Mines now follows the conventional approach of offering a completely

blank grid until you make the first click; to ensure solubility, it
does not generate the mine layout until that click, and then ensures
it is solvable starting from that position.

This has involved three infrastructure changes:

 - random.c now offers functions to encode and decode an entire
   random_state as a string
 - each puzzle's new_game() is now passed a pointer to the midend
   itself, which most of them ignore
 - there's a function in the midend which a game can call back to
   _rewrite_ its current game description.

So Mines now has two entirely separate forms of game ID. One
contains the generation-time parameters (n and unique) plus an
encoding of a random_state; the other actually encodes the grid once
it's been generated, and also contains the initial click position.
When called with the latter, new_game() does plausibly normal stuff.
When called with the former, it notes down all the details and waits
until the first square is opened, and _then_ does the grid
generation and updates the game description in the midend. So if,
_after_ your first click, you decide you want to share this
particular puzzle with someone else, you can do that fine.

Also in this checkin, the mine layout is no longer _copied_ between
all the game_states on the undo chain. Instead, it's in a separate
structure and all game_states share a pointer to it - and the
structure is reference-counted to ensure deallocation.

[originally from svn r5862]

cube.c

@@ -868,7 +868,7 @@ static char *validate_desc(game_params *params, char *desc)
     return NULL;
 }
 
-static game_state *new_game(game_params *params, char *desc)
+static game_state *new_game(midend_data *me, game_params *params, char *desc)
 {
     game_state *state = snew(game_state);
     int area;

fifteen.c

@@ -322,7 +322,7 @@ static char *validate_desc(game_params *params, char *desc)
     return err;
 }
 
-static game_state *new_game(game_params *params, char *desc)
+static game_state *new_game(midend_data *me, game_params *params, char *desc)
 {
     game_state *state = snew(game_state);
     int i;

midend.c

@@ -165,7 +165,8 @@ void midend_new_game(midend_data *me)
     }
 
     ensure(me);
-    me->states[me->nstates].state = me->ourgame->new_game(me->params, me->desc);
+    me->states[me->nstates].state =
+	me->ourgame->new_game(me, me->params, me->desc);
     me->states[me->nstates].special = TRUE;
     me->nstates++;
     me->statepos = 1;
@@ -495,7 +496,7 @@ float *midend_colours(midend_data *me, int *ncolours)
     if (me->nstates == 0) {
 	game_aux_info *aux = NULL;
         char *desc = me->ourgame->new_desc(me->params, me->random, &aux);
-        state = me->ourgame->new_game(me->params, desc);
+        state = me->ourgame->new_game(me, me->params, desc);
         sfree(desc);
 	if (aux)
 	    me->ourgame->free_aux_info(aux);
@@ -626,6 +627,12 @@ int midend_wants_statusbar(midend_data *me)
     return me->ourgame->wants_statusbar();
 }
 
+void midend_supersede_game_desc(midend_data *me, char *desc)
+{
+    sfree(me->desc);
+    me->desc = dupstr(desc);
+}
+
 config_item *midend_get_config(midend_data *me, int which, char **wintitle)
 {
     char *titlebuf, *parstr;

mines.c

@@ -60,9 +60,25 @@ struct game_params {
     int unique;
 };
 
+struct mine_layout {
+    /*
+     * This structure is shared between all the game_states for a
+     * given instance of the puzzle, so we reference-count it.
+     */
+    int refcount;
+    char *mines;
+    /*
+     * If we haven't yet actually generated the mine layout, here's
+     * all the data we will need to do so.
+     */
+    int n, unique;
+    random_state *rs;
+    midend_data *me;		       /* to give back the new game desc */
+};
+
 struct game_state {
     int w, h, n, dead, won;
-    char *mines;		       /* real mine positions */
+    struct mine_layout *layout;	       /* real mine positions */
     char *grid;			       /* player knowledge */
     /*
      * Each item in the `grid' array is one of the following values:
@@ -1790,25 +1806,20 @@ static void obfuscate_bitmap(unsigned char *bmp, int bits, int decode)
     }
 }
 
