Salesforce Email Merge

EmailLogic.cls

public class EmailLogic {

    public static String renderTemplate(sObject sobj, String template) {
        for (String fieldName : fields(sobj.getSObjectType())) {
            String key = '{!' + fieldName + '}';
            while (template.containsIgnoreCase(key)) {
                try {
                    Integer foundPosition = template.indexOfIgnoreCase(key, 0);
                    template = template.left(foundPosition) +
                        String.valueOf(sobj.get(fieldName)) +
                        template.substring(foundPosition + key.length());
                } catch (Exception e) {
                    // ignoring field not queried error for now because not sure if we want to query everything
                }
            }
        }
        return template;
    }

    public static String renderTemplate(Id id, String template) {
        Schema.sObjectType t = id.getSObjectType();
        String query = 
            'select ' + joinStrings(',', queryableFields(t)) + 
            ' from ' + t + 
            ' where Id = :id ';
        for (sObject sobj : Database.query(query)) {
            return renderTemplate(sobj, template);
        }
        return null;
    }
    
    private static String joinStrings (String delimiter, Set<String> items) {
        String result = '';
        for (String item : items) {
            if (result != '') result += delimiter;
            result += item;
        }
        return result;
    }
    
    private static Set<String> fields(Schema.sObjectType t) {
        Set<String> result = new Set<String>();
        Map<String, Schema.SObjectField> fields = t.getDescribe().fields.getMap();
        return fields.keySet();
    }

    private static Set<String> editableFields(Schema.sObjectType t) {
        Set<String> result = new Set<String>();
        Map<String, Schema.SObjectField> fields = t.getDescribe().fields.getMap();
        for(String fieldName : fields.keySet()) {
            if(fields.get(fieldName).getDescribe().isUpdateable()) {
                result.add(fieldName);
            }
        }
        return result;
    }

    private static Set<String> queryableFields(Schema.sObjectType t) {
        Set<String> result = new Set<String>();
        Map<String, Schema.SObjectField> fields = t.getDescribe().fields.getMap();
        for(String fieldName : fields.keySet()) {
            if(fields.get(fieldName).getDescribe().isUpdateable()) {
                result.add(fieldName);
            }
        }
        return result;
    }
    
    private static Set<String> createableFields(Schema.sObjectType t) {
        Set<String> result = new Set<String>();
        Map<String, Schema.SObjectField> fields = t.getDescribe().fields.getMap();
        for(String fieldName : fields.keySet()) {
            if(fields.get(fieldName).getDescribe().isCreateable()) {
                result.add(fieldName);
            }
        }
        return result;
    }
    
}

EmailLogicTests.cls

@isTest
private class EmailLogicTests {
    
    @isTest static void editableField () {
        System.assertEquals(
            '___TEST___', 
            EmailLogic.renderTemplate(
                new Account(Name='TEST'), 
                '___{!name}___'
            )
        );
    }

    @isTest static void caseInsensitive () {
        System.assertEquals(
            '___TEST___', 
            EmailLogic.renderTemplate(
                new Account(Name='TEST'), 
                '___{!NamE}___'
            )
        );
    }
    
    @isTest static void id() {
        // Implement test code
        TestFactory.accountSetup();
        System.assertEquals(
            '___'+TestFactory.testAccount.Id+'___', 
            EmailLogic.renderTemplate(
                TestFactory.testAccount, 
                '___{!id}___'
            )
        );
    }
    
}