6 files changed, 183 insertions, 0 deletions
diff --git a/src/omd.c b/src/omd.c
new file mode 100644
index 0000000..5568d27
--- /dev/null
+++ b/src/omd.c
@@ -0,0 +1,145 @@
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include "util/versie.h"
+#include "util/error.h"
+#include "util/debug.h"
+
+static void usage(FILE *f) {
+  fprintf(f,
+      "Gebruik: omd [-hV] <bestand...>\n"
+      "\n"
+      "  -h    Toon deze hulptekst\n"
+      "  -V    Toon versienummer\n");
+}
+
+// Returns pointer to argument array containing the file names
+static char** parse_options(int argc, char **argv) {
+  int opt;
+  while ((opt = getopt(argc, argv, "hV")) != -1) {
+    switch (opt) {
+      case 'h':
+        usage(stdout);
+        exit(0);
+
+      case 'V':
+        drukkedoos_print_versie(stdout, "omd");
+        exit(0);
+
+      case '?':
+        usage(stderr);
+        exit(1);
+    }
+  }
+
+  return argv + optind;
+}
+
+static void reverse_in_place(char *buf, size_t len) {
+  for (size_t i = 0, j = len - 1; i < len / 2; i++, j--) {
+    char c = buf[i];
+    buf[i] = buf[j];
+    buf[j] = c;
+  }
+}
+
+static void process(const char *fname, FILE *f) {
+  size_t cap = 4096;
+  char *buffer = malloc(cap);
+  if (!buffer) print_error_nomem("omd");
+
+  size_t cursor = 0;
+
+  while (true) {
+    DEBUG("cursor=%zu\n", cursor);
+
+    // read a line
+    size_t linelen = 0;
+    while (true) {
+      // grow buffer when small
+      if (cap - cursor < 1024) {
+        cap *= 2;
+        if (cap == 0) {
+          fprintf(stderr, "omd: Regel te lang\n");
+          exit(1);
+        }
+        DEBUG("realloc to cap %zu\n", cap);
+        buffer = realloc(buffer, cap);
+        if (!buffer) print_error_nomem("omd");
+      }
+
+      size_t nr = fread(buffer + cursor, 1, cap - cursor, f);
+      DEBUG("nr=%zu\n", nr);
+      if (nr == 0) {
+        if (feof(f)) {
+          if (cursor == 0) return;
+          linelen = cursor;
+          break;
+        }
+        if (fname) fprintf(stderr, "omd: Fout bij lezen van bestand '%s'\n", fname);
+        else fprintf(stderr, "omd: Fout bij lezen van standaardinvoer\n");
+        exit(1);
+      }
+      char *p = memchr(buffer + cursor, '\n', nr);
+      cursor += nr;
+      if (p != NULL) {
+        linelen = p - buffer;
+        break;
+      }
+    }
+
+    DEBUG("line with len %zu (cursor=%zu)\n", linelen, cursor);
+
+    // we have a newline at cursor+linelen; print all lines that we already have in full
+    size_t linestart = 0;
+    while (true) {
+      reverse_in_place(buffer + linestart, linelen);
+      if (linestart + linelen < cap && buffer[linestart + linelen] == '\n') {
+        size_t nw = fwrite(buffer + linestart, 1, linelen + 1, stdout);
+        if (nw < linelen + 1) exit(1);
+      } else {
+        size_t nw = fwrite(buffer + linestart, 1, linelen, stdout);
+        if (nw < linelen) exit(1);
+        putchar('\n');
+        // no newline in the buffer but nevertheless a completed line means that input is at EOF
+        goto cleanup;
+      }
+
+      linestart += linelen + 1;
+      char *p = memchr(buffer + linestart, '\n', cursor - linestart);
+      if (p == NULL) {
+        DEBUG("no more newlines, moving back from %zu len %zu\n", linestart, cursor - linestart);
+        // move back whatever we have left
+        memmove(buffer, buffer + linestart, cursor - linestart);
+        cursor -= linestart;
+        break;
+      }
+      linelen = p - (buffer + linestart);
+      DEBUG("next line from %zu len %zu\n", linestart, linelen);
+    }
+  }
+
+cleanup:
+  free(buffer);
+}
+
+int entry_omd(int argc, char **argv) {
+  char **args = parse_options(argc, argv);
+  if (*args == NULL) {
+    process(NULL, stdin);
+  } else {
+    while (*args != NULL) {
+      FILE *f = fopen(*args, "r");
+      if (!f) {
+        fprintf(stderr, "omd: Kon bestand '%s' niet openen\n", *args);
+        return 1;
+      }
+      process(*args, f);
+      fclose(f);
+      args++;
+    }
+  }
+  return 0;
+}
diff --git a/src/util/debug.h b/src/util/debug.h
new file mode 100644
index 0000000..9ee7c5f
--- /dev/null
+++ b/src/util/debug.h
@@ -0,0 +1,11 @@
+#pragma once
+
+
+// Uncomment this to enable DEBUG() statements.
+// #define ENABLE_DEBUG
+
+#ifdef ENABLE_DEBUG
+#define DEBUG(...) fprintf(stderr, ">> " __VA_ARGS__)
+#else
+#define DEBUG(...)
+#endif
diff --git a/src/util/error.c b/src/util/error.c
new file mode 100644
index 0000000..e7f1f02
--- /dev/null
+++ b/src/util/error.c
@@ -0,0 +1,9 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include "error.h"
+
+
+void print_error_nomem(const char *progname) {
+  fprintf(stderr, "%s: Kon geen geheugen reserveren!\n", progname);
+  exit(1);
+}
diff --git a/src/util/error.h b/src/util/error.h
new file mode 100644
index 0000000..99a9c77
--- /dev/null
+++ b/src/util/error.h
@@ -0,0 +1,5 @@
+#pragma once
+
+
+__attribute__((noreturn))
+void print_error_nomem(const char *progname);
diff --git a/src/util/versie.c b/src/util/versie.c
new file mode 100644
index 0000000..880823a
--- /dev/null
+++ b/src/util/versie.c
@@ -0,0 +1,7 @@
+#include "versie.h"
+
+void drukkedoos_print_versie(FILE *f, const char *progname) {
+  fprintf(f,
+      "%s, deel van drukkedoos versie %s\n",
+      progname, DRUKKEDOOS_VERSIE);
+}
diff --git a/src/util/versie.h b/src/util/versie.h
new file mode 100644
index 0000000..0f1dafb
--- /dev/null
+++ b/src/util/versie.h
@@ -0,0 +1,6 @@
+#pragma once
+
+#include <stdio.h>
+
+
+void drukkedoos_print_versie(FILE *f, const char *progname);