src/main/java/com/andrewlalis/perfin/PerfinApp.java

@@ -91,6 +91,8 @@ public class PerfinApp extends Application {
             router.map("edit-transaction", PerfinApp.class.getResource("/edit-transaction.fxml"));
             router.map("create-balance-record", PerfinApp.class.getResource("/create-balance-record.fxml"));
             router.map("balance-record", PerfinApp.class.getResource("/balance-record-view.fxml"));
+            router.map("vendors", PerfinApp.class.getResource("/vendors-view.fxml"));
+            router.map("edit-vendor", PerfinApp.class.getResource("/edit-vendor.fxml"));
 
             // Help pages.
             helpRouter.map("home", PerfinApp.class.getResource("/help-pages/home.fxml"));

src/main/java/com/andrewlalis/perfin/control/CreateBalanceRecordController.java

@@ -11,6 +11,7 @@ import com.andrewlalis.perfin.model.Profile;
 import com.andrewlalis.perfin.view.component.FileSelectionArea;
 import com.andrewlalis.perfin.view.component.PropertiesPane;
 import com.andrewlalis.perfin.view.component.validation.ValidationApplier;
+import com.andrewlalis.perfin.view.component.validation.ValidationFunction;
 import com.andrewlalis.perfin.view.component.validation.ValidationResult;
 import com.andrewlalis.perfin.view.component.validation.validators.CurrencyAmountValidator;
 import javafx.application.Platform;
@@ -39,7 +40,7 @@ public class CreateBalanceRecordController implements RouteSelectionListener {
     private Account account;
 
     @FXML public void initialize() {
-        var timestampValid = new ValidationApplier<String>(input -> {
+        var timestampValid = new ValidationApplier<>((ValidationFunction<String>)  input -> {
             try {
                 DateUtil.DEFAULT_DATETIME_FORMAT.parse(input);
                 return ValidationResult.valid();

src/main/java/com/andrewlalis/perfin/control/EditTransactionController.java

@@ -60,6 +60,7 @@ public class EditTransactionController implements RouteSelectionListener {
     @FXML public AccountSelectionBox creditAccountSelector;
 
     @FXML public ComboBox<String> vendorComboBox;
+    @FXML public Hyperlink vendorsHyperlink;
     @FXML public ComboBox<String> categoryComboBox;
     @FXML public ComboBox<String> tagsComboBox;
     @FXML public Button addTagButton;
@@ -89,6 +90,8 @@ public class EditTransactionController implements RouteSelectionListener {
         ).validatedInitially().attach(descriptionField, descriptionField.textProperty());
         var linkedAccountsValid = initializeLinkedAccountsValidationUi();
         initializeTagSelectionUi();
+        // Setup hyperlinks.
+        vendorsHyperlink.setOnAction(event -> router.navigate("vendors"));
 
         var formValid = timestampValid.and(amountValid).and(descriptionValid).and(linkedAccountsValid);
         saveButton.disableProperty().bind(formValid.not());

