use nix::{libc::STDOUT_FILENO, unistd::{Whence, lseek, write}};

use crate::{getopt::{Opt, OptSpec, get_opts_from_tokens}, libsh::error::{ShErr, ShErrKind, ShResult}, parse::{NdRule, Node, execute::prepare_argv}, procio::borrow_fd, state};

pub const LSEEK_OPTS: [OptSpec;2] = [
	OptSpec {
		opt: Opt::Short('c'),
		takes_arg: false
	},
	OptSpec {
		opt: Opt::Short('e'),
		takes_arg: false
	},
];

pub struct LseekOpts {
	cursor_rel: bool,
	end_rel: bool
}

pub fn seek(node: Node) -> ShResult<()> {
	let NdRule::Command {
		assignments: _,
		argv,
	} = node.class else { unreachable!() };

	let (argv, opts) = get_opts_from_tokens(argv, &LSEEK_OPTS)?;
	let lseek_opts = get_lseek_opts(opts)?;
	let mut argv = prepare_argv(argv)?.into_iter();
	argv.next(); // drop 'seek'

	let Some(fd) = argv.next() else {
		return Err(ShErr::simple(
			ShErrKind::ExecFail,
			"lseek: Missing required argument 'fd'",
		));
	};
	let Ok(fd) = fd.0.parse::<u32>() else {
		return Err(ShErr::at(
			ShErrKind::ExecFail,
			fd.1,
			"Invalid file descriptor",
		).with_note("file descriptors are integers"));
	};

	let Some(offset) = argv.next() else {
		return Err(ShErr::simple(
			ShErrKind::ExecFail,
			"lseek: Missing required argument 'offset'",
		));
	};
	let Ok(offset) = offset.0.parse::<i64>() else {
		return Err(ShErr::at(
			ShErrKind::ExecFail,
			offset.1,
			"Invalid offset",
		).with_note("offset can be a positive or negative integer"));
	};

	let whence = if lseek_opts.cursor_rel {
		Whence::SeekCur
	} else if lseek_opts.end_rel {
		Whence::SeekEnd
	} else {
		Whence::SeekSet
	};

	match lseek(fd as i32, offset, whence) {
		Ok(new_offset) => {
			let stdout = borrow_fd(STDOUT_FILENO);
			let buf = new_offset.to_string() + "\n";
			write(stdout, buf.as_bytes())?;
		}
		Err(e) => {
			state::set_status(1);
			return Err(e.into())
		}
	}

	state::set_status(0);
	Ok(())
}

pub fn get_lseek_opts(opts: Vec<Opt>) -> ShResult<LseekOpts> {
	let mut lseek_opts = LseekOpts {
		cursor_rel: false,
		end_rel: false,
	};

  for opt in opts {
    match opt {
      Opt::Short('c') => lseek_opts.cursor_rel = true,
      Opt::Short('e') => lseek_opts.end_rel = true,
      _ => {
        return Err(ShErr::simple(
          ShErrKind::ExecFail,
          format!("lseek: Unexpected flag '{opt}'"),
        ));
      }
    }
  }

  Ok(lseek_opts)
}

#[cfg(test)]
mod tests {
  use crate::testutil::{TestGuard, test_input};
  use pretty_assertions::assert_eq;

  #[test]
  fn seek_set_beginning() {
    let dir = tempfile::TempDir::new().unwrap();
    let path = dir.path().join("seek.txt");
    std::fs::write(&path, "hello world\n").unwrap();
    let g = TestGuard::new();

    test_input(format!("exec 9<> {}", path.display())).unwrap();
    test_input("seek 9 0").unwrap();

    let out = g.read_output();
    assert_eq!(out, "0\n");
  }

  #[test]
  fn seek_set_offset() {
    let dir = tempfile::TempDir::new().unwrap();
    let path = dir.path().join("seek.txt");
    std::fs::write(&path, "hello world\n").unwrap();
    let g = TestGuard::new();

    test_input(format!("exec 9<> {}", path.display())).unwrap();
    test_input("seek 9 6").unwrap();

    let out = g.read_output();
    assert_eq!(out, "6\n");
  }

  #[test]
  fn seek_then_read() {
    let dir = tempfile::TempDir::new().unwrap();
    let path = dir.path().join("seek.txt");
    std::fs::write(&path, "hello world\n").unwrap();
    let g = TestGuard::new();

    test_input(format!("exec 9<> {}", path.display())).unwrap();
    test_input("seek 9 6").unwrap();
    // Clear the seek output
    g.read_output();

    test_input("read line <&9").unwrap();
    let val = crate::state::read_vars(|v| v.get_var("line"));
    assert_eq!(val, "world");
  }

  #[test]
  fn seek_cur_relative() {
    let dir = tempfile::TempDir::new().unwrap();
    let path = dir.path().join("seek.txt");
    std::fs::write(&path, "abcdefghij\n").unwrap();
    let g = TestGuard::new();

    test_input(format!("exec 9<> {}", path.display())).unwrap();
    test_input("seek 9 3").unwrap();
    test_input("seek -c 9 4").unwrap();

    let out = g.read_output();
    assert_eq!(out, "3\n7\n");
  }

  #[test]
  fn seek_end() {
    let dir = tempfile::TempDir::new().unwrap();
    let path = dir.path().join("seek.txt");
    std::fs::write(&path, "hello\n").unwrap(); // 6 bytes
    let g = TestGuard::new();

    test_input(format!("exec 9<> {}", path.display())).unwrap();
    test_input("seek -e 9 0").unwrap();

    let out = g.read_output();
    assert_eq!(out, "6\n");
  }

  #[test]
  fn seek_end_negative() {
    let dir = tempfile::TempDir::new().unwrap();
    let path = dir.path().join("seek.txt");
    std::fs::write(&path, "hello\n").unwrap(); // 6 bytes
    let g = TestGuard::new();

    test_input(format!("exec 9<> {}", path.display())).unwrap();
    test_input("seek -e 9 -2").unwrap();

    let out = g.read_output();
    assert_eq!(out, "4\n");
  }

  #[test]
  fn seek_write_overwrite() {
    let dir = tempfile::TempDir::new().unