home-lab/packages/lab-tool/REFACTORING_SUMMARY.md

K.I.S.S Refactoring Summary

Applied Principles

1. Modularization (Keep It Simple, Keep It Small)

• Before: Large monolithic modules (138+ lines)
• After: Small focused modules (each under 50 lines)
• Example: SSH module split into 5 specialized modules

2. Single Responsibility Principle (UNIX Philosophy: Do One Thing Well)

• connection-test.scm: Only SSH connectivity testing
• remote-command.scm: Only remote command execution
• file-copy.scm: Only file transfer operations
• retry.scm: Only retry logic
• context.scm: Only connection context management

3. Functional Programming Patterns

• Pure Functions First: All core logic implemented as pure functions
• Immutable Data: Configuration and data structures remain immutable
• Separation of Concerns: Pure functions separated from side effects

4. Function-Level Modularity

Each module exports both:

• Pure functions: For testing, composition, and functional programming
• Impure wrappers: For convenience and logging

Module Structure

utils/
├── ssh/
│   ├── connection-test.scm    # Pure SSH connectivity testing
│   ├── remote-command.scm     # Pure command execution logic
│   ├── file-copy.scm          # Pure file transfer operations
│   ├── retry.scm              # Pure retry logic with backoff
│   └── context.scm            # Connection context management
├── config/
│   ├── defaults.scm           # Pure data: default configuration
│   ├── loader.scm             # File I/O operations
│   ├── accessor.scm           # Pure configuration access functions
│   └── state.scm              # Mutable state management
├── logging/
│   ├── format.scm             # Pure formatting and color codes
│   ├── level.scm              # Pure log level management
│   ├── state.scm              # Mutable log level state
│   ├── output.scm             # Pure output formatting
│   ├── core.scm               # Main logging functions
│   └── spinner.scm            # Progress indication
└── json/
    ├── parse.scm              # Pure JSON parsing
    ├── serialize.scm          # Pure JSON serialization
    ├── file-io.scm            # File I/O with pure/impure versions
    ├── validation.scm         # Pure schema validation
    ├── manipulation.scm       # Pure object manipulation
    └── pretty-print.scm       # Output formatting

Benefits Achieved

1. Testability

• Pure functions can be tested in isolation
• No side effects to mock or manage
• Clear input/output contracts

2. Composability

• Small functions can be easily combined
• Pure functions enable functional composition
• Reusable building blocks

3. Maintainability

• Single responsibility makes modules easy to understand
• Changes are localized to specific modules
• Clear separation between pure and impure code

4. Code Reuse

• Pure functions can be reused across different contexts
• Both pure and impure versions available
• Facade modules provide convenient interfaces

Usage Examples

Pure Function Composition

;; Test connection and get config in one go
(let ((ssh-config (get-ssh-config-pure config "machine-name")))
  (if (test-ssh-connection-pure ssh-config)
      (run-remote-command-pure ssh-config "uptime" '())
      #f))

Convenient Impure Wrappers

;; Same operation with logging and error handling
(with-ssh-connection "machine-name"
  (lambda () (run-remote-command "machine-name" "uptime")))

Functional Pipeline

;; Pure validation pipeline
(let* ((config (load-config-from-file "config.json"))
       (valid? (validate-json-schema config machine-schema))
       (machines (if valid? (get-all-machines-pure config) '())))
  machines)

This refactoring transforms the codebase from monolithic modules into a collection of small, focused, composable functions that follow functional programming principles while maintaining practical usability.