src/main/java/com/andrewlalis/perfin/control/EditVendorController.java

@@ -0,0 +1,93 @@
+package com.andrewlalis.perfin.control;
+
+import com.andrewlalis.javafx_scene_router.RouteSelectionListener;
+import com.andrewlalis.perfin.data.DataSource;
+import com.andrewlalis.perfin.data.TransactionVendorRepository;
+import com.andrewlalis.perfin.model.Profile;
+import com.andrewlalis.perfin.model.TransactionVendor;
+import com.andrewlalis.perfin.view.component.validation.ValidationApplier;
+import com.andrewlalis.perfin.view.component.validation.validators.PredicateValidator;
+import javafx.fxml.FXML;
+import javafx.scene.control.Button;
+import javafx.scene.control.TextArea;
+import javafx.scene.control.TextField;
+
+import java.util.Objects;
+import java.util.concurrent.CompletableFuture;
+
+import static com.andrewlalis.perfin.PerfinApp.router;
+
+public class EditVendorController implements RouteSelectionListener {
+    private TransactionVendor vendor;
+
+    @FXML public TextField nameField;
+    @FXML public TextArea descriptionField;
+    @FXML public Button saveButton;
+
+    @FXML public void initialize() {
+        var nameValid = new ValidationApplier<>(new PredicateValidator<String>()
+                .addTerminalPredicate(s -> s != null && !s.isBlank(), "Name is required.")
+                .addPredicate(s -> s.strip().length() <= TransactionVendor.NAME_MAX_LENGTH, "Name is too long.")
+                // A predicate that prevents duplicate names.
+                .addAsyncPredicate(
+                        s -> {
+                            if (Profile.getCurrent() == null) return CompletableFuture.completedFuture(false);
+                            return Profile.getCurrent().dataSource().mapRepoAsync(
+                                    TransactionVendorRepository.class,
+                                    repo -> {
+                                        var vendorByName = repo.findByName(s).orElse(null);
+                                        if (this.vendor != null) {
+                                            return this.vendor.equals(vendorByName) || vendorByName == null;
+                                        }
+                                        return vendorByName == null;
+                                    }
+                            );
+                        },
+                        "Vendor with this name already exists."
+                )
+            ).validatedInitially().attachToTextField(nameField);
+        var descriptionValid = new ValidationApplier<>(new PredicateValidator<String>()
+                .addPredicate(
+                        s -> s == null || s.strip().length() <= TransactionVendor.DESCRIPTION_MAX_LENGTH,
+                        "Description is too long."
+                )
+            ).validatedInitially().attach(descriptionField, descriptionField.textProperty());
+
+        var formValid = nameValid.and(descriptionValid);
+        saveButton.disableProperty().bind(formValid.not());
+    }
+
+    @Override
+    public void onRouteSelected(Object context) {
+        if (context instanceof TransactionVendor tv) {
+            this.vendor = tv;
+            nameField.setText(vendor.getName());
+            descriptionField.setText(vendor.getDescription());
+        } else {
+            nameField.setText(null);
+            descriptionField.setText(null);
+        }
+    }
+
+    @FXML public void save() {
+        String name = nameField.getText().strip();
+        String description = descriptionField.getText() == null ? null : descriptionField.getText().strip();
+        DataSource ds = Profile.getCurrent().dataSource();
+        if (vendor != null) {
+            ds.useRepo(TransactionVendorRepository.class, repo -> repo.update(vendor.id, name, description));
+        } else {
+            ds.useRepo(TransactionVendorRepository.class, repo -> {
+                if (description == null || description.isEmpty()) {
+                    repo.insert(name);
+                } else {
+                    repo.insert(name, description);
+                }
+            });
+        }
+        router.replace("vendors");
+    }
+
+    @FXML public void cancel() {
+        router.navigateBackAndClear();
+    }
+}

