CodeGen.h

//This files takes AST as a input and gives TAC as output 
// File: include/CodeGen.h
// Purpose: INTERMEDIATE CODE GENERATION (Phase 4)
//          Translates the AST into Three-Address Code (TAC),
//          a simple IR (Intermediate Representation) that looks
//          like assembly but is still platform-independent.


// Input: AST
//Output: TAC Three address code
//   int x = 5 + 3 * 2;
//AST::
            //       =
            //    x       +
            //         5   *
            //            3   2   
            
//      t0 = 3 * 2
//      t1 = 5 + t0
//      x  = t1


#ifndef CODEGEN_H
#define CODEGEN_H

#include "AST.h"
#include <string>
#include <vector>

// A single Three-Address Code instruction
struct TACInstruction {
    std::string result;  // Destination operand  e.g. "t0" or "x"
    std::string op;      // Operator or opcode   e.g. "+" or "GOTO" or "PRINT"
    std::string arg1;    // First source operand
    std::string arg2;    // Second source operand (empty for unary ops)

    // Format instruction as readable string  e.g.  "t0 = 5 + 3"
    std::string toString() const;
};

class CodeGen {
public:
    CodeGen();
public:
    // generate() – walk AST, emit TAC instructions
    std::vector<TACInstruction> generate(const std::vector<ASTNodePtr>& stmts);

    // Print all generated instructions to stdout
    void printInstructions() const;

private:
    std::vector<TACInstruction> instructions_;  // Accumulated TAC
    int tempCount_;   // Counter for unique temp names: t0, t1, t2 …
    int labelCount_;  // Counter for unique labels:  L0, L1, L2 …

    std::string newTemp();   // Allocate next temp name
    std::string newLabel();  // Allocate next label name

    // Emit a TAC instruction into instructions_
    void emit(const std::string& result,
              const std::string& op,
              const std::string& arg1 = "",
              const std::string& arg2 = "");

    // Recursively generate code for an expression; returns temp holding result
    std::string genExpr(const ASTNode* node);

    // Generate code for a statement (no return value needed)
    void genStmt(const ASTNode* node);
};

#endif // CODEGEN_H