(core) Implement 'Print widget' option to print individual view sections.

Summary:
- Supports multi-page printing with some aggressive css overrides.
- Relies on a new function implemented by grist-plugin-api to print a
  multi-page CustomView.
- Renders all rows for printing for scrolly-based views.

Test Plan:
Doesn't seem possible to do a selenium test for printing. Tested
manually on Chrome, Firefox, and Safari.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2635

app/client/components/BaseView.js

@@ -230,6 +230,9 @@ function BaseView(gristDoc, viewSectionModel, options) {
   this.autoDispose(this.viewSection.activeSortSpec.subscribe(() => this.setCursorPos({rowIndex: 0})));
 
   this.copySelection = ko.observable(null);
+
+  // Whether parts needed for printing should be rendered now.
+  this._isPrinting = ko.observable(false);
 }
 Base.setBaseFor(BaseView);
 _.extend(Base.prototype, BackboneEvents);
@@ -612,6 +615,13 @@ BaseView.prototype.onResize = function() {
 BaseView.prototype.onRowResize = function(rowModels) {
 };
 
+/**
+ * Called before and after printing this section.
+ */
+BaseView.prototype.prepareToPrint = function(onOff) {
+  this._isPrinting(onOff);
+};
+
 /**
  * Called to obtain the rowModel for the given rowId. Returns a rowModel if it belongs to the
  * section and is rendered, otherwise returns null.

app/client/components/CustomView.ts

@@ -89,6 +89,12 @@ export class CustomView extends Disposable {
     this.autoDispose(this.cursor.rowIndex.subscribe(this._updateCursor));
   }
 
+  public async triggerPrint() {
+    if (!this.isDisposed() && this._rpc) {
+      return await this._rpc.callRemoteFunc("print");
+    }
+  }
+
   private _updateView(dataChange: boolean) {
     if (this.isDisposed()) { return; }
     if (this._rpc) {

app/client/components/DetailView.css

@@ -79,11 +79,13 @@
   margin-left: -3px;
 }
 
+@media not print {
   .detailview_record_detail.active {
     /* highlight active record in Card List by overlaying the active-section highlight */
     margin-left: -3px;
     border-left: 3px solid var(--grist-color-light-green);
   }
+}
 
 /*** single record ***/
 .detailview_single {

app/client/components/DetailView.js

@@ -4,6 +4,7 @@ var ko            = require('knockout');
 var dom           = require('app/client/lib/dom');
 var kd            = require('app/client/lib/koDom');
 var koDomScrolly  = require('app/client/lib/koDomScrolly');
+const {renderAllRows} = require('app/client/components/Printing');
 
 require('app/client/lib/koUtil'); // Needed for subscribeInit.
 
@@ -282,6 +283,11 @@ DetailView.prototype.buildDom = function() {
           }),
           koDomScrolly.scrolly(this.viewData, {fitToWidth: true},
             row => this.makeRecord(row)),
+
+          kd.maybe(this._isPrinting, () =>
+            renderAllRows(this.tableModel, this.sortedRows.getKoArray().peek(), row =>
+              this.makeRecord(row))
+          ),
         );
       } else {
         return dom(

app/client/components/GridView.css

@@ -71,6 +71,7 @@
   left: 0px;
   overflow: hidden;
   width: 4rem; /* Also should match width for .gridview_header_corner, and the overlay elements */
+  flex: none;
 
   border-bottom: 1px solid var(--grist-color-dark-grey);
   background-color: var(--grist-color-light-grey);
@@ -89,6 +90,15 @@
   .gridview_data_row_num {
     background-color: var(--grist-color-light-grey) !important;
   }
+  .gridview_header_backdrop_top {
+    display: none;
+  }
+  .column_name.mod-add-column {
+    display: none;
+  }
+  .gridview_data_header {
+    background-color: var(--grist-color-light-grey) !important;
+  }
 }
 
 /* ========= Overlay styles ========== */

app/client/components/GridView.js

@@ -21,6 +21,7 @@ var BaseView      = require('./BaseView');
 var selector      = require('./Selector');
 var CopySelection = require('./CopySelection');
 
