1 files changed, 149 insertions, 0 deletions
diff --git a/src/timediff.c b/src/timediff.c
new file mode 100644
index 0000000..3a988e0
--- /dev/null
+++ b/src/timediff.c
@@ -0,0 +1,149 @@
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+
+static char *
+get_tty_name(void)
+{ /* Returns the name of the tty connected to the file descriptor for
+     `stdin'. */
+  return ttyname(STDIN_FILENO);
+}
+
+static char *
+get_filename(void)
+{ /* Generate the filename to be used for the current tty. Uses both
+     the user ID of the calling user and the name of the current tty
+     to make it unique. */
+  char *filename = malloc(sizeof(char) * 255);
+  char *tty = get_tty_name();
+  char *pch;
+
+  while ((pch = strchr(tty, '/')))
+    *pch = '_';
+
+  sprintf(filename, "/tmp/baps1_%u_%s", getuid(), tty);
+
+  return filename;
+}
+
+static time_t
+load_previous_time(char *filename)
+{ /* Loads the previously saved timestamp from FILENAME. This function
+     assumes the file exists and is readable. */
+  FILE *timefile = fopen(filename, "r");
+  time_t prev;
+
+  fscanf(timefile, "%ld", &prev);
+  fclose(timefile);
+
+  return prev;
+}
+
+static time_t
+get_previous_time(char *filename)
+{ /* Tries to get the previously saved timestamp from FILENAME, but if
+     it can't read the file returns 0. */
+  time_t prev;
+
+  if (access(filename, R_OK) == 0) {
+    prev = load_previous_time(filename);
+  }
+  else {
+    prev = 0;
+  }
+
+  return prev;
+}
+
+static int
+get_tty_number(void)
+{ /* Gets the number of the current tty. It assumes that the number is
+     an integer and consists of everything after the last `/' of the
+     tty's name. */
+  char *tty = get_tty_name();
+  char *num = strrchr(tty, '/') + 1;
+
+  return atoi(num);
+}
+
+static char
+get_tty_type(void)
+{ /* Gets the type of the tty represented by the first letter of the
+     type, either `t' or `p'. Assumes that the type comes immediately
+     after `/dev/'. */
+  char *tty = get_tty_name();
+
+  strtok(tty, "/");             /* dev */
+
+  return strtok(NULL, "/")[0];
+}
+
+static int
+save_current_time(char *filename)
+{ /* Save the timestamp for this moment to FILENAME. Returns `1' when
+     succesful, `0' when the file couldn't be opened. */
+  FILE *timefile = fopen(filename, "w");
+  time_t now;
+
+  if (!timefile)
+    return 0;
+
+  time(&now);
+  fprintf(timefile, "%ld", now);
+  fclose(timefile);
+
+  return 1;
+}
+
+static void
+print_time_since(time_t lasttime)
+{ /* Print the hours, minutes and seconds that have passed since
+     LASTTIME to `stdout'. */
+  double h, m, s;
+  time_t now;
+
+  time(&now);
+  s = difftime(now, lasttime);
+
+  if (s >= 60.0) {
+    m = floor(s / 60.0);
+    s -= m * 60;
+
+    if (m >= 60.0) {
+      h = floor(m / 60.0);
+      m -= h * 60;
+
+      printf("%.0lfh", h);
+    }
+
+    printf("%.0lfm", m);
+  }
+
+  printf("%.0lfs", s);
+}
+
+void
+timediff(void)
+{ /* This function prints a single letter represetation of the type
+     and number of the current tty and the time elapsed since the last
+     call to this program on this tty, or `new'. It then saves a
+     timestamp to a file in /tmp/ so that it can check the elapsed
+     time during its next run. */
+  char *filename = get_filename();
+  time_t lasttime = get_previous_time(filename);
+
+  printf("%c%d:", get_tty_type(), get_tty_number());
+
+  if (lasttime > 0) {
+    print_time_since(lasttime);
+  }
+  else {
+    puts("new");
+  }
+
+  save_current_time(filename);
+  free(filename);
+}