// How Java FILIUS finds a file by path (Dateisystem.holeDatei): the first
// node in preorder whose path equals the path ignoring case, and only if that
// node is a file.

import type { FlsFileTree } from './systemSoftware.js';

/**
 * The content of the file at an ASCII path as `Dateisystem.holeDatei` finds
 * it. Undefined when there is none; a file without content reads as empty
 * (Java would fail on it).
 */
export function javaFileContent(root: FlsFileTree | undefined, asciiPath: string): string | undefined {
  if (root === undefined) return undefined;
  const found = firstInPreorder(root, '', (path) => javaEqualsIgnoreCase(path, asciiPath));
  return found?.kind === 'file' ? (found.content ?? '') : undefined;
}

/** Preorder below the root; a node's path is "/" plus each name after the root's. */
function firstInPreorder(node: FlsFileTree, path: string, matches: (path: string) => boolean): FlsFileTree | undefined {
  for (const child of node.children) {
    const childPath = `${path}/${child.kind === 'other' ? child.className : String(child.name)}`;
    if (matches(childPath)) return child;
    const found = firstInPreorder(child, childPath, matches);
    if (found !== undefined) return found;
  }
  return undefined;
}

// Besides ASCII case, String.equalsIgnoreCase takes these BMP units for an
// ASCII letter (measured on the JDK over every unit): dotted and dotless I,
// the Kelvin sign and the long s.
const JAVA_ASCII_CASE_FOLDS = new Map([
  ['\u0130', 'i'],
  ['\u0131', 'i'],
  ['\u212A', 'k'],
  ['\u017F', 's'],
]);

/** `String.equalsIgnoreCase` against an ASCII path, unit by unit. */
function javaEqualsIgnoreCase(text: string, asciiPath: string): boolean {
  if (text.length !== asciiPath.length) return false;
  for (let index = 0; index < text.length; index++) {
    if (asciiFold(text[index]!) !== asciiFold(asciiPath[index]!)) return false;
  }
  return true;
}

function asciiFold(unit: string): string {
  if (unit >= 'A' && unit <= 'Z') return unit.toLowerCase();
  return JAVA_ASCII_CASE_FOLDS.get(unit) ?? unit;
}