require "option_parser"

BASE_SHAPE = [
  "      #      ",
  "     ###     ",
  "    #####    ",
  "   #######   ",
  "  #########  ",
  "   #######   ",
  "    #####    ",
  "     ###     ",
  "      #      ",
]

struct TermSize
  getter cols : Int32
  getter rows : Int32
  def initialize(@cols : Int32, @rows : Int32); end
end

def terminal_size : TermSize
  if STDOUT.tty?
    if (cols_env = ENV["COLUMNS"]?) && (rows_env = ENV["LINES"]?)
      cols = cols_env.to_i
      rows = rows_env.to_i
      return TermSize.new(cols: cols, rows: rows) if cols > 0 && rows > 0
    end
    buf = IO::Memory.new
    status = Process.run("stty", ["size"], output: buf, input: Process::Redirect::Close, error: Process::Redirect::Close)
    if status.success?
      parts = buf.to_s.strip.split(/\s+/)
      if parts.size == 2
        rows = parts[0].to_i
        cols = parts[1].to_i
        return TermSize.new(cols: cols, rows: rows) if cols > 0 && rows > 0
      end
    end
  end
  TermSize.new(cols: 80, rows: 24)
end

def enter_alt(io : IO)
  io << "\e[?1049h\e[?25l"
end

def leave_alt(io : IO)
  io << "\e[0m\e[?25h\e[?1049l"
end

def move_cursor(io : IO, row : Int32, col : Int32)
  io << "\e[#{row};#{col}H"
end

def scale_shape(shape : Array(String), factor : Int32) : Array(String)
  return shape if factor <= 1
  scaled = [] of String
  shape.each do |row|
    expanded = String.build do |io|
      row.each_char do |ch|
        fill = ch == ' ' ? ' ' : '#'
        factor.times { io << fill }
      end
    end
    factor.times { scaled << expanded }
  end
  scaled
end

fps = 24
scale = 1
band = 2
frames : Int32? = nil
no_color = false
use_alt = true
show_last = false

OptionParser.parse do |p|
  p.banner = "Animated crystal"
  p.on("--fps=FPS", "Frames per second") { |s| fps = s.to_i }
  p.on("--scale=N", "Integer scale >=1") { |s| scale = s.to_i; scale = 1 if scale < 1; scale = 8 if scale > 8 }
  p.on("--band=W", "Highlight band width") { |s| band = s.to_i; band = 1 if band < 1; band = 10 if band > 10 }
  p.on("--frames=N", "Stop after N frames") { |s| frames = s.to_i }
  p.on("--no-color", "Disable ANSI colors") { no_color = true }
  p.on("--no-alt", "Do not use alternate screen") { use_alt = false }
  p.on("--show-last", "Print last frame after exit") { show_last = true }
  p.on("-h", "--help", "Show help") { puts p; exit 0 }
end

shape = scale_shape(BASE_SHAPE, scale)
height = shape.size
width = shape.max_of(&.size)

base_color = no_color ? nil : "\e[38;5;45m"
highlight_color = no_color ? nil : "\e[38;5;123m"
reset = no_color ? nil : "\e[0m"

running = true
Signal::INT.trap { running = false }

phase = 0
period = (width + height)
band_units = band * scale

if use_alt
  STDOUT << String.build { |io| enter_alt(io) }
else
  STDOUT << "\e[?25l"
end
STDOUT.flush

begin
  frame_target_ns = (1_000_000_000_i64 // fps)
  frames_left = frames
  last_frame : String? = nil
  while running
    sz = terminal_size
    top = ((sz.rows - height) // 2) + 1
    left = ((sz.cols - width) // 2) + 1
    top = 1 if top < 1
    left = 1 if left < 1

    start = Time.monotonic

    frame_str = String.build do |io|
      io << "\e[2J"
      y = 0
      while y < height
        move_cursor(io, top + y, left)
        row = shape[y]
        x = 0
        while x < row.size
          ch = row.byte_at(x).unsafe_chr
          if ch != ' '
            sum = x + y
            d = sum - phase
            d %= period
            d += period if d < 0
            d = period - d if d > period // 2
            if d <= band_units
              io << highlight_color if highlight_color
            else
              io << base_color if base_color
            end
            io << '#'
          else
            io << ' '
          end
          x += 1
        end
        io << reset if reset
        y += 1
      end
      io << reset if reset
    end
    last_frame = frame_str
    STDOUT << frame_str
    STDOUT.flush

    phase += 1
    phase = 0 if phase >= period

    if frames_left
      frames_left -= 1
      break if frames_left <= 0
    end

    elapsed = Time.monotonic - start
    sleep_ns = frame_target_ns - elapsed.nanoseconds
    if sleep_ns > 0
      sleep sleep_ns.nanoseconds
    end
  end
ensure
  if use_alt
    STDOUT << String.build { |io| leave_alt(io) }
  else
    STDOUT << "\e[0m\e[?25h"
  end
  STDOUT.flush
  if show_last && last_frame
    STDOUT << last_frame
    STDOUT.flush
  end
end