Add bulk selection UI controls (#840)

* Add bulk selection UI

* Handle bulk selection with Stimulus controller instead of session

* Update tests

* Remove stale routes

* Remove old system test helper methods

app/javascript/controllers/bulk_select_controller.js

@@ -0,0 +1,101 @@
+import {Controller} from "@hotwired/stimulus"
+
+// Connects to data-controller="bulk-select"
+export default class extends Controller {
+  static targets = ["row", "group", "selectionBar", "selectionBarText"]
+  static values = {
+    resource: String,
+    selectedIds: {type: Array, default: []}
+  }
+
+  connect() {
+    document.addEventListener("turbo:load", this.#updateView)
+
+    this.#updateView()
+  }
+
+  disconnect() {
+    document.removeEventListener("turbo:load", this.#updateView)
+  }
+
+  togglePageSelection(e) {
+    if (e.target.checked) {
+      this.#selectAll()
+    } else {
+      this.deselectAll()
+    }
+  }
+
+  toggleGroupSelection(e) {
+    const group = this.groupTargets.find(group => group.contains(e.target))
+
+    this.#rowsForGroup(group).forEach(row => {
+      if (e.target.checked) {
+        this.#addToSelection(row.dataset.id)
+      } else {
+        this.#removeFromSelection(row.dataset.id)
+      }
+    })
+  }
+
+  toggleRowSelection(e) {
+    if (e.target.checked) {
+      this.#addToSelection(e.target.dataset.id)
+    } else {
+      this.#removeFromSelection(e.target.dataset.id)
+    }
+  }
+
+  deselectAll() {
+    this.selectedIdsValue = []
+  }
+
+  selectedIdsValueChanged() {
+    this.#updateView()
+  }
+
+  #rowsForGroup(group) {
+    return this.rowTargets.filter(row => group.contains(row))
+  }
+
+  #addToSelection(idToAdd) {
+    this.selectedIdsValue = Array.from(
+      new Set([...this.selectedIdsValue, idToAdd])
+    )
+  }
+
+  #removeFromSelection(idToRemove) {
+    this.selectedIdsValue = this.selectedIdsValue.filter(id => id !== idToRemove)
+  }
+
+  #selectAll() {
+    this.selectedIdsValue = this.rowTargets.map(t => t.dataset.id)
+  }
+
+  #updateView = () => {
+    this.#updateSelectionBar()
+    this.#updateGroups()
+    this.#updateRows()
+  }
+
+  #updateSelectionBar() {
+    const count = this.selectedIdsValue.length
+    this.selectionBarTextTarget.innerText = `${count} ${this.resourceValue}${count === 1 ? "" : "s"} selected`
+    this.selectionBarTarget.hidden = count === 0
+    this.selectionBarTarget.querySelector("input[type='checkbox']").checked = count > 0
+  }
+
+  #updateGroups() {
+    this.groupTargets.forEach(group => {
+      const rows = this.rowTargets.filter(row => group.contains(row))
+      const groupSelected = rows.every(row => this.selectedIdsValue.includes(row.dataset.id))
+      group.querySelector("input[type='checkbox']").checked = groupSelected
+    })
+  }
+
+  #updateRows() {
+    this.rowTargets.forEach(row => {
+      row.checked = this.selectedIdsValue.includes(row.dataset.id)
+    })
+  }
+}