Introduce example flash card program named rote

examples/rote.c

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+#/*────────────────────────────────────────────────────────────────╗
+┌┘ To the extent possible under law, Justine Tunney has waived     │
+│  all copyright and related or neighboring rights to this file,   │
+│  as it is written in the following disclaimers:                  │
+│    • http://unlicense.org/                                       │
+│    • http://creativecommons.org/publicdomain/zero/1.0/           │
+╚─────────────────────────────────────────────────────────────────*/
+#include <ctype.h>
+#include <signal.h>
+#include <stdatomic.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <termios.h>
+
+/**
+ * @fileoverview cosmopolitan flash cards viewer
+ */
+
+struct Card {
+  char* qa[2];
+};
+
+atomic_int g_done;
+
+void onsig(int sig) {
+  g_done = 1;
+}
+
+void* xmalloc(int n) {
+  void* p;
+  if ((p = malloc(n)))
+    return p;
+  perror("malloc");
+  exit(1);
+}
+
+void* xrealloc(void* p, int n) {
+  if ((p = realloc(p, n)))
+    return p;
+  perror("realloc");
+  exit(1);
+}
+
+char* xstrcat(const char* a, const char* b) {
+  char* p;
+  size_t n, m;
+  n = strlen(a);
+  m = strlen(b);
+  p = xmalloc(n + m + 1);
+  memcpy(p, a, n);
+  memcpy(p + n, b, m + 1);
+  return p;
+}
+
+void shuffle(struct Card* a, int n) {
+  while (n > 1) {
+    int i = rand() % n--;
+    struct Card t = a[i];
+    a[i] = a[n];
+    a[n] = t;
+  }
+}
+
+char* trim(char* s) {
+  int i;
+  if (s) {
+    while (isspace(*s))
+      ++s;
+    for (i = strlen(s); i--;) {
+      if (isspace(s[i])) {
+        s[i] = 0;
+      } else {
+        break;
+      }
+    }
+  }
+  return s;
+}
+
+char* readline(FILE* f) {
+  for (;;) {
+    char* line = trim(fgetln(f, 0));
+    if (!line)
+      return 0;
+    if (*line != '#')
+      if (*line)
+        return line;
+  }
+}
+
+char* fill(const char* text, int max_line_width, int* out_line_count) {
+  int text_len = strlen(text);
+  char* result = xmalloc(text_len * 2 + 1);
+  int result_pos = 0;
+  int line_start = 0;
+  int line_count = 1;
+  int i = 0;
+  while (i < text_len && isspace(text[i]))
+    i++;
+  while (i < text_len) {
+    int word_end = i;
+    while (word_end < text_len && !isspace(text[word_end]))
+      word_end++;
+    int word_length = word_end - i;
+    if ((result_pos - line_start) + (result_pos > line_start ? 1 : 0) +
+            word_length >
+        max_line_width) {
+      if (result_pos > line_start) {
+        ++line_count;
+        result[result_pos++] = '\n';
+        line_start = result_pos;
+      }
+    } else if (result_pos > line_start) {
+      result[result_pos++] = ' ';
+    }
+    memcpy(result + result_pos, text + i, word_length);
+    result_pos += word_length;
+    i = word_end;
+    while (i < text_len && isspace(text[i]))
+      i++;
+  }
+  result[result_pos] = '\0';
+  result = xrealloc(result, result_pos + 1);
+  if (out_line_count)
+    *out_line_count = line_count;
+  return result;
+}
+
+void show(const char* text, int i, int n) {
+
+  // get pseudoteletypewriter dimensions
+  struct winsize ws = {80, 25};
+  tcgetwinsize(1, &ws);
+  int width = ws.ws_col;
+  if (width > (int)(ws.ws_col * .9))
+    width = ws.ws_col * .9;
+  if (width > 80)
+    width = 80;
+  width &= -2;
+
+  // clear display
+  printf("\033[H\033[J");
+
+  // display flash card text in middle of display
+  char buf[32];
+  int line_count;
+  char* lines = fill(text, width, &line_count);
+  sprintf(buf, "%d/%d\r\n\r\n", i + 1, n);
+  line_count += 2;
+  char* extra = xstrcat(buf, lines);
+  free(lines);
+  char* tokens = extra;
+  for (int j = 0;; ++j) {
+    char* line = strtok(tokens, "\n");
+    tokens = 0;
+    if (!line)
+      break;
+    printf("\033[%d;%dH%s", ws.ws_row / 2 - line_count / 2 + j + 1,
+           ws.ws_col / 2 - strlen(line) / 2 + 1, line);
