Merge two sorted ready/valid streams

module sorted_stream_merger (
  input  logic        clk,
  input  logic        rst_n,
  input  logic        a_valid,
  input  logic [15:0] a_data,
  input  logic        a_last,
  output logic        a_ready,
  input  logic        b_valid,
  input  logic [15:0] b_data,
  input  logic        b_last,
  output logic        b_ready,
  output logic        out_valid,
  output logic [15:0] out_data,
  output logic        out_last,
  input  logic        out_ready
);
  logic a_head_valid, b_head_valid;
  logic [15:0] a_head_data, b_head_data;
  logic a_head_last, b_head_last;
  logic a_eof_seen, b_eof_seen;
  logic choose_a;

  assign a_ready = !a_head_valid && !a_eof_seen;
  assign b_ready = !b_head_valid && !b_eof_seen;

  always_comb begin : select_head
    // TODO: Implement select_head using the supplied state and interface.
  end

  always_ff @(posedge clk) begin : capture_and_retire_heads
    // TODO: Implement capture_and_retire_heads using the supplied state and interface.
  end
endmodule