/**
 * Zen Mode — distraction-free writing mode
 * Provides typewriter scrolling, line dimming, centered content, and a floating HUD.
 * Toggle with F11, exit with Escape.
 */

const { EditorView, ViewPlugin, Decoration } = require('@codemirror/view');
const { RangeSetBuilder } = require('@codemirror/state');

class ZenMode {
  /**
   * @param {import('./renderer').TabManager} tabManager
   */
  constructor(tabManager) {
    this.tabManager = tabManager;
    this.active = false;
    this._hud = null;
    this._timerInterval = null;
    this._sessionStart = null;
    this._extensions = [];
  }

  activate() {
    if (this.active) return;
    this.active = true;

    document.body.classList.add('zen-mode');

    // Collapse sidebar
    const sidebar = document.getElementById('sidebar');
    if (sidebar) sidebar.classList.add('collapsed');

    // Hide preview pane for the active tab
    const tab = this.tabManager.tabs.get(this.tabManager.activeTabId);
    if (tab) {
      const previewContainer = document.getElementById(`preview-pane-${tab.id}`);
      if (previewContainer) previewContainer.classList.add('hidden');
      const editorPane = document.getElementById(`editor-pane-${tab.id}`);
      if (editorPane) editorPane.classList.add('full-width');

      // Add CM6 extensions to the active editor
      if (tab.editorView) {
        this._extensions = [typewriterScrollExtension, lineDimmingExtension];
        // Reconfigure is not straightforward with CM6's immutable state.
        // Instead we dispatch effects or simply rebuild with new extensions.
        // Since we cannot hot-swap extensions on an existing EditorView,
        // we store a reference and the CSS + updateListener handle the rest.
        // The typewriter + dimming plugins are applied via a compartment approach
        // would be ideal, but for simplicity we use DOM + updateListener.
        this._applyTypewriterBehavior(tab.editorView);
      }
    }

    // Create HUD
    this._createHUD();

    // Start session timer
    this._sessionStart = Date.now();
    this._timerInterval = setInterval(() => this._updateHUD(), 1000);

    // Focus editor
    if (tab?.editorView) tab.editorView.focus();
  }

  deactivate() {
    if (!this.active) return;
    this.active = false;

    document.body.classList.remove('zen-mode');

    // Restore preview pane for the active tab
    const tab = this.tabManager.tabs.get(this.tabManager.activeTabId);
    if (tab) {
      const previewContainer = document.getElementById(`preview-pane-${tab.id}`);
      if (previewContainer) previewContainer.classList.remove('hidden');
      const editorPane = document.getElementById(`editor-pane-${tab.id}`);
      if (editorPane) editorPane.classList.remove('full-width');

      // Remove typewriter listener
      if (tab.editorView && this._selectionListener) {
        window.removeEventListener('zen-typewriter', this._selectionListener);
        this._selectionListener = null;
      }
    }

    // Remove HUD
    if (this._hud && this._hud.parentNode) {
      this._hud.parentNode.removeChild(this._hud);
      this._hud = null;
    }

    // Stop timer
    if (this._timerInterval) {
      clearInterval(this._timerInterval);
      this._timerInterval = null;
    }
    this._sessionStart = null;
    this._extensions = [];
  }

  toggle() {
    if (this.active) {
      this.deactivate();
    } else {
      this.activate();
    }
  }

  _applyTypewriterBehavior(view) {
    // We use a custom update listener that scrolls the cursor to center.
    const scrollFn = () => {
      if (!this.active) return;
      const pos = view.state.selection.main.head;
      requestAnimationFrame(() => {
        view.dispatch({
          effects: EditorView.scrollIntoView(pos, { y: 'center' }),
        });
      });
    };

    // Use interval to keep cursor centered during typing
    this._scrollInterval = setInterval(() => {
      if (!this.active) {
        clearInterval(this._scrollInterval);
        this._scrollInterval = null;
        return;
      }
      // Typewriter scroll: center the cursor line
      try {
        const pos = view.state.selection.main.head;
        const coords = view.coordsAtPos(pos);
        const scroller = view.scrollDOM;
        if (coords && scroller) {
          const scrollerRect = scroller.getBoundingClientRect();
          const cursorCenter = coords.top + (coords.bottom - coords.top) / 2;
          const viewCenter = scrollerRect.top + scrollerRect.height / 2;
          const diff = cursorCenter - viewCenter;
          if (Math.abs(diff) > 30) {
            scroller.scrollTop += diff;
          }
        }
      } catch {
        // Ignore errors from destroyed views
      }
    }, 200);

    // Initial scroll to center
    scrollFn();
  }

  _createHUD() {
    const hud = document.createElement('div');
    hud.className = 'zen-hud';
    hud.innerHTML = `
            <span class="zen-hud-item" id="zen-words">0 words</span>
            <span class="zen-hud-sep">&middot;</span>
            <span class="zen-hud-item" id="zen-reading-time">0 min read</span>
            <span class="zen-hud-sep">&middot;</span>
            <span class="zen-hud-item" id="zen-timer">00:00</span>
            <span class="zen-hud-sep">&middot;</span>
            <button class="zen-hud-item zen-goal-btn" id="zen-goal-btn" type="button"
              title="Set a session word goal">&#9878; goal</button>
            <div class="zen-progress-container" id="zen-progress-container">
                <div class="zen-progress-bar" id="zen-progress-bar"></div>
            </div>
        `;
    document.body.appendChild(hud);
    this._hud = hud;
    this._wireGoalButton();
    this._updateHUD();
  }

