From 14419f066973d26192bea9b97707bd872af772c7 Mon Sep 17 00:00:00 2001
From: Paul Duncan <pabs@pablotron.org>
Date: Thu, 2 Mar 2023 17:09:02 -0500
Subject: initial commit

---
 section-parse.c | 120 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 120 insertions(+)
 create mode 100644 section-parse.c

(limited to 'section-parse.c')

diff --git a/section-parse.c b/section-parse.c
new file mode 100644
index 0000000..78fda1f
--- /dev/null
+++ b/section-parse.c
@@ -0,0 +1,120 @@
+//
+// section-parse: scan standard input and do the following:
+//
+// 1. look for a section that begins with "test-text "STUFF/foo" and ends
+//    with a blank line.
+// 2. print the "bar.DIGITS" suffix for each line in the section
+//
+// Build:
+//   cc -std=c17 -W -Wall -Wextra -Werror -pedantic -O2 -o section-parse{,.c}
+//
+// Example:
+//   > cc -std=c17 -W -Wall -Wextra -Werror -pedantic -O2 -o section-parse{,.c}
+//   > ./section-parse < input.txt
+//   bar.1
+//   bar.2
+//   bar.3
+//   bar.4
+//
+
+#include <stdlib.h> // exit()
+#include <stdio.h> // fgets(), feof()
+#include <string.h> // memcmp(), strlen()
+#include <stdbool.h> // bool
+
+// section header line prefix
+// (used by is_header())
+static const char HEAD_PREFIX[] = "test-text \"";
+static const size_t HEAD_PREFIX_LEN = sizeof(HEAD_PREFIX) - 1;
+
+// section footer line suffix
+// (used by is_header())
+static const char HEAD_SUFFIX[] = "/foo\"\n";
+static const size_t HEAD_SUFFIX_LEN = sizeof(HEAD_SUFFIX) - 1;
+
+/**
+ * Return true if the given line is a section header, and false
+ * otherwise.
+ */
+static bool is_header(const char * const s) {
+  const size_t len = strlen(s);
+
+  // check string length
+  if (len < (HEAD_PREFIX_LEN + HEAD_SUFFIX_LEN)) {
+    return false;
+  }
+
+  // compare line prefix and suffix and return true if they both match
+  return !memcmp(s, HEAD_PREFIX, HEAD_PREFIX_LEN) &&
+         !memcmp(s + len - HEAD_SUFFIX_LEN, HEAD_SUFFIX, HEAD_SUFFIX_LEN);
+}
+
+/**
+ * Return true if the given line is a section footer, and false
+ * otherwise.
+ */
+static bool is_footer(const char * const s) {
+  const size_t len = strlen(s);
+
+  for (size_t i = 0; i < len; i++) {
+    if (s[i] != ' ' && s[i] != '\n') {
+      // found non-space character, return false
+      return false;
+    }
+  }
+
+  // return true
+  return true;
+}
+
+/**
+ * Match ".DIGITS" suffix on given line and print "bar.DIGITS" to standard
+ * output.
+ *
+ * Exits with a non-zero error code if the given line is invalid.
+ */
+static void print_body_line(const char * const s) {
+  const size_t len = strlen(s);
+
+  // check line length
+  if (len < 2) {
+    fprintf(stderr, "short line\n");
+    exit(-1);
+  }
+
+  // find trailing '.'
+  // (note: technically this should probably use isdigit() too)
+  size_t pos = len - 2;
+  while (pos > 0 && s[pos] != '.') {
+    pos--;
+  }
+
+  // check to make sure we found trailing '.'
+  if (s[pos] != '.') {
+    fprintf(stderr, "invalid line: %s", s);
+    exit(-1);
+  }
+
+  // print trailing digits
+  // (note: match also includes trailing newline)
+  printf("bar.%s", s + pos + 1);
+}
+
+int main() {
+  char buf[1024]; // line buffer
+  bool in_body = false; // parse state
+
+  // read lines from standard input
+  while (fgets(buf, sizeof(buf), stdin) && !feof(stdin)) {
+    if ((!in_body && is_header(buf)) || (in_body && is_footer(buf))) {
+      // toggle state
+      in_body = !in_body;
+    } else if (in_body) {
+      // print body line
+      print_body_line(buf);
+    }
+  }
+
+  // return success
+  return 0;
+}
-- 
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