config: add (non-working) implementation

I believe there's a lot that's missing here, and honestly I don't
like how messy it feels. I can already see a couple edge cases
where things might break or work weirdly, but for now we can probably
gloss over them...

src/config.c

@@ -1 +1,174 @@
-/* TODO */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "config.h"
+
+#define PMSG(t, x) fprintf(stderr, t ":%s:%d: " x "\n", path, line)
+
+#define BUF_STORE(name) { \
+    if (i >= 10) { \
+        PMSG("error", name " is too big"); \
+        err = 1; \
+    } else { \
+        ibuf[i] = ch; \
+        i++; \
+    } \
+}
+
+config_t *
+parse_config(char *path)
+{
+    FILE *fd;
+    int res, state, line, ws, comment, err, i;
+#define ST_FILENAME     0
+#define ST_EXT          1
+#define ST_START        2
+#define ST_END          3
+#define ST_SKIP_A       4
+#define ST_SKIP_B       5
+#define ST_OPTS         6
+    char ch;
+    char ibuf[11];
+    config_t *conf, *cur;
+
+    fd = fopen(path, "r");
+    if (fd == NULL) {
+        perror("couldn't open config");
+        return NULL;
+    }
+
+    conf = malloc(sizeof(config_t));
+    if (conf == NULL) {
+        perror("couldn't allocate config");
+        return NULL;
+    }
+    memset(conf, 0, sizeof(config_t));
+
+    state = ST_FILENAME;
+    line = 1;
+    ws = comment = err = 0;
+    i = 0;
+    while ((ch = getc(fd)) != EOF) {
+        switch (ch) {
+        case '\t':
+        case ' ':
+            if (comment)
+                continue;
+
+            if (!ws) {
+                i = 0;
+                ws = 1;
+                state++;
+                /* convert offsets to uint32_t (or close enough) */
+                switch (state) {
+                case ST_START:
+                    cur->start = strtoul(ibuf, ibuf+strlen(ibuf), 10);
+                    break;
+                case ST_END:
+                    cur->end = strtoul(ibuf, ibuf+strlen(ibuf), 10);
+                    break;
+                case ST_SKIP_A:
+                    cur->skip_a = strtoul(ibuf, ibuf+strlen(ibuf), 10);
+                    break;
+                case ST_SKIP_B:
+                    cur->skip_b = strtoul(ibuf, ibuf+strlen(ibuf), 10);
+                    break;
+                /* TODO: probably handle ST_OPTS here? */
+                }
+                memset(ibuf, 0, 11);
+            }
+            break;
+        case '\r': /* dos line end */
+            (void)getc(fd);
+        /* FALLTHROUGH */
+        case '\n':
+            cur->next = malloc(sizeof(config_t));
+            if (cur == NULL) {
+                perror("couldn't allocate config");
+                err = 1;
+                break;
+            }
+
+            if (state != ST_OPTS) {
+                PMSG("warn", "line ends early")
+            }
+
+            /* reset state for next line */
+            state = ST_FILENAME;
+            cur = cur->next;
+            memset(cur, 0, sizeof(config_t));
+            ws = i = comment = 0;
+            line++;
+            break;
+        case '#':
+            comment = 1;
+            break;
+        default:
+            if (comment)
+                continue;
+
+            ws = 0;
+
+            /* not a special character, store into buffer */
+            switch (state) {
+            case ST_FILENAME:
+                if (i >= 8) {
+                    PMSG("error", "filename must be less than eight characters");
+                    err = 1;
+                } else {
+                    cur->filename[i] = ch;
+                    i++;
+                }
+                break;
+            case ST_EXT:
+                if (i >= 3) {
+                    PMSG("error", "ext must be less than three characters");
+                    err = 1;
+                } else {
+                    cur->ext[i] = ch;
+                    i++;
+                }
+                break;
+            case ST_START:
+                BUF_STORE("start byte")
+            case ST_END:
+                BUF_STORE("end byte")
+            case ST_SKIP_A:
+                BUF_STORE("first byte skip")
+            case ST_SKIP_B:
+                BUF_STORE("second byte skip")
+            case ST_OPTS:
+                /* TODO */
+            default:
+                PMSG("error", "too many columns");
+                err = 1;
+            }
+        }
+
+        if (err)
+            break;
+    }
+
+
+    if (err) {
+        free_config(conf);
+        conf = NULL;
+    }
+
+    fclose(fd);
+    return conf;
+}
+
+void
+free_config(config_t *conf)
+{
+    config_t *cur, *prev;
+
+    cur = conf;
+    while (cur != NULL) {
+        prev = cur;
+        cur = cur->next;
+        free(prev);
+    }
+}

src/config.h

@@ -11,8 +11,8 @@ struct conf_opts_t {
 typedef struct config_t {
     char     filename[9];
     char     ext[4];
-    uint16_t start;
+    uint32_t start;
-    uint16_t end;
+    uint32_t end;
     uint16_t skip_a;
     uint16_t skip_b;
     struct conf_opts_t opts;