From 8f4d2dd417e7fd7a77a1d403101f1b47c13affdf Mon Sep 17 00:00:00 2001
From: Artyom <yom@artyom.me>
Date: Sun, 19 Jun 2016 19:20:28 +0300
Subject: [PATCH] Merging for item notes

---
 src/JS.hs      | 52 ++++++++++++++++++++++++++++++++++++++------------
 src/Main.hs    | 19 +++++++++++++-----
 src/View.hs    |  6 ++++--
 static/css.css |  2 ++
 4 files changed, 60 insertions(+), 19 deletions(-)

diff --git a/src/JS.hs b/src/JS.hs
index 9caba07..4bcd483 100644
--- a/src/JS.hs
+++ b/src/JS.hs
@@ -405,12 +405,28 @@ makeTraitEditor =
     $(sectionNode).append(area, br, cancelBtn, markdown);
   |]
 
--- | Dynamically creates a 'View.markdownEdito' (but specifically for item
+{- Note [blurb diffing]
+~~~~~~~~~~~~~~~~~~~~~~~
+
+A note on why we need 'empty' in 'makeItemNotesEditor'.
+
+Assume that the notes are empty. The text in the area, therefore, will be some default blurb (“# Links, #Imports, #Usage”, etc). Suppose the user edits it. What will be sent to the server?
+
+  * original: blurb
+  * our version: modified blurb
+
+What will happen next? The server will compare it to the value currently at the server (i.e. an empty string), and think that the blurb *was* on the server but got deleted while the client was doing editing. This is wrong, and will result in a diff popup comparing an edited blurb to an empty string. To prevent this, we pass 'empty' to 'makeItemNotesEditor' – if we're using a blurb, we'll pass an empty string as the original.
+
+-}
+
+-- | Dynamically creates a 'View.markdownEditor' (but specifically for item
 -- notes). See Note [dynamic interface].
 makeItemNotesEditor :: JSFunction a => a
 makeItemNotesEditor =
+  -- See Note [blurb diffing]
   makeJSFunction "makeItemNotesEditor"
-    ["notesNode", "sectionNode", "textareaUid", "content", "itemId"]
+                 ["notesNode", "sectionNode", "textareaUid",
+                  "empty", "content", "itemId"]
   [text|
     $(sectionNode).html("");
     area = $("<textarea>", {
@@ -423,7 +439,7 @@ makeItemNotesEditor =
       "value" : "Save",
       "type"  : "button" })[0];
     saveBtn.onclick = function () {
-      submitItemNotes(notesNode, itemId, area.value); };
+      submitItemNotes(notesNode, itemId, empty ? "" : content, area.value); };
     // Can't use $()-generation here because then the <span> would have
     // to be cloned (since we're inserting it multiple times) and I don't
     // know how to do that.
@@ -508,16 +524,28 @@ submitItemEcosystem =
 
 submitItemNotes :: JSFunction a => a
 submitItemNotes =
-  makeJSFunction "submitItemNotes" ["node", "itemId", "s"]
+  makeJSFunction "submitItemNotes"
+                 ["node", "itemId", "original", "ours"]
   [text|
-    $.post("/haskell/set/item/"+itemId+"/notes", {content: s})
-     .done(function (data) {
+    $.post({
+      url: "/haskell/set/item/"+itemId+"/notes",
+      data: {
+        original: original,
+        content: ours },
+      success: function (data) {
+        $.magnificPopup.close();
         $(node).replaceWith(data);
-        switchSection(node, "expanded");
+        // Switching has to be done here and not in 'Main.renderItemNotes'
+        // because $.post is asynchronous and will be done *after*
+        // switchSection has worked.
+        switchSection(node, "expanded"); },
+      statusCode: {
+        409: function (xhr, st, err) {
+          modified = xhr.responseJSON["modified"];
+          merged   = xhr.responseJSON["merged"];
+          showDiffPopup(ours, modified, merged, function (x) {
+            submitItemNotes(node, itemId, modified, x) }); } }
       });
-    // Switching has to be done here and not in 'Main.renderItemNotes'
-    // because $.post is asynchronous and will be done *after*
-    // switchSection has worked.
   |]
 
