Class: Clacky::UI2::TerminalDetector

Inherits:
Object
  • Object
show all
Defined in:
lib/clacky/ui2/terminal_detector.rb

Overview

TerminalDetector - Detect terminal background color before UI starts

Class Method Summary collapse

Class Method Details

.detect_dark_background ⇒ Boolean

Detect if terminal has dark background Uses multiple strategies to determine background color

Returns:

  • (Boolean) —

    true if dark background, false if light background



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# File 'lib/clacky/ui2/terminal_detector.rb', line 10

def self.detect_dark_background
  # Strategy 1: Check $COLORFGBG environment variable (fast, set by some terminals)
  if ENV.key?('COLORFGBG')
    # Format is like "15;0" where second number is background ANSI code
    # 0-7 are dark, 8-15 are light
    parts = ENV['COLORFGBG'].split(';')
    if parts.size >= 2
      bg_code = parts.last.to_i
      if bg_code >= 0 && bg_code <= 15
        return bg_code < 8
      end
    end
  end
  
  # Strategy 2: Query terminal background using OSC 11 sequence
  begin
    rgb = query_terminal_background_color
    if rgb
      # Calculate luma (perceived brightness): 0.0 (black) to 1.0 (white)
      # Formula: 0.299*R + 0.587*G + 0.114*B
      luma = (0.299 * rgb[:r] + 0.587 * rgb[:g] + 0.114 * rgb[:b]) / 255.0
      return luma < 0.5
    end
  rescue => e
    # Silently fall through to default
  end
  
  # Default: assume dark background (most common for terminals)
  true
end

.query_terminal_background_color ⇒ Hash?

Query terminal background color using OSC 11 sequence This should be called BEFORE UI starts to avoid interference

Returns:

  • (Hash, nil) —

    RGB hash like 26, g: 43, b: 60 or nil if failed



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# File 'lib/clacky/ui2/terminal_detector.rb', line 44

def self.query_terminal_background_color
  require 'io/console'
  
  # Only works on TTY
  return nil unless $stdin.tty?
  return nil unless $stdout.tty?
  
  old_state = nil
  begin
    # Save current terminal state
    old_state = $stdin.raw!
    
    # Clear any pending input first
    while IO.select([$stdin], nil, nil, 0)
      $stdin.read_nonblock(1000) rescue break
    end
    
    # Send OSC 11 query: ESC ] 11 ; ? ST
    # Use ST terminator (ESC \) instead of BEL for better compatibility
    $stdout.print "\e]11;?\e\\\\"
    $stdout.flush
    
    # Read response with timeout (terminal should respond quickly)
    response = String.new  # Use String.new to create mutable string
    timeout = 0.1  # 100ms timeout
    start_time = Time.now
    
    while Time.now - start_time < timeout
      if IO.select([$stdin], nil, nil, 0.01)
        char = $stdin.read_nonblock(1) rescue nil
        break unless char
        response << char
        
        # Look for complete response pattern
        # Response format: ESC ] 11 ; rgb:RRRR/GGGG/BBBB BEL or ST
        if response.match?(/\e\]11;rgb:[0-9a-fA-F]+\/[0-9a-fA-F]+\/[0-9a-fA-F]+(\e\\|\a)/)
          break
        end
        
        # Safety: stop if response gets too long (probably garbage)
        break if response.length > 100
      end
    end
    
    # Parse response: look for rgb:RRRR/GGGG/BBBB
    # Example: ]11;rgb:1a2b/3c4d/5e6f or ]11;rgb:ffff/ffff/ffff
    if response =~ /rgb:([0-9a-fA-F]+)\/([0-9a-fA-F]+)\/([0-9a-fA-F]+)/
      r_hex, g_hex, b_hex = $1, $2, $3
      # Take first 2 hex digits (terminals may return 4 or 2 hex digits per channel)
      r = r_hex[0, 2].to_i(16)
      g = g_hex[0, 2].to_i(16)
      b = b_hex[0, 2].to_i(16)
      return { r: r, g: g, b: b }
    end
    
    nil
  rescue => e
    # If anything goes wrong, return nil to fall back to default
    nil
  ensure
    # Make sure we restore terminal state even if error occurs
    old_state.restore if old_state rescue nil
    
    # Clear any remaining input to prevent leakage
    begin
      while IO.select([$stdin], nil, nil, 0)
        $stdin.read_nonblock(1000) rescue break
      end
    rescue
      # Ignore cleanup errors
    end
  end
end