+  }
+  free(extra);
+  fflush(stdout);
+}
+
+void usage(FILE* f, const char* prog) {
+  fprintf(f,
+          "usage: %s FILE\n"
+          "\n"
+          "here's an example of what your file should look like:\n"
+          "\n"
+          "  # cosmopolitan flash cards\n"
+          "  # california dmv drivers test\n"
+          "  \n"
+          "  which of the following point totals could result in "
+          "your license being suspended by the dmv?\n"
+          "  4 points in 12 months (middle)\n"
+          "  \n"
+          "  at 55 mph under good conditions a passenger vehicle can stop "
+          "within\n"
+          "  300 feet (not 200, not 400, middle)\n"
+          "  \n"
+          "  two sets of solid double yellow lines spaced two or more feet "
+          "apart indicate\n"
+          "  a BARRIER (do not cross unless there's an opening)\n"
+          "\n"
+          "more specifically, empty lines are ignored, lines starting with\n"
+          "a hash are ignored, then an even number of lines must remain,\n"
+          "where each two lines is a card, holding question and answer.\n",
+          prog);
+}
+
+int main(int argc, char* argv[]) {
+
+  // show help
+  if (argc != 2) {
+    usage(stderr, argv[0]);
+    return 1;
+  }
+  if (!strcmp(argv[1], "-?") ||  //
+      !strcmp(argv[1], "-h") ||  //
+      !strcmp(argv[1], "--help")) {
+    usage(stdout, argv[0]);
+    return 0;
+  }
+
+  // teletypewriter is required
+  if (!isatty(0) || !isatty(1)) {
+    perror("isatty");
+    return 2;
+  }
+
+  // load cards
+  FILE* f = fopen(argv[1], "r");
+  if (!f) {
+    perror(argv[1]);
+    return 3;
+  }
+  int count = 0;
+  struct Card* cards = 0;
+  for (;;) {
+    struct Card card;
+    if (!(card.qa[0] = readline(f)))
+      break;
+    card.qa[0] = strdup(card.qa[0]);
+    if (!(card.qa[1] = readline(f))) {
+      fprintf(stderr, "%s: flash card file has odd number of lines\n", argv[1]);
+      exit(1);
+    }
+    card.qa[1] = strdup(card.qa[1]);
+    cards = xrealloc(cards, (count + 1) * sizeof(struct Card));
+    cards[count++] = card;
+  }
+  fclose(f);
+
+  // randomize
+  srand(time(0));
+  shuffle(cards, count);
+
+  // catch ctrl-c
+  struct sigaction sa;
+  sa.sa_flags = 0;
+  sa.sa_handler = onsig;
+  sigemptyset(&sa.sa_mask);
+  sigaction(SIGINT, &sa, 0);
+
+  // enter raw mode
+  struct termios ot;
+  tcgetattr(1, &ot);
+  struct termios nt = ot;
+  cfmakeraw(&nt);
+  nt.c_lflag |= ISIG;
+  tcsetattr(1, TCSANOW, &nt);
+  printf("\033[?25l");
+
+  // show flash cards
+  int i = 0;
+  while (!g_done) {
+    show(cards[i / 2].qa[i % 2], i / 2, count);
+
+    // press any key
+    char b[8] = {0};
+    read(0, b, sizeof(b));
+
+    // q quits
+    if (b[0] == 'q')
+      break;
+
+    // b or ctrl-b goes backward
+    if (b[0] == 'b' ||  //
+        b[0] == ('B' ^ 0100)) {
+      if (--i < 0)
+        i = count * 2 - 1;
+      i &= -2;
+      continue;
+    }
+
+    // p or ctrl-p goes backward
+    if (b[0] == 'p' ||  //
+        b[0] == ('P' ^ 0100)) {
+      if (--i < 0)
+        i = count * 2 - 1;
+      i &= -2;
+      continue;
+    }
+
+    // up arrow goes backward
+    if (b[0] == 033 &&  //
+        b[1] == '[' &&  //
+        b[2] == 'A') {
+      if (--i < 0)
+        i = count * 2 - 1;
+      i &= -2;
+      continue;
+    }
+
+    // left arrow goes backward
+    if (b[0] == 033 &&  //
+        b[1] == '[' &&  //
+        b[2] == 'D') {
+      if (--i < 0)
+        i = count * 2 - 1;
+      i &= -2;
+      continue;
+    }
+
+    // only advance
+    if (++i == count * 2)
+      i = 0;
+  }
+
+  // free memory
+  for (int i = 0; i < count; ++i)
+    for (int j = 0; j < 2; ++j)
+      free(cards[i].qa[j]);
+  free(cards);
+
+  // cleanup terminal and show cursor
+  tcsetattr(1, TCSANOW, &ot);
+  printf("\033[?25h");
+  printf("\n");
+}