (matchTagOpen("while", pos)) { flush(); nodes.push_back(parseWhile()); continue; }
            flush();
            nodes.push_back(parseFallback());
            continue;
         }
         if (starts("$[") || starts("#[")) {
            flush();
            nodes.push_back(parseVar());
            continue;
         }
         textBuf += s[pos++];
      }
      flush();
      return nodes;
   }

}