// 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 "";

    }

  }

}