messagegui: hw btn on scroller goes back

Author: thyttan

apps/messagegui/app.js

@@ -338,7 +338,21 @@ function showMessagesScroller(msg, persist, alreadyProcessed) {
       stop : Math.max(idxSpan.stop, alreadyProcessed.idxSpan.stop||0)}
   };
 
+  function identifyDisplayedMsg(scrollIdx) {
+    let firstTitleLinePerMsg = [titleLines[0]];
+    for (let i=1; i<titleLines.length; i++) {
+      if (titleLines[i]-titleLines[i-1] === 1) {continue;}
+      firstTitleLinePerMsg.push(titleLines[i]);
+    }
+    for (let i=titleLines.length-1; i>=0 ; i--) {
+      if (scrollIdx>=firstTitleLinePerMsg[i]) {
+        return MESSAGES[i + alreadyProcessed.idxSpan.start];
+      }
+    }
+  }
+
   let prevScrollIdx; // Used for stopping repeated triggering of next message by the scroller.
+  let prevPrevScrollIdx; // Used to chose how to identify displayed message when selecting with button.
 
   E.showScroller({
     scroll : initScroll*g.getFontHeight(),
@@ -367,32 +381,29 @@ function showMessagesScroller(msg, persist, alreadyProcessed) {
             true, alreadyProcessed);
         }, 40);
       }
+      if (prevPrevScrollIdx!==prevScrollIdx) {prevPrevScrollIdx = prevScrollIdx;}
       prevScrollIdx = scrollIdx;
     },
     select : function(scrollIdx, touch) {
-      let msgSelect;
-      let firstTitleLinePerMsg = [titleLines[0]];
-      for (let i=1; i<titleLines.length; i++) {
-        if (titleLines[i]-titleLines[i-1] === 1) {continue;}
-        firstTitleLinePerMsg.push(titleLines[i]);
-      }
-      for (let i=titleLines.length-1; i>=0 ; i--) {
-        if (scrollIdx>=firstTitleLinePerMsg[i]) {
-          msgSelect = MESSAGES[i + alreadyProcessed.idxSpan.start];
-          break;
-        }
-      }
+      const MSG_SELECT = identifyDisplayedMsg(scrollIdx);
       if (touch.type == 0) {
         WU.show();
-        showMessage(msgSelect.id, true)
+        if (BTN_WATCH) {clearWatch(BTN_WATCH);}
+        showMessage(MSG_SELECT.id, true);
       }
       if (touch.type == 2) {
         WU.show();
-        showMessageSettings(msgSelect)
+        if (BTN_WATCH) {clearWatch(BTN_WATCH);}
+        showMessageSettings(MSG_SELECT);
       }
-    },
-    //back : () => showMessage(messages[idx].id, true)
+    }
   });
+  const BTN_WATCH = setWatch(()=>{
+    WU.show();
+    const SCROLL_IDX_CENTER_SCREEN = prevScrollIdx>prevPrevScrollIdx ?
+      prevScrollIdx-5 : prevScrollIdx+5; // FIXME: `±5` should depend on screen height and font height.
+    showMessage(identifyDisplayedMsg(SCROLL_IDX_CENTER_SCREEN).id, true);
+  }, BTN, {edge:'rising'});
 }
 
 function showMessageSettings(msg) {