Added solution for browser design

YogenRaii · YogenRaii · commit ef8cbbb6745d · 2019-06-26T18:14:01.000-05:00
diff --git a/src/main/java/com/eprogrammerz/examples/ds/browser/Browser.java b/src/main/java/com/eprogrammerz/examples/ds/browser/Browser.java
@@ -0,0 +1,98 @@
+package com.eprogrammerz.examples.ds.browser;
+
+/**
+ * Design a browser
+ * 1. Enter address on address bar
+ * 2. Click on link to go to new page
+ * 2. User should be able to click on back button to get to the earlier back page
+ * 3. User should be able to click on forward to get the earlier forward page
+ * 3. If user enters new address on address bar, loses forward pages but retains backward pages
+ */
+public class Browser {
+    private class BrowserState {
+        String address;
+        BrowserState back;
+        BrowserState forward;
+
+        BrowserState(String address) {
+            this.address = address;
+        }
+    }
+
+    private BrowserState browserState;
+
+    /**
+     * Browser starts with no particular address
+     */
+    public Browser() {
+        this.browserState = new BrowserState("");
+    }
+
+    /**
+     * When new address is entered in url input, then it adds new node into list
+     * @param address
+     */
+    void newPage(String address) {
+        BrowserState current = browserState;
+        if (current.forward != null) {
+            current.forward.back = null;
+        }
+
+        BrowserState newState = new BrowserState(address);
+        newState.forward = null;
+        newState.back = current;
+
+        current.forward = newState;
+
+        browserState = newState;
+    }
+
+    /**
+     * If link within current page is linked, history will be updated
+     * @param newAddress
+     * @return
+     */
+    String click(String newAddress) {
+        BrowserState newState = new BrowserState(newAddress);
+        newState.forward = null;
+        newState.back = browserState;
+
+        browserState.forward = newState;
+        browserState = newState;
+        return browserState.address;
+    }
+
+    /**
+     * Clicking on back doesn't takes to the previous page in the history if exists
+     *
+     * @return
+     */
+    String back() {
+        BrowserState currentState = browserState;
+        if (currentState.back != null) {
+            currentState = currentState.back;
+            browserState = currentState;
+        }
+        return browserState.address;
+    }
+
+    /**
+     * Clicking on forward takes to the forward page in history if exists
+     * @return
+     */
+    String forward() {
+        if (browserState.forward != null) {
+            browserState = browserState.forward;
+            return browserState.address;
+        }
+        return null;
+    }
+
+    /**
+     * Gives current address
+     * @return
+     */
+    String getCurrentAddress() {
+        return this.browserState.address;
+    }
+}
diff --git a/src/main/java/com/eprogrammerz/examples/ds/browser/BrowserTest.java b/src/main/java/com/eprogrammerz/examples/ds/browser/BrowserTest.java
@@ -0,0 +1,48 @@
+package com.eprogrammerz.examples.ds.browser;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+
+public class BrowserTest {
+
+    @Test
+    public void testBrowser() {
+        Browser browser = new Browser();
+        browser.newPage("yogen.rai");
+        assertEquals("yogen.rai", browser.getCurrentAddress());
+
+        browser.back();
+        assertEquals("", browser.getCurrentAddress());
+
+        browser.forward();
+        assertEquals("yogen.rai", browser.getCurrentAddress());
+
+
+        browser.newPage("new.yogen.rai");
+        assertEquals("new.yogen.rai", browser.getCurrentAddress());
+
+        browser.back();
+        assertEquals("yogen.rai", browser.getCurrentAddress());
+
+        browser.forward();
+        assertEquals("new.yogen.rai", browser.getCurrentAddress());
+
+        browser.back();
+        assertEquals("yogen.rai", browser.getCurrentAddress());
+
+        browser.newPage("very.new.yogen.rai");
+        assertEquals("very.new.yogen.rai", browser.getCurrentAddress());
+
+        assertNull(browser.forward());
+
+        assertEquals("yogen.rai", browser.back());
+
+        assertEquals("click.yogen.rai", browser.click("click.yogen.rai"));
+        assertEquals("click.yogen.rai", browser.getCurrentAddress());
+
+        assertEquals("yogen.rai", browser.back());
+        assertEquals("click.yogen.rai", browser.forward());
+    }
+}
