import gleam/bit_array
import gleam/string
import gleam/result
import gleam/list

/// This type represents all of the reasons for why a file system operation could fail.
///
/// Most of these reasons are POSIX errors, which come from the operating system
/// and start with E. Others have been added to represent other issues that may
/// arise specific to this library.
///
pub type FileError {
  /// Permission denied.
  Eacces
  /// Resource temporarily unavailable.
  Eagain
  /// Bad file number
  Ebadf
  /// Bad message.
  Ebadmsg
  /// File busy.
  Ebusy
  /// Resource deadlock avoided.
  Edeadlk
  /// On most architectures, same as `Edeadlk`. On some architectures, it
  /// means "File locking deadlock error."
  Edeadlock
  /// Disk quota exceeded.
  Edquot
  /// File already exists.
  Eexist
  /// Bad address in system call argument.
  Efault
  /// File too large.
  Efbig
  /// Inappropriate file type or format. Usually caused by trying to set the
  /// "sticky bit" on a regular file (not a directory).
  Eftype
  /// Interrupted system call.
  Eintr
  /// Invalid argument.
  Einval
  /// I/O error.
  Eio
  /// Illegal operation on a directory.
  Eisdir
  /// Too many levels of symbolic links.
  Eloop
  /// Too many open files.
  Emfile
  /// Too many links.
  Emlink
  /// Multihop attempted.
  Emultihop
  /// Filename too long
  Enametoolong
  /// File table overflow
  Enfile
  /// No buffer space available.
  Enobufs
  /// No such device.
  Enodev
  /// No locks available.
  Enolck
  /// Link has been severed.
  Enolink
  /// No such file or directory.
  Enoent
  /// Not enough memory.
  Enomem
  /// No space left on device.
  Enospc
  /// No STREAM resources.
  Enosr
  /// Not a STREAM.
  Enostr
  /// Function not implemented.
  Enosys
  /// Block device required.
  Enotblk
  /// Not a directory.
  Enotdir
  /// Operation not supported.
  Enotsup
  /// No such device or address.
  Enxio
  /// Operation not supported on socket.
  Eopnotsupp
  /// Value too large to be stored in data type.
  Eoverflow
  /// Not owner.
  Eperm
  /// Broken pipe.
  Epipe
  /// Result too large.
  Erange
  /// Read-only file system.
  Erofs
  /// Invalid seek.
  Espipe
  /// No such process.
  Esrch
  /// Stale remote file handle.
  Estale
  /// Text file busy.
  Etxtbsy
  /// Cross-domain link.
  Exdev
  /// File was requested to be read as UTF-8, but is not UTF-8 encoded.
  NotUtf8
  /// Any error not accounted for by this type
  Unknown
}

/// Read a files contents as a string
/// ## Example
/// ```gleam
/// let assert Ok(records) = read(from: "./users.csv")
/// ```
///
pub fn read(from filepath: String) -> Result(String, FileError) {
  do_read(filepath)
  |> cast_error
}

/// Write a string to a file at the given path
/// ## Example
/// ```gleam
/// let assert Ok(Nil) = write("Hello, World!", to: "./hello_world.txt")
/// ```
///
pub fn write(
  to filepath: String,
  contents contents: String,
) -> Result(Nil, FileError) {
  do_write(contents, to: filepath)
  |> cast_error
}

/// Delete a file or directory at a given path. Performs a recursive
/// delete on a directory.
/// Throws an error if the path does not exist.
/// ## Example
/// ```gleam
/// let assert Ok(Nil) = delete(file_at: "./delete_me.txt")
/// ```
///
pub fn delete(file_or_dir_at path: String) -> Result(Nil, FileError) {
  do_delete(path)
  |> cast_error
}

/// Delete all files/directories specified in a list of paths.
/// Recursively deletes provided directories.
/// Does not return an error if one or more of the provided paths 
/// do not exist. 
/// 
pub fn delete_all(paths paths: List(String)) -> Result(Nil, FileError) {
  case paths {
    [] -> Ok(Nil)
    [path, ..rest] -> {
      case delete(path) {
        Ok(Nil) | Error(Enoent) -> delete_all(rest)
        e -> e
      }
    }
  }
}

