module decode
import riscv_types::*;
#(
  )
  (
    input  logic        clk,
    input  logic        rst_l,

    // I-MEM Interface
    input  logic [31:0] imem_id_instr_ID,

    // Fetch Interface
    input  logic [31:0] imem_id_pc_ID

    // Dispatch Interface
  );

// OpCode
opcode_t instrOpCode_ID;

// Instruction Type
logic instrTypeR_ID;
logic instrTypeI_ID;
logic instrTypeS_ID;
logic instrTypeB_ID;
logic instrTypeU_ID;
logic instrTypeJ_ID;

  // Immediate
logic [31:0] instrImm_ID;
logic        instrImmSign_ID;

// Register Indices
logic [4:0] instrRs1Idx_ID;
logic       instrRs1Vld_ID;
logic [4:0] instrRs2Idx_ID;
logic       instrRs2Vld_ID;
logic [4:0] instrRdIdx_ID;
logic       instrRdVld_ID;

// Funct3 and Funct7
logic [2:0] instrFunct3_ID;
logic       instrFunct7_ID;

// Control Bits

// Memory Op
mem_op_t instrMemOp_ID;

// Branch OP
brjmp_op_t instrBrJmpOp_ID;

// ALU Operand Selection
aluSelOp1_t instrAluOp1_ID;
aluSelOp2_t instrAluOp2_ID;

// DEBUG: Display decode instr
always_ff @(clk) begin : f_print_decode
  $display("OpCode: %s",     instrOpCode_ID.name());
  $display("Immediate: %0d", instrImm_ID);
  $display("Memory: %s",     instrMemOp_ID.name());
  $display("Branch: %s",     instrBrJmpOp_ID.name());
  $display("ALU Sel 1: %s",  instrAluOp1_ID.name());
  $display("ALU Sel 2: %s",  instrAluOp2_ID.name());
  $display("Funct3: %0x",    instrFunct3_ID);
  $display("Funct7: %0x",    instrFunct7_ID);
end

// Instruction Type Decode
// FIXME: Add support for FENCE + ECALL + EBREAK + CSRs
assign instrTypeI_ID = (instrOpCode_ID == INSTR_TYPE_IMM)
                     | (instrOpCode_ID == INSTR_TYPE_JALR)
                     | (instrOpCode_ID == INSTR_TYPE_LD);
assign instrTypeU_ID = (instrOpCode_ID == INSTR_TYPE_LUI)
                     | (instrOpCode_ID == INSTR_TYPE_AUIPC);
assign instrTypeR_ID = (instrOpCode_ID == INSTR_TYPE_REG);
assign instrTypeS_ID = (instrOpCode_ID == INSTR_TYPE_ST);
assign instrTypeB_ID = (instrOpCode_ID == INSTR_TYPE_BR);
assign instrTypeJ_ID = (instrOpCode_ID == INSTR_TYPE_JAL);

// Register Index Decode
assign instrRs1Idx_ID = imem_id_instr_ID[19:15];
assign instrRs1Vld_ID = instrTypeR_ID | instrTypeI_ID | instrTypeS_ID | instrTypeB_ID;

assign instrRs2Idx_ID = imem_id_instr_ID[24:20];
assign instrRs2Vld_ID = instrTypeR_ID | instrTypeS_ID | instrTypeB_ID;

assign instrRdIdx_ID  = imem_id_instr_ID[11:7];
assign instrRdVld_ID  = instrTypeR_ID | instrTypeI_ID | instrTypeU_ID | instrTypeJ_ID;

// Func Bit decode
assign instrFunct7_ID = imem_id_instr_ID[30];
assign instrFunct3_ID = imem_id_instr_ID[14:12];

// Instruction Type (OpCode) Decode
assign instrImmSign_ID  = imem_id_instr_ID[31];
assign instrOpCode_ID = opcode_t'(imem_id_instr_ID[6:0]);

// Immediate Decode
assign instrImm_ID[0]   = instrTypeJ_ID ? imem_id_instr_ID[25] : // Bit 25 for I-Type 
                          instrTypeS_ID ? imem_id_instr_ID[7]  : // Bit 7 for S-Type
                                          '0;                    // All other instructions set to 0

assign instrImm_ID[4:1] =  instrTypeI_ID                  ? imem_id_instr_ID[24:21] : // I-Type bits
                          (instrTypeS_ID | instrTypeB_ID) ? imem_id_instr_ID[11:8]  : // S-Type + B-Type bits
                                                            '0;                       // All other instructions set to 0

assign instrImm_ID[10:5] = instrTypeU_ID ? '0 : imem_id_instr_ID[30:25]; // Only J type is an immediate instruction that doesn't have it in 30:25


assign instrImm_ID[11]   = (instrTypeI_ID | instrTypeS_ID) ? imem_id_instr_ID[31] :
                           (instrTypeB_ID)                 ? imem_id_instr_ID[7]  :
                           (instrTypeJ_ID)                 ? imem_id_instr_ID[20] :
                                                           '0;

assign instrImm_ID[19:12] = (instrTypeU_ID | instrTypeJ_ID) ? imem_id_instr_ID[19:12] : { 8{instrImmSign_ID}}; // Only J and U types use 19:12 as not sign bit
assign instrImm_ID[31:20] = (instrTypeU_ID)                 ? imem_id_instr_ID[31:20] : {12{instrImmSign_ID}}; // Only U type use 31:20 as not sign bit

// Control Bits
assign instrMemOp_ID = (instrOpCode_ID == INSTR_TYPE_ST) ? MEM_OP_STORE :
                       (instrOpCode_ID == INSTR_TYPE_LD) ? MEM_OP_LOAD  :
                                                           MEM_OP_NONE;

assign instrBrJmpOp_ID  = (instrOpCode_ID == INSTR_TYPE_JALR)                                  ? REG_IMM_OFFSET : 
                          (instrOpCode_ID == INSTR_TYPE_BR | instrOpCode_ID == INSTR_TYPE_JAL) ? PC_IMM_OFFSET  :
                                                                                                 OFFSET_NONE;

assign instrAluOp1_ID      = (instrOpCode_ID == INSTR_TYPE_AUIPC) | (instrOpCode_ID == INSTR_TYPE_JAL) ? PC   : // Loading PC for AUIPC, PC Offset for JAL
                             (instrOpCode_ID == INSTR_TYPE_LUI)                                        ? OP_NONE : // Only loading immediate for LUI
                                                                                                         RS1;   // All else use RS1 value

assign instrAluOp2_ID      = (instrOpCode_ID == INSTR_TYPE_REG) ? RS2 : IMM; // Only R2R needs non-immediate op in ALU


endmodule