fix: same values but different casing creates conflicting enums (#1259)

Enums in schema which has same value but different casing creates same
enum values which conflicts with each other. For instance,
[observed](cdk8s-team/cdk8s-cli#578 (comment))
while importing a custom resource definition in cdk8s.

```
\| 1086   REPLACE = 'replace',
--
\|        ~~~~~~~
\| com.coreos.monitoring.ts:1088:3 - error TS2300: Duplicate identifier 'REPLACE'.
\| 1088   REPLACE = 'Replace',
\|        ~~~~~~~
\| com.coreos.monitoring.ts:1090:3 - error TS2300: Duplicate identifier 'KEEP'.
\| 1090   KEEP = 'keep',
\|        ~~~~
\| com.coreos.monitoring.ts:1092:3 - error TS2300: Duplicate identifier 'KEEP'.
\| 1092   KEEP = 'Keep',
\|        ~~~~
\| com.coreos.monitoring.ts:1094:3 - error TS2300: Duplicate identifier 'DROP'.
\| 1094   DROP = 'drop',
\|        ~~~~
\| com.coreos.monitoring.ts:1096:3 - error TS2300: Duplicate identifier 'DROP'.
\| 1096   DROP = 'Drop',
```

Fixes cdk8s-team/cdk8s-cli#578

---------

Signed-off-by: Vinayak Kukreja <vinakuk@amazon.com>

src/type-generator.ts

@@ -521,6 +521,8 @@ export class TypeGenerator {
 
       code.openBlock(`export enum ${typeName}`);
 
+      const processedValues = new Set<string>();
+
       for (const value of def.enum) {
         if (!['string', 'number'].includes(typeof(value))) {
           throw new Error('only enums with string or number values are supported');
@@ -529,6 +531,15 @@ export class TypeGenerator {
         // sluggify and turn to UPPER_SNAKE_CASE
         let memberName = snakeCase(`${value}`.replace(/[^a-z0-9]/gi, '_')).split('_').filter(x => x).join('_').toUpperCase();
 
+        // If enums of same value exists, then we choose one of them and skip adding others
+        // since that would cause conflict
+        const lowerCaseValue = value?.toString().toLowerCase();
+        if (lowerCaseValue && !processedValues.has(lowerCaseValue)) {
+          processedValues.add(lowerCaseValue);
+        } else {
+          continue;
+        }
+
         // if member name starts with a non-alpha character, add a prefix so it becomes a symbol
         if (!/^[A-Z].*/i.test(memberName)) {
           memberName = 'VALUE_' + memberName;

test/type-generator.test.ts

@@ -300,6 +300,26 @@ describe('enums', () => {
       },
     },
   });
+
+  which('has repeated values', {
+    properties: {
+      Same: {
+        type: 'string',
+        enum: [
+          'replace',
+          'Replace',
+          'keep',
+          'Keep',
+          'hashmod',
+          'HashMod',
+          'labelmap',
+          'LabelMap',
+          '24',
+          '0.99',
+        ],
+      },
+    },
+  });
 });
 
 which('primitives', {