import { DEFAULT_COLORS, INSTANCE_DEFAULTS, baseColor } from './settings-sync.js';
import { getLocale } from './i18n.js';

export function isToday(d) {
  const now = new Date();
  return d.getFullYear() === now.getFullYear() &&
         d.getMonth()    === now.getMonth()    &&
         d.getDate()     === now.getDate();
}

export function isSameDay(a, b) {
  return a.getFullYear() === b.getFullYear() &&
         a.getMonth()    === b.getMonth()    &&
         a.getDate()     === b.getDate();
}

export function isPast(ev) {
  const end = new Date(ev.end);
  return end < new Date();
}

// Title to render for an event: the server-decorated one (birthday age, group
// prefix) wins over the raw title, which stays untouched for editing.
export function eventTitle(ev) {
  return ev.display_title || ev.title || '';
}

// Small inline cake icon for birthday events, sized to the surrounding text and
// tinted with the current text colour so it matches every bar it's dropped into.
export function birthdayIconSvg() {
  return '<svg viewBox="0 0 24 24" aria-hidden="true" '
    + 'style="width:0.85em;height:0.85em;vertical-align:-0.1em;margin-right:2px;flex:0 0 auto">'
    + '<path fill="currentColor" d="M12 6c1.11 0 2-.9 2-2 0-.38-.1-.73-.29-1.03L12 0l-1.71 2.97'
    + 'c-.19.3-.29.65-.29 1.03 0 1.1.9 2 2 2zm4.6 9.99l-1.07-1.07-1.08 1.07c-1.3 1.3-3.58 1.31-4.89 0'
    + 'l-1.07-1.07-1.09 1.07C6.75 16.64 5.88 17 4.96 17c-.73 0-1.4-.23-1.96-.61V21c0 .55.45 1 1 1h16'
    + 'c.55 0 1-.45 1-1v-4.61c-.56.38-1.23.61-1.96.61-.92 0-1.79-.36-2.44-1.01zM18 9h-5V7h-2v2H6'
    + 'c-1.66 0-3 1.34-3 3v1.54c0 1.08.88 1.96 1.96 1.96.52 0 1.02-.2 1.38-.57l2.14-2.13 2.13 2.13'
    + 'c.74.74 2.03.74 2.77 0l2.14-2.13 2.13 2.13c.37.37.86.57 1.38.57 1.08 0 1.96-.88 1.96-1.96V12'
    + 'c.01-1.66-1.33-3-2.99-3z"/></svg>';
}

export function formatDate(d, opts = {}) {
  return d.toLocaleDateString(getLocale(), opts);
}

export function dateKey(d) {
  return `${d.getFullYear()}-${String(d.getMonth()+1).padStart(2,'0')}-${String(d.getDate()).padStart(2,'0')}`;
}

export function toLocalDatetimeInput(d) {
  const Y = d.getFullYear();
  const M = String(d.getMonth()+1).padStart(2,'0');
  const D = String(d.getDate()).padStart(2,'0');
  const h = String(d.getHours()).padStart(2,'0');
  const m = String(d.getMinutes()).padStart(2,'0');
  return `${Y}-${M}-${D}T${h}:${m}`;
}

export function toDateInput(d) {
  return `${d.getFullYear()}-${String(d.getMonth()+1).padStart(2,'0')}-${String(d.getDate()).padStart(2,'0')}`;
}

// Monday-first: returns 0=Mo, 1=Di, ..., 6=So
export function dayOfWeek(d, weekStartDay = 'monday') {
  if (weekStartDay === 'sunday') {
    return d.getDay(); // 0=So, 1=Mo, ..., 6=Sa
  }
  return (d.getDay() + 6) % 7; // 0=Mo, 1=Di, ..., 6=So
}

// Returns the start-of-week date for d
export function weekStart(d, weekStartDay = 'monday') {
  const m = new Date(d);
  m.setDate(m.getDate() - dayOfWeek(m, weekStartDay));
  m.setHours(0, 0, 0, 0);
  return m;
}