/// Append a string to the contents of a file at the given path
/// ## Example
/// ```gleam
/// let assert Ok(Nil) = append("more text", to: "./needs_more_text.txt")
/// ```
///
pub fn append(
  to filepath: String,
  contents contents: String,
) -> Result(Nil, FileError) {
  do_append(contents, to: filepath)
  |> cast_error
}

/// Read a files contents as a bitstring
/// ## Example
/// ```gleam
/// let assert Ok(records) = read_bits(from: "./users.csv")
/// ```
///
pub fn read_bits(from filepath: String) -> Result(BitArray, FileError) {
  do_read_bits(filepath)
  |> cast_error
}

/// Write a bitstring to a file at the given path
/// ## Example
/// ```gleam
/// let assert Ok(Nil) = write_bits(<<"Hello, World!":utf8>>, to: "./hello_world.txt")
/// ```
///
pub fn write_bits(
  to filepath: String,
  bits bits: BitArray,
) -> Result(Nil, FileError) {
  do_write_bits(bits, filepath)
  |> cast_error
}

/// Append a bitstring to the contents of a file at the given path
/// ## Example
/// ```gleam
/// let assert Ok(Nil) = append_bits(<<"more text":utf8>>, to: "./needs_more_text.txt")
/// ```
///
pub fn append_bits(
  to filepath: String,
  bits bits: BitArray,
) -> Result(Nil, FileError) {
  do_append_bits(bits, filepath)
  |> cast_error
}

/// Checks if the provided filepath is a directory
/// ## Example
/// ```gleam
/// let assert True = is_directory("./test")
/// ```
pub fn is_directory(filepath: String) -> Bool {
  do_is_directory(filepath)
}

/// Create a directory at the provided filepath. Returns an error if
/// the directory already exists.
///
/// ## Example
/// ```gleam
/// create_directory("./test")
/// ```
pub fn create_directory(filepath: String) -> Result(Nil, FileError) {
  do_make_directory(filepath)
  |> cast_error
}

/// Lists the contents of a directory.
/// The list contains directory and file names, and is not recursive.
/// 
/// ## Example
/// ```gleam
/// let assert Ok(files_and_folders) = read_directory(at: "./Folder1")
/// ```
/// 
pub fn read_directory(at path: String) -> Result(List(String), FileError) {
  do_read_directory(path)
  |> cast_error
}

/// Returns `True` if there is a file at the given path, false otherwise.
/// 
pub fn is_file(filepath: String) -> Bool {
  do_is_file(filepath)
}

/// Creates an empty file at the given filepath. Returns an `Error(Eexist)`
/// if the file already exists.
/// 
pub fn create_file(at filepath: String) -> Result(Nil, FileError) {
  case
    filepath
    |> is_file || filepath
    |> is_directory
  {
    True -> Error(Eexist)
    False -> write_bits(<<>>, to: filepath)
  }
}

/// Recursively creates necessary directories for a given directory
/// path. Note that if you pass a path that "looks like" a file, i.e.
/// `./a/b.txt`, a folder named `b.txt` will be created, so be sure
/// to pass only the path to the required directory.
pub fn create_directory_all(dirpath: String) -> Result(Nil, FileError) {
  let path = case
    dirpath
    |> string.ends_with("/")
  {
    True -> dirpath
    False -> dirpath <> "/"
  }
  do_create_dir_all(path)
  |> cast_error
}

/// Copy a file at a given path to another path.
/// Note: destination should include the filename, not just the directory
pub fn copy_file(at src: String, to dest: String) -> Result(Nil, FileError) {
  do_copy_file(src, dest)
  |> result.replace(Nil)
  |> cast_error
}

/// Rename a file at a given path to another path.
/// Note: destination should include the filename, not just the directory
pub fn rename_file(at src: String, to dest: String) -> Result(Nil, FileError) {
  do_rename_file(src, dest)
  |> cast_error
}

/// Copy a directory recursively
pub fn copy_directory(at src: String, to dest: String) -> Result(Nil, FileError) {
  // Erlang does not provide a built in `copy_dir` function, 
  // and Deno doesn't support Node's `fs.cpSync`, so we'll just roll 
  // our own for now.
  use _ <- result.try(create_directory_all(dest))
  do_copy_directory(src, dest)
}

fn do_copy_directory(src: String, dest: String) -> Result(Nil, FileError) {
  // Iterate over the segments of the file
  use segments <- result.try(read_directory(src))
  segments
  |> list.each(fn(segment) {
    let src_path = src <> "/" <> segment
    let dest_path = dest <> "/" <> segment

    case is_file(src_path), is_directory(src_path) {
      True, False -> {
        // For a file, create the file in the new directory
        use content <- result.try(read_bits(src_path))
        content
        |> write_bits(to: dest_path)
      }
      False, True -> {
        // Create the target directory and recurs
        use _ <- result.try(create_directory(dest_path))
        do_copy_directory(src_path, dest_path)
      }
      _, _ -> {
        // This should be unreachable. The src_path can't be both a file
        // and a directory, and it's definitely one of the two because it's
        // coming from list_contents
        panic as "unreachable"
      }
    }
  })
  Ok(Nil)
}

/// Copy a directory recursively and then delete the old one.
pub fn rename_directory(
  at src: String,
  to dest: String,
) -> Result(Nil, FileError) {
  use _ <- result.try(copy_directory(src, dest))
  delete(src)
}

/// Returns a list of filepaths for every file in the directory, including nested
/// files.
/// 
pub fn get_files(in directory: String) -> Result(List(String), FileError) {
  use contents <- result.try(read_directory(directory))
  let paths = list.map(contents, fn(segment) { directory <> "/" <> segment })
  let files = list.filter(paths, is_file)
  case list.filter(paths, is_directory) {
    [] -> Ok(files)
    directories -> {
      use nested_files <- result.try(list.try_map(directories, get_files))
      Ok(list.append(files, list.flatten(nested_files)))
    }
  }
}

@target(javascript)
fn do_read(from filepath: String) -> Result(String, String) {
  case do_read_bits(filepath) {
    Ok(bits) -> {
      case bit_array.to_string(bits) {
        Ok(str) -> Ok(str)
        _ -> Error("NOTUTF8")
      }
    }
    Error(e) -> Error(e)
  }
}

@target(javascript)
fn do_write(content: String, to filepath: String) -> Result(Nil, String) {
  content
  |> bit_array.from_string
  |> do_write_bits(to: filepath)
}

@target(javascript)
@external(javascript, "./simplifile_js.mjs", "deleteFileOrDirRecursive")
fn do_delete(file_or_dir_at: String) -> Result(Nil, String)

@target(javascript)
fn do_append(content: String, to filepath: String) -> Result(Nil, String) {
  content
  |> bit_array.from_string
  |> do_append_bits(to: filepath)
}

@target(javascript)
@external(javascript, "./simplifile_js.mjs", "readBits")
fn do_read_bits(from: String) -> Result(BitArray, String)

@target(javascript)
@external(javascript, "./simplifile_js.mjs", "writeBits")
fn do_write_bits(content: BitArray, to filepath: String) -> Result(Nil, String)

@target(javascript)
@external(javascript, "./simplifile_js.mjs", "appendBits")
fn do_append_bits(content: BitArray, to filepath: String) -> Result(Nil, String)

@target(javascript)
@external(javascript, "./simplifile_js.mjs", "isDirectory")
fn do_is_directory(filepath: String) -> Bool

@target(javascript)
@external(javascript, "./simplifile_js.mjs", "makeDirectory")
fn do_make_directory(filepath: String) -> Result(Nil, String)

@target(javascript)
@external(javascript, "./simplifile_js.mjs", "createDirAll")
fn do_create_dir_all(dirpath: String) -> Result(Nil, String)

@target(javascript)
@external(javascript, "./simplifile_js.mjs", "listContents")
fn do_read_directory(directory_path: String) -> Result(List(String), String)

@target(javascript)
@external(javascript, "./simplifile_js.mjs", "copyFile")
fn do_copy_file(at: String, to: String) -> Result(Nil, String)

@target(javascript)
@external(javascript, "./simplifile_js.mjs", "renameFile")
fn do_rename_file(at: String, to: String) -> Result(Nil, String)

