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	cal.c - 9base - revived minimalist port of Plan 9 userland to Unix
	git clone git://git.suckless.org/9base
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	---
	cal.c (4204B)
	---
	1 #include <u.h>
	2 #include <libc.h>
	3 #include <bio.h>
	4
	5 char dayw[] =
	6 {
	7 " S M Tu W Th F S"
	8 };
	9 char *smon[] =
	10 {
	11 "January", "February", "March", "April",
	12 "May", "June", "July", "August",
	13 "September", "October", "November", "December",
	14 };
	15 char mon[] =
	16 {
	17 0,
	18 31, 29, 31, 30,
	19 31, 30, 31, 31,
	20 30, 31, 30, 31,
	21 };
	22 char string[432];
	23 Biobuf bout;
	24
	25 void main(int argc, char *argv[]);
	26 int number(char *str);
	27 void pstr(char *str, int n);
	28 void cal(int m, int y, char *p, int w);
	29 int jan1(int yr);
	30 int curmo(void);
	31 int curyr(void);
	32
	33 void
	34 main(int argc, char *argv[])
	35 {
	36 int y, i, j, m;
	37
	38 if(argc > 3) {
	39 fprint(2, "usage: cal [month] [year]\n");
	40 exits("usage");
	41 }
	42 Binit(&bout, 1, OWRITE);
	43
	44 /*
	45 * no arg, print current month
	46 */
	47 if(argc == 1) {
	48 m = curmo();
	49 y = curyr();
	50 goto xshort;
	51 }
	52
	53 /*
	54 * one arg
	55 * if looks like a month, print month
	56 * else print year
	57 */
	58 if(argc == 2) {
	59 y = number(argv[1]);
	60 if(y < 0)
	61 y = -y;
	62 if(y >= 1 && y <= 12) {
	63 m = y;
	64 y = curyr();
	65 goto xshort;
	66 }
	67 goto xlong;
	68 }
	69
	70 /*
	71 * two arg, month and year
	72 */
	73 m = number(argv[1]);
	74 if(m < 0)
	75 m = -m;
	76 y = number(argv[2]);
	77 goto xshort;
	78
	79 /*
	80 * print out just month
	81 */
	82 xshort:
	83 if(m < 1 \|\| m > 12)
	84 goto badarg;
	85 if(y < 1 \|\| y > 9999)
	86 goto badarg;
	87 Bprint(&bout, " %s %d\n", smon[m-1], y);
	88 Bprint(&bout, "%s\n", dayw);
	89 cal(m, y, string, 24);
	90 for(i=0; i<6*24; i+=24)
	91 pstr(string+i, 24);
	92 exits(0);
	93
	94 /*
	95 * print out complete year
	96 */
	97 xlong:
	98 y = number(argv[1]);
	99 if(y<1 \|\| y>9999)
	100 goto badarg;
	101 Bprint(&bout, "\n\n\n");
	102 Bprint(&bout, " %d\n", y);
	103 Bprint(&bout, "\n");
	104 for(i=0; i<12; i+=3) {
	105 for(j=0; j<6*72; j++)
	106 string[j] = '\0';
	107 Bprint(&bout, " %.3s", smon[i]);
	108 Bprint(&bout, " %.3s", smon[i+1]);
	109 Bprint(&bout, " %.3s\n", smon[i+2]);
	110 Bprint(&bout, "%s %s %s\n", dayw, dayw, dayw);
	111 cal(i+1, y, string, 72);
	112 cal(i+2, y, string+23, 72);
	113 cal(i+3, y, string+46, 72);
	114 for(j=0; j<6*72; j+=72)
	115 pstr(string+j, 72);
	116 }
	117 Bprint(&bout, "\n\n\n");
	118 exits(0);
	119
	120 badarg:
	121 Bprint(&bout, "cal: bad argument\n");
	122 }
	123
	124 struct
	125 {
	126 char* word;
	127 int val;
	128 } dict[] =
	129 {
	130 "jan", 1,
	131 "january", 1,
	132 "feb", 2,
	133 "february", 2,
	134 "mar", 3,
	135 "march", 3,
	136 "apr", 4,
	137 "april", 4,
	138 "may", 5,
	139 "jun", 6,
	140 "june", 6,
	141 "jul", 7,
	142 "july", 7,
	143 "aug", 8,
	144 "august", 8,
	145 "sep", 9,
	146 "sept", 9,
	147 "september", 9,
	148 "oct", 10,
	149 "october", 10,
	150 "nov", 11,
	151 "november", 11,
	152 "dec", 12,
	153 "december", 12,
	154 0
	155 };
	156
	157 /*
	158 * convert to a number.
