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

export interface ProviderOptions {
  fetchLabelNamesRef: MutableRefObject<((currentMatchers: LabelMatcher[]) => Promise<string[]>) | undefined>;
  fetchLabelValuesRef: MutableRefObject<((labelName: string, currentMatchers: LabelMatcher[]) => Promise<string[]>) | undefined>;
  variablesRef: MutableRefObject<string[]>;
  editorRef: MutableRefObject<editor.IStandaloneCodeEditor | null>;
}

export function getLokiCompletionProvider(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);

      // Parse and locate
      const { ast, situation } = parseAndLocate(value, offset);

      // Extract current matchers from the AST stream selector for context,
      // excluding the matcher currently being edited (identified by matcherIndex).
      let currentMatchers: LabelMatcher[] =
        ast.streamSelector?.matchers.map((m) => ({
          label: m.label,
          operator: m.operator,
          value: m.value,
        })) ?? [];
      if (situation.matcherIndex !== undefined) {
        currentMatchers = currentMatchers.filter((_, i) => i !== situation.matcherIndex);
      }

      // Build the Monaco range from the situation's replaceRange
      const startPos = offsetToPosition(value, situation.replaceRange.start);
      const endPos = position; // current cursor position
      const range = {
        startLineNumber: startPos.lineNumber,
        startColumn: startPos.column,
        endLineNumber: endPos.lineNumber,
        endColumn: endPos.column,
      };

      const suggestions = await buildCompletions({
        situation,
        range,
        variables: opts.variablesRef.current,
        currentMatchers,
        fetchLabelNames: opts.fetchLabelNamesRef.current,
        fetchLabelValues: opts.fetchLabelValuesRef.current,
      });

      return { suggestions };
    },
  };
}