module VGA_Pattern_Generator(
  input i_Clk,
  input [3:0] i_Pattern,
  input i_HSync,
  input i_VSync,

  output reg o_HSync = 0,
  output reg o_VSync = 0,
  output reg [VIDEO_WIDTH-1:0] o_Red,
  output reg [VIDEO_WIDTH-1:0] o_Green,
  output reg [VIDEO_WIDTH-1:0] o_Blue
);
  // Go Board only supports 3 bits per channel. That's even less than the
  // Amiga!
  parameter VIDEO_WIDTH = 3;

  parameter TOTAL_COLUMNS = 800;
  parameter TOTAL_ROWS = 525;

  parameter ACTIVE_COLUMNS = 640;
  parameter ACTIVE_ROWS = 480;

  localparam COLOR_BAR_WIDTH = ACTIVE_COLUMNS / 8;

  wire w_HSync, w_VSync;

  wire [VIDEO_WIDTH-1:0] w_Red[0:15];
  wire [VIDEO_WIDTH-1:0] w_Green[0:15];
  wire [VIDEO_WIDTH-1:0] w_Blue[0:15];

  wire [$clog2(TOTAL_COLUMNS)-1:0] w_X;
  wire [$clog2(TOTAL_ROWS)-1:0] w_Y;

  VGA_Current_Beam_Position #(
    .TOTAL_COLUMNS(TOTAL_COLUMNS),
    .TOTAL_ROWS(TOTAL_ROWS)
  ) CurrentPosition (
    .i_Clk(i_Clk),
    .i_HSync(i_HSync),
    .i_VSync(i_VSync),
    .o_HSync(w_HSync),
    .o_VSync(w_VSync),
    .o_X(w_X),
    .o_Y(w_Y)
  );

  // all these pattern operations take one clock tick
  // so delay sync signals by that much
  always @(posedge i_Clk) begin
    o_HSync <= w_HSync;
    o_VSync <= w_VSync;
  end

  // none more black
  assign w_Red[0] = 0;
  assign w_Green[0] = 0;
  assign w_Blue[0] = 0;

  // red
  assign w_Red[1] = (
    (w_X < ACTIVE_COLUMNS && w_Y < ACTIVE_ROWS) ?
    {VIDEO_WIDTH{1'b1}} :
    0
  );
  assign w_Green[1] = 0;
  assign w_Blue[1] = 0;

  // green
  assign w_Red[2] = 0;
  assign w_Green[2] = (
    (w_X < ACTIVE_COLUMNS && w_Y < ACTIVE_ROWS) ?
    {VIDEO_WIDTH{1'b1}} :
    0
  );
  assign w_Blue[2] = 0;

  // blue
  assign w_Red[3] = 0;
  assign w_Green[3] = 0;
  assign w_Blue[3] = (
    (w_X < ACTIVE_COLUMNS && w_Y < ACTIVE_ROWS) ?
    {VIDEO_WIDTH{1'b1}} :
    0
  );

  // checkerboard
  // cell size is 32 pixels
  assign w_Red[4] = (w_X[5] ^ w_Y[5]) ? {VIDEO_WIDTH{1'b1}} : 0;
  assign w_Green[4] = w_Red[4];
  assign w_Blue[4] = w_Red[4];

  wire [2:0] w_colorBarSelect;

  // color bars
  // yes this is the hardware way to do this b/c multi/div
  assign w_colorBarSelect =
    w_X < COLOR_BAR_WIDTH ? 0 :
      w_X < COLOR_BAR_WIDTH * 2 ? 1 :
      w_X < COLOR_BAR_WIDTH * 3 ? 2 :
      w_X < COLOR_BAR_WIDTH * 4 ? 3 :
      w_X < COLOR_BAR_WIDTH * 5 ? 4 :
      w_X < COLOR_BAR_WIDTH * 6 ? 5 :
      w_X < COLOR_BAR_WIDTH * 7 ? 6 :7;

  assign w_Red[5] = (
    w_colorBarSelect == 4 ||
    w_colorBarSelect == 5 ||
    w_colorBarSelect == 6 ||
    w_colorBarSelect == 7
  ) ? {VIDEO_WIDTH{1'b1}} : 0;

  assign w_Green[5] = (
    w_colorBarSelect == 2 ||
    w_colorBarSelect == 3 ||
    w_colorBarSelect == 6 ||
    w_colorBarSelect == 7
  ) ? {VIDEO_WIDTH{1'b1}} : 0;

  assign w_Blue[5] = (
    w_colorBarSelect == 1 ||
    w_colorBarSelect == 3 ||
    w_colorBarSelect == 5 ||
    w_colorBarSelect == 7
  ) ? {VIDEO_WIDTH{1'b1}} : 0;

  // border

  localparam BORDER_WIDTH = 2;

  assign w_Red[6] = (
    w_X < BORDER_WIDTH || w_X >= ACTIVE_COLUMNS - BORDER_WIDTH ||
    w_Y < BORDER_WIDTH || w_Y >= ACTIVE_ROWS - BORDER_WIDTH
  ) ? {VIDEO_WIDTH{1'b1}} : 0;
  assign w_Green[6] = 0;
  assign w_Blue[6] = 0;

  always @(posedge i_Clk) begin
    case (i_Pattern)
      0:
      begin
        o_Red <= w_Red[0];
        o_Green <= w_Green[0];
        o_Blue <= w_Blue[0];
      end
      1:
      begin
        o_Red <= w_Red[1];
        o_Green <= w_Green[1];
        o_Blue <= w_Blue[1];
      end
      2:
      begin
        o_Red <= w_Red[2];
        o_Green <= w_Green[2];
        o_Blue <= w_Blue[2];
      end
      3:
      begin
        o_Red <= w_Red[3];
        o_Green <= w_Green[3];
        o_Blue <= w_Blue[3];
      end
      4:
      begin
        o_Red <= w_Red[4];
        o_Green <= w_Green[4];
        o_Blue <= w_Blue[4];
      end
      5:
      begin
        o_Red <= w_Red[5];
        o_Green <= w_Green[5];
        o_Blue <= w_Blue[5];
      end
      6:
      begin
        o_Red <= w_Red[6];
        o_Green <= w_Green[6];
        o_Blue <= w_Blue[6];
      end
      default:
      begin
        o_Red <= w_Red[0];
        o_Green <= w_Green[0];
        o_Blue <= w_Blue[0];
      end
    endcase
  end
endmodule