-static char *new_game_desc(game_params *params, random_state *rs,
+static char *new_mine_layout(int w, int h, int n, int x, int y, int unique,
-			   game_aux_info **aux)
+			     random_state *rs, char **game_desc)
 {
     char *grid, *ret, *p;
     unsigned char *bmp;
-    int x, y, i, area;
+    int i, area;
 
-    /*
+    grid = minegen(w, h, n, x, y, unique, rs);
-     * FIXME: allow user to specify initial open square.
-     */
-    x = random_upto(rs, params->w);
-    y = random_upto(rs, params->h);
-
-    grid = minegen(params->w, params->h, params->n, x, y, params->unique, rs);
 
+    if (game_desc) {
 	/*
 	 * Set up the mine bitmap and obfuscate it.
 	 */
-    area = params->w * params->h;
+	area = w * h;
 	bmp = snewn((area + 7) / 8, unsigned char);
 	memset(bmp, 0, (area + 7) / 8);
 	for (i = 0; i < area; i++) {
@@ -1835,7 +1846,31 @@ static char *new_game_desc(game_params *params, random_state *rs,
 
 	sfree(bmp);
 
-    return ret;
+	*game_desc = ret;
+    }	
+
+    return grid;
+}
+
+static char *new_game_desc(game_params *params, random_state *rs,
+			   game_aux_info **aux)
+{
+#ifdef PREOPENED
+    int x = random_upto(rs, params->w);
+    int y = random_upto(rs, params->h);
+    char *grid, *desc;
+
+    grid = new_mine_layout(params->w, params->h, params->n,
+			   x, y, params->unique, rs);
+#else
+    char *rsdesc, *desc;
+
+    rsdesc = random_state_encode(rs);
+    desc = snewn(strlen(rsdesc) + 100, char);
+    sprintf(desc, "r%d,%c,%s", params->n, params->unique ? 'u' : 'a', rsdesc);
+    sfree(rsdesc);
+    return desc;
+#endif
 }
 
 static void game_free_aux_info(game_aux_info *aux)
@@ -1848,6 +1883,21 @@ static char *validate_desc(game_params *params, char *desc)
     int wh = params->w * params->h;
     int x, y;
 
+    if (*desc == 'r') {
+	if (!*desc || !isdigit((unsigned char)*desc))
+	    return "No initial mine count in game description";
+	while (*desc && isdigit((unsigned char)*desc))
+	    desc++;		       /* skip over mine count */
+	if (*desc != ',')
+	    return "No ',' after initial x-coordinate in game description";
+	desc++;
+	if (*desc != 'u' && *desc != 'a')
+	    return "No uniqueness specifier in game description";
+	desc++;
+	if (*desc != ',')
+	    return "No ',' after uniqueness specifier in game description";
+	/* now ignore the rest */
+    } else {
 	if (!*desc || !isdigit((unsigned char)*desc))
 	    return "No initial x-coordinate in game description";
 	x = atoi(desc);
@@ -1874,6 +1924,7 @@ static char *validate_desc(game_params *params, char *desc)
 	/* now just check length of remainder */
 	if (strlen(desc) != (wh+3)/4)
 	    return "Game description is wrong length";
+    }
 
     return NULL;
 }
@@ -1883,7 +1934,24 @@ static int open_square(game_state *state, int x, int y)
     int w = state->w, h = state->h;
     int xx, yy, nmines, ncovered;
 
