/* Program to produce a set of round robin pairing tables.
   Written by Warren Porter 06/15/94 07:20 am


           <- 6 <- 2 <- 7 <- 3
  10 B W 1    W    B    W    B  ^
  bye    |    B    W    B    W  |
  board  V -> 5 -> 9 -> 4 -> 8

  Note players are placed at every other location in a clockwise
  rotation but will move counterclockwise between every round.
    */

#include <stdio.h>

typedef struct {
   int pw,pb; } dtab;

typedef struct {
   int bd_no, dir;
   char color; }  ptab;

main (int argc, char *argv[])
{
   int x1, max_board, rot_dir, dir, board_no, rd_no, no_players, i,
       min=4,max=24;
   ptab p[37];
   dtab d[20];
   if (argc == 2)
      max=min=atoi(argv[1]);
   else
      if (argc == 3) {
         min=atoi(argv[1]);
         max=atoi(argv[2]);
      }

   if (min % 2)
      min++;

   if (max % 2)
      max++;

   if (min < 4) {
      fprintf(stderr,"Min too low %i, substituting 4\a\n",min);
      if (max == min)
         max=min = 4;
      else
         min=4; }

   if (max > 38) {
      fprintf(stderr,"Max too high %i, substituting 38\a\n",max);
      if (max == min)
         max=min = 38;
      else
         max=38; }

   for (no_players = min; no_players <= max; no_players +=2) {
      max_board = no_players / 2;
      board_no = p[0].bd_no = 1;
      p[0].color = 'w';
      p[0].dir = 1;  /* Player 1's color and direction 1st rd */
      rot_dir = 2;   /* Where program will seat next player */
      dir = -1;
      printf("\n\nPairings for %i or %i players\n\nRD",
              no_players - 1, no_players);
      x1 = max_board * 3 - 2;

      for (i=2;i <= x1;i++)
         putchar(' ');

      printf("PAIRINGS\n");

      /* Next routine initially places the players for the 1st
         round (except for 1, placed "by hand" earlier).  To initially
         fill the circuit, players are seated in order in every other
         position.  "dir" tells the player where to move for the next
         round and "rot_dir" tells the program where to put the next
         player initially.  When it initially says to put someone
         outside the range of permissible boards, "rot_dir" is changed
         along with other corrections. */

      for (x1 = 2;x1 < no_players;x1++) {
         if (x1 <= max_board)
            p[x1 - 1].color = 'b';
         else
            p[x1 - 1].color = 'w';

         board_no += rot_dir;
         p[x1 - 1].dir = dir;
         p[x1 - 1].bd_no = board_no;
         if (!board_no) {
            board_no = p[x1 - 1].bd_no = 2;
            dir = p[x1 - 1].dir = -1;
            rot_dir = 2; }
         else
            if (board_no == max_board) {
               p[x1 - 1].dir = -1;
               board_no++;
               rot_dir = -2;
               dir = 1; }
            else
               if (board_no > max_board) {
                  board_no = p[x1 - 1].bd_no = max_board;
                  rot_dir = -2;
                  dir = 1;
                  p[x1 - 1].dir = 0; }
      }

      /* Initially builds the display table from the player table. */

      for (rd_no = 1; rd_no < no_players; rd_no++) {
         printf("\n%2d",rd_no);
         for (x1 = 1; x1 < no_players;x1++) {
            board_no = p[x1 - 1].bd_no;
            if (board_no != 1)               /* Normal boards */
               if (p[x1 - 1].color == 'w')
                  d[board_no - 1].pw = x1;
               else
                  d[board_no - 1].pb = x1;
            else                             /* Bye board */
               if (x1 > max_board) {
                  d[0].pb = x1;
                  d[0].pw = no_players; }
               else {
                  d[0].pb = no_players;
                  d[0].pw = x1; }
         }

         /* Print the pairings for this round */

         for (x1 = 0;x1 < max_board;x1++)
            printf(" %2d:%-2d",d[x1].pw,d[x1].pb);

         /* If another round follows, ask the players to move */

         if ((no_players - rd_no) > 1)
            for (x1 = 1;x1 < no_players;x1++) {
               p[x1 - 1].bd_no += p[x1 - 1].dir;
               if (p[x1 - 1].bd_no != 1)
                  if (p[x1 - 1].color == 'w')
                     p[x1 - 1].color = 'b';
                  else
                     p[x1 - 1].color = 'w';
               else
                  dir = p[x1 - 1].dir = 1;

               if (!p[x1 - 1].dir)
                  dir=p[x1 - 1].dir=-1;
               else
                  if (p[x1 - 1].bd_no == max_board)
                     dir=p[x1 - 1].dir= 0;
         }
      }
   }
   printf("\n");
}