import { describe, expect, it } from "vitest";
import themeCss from "./styles/theme-vars.css?raw";

interface ParsedColor {
  rgb: [number, number, number];
  alpha: number;
}

function parseThemeVars() {
  const matches = [
    ...themeCss.matchAll(/:root([^{]*)\{([\s\S]*?)\n {2}\}/g),
  ];

  const byTheme: Record<string, Record<string, string>> = {};

  for (const match of matches) {
    const selector = match[1];
    const body = match[2];
    const themes = [
      ...selector.matchAll(/data-theme="([^"]+)"/g),
    ].map((themeMatch) => themeMatch[1]);

    if (themes.length === 0) continue;

    const vars: Record<string, string> = {};
    for (const varMatch of body.matchAll(/--([\w-]+):\s*([^;]+);/g)) {
      vars[varMatch[1]] = varMatch[2].trim();
    }

    for (const theme of themes) {
      byTheme[theme] = { ...(byTheme[theme] ?? {}), ...vars };
    }
  }

  return byTheme;
}

function parseColor(value: string | undefined): ParsedColor {
  if (!value) {
    throw new Error("Missing color token.");
  }

  const hexMatch = value.match(/^#([\da-f]{3,8})$/i);
  if (hexMatch) {
    let hex = hexMatch[1];
    if (hex.length === 3) {
      hex = hex
        .split("")
        .map((char) => char + char)
        .join("");
    }

    let alpha = 1;
    if (hex.length === 8) {
      alpha = parseInt(hex.slice(6), 16) / 255;
      hex = hex.slice(0, 6);
    }

    return {
      rgb: [
        parseInt(hex.slice(0, 2), 16),
        parseInt(hex.slice(2, 4), 16),
        parseInt(hex.slice(4, 6), 16),
      ],
      alpha,
    };
  }

  const rgbMatch = value.match(/^rgba?\(([^)]+)\)$/i);
  if (rgbMatch) {
    const parts = rgbMatch[1].split(",").map((part) => part.trim());
    return {
      rgb: [
        Number(parts[0]),
        Number(parts[1]),
        Number(parts[2]),
      ],
      alpha: parts[3] === undefined ? 1 : Number(parts[3]),
    };
  }

  throw new Error(`Unsupported color format: ${value}`);
}

function blendColor(foreground: ParsedColor, background: ParsedColor): ParsedColor {
  if (foreground.alpha >= 1) return foreground;

  return {
    rgb: foreground.rgb.map((channel, index) =>
      channel * foreground.alpha + background.rgb[index] * (1 - foreground.alpha),
    ) as [number, number, number],
    alpha: 1,
  };
}

function relativeChannel(channel: number) {
  const normalized = channel / 255;
  return normalized <= 0.03928
    ? normalized / 12.92
    : ((normalized + 0.055) / 1.055) ** 2.4;
}

function luminance(color: ParsedColor) {
  const [r, g, b] = color.rgb;
  return (
    0.2126 * relativeChannel(r)
    + 0.7152 * relativeChannel(g)
    + 0.0722 * relativeChannel(b)
  );
}

function contrastRatio(foreground: ParsedColor, background: ParsedColor) {
  const a = luminance(foreground);
  const b = luminance(background);
  const [lighter, darker] = a >= b ? [a, b] : [b, a];
  return (lighter + 0.05) / (darker + 0.05);
}

describe("theme contrast tokens", () => {
  const themeVars = parseThemeVars();
  const themeIds = Object.keys(themeVars);

  it("keeps secondary text readable on the dashboard surfaces", () => {
    for (const themeId of themeIds) {
      const vars = themeVars[themeId];
      const surface = parseColor(vars["app-surface"]);
      const elevated = parseColor(vars["app-surface-elevated"]);
      const muted = parseColor(vars["app-text-muted"]);
      const soft = parseColor(vars["app-text-soft"]);
      const faint = parseColor(vars["app-text-faint"]);

      expect(
        contrastRatio(muted, surface),
        `${themeId} muted text should stay comfortably readable on the base surface`,
      ).toBeGreaterThanOrEqual(7);

      expect(
        contrastRatio(soft, surface),
        `${themeId} soft text should stay readable on the base surface`,
      ).toBeGreaterThanOrEqual(5);

      expect(
        contrastRatio(faint, elevated),
        `${themeId} faint text should still clear caption contrast on elevated surfaces`,
      ).toBeGreaterThanOrEqual(4.5);
    }
  });

  it("preserves a descending text hierarchy in every theme", () => {
    for (const themeId of themeIds) {
      const vars = themeVars[themeId];
      const surface = parseColor(vars["app-surface"]);
      const muted = parseColor(vars["app-text-muted"]);
      const soft = parseColor(vars["app-text-soft"]);
      const faint = parseColor(vars["app-text-faint"]);

      const mutedContrast = contrastRatio(muted, surface);
      const softContrast = contrastRatio(soft, surface);
      const faintContrast = contrastRatio(faint, surface);

      expect(
        mutedContrast,
        `${themeId} muted text should remain stronger than soft text`,
      ).toBeGreaterThan(softContrast);
      expect(
        softContrast,
        `${themeId} soft text should remain stronger than faint text`,
      ).toBeGreaterThan(faintContrast);
    }
  });

  it("keeps semantic chips readable when translucent fills sit on app surfaces", () => {
    const chipPairs = [
      ["app-attention-text", "app-attention-background"],
      ["app-success-text", "app-success-background"],
      ["app-danger-text", "app-danger-background"],
      ["app-info-text", "app-info-background"],
      ["role-leader-badge-text", "role-leader-badge-bg"],
      ["role-worker-badge-text", "role-worker-badge-bg"],
      ["stage-plan-text", "stage-plan-bg"],
      ["stage-review-text", "stage-review-bg"],
      ["stage-freeze-text", "stage-freeze-bg"],
      ["stage-execution-text", "stage-execution-bg"],
      ["stage-verification-text", "stage-verification-bg"],
    ] as const;

    for (const themeId of themeIds) {
      const vars = themeVars[themeId];
      const surface = parseColor(vars["app-surface"]);

      for (const [textToken, backgroundToken] of chipPairs) {
        const text = parseColor(vars[textToken]);
        const translucentBackground = parseColor(vars[backgroundToken]);
        const background = blendColor(translucentBackground, surface);

        expect(
          contrastRatio(text, background),
          `${themeId} ${textToken} on ${backgroundToken} should remain readable`,
        ).toBeGreaterThanOrEqual(4.5);
      }
    }
  });
});