package compiler;

/**
 * @author Cherry
 * @date 2022年1月6日
 * @time 11:21
 * @brief 代码生成
 * 修复了对于输入空格产生的错误
 */


public class Parser {
 private Lexer lexer;

 //寄存器空间(栈),设置8个寄存器
 String[] names = {"t0", "t1", "t2", "t3", "t4", "t5", "t6", "t7"};
 //堆栈指针,指向各个寄存器
 private int nameP = 0;

 /**
 * 分配新的寄存器
 *
 * @return 寄存器名
 */
 private String newName() {
 if (nameP >= names.length) {
 System.out.println("Expression too complex: " + lexer.yylineno);
 System.exit(1);
 }

 String reg = names[nameP];
 nameP++;

 return reg;
 }

 private void freeNames(String s) {
 if (nameP > 0) {
 nameP--;
 names[nameP] = s;
 } else {
 System.out.println("(Internal error) Name stack underflow: " + lexer.yylineno);
 }
 }

 public Parser(Lexer lexer) {
 this.lexer = lexer;
 lexer.current = Lexer.input_buffer;
 lexer.lookAhead = -1;
 System.out.println("================== 代码生成 ==================");
 }

 public void statements() {
 String tempvar;
 //expression(tempvar);

 while (!lexer.match(Lexer.EOI)) {
 //if (!lexer.match(compiler.Lexer.BLANK)) {
 tempvar = newName();
 expression(tempvar);
 freeNames(tempvar);
 if (lexer.match(Lexer.SEMI)) {
 lexer.advance();
 } else {
 System.out.println("Inserting missing semicolon: " + lexer.yylineno);
 }
 //}
 }
 }

 private void expression(String tempVar) {
 String tempVar2;
 term(tempVar);
 while (lexer.match(Lexer.PLUS)) {
 lexer.advance();
 tempVar2 = newName();
 term(tempVar2);
 System.out.println(tempVar + " += " + tempVar2);
 freeNames(tempVar2);
 }
 }


 private void term(String tempVar) {
 String tempVar2;
 factor(tempVar);
 while (lexer.match(Lexer.TIMES)) {
 lexer.advance();
 tempVar2 = newName();
 factor(tempVar2);
 System.out.println(tempVar + " *= " + tempVar2);
 freeNames(tempVar2);
 }

 }

 private void factor(String tempVar) {
 if (lexer.match(Lexer.NUM_OR_ID)) {
 System.out.println(tempVar + " = " + lexer.yytext);
 lexer.advance();
 } else if (lexer.match(Lexer.LP)) {
 lexer.advance();
 expression(tempVar);
 if (lexer.match(Lexer.RP)) {
 lexer.advance();
 } else {
 //括号不匹配
 System.out.println("Mismatched parenthesis: " + lexer.yylineno);
 System.exit(1);
 }
 } else {
 System.out.println("Number or identifier expected: " + lexer.yylineno);
 System.exit(1);
 }
 }
}