/**
 * Go module path detection.
 *
 * A Go monorepo's cross-package calls (`pkga.FuncX(...)`) only resolve when
 * the resolver knows the project's module path (the `module ...` directive
 * in `go.mod`). Without it, `isExternalImport` treats every in-module import
 * — `github.com/example/myproject/pkga` — as a third-party package, so
 * resolution falls through to name-matching with path proximity and returns
 * a tiny fraction of the real call sites. See issue #388.
 */

import * as fs from 'fs';
import * as path from 'path';

export interface GoModule {
  /** The module path declared in `go.mod`, e.g. `github.com/example/myproject` */
  modulePath: string;
  /** Absolute path to the directory containing the `go.mod` file. */
  rootDir: string;
}

/**
 * Read the `go.mod` file at the project root and extract the module path.
 * Returns `null` if no `go.mod` exists or it has no `module` directive.
 *
 * Limitation: only the project-root `go.mod` is read. Nested `go.mod` files
 * (Go workspaces, monorepos with multiple modules) are not yet resolved —
 * a follow-up if a real repro shows up.
 */
export function loadGoModule(projectRoot: string): GoModule | null {
  const goModPath = path.join(projectRoot, 'go.mod');
  let content: string;
  try {
    content = fs.readFileSync(goModPath, 'utf-8');
  } catch {
    return null;
  }
  // `module <path>` is the first non-comment directive in any valid go.mod.
  // Strip line comments so a `// module foo` doesn't false-match.
  const stripped = content.replace(/\/\/[^\n]*/g, '');
  const match = stripped.match(/^\s*module\s+(\S+)\s*$/m);
  if (!match) return null;
  // Strip optional quoting around the module path.
  const modulePath = match[1]!.replace(/^["']|["']$/g, '');
  if (!modulePath) return null;
  return { modulePath, rootDir: projectRoot };
}