import * as monaco from 'monaco-editor';
import type { editor } from 'monaco-editor';
import { locate } from '../parser/locate';
import { offsetToPosition } from '../parser/lexer';
import { buildCompletions } from './completions';
import type { MutableRefObject } from 'react';

export interface ProviderOptions {
  fetchFieldNamesRef: MutableRefObject<((nestedPath?: string) => Promise<string[]>) | undefined>;
  fetchFieldValuesRef: MutableRefObject<((fieldName: string) => Promise<string[]>) | undefined>;
  variablesRef: MutableRefObject<string[]>;
  editorRef: MutableRefObject<editor.IStandaloneCodeEditor | null>;
}

export function getKQLCompletionProvider(opts: ProviderOptions): monaco.languages.CompletionItemProvider {
  return {
    triggerCharacters: [':', '(', '{', ' ', '"', '$', '*'],

    provideCompletionItems: async (model, position) => {
      // Only serve requests from this editor's own model
      if (opts.editorRef.current?.getModel()?.id !== model.id) {
        return { suggestions: [] };
      }

      const value = model.getValue();
      const offset = model.getOffsetAt(position);

      // locate() only needs the token stream — a full parse() here would be wasted work per keystroke
      const situation = locate(value, offset);

      const startPos = offsetToPosition(value, situation.replaceRange.start);
      const range = {
        startLineNumber: startPos.lineNumber,
        startColumn: startPos.column,
        endLineNumber: position.lineNumber,
        endColumn: position.column,
      };

      const suggestions = await buildCompletions({
        situation,
        range,
        variables: opts.variablesRef.current,
        fetchFieldNames: opts.fetchFieldNamesRef.current,
        fetchFieldValues: opts.fetchFieldValuesRef.current,
      });

      return { suggestions };
    },
  };
}