+const {renderAllRows} = require('app/client/components/Printing');
 const {reportError} = require('app/client/models/AppModel');
 
 // Grist UI Components
@@ -831,7 +832,15 @@ GridView.prototype.buildDom = function() {
         ) //end hbox
       ), // END COL HEADER BOX
 
-      koDomScrolly.scrolly(data, { paddingBottom: 80, paddingRight: 28 }, function(row) {
+      koDomScrolly.scrolly(data, { paddingBottom: 80, paddingRight: 28 }, renderRow),
+
+      kd.maybe(this._isPrinting, () =>
+        renderAllRows(this.tableModel, this.sortedRows.getKoArray().peek(), renderRow)
+      ),
+    ) // end scrollpane
+  );// END MAIN VIEW BOX
+
+  function renderRow(row) {
     // TODO. There are several ways to implement a cursor; similar concerns may arise
     // when implementing selection and cell editor.
     // (1) Class on 'div.field.field_clip'. Fewest elements, seems possibly best for
@@ -948,10 +957,7 @@ GridView.prototype.buildDom = function() {
         })
       )
     );
-      }) //end scrolly
+  }
-
-    ) // end scrollpane
-  );// END MAIN VIEW BOX
 };
 
 /** @inheritdoc */

app/client/components/GristDoc.ts

@@ -690,4 +690,9 @@ const cssViewContentPane = styled('div', `
   position: relative;
   min-width: 240px;
   margin: 12px;
+  @media print {
+    & {
+      margin: 0px;
+    }
+  }
 `);

app/client/components/Printing.css

@@ -0,0 +1,60 @@
+@media print {
+  /* Various style overrides needed to print a single section (page widget). */
+
+  .print-hide {
+    display: none;
+  }
+
+  .print-parent {
+    display: block !important;
+    position: relative !important;
+    height: max-content !important;
+    overflow: visible !important;
+  }
+
+  .print-widget {
+    margin: 0px !important;
+  }
+
+  .print-widget .viewsection_title {
+    display: none !important;
+  }
+  .print-widget .view_data_pane_container {
+    border: none !important;
+  }
+  .print-widget .viewsection_content {
+    margin: 0px !important;
+  }
+
+  .print-widget .detailview_single {
+    overflow: visible;
+  }
+
+  .print-widget .gridview_data_pane {
+    display: block !important;
+    position: relative !important;
+    height: max-content !important;
+    overflow: visible !important;
+    border-top: 1px solid var(--grist-color-dark-grey);
+    border-left: 1px solid var(--grist-color-dark-grey);
+  }
+
+  .print-widget .gridview_data_scroll {
+    position: relative !important;
+    height: max-content !important;
+  }
+
+  .print-widget .scrolly_outer {
+    display: none;
+  }
+
+  .print-widget .custom_view {
+    height: calc(100vh - 24px);
+  }
+}
+
+@media not print {
+  .print-all-rows {
+    display: none;
+  }
+}

