fix(screens/log): jump-to-top if entries_.size() > capacity()

Resolves #89

CHANGELOG.md

@@ -12,6 +12,7 @@ This project adheres to [Semantic Versioning](https://semver.org)
 * Screens/details: Correctly print empty fields.
 * Screens/index: Correctly print Unicode strings. #83
 * Screens/log: Possible MT-related crashes when marking log entries as seen.
+* Screens/log: Correctly jump-to-top if entries do not fit in screen. #89
 
 ## [v0.8.0] - 2019-05-26
 

src/tui/screens/log.cpp

@@ -45,7 +45,7 @@ namespace bookwyrm::tui::screen {
         });
     }
 
-    /* Figure out how many entries we can fit on screen given an entry to start from. */
+    /* Figure out how many entries we can fit on screen given a reverse entry to start from. */
     int log::capacity(const entry_ri &start) const
     {
         assert(!entries_mutex_.try_lock());
@@ -57,6 +57,18 @@ namespace bookwyrm::tui::screen {
         });
     }
 
+    /* Figure out how many entries we can fit on screen given a forward entry to start from. */
+    int log::fcapacity(const entry_i &start) const
+    {
+        assert(!entries_mutex_.try_lock());
+
+        int lines = get_height();
+        return std::count_if(start, cend(entries_), [&](const auto e) {
+            lines -= std::ceil(static_cast<double>(e.second.length()) / get_width());
+            return lines >= 0;
+        });
+    }
+
     void log::paint()
     {
         erase();
@@ -204,7 +216,7 @@ namespace bookwyrm::tui::screen {
             (*detached_at_)--;
             break;
         case top:
-            detached_at_ = entries_.crend() - 1;
+            detached_at_ = entries_.crend() - fcapacity(entries_.cbegin());
             break;
         case bot:
             detached_at_ = entries_.crbegin();

src/tui/screens/log.hpp

@@ -31,12 +31,20 @@ namespace bookwyrm::tui::screen {
         std::function<bool(void)> is_log_focused_;
 
         std::vector<core::log_pair> entries_, unread_entries_;
-
         using entry_ri = decltype(entries_.crbegin());
+        using entry_i = decltype(entries_.cbegin());
         std::optional<entry_ri> detached_at_;
 
+        /*
+         * Entries will be modified both by calls to `log_entry()` from plugins
+         * and by calls to `mark_read()` when the log is toggled.
+         * Protects `{,unread_}entries_` and `detached_at_` above.
+         */
+        mutable std::mutex entries_mutex_;
+
         void maybe_update_detached(std::function<void()> &&fun);
         int capacity(const entry_ri &start) const;
+        int fcapacity(const entry_i &start) const;
         void print_entry(int &y, const entry_ri entry);
     };