@target(javascript)
fn cast_error(input: Result(a, String)) -> Result(a, FileError) {
  result.map_error(
    input,
    fn(e) {
      case e {
        "EACCES" -> Eacces
        "EAGAIN" -> Eagain
        "EBADF" -> Ebadf
        "EBADMSG" -> Ebadmsg
        "EBUSY" -> Ebusy
        "EDEADLK" -> Edeadlk
        "EDEADLOCK" -> Edeadlock
        "EDQUOT" -> Edquot
        "EEXIST" -> Eexist
        "EFAULT" -> Efault
        "EFBIG" -> Efbig
        "EFTYPE" -> Eftype
        "EINTR" -> Eintr
        "EINVAL" -> Einval
        "EIO" -> Eio
        "EISDIR" -> Eisdir
        "ELOOP" -> Eloop
        "EMFILE" -> Emfile
        "EMLINK" -> Emlink
        "EMULTIHOP" -> Emultihop
        "ENAMETOOLONG" -> Enametoolong
        "ENFILE" -> Enfile
        "ENOBUFS" -> Enobufs
        "ENODEV" -> Enodev
        "ENOLCK" -> Enolck
        "ENOLINK" -> Enolink
        "ENOENT" -> Enoent
        "ENOMEM" -> Enomem
        "ENOSPC" -> Enospc
        "ENOSR" -> Enosr
        "ENOSTR" -> Enostr
        "ENOSYS" -> Enosys
        "ENOBLK" -> Enotblk
        "ENODIR" -> Enotdir
        "ENOTSUP" -> Enotsup
        "ENXIO" -> Enxio
        "EOPNOTSUPP" -> Eopnotsupp
        "EOVERFLOW" -> Eoverflow
        "EPERM" -> Eperm
        "EPIPE" -> Epipe
        "ERANGE" -> Erange
        "EROFS" -> Erofs
        "ESPIPE" -> Espipe
        "ESRCH" -> Esrch
        "ESTALE" -> Estale
        "ETXTBSY" -> Etxtbsy
        "EXDEV" -> Exdev
        "NOTUTF8" -> NotUtf8
        _ -> Unknown
      }
    },
  )
}

@target(erlang)
@external(erlang, "simplifile_erl", "append_file")
fn do_append_bits(
  content: BitArray,
  to filepath: String,
) -> Result(Nil, FileError)

@target(erlang)
@external(erlang, "simplifile_erl", "write_file")
fn do_write_bits(
  content: BitArray,
  to filepath: String,
) -> Result(Nil, FileError)

@target(erlang)
@external(erlang, "simplifile_erl", "read_file")
fn do_read_bits(from: String) -> Result(BitArray, FileError)

@target(erlang)
@external(erlang, "simplifile_erl", "recursive_delete")
fn do_delete(file_or_dir_at: String) -> Result(Nil, FileError)

@target(erlang)
fn do_append(content: String, to filepath: String) -> Result(Nil, FileError) {
  content
  |> bit_array.from_string
  |> do_append_bits(filepath)
}

@target(erlang)
fn do_write(content: String, to filepath: String) -> Result(Nil, FileError) {
  content
  |> bit_array.from_string
  |> do_write_bits(filepath)
}

@target(erlang)
fn do_read(from filepath: String) -> Result(String, FileError) {
  case do_read_bits(filepath) {
    Ok(bits) -> {
      case bit_array.to_string(bits) {
        Ok(str) -> Ok(str)
        _ -> Error(NotUtf8)
      }
    }
    Error(e) -> Error(e)
  }
}

@target(erlang)
fn cast_error(input: Result(a, FileError)) -> Result(a, FileError) {
  input
}

@target(erlang)
@external(erlang, "filelib", "is_dir")
fn do_is_directory(path: String) -> Bool

@target(erlang)
@external(erlang, "simplifile_erl", "make_directory")
fn do_make_directory(directory: String) -> Result(Nil, FileError)

@target(erlang)
@external(erlang, "simplifile_erl", "list_directory")
fn do_read_directory(directory: String) -> Result(List(String), FileError)

@external(erlang, "simplifile_erl", "is_file")
@external(javascript, "./simplifile_js.mjs", "isFile")
fn do_is_file(filepath: String) -> Bool

@target(erlang)
@external(erlang, "simplifile_erl", "create_dir_all")
fn do_create_dir_all(dirpath: String) -> Result(Nil, FileError)

@target(erlang)
@external(erlang, "file", "copy")
fn do_copy_file(src: String, dest: String) -> Result(Int, FileError)

@target(erlang)
@external(erlang, "simplifile_erl", "rename_file")
fn do_rename_file(src: String, dest: String) -> Result(Nil, FileError)