src/main/java/com/andrewlalis/perfin/control/VendorsViewController.java

@@ -0,0 +1,78 @@
+package com.andrewlalis.perfin.control;
+
+import com.andrewlalis.javafx_scene_router.RouteSelectionListener;
+import com.andrewlalis.perfin.data.TransactionVendorRepository;
+import com.andrewlalis.perfin.model.Profile;
+import com.andrewlalis.perfin.model.TransactionVendor;
+import com.andrewlalis.perfin.view.BindingUtil;
+import javafx.application.Platform;
+import javafx.collections.FXCollections;
+import javafx.collections.ObservableList;
+import javafx.fxml.FXML;
+import javafx.geometry.Pos;
+import javafx.scene.Node;
+import javafx.scene.control.Button;
+import javafx.scene.control.Label;
+import javafx.scene.layout.BorderPane;
+import javafx.scene.layout.VBox;
+
+import java.util.List;
+
+import static com.andrewlalis.perfin.PerfinApp.router;
+
+public class VendorsViewController implements RouteSelectionListener {
+    @FXML public VBox vendorsVBox;
+    private final ObservableList<TransactionVendor> vendors = FXCollections.observableArrayList();
+
+    @FXML public void initialize() {
+        BindingUtil.mapContent(vendorsVBox.getChildren(), vendors, this::buildVendorTile);
+    }
+
+    private Node buildVendorTile(TransactionVendor transactionVendor) {
+        BorderPane pane = new BorderPane();
+        pane.getStyleClass().addAll("tile", "std-spacing");
+        pane.setOnMouseClicked(event -> router.navigate("edit-vendor", transactionVendor));
+
+        Label nameLabel = new Label(transactionVendor.getName());
+        nameLabel.getStyleClass().addAll("bold-text");
+        Label descriptionLabel = new Label(transactionVendor.getDescription());
+        descriptionLabel.setWrapText(true);
+        VBox contentVBox = new VBox(nameLabel, descriptionLabel);
+        contentVBox.getStyleClass().addAll("std-spacing");
+        pane.setCenter(contentVBox);
+        BorderPane.setAlignment(contentVBox, Pos.TOP_LEFT);
+
+        Button removeButton = new Button("Remove");
+        removeButton.setOnAction(event -> {
+            boolean confirm = Popups.confirm(removeButton, "Are you sure you want to remove this vendor? Any transactions with assigned to this vendor will have their vendor field cleared. This cannot be undone.");
+            if (confirm) {
+                Profile.getCurrent().dataSource().useRepo(TransactionVendorRepository.class, repo -> {
+                    repo.deleteById(transactionVendor.id);
+                });
+                refreshVendors();
+            }
+        });
+        pane.setRight(removeButton);
+
+        return pane;
+    }
+
+    @Override
+    public void onRouteSelected(Object context) {
+        refreshVendors();
+    }
+
+    @FXML public void addVendor() {
+        router.navigate("edit-vendor");
+    }
+
+    private void refreshVendors() {
+        Profile.getCurrent().dataSource().useRepoAsync(TransactionVendorRepository.class, repo -> {
+            final List<TransactionVendor> vendors = repo.findAll();
+            Platform.runLater(() -> {
+                this.vendors.clear();
+                this.vendors.addAll(vendors);
+            });
+        });
+    }
+}

src/main/java/com/andrewlalis/perfin/data/TransactionVendorRepository.java

@@ -11,5 +11,6 @@ public interface TransactionVendorRepository extends Repository, AutoCloseable {
     List<TransactionVendor> findAll();
     long insert(String name, String description);
     long insert(String name);
+    void update(long id, String name, String description);
     void deleteById(long id);
 }

src/main/java/com/andrewlalis/perfin/data/impl/JdbcTransactionVendorRepository.java

@@ -8,6 +8,7 @@ import java.sql.Connection;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.util.List;
+import java.util.Objects;
 import java.util.Optional;
 
 public record JdbcTransactionVendorRepository(Connection conn) implements TransactionVendorRepository {
@@ -58,6 +59,29 @@ public record JdbcTransactionVendorRepository(Connection conn) implements Transa
         );
     }
 
+    @Override
+    public void update(long id, String name, String description) {
+        DbUtil.doTransaction(conn, () -> {
+            TransactionVendor vendor = findById(id).orElseThrow();
+            if (!vendor.getName().equals(name)) {
+                DbUtil.updateOne(
+                        conn,
+                        "UPDATE transaction_vendor SET name = ? WHERE id = ?",
+                        name,
+                        id
+                );
+            }
+            if (!Objects.equals(vendor.getDescription(), description)) {
+                DbUtil.updateOne(
+                        conn,
+                        "UPDATE transaction_vendor SET description = ? WHERE id = ?",
+                        description,
+                        id
+                );
+            }
+        });
+    }
+
     @Override
     public void deleteById(long id) {
         DbUtil.update(conn, "DELETE FROM transaction_vendor WHERE id = ?", List.of(id));

src/main/java/com/andrewlalis/perfin/view/component/validation/AsyncValidationFunction.java