app/client/components/Printing.ts

@@ -0,0 +1,108 @@
+import {CustomView} from 'app/client/components/CustomView';
+import {DataRowModel} from 'app/client/models/DataRowModel';
+import * as DataTableModel from 'app/client/models/DataTableModel';
+import {ViewSectionRec} from 'app/client/models/DocModel';
+import {dom} from 'grainjs';
+
+type RowId = number|'new';
+
+/**
+ * Print the specified viewSection (aka page widget). We use the existing view instance rather
+ * than render a new one, since it may have state local to this instance view, such as current
+ * filters.
+ *
+ * Views get a chance to render things specially for printing (which is needed when they use
+ * scrolly for normal rendering).
+ *
+ * To let an existing view print across multiple pages, we can't have it nested in a flexbox or a
+ * div with 'height: 100%'. We achieve it by forcing all parents of our view to have a simple
+ * layout. This is potentially fragile.
+ */
+export async function printViewSection(layout: any, viewSection: ViewSectionRec) {
+  const viewInstance = viewSection.viewInstance.peek();
+  const sectionElem = viewInstance?.viewPane?.closest('.viewsection_content');
+  if (!sectionElem) {
+    throw new Error("No page widget to print");
+  }
+  if (viewInstance instanceof CustomView) {
+    try {
+      await viewInstance.triggerPrint();
+      return;
+    } catch (e) {
+      // tslint:disable-next-line:no-console
+      console.warn(`Failed to trigger print in CustomView: ${e}`);
+      // continue on to trying to print from outside, which should work OK for a single page.
+    }
+  }
+
+  function prepareToPrint(onOff: boolean) {
+    // Hide all layout boxes that do NOT contain the section to be printed.
+    layout.forEachBox((box: any) => {
+      if (!box.dom.contains(sectionElem)) {
+        box.dom.classList.toggle('print-hide', onOff);
+      }
+    });
+
+    // Mark the section to be printed.
+    sectionElem.classList.toggle('print-widget', onOff);
+
+    // Let the view instance update its rendering, e.g. to render all rows when scrolly is in use.
+    viewInstance?.prepareToPrint(onOff);
+
+    // If .print-all-rows element is present (created for scrolly-based views), use it as the
+    // start element for the loop below, to ensure it's rendered flexbox-free.
+    const keyElem = sectionElem.querySelector('.print-all-rows') || sectionElem;
+
+    // Go through all parents of the element to be printed. For @media print, we override their
+    // layout in a heavy-handed way, forcing them all to be non-flexbox and sized to content,
+    // since our normal flexbox-based layout is sized to screen and would not print multiple pages.
+    let elem = keyElem.parentElement;
+    while (elem) {
+      elem.classList.toggle('print-parent', onOff);
+      elem = elem.parentElement;
+    }
+  }
+
+  const sub1 = dom.onElem(window, 'beforeprint', () => prepareToPrint(true));
+  const sub2 = dom.onElem(window, 'afterprint', () => {
+    sub1.dispose();
+    sub2.dispose();
+    // To debug printing, set window.debugPringint=1 in the console, then print a section, dismiss
+    // the print dialog, switch to "@media print" emulation, and you can explore the styles. You'd
+    // need to reload the page to do it again.
+    if (!(window as any).debugPrinting) {
+      prepareToPrint(false);
+    }
+  });
+
+  window.print();
+}
+
+
+/**
+ * Produces a div with all requested rows using the same renderRow() function as used with scrolly
+ * for dynamically rendered views. This is used for printing, so these rows do not subscribe to
+ * data.
+ *
+ * To avoid creating a lot of subscriptions when rendering rows this way, we render one DOM row at
+ * a time, copy the produced HTML, and dispose the produced DOM.
+ */
+export function renderAllRows(
+  tableModel: DataTableModel, rowIds: RowId[], renderRow: (r: DataRowModel) => Element,
+) {
+  const rowModel = tableModel.createFloatingRowModel(null) as DataRowModel;
+  const html: string[] = [];
+  rowIds.forEach((rowId, index) => {
+    if (rowId !== 'new') {
+      rowModel._index(index);
+      rowModel.assign(rowId);
+      const elem = renderRow(rowModel);
+      html.push(elem.outerHTML);
+      dom.domDispose(elem);
+    }
+  });
+  rowModel.dispose();
+  const result = dom('div.print-all-rows');
+  result.innerHTML = html.join("\n");
+  return result;
+}

app/client/components/ViewLayout.ts

@@ -7,6 +7,7 @@ import * as GridView from 'app/client/components/GridView';
 import {GristDoc} from 'app/client/components/GristDoc';
 import {Layout} from 'app/client/components/Layout';
 import {LayoutEditor} from 'app/client/components/LayoutEditor';
+import {printViewSection} from 'app/client/components/Printing';
 import {Delay} from 'app/client/lib/Delay';
 import {createObsArray} from 'app/client/lib/koArrayWrap';
 import {ViewRec, ViewSectionRec} from 'app/client/models/DocModel';
@@ -124,6 +125,7 @@ export class ViewLayout extends DisposableWithEvents implements IDomComponent {
       deleteSection: () => { this._removeViewSection(this.viewModel.activeSectionId()); },
       nextSection: () => { this._otherSection(+1); },
       prevSection: () => { this._otherSection(-1); },
+      printSection: () => { printViewSection(this._layout, this.viewModel.activeSection()).catch(reportError); },
     };
     this.autoDispose(commands.createGroup(commandGroup, this, true));
   }

