Implement support for custom ids

shortener/src/main/angular/shortener/src/app/shortener-form.component.ts

 import { Component } from "@angular/core";
-import {HttpClient, HttpHeaders, HttpParams} from "@angular/common/http";
+import { HttpClient, HttpHeaders, HttpParams } from "@angular/common/http";
 
 class ShortenerFormModel {
     url: string = ""
+    id:  string = ""
 }
 
 @Component({
     selector: 'shortener-form',
     template: `
         <form id="shortener-form" (ngSubmit)="submit()" method="post">
-            <input id="long-url-input" name="url" type="text" placeholder="Enter a long URL" [(ngModel)]="model.url">
-            <button type="submit">Shorten URL</button>
+            <ul>
+                <li>
+                    <input id="long-url-input" name="url" type="text" placeholder="Enter a long URL"
+                           title="The URL to be shortened" [(ngModel)]="model.url">
+                </li>
+                <li>
+                    <p>and optionally specify a custom id:</p>
+                </li>
+                <li>
+                    <input id="short-url-id-input" name="id" type="text" placeholder="optionally enter a custom id"
+                           pattern="[a-zA-Z0-9]+" title="Custom id for the short URL" [(ngModel)]="model.id">
+                    <button type="submit">Shorten URL</button>
+                </li>
+            </ul>
         </form>
         <div id="shortener-form-output">
-            <label id="short-url-label" for="short-url">Your short URL:</label>
+            <label id="short-url-label" for="short-url">Click to copy your short URL:</label>
             <input id="short-url-output" name="short-url" (click)="copyContent($event)" readonly/>
         </div>
     `
@@ -29,9 +42,10 @@ export class ShortenerFormComponent {
         const headers =
             new HttpHeaders()
                 .set("Content-Type", "application/x-www-form-urlencoded")
-        const body =
-            new HttpParams()
-                .append("url", encodeURIComponent(this.model.url));
+
+        let body = new HttpParams().append("url", encodeURIComponent(this.model.url));
+        if (this.model.id !== "")
+            body = body.append("id", this.model.id.toLowerCase());
 
         this.http
             .post("http://upbshrt.xyz/", body, { headers: headers, responseType: "text" })
@@ -43,7 +57,10 @@ export class ShortenerFormComponent {
                     (document.getElementById("short-url-output") as HTMLInputElement)
                         .value = decodeURIComponent(data);
                 },
-                error => console.log(error));
+                error => {
+                    console.log(error);
+                    alert(error.message);
+                });
     }
 
     copyContent(event: MouseEvent): void {

shortener/src/main/angular/shortener/src/styles.css

@@ -23,12 +23,22 @@ html {
     justify-content: center;
 }
 
-#long-url-input {
+#shortener-form > ul {
+    list-style: none;
+    padding: 0;
+    margin: 0;
+}
+
+#short-url-id-input {
     margin-right: 10px;
 }
 
+#short-url-id-input:invalid {
+    color: red;
+}
+
 #shortener-form-output {
-    margin-top: 10px;
+    margin-top: 50px;
     visibility: hidden;
 }
 

shortener/src/main/kotlin/xyz/upbshrt/shortener/controller/UrlShorteningController.kt

@@ -4,6 +4,7 @@ import java.net.URI
 import java.net.URLDecoder
 import java.net.URLEncoder
 import java.nio.charset.StandardCharsets
+import java.math.BigInteger
 
 import javax.validation.constraints.Pattern
 
@@ -68,7 +69,8 @@ class UrlShorteningController @Autowired constructor(private val repository: Url
             )
         }
 