	159 * if its a dictionary word,
	160 * return negative number
	161 */
	162 int
	163 number(char *str)
	164 {
	165 int n, c;
	166 char *s;
	167
	168 for(n=0; s=dict[n].word; n++)
	169 if(strcmp(s, str) == 0)
	170 return -dict[n].val;
	171 n = 0;
	172 s = str;
	173 while(c = *s++) {
	174 if(c<'0' \|\| c>'9')
	175 return 0;
	176 n = n*10 + c-'0';
	177 }
	178 return n;
	179 }
	180
	181 void
	182 pstr(char *str, int n)
	183 {
	184 int i;
	185 char *s;
	186
	187 s = str;
	188 i = n;
	189 while(i--)
	190 if(*s++ == '\0')
	191 s[-1] = ' ';
	192 i = n+1;
	193 while(i--)
	194 if(*--s != ' ')
	195 break;
	196 s[1] = '\0';
	197 Bprint(&bout, "%s\n", str);
	198 }
	199
	200 void
	201 cal(int m, int y, char *p, int w)
	202 {
	203 int d, i;
	204 char *s;
	205
	206 s = p;
	207 d = jan1(y);
	208 mon[2] = 29;
	209 mon[9] = 30;
	210
	211 switch((jan1(y+1)+7-d)%7) {
	212
	213 /*
	214 * non-leap year
	215 */
	216 case 1:
	217 mon[2] = 28;
	218 break;
	219
	220 /*
	221 * 1752
	222 */
	223 default:
	224 mon[9] = 19;
	225 break;
	226
	227 /*
	228 * leap year
	229 */
	230 case 2:
	231 ;
	232 }
	233 for(i=1; i<m; i++)
	234 d += mon[i];
	235 d %= 7;
	236 s += 3*d;
	237 for(i=1; i<=mon[m]; i++) {
	238 if(i==3 && mon[m]==19) {
	239 i += 11;
	240 mon[m] += 11;
	241 }
	242 if(i > 9)
	243 *s = i/10+'0';
	244 s++;
	245 *s++ = i%10+'0';
	246 s++;
	247 if(++d == 7) {
	248 d = 0;
	249 s = p+w;
	250 p = s;
	251 }
	252 }
	253 }
	254
	255 /*
	256 * return day of the week
	257 * of jan 1 of given year
	258 */
	259 int
	260 jan1(int yr)
	261 {
	262 int y, d;
	263
	264 /*
	265 * normal gregorian calendar
	266 * one extra day per four years
	267 */
	268
	269 y = yr;
	270 d = 4+y+(y+3)/4;
	271
	272 /*
	273 * julian calendar
	274 * regular gregorian
	275 * less three days per 400
	276 */
	277
	278 if(y > 1800) {
	279 d -= (y-1701)/100;
	280 d += (y-1601)/400;
	281 }
	282
	283 /*
	284 * great calendar changeover instant
	285 */
	286
	287 if(y > 1752)
	288 d += 3;
	289
	290 return d%7;
	291 }
	292
	293 /*
	294 * system dependent
	295 * get current month and year
	296 */
	297 int
	298 curmo(void)
	299 {
	300 Tm *tm;
	301
	302 tm = localtime(time(0));
	303 return tm->mon+1;
	304 }
	305
	306 int
	307 curyr(void)
	308 {
	309 Tm *tm;
	310
	311 tm = localtime(time(0));
	312 return tm->year+1900;
	313 }