// Returns the ISO week number (Monday-based, ISO 8601)
export function getISOWeekNumber(d) {
  const date = new Date(Date.UTC(d.getFullYear(), d.getMonth(), d.getDate()));
  // ISO week: weeks start on Monday, week 1 contains the first Thursday
  const day = date.getUTCDay() || 7; // make Sunday = 7
  date.setUTCDate(date.getUTCDate() + 4 - day);
  const yearStart = new Date(Date.UTC(date.getUTCFullYear(), 0, 1));
  return Math.ceil((((date - yearStart) / 86400000) + 1) / 7);
}

const TEXT_CONTRAST = {
  1: { t1: '#606070', t2: '#484858', t3: '#303040' },
  2: { t1: '#9090a8', t2: '#6a6a80', t3: '#484860' },
  3: { t1: '#c8c8d8', t2: '#9090aa', t3: '#55556a' },
  4: { t1: '#ffffff', t2: '#c0c0d8', t3: '#8888a0' },
};
const LINE_CONTRAST = {
  1: { border: '#1e1e2c', light: '#181826' },
  2: { border: '#2a2a3c', light: '#222230' },
  3: { border: '#3a3a52', light: '#2e2e40' },
  4: { border: '#5a5a78', light: '#484860' },
};

// Default-Farben: EINZIGE Quelle ist DEFAULT_COLORS in settings-sync.js.
// Dort ändern → wirkt für Reset (Tabelle) und diese Theme-Fallbacks gleichzeitig.
export const DEFAULT_TEXT_COLOR = DEFAULT_COLORS.text_color;
export const DEFAULT_LINE_COLOR = DEFAULT_COLORS.line_color;
export const DEFAULT_BG_COLOR   = DEFAULT_COLORS.bg_color;

export function applyTheme(settings) {
  const root = document.documentElement;
  // Fallback chain for a colour that has no per-user value: admin instance
  // default → built-in default (baseColor()).
  const primary = settings.primary_color || baseColor('primary_color');
  root.style.setProperty('--primary',     primary);
  root.style.setProperty('--primary-dim', hexToRgba(primary, 0.15));
  root.style.setProperty('--accent',      settings.accent_color  || baseColor('accent_color'));
  root.style.setProperty('--today-color', settings.today_color   || baseColor('today_color'));

  // Effektive Farben bestimmen (Override > Admin-Default > eingebauter Default).
  let textColor = settings.text_color || baseColor('text_color');
  let lineColor = settings.line_color || baseColor('line_color');
  let bgColor   = settings.bg_color   || baseColor('bg_color');

  // Sicherheitsbremse: Wenn Schrift- und Hintergrundfarbe nicht genug
  // Kontrast haben (passiert wenn man aus Versehen text=bg eingibt),
  // erzwinge weiss-auf-schwarz, damit man nicht in einer unbedienbaren
  // Seite landet.
  if (contrastRatio(textColor, bgColor) < 2.5) {
    textColor = DEFAULT_TEXT_COLOR;
    bgColor   = DEFAULT_BG_COLOR;
  }

  root.style.setProperty('--text-1', textColor);
  root.style.setProperty('--text-2', shadeHex(textColor, -0.25));
  root.style.setProperty('--text-3', shadeHex(textColor, -0.55));

  root.style.setProperty('--border',       lineColor);
  root.style.setProperty('--border-light', shadeHex(lineColor, -0.25));

