[ADD] Basic header check in configure

It doesn't exactly conform to C99 standards, but it is good enough for
Parsee as a whole.

configure.c

@@ -11,6 +11,7 @@
 #include <sys/stat.h>
 #include <stdbool.h>
 #include <dirent.h>
+#include <ctype.h>
 #include <errno.h>
 #include <unistd.h>
 #include <stdlib.h>
@@ -431,6 +432,81 @@ write_ayas(FILE *makefile, str_array_t *sources)
         free(obj);
     }
 }
+
+static void
+analyse_dependencies(FILE *makefile, char *src)
+{
+    FILE *source = fopen(src, "r");
+    char *lineptr = NULL;
+    char *dn = strdup(src), *dirn;
+    size_t len = 0;
+
+    dirn = dirname(dn);
+
+    while (getline(&lineptr, &len, source) != -1)
+    {
+        char *corrptr = lineptr, *nl, *chevron, *quote, *cutoff;
+        char *basedir, *srcdir, *incdir, *tmp;
+        struct stat statinfo;
+
+        /* try to parse the line */
+        if ((nl = strchr(corrptr, '\n')))
+        {
+            *nl = '\0';
+        }
+
+        while (*corrptr && isblank(*corrptr))
+        {
+            corrptr++;
+        }
+        if (strncmp(corrptr, "#include \"", 10) &&
+            strncmp(corrptr, "#include <", 10))
+        {
+            continue;
+        }
+        corrptr += 10;
+        chevron = strchr(corrptr, '>');
+        chevron = chevron ? chevron : corrptr + strlen(corrptr);
+        quote = strchr(corrptr, '"');
+        quote = quote ? quote : corrptr + strlen(corrptr);
+        cutoff = chevron < quote ? chevron : quote;
+
+        *cutoff = '\0';
+
+        /* if we found something, try to resolve it */
+        tmp = string_cat(dirn, "/");
+        basedir = string_cat(tmp, corrptr);
+        free(tmp);
+        if (!stat(basedir, &statinfo))
+        {
+            fprintf(makefile, " %s", basedir);
+            free(basedir);
+            continue;
+        }
+        free(basedir);
+
+        srcdir = string_cat("src/", corrptr);
+        if (!stat(srcdir, &statinfo))
+        {
+            fprintf(makefile, " %s", srcdir);
+            free(srcdir);
+            continue;
+        }
+        free(srcdir);
+
+        incdir = string_cat("src/include/", corrptr);
+        if (!stat(incdir, &statinfo))
+        {
+            fprintf(makefile, " %s", incdir);
+            free(incdir);
+            continue;
+        }
+        free(incdir);
+    }
+    free(lineptr);
+    free(dn);
+    fclose(source);
+}
 static int
 main_build(int argc, char *argv[])
 {
@@ -513,7 +589,9 @@ main_build(int argc, char *argv[])
         char *ofl = string_rep_ext(src, ".c", ".o");
         char *obj = string_cat("build", ofl + 3);
 
-        fprintf(makefile, "%s: %s\n", obj, src);
+        fprintf(makefile, "%s: %s", obj, src);
+        analyse_dependencies(makefile, src);
+        fprintf(makefile, "\n");
         {
             str_array_t *s = split(obj);
             ssize_t j;