@@ -0,0 +1,7 @@
+package com.andrewlalis.perfin.view.component.validation;
+
+import java.util.concurrent.CompletableFuture;
+
+public interface AsyncValidationFunction<T> {
+    CompletableFuture<ValidationResult> validate(T input);
+}

src/main/java/com/andrewlalis/perfin/view/component/validation/ValidationApplier.java

@@ -1,24 +1,40 @@
 package com.andrewlalis.perfin.view.component.validation;
 
 import com.andrewlalis.perfin.view.component.validation.decorators.FieldSubtextDecorator;
+import javafx.application.Platform;
 import javafx.beans.binding.BooleanExpression;
 import javafx.beans.property.Property;
+import javafx.beans.property.SimpleBooleanProperty;
 import javafx.scene.Node;
 import javafx.scene.control.TextField;
 
+import java.util.concurrent.CompletableFuture;
+
 /**
  * Fluent interface for applying a validator to one or more controls.
  * @param <T> The value type.
  */
 public class ValidationApplier<T> {
-    private final ValidationFunction<T> validator;
+    private final AsyncValidationFunction<T> validator;
     private ValidationDecorator decorator = new FieldSubtextDecorator();
     private boolean validateInitially = false;
 
     public ValidationApplier(ValidationFunction<T> validator) {
+        this.validator = input -> CompletableFuture.completedFuture(validator.validate(input));
+    }
+
+    public ValidationApplier(AsyncValidationFunction<T> validator) {
         this.validator = validator;
     }
 
+    public static <T> ValidationApplier<T> of(ValidationFunction<T> validator) {
+        return new ValidationApplier<>(validator);
+    }
+
+    public static <T> ValidationApplier<T> ofAsync(AsyncValidationFunction<T> validator) {
+        return new ValidationApplier<>(validator);
+    }
+
     public ValidationApplier<T> decoratedWith(ValidationDecorator decorator) {
         this.decorator = decorator;
         return this;
@@ -29,24 +45,47 @@ public class ValidationApplier<T> {
         return this;
     }
 
+    /**
+     * Attaches the configured validator and decorator to a node, so that when
+     * the node's specified valueProperty changes, the validator will be called
+     * and if the new value is invalid, the decorator will update the UI to
+     * show the message(s) to the user.
+     * @param node The node to attach to.
+     * @param valueProperty The property to listen for changes and validate on.
+     * @param triggerProperties Additional properties that, when changed, can
+     *                          trigger validation.
+     * @return A boolean expression that tells whether the given valueProperty
+     * is valid at any given time.
+     */
     public BooleanExpression attach(Node node, Property<T> valueProperty, Property<?>... triggerProperties) {
-        BooleanExpression validProperty = BooleanExpression.booleanExpression(
-                valueProperty.map(value -> validator.validate(value).isValid())
-        );
+        final SimpleBooleanProperty validProperty = new SimpleBooleanProperty();
         valueProperty.addListener((observable, oldValue, newValue) -> {
-            ValidationResult result = validator.validate(newValue);
+            validProperty.set(false); // Always set valid to false before we start validation.
+            validator.validate(newValue)
+                .thenAccept(result -> Platform.runLater(() -> {
+                    validProperty.set(result.isValid());
                     decorator.decorate(node, result);
+                }));
         });
         for (Property<?> influencingProperty : triggerProperties) {
             influencingProperty.addListener((observable, oldValue, newValue) -> {
-                ValidationResult result = validator.validate(valueProperty.getValue());
+                validProperty.set(false); // Always set valid to false before we start validation.
+                validator.validate(valueProperty.getValue())
+                    .thenAccept(result -> Platform.runLater(() -> {
+                        validProperty.set(result.isValid());
                         decorator.decorate(node, result);
+                    }));
             });
         }
 
         if (validateInitially) {
             // Call the decorator once to perform validation right away.
-            decorator.decorate(node, validator.validate(valueProperty.getValue()));
+            validProperty.set(false); // Always set valid to false before we start validation.
+            validator.validate(valueProperty.getValue())
+                .thenAccept(result -> Platform.runLater(() -> {
+                    validProperty.set(result.isValid());
+                    decorator.decorate(node, result);
+                }));
         }
         return validProperty;
     }

src/main/java/com/andrewlalis/perfin/view/component/validation/validators/PredicateValidator.java