  // Surface family (sidebar / top bar / cards). Explicit surface_color drives
  // it; otherwise derive from the app background as before.
  const surfaceBase = settings.surface_color || shadeHex(bgColor, 0.10);
  root.style.setProperty('--bg-app',     bgColor);
  root.style.setProperty('--bg-topbar',  surfaceBase);
  root.style.setProperty('--bg-sidebar', surfaceBase);
  root.style.setProperty('--bg-surface', shadeHex(surfaceBase, 0.10));
  root.style.setProperty('--bg-hover',   shadeHex(surfaceBase, 0.20));
  root.style.setProperty('--bg-active',  shadeHex(surfaceBase, 0.34));

  const hh = settings.hour_height || 44;
  root.style.setProperty('--hour-h', hh + 'px');

  root.style.setProperty('--month-divider-color', settings.month_divider_color || baseColor('month_divider_color'));
  root.style.setProperty('--month-label-color',   settings.month_label_color   || baseColor('month_label_color'));

  // Fine-grained element colours. Each is applied ONLY when the user set an
  // explicit value; otherwise the :root default (which references a derived
  // variable) stays in effect, so the look is unchanged until customised.
  // day_selected_color / today_bg_color feed a *-base variable that CSS turns
  // into a subtle tint via color-mix; the rest are applied as-is.
  // User value → admin instance default (if any). When neither is set the
  // property stays unset so the derived :root default keeps the current look.
  const setIf = (varName, key) => {
    const value = settings[key] || INSTANCE_DEFAULTS[key];
    if (value) root.style.setProperty(varName, value);
  };
  setIf('--hover-highlight',     'hover_highlight_color');
  setIf('--icon-inactive-color', 'icon_inactive_color');
  setIf('--icon-active-color',   'icon_active_color');
  setIf('--day-hover-color',     'day_hover_color');
  setIf('--day-selected-base',   'day_selected_color');
  setIf('--day-bg',              'day_bg_color');
  setIf('--today-bg-base',       'today_bg_color');
}

// Instance custom favicon URL (set by the branding loader). When present it
// overrides the primary-colour tinting.
let customFaviconUrl = null;
export function setCustomFavicon(url) { customFaviconUrl = url || null; }

// Tint the favicon (and browser theme-colour) to the current primary colour so
// the tab icon reflects the user's theme. Called at load and after saving —
// NOT on every live keystroke. Reuses the calendar glyph from favicon.svg.
export function applyFavicon(primaryColor) {
  const color = primaryColor || baseColor('primary_color');
  let link = document.querySelector('link[rel="icon"]');
  if (!link) {
    link = document.createElement('link');
    link.rel = 'icon';
    document.head.appendChild(link);
  }
  if (customFaviconUrl) {
    // Admin-uploaded favicon: use as-is (no primary-colour tinting).
    link.type = 'image/png';
    link.href = customFaviconUrl;
  } else {
    const svg = `<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="${color}" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">`
      + '<rect x="3" y="4" width="18" height="18" rx="2"/>'
      + '<line x1="16" y1="2" x2="16" y2="6"/>'
      + '<line x1="8" y1="2" x2="8" y2="6"/>'
      + '<line x1="3" y1="10" x2="21" y2="10"/></svg>';
    link.type = 'image/svg+xml';
    link.href = 'data:image/svg+xml;base64,' + btoa(svg);
  }
  const meta = document.querySelector('meta[name="theme-color"]');
  if (meta) meta.setAttribute('content', color);
}

function luminance(hex) {
  const c = (n) => {
    const v = n / 255;
    return v <= 0.03928 ? v / 12.92 : Math.pow((v + 0.055) / 1.055, 2.4);
  };
  const r = c(parseInt(hex.slice(1, 3), 16));
  const g = c(parseInt(hex.slice(3, 5), 16));
  const b = c(parseInt(hex.slice(5, 7), 16));
  return 0.2126 * r + 0.7152 * g + 0.0722 * b;
}
function contrastRatio(c1, c2) {
  try {
    const l1 = luminance(c1);
    const l2 = luminance(c2);
    return (Math.max(l1, l2) + 0.05) / (Math.min(l1, l2) + 0.05);
  } catch { return 21; }
}

