9: Add POC for actor templates

- This commit adds a proof-of-concept for retrieving actor template
  types. These are actors using the `worldbuilding.isTemplate` flag set
  to true. If there are multiple actors with that flag set to true,
  clicking the create actor button will pull up a prompt to choose from
  one of those types, which will then create an actor by duplicating
  the template actor's data. The flag will be unset on the new actor.

module/simple.js

@@ -8,6 +8,7 @@
 import { SimpleActor } from "./actor.js";
 import { SimpleItemSheet } from "./item-sheet.js";
 import { SimpleActorSheet } from "./actor-sheet.js";
+import { preloadHandlebarsTemplates } from "./templates.js";
 
 /* -------------------------------------------- */
 /*  Foundry VTT Initialization                  */
@@ -89,4 +90,184 @@ Hooks.once("init", async function() {
     return value.slugify({strict: true});
   });
 
+  // Preload template partials.
+  preloadHandlebarsTemplates();
 });
+
+/**
+ * Adds the actor template context menu.
+ */
+Hooks.on("getActorDirectoryEntryContext", (html, options) => {
+  // Define an actor as a template.
+  options.push({
+    name: game.i18n.localize("SIMPLE.DefineTemplate"),
+    icon: '<i class="fas fa-stamp"></i>',
+    condition: li => {
+      const actor = game.actors.get(li.data("entityId"));
+      return !actor.getFlag("worldbuilding", "isTemplate");
+    },
+    callback: li => {
+      const actor = game.actors.get(li.data("entityId"));
+      actor.setFlag("worldbuilding", "isTemplate", true);
+    }
+  });
+
+  // Undefine an actor as a template.
+  options.push({
+    name: game.i18n.localize("SIMPLE.UnsetTemplate"),
+    icon: '<i class="fas fa-times"></i>',
+    condition: li => {
+      const actor = game.actors.get(li.data("entityId"));
+      return actor.getFlag("worldbuilding", "isTemplate");
+    },
+    callback: li => {
+      const actor = game.actors.get(li.data("entityId"));
+      actor.setFlag("worldbuilding", "isTemplate", false);
+    }
+  });
+});
+
+/**
+ * Adds the item template context menu.
+ */
+Hooks.on("getItemDirectoryEntryContext", (html, options) => {
+  // Define an item as a template.
+  options.push({
+    name: game.i18n.localize("SIMPLE.DefineTemplate"),
+    icon: '<i class="fas fa-stamp"></i>',
+    condition: li => {
+      const item = game.items.get(li.data("entityId"));
+      return !item.getFlag("worldbuilding", "isTemplate");
+    },
+    callback: li => {
+      const item = game.items.get(li.data("entityId"));
+      item.setFlag("worldbuilding", "isTemplate", true);
+    }
+  });
+
+  // Undefine an item as a template.
+  options.push({
+    name: game.i18n.localize("SIMPLE.UnsetTemplate"),
+    icon: '<i class="fas fa-times"></i>',
+    condition: li => {
+      const item = game.items.get(li.data("entityId"));
+      return item.getFlag("worldbuilding", "isTemplate");
+    },
+    callback: li => {
+      const item = game.items.get(li.data("entityId"));
+      item.setFlag("worldbuilding", "isTemplate", false);
+    }
+  });
+});
+
+
+/**
+ * Adds the actor template selection dialog.
+ */
+ActorDirectory.prototype._onCreate = async (event) => {
+  // Do not allow the creation event to bubble to other listeners
+  event.preventDefault();
+  event.stopPropagation();
+
+  _simpleDirectoryTemplates('actor');
+}
+
+/**
+ * Adds the item template selection dialog.
+ */
+ItemDirectory.prototype._onCreate = async (event) => {
+  // Do not allow the creation event to bubble to other listeners
+  event.preventDefault();
+  event.stopPropagation();
+
+  _simpleDirectoryTemplates('item');
+}
+
+/**
+ * Display the entity template dialog.
+ *
+ * Helper function to display a dialog if there are multiple template types
+ * defined for the entity type.
+ *
+ * @param {string} entityType - 'actor' or 'item'
+ */
+async function _simpleDirectoryTemplates(entityType = 'actor') {
+  // Retrieve the collection and class.
+  const entityCollection = entityType == 'actor' ? game.actors : game.items;
+  const cls = entityType == 'actor' ? Actor : Item;
+
+  // Query for all entities of this type using the "isTemplate" flag.
+  let entities = entityCollection.filter(a => a.data.flags?.worldbuilding?.isTemplate === true);
+
+  // Initialize variables related to the entity class.
+  let ent = game.i18n.localize(cls.config.label);
+
+  // Setup entity data.
+  let type = entityType == 'actor' ? 'character' : 'item';
+  let createData = {
+    name: `New ${ent}`,
+    type: type,
+    folder: event.currentTarget.dataset.folder
+  };
+
+  // If there's more than one entity template type, create a form.
+  if (entities.length > 0) {
+    // Build an array of types for the form, including an empty default.
+    let types = [{
+      value: null,
+      label: game.i18n.localize("SIMPLE.NoTemplate")
+    }];
+
+    // Append each of the user-defined actor/item types.
+    types = types.concat(entities.map(a => {
+      return {
+        value: a.data.name,
+        label: a.data.name
+      }
+    }));
+
+    // Render the entity creation form
+    let templateData = {upper: ent, lower: ent.toLowerCase(), types: types},
+        dlg = await renderTemplate(`systems/worldbuilding/templates/sidebar/entity-create.html`, templateData);
+
+    // Render the confirmation dialog window
+    new Dialog({
+      title: `Create ${createData.name}`,
+      content: dlg,
+      buttons: {
+        create: {
+          icon: '<i class="fas fa-check"></i>',
+          label: `Create ${ent}`,
+          callback: html => {
+            // Get the form data.
+            const form = html[0].querySelector("form");
+            mergeObject(createData, validateForm(form));
+
+            // Store the type and name values, and retrieve the template entity.
+            let templateActor = entityCollection.getName(createData.type);
+
+            // If there's a template entity, handle the data.
+            if (templateActor) {
+              // Update the object with the existing template's values.
+              createData = mergeObject(templateActor.data, createData, {inplace: false});
+              createData.type = templateActor.data.type;
+              // Clear the flag so that this doesn't become a new template.
+              delete createData.flags.worldbuilding.isTemplate;
+            }
+            // Otherwise, restore to a valid entity type (character/item).
+            else {
+              createData.type = type;
+            }
+
+            cls.create(createData, {renderSheet: true});
+          }
+        }
+      },
+      default: "create"
+    }).render(true);
+  }
+  // Otherwise, just create a blank entity.
+  else {
+    cls.create(createData, {renderSheet: true});
+  }
+}