@@ -1,10 +1,14 @@
 package com.andrewlalis.perfin.view.component.validation.validators;
 
-import com.andrewlalis.perfin.view.component.validation.ValidationFunction;
+import com.andrewlalis.perfin.view.component.validation.AsyncValidationFunction;
 import com.andrewlalis.perfin.view.component.validation.ValidationResult;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
 import java.util.function.Function;
 
 /**
@@ -12,32 +16,73 @@ import java.util.function.Function;
  * determine if it's valid. If invalid, a message is added.
  * @param <T> The value type.
  */
-public class PredicateValidator<T> implements ValidationFunction<T> {
-    private record ValidationStep<T>(Function<T, Boolean> predicate, String message, boolean terminal) {}
+public class PredicateValidator<T> implements AsyncValidationFunction<T> {
+    private static final Logger logger = LoggerFactory.getLogger(PredicateValidator.class);
+
+    private record ValidationStep<T>(Function<T, CompletableFuture<Boolean>> predicate, String message, boolean terminal) {}
 
     private final List<ValidationStep<T>> steps = new ArrayList<>();
 
-    public PredicateValidator<T> addPredicate(Function<T, Boolean> predicate, String errorMessage) {
-        steps.add(new ValidationStep<>(predicate, errorMessage, false));
+    private PredicateValidator<T> addPredicate(Function<T, Boolean> predicate, String errorMessage, boolean terminal) {
+        steps.add(new ValidationStep<>(
+                v -> CompletableFuture.completedFuture(predicate.apply(v)),
+                errorMessage,
+                terminal
+        ));
         return this;
     }
 
-    public PredicateValidator<T> addTerminalPredicate(Function<T, Boolean> predicate, String errorMessage) {
-        steps.add(new ValidationStep<>(predicate, errorMessage, true));
+    private PredicateValidator<T> addAsyncPredicate(Function<T, CompletableFuture<Boolean>> asyncPredicate, String errorMessage, boolean terminal) {
+        steps.add(new ValidationStep<>(asyncPredicate, errorMessage, terminal));
         return this;
     }
 
+    public PredicateValidator<T> addPredicate(Function<T, Boolean> predicate, String errorMessage) {
+        return addPredicate(predicate, errorMessage, false);
+    }
+
+    public PredicateValidator<T> addAsyncPredicate(Function<T, CompletableFuture<Boolean>> asyncPredicate, String errorMessage) {
+        return addAsyncPredicate(asyncPredicate, errorMessage, false);
+    }
+
+    /**
+     * Adds a terminal predicate, that is, if the given boolean function
+     * evaluates to false, then no further predicates are evaluated.
+     * @param predicate The predicate function.
+     * @param errorMessage The error message to display if the predicate
+     *                     evaluates to false for a given value.
+     * @return A reference to the validator, for method chaining.
+     */
+    public PredicateValidator<T> addTerminalPredicate(Function<T, Boolean> predicate, String errorMessage) {
+        return addPredicate(predicate, errorMessage, true);
+    }
+
+    public PredicateValidator<T> addTerminalAsyncPredicate(Function<T, CompletableFuture<Boolean>> asyncPredicate, String errorMessage) {
+        return addAsyncPredicate(asyncPredicate, errorMessage);
+    }
+
     @Override
-    public ValidationResult validate(T input) {
+    public CompletableFuture<ValidationResult> validate(T input) {
+        CompletableFuture<ValidationResult> cf = new CompletableFuture<>();
+        Thread.ofVirtual().start(() -> {
             List<String> messages = new ArrayList<>();
             for (var step : steps) {
-            if (!step.predicate().apply(input)) {
+                try {
+                    boolean success = step.predicate().apply(input).get();
+                    if (!success) {
                         messages.add(step.message());
                         if (step.terminal()) {
-                    return new ValidationResult(messages);
+                            cf.complete(new ValidationResult(messages));
+                            return; // Exit if this is a terminal step and it failed.
                         }
                     }
-        }
-        return new ValidationResult(messages);
+                } catch (InterruptedException | ExecutionException e) {
+                    logger.error("Applying a predicate to input failed.", e);
+                    cf.completeExceptionally(e);
+                }
+            }
+            cf.complete(new ValidationResult(messages));
+        });
+        return cf;
     }
 }

