export interface ParsedCliArgs {
  readonly flags: Record<string, string | null>;
  readonly positionals: string[];
}

export interface ParseCliArgsOptions {
  readonly booleanFlags?: readonly string[];
}

export function tokenizeCliArgs(args?: string): ReadonlyArray<string> {
  const input = args?.trim();
  if (!input) return [];

  const tokens: string[] = [];
  let current = "";
  let quote: "'" | '"' | undefined;
  let quoted = false;

  for (let index = 0; index < input.length; index++) {
    const char = input[index];
    if (char === undefined) continue;

    if (quote) {
      if (char === quote) {
        quote = undefined;
        quoted = true;
      } else if (char === "\\" && quote === '"') {
        const next = input[index + 1];
        if (next !== undefined && ['"', "\\", "$", "`"].includes(next)) {
          current += next;
          index++;
        } else {
          current += char;
        }
      } else {
        current += char;
      }
      continue;
    }

    if (char === "'" || char === '"') {
      quote = char;
      quoted = true;
    } else if (/\s/.test(char)) {
      if (current || quoted) {
        tokens.push(current);
        current = "";
        quoted = false;
      }
    } else if (char === "\\") {
      const next = input[index + 1];
      if (next !== undefined && /\s/.test(next)) {
        current += next;
        index++;
      } else {
        current += char;
      }
    } else {
      current += char;
    }
  }

  if (current || quoted) tokens.push(current);
  return tokens;
}

/**
 * Parse CLI-style arguments into flags and positionals.
 *
 * Accepts a string (quote-aware tokenized) or a pre-split argv array.
 * Supports `--key value`, `--key=value`, and `--flag` (boolean) syntax.
 *
 *   parseCliArgs("")
 *     → { flags: {}, positionals: [] }
 *
 *   parseCliArgs("--chrome")
 *     → { flags: { chrome: null }, positionals: [] }
 *
 *   parseCliArgs("--chrome --effort high")
 *     → { flags: { chrome: null, effort: "high" }, positionals: [] }
 *
 *   parseCliArgs("--effort=high")
 *     → { flags: { effort: "high" }, positionals: [] }
 *
 *   parseCliArgs(["1.2.3", "--root", "/path", "--github-output"], { booleanFlags: ["github-output"] })
 *     → { flags: { root: "/path", "github-output": null }, positionals: ["1.2.3"] }
 */
export function parseCliArgs(
  args: string | readonly string[],
  options?: ParseCliArgsOptions,
): ParsedCliArgs {
  const tokens = typeof args === "string" ? tokenizeCliArgs(args) : Array.from(args);
  const booleanSet = options?.booleanFlags ? new Set(options.booleanFlags) : undefined;

  const flags: Record<string, string | null> = {};
  const positionals: string[] = [];

  for (let i = 0; i < tokens.length; i++) {
    const token = tokens[i]!;

    if (token.startsWith("--")) {
      const rest = token.slice(2);
      if (!rest) continue;

      // Handle --key=value syntax
      const eqIndex = rest.indexOf("=");
      if (eqIndex !== -1) {
        flags[rest.slice(0, eqIndex)] = rest.slice(eqIndex + 1);
        continue;
      }

      // Known boolean flag — never consumes next token
      if (booleanSet?.has(rest)) {
        flags[rest] = null;
        continue;
      }

      // Handle --key value or --flag (boolean)
      const next = tokens[i + 1];
      if (next !== undefined && !next.startsWith("--")) {
        flags[rest] = next;
        i++;
      } else {
        flags[rest] = null;
      }
    } else {
      positionals.push(token);
    }
  }

  return { flags, positionals };
}