1 files changed, 111 insertions, 0 deletions
diff --git a/src/creole.c b/src/creole.c
new file mode 100644
index 0000000..f69c543
--- /dev/null
+++ b/src/creole.c
@@ -0,0 +1,111 @@
+#include "creole.h"
+
+#include <assert.h>
+#include <ctype.h>
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define LENGTH(x)  (sizeof(x)/sizeof((x)[0]))
+
+#define DEBUG(...) (fprintf(stderr, __VA_ARGS__), fflush(stderr))
+
+void process(const char *begin, const char *end, bool new_block, FILE *out);
+int do_headers(const char *begin, const char *end, bool new_block, FILE *out);
+
+// A parser takes a (sub)string and returns the number of characters consumed, if any.
+//
+// The parameter `new_block` determines whether `begin` points to the beginning of a new block.
+// The sign of the return value determines whether a new block should begin, after the consumed text.
+typedef int (* parser_t)(const char *begin, const char *end, bool new_block, FILE *out);
+
+static parser_t parsers[] = { do_headers };
+
+int do_headers(const char *begin, const char *end, bool new_block, FILE *out) {
+	if (!new_block) { // Headers are block-level elements.
+		return 0;
+	}
+
+	if (*begin != '=') {
+		return 0;
+	}
+
+	unsigned level = 0;
+	while (*begin == '=') {
+		level += 1;
+		begin += 1;
+	}
+	DEBUG("level %d\n", level);
+
+	while (isspace(*begin)) {
+		begin += 1;
+	}
+
+	const char *stop = end;
+	while (stop + 1 != end && stop[1] != '\n') {
+		stop += 1;
+	}
+	while (*stop == '=') {
+		stop -= 1;
+	}
+
+	fprintf(out, "<h%u>", level);
+	process(begin, stop, false, out);
+	fprintf(out, "</h%u>", level);
+
+	return -(stop - begin);
+}
+
+void process(const char *begin, const char *end, bool new_block, FILE *out) {
+	const char *p = begin;
+	while (p < end) {
+		// Eat all newlines if we're starting a block.
+		if (new_block) {
+			while (*p == '\n') {
+				p += 1;
+				if (p == end) {
+					return;
+				}
+			}
+		}
+
+		// Greedily try all parsers.
+		int affected;
+		for (unsigned i = 0; i < LENGTH(parsers); ++i) {
+			DEBUG("%p\n", parsers[i]);
+			affected = parsers[i](p, end, new_block, out);
+			if (affected) {
+				break;
+			}
+		}
+		if (affected) {
+			p += abs(affected);
+		} else {
+			fputc(*p, out);
+			p += 1;
+		}
+
+		if (p + 1 == end) {
+			// Don't print single newline at end.
+			if (*p == '\n') {
+				return;
+			}
+		} else {
+			// Determine whether we've reached a new block.
+			if (p[0] == '\n' && p[1] == '\n') {
+				// Double newline characters separate blocks;
+				// if we've found them, we're starting a new block
+				new_block = true;
+			} else {
+				// ...otherwise the parser gets to decide.
+				new_block = affected < 0;
+			}
+		}
+	}
+}
+
+void render_creole(FILE *out, const char *source, size_t source_length)
+{
+	process(source, source + source_length, true, out);
+}