package projet.op

import chisel3._
import chisel3.util.switch
import projet.CUInterface
import projet.AluOpCode
import chisel3.util.is
import projet.OpType

object OpRW {
    // Implements functions for all instruction of the opImm, w  kind
    def opRW(io: CUInterface) = {
        val funct3 = io.instruction(14, 12);
        val funct7 = io.instruction(31, 25);

        // Meaning of Funct3 in the context of an OpImm instruction
        object Funct3 extends ChiselEnum {
            // Type I
            val AdditionSubstraction = "b000".U
            val SLLW = "b001".U
            val ShiftRight = "b101".U

            // Unimplemented
            val ShiftWordRight = "b101".U // Right shifts
        }

        object AdditionSubstractionFunct7 extends ChiselEnum {
            val ADDW = "b0000000".U
            val SUBW = "b0100000".U
        }

        object ShiftWordRightFunct7 extends ChiselEnum {
            val SRLW = "b0000000".U
            val SRAW = "b0100000".U
        }

        io.reg_file_we := true.B // Write to regfile
        io.alu_word_mode := true.B
        io.mux_regb_imm := true.B; // OpImm are operations with imm, so send imm to ALU
        io.mux_rega_pc := true.B;
        io.mux_alu_imm := true.B;
        switch(funct3) {
            // Type I
            is(Funct3.AdditionSubstraction) {
                switch(funct7) {
                    is(AdditionSubstractionFunct7.ADDW) {
                        io.alu_opcode := AluOpCode.Add
                    }
                    is(AdditionSubstractionFunct7.SUBW) {
                        io.alu_opcode := AluOpCode.Sub
                    }
                }
            }

            is(Funct3.SLLW) {
                io.alu_opcode := AluOpCode.ShiftLeft
            }

            is(Funct3.ShiftWordRight) {
                switch(funct7) {
                    is(ShiftWordRightFunct7.SRAW) {
                        io.alu_opcode := AluOpCode.ShiftArithmeticRight
                    }
                    is(ShiftWordRightFunct7.SRLW) {
                        io.alu_opcode := AluOpCode.ShiftRight
                    }
                }
            }
        }
    }
}