Entity-Component-System Helper Window for easy creation of files http://bengsfort.github.io/dev-logs/down-the-ecs-rabbit-hole/

ComponentTemplate.cs.tmpl

// {0}
// Created by {1} @ {2:d}
using System;
using FlyingIsHard.Assets.Bengsfort.Components.Core;

namespace FlyingIsHard.Assets.Bengsfort.Components
{{
	[Serializable]
	public class {0} : BaseComponent
	{{	
	}}
}}

ECSScaffoldingWindow.cs

using UnityEngine;
using UnityEditor;
using System;
using System.IO;

namespace FlyingIsHard.Assets.Bengsfort.EditorTools
{
    public enum ScaffoldDialogType
    {
        Component,
        System,
        Entity
    }

    public class ECSScaffoldingWindow : EditorWindow
    {
        // Default menu base
        const string c_MenuPath = "ECS Scaffold";
        // What sort of file does the user want to scaffold?
        public ScaffoldDialogType type = ScaffoldDialogType.Component;
        
        string[] m_DialogTitles = new string[]
        {
            "Component",
            "System",
            "Entity"
        };
        
        // The user-input class name
        string m_ClassName = "";
        // The user-input template file
        string m_TemplateFile = "";

        // Store the users name so they dont have to constantly re-type it
        public string DevName
        {
            get
            {
                return EditorPrefs.GetString("FIH_ECS_Name", "");
            }
            set
            {
                EditorPrefs.SetString("FIH_ECS_Name", value);
            }
        }


        [MenuItem(c_MenuPath + "/New Entity")]
        static void CreateEntity()
        {
            // Create and position the window
            var window = ScriptableObject.CreateInstance<ECSScaffoldingWindow>();
            window.position = new Rect(
                Screen.width / 2.0f, Screen.height / 2.0f,
                250.0f, 150.0f
            );
            window.type = ScaffoldDialogType.Entity;
            window.ShowPopup();
        }

        [MenuItem(c_MenuPath + "/New Component")]
        static void CreateComponent()
        {
            // Create and position the window
            var window = ScriptableObject.CreateInstance<ECSScaffoldingWindow>();
            window.position = new Rect(
                Screen.width / 2.0f, Screen.height / 2.0f,
                250.0f, 150.0f
            );
            window.type = ScaffoldDialogType.Component;
            window.ShowPopup();
        }

        [MenuItem(c_MenuPath + "/New System")]
        static void CreateSystem()
        {
            // Create and position the window
            var window = ScriptableObject.CreateInstance<ECSScaffoldingWindow>();
            window.position = new Rect(
                Screen.width / 2.0f, Screen.height / 2.0f,
                250.0f, 150.0f
            );
            window.type = ScaffoldDialogType.System;
            window.ShowPopup();
        }

        void CreateClassFromTemplate()
        {
            // Get the template path
            var tmplPathPrefix = Application.dataPath + "/Bengsfort/Editor/Scaffolding/Templates";
            var tmplFile = (tmplPathPrefix + "/" + m_DialogTitles[(int)type] + "Template.cs.tmpl")
                .Replace('/', Path.DirectorySeparatorChar);
            
            // Check for the existence of the template
            if (!File.Exists(tmplFile))
            {
                Debug.LogError("Missing the template file!");
                return;
            }
            
            // Try to create the new template
            try
            {
                // Read the file to a variable than format it with the new data
                var template = File.ReadAllText(tmplFile, System.Text.Encoding.UTF8);
                m_TemplateFile = string.Format(template,
                    m_ClassName,
                    DevName,
                    DateTime.Now
                );
                
                // Determine the correct output file
                var targetFile = Application.dataPath + "/Bengsfort";
                switch (type)
                {
                    case ScaffoldDialogType.Component:
                        targetFile += "/Components/" + m_ClassName + ".cs";
                        break;
                    case ScaffoldDialogType.Entity:
                        targetFile += "/Entities/" + m_ClassName + ".cs";
                        break;
                    case ScaffoldDialogType.System:
                        targetFile += "/Systems/" + m_ClassName + ".cs";
                        break;
                }
                
                // Reformat the path to the output file to be platform agnostic
                var newClass = targetFile.Replace('/', Path.DirectorySeparatorChar);

                // Write the shiny new file to disk
                File.WriteAllText(
                    newClass,
                    m_TemplateFile
                );
                
                // Tell Unity to import the asset
                AssetDatabase.ImportAsset(
                    newClass.Substring(newClass.IndexOf("Assets" + Path.DirectorySeparatorChar + "Bengsfort")), 
                    ImportAssetOptions.ForceUpdate
                );
            }
            catch (FormatException e)
            {
                // Oh noes! D: It failed!
                Debug.LogError("There was an error creating the new class!");
                Debug.LogError(e.Message);
            }
        }

        void OnGUI()
        {
            // Title
            EditorGUILayout.LabelField(
                "Create new " + m_DialogTitles[(int)type],
                EditorStyles.boldLabel
            );

            // Name field
            EditorGUILayout.BeginHorizontal();
            EditorGUILayout.PrefixLabel("Creator Name");
            EditorGUILayout.BeginVertical();
            DevName = EditorGUILayout.TextField(DevName);
            EditorGUILayout.EndVertical();
            EditorGUILayout.EndHorizontal();

            // Title
            EditorGUILayout.BeginHorizontal();
            EditorGUILayout.PrefixLabel("Class name");
            EditorGUILayout.BeginVertical();
            m_ClassName = EditorGUILayout.TextField(m_ClassName);
            EditorGUILayout.EndVertical();
            EditorGUILayout.EndHorizontal();

            // Create!
            if (GUILayout.Button("Create"))
            {
                if (m_ClassName == "")
                {
                    this.Close();
                }

                Debug.Log("Creating class " + m_ClassName);
                CreateClassFromTemplate();
                this.Close();
            }

            // Cancel
            if (GUILayout.Button("Cancel"))
            {
                this.Close();
            }
        }
    }
}

EntityTemplate.cs.tmpl

// {0}
// Created by {1} @ {2:d}
using System;
using UnityEngine;
using FlyingIsHard.Assets.Bengsfort.Entities.Core;
using FlyingIsHard.Assets.Bengsfort.Components;
using FlyingIsHard.Assets.Bengsfort.Systems;

namespace FlyingIsHard.Assets.Bengsfort.Entities
{{
    public class {0} : BaseEntity
    {{
        // public MyComponent component;

		    // private MySystem m_System;

        void Start()
        {{
            // m_System = new MySystem(component);
        }}

        void Update()
        {{
            // m_System.Tick();
        }}
    }}
}}

SystemTemplate.cs.tmpl

// {0}
// Created by {1} @ {2:d}
using FlyingIsHard.Assets.Bengsfort.Systems.Core;
using FlyingIsHard.Assets.Bengsfort.Components;

namespace FlyingIsHard.Assets.Bengsfort.Systems
{{
    public class {0} : BaseSystem
    {{
        // private MyComponent m_Component;

		    // Loop Tick
        public override void Tick()
        {{
        }}

		    // Constructor
        public {0}()
        {{
            // m_Component = providedComponent;
        }}
    }}
}}