import { Editor, EditorConfiguration } from 'codemirror';
import 'codemirror/addon/selection/active-line';
import {
  createAtom,
  makeAutoObservable,
  observable,
} from 'mobx';
import 'mode-problem';
import {
  IXtextOptions,
  IXtextServices,
  createServices,
  removeServices,
} from 'xtext/xtext-codemirror';

import { ThemeStore } from '../theme/ThemeStore';

const xtextLang = 'problem';

const xtextOptions: IXtextOptions = {
  xtextLang,
  enableFormattingAction: true,
};

const codeMirrorGlobalOptions: EditorConfiguration = {
  mode: `xtext/${xtextLang}`,
  indentUnit: 2,
  styleActiveLine: true,
};

export class EditorStore {
  themeStore;

  atom;

  editor?: Editor;

  xtextServices?: IXtextServices;

  value = '';

  showLineNumbers = false;

  constructor(themeStore: ThemeStore) {
    this.themeStore = themeStore;
    this.atom = createAtom('EditorStore');
    makeAutoObservable(this, {
      themeStore: false,
      atom: false,
      editor: observable.ref,
      xtextServices: observable.ref,
    });
  }

  /**
   * Attaches a new CodeMirror instance and creates Xtext services.
   *
   * The store will not subscribe to any CodeMirror events. Instead,
   * the editor component should subscribe to them and relay them to the store.
   *
   * @param newEditor The new CodeMirror instance
   */
  editorDidMount(newEditor: Editor): void {
    if (this.editor) {
      throw new Error('CoreMirror editor mounted before unmounting');
    }
    this.editor = newEditor;
    this.xtextServices = createServices(newEditor, xtextOptions);
  }

  editorWillUnmount(): void {
    if (this.editor) {
      removeServices(this.editor);
    }
    delete this.editor;
    delete this.xtextServices;
  }

  /**
   * Updates the contents of the editor.
   *
   * @param newValue The new contents of the editor
   */
  updateValue(newValue: string): void {
    this.value = newValue;
  }

  reportChanged(): void {
    this.atom.reportChanged();
  }

  protected observeEditorChanges(): void {
    this.atom.reportObserved();
  }

  get codeMirrorOptions(): EditorConfiguration {
    return {
      ...codeMirrorGlobalOptions,
      theme: this.themeStore.codeMirrorTheme,
      lineNumbers: this.showLineNumbers,
    };
  }

  /**
   * @returns `true` if there is history to undo
   */
  get canUndo(): boolean {
    this.observeEditorChanges();
    if (!this.editor) {
      return false;
    }
    const { undo: undoSize } = this.editor.historySize();
    return undoSize > 0;
  }

  undo(): void {
    this.editor?.undo();
  }

  /**
   * @returns `true` if there is history to redo
   */
  get canRedo(): boolean {
    this.observeEditorChanges();
    if (!this.editor) {
      return false;
    }
    const { redo: redoSize } = this.editor.historySize();
    return redoSize > 0;
  }

  redo(): void {
    this.editor?.redo();
  }

  toggleLineNumbers(): void {
    this.showLineNumbers = !this.showLineNumbers;
  }
}