// ── Safe HTML rendering for event descriptions ───────────────────────────
// External calendars (CalDAV, iCal) often store rich-text descriptions as raw
// HTML. We render a small allowlist of formatting tags so links/line breaks
// look right, but strip everything dangerous (scripts, event handlers, inline
// styles) — we never execute code from a description.
const ALLOWED_TAGS = new Set(['A', 'BR', 'P', 'DIV', 'B', 'STRONG', 'I', 'EM', 'U', 'UL', 'OL', 'LI', 'SPAN']);
const URL_RE = /(https?:\/\/[^\s<]+[^\s<.,:;!?)\]}'"])/g;

function makeSafeLink(href, text) {
  const a = document.createElement('a');
  a.href = href;
  a.textContent = text;
  a.target = '_blank';
  a.rel = 'noopener noreferrer';
  return a;
}

// Replace bare URLs inside a text node with clickable <a> elements.
function linkifyTextNode(node, out) {
  const text = node.nodeValue;
  let last = 0;
  let m;
  URL_RE.lastIndex = 0;
  while ((m = URL_RE.exec(text)) !== null) {
    if (m.index > last) out.appendChild(document.createTextNode(text.slice(last, m.index)));
    out.appendChild(makeSafeLink(m[0], m[0]));
    last = m.index + m[0].length;
  }
  if (last < text.length) out.appendChild(document.createTextNode(text.slice(last)));
}

// Recursively copy `src` into `dest`, keeping only allowlisted tags/attributes.
function sanitizeInto(src, dest) {
  src.childNodes.forEach(node => {
    if (node.nodeType === Node.TEXT_NODE) {
      linkifyTextNode(node, dest);
      return;
    }
    if (node.nodeType !== Node.ELEMENT_NODE) return;
    const tag = node.tagName;
    if (!ALLOWED_TAGS.has(tag)) {
      // Drop the tag but keep its (sanitized) contents.
      sanitizeInto(node, dest);
      return;
    }
    let el;
    if (tag === 'A') {
      const href = node.getAttribute('href') || '';
      if (/^(https?:|mailto:)/i.test(href)) {
        el = makeSafeLink(href, '');
      } else {
        // Unsafe/relative href: render as plain text container.
        el = document.createElement('span');
      }
    } else {
      el = document.createElement(tag.toLowerCase());
    }
    sanitizeInto(node, el);
    dest.appendChild(el);
  });
}

// Returns a sanitized HTML string for an event description, safe for innerHTML.
export function renderDescriptionHtml(raw) {
  if (!raw) return '';
  const hasHtml = /<[a-z][\s\S]*>/i.test(raw);
  const doc = new DOMParser().parseFromString(
    hasHtml ? raw : raw.replace(/\n/g, '<br>'), 'text/html');
  const out = document.createElement('div');
  sanitizeInto(doc.body, out);
  return out.innerHTML;
}

function hexToRgba(hex, alpha) {
  const r = parseInt(hex.slice(1,3), 16);
  const g = parseInt(hex.slice(3,5), 16);
  const b = parseInt(hex.slice(5,7), 16);
  return `rgba(${r},${g},${b},${alpha})`;
}

// Brighten (positive amount) or darken (negative) a hex colour.
// Used to derive supporting shades (sidebar bg, hover bg, secondary text…)
// from a single user-picked colour so the whole UI stays in the same family.
function shadeHex(hex, amount) {
  let r = parseInt(hex.slice(1,3), 16);
  let g = parseInt(hex.slice(3,5), 16);
  let b = parseInt(hex.slice(5,7), 16);
  if (amount >= 0) {
    r = Math.round(r + (255 - r) * amount);
    g = Math.round(g + (255 - g) * amount);
    b = Math.round(b + (255 - b) * amount);
  } else {
    const a = 1 + amount; // amount is negative: e.g. -0.25 → keep 75%
    r = Math.round(r * a);
    g = Math.round(g * a);
    b = Math.round(b * a);
  }
  const h = n => Math.max(0, Math.min(255, n)).toString(16).padStart(2, '0');
  return '#' + h(r) + h(g) + h(b);
}