src/main/resources/edit-transaction.fxml

@@ -62,7 +62,7 @@
 
                     <VBox>
                         <Label text="Vendor" labelFor="${vendorComboBox}" styleClass="bold-text"/>
-                        <Hyperlink text="Manage vendors" styleClass="small-font"/>
+                        <Hyperlink fx:id="vendorsHyperlink" text="Manage vendors" styleClass="small-font"/>
                     </VBox>
                     <ComboBox fx:id="vendorComboBox" editable="true" maxWidth="Infinity"/>
 

src/main/resources/edit-vendor.fxml

@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<?import com.andrewlalis.perfin.view.component.PropertiesPane?>
+<?import javafx.scene.control.*?>
+<?import javafx.scene.layout.*?>
+<BorderPane xmlns="http://javafx.com/javafx"
+            xmlns:fx="http://javafx.com/fxml"
+            fx:controller="com.andrewlalis.perfin.control.EditVendorController"
+>
+    <top>
+        <Label text="Edit Vendor" styleClass="bold-text,large-font,std-padding"/>
+    </top>
+    <center>
+        <VBox>
+            <PropertiesPane hgap="5" vgap="5" styleClass="std-padding" maxWidth="500">
+                <columnConstraints>
+                    <ColumnConstraints hgrow="NEVER" halignment="LEFT" minWidth="150"/>
+                    <ColumnConstraints hgrow="ALWAYS" halignment="RIGHT"/>
+                </columnConstraints>
+
+                <Label text="Name" labelFor="${nameField}"/>
+                <TextField fx:id="nameField"/>
+
+                <Label text="Description" labelFor="${descriptionField}"/>
+                <TextArea fx:id="descriptionField" wrapText="true"/>
+            </PropertiesPane>
+            <HBox styleClass="std-padding,std-spacing">
+                <Button text="Save" fx:id="saveButton" onAction="#save"/>
+                <Button text="Cancel" onAction="#cancel"/>
+            </HBox>
+        </VBox>
+    </center>
+</BorderPane>

src/main/resources/vendors-view.fxml

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<?import javafx.scene.control.Button?>
+<?import javafx.scene.control.Label?>
+<?import javafx.scene.control.ScrollPane?>
+<?import javafx.scene.layout.BorderPane?>
+<?import javafx.scene.layout.HBox?>
+<?import javafx.scene.layout.VBox?>
+<?import javafx.scene.text.Text?>
+<BorderPane xmlns="http://javafx.com/javafx"
+            xmlns:fx="http://javafx.com/fxml"
+            fx:controller="com.andrewlalis.perfin.control.VendorsViewController"
+>
+    <top>
+        <Label text="Vendors" styleClass="large-font,bold-text,std-padding"/>
+    </top>
+    <center>
+        <VBox>
+            <HBox styleClass="std-padding,std-spacing" VBox.vgrow="NEVER">
+                <Button text="Add Vendor" onAction="#addVendor"/>
+            </HBox>
+            <ScrollPane styleClass="tile-container-scroll" VBox.vgrow="ALWAYS">
+                <VBox fx:id="vendorsVBox" styleClass="tile-container"/>
+            </ScrollPane>
+        </VBox>
+    </center>
+</BorderPane>