 -- | Add a pro to some item.
@@ -554,8 +582,8 @@ submitTrait =
     $.post({
       url: "/haskell/set/item/"+itemId+"/trait/"+traitId,
       data: {
-        original : original,
-        content  : ours },
+        original: original,
+        content: ours },
       success: function (data) {
         $.magnificPopup.close();
         $(node).replaceWith(data);
diff --git a/src/Main.hs b/src/Main.hs
index 646ecac..37d0e88 100644
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -475,12 +475,21 @@ setMethods = Spock.subcomponent "set" $ do
     lucidIO $ renderItemEcosystem item
   -- Item notes
   Spock.post (itemVar <//> "notes") $ \itemId -> do
+    original <- param' "original"
     content' <- param' "content"
-    invalidateCache' (CacheItemNotes itemId)
-    (edit, item) <- dbUpdate (SetItemNotes itemId content')
-    addEdit edit
-    category <- dbQuery (GetCategoryByItem itemId)
-    lucidIO $ renderItemNotes category item
+    modified <- view (notes.mdText) <$> dbQuery (GetItem itemId)
+    if modified == original
+      then do
+        invalidateCache' (CacheItemNotes itemId)
+        (edit, item) <- dbUpdate (SetItemNotes itemId content')
+        addEdit edit
+        category <- dbQuery (GetCategoryByItem itemId)
+        lucidIO $ renderItemNotes category item
+      else do
+        setStatus HTTP.status409
+        json $ M.fromList [
+          ("modified" :: Text, modified),
+          ("merged" :: Text, merge original content' modified)]
   -- Trait
   Spock.post (itemVar <//> traitVar) $ \itemId traitId -> do
     original <- param' "original"
diff --git a/src/View.hs b/src/View.hs
index 90249fb..4ec4321 100644
--- a/src/View.hs
+++ b/src/View.hs
@@ -810,6 +810,8 @@ renderItemInfo cat item = cached (CacheItemInfo (item^.uid)) $ do
   let bg = hueToDarkColor $ getItemHue cat item
   let thisId = "item-info-" <> uidToText (item^.uid)
       this   = JS.selectId thisId
+  let bodyNode = JS.selectChildren (JS.selectParent this)
+                                   (JS.selectClass "item-body")
   div_ [id_ thisId, class_ "item-info",
         style_ ("background-color:" <> bg)] $ do
 
@@ -836,8 +838,6 @@ renderItemInfo cat item = cached (CacheItemInfo (item^.uid)) $ do
     section "editing" [] $ do
       -- When the info/header node changes its group (and is hence
       -- recolored), item's body has to be recolored too
-      let bodyNode = JS.selectChildren (JS.selectParent this)
-                                       (JS.selectClass "item-body")
       let formSubmitHandler formNode =
             JS.submitItemInfo (this, bodyNode, item^.uid, formNode)
       form_ [onFormSubmit formSubmitHandler] $ do
@@ -1124,6 +1124,8 @@ renderItemNotes category item = cached (CacheItemNotes (item^.uid)) $ do
               JS.makeItemNotesEditor (
                    this, JS.selectUid editingSectionUid,
                    textareaUid,
+                   -- See Note [blurb diffing]
+                   markdownNull (item^.notes),
                    contents,
                    item^.uid) <>
               JS.switchSection (this, "editing" :: Text) <>
diff --git a/static/css.css b/static/css.css
index afbcdb3..a856f9d 100644
--- a/static/css.css
+++ b/static/css.css
@@ -216,6 +216,8 @@ textarea.fullwidth {
 }
 
 .diff-choices > * > .text {
+  white-space: pre-wrap;
+  font-family: monospace;
   border: 1px solid gray;
   padding: 5px 10px;
   margin: 5px 0px;