From b5c5c5cb9e1c728a83596dcc7c4191d012fe1332 Mon Sep 17 00:00:00 2001
From: Paul Martin
Date: Wed, 15 Jan 2025 00:40:32 +0000
Subject: Implement faster min_id handling

---
 data.c     | 31 +++++++++++++++++++++++++++++++
 mastoapi.c | 46 ++++++++++++++++++++++++++++------------------
 snac.h     |  2 ++
 3 files changed, 61 insertions(+), 18 deletions(-)

diff --git a/data.c b/data.c
index ca63084..33947ff 100644
--- a/data.c
+++ b/data.c
@@ -679,6 +679,37 @@ int index_desc_first(FILE *f, char md5[MD5_HEX_SIZE], int skip)
     return 1;
 }
 
+int index_asc_first(FILE *f,char md5[MD5_HEX_SIZE], const char *seek_md5)
+/* reads the first entry of an ascending index, starting from a given md5 */
+{
+    fseek(f, SEEK_SET, 0);
+    while (fread(md5, MD5_HEX_SIZE, 1, f)) {
+        md5[MD5_HEX_SIZE - 1] = '\0';
+        if (strcmp(md5,seek_md5) == 0) {
+            return index_asc_next(f, md5);
+        }
+    }
+    return 0;
+}
+
+int index_asc_next(FILE *f, char md5[MD5_HEX_SIZE])
+/* reads the next entry of an ascending index */
+{
+    for (;;) {
+        /* read an md5 */
+        if (!fread(md5, MD5_HEX_SIZE, 1, f))
+            return 0;
+
+        /* deleted, skip */
+        if (md5[0] != '-')
+            break;
+    }
+
+    md5[MD5_HEX_SIZE - 1] = '\0';
+
+    return 1;
+}
+
 
 xs_list *index_list_desc(const char *fn, int skip, int show)
 /* returns an index as a list, in reverse order */
diff --git a/mastoapi.c b/mastoapi.c
index 21e2a78..c25f78b 100644
--- a/mastoapi.c
+++ b/mastoapi.c
@@ -1339,6 +1339,9 @@ xs_list *mastoapi_timeline(snac *user, const xs_dict *args, const char *index_fn
     const char *since_id = xs_dict_get(args, "since_id");
     const char *min_id   = xs_dict_get(args, "min_id"); /* unsupported old-to-new navigation */
     const char *limit_s  = xs_dict_get(args, "limit");
+    int (*iterator)(FILE *, char *);
+    int initial_status = 0;
+    int ascending = 0;
     int limit = 0;
     int cnt   = 0;
 
@@ -1348,27 +1351,40 @@ xs_list *mastoapi_timeline(snac *user, const xs_dict *args, const char *index_fn
     if (limit == 0)
         limit = 20;
 
-    if (index_desc_first(f, md5, 0)) {
+    if (min_id) {
+        iterator = &index_asc_next;
+        initial_status = index_asc_first(f, md5, MID_TO_MD5(min_id));
+        ascending = 1;
+    }
+    else {
+        iterator = &index_desc_next;
+        initial_status = index_desc_first(f, md5, 0);
+    }
+
+    if (initial_status) {
         do {
             xs *msg = NULL;
 
             /* only return entries older that max_id */
             if (max_id) {
-                if (strcmp(md5, MID_TO_MD5(max_id)) == 0)
+                if (strcmp(md5, MID_TO_MD5(max_id)) == 0) {
                     max_id = NULL;
-
-                continue;
+                    if (ascending)
+                        break;
+                }
+                if (!ascending)
+                    continue;
             }
 
             /* only returns entries newer than since_id */
             if (since_id) {
-                if (strcmp(md5, MID_TO_MD5(since_id)) == 0)
-                    break;
-            }
-
-            if (min_id) {
-                if (strcmp(md5, MID_TO_MD5(min_id)) == 0)
-                    break;
+                if (strcmp(md5, MID_TO_MD5(since_id)) == 0) {
+                    if (!ascending)
+                        break;
+                    since_id = NULL;
+                }
+                if (ascending)
+                    continue;
             }
 
             /* get the entry */
@@ -1440,14 +1456,8 @@ xs_list *mastoapi_timeline(snac *user, const xs_dict *args, const char *index_fn
                 out = xs_list_append(out, st);
                 cnt++;
             }
-            if (min_id) {
-                while (cnt > limit) {
-                    out = xs_list_del(out, 0);
-                    cnt--;
-                }
-            }
 
-        } while ((min_id || (cnt < limit)) && index_desc_next(f, md5));
+        } while ((cnt < limit) && (*iterator)(f, md5));
     }
 
     int more = index_desc_next(f, md5);
diff --git a/snac.h b/snac.h
index 5729a22..65ece5d 100644
--- a/snac.h
+++ b/snac.h
@@ -108,6 +108,8 @@ int index_len(const char *fn);
 xs_list *index_list(const char *fn, int max);
 int index_desc_next(FILE *f, char md5[MD5_HEX_SIZE]);
 int index_desc_first(FILE *f, char md5[MD5_HEX_SIZE], int skip);
+int index_asc_next(FILE *f, char md5[MD5_HEX_SIZE]);
+int index_asc_first(FILE *f, char md5[MD5_HEX_SIZE], const char *seek_md5);
 xs_list *index_list_desc(const char *fn, int skip, int show);
 
 int object_add(const char *id, const xs_dict *obj);
-- 
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