-    if (state->mines[y*w+x]) {
+    if (!state->layout->mines) {
+	/*
+	 * We have a preliminary game in which the mine layout
+	 * hasn't been generated yet. Generate it based on the
+	 * initial click location.
+	 */
+	char *desc;
+	state->layout->mines = new_mine_layout(w, h, state->layout->n,
+					       x, y, state->layout->unique,
+					       state->layout->rs,
+					       &desc);
+	midend_supersede_game_desc(state->layout->me, desc);
+	sfree(desc);
+	random_free(state->layout->rs);
+	state->layout->rs = NULL;
+    }
+
+    if (state->layout->mines[y*w+x]) {
 	/*
 	 * The player has landed on a mine. Bad luck. Expose all
 	 * the mines.
@@ -1891,12 +1959,12 @@ static int open_square(game_state *state, int x, int y)
 	state->dead = TRUE;
 	for (yy = 0; yy < h; yy++)
 	    for (xx = 0; xx < w; xx++) {
-		if (state->mines[yy*w+xx] &&
+		if (state->layout->mines[yy*w+xx] &&
 		    (state->grid[yy*w+xx] == -2 ||
 		     state->grid[yy*w+xx] == -3)) {
 		    state->grid[yy*w+xx] = 64;
 		}
-		if (!state->mines[yy*w+xx] &&
+		if (!state->layout->mines[yy*w+xx] &&
 		    state->grid[yy*w+xx] == -1) {
 		    state->grid[yy*w+xx] = 66;
 		}
@@ -1927,7 +1995,7 @@ static int open_square(game_state *state, int x, int y)
 		if (state->grid[yy*w+xx] == -10) {
 		    int dx, dy, v;
 
-		    assert(!state->mines[yy*w+xx]);
+		    assert(!state->layout->mines[yy*w+xx]);
 
 		    v = 0;
 
@@ -1935,7 +2003,7 @@ static int open_square(game_state *state, int x, int y)
 			for (dy = -1; dy <= +1; dy++)
 			    if (xx+dx >= 0 && xx+dx < state->w &&
 				yy+dy >= 0 && yy+dy < state->h &&
-				state->mines[(yy+dy)*w+(xx+dx)])
+				state->layout->mines[(yy+dy)*w+(xx+dx)])
 				v++;
 
 		    state->grid[yy*w+xx] = v;
@@ -1966,7 +2034,7 @@ static int open_square(game_state *state, int x, int y)
 	for (xx = 0; xx < w; xx++) {
 	    if (state->grid[yy*w+xx] < 0)
 		ncovered++;
-	    if (state->mines[yy*w+xx])
+	    if (state->layout->mines[yy*w+xx])
 		nmines++;
 	}
     assert(ncovered >= nmines);
@@ -1982,7 +2050,7 @@ static int open_square(game_state *state, int x, int y)
     return 0;
 }
 
-static game_state *new_game(game_params *params, char *desc)
+static game_state *new_game(midend_data *me, game_params *params, char *desc)
 {
     game_state *state = snew(game_state);
     int i, wh, x, y, ret, masked;
@@ -1994,8 +2062,33 @@ static game_state *new_game(game_params *params, char *desc)
     state->dead = state->won = FALSE;
 
     wh = state->w * state->h;
-    state->mines = snewn(wh, char);
 
+    state->layout = snew(struct mine_layout);
+    state->layout->refcount = 1;
+
+    state->grid = snewn(wh, char);
+    memset(state->grid, -2, wh);
+
+    if (*desc == 'r') {
+	desc++;
+	state->layout->n = atoi(desc);
+	while (*desc && isdigit((unsigned char)*desc))
+	    desc++;		       /* skip over mine count */
+	if (*desc) desc++;	       /* eat comma */
+	if (*desc == 'a')
+	    state->layout->unique = FALSE;
+	else
+	    state->layout->unique = TRUE;
+	desc++;
+	if (*desc) desc++;	       /* eat comma */
+
+	state->layout->mines = NULL;
+	state->layout->rs = random_state_decode(desc);
+	state->layout->me = me;
+
+    } else {
+
+	state->layout->mines = snewn(wh, char);
 	x = atoi(desc);
 	while (*desc && isdigit((unsigned char)*desc))
 	    desc++;		       /* skip over x coordinate */
@@ -2038,23 +2131,14 @@ static game_state *new_game(game_params *params, char *desc)
 	if (masked)
 	    obfuscate_bitmap(bmp, wh, TRUE);
 
-    memset(state->mines, 0, wh);
+	memset(state->layout->mines, 0, wh);
 	for (i = 0; i < wh; i++) {
 	    if (bmp[i / 8] & (0x80 >> (i % 8)))
-	    state->mines[i] = 1;
+		state->layout->mines[i] = 1;
 	}
 
