[doc] book: Added hello_wiki_mongo.opa example.

doc/book/hello_wiki/hello_wiki_mongo.opa

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+/**
+ * {1 Import the high-level MongoDB API module}
+ *
+ * For the low-level API see the package stdlib.apis.mongo
+ */
+import stdlib.apis.{mongo}
+
+/**
+ * {1 Import standard classes of bootstrap css}
+ *
+ * see http://twitter.github.com/bootstrap/
+ */
+import stdlib.themes.bootstrap
+
+/**
+ * {1 Import templates}
+ */
+import stdlib.web.template
+
+/**
+ * {1 Database and database interaction}
+ */
+
+/**
+ * The basic info. about the database and table location.
+ */
+type page = {
+  _id : string;
+  _rev : Bson.int32;
+  content : string;
+}
+
+/**
+ * We work at level 1, run-time type-checked storage of a collection of OPA values.
+ *
+ * The Mongo.pkg type provides convenience functions for building select and update documents.
+ **/
+(wiki_collection,wiki_pkg) = (MongoCollection.openpkgfatal("default","db","wiki"):Mongo.pkg(page))
+pageselect(v) = wiki_pkg.select(Bson.opa2doc(v))
+pageupdate(v) = wiki_pkg.update(Bson.opa2doc(v))
+
+/**
+ * Indexes aren't automatic in MongoDB apart from the non-removable _id index.
+ * Since we're searching on _rev as well, we need a separate index.
+ **/
+_ = MongoCollection.create_index(wiki_collection, "db.wiki", Bson.opa2doc({_id=1; _rev=1}), 0)
+
+/**
+ * Retrieves a json document from the database
+ *
+ * @param docid The id of the document to retrieve (arbitrary string)
+ * @return A Template.content
+ */
+get_content(docid) =
+  default = Template.text("This page is empty. Double-click to edit.")
+  extract_content(record:page) = record.content
+  // Order by reverse _rev to get highest numbered _rev.
+  orderby = {some=Bson.opa2doc({_rev=-1})}
+  match MongoCollection.find_one(MongoCollection.orderby(wiki_collection,orderby),pageselect({_id=docid})) with
+  | {success=page} ->
+     source = extract_content(page)
+     (match Template.try_parse(Template.default, source) with
+      | {~success} -> success
+      | {failure=_} -> Template.text(source))
+  | {failure={NotFound}} ->
+     default
+  | {~failure} ->
+     do jlog("hello_wiki_mongo: failure={MongoDriver.string_of_failure(failure)}")
+     default
+
+/**
+ * Read the content associated to a topic from the database and return the
+ * corresponding source code.
+ *
+ * @param topic A topic (arbitrary string).
+ * @return If a page has been saved in for [topic], the source code for this
+ * page. Otherwise, the source code for the default page.
+ */
+@publish load_source(topic) =
+  Template.to_source(Template.default, get_content(topic))
+
+/**
+ * Read the content associated to a topic from the database and return the
+ * corresponding xhtml, ready to insert.
+ *
+ * @param topic A topic (arbitrary string).
+ * @return If a page has been saved in for [topic], the xhtml for this
+ * page. Otherwise, the xhtml for the default page.
+ *
+ * Note: This function does not perform any caching.
+ */
+@publish load_rendered(topic) =
+  Template.to_xhtml(Template.default, get_content(topic))
+
+/**
+ * Accept source code, save the corresponding document in the database.
+ *
+ * @param topic A topic (arbitrary string).
+ * @param source Source code to store at this topic. If this source code
+ * is syntactically valid, store the template datastructure
+ * corresponding to its content [Template.content].
+ * Otherwise, the source code is implicitly replaced by the document
+ * representing this raw code and this document is saved in the database.
+ *
+ * @return In case of success, the xhtml for the page that has just been
+ * saved. In case of failure, an error message.
+ */
+@publish save_source(topic, source) =
+  select = pageselect({_id=topic})
+  update = pageupdate({`$set`={content=source}; `$inc`={_rev=(1:Bson.int32)}})
+  // Upsert this so we create it if it isn't there
+  result = MongoCollection.updatee(MongoCollection.upsert(wiki_collection),select,update)
+  if MongoDriver.is_error(result)
+  then <>Error: {MongoDriver.pretty_of_result(result)}</>
+  else
+    match Template.try_parse(Template.default, source) with
+    | ~{success}    -> Template.to_xhtml(Template.default, success)
+    | {failure = _} -> <>Error: {source}</>
+
+/**
+ * {1 User interface}
+ */
+
+/**
+ * Set the user interface in edition mode.
+ *
+ * Load the source code for a topic, display an editable zone for this source code.
+ *
+ * @param topic The topic to edit.
+ */
+edit(topic) =
+   do Dom.set_value(#edit_content, load_source(topic))
+   do Dom.hide(#show_content)
+   do Dom.show(#edit_content)
+   do Dom.give_focus(#edit_content)
+   void
+
+/**
+ * Set the user interface in reading mode.
+ *
+ * Save the source code for a topic (extracted from [#edit_content]),
+ * display the rendered version.
+ *
+ * @param topic The topic to save.
+ */
+save(topic) =
+   content = save_source(topic, Dom.get_value(#edit_content))
+   do Dom.transform([#show_content <- content])
+   do Dom.hide(#edit_content)
+   do Dom.show(#show_content)
+   void
+
+/**
+ * Main user interface
+ *
+ * @param topic The topic being consulted
+ * @return A resource, ready to be passed to a dispatcher.
+ */
+display(topic) =
+   Resource.styled_page("About {topic}", ["/resources/css.css"],
+     <div class="topbar"><div class="fill"><div class="container">
+       <div id=#logo></div>
+     </div></div></div>
+     <div class="content container">
+       <div class="page-header"><h1>About {topic}</></>
+       <div class="well" id=#show_content ondblclick={_ -> edit(topic)}>
+         {load_rendered(topic)}
+       </>
+       <textarea rows="30" id=#edit_content onblur={_ -> save(topic)}></>
+     </div>
+   )
+
+/**
+ * {1 Main application}
+ */
+
+/**
+ * Dispatch requests to the user interface
+ *
+ * Note: The empty request is dispatched as if it were "Hello".
+ */
+start =
+   | {path = [] ... } ->
+       display("Hello")
+   | {~path ...}      ->
+       display(String.capitalize(String.to_lower(String.concat("::", path))))
+
+/**
+ * Statically embed a bundle of resources
+ */
+server = Server.of_bundle([@static_include_directory("resources")])
+
+/**
+ * Launch the [start] dispatcher
+ */
+server = Server.simple_dispatch(start)