  /**
   * The word-goal progress bar reads localStorage('zen-word-goal'), but until
   * now nothing in the app ever set it. The HUD button opens a small inline
   * input (window.prompt is unavailable in Electron) that sets or clears it.
   */
  _wireGoalButton() {
    const btn = this._hud?.querySelector('#zen-goal-btn');
    if (!btn) return;
    btn.addEventListener('click', () => {
      const current = localStorage.getItem('zen-word-goal') || '';
      const overlay = document.createElement('div');
      overlay.className = 'zen-goal-overlay';
      overlay.setAttribute('role', 'dialog');
      overlay.setAttribute('aria-modal', 'true');
      overlay.innerHTML = `
        <div class="zen-goal-dialog">
          <h3>Session word goal</h3>
          <input type="number" min="0" step="50" value="${current}"
            placeholder="e.g. 500 (0 clears the goal)" aria-label="Word goal" />
          <div class="zen-goal-actions">
            <button type="button" data-role="ok">Set</button>
            <button type="button" data-role="cancel">Cancel</button>
          </div>
        </div>`;
      const input = overlay.querySelector('input');
      const done = () => overlay.remove();
      overlay.querySelector('[data-role="ok"]').addEventListener('click', () => {
        const value = parseInt(input.value, 10);
        if (Number.isFinite(value) && value > 0) {
          localStorage.setItem('zen-word-goal', String(value));
        } else {
          localStorage.removeItem('zen-word-goal');
        }
        done();
        this._updateHUD();
      });
      overlay.querySelector('[data-role="cancel"]').addEventListener('click', done);
      overlay.addEventListener('click', (event) => {
        if (event.target === overlay) done();
      });
      input.addEventListener('keydown', (event) => {
        if (event.key === 'Enter') overlay.querySelector('[data-role="ok"]').click();
        if (event.key === 'Escape') done();
      });
      document.body.appendChild(overlay);
      input.focus();
      input.select();
    });
  }

  _updateHUD() {
    if (!this.active || !this._hud) return;

    const content = this.tabManager.getEditorContent();
    const words = content.trim()
      ? content
          .trim()
          .split(/\s+/)
          .filter((w) => w.length > 0).length
      : 0;
    const readingTime = Math.max(1, Math.ceil(words / 200));

    const wordsEl = document.getElementById('zen-words');
    const readingEl = document.getElementById('zen-reading-time');
    const timerEl = document.getElementById('zen-timer');

    if (wordsEl) wordsEl.textContent = `${words.toLocaleString()} words`;
    if (readingEl) readingEl.textContent = `${readingTime} min read`;

    // Session timer
    if (this._sessionStart) {
      const elapsed = Math.floor((Date.now() - this._sessionStart) / 1000);
      const minutes = String(Math.floor(elapsed / 60)).padStart(2, '0');
      const seconds = String(elapsed % 60).padStart(2, '0');
      if (timerEl) timerEl.textContent = `${minutes}:${seconds}`;
    }

    // Word goal progress
    const goalStr = localStorage.getItem('zen-word-goal');
    const progressBar = document.getElementById('zen-progress-bar');
    const progressContainer = document.getElementById('zen-progress-container');
    if (progressBar && progressContainer) {
      if (goalStr) {
        const goal = parseInt(goalStr, 10);
        if (goal > 0) {
          const pct = Math.min(100, Math.round((words / goal) * 100));
          progressBar.style.width = `${pct}%`;
          progressContainer.style.display = 'block';
        } else {
          progressContainer.style.display = 'none';
        }
      } else {
        progressContainer.style.display = 'none';
      }
    }
  }
}

// Typewriter scroll ViewPlugin
const typewriterScrollExtension = ViewPlugin.fromClass(
  class {
    constructor(view) {
      this.view = view;
    }

    update(update) {
      if (update.selectionSet || update.docChanged) {
        const pos = update.state.selection.main.head;
        requestAnimationFrame(() => {
          if (this.view.dom && this.view.dom.isConnected) {
            this.view.dispatch({
              effects: EditorView.scrollIntoView(pos, { y: 'center' }),
            });
          }
        });
      }
    }
  }
);

// Line dimming ViewPlugin
function getOpacity(distance) {
  if (distance === 0) return 1.0;
  if (distance === 1) return 0.7;
  if (distance === 2) return 0.6;
  if (distance === 3) return 0.45;
  return 0.3;
}

const lineDimmingExtension = ViewPlugin.fromClass(
  class {
    constructor(view) {
      this.decorations = this.buildDecorations(view);
    }

    update(update) {
      if (update.docChanged || update.selectionSet || update.viewportChanged) {
        this.decorations = this.buildDecorations(update.view);
      }
    }

    buildDecorations(view) {
      const builder = new RangeSetBuilder();
      const pos = view.state.selection.main.head;
      const activeLine = view.state.doc.lineAt(pos).number;
      const doc = view.state.doc;

      for (let lineNum = 1; lineNum <= doc.lines; lineNum++) {
        const line = doc.line(lineNum);
        const distance = Math.abs(lineNum - activeLine);
        const opacity = getOpacity(distance);
        const deco = Decoration.line({
          attributes: { style: `opacity:${opacity};transition:opacity 0.15s ease` },
        });
        builder.add(line.from, line.from, deco);
      }

      return builder.finish();
    }
  },
  {
    decorations: (v) => v.decorations,
  }
);

module.exports = { ZenMode };