// src/lib/stores/preferences.svelte.js
import { invoke } from '@tauri-apps/api/core';
import { toasts } from './toasts.svelte.js';

const DEFAULTS = {
  theme: 'dark',
  zone: 'default',
  accessibility: {
    fontFamily: 'lexend',
    fontSize: 16,
    letterSpacing: 0,
    lineHeight: 1.5,
    transcriptSize: 16,
    bionicReading: false,
    reduceMotion: 'system'
  }
};

const FONT_FAMILIES = {
  lexend: "'Lexend', system-ui, sans-serif",
  atkinson: "'Atkinson Hyperlegible Next', system-ui, sans-serif",
  opendyslexic: "'OpenDyslexic', system-ui, sans-serif"
};

function readFromDOM() {
  const el = document.documentElement;
  return {
    theme: el.dataset.theme || DEFAULTS.theme,
    zone: el.dataset.zone || DEFAULTS.zone,
    accessibility: {
      fontFamily: el.dataset.fontFamily || DEFAULTS.accessibility.fontFamily,
      fontSize: parseFloat(el.style.getPropertyValue('--font-size-body')) || DEFAULTS.accessibility.fontSize,
      letterSpacing: parseFloat(el.style.getPropertyValue('--letter-spacing-body')) || DEFAULTS.accessibility.letterSpacing,
      lineHeight: parseFloat(el.style.getPropertyValue('--line-height-body')) || DEFAULTS.accessibility.lineHeight,
      transcriptSize: DEFAULTS.accessibility.transcriptSize,
      bionicReading: el.dataset.bionicReading === 'true',
      reduceMotion: el.dataset.reduceMotion || DEFAULTS.accessibility.reduceMotion
    }
  };
}

function applyToDOM(prefs) {
  const el = document.documentElement;

  // Theme — resolve 'system' to actual value
  el.dataset.theme = prefs.theme === 'system'
    ? (window.matchMedia('(prefers-color-scheme: light)').matches ? 'light' : 'dark')
    : prefs.theme;

  // Zone
  if (prefs.zone === 'default') {
    delete el.dataset.zone;
  } else {
    el.dataset.zone = prefs.zone;
  }

  // Accessibility — inline styles for highest specificity
  const a = prefs.accessibility;
  el.style.setProperty('--font-family-body', FONT_FAMILIES[a.fontFamily] || FONT_FAMILIES.lexend);
  el.style.setProperty('--font-size-body', `${a.fontSize}px`);
  el.style.setProperty('--letter-spacing-body', `${a.letterSpacing}em`);
  el.style.setProperty('--line-height-body', String(a.lineHeight));

  el.dataset.bionicReading = String(a.bionicReading);
  el.dataset.fontFamily = a.fontFamily;

  // Reduce motion — three-value resolution
  const motionReduced = a.reduceMotion === 'on'
    || (a.reduceMotion === 'system' && window.matchMedia('(prefers-reduced-motion: reduce)').matches);
  if (motionReduced) {
    el.dataset.reduceMotion = 'true';
  } else {
    delete el.dataset.reduceMotion;
  }
}

let saveTimeout = null;
// Show the failure toast at most once per process so a stuck SQLite path
// doesn't spam the user every time they nudge a slider.
let saveFailureToastShown = false;
function persistToSQLite(prefs) {
  clearTimeout(saveTimeout);
  saveTimeout = setTimeout(async () => {
    try {
      await invoke('save_preferences', { preferences: JSON.stringify(prefs) });
      saveFailureToastShown = false;
    } catch (e) {
      console.error('Failed to save preferences:', e);
      if (!saveFailureToastShown) {
        const msg = typeof e === 'string' ? e : (e?.message ?? String(e));
        toasts.warn(
          'Could not save preferences',
          `${msg}. Your changes still apply for this session.`,
        );
        saveFailureToastShown = true;
      }
    }
  }, 500);
}

let preferences = $state(readFromDOM());

export function getPreferences() {
  return preferences;
}

export function updatePreferences(updates) {
  preferences = { ...preferences, ...updates };
  applyToDOM(preferences);
  persistToSQLite(preferences);
}

export function updateAccessibility(updates) {
  preferences = {
    ...preferences,
    accessibility: { ...preferences.accessibility, ...updates }
  };
  applyToDOM(preferences);
  persistToSQLite(preferences);
}

// Re-resolve when OS preferences change
if (typeof window !== 'undefined') {
  window.matchMedia('(prefers-color-scheme: light)').addEventListener('change', () => {
    if (preferences.theme === 'system') applyToDOM(preferences);
  });
  window.matchMedia('(prefers-reduced-motion: reduce)').addEventListener('change', () => {
    if (preferences.accessibility.reduceMotion === 'system') applyToDOM(preferences);
  });
}