add option parsing code

src/game/opts.c

@@ -1,21 +1,62 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+
 #include "../error.h"
 #include "../util/compat.h"
 #include "paths.h"
 
+#define BUF_SIZE 32
+
 /* attempts to load the options,
    returns 1 upon failure */
 int load_opts(void) {
     if (!path_opts) return 1;
-    if (!faccess(path_opts, FA_W | FA_R)) {
-        error("attempted to load opts file, but the given path wasn't writable");
+    if (faccess(path_opts, FA_R)) {
+        error("attempted to load opts file, but the given path wasn't readable");
         return 1;
     }
 
+    // open the file in read mode
+    FILE* fptr = fopen(path_opts, "r");
+    if (!fptr) return 1;
+
+    // read the file line by line
+    char buf[BUF_SIZE]; // buffer will contain \0 terminated string. fgets stores into the buffer until \n or EOF
+    while (fgets(buf, BUF_SIZE, fptr)) {
+        unsigned key_len = 0;
+        unsigned val_len = 0;
+        char* key = NULL;
+        char* val = NULL;
+        bool feq = false; // whether we found the equal sign
+
+        for (unsigned i = 0; i < BUF_SIZE; i++) {
+            // handling of special characters (in the order of most common to least)
+            if (buf[i] == ' ') continue;  // spaces are ignored; neither keys or values can contain spaces
+            if (buf[i] == '\t') continue; // ^ same with tabs
+            if (buf[i] == '\n') break;    // don't check \0, since if \n isn't present, the string will be BUF_SIZE length
+            if (buf[i] == '#') break;     // stop the rest of the data is a comment
+
+            // increment the key/value length if set
+            if (val) val_len++; // first check if value is set, as it is set last
+            else if (key) key_len++;
+
+            // get the values
+            if (!key) key = &buf[i];              // store the key's pointer at this point
+            else if (!feq) feq = (buf[i] == '='); // otherwise store whether we've found the equal sign
+            else if (!val) val = &buf[i];       // otherwise store the start of the value pointer PERF: we can optimise this further by stopping the loop as soon as we reach another space at this point
+            else { }
+        }
+
+        // ignore if either the key or value haven't been set
+        if (!key || !val) continue;
         // TODO: load opts from the file
         // the options shall be loaded as key-value-pairs
         // lines starting with # are seen as comments
         // the keys are stored on the left size, and the values on the right.
         // if a field couldn't be parsed the program is not allowed to fail. I'd say we fix the field for the user.
+    }
 
+    fclose(fptr);
     return 0;
 }