import * as vscode from 'vscode';
import { RegistryElement } from '../model/format';
import { ModelService } from '../model/service';

export const REF_SELECTOR: vscode.DocumentSelector = [{ pattern: '**/*.archify' }];

/** `ref: api` or `{ ref: ap` → what has been typed of the value. */
export function refValueAt(linePrefix: string): { typed: string } | undefined {
  const match = /(?:^|[\s{,])ref:\s*["']?([\w.-]*)$/.exec(linePrefix);
  return match ? { typed: match[1] } : undefined;
}

/** The `ref` value under a position, with its range, or undefined. */
export function refAt(line: string, character: number): { id: string; start: number; end: number } | undefined {
  const match = /(?:^|[\s{,])ref:\s*["']?([\w.-]+)/.exec(line);
  if (!match) return undefined;
  const start = match.index + match[0].length - match[1].length;
  const end = start + match[1].length;
  return character >= start && character <= end ? { id: match[1], start, end } : undefined;
}

function describe(element: RegistryElement): vscode.MarkdownString {
  const md = new vscode.MarkdownString();
  md.appendMarkdown(`**${element.label ?? element.id}**${element.sublabel ? ` · ${element.sublabel}` : ''}${element.type ? ` \`${element.type}\`` : ''}\n\n`);
  if (element.description) md.appendMarkdown(`${element.description.trim()}\n\n`);
  if (element.diagram) md.appendMarkdown(`Opens: \`${element.diagram}\`\n\n`);
  md.appendMarkdown(`*Defined in ${element.file}, line ${element.line + 1}*`);
  return md;
}

/** Completion, hover and go-to-definition for `ref:` values in diagrams of a model. */
export class RefLanguage implements vscode.CompletionItemProvider, vscode.HoverProvider, vscode.DefinitionProvider {
  constructor(private readonly models: ModelService) {}

  async provideCompletionItems(document: vscode.TextDocument, position: vscode.Position): Promise<vscode.CompletionItem[] | undefined> {
    const value = refValueAt(document.lineAt(position.line).text.slice(0, position.character));
    if (!value) return undefined;
    const found = await this.models.registryFor(document.uri);
    if (!found) return undefined;
    const range = new vscode.Range(position.translate(0, -value.typed.length), position);
    return [...found.registry.elements.values()].map((element) => {
      const item = new vscode.CompletionItem({ label: element.id, description: element.label }, vscode.CompletionItemKind.Reference);
      item.detail = [element.label, element.sublabel, element.type].filter(Boolean).join(' · ');
      item.documentation = describe(element);
      item.filterText = [element.id, element.label ?? '', element.sublabel ?? ''].join(' ');
      item.range = range;
      return item;
    });
  }

  async provideHover(document: vscode.TextDocument, position: vscode.Position): Promise<vscode.Hover | undefined> {
    const ref = refAt(document.lineAt(position.line).text, position.character);
    if (!ref) return undefined;
    const found = await this.models.registryFor(document.uri);
    const element = found?.registry.elements.get(ref.id);
    const range = new vscode.Range(position.line, ref.start, position.line, ref.end);
    if (!element) {
      return new vscode.Hover(found ? `Unknown element \`${ref.id}\`: no registry of this model defines it.` : `\`${ref.id}\` cannot be resolved: this file is not inside a model.`, range);
    }
    return new vscode.Hover(describe(element), range);
  }

  async provideDefinition(document: vscode.TextDocument, position: vscode.Position): Promise<vscode.Location | undefined> {
    const ref = refAt(document.lineAt(position.line).text, position.character);
    if (!ref) return undefined;
    const found = await this.models.registryFor(document.uri);
    const element = found?.registry.elements.get(ref.id);
    if (!found || !element) return undefined;
    const file = vscode.Uri.joinPath(found.root, ...element.file.split(/[\\/]/));
    return new vscode.Location(file, new vscode.Position(element.line, 2));
  }
}