Inital commit.

Author: Nilan

.gitignore

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+*.jar
+.idea
+build
+.gradle

README.md

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+# cuid-java

build.gradle

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+group 'cool.graph.cuid-java'
+version '0.1.0-SNAPSHOT'
+
+apply plugin: 'java'
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    testCompile group: 'junit', name: 'junit', version: '4.11'
+}

gradle/wrapper/gradle-wrapper.properties

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+#Wed Jun 08 23:34:24 CEST 2016
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-2.9-all.zip

gradlew

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+rootProject.name = 'cuid-java'
+

gradlew.bat

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+import java.lang.management.ManagementFactory;
+import java.util.Date;
+
+public class Cuid {
+    private static final int BASE = 36;
+    private static final int BLOCK_SIZE = 4;
+    private static final int DISCRETE_VALUES = (int) Math.pow(BASE, BLOCK_SIZE);
+    private static final String LETTER = "c";
+
+    private static final String FINGERPRINT;
+
+    static {
+        FINGERPRINT = getFingerprint();
+    }
+
+    private static int counter = 0;
+
+    private static String getHostInfo(String idFallback, String nameFallback) {
+        String jvmName = ManagementFactory.getRuntimeMXBean().getName();
+        final int index = jvmName.indexOf('@');
+        if (index < 1) {
+            return String.format("%s@%s", idFallback, nameFallback);
+        }
+
+        return jvmName;
+    }
+
+    private static String getFingerprint() {
+        String hostInfo = getHostInfo(Long.toString(new Date().getTime()), "dummy-host");
+
+        String hostId = hostInfo.split("@")[0];
+        String hostname = hostInfo.split("@")[1];
+
+        int acc = hostname.length() + BASE;
+        for (int i = 0; i < hostname.length(); i++) {
+            acc += acc + (int) hostname.charAt(i);
+        }
+
+        String idBlock = pad(Long.toString(Long.parseLong(hostId), BASE), 2);
+        String nameBlock = pad(Integer.toString(acc), 2);
+
+        return idBlock + nameBlock;
+    }
+
+    private static String pad(String input, int size) {
+        // courtesy of http://stackoverflow.com/a/4903603/1176596
+        String repeatedZero = new String(new char[size]).replace("\0", "0");
+        String padded = repeatedZero + input;
+        return (padded).substring(padded.length() - size);
+    }
+
+    private static String getRandomBlock() {
+        return pad(Integer.toString((int) (Math.random() * DISCRETE_VALUES), BASE), BLOCK_SIZE);
+    }
+
+    private static int safeCounter() {
+        counter = counter < DISCRETE_VALUES ? counter : 0;
+        return counter++;
+    }
+
+    public static String createCuid() {
+        String timestamp = Long.toString(new Date().getTime(), BASE);
+        String counter = pad(Integer.toString(safeCounter(), BASE), BLOCK_SIZE);
+        String random = getRandomBlock() + getRandomBlock();
+
+        return String.join("", LETTER, timestamp, counter, FINGERPRINT , random);
+    }
+}

settings.gradle

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+import org.junit.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.junit.Assert.*;
+
+public class CuidTest {
+    @Test
+    public void createCuid() throws Exception {
+        // more sane tests?
+        assertEquals(Cuid.createCuid().charAt(0), 'c');
+    }
+
+    private boolean hasNoCollisions() {
+        int iterations = 4200000;
+        Map<String, String> cuids = new HashMap<>();
+
+        for (int i = 0; i < iterations; ++i) {
+            String cuid = Cuid.createCuid();
+            if (cuids.containsKey(cuid)) {
+                return false;
+            } else {
+                cuids.put(cuid, cuid);
+            }
+        }
+
+        return true;
+    }
+
+    @Test
+    public void testForCollisions() {
+        assertEquals(hasNoCollisions(), true);
+    }
+}