// The `oxy:` URI scheme serves file content at a state through `oxy cat`
// (spec §3): oxy:/<repository-relative path>?root=<repository root>&change=<change>
// where `change` is `@base` (the working copy's base) or anything
// `oxy cat -r` accepts.

import * as vscode from "vscode";
import { Oxy } from "./oxy";

export const SCHEME = "oxy";

export function oxyUri(root: string, path: string, change: string): vscode.Uri {
  const query = new URLSearchParams({ root, change }).toString();
  return vscode.Uri.from({ scheme: SCHEME, path: "/" + path, query });
}

export function baseUri(root: string, path: string): vscode.Uri {
  return oxyUri(root, path, "@base");
}

export function parseOxyUri(uri: vscode.Uri): { root: string; path: string; change: string } | undefined {
  if (uri.scheme !== SCHEME) {
    return undefined;
  }
  const q = new URLSearchParams(uri.query);
  const root = q.get("root");
  const change = q.get("change") ?? "@base";
  if (!root) {
    return undefined;
  }
  return { root, path: uri.path.replace(/^\//, ""), change };
}

export class OxyContentProvider implements vscode.TextDocumentContentProvider {
  private readonly emitter = new vscode.EventEmitter<vscode.Uri>();
  readonly onDidChange = this.emitter.event;

  constructor(private readonly oxy: Oxy) {}

  /** Tell open `oxy:` documents under `root` to reload (after an operation). */
  invalidate(root: string): void {
    for (const doc of vscode.workspace.textDocuments) {
      const parsed = parseOxyUri(doc.uri);
      if (parsed && parsed.root === root && parsed.change === "@base") {
        this.emitter.fire(doc.uri);
      }
    }
  }

  async provideTextDocumentContent(uri: vscode.Uri): Promise<string> {
    const parsed = parseOxyUri(uri);
    if (!parsed) {
      return "";
    }
    try {
      const bytes = await this.oxy.cat(parsed.root, parsed.path, parsed.change === "@base" ? undefined : parsed.change);
      return bytes.toString("utf8");
    } catch {
      // A path absent from that state (an added file's base) is empty.
      return "";
    }
  }
}