-    state->grid = snewn(wh, char);
-    memset(state->grid, -2, wh);
-
 	ret = open_square(state, x, y);
-    /*
+    }
-     * FIXME: This shouldn't be an assert. Perhaps we actually
-     * ought to check it in validate_params! Alternatively, we can
-     * remove the assert completely and actually permit a game
-     * description to start you off dead.
-     */
-    assert(ret != -1);
 
     return state;
 }
@@ -2068,8 +2152,8 @@ static game_state *dup_game(game_state *state)
     ret->n = state->n;
     ret->dead = state->dead;
     ret->won = state->won;
-    ret->mines = snewn(ret->w * ret->h, char);
+    ret->layout = state->layout;
-    memcpy(ret->mines, state->mines, ret->w * ret->h);
+    ret->layout->refcount++;
     ret->grid = snewn(ret->w * ret->h, char);
     memcpy(ret->grid, state->grid, ret->w * ret->h);
 
@@ -2078,7 +2162,12 @@ static game_state *dup_game(game_state *state)
 
 static void free_game(game_state *state)
 {
-    sfree(state->mines);
+    if (--state->layout->refcount <= 0) {
+	sfree(state->layout->mines);
+	if (state->layout->rs)
+	    random_free(state->layout->rs);
+	sfree(state->layout);
+    }
     sfree(state->grid);
     sfree(state);
 }
@@ -2558,7 +2647,7 @@ static void game_redraw(frontend *fe, game_drawstate *ds, game_state *oldstate,
 
 	    if (v == -1)
 		markers++;
-	    if (state->mines[y*ds->w+x])
+	    if (state->layout->mines && state->layout->mines[y*ds->w+x])
 		mines++;
 
 	    if ((v == -2 || v == -3) &&
@@ -2571,6 +2660,9 @@ static void game_redraw(frontend *fe, game_drawstate *ds, game_state *oldstate,
 	    }
 	}
 
+    if (!state->layout->mines)
+	mines = state->layout->n;
+
     /*
      * Update the status bar.
      */

net.c

@@ -1558,7 +1558,7 @@ static char *validate_desc(game_params *params, char *desc)
  * Construct an initial game state, given a description and parameters.
  */
 
-static game_state *new_game(game_params *params, char *desc)
+static game_state *new_game(midend_data *me, game_params *params, char *desc)
 {
     game_state *state;
     int w, h, x, y;

netslide.c

@@ -738,7 +738,7 @@ static char *validate_desc(game_params *params, char *desc)
  * Construct an initial game state, given a description and parameters.
  */
 
-static game_state *new_game(game_params *params, char *desc)
+static game_state *new_game(midend_data *me, game_params *params, char *desc)
 {
     game_state *state;
     int w, h, x, y;

nullgame.c

@@ -99,7 +99,7 @@ static char *validate_desc(game_params *params, char *desc)
     return NULL;
 }
 
-static game_state *new_game(game_params *params, char *desc)
+static game_state *new_game(midend_data *me, game_params *params, char *desc)
 {
     game_state *state = snew(game_state);
 

pattern.c

@@ -601,7 +601,7 @@ static char *validate_desc(game_params *params, char *desc)
     return NULL;
 }
 
-static game_state *new_game(game_params *params, char *desc)
+static game_state *new_game(midend_data *me, game_params *params, char *desc)
 {
     int i;
     char *p;

puzzles.h

@@ -144,6 +144,7 @@ char *midend_set_config(midend_data *me, int which, config_item *cfg);
 char *midend_game_id(midend_data *me, char *id);
 char *midend_text_format(midend_data *me);
 char *midend_solve(midend_data *me);
+void midend_supersede_game_desc(midend_data *me, char *desc);
 
