#include"globals.h"
#include"util.h"
#include"scan.h"
#include"parse.h"
static TokenType token;
static TreeNode* stmt_sequence();
static TreeNode* statement();
static TreeNode* if_stmt();
static TreeNode* repeat_stmt();
static TreeNode* assign_stmt();
static TreeNode* read_stmt();
static TreeNode* write_stmt();
static TreeNode* expt();
static TreeNode* simple_exp();
static TreeNode* term();
static TreeNode* factor();

static void syntaxError(char *message)
{fprintf(listing,"\n>>>");
 fprintf(listing,"Syntax error at line %d:%s",lineno,message);
 Error=TRUE;
}
static void match(TokenType expected)
{
 if(token==expected) token=getToken();
 else {
   syntaxError("unexpected token->");
   printToken(token,tokenString);
   fprintf(listing,"  匹配錯(cuò)誤 ");
  }
}

TreeNode * stmt_sequence()
{
TreeNode * t=statement();
TreeNode * p=t;
while((token!=ENDFILE)&&(token!=END)&&(token!=ELSE)&&(token!=UNTIL))
{TreeNode* q;
 match(SEMI);
 q=statement();
 if(q!=NULL){
     if(t==NULL) t=p=q;
      else
      {p->sibling=q;
       p=q;
       }
   }
 }
return t;
}



TreeNode *statement()
{  TreeNode *t=NULL;
   switch(token){
    case IF: t=if_stmt();break;
    case REPEAT: t=repeat_stmt();break;
    case ID: t=assign_stmt();break;
    case READ: t=read_stmt();break;
    case WRITE: t=write_stmt();break;
    default:syntaxError("unexpected token->");
        printToken(token,tokenString);
       token=getToken();
       break;
     }//end case
  return t;
}

TreeNode * if_stmt()
{  TreeNode *t=newStmtNode(IfK);
   match(IF);
   if(t!=NULL) t->child[0]=expt();
   match(THEN);
   if(t!=NULL) t->child[1]=stmt_sequence();
   if(token==ELSE){
   match(ELSE);
   if(t!=NULL) t->child[2]=stmt_sequence();
   }
   match(END);
  return t;
}

TreeNode * repeat_stmt()
{ TreeNode *t=newStmtNode(RepeatK);
  match(REPEAT);
  if(t!=NULL) t->child[0]=stmt_sequence();
  match(UNTIL);
  if(t!=NULL) t->child[1]=expt();
  return t;
}
TreeNode *assign_stmt()
{
TreeNode *t=newStmtNode(AssignK);
 if((t!=NULL)&&(token==ID))
    t->attr.name=copyString(tokenString);
 match(ID);
 match(ASSIGN);
 if(t!=NULL) t->child[0]=expt();
 return t;
}

TreeNode *read_stmt()
{
TreeNode *t=newStmtNode(ReadK);
match(READ);
if((t!=NULL) &&(token==ID))
  t->attr.name=copyString(tokenString);
match(ID);
return t;
}

TreeNode *write_stmt()
{
TreeNode *t=newStmtNode(WriteK);
match(WRITE);
if(t!=NULL) t->child[0]=expt();
return t;
}
TreeNode *expt()
{
TreeNode *t=simple_exp();
if((token==LT)||(token==EQ))
  {
   TreeNode *p=newExpNode(OpK);
   if(p!=NULL) {
    p->child[0]=t;
    p->attr.op=token;
   t=p;
  }
  match(token);
  if(t!=NULL)
    t->child[1]=simple_exp();
 }
 return t;
}


TreeNode *simple_exp()
{ TreeNode *t=term();
  while((token==PLUS)||(token==MINUS))
  {
   TreeNode *p=newExpNode(OpK);
   if(p!=NULL) {
      p->child[0]=t;
      p->attr.op=token;
      t=p;
      match(token);
      t->child[1]=term();
    }
   }
return t;
}

TreeNode *term()
{
  TreeNode * t=factor();
    while((token==TIMES)||(token==OVER))
    {
     TreeNode * p=newExpNode(OpK);
      if(p!=NULL){
         p->child[0]=t;
         p->attr.op=token;
         t=p;
         match(token);
         p->child[1]=factor();
       }
    }
  return t;
}

TreeNode *factor()
{
  TreeNode *t=NULL;
   switch(token){
   case NUM:
     t=newExpNode(ConstK);
     if((t!=NULL)&&(token=NUM))
       t->attr.val=atoi(tokenString);
      match(NUM);
     break;
   case ID:
     t=newExpNode(IdK);
     if((t!=NULL)&&(token==ID))
       t->attr.name=copyString(tokenString);
    match(ID);
    break;
   case  LPAREN:
       match(LPAREN);
       t=expt();  
       match(RPAREN);
       break;
   default:
      syntaxError("unexpected token->");
      printToken(token,tokenString);
      token=getToken();
      break;
   }
   return t;
}


TreeNode *parse()
{
  TreeNode *t;
  token=getToken();
  t=stmt_sequence();
  if(token!=ENDFILE)
    syntaxError("Code ends before file\n");
    return t;
}