-        val numericId: Int? = id?.toInt(UrlMapping.ID_RADIX)
+        val numericId: BigInteger? =
+            if (id != null) BigInteger(id, UrlMapping.ID_RADIX) else null
         if ((numericId != null) && repository.existsById(numericId))
             throw ResponseStatusException(
                 HttpStatus.UNPROCESSABLE_ENTITY,
@@ -95,8 +97,8 @@ class UrlShorteningController @Autowired constructor(private val repository: Url
      */
     @GetMapping("/{id:^[a-z0-9]+$}")
     fun resolveUrl(@PathVariable id: String): ResponseEntity<Nothing> {
-        val numericId: Int = try {
-            id.toInt(UrlMapping.ID_RADIX)
+        val numericId: BigInteger = try {
+            BigInteger(id, UrlMapping.ID_RADIX)
         } catch (exception: NumberFormatException) {
             handleMalformedId(id)
         }

shortener/src/main/kotlin/xyz/upbshrt/shortener/entity/UrlMapping.kt

 package xyz.upbshrt.shortener.entity
 
+import java.math.BigInteger
+
 import javax.persistence.Column
 import javax.persistence.Entity
 import javax.persistence.Id
 
 import javax.persistence.GeneratedValue
 import javax.persistence.GenerationType
-import javax.persistence.SequenceGenerator
+
+import org.hibernate.annotations.GenericGenerator
+import org.hibernate.annotations.Parameter
+import org.hibernate.id.enhanced.SequenceStyleGenerator
 
 @Entity
-class UrlMapping(id: Int?, url: String) {
+class UrlMapping(id: BigInteger?, url: String) {
 
     @Id
     @Suppress("CanBePrimaryConstructorProperty")
     @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "UrlMappingIdSequence")
-    @SequenceGenerator(
-        name           = "UrlMappingIdSequence",
-        sequenceName   = "url_mapping_id_sequence",
-        allocationSize = 1
+    @GenericGenerator(
+        name       = "UrlMappingIdSequence",
+        strategy   = "xyz.upbshrt.shortener.hibernate.SequenceStyleGenerator",
+        parameters = [
+            Parameter(name = SequenceStyleGenerator.DEF_SEQUENCE_NAME, value = "url_mapping_id_sequence"),
+            Parameter(name = SequenceStyleGenerator.INCREMENT_PARAM,   value = "1")
+        ]
     )
-    private var id: Int? = id
+    private var id: BigInteger? = id
 
     @Column(length = 2048, nullable = false)
     var url: String = url

shortener/src/main/kotlin/xyz/upbshrt/shortener/hibernate/SequenceStyleGenerator.kt

+package xyz.upbshrt.shortener.hibernate
+
+import java.io.Serializable
+import java.util.Properties
+
+import org.hibernate.MappingException
+import org.hibernate.engine.spi.SharedSessionContractImplementor
+import org.hibernate.service.ServiceRegistry
+import org.hibernate.type.Type
+
+/**
+ * Overrides Hibernate's default [org.hibernate.id.enhanced.SequenceStyleGenerator] to add support for manually
+ * assigned ids.
+ */
+class SequenceStyleGenerator : org.hibernate.id.enhanced.SequenceStyleGenerator() {
+
+    lateinit var entityName: String
+
+    override fun configure(type: Type?, params: Properties, serviceRegistry: ServiceRegistry?) {
+        entityName = params.getProperty(ENTITY_NAME) ?: throw MappingException("no entity name")
+        super.configure(type, params, serviceRegistry)
+    }
+
+    override fun generate(session: SharedSessionContractImplementor, `object`: Any?): Serializable =
+        session
+            .getEntityPersister("", `object`)
+            .getIdentifier(`object`, session)
+        ?: super.generate(session, `object`)
+}

shortener/src/main/kotlin/xyz/upbshrt/shortener/repository/UrlMappingRepository.kt

 package xyz.upbshrt.shortener.repository
 
+import java.math.BigInteger
+
 import org.springframework.data.jpa.repository.JpaRepository
 import org.springframework.stereotype.Repository
 
 import xyz.upbshrt.shortener.entity.UrlMapping
 
 @Repository
-interface UrlMappingRepository : JpaRepository<UrlMapping, Int>
+interface UrlMappingRepository : JpaRepository<UrlMapping, BigInteger>