app/client/components/commandList.js

@@ -92,6 +92,11 @@ exports.groups = [{
       name: 'dataSelectionTabOpen',
       keys: [],
       desc: 'Shortcut to data selection tab'
+    },
+    {
+      name: 'printSection',
+      keys: [],
+      desc: 'Print currently selected page widget',
     }
   ]
 }, {

app/client/declarations.d.ts

@@ -68,6 +68,7 @@ declare module "app/client/components/BaseView" {
     public buildTitleControls(): DomArg;
     public getLoadingDonePromise(): Promise<void>;
     public onResize(): void;
+    public prepareToPrint(onOff: boolean): void;
   }
   export = BaseView;
 }

app/client/ui/PagePanels.ts

@@ -199,6 +199,12 @@ const cssTopHeader = styled('div', `
 const cssResizeFlexVHandle = styled(resizeFlexVHandle, `
   --resize-handle-color: ${colors.mediumGrey};
   --resize-handle-highlight: ${colors.lightGreen};
+
+  @media print {
+    & {
+      display: none;
+    }
+  }
 `);
 const cssResizeDisabledBorder = styled('div', `
   flex: none;

app/client/ui/ViewLayoutMenu.ts

@@ -9,17 +9,19 @@ import {dom} from 'grainjs';
  */
 export function makeViewLayoutMenu(viewModel: ViewRec, viewSection: ViewSectionRec, isReadonly: boolean) {
   return [
+    menuItemCmd(allCommands.printSection, 'Print widget', testId('print-section')),
     dom.maybe((use) => ['detail', 'single'].includes(use(viewSection.parentKey)), () =>
       menuItemCmd(allCommands.editLayout, 'Edit Card Layout',
         dom.cls('disabled', isReadonly))),
 
+    menuDivider(),
+    menuItemCmd(allCommands.viewTabOpen, 'Widget options', testId('widget-options')),
+    menuItemCmd(allCommands.sortFilterTabOpen, 'Advanced Sort & Filter'),
+    menuItemCmd(allCommands.dataSelectionTabOpen, 'Data selection'),
+
+    menuDivider(),
     menuItemCmd(allCommands.deleteSection, 'Delete widget',
       dom.cls('disabled', viewModel.viewSections().peekLength <= 1 || isReadonly),
       testId('section-delete')),
-    menuDivider(),
-
-    menuItemCmd(allCommands.viewTabOpen, 'Widget options', testId('widget-options')),
-    menuItemCmd(allCommands.sortFilterTabOpen, 'Advanced Sort & Filter'),
-    menuItemCmd(allCommands.dataSelectionTabOpen, 'Data selection')
   ];
 }

app/client/ui2018/menus.ts

@@ -45,6 +45,12 @@ const cssMenuElem = styled('div', `
   z-index: 999;
   --weaseljs-selected-background-color: ${vars.primaryBg};
   --weaseljs-menu-item-padding: 8px 24px;
+
+  @media print {
+    & {
+      display: none;
+    }
+  }
 `);
 
 const menuItemStyle = `

app/plugin/grist-plugin-api.ts

@@ -150,6 +150,11 @@ if (typeof window !== 'undefined') {
     rpc.setSendMessage(msg => window.parent.postMessage(msg, "*"));
     window.onmessage = (e: MessageEvent) => rpc.receiveMessage(e.data);
   }
+
+  // Allow outer Grist application to trigger printing. This is similar to using
+  // iframe.contentWindow.print(), but that call does not work cross-domain.
+  rpc.registerFunc("print", () => window.print());
+
 } else if (typeof process === 'undefined') {
   // Web worker. We can't really bring in the types for WebWorker (available with --lib flag)
   // without conflicting with a regular window, so use just use `self as any` here.