public handleKeyDown()

in packages/web-components/fast-foundation/src/picker/picker.ts [577:707]
93 lines of code
22 McCabe index (conditional complexity)

    public handleKeyDown(e: KeyboardEvent): boolean {
        if (e.defaultPrevented) {
            return false;
        }
        switch (e.key) {
            // TODO: what should "home" and "end" keys do, exactly?
            //
            // case keyHome: {
            //     if (!this.flyoutOpen) {
            //         this.toggleFlyout(true);
            //     } else {
            //         if (this.menuElement.optionElements.length > 0) {
            //             this.setFocusedOption(0);
            //         }
            //     }
            //     return false;
            // }

            // case keyEnd: {
            //     if (!this.flyoutOpen) {
            //         this.toggleFlyout(true);
            //     } else {
            //         if (this.menuElement.optionElements.length > 0) {
            //             this.toggleFlyout(true);
            //             this.setFocusedOption(this.menuElement.optionElements.length - 1);
            //         }
            //     }
            //     return false;
            // }

            case keyArrowDown: {
                if (!this.flyoutOpen) {
                    this.toggleFlyout(true);
                } else {
                    const nextFocusOptionIndex = this.flyoutOpen
                        ? Math.min(
                              this.menuFocusIndex + 1,
                              this.menuElement.optionElements.length - 1
                          )
                        : 0;
                    this.setFocusedOption(nextFocusOptionIndex);
                }
                return false;
            }

            case keyArrowUp: {
                if (!this.flyoutOpen) {
                    this.toggleFlyout(true);
                } else {
                    const previousFocusOptionIndex = this.flyoutOpen
                        ? Math.max(this.menuFocusIndex - 1, 0)
                        : 0;
                    this.setFocusedOption(previousFocusOptionIndex);
                }
                return false;
            }

            case keyEscape: {
                this.toggleFlyout(false);
                return false;
            }

            case keyEnter: {
                if (
                    this.menuFocusIndex !== -1 &&
                    this.menuElement.optionElements.length > this.menuFocusIndex
                ) {
                    this.menuElement.optionElements[this.menuFocusIndex].click();
                }
                return false;
            }

            case keyArrowRight: {
                if (document.activeElement !== this.inputElement) {
                    this.incrementFocusedItem(1);
                    return false;
                }
                // don't block if arrow keys moving caret in input element
                return true;
            }

            case keyArrowLeft: {
                if (this.inputElement.selectionStart === 0) {
                    this.incrementFocusedItem(-1);
                    return false;
                }
                // don't block if arrow keys moving caret in input element
                return true;
            }

            case keyDelete:
            case keyBackspace: {
                if (document.activeElement === null) {
                    return true;
                }

                if (document.activeElement === this.inputElement) {
                    if (this.inputElement.selectionStart === 0) {
                        this.selection = this.selectedItems
                            .slice(0, this.selectedItems.length - 1)
                            .toString();
                        this.toggleFlyout(false);
                        return false;
                    }
                    // let text deletion proceed
                    return true;
                }

                const selectedItems: Element[] = Array.from(this.listElement.children);
                const currentFocusedItemIndex: number = selectedItems.indexOf(
                    document.activeElement
                );

                if (currentFocusedItemIndex > -1) {
                    // delete currently focused item
                    this.selection = this.selectedItems
                        .splice(currentFocusedItemIndex, 1)
                        .toString();
                    DOM.queueUpdate(() => {
                        (selectedItems[
                            Math.min(selectedItems.length, currentFocusedItemIndex)
                        ] as HTMLElement).focus();
                    });
                    return false;
                }
                return true;
            }
        }
        this.toggleFlyout(true);
        return true;
    }