[Init] Initial commit - NetMesh terminal manager

domain/cursorLineHighlight.ts

@@ -0,0 +1,127 @@
+/** Pure helpers for the terminal cursor-line highlight (WindTerm-style). */
+
+export type CursorLineHighlightColors = {
+  background: string;
+  foreground: string;
+  selection: string;
+};
+
+const HEX_RGB_RE = /^#([0-9a-f]{3}|[0-9a-f]{6}|[0-9a-f]{8})$/i;
+
+type Rgb = { r: number; g: number; b: number };
+
+const MIN_CURSOR_LINE_CONTRAST = 4.5;
+
+const parseHexRgb = (value: string): Rgb | null => {
+  const match = value.trim().match(HEX_RGB_RE);
+  if (!match) return null;
+  let hex = match[1];
+  if (hex.length === 3) {
+    hex = hex.split('').map((ch) => ch + ch).join('');
+  } else if (hex.length === 8) {
+    hex = hex.slice(0, 6);
+  }
+  const r = Number.parseInt(hex.slice(0, 2), 16);
+  const g = Number.parseInt(hex.slice(2, 4), 16);
+  const b = Number.parseInt(hex.slice(4, 6), 16);
+  if (![r, g, b].every((channel) => Number.isFinite(channel))) return null;
+  return { r, g, b };
+};
+
+const relativeLuminance = ({ r, g, b }: Rgb): number => {
+  const linearize = (channel: number) => {
+    const normalized = channel / 255;
+    return normalized <= 0.03928
+      ? normalized / 12.92
+      : ((normalized + 0.055) / 1.055) ** 2.4;
+  };
+  return 0.2126 * linearize(r) + 0.7152 * linearize(g) + 0.0722 * linearize(b);
+};
+
+const contrastRatio = (left: Rgb, right: Rgb): number => {
+  const brighter = Math.max(relativeLuminance(left), relativeLuminance(right));
+  const darker = Math.min(relativeLuminance(left), relativeLuminance(right));
+  return (brighter + 0.05) / (darker + 0.05);
+};
+
+const mixRgb = (base: Rgb, accent: Rgb, amount: number): Rgb => ({
+  r: Math.round(base.r + (accent.r - base.r) * amount),
+  g: Math.round(base.g + (accent.g - base.g) * amount),
+  b: Math.round(base.b + (accent.b - base.b) * amount),
+});
+
+const toHex = ({ r, g, b }: Rgb): string =>
+  `#${[r, g, b].map((channel) => channel.toString(16).padStart(2, '0')).join('')}`;
+
+/** Keep the cursor-row background readable against other foreground decorations. */
+export const ensureCursorLineHighlightContrast = (
+  backgroundColor: string,
+  foregroundColors: readonly string[],
+): string => {
+  const background = parseHexRgb(backgroundColor);
+  const foregrounds = foregroundColors
+    .map(parseHexRgb)
+    .filter((color): color is Rgb => color !== null);
+  if (!background || foregrounds.length === 0) return backgroundColor;
+  const contrastScore = (candidate: Rgb) =>
+    Math.min(...foregrounds.map((foreground) => contrastRatio(candidate, foreground)));
+  const baseScore = contrastScore(background);
+  if (baseScore >= MIN_CURSOR_LINE_CONTRAST) return backgroundColor;
+
+  const black = { r: 0, g: 0, b: 0 };
+  const white = { r: 255, g: 255, b: 255 };
+  const blackScore = contrastScore(black);
+  const whiteScore = contrastScore(white);
+  if (blackScore >= MIN_CURSOR_LINE_CONTRAST && blackScore >= whiteScore) return '#000000';
+  if (whiteScore >= MIN_CURSOR_LINE_CONTRAST) return '#ffffff';
+  return blackScore >= Math.max(baseScore, whiteScore) ? '#000000' : '#ffffff';
+};
+
+/** Strength of the theme accent mixed into the terminal background. */
+export const CURSOR_LINE_HIGHLIGHT_BLEND = 0.55;
+
+/**
+ * Resolve an opaque background for the cursor line decoration.
+ * Prefers selection over foreground so the highlight stays theme-aligned.
+ * The renderer applies this only to cells with the default background, which
+ * keeps ANSI-colored cells and the terminal's text foreground untouched.
+ */
+export const resolveCursorLineHighlightBackground = (
+  colors: CursorLineHighlightColors,
+): string => {
+  const background = parseHexRgb(colors.background) ?? { r: 13, g: 17, b: 23 };
+  const backgroundLuminance =
+    background.r * 0.299 + background.g * 0.587 + background.b * 0.114;
+  const overlay =
+    parseHexRgb(colors.selection) ??
+    parseHexRgb(colors.foreground) ??
+    (backgroundLuminance >= 128
+      ? { r: 0, g: 0, b: 0 }
+      : { r: 255, g: 255, b: 255 });
+  const foreground =
+    parseHexRgb(colors.foreground) ??
+    (backgroundLuminance >= 128
+      ? { r: 0, g: 0, b: 0 }
+      : { r: 255, g: 255, b: 255 });
+  const contrastSafeAccents = [overlay, { r: 0, g: 0, b: 0 }, { r: 255, g: 255, b: 255 }];
+  const baseContrast = contrastRatio(background, foreground);
+  let mixed = background;
+  let bestContrast = baseContrast;
+  for (const [accentIndex, accent] of contrastSafeAccents.entries()) {
+    const maxAmount = accentIndex === 0 ? CURSOR_LINE_HIGHLIGHT_BLEND : 1;
+    for (let step = 20; step >= 0; step -= 1) {
+      const amount = maxAmount * (step / 20);
+      const candidate = mixRgb(background, accent, amount);
+      const candidateContrast = contrastRatio(candidate, foreground);
+      if (candidateContrast > bestContrast) {
+        mixed = candidate;
+        bestContrast = candidateContrast;
+      }
+      if (step > 0 && candidateContrast >= MIN_CURSOR_LINE_CONTRAST) {
+        mixed = candidate;
+        return toHex(mixed);
+      }
+    }
+  }
+  return toHex(mixed);
+};