type CommandWrapper = "env" | "sudo";

const COMMAND_WRAPPER_OPTIONS_WITH_VALUE: Record<CommandWrapper, ReadonlySet<string>> = {
  env: new Set(["-C", "--chdir", "-S", "--split-string", "-u", "--unset"]),
  sudo: new Set(["-C", "--close-from", "-D", "--chdir", "-g", "--group", "-u", "--user"]),
};

const COMMAND_WRAPPER_FLAGS: Record<CommandWrapper, ReadonlySet<string>> = {
  env: new Set(["-0", "--null", "-i", "--ignore-environment", "--debug", "-v"]),
  sudo: new Set(["-A", "--askpass", "-b", "--background", "-E", "-H", "-i", "-n", "-S"]),
};

function tokenizeShellCommand(command: string): string[] | null {
  const input = command.trim();
  const tokens: string[] = [];
  let current = "";
  let quote: '"' | "'" | null = null;
  let escaping = false;
  let substitutionDepth = 0;
  let tokenStarted = false;

  for (let index = 0; index < input.length; index += 1) {
    const character = input[index]!;
    if (escaping) {
      current += character;
      escaping = false;
      tokenStarted = true;
      continue;
    }
    if (character === "\\" && quote !== "'") {
      const nextCharacter = input[index + 1];
      const isWindowsDrivePath = quote === null && /^[A-Za-z]:/.test(current);
      if (
        (quote === '"' || isWindowsDrivePath) &&
        nextCharacter !== undefined &&
        nextCharacter !== '"' &&
        nextCharacter !== "\\" &&
        nextCharacter !== "$" &&
        nextCharacter !== "`" &&
        nextCharacter !== "\n"
      ) {
        current += character;
        tokenStarted = true;
        continue;
      }
      escaping = true;
      tokenStarted = true;
      continue;
    }
    if (quote !== null) {
      if (character === quote) {
        quote = null;
      } else {
        current += character;
      }
      tokenStarted = true;
      continue;
    }
    if (character === "$" && input[index + 1] === "(") {
      current += "$(";
      substitutionDepth += 1;
      tokenStarted = true;
      index += 1;
      continue;
    }
    if (character === ")" && substitutionDepth > 0) {
      current += character;
      substitutionDepth -= 1;
      tokenStarted = true;
      continue;
    }
    if (character === '"' || character === "'") {
      quote = character;
      tokenStarted = true;
      continue;
    }
    if (/\s/u.test(character)) {
      if (substitutionDepth > 0) {
        current += character;
        tokenStarted = true;
        continue;
      }
      if (tokenStarted) {
        tokens.push(current);
        current = "";
        tokenStarted = false;
      }
      continue;
    }
    current += character;
    tokenStarted = true;
  }

  if (quote !== null || escaping || substitutionDepth > 0) return null;
  if (tokenStarted) tokens.push(current);
  return tokens;
}

export function commandProgramName(command: string, depth = 0): string | null {
  if (depth >= 8) return null;
  const tokens = tokenizeShellCommand(command);
  if (tokens === null) return null;
  let index = 0;
  let wrapper: CommandWrapper | null = null;

  while (index < tokens.length) {
    const token = tokens[index];
    if (!token) return null;
    if (/^[A-Za-z_][A-Za-z0-9_]*=/.test(token)) {
      index += 1;
      continue;
    }
    const tokenProgram = token.split(/[\\/]/).at(-1);
    if (tokenProgram === "env" || tokenProgram === "sudo") {
      wrapper = tokenProgram;
      index += 1;
      continue;
    }
    if (wrapper !== null && token === "--") {
      wrapper = null;
      index += 1;
      continue;
    }
    if (wrapper !== null && token.startsWith("-")) {
      if (wrapper === "env" && (token === "-S" || token === "--split-string")) {
        const splitCommand = tokens[index + 1];
        return splitCommand ? commandProgramName(splitCommand, depth + 1) : null;
      }
      if (wrapper === "env" && token.startsWith("--split-string=")) {
        return commandProgramName(token.slice("--split-string=".length), depth + 1);
      }
      if (COMMAND_WRAPPER_OPTIONS_WITH_VALUE[wrapper].has(token)) {
        if (tokens[index + 1] === undefined) return null;
        index += 2;
        continue;
      }
      if (COMMAND_WRAPPER_FLAGS[wrapper].has(token)) {
        index += 1;
        continue;
      }
      const equalsIndex = token.indexOf("=");
      if (token.startsWith("--") && equalsIndex > 2) {
        if (!COMMAND_WRAPPER_OPTIONS_WITH_VALUE[wrapper].has(token.slice(0, equalsIndex))) {
          return null;
        }
        index += 1;
        continue;
      }
      if (/^-[A-Za-z].+/.test(token) && !token.startsWith("--")) {
        let consumesNextToken = false;
        for (const [optionIndex, option] of token.slice(1).split("").entries()) {
          const shortOption = `-${option}`;
          if (COMMAND_WRAPPER_OPTIONS_WITH_VALUE[wrapper].has(shortOption)) {
            consumesNextToken = optionIndex === token.length - 2;
            break;
          }
          if (!COMMAND_WRAPPER_FLAGS[wrapper].has(shortOption)) return null;
        }
        if (consumesNextToken && tokens[index + 1] === undefined) return null;
        index += consumesNextToken ? 2 : 1;
        continue;
      }
      return null;
    }
    return token.split(/[\\/]/).at(-1) || null;
  }

  return null;
}