defmodule SimpleshopTheme.Theme.CSSGenerator do
  @moduledoc """
  Generates CSS custom properties (Layer 2: Theme Tokens) from theme settings.

  This module converts ThemeSettings into CSS variables that bridge the gap
  between fixed primitives (Layer 1) and semantic aliases (Layer 3).
  """

  alias SimpleshopTheme.Settings.ThemeSettings

  @doc """
  Generates CSS for theme settings.

  Returns a string of CSS custom properties that can be injected into a <style> tag.
  """
  def generate(%ThemeSettings{} = settings) do
    """
    /* Theme Tokens - Layer 2 (dynamically generated) */
    .preview-frame, .shop-root {
      #{generate_accent(settings.accent_color)}
      #{generate_secondary_colors(settings)}
      #{generate_mood(settings.mood)}
      #{generate_typography(settings.typography)}
      #{generate_shape(settings.shape)}
      #{generate_density(settings.density)}
    }
    """
    |> String.trim()
  end

  # Accent color with HSL breakdown
  defp generate_accent(hex_color) do
    {h, s, l} = hex_to_hsl(hex_color)

    """
      --t-accent-h: #{h};
      --t-accent-s: #{s}%;
      --t-accent-l: #{l}%;
    """
  end

  # Secondary colors
  defp generate_secondary_colors(settings) do
    """
      --t-secondary-accent: #{settings.secondary_accent_color};
      --t-sale-color: #{settings.sale_color};
    """
  end

  # Mood variations (color schemes)
  defp generate_mood("neutral") do
    """
      --t-surface-base: #ffffff;
      --t-surface-raised: #ffffff;
      --t-surface-sunken: #f5f5f5;
      --t-surface-overlay: rgba(255, 255, 255, 0.95);
      --t-text-primary: #171717;
      --t-text-secondary: #525252;
      --t-text-tertiary: #a3a3a3;
      --t-text-inverse: #ffffff;
      --t-border-default: #e5e5e5;
      --t-border-subtle: #f0f0f0;
    """
  end

  defp generate_mood("warm") do
    """
      --t-surface-base: #fdf8f3;
      --t-surface-raised: #fffcf8;
      --t-surface-sunken: #f5ebe0;
      --t-surface-overlay: rgba(253, 248, 243, 0.95);
      --t-text-primary: #1c1917;
      --t-text-secondary: #57534e;
      --t-text-tertiary: #a8a29e;
      --t-text-inverse: #ffffff;
      --t-border-default: #e7e0d8;
      --t-border-subtle: #f0ebe4;
    """
  end

  defp generate_mood("cool") do
    """
      --t-surface-base: #f4f7fb;
      --t-surface-raised: #f8fafc;
      --t-surface-sunken: #e8eff7;
      --t-surface-overlay: rgba(244, 247, 251, 0.95);
      --t-text-primary: #0f172a;
      --t-text-secondary: #475569;
      --t-text-tertiary: #94a3b8;
      --t-text-inverse: #ffffff;
      --t-border-default: #d4dce8;
      --t-border-subtle: #e8eff5;
    """
  end

  defp generate_mood("dark") do
    """
      --t-surface-base: #0a0a0a;
      --t-surface-raised: #171717;
      --t-surface-sunken: #000000;
      --t-surface-overlay: rgba(23, 23, 23, 0.95);
      --t-text-primary: #fafafa;
      --t-text-secondary: #a3a3a3;
      --t-text-tertiary: #737373;
      --t-text-inverse: #171717;
      --t-border-default: #262626;
      --t-border-subtle: #1c1c1c;
      --p-shadow-strength: 0.25;
    """
  end

  # Typography styles
  defp generate_typography("clean") do
    """
      --t-font-heading: var(--p-font-inter);
      --t-font-body: var(--p-font-inter);
      --t-heading-weight: 600;
      --t-heading-tracking: -0.025em;
    """
  end

  defp generate_typography("editorial") do
    """
      --t-font-heading: var(--p-font-fraunces);
      --t-font-body: var(--p-font-source);
      --t-heading-weight: 600;
      --t-heading-tracking: -0.02em;
    """
  end

  defp generate_typography("modern") do
    """
      --t-font-heading: var(--p-font-space);
      --t-font-body: var(--p-font-space);
      --t-heading-weight: 500;
      --t-heading-tracking: -0.03em;
    """
  end

  defp generate_typography("classic") do
    """
      --t-font-heading: var(--p-font-baskerville);
      --t-font-body: var(--p-font-source);
      --t-heading-weight: 400;
      --t-heading-tracking: 0;
    """
  end

  defp generate_typography("friendly") do
    """
      --t-font-heading: var(--p-font-nunito);
      --t-font-body: var(--p-font-nunito);
      --t-heading-weight: 700;
      --t-heading-tracking: -0.01em;
    """
  end

  defp generate_typography("minimal") do
    """
      --t-font-heading: var(--p-font-outfit);
      --t-font-body: var(--p-font-outfit);
      --t-heading-weight: 300;
      --t-heading-tracking: 0;
    """
  end

  defp generate_typography("impulse") do
    """
      --t-font-heading: var(--p-font-avenir);
      --t-font-body: var(--p-font-avenir);
      --t-heading-weight: 300;
      --t-heading-tracking: 0.02em;
    """
  end

  # Shape variations (border radius)
  defp generate_shape("sharp") do
    """
      --t-radius-button: 0;
      --t-radius-card: 0;
      --t-radius-input: 0;
      --t-radius-image: 0;
    """
  end

  defp generate_shape("soft") do
    """
      --t-radius-button: var(--p-radius-md);
      --t-radius-card: var(--p-radius-lg);
      --t-radius-input: var(--p-radius-md);
      --t-radius-image: var(--p-radius-md);
    """
  end

  defp generate_shape("round") do
    """
      --t-radius-button: var(--p-radius-lg);
      --t-radius-card: var(--p-radius-xl);
      --t-radius-input: var(--p-radius-lg);
      --t-radius-image: var(--p-radius-lg);
    """
  end

  defp generate_shape("pill") do
    """
      --t-radius-button: var(--p-radius-full);
      --t-radius-card: var(--p-radius-xl);
      --t-radius-input: var(--p-radius-full);
      --t-radius-image: var(--p-radius-lg);
    """
  end

  # Density variations (spacing multiplier)
  defp generate_density("spacious") do
    """
      --t-density: 1.25;
    """
  end

  defp generate_density("balanced") do
    """
      --t-density: 1;
    """
  end

  defp generate_density("compact") do
    """
      --t-density: 0.85;
    """
  end

  # Convert hex color to HSL
  defp hex_to_hsl("#" <> hex), do: hex_to_hsl(hex)

  defp hex_to_hsl(hex) when byte_size(hex) == 6 do
    {r, ""} = Integer.parse(String.slice(hex, 0..1), 16)
    {g, ""} = Integer.parse(String.slice(hex, 2..3), 16)
    {b, ""} = Integer.parse(String.slice(hex, 4..5), 16)

    # Normalize RGB values to 0-1
    r = r / 255
    g = g / 255
    b = b / 255

    max = Enum.max([r, g, b])
    min = Enum.min([r, g, b])
    delta = max - min

    # Calculate lightness
    l = (max + min) / 2

    # Calculate saturation and hue
    {h, s} =
      if delta == 0 do
        {0, 0}
      else
        s = if l > 0.5, do: delta / (2 - max - min), else: delta / (max + min)

        h =
          cond do
            max == r -> (g - b) / delta + if(g < b, do: 6, else: 0)
            max == g -> (b - r) / delta + 2
            max == b -> (r - g) / delta + 4
          end

        {h * 60, s}
      end

    {round(h), round(s * 100), round(l * 100)}
  end

  # Handle invalid hex values
  defp hex_to_hsl(_), do: {0, 0, 50}
end