 /*
  * malloc.c
@@ -176,6 +177,8 @@ random_state *random_init(char *seed, int len);
 unsigned long random_bits(random_state *state, int bits);
 unsigned long random_upto(random_state *state, unsigned long limit);
 void random_free(random_state *state);
+char *random_state_encode(random_state *state);
+random_state *random_state_decode(char *input);
 /* random.c also exports SHA, which occasionally comes in useful. */
 typedef unsigned long uint32;
 typedef struct {
@@ -213,7 +216,7 @@ struct game {
 		      game_aux_info **aux);
     void (*free_aux_info)(game_aux_info *aux);
     char *(*validate_desc)(game_params *params, char *desc);
-    game_state *(*new_game)(game_params *params, char *desc);
+    game_state *(*new_game)(midend_data *me, game_params *params, char *desc);
     game_state *(*dup_game)(game_state *state);
     void (*free_game)(game_state *state);
     int can_solve;

random.c

@@ -12,6 +12,7 @@
 
 #include <assert.h>
 #include <string.h>
+#include <stdio.h>
 
 #include "puzzles.h"
 
@@ -278,3 +279,63 @@ void random_free(random_state *state)
 {
     sfree(state);
 }
+
+char *random_state_encode(random_state *state)
+{
+    char retbuf[256];
+    int len = 0, i;
+
+    for (i = 0; i < lenof(state->seedbuf); i++)
+	len += sprintf(retbuf+len, "%02x", state->seedbuf[i]);
+    for (i = 0; i < lenof(state->databuf); i++)
+	len += sprintf(retbuf+len, "%02x", state->databuf[i]);
+    len += sprintf(retbuf+len, "%02x", state->pos);
+
+    return dupstr(retbuf);
+}
+
+random_state *random_state_decode(char *input)
+{
+    random_state *state;
+    int pos, byte, digits;
+
+    state = snew(random_state);
+
+    memset(state->seedbuf, 0, sizeof(state->seedbuf));
+    memset(state->databuf, 0, sizeof(state->databuf));
+    state->pos = 0;
+
+    byte = digits = 0;
+    pos = 0;
+    while (*input) {
+	int v = *input++;
+
+	if (v >= '0' && v <= '9')
+	    v = v - '0';
+	else if (v >= 'A' && v <= 'F')
+	    v = v - 'A' + 10;
+	else if (v >= 'a' && v <= 'f')
+	    v = v - 'a' + 10;
+	else
+	    v = 0;
+
+	byte = (byte << 4) | v;
+	digits++;
+
+	if (digits == 2) {
+	    /*
+	     * We have a byte. Put it somewhere.
+	     */
+	    if (pos < lenof(state->seedbuf))
+		state->seedbuf[pos++] = byte;
+	    else if (pos < lenof(state->seedbuf) + lenof(state->databuf))
+		state->databuf[pos++ - lenof(state->seedbuf)] = byte;
+	    else if (pos == lenof(state->seedbuf) + lenof(state->databuf) &&
+		     byte <= lenof(state->databuf))
+		state->pos = byte;
+	    byte = digits = 0;
+	}
+    }
+
+    return state;
+}

rect.c

@@ -1691,7 +1691,7 @@ static char *validate_desc(game_params *params, char *desc)
     return NULL;
 }
 
-static game_state *new_game(game_params *params, char *desc)
+static game_state *new_game(midend_data *me, game_params *params, char *desc)
 {
     game_state *state = snew(game_state);
     int x, y, i, area;

sixteen.c

@@ -442,7 +442,7 @@ static char *validate_desc(game_params *params, char *desc)
     return err;
 }
 
-static game_state *new_game(game_params *params, char *desc)
+static game_state *new_game(midend_data *me, game_params *params, char *desc)
 {
     game_state *state = snew(game_state);
     int i;

solo.c

@@ -1620,7 +1620,7 @@ static char *validate_desc(game_params *params, char *desc)
     return NULL;
 }
 
-static game_state *new_game(game_params *params, char *desc)
+static game_state *new_game(midend_data *me, game_params *params, char *desc)
 {
     game_state *state = snew(game_state);
     int c = params->c, r = params->r, cr = c*r, area = cr * cr;

twiddle.c

@@ -428,7 +428,7 @@ static char *validate_desc(game_params *params, char *desc)
     return NULL;
 }
 
-static game_state *new_game(game_params *params, char *desc)
+static game_state *new_game(midend_data *me, game_params *params, char *desc)
 {
     game_state *state = snew(game_state);
     int w = params->w, h = params->h, n = params->n, wh = w*h;