module vending_fsm
(
    input clk_i
    , input rst_i

    , input coin_put_i                  // 1-cycle tick
    , input [7:0] coin_sum_bi

    , input select_good_i               // 1-cycle tick
    , input [7:0] select_good_num_bi
    , input [31:0] select_good_cost_bi

    , input cancel_i                    // 1-cycle tick

    , output logic give_order_o                 // 1-cycle tick
    , output logic [7:0]  give_order_num_bo

    , output logic give_change_o                // 1-cycle tick
    , output logic [31:0] give_change_sum_bo
);

enum {IDLE, CREDIT, DELIIVERY, CHANGE} state;

logic [7:0] selected_good;
logic [31:0] credit_accumulated;

always @(posedge clk_i)
    begin
    if (rst_i)
        begin
        state <= IDLE;
        give_order_o <= 1'b0;
        give_order_num_bo <= 0;
        give_change_o <= 1'b0;
        give_change_sum_bo <= 0;
        end
    else
        begin

        // default values for "ticks"
        give_order_o <= 1'b0;
        give_change_o <= 1'b0;

        case (state)

            IDLE:
                begin
                if (coin_put_i)
                    begin
                    credit_accumulated <= coin_sum_bi;
                    state <= CREDIT;
                    end
                end

            CREDIT:
                begin
                if (coin_put_i)
                    begin
                    credit_accumulated <= credit_accumulated + coin_sum_bi;
                    end
                else if (select_good_i)
                    begin
                    selected_good <= select_good_num_bi;
                    credit_accumulated <= credit_accumulated - select_good_cost_bi;
                    state <= DELIIVERY;
                    end
                else if (cancel_i)
                    begin
                    state <= CHANGE;
                    end
                end

            DELIIVERY:
                begin
                give_order_o <= 1'b1;
                give_order_num_bo <= selected_good;
                state <= CHANGE;
                end

            CHANGE:
                begin
                give_change_o <= 1'b1;
                give_change_sum_bo <= credit_accumulated;
                state <= IDLE;
                end

        endcase

        end
    end

endmodule // vending_fsm