Build a Full-Featured Text Editor From Scratch | 0xKiire

This article covers Build a Full-Featured Text Editor From Scratch — Architecture, Design Patterns & Complete Checklist. Language-agnostic & pattern-driven. Every step describes what to build, why it is designed that way, and which Gang ...

Table of Contents

Understand the Architecture: A Bird's-Eye View

The Buffer — Storing Text Efficiently

The Piece Table — The Heart of Editing

The Cursor & Selection Model

The Command Pattern — Undo & Redo

The Observer Pattern — Event System

The View Layer — Rendering the Buffer

The Viewport & Scrolling

Syntax Highlighting

The Mode System (Modal Editing)

The Plugin Architecture

The Language Server Protocol (LSP) Client

LSP Features — Autocomplete, Diagnostics & Code Actions

The File System & Buffer Manager

Search & Replace

Configuration System

The Workspace & Project Model

The Keybinding System

Test Suites

Recommended Build Order

SOLID Principles: Your Constant Compass

Throughout this guide, every architectural decision is evaluated against the five SOLID principles. Internalize these before writing a single line:

Principle<br>One-line definition<br>What it prevents in a text editor

S ingle Responsibility<br>Every class has one reason to change<br>Buffer logic leaking into rendering; cursor logic mixed with file I/O

O pen/Closed<br>Open for extension, closed for modification<br>Adding a new language requires editing the core syntax engine

L iskov Substitution<br>Subtypes must be substitutable for their base type<br>A ReadOnlyBuffer that silently ignores writes, breaking callers

I nterface Segregation<br>No client should depend on methods it doesn't use<br>Forcing a simple file loader to implement LSP notification methods

D ependency Inversion<br>Depend on abstractions, not concretions<br>The editor core importing a specific LSP library directly

These are not theoretical — each step below calls out exactly which principle is at stake.

1. Understand the Architecture: A Bird's-Eye View

The Layered Architecture

A professional text editor separates concerns into discrete, testable layers. Each layer communicates with adjacent layers only through well-defined interfaces (DIP). No layer reaches across to a non-adjacent layer.

┌─────────────────────────────────────────────────────────────────┐<br>│ USER INTERFACE LAYER │<br>│ Keybindings │ Command Palette │ Status Bar │ Tab Bar │<br>├─────────────────────────────────────────────────────────────────┤<br>│ VIEW LAYER │<br>│ Viewport │ Line Renderer │ Cursor Renderer │ Decorations │<br>├─────────────────────────────────────────────────────────────────┤<br>│ FEATURE LAYER │<br>│ Syntax Highlighting │ LSP Client │ Search │ Autocomplete │<br>├─────────────────────────────────────────────────────────────────┤<br>│ EDITOR CORE │<br>│ Buffer (Piece Table) │ Cursor Model │ Selection │ Undo │<br>├─────────────────────────────────────────────────────────────────┤<br>│ INFRASTRUCTURE LAYER │<br>│ File System │ Process Spawner │ Config Loader │ Plugins │<br>└─────────────────────────────────────────────────────────────────┘

Component Relationships (Dependency Graph)

Config ──────────────────► Editor<br>┌──────────────┤<br>│ │<br>BufferManager KeyBindings<br>┌──────┤<br>│ │<br>Buffer Buffer (one per open file)<br>┌────┴────────┐<br>│ │<br>PieceTable UndoStack<br>Commands[]

GoF Patterns Used in This Project (Quick Map)

Pattern<br>Category<br>Where used

Command<br>Behavioral<br>Undo/Redo system

Observer<br>Behavioral<br>Event bus between components

State<br>Behavioral<br>Editor modes (Normal, Insert, Visual)

Strategy<br>Behavioral<br>Syntax highlighting engines, diff algorithms

Decorator<br>Structural<br>Buffer decorations, diagnostic overlays

Composite<br>Structural<br>Workspace tree, document AST

Facade<br>Structural<br>LSP client API

Factory Method<br>Creational<br>Buffer creation, language detector

Singleton<br>Creational<br>Event bus, config registry (use sparingly)

Iterator<br>Behavioral<br>Buffer line/character traversal

Chain of Responsibility<br>Behavioral<br>Keybinding processing pipeline

Flyweight<br>Structural<br>Token color caching, glyph reuse

Checklist

Draw the full layer diagram for your implementation before writing any code.

Define each layer's public interface (the abstraction) before implementing it.

Establish the rule: upper layers depend on lower layers; lower layers never import upper layers.

Choose your rendering target early: terminal (TUI), native GUI (OpenGL/Metal/D2D), or web (Canvas/WebGL). This affects only the View layer — the core remains identical.

Decide on your concurrency model: async I/O for LSP, synchronous editing core.

2. The Buffer — Storing Text Efficiently

Why a Naive String Doesn't Work

The most obvious representation — a single string or array of characters — fails badly for a text editor:

// Naive: insert 'X' at position 50,000 in a 1 MB file<br>buffer = buffer[0..50000] + 'X' + buffer[50000..]<br>// This copies ~950,000 characters on every single keystroke.<br>// At 60 WPM, the editor becomes unusable within seconds.

Three Real-World Approaches

Structure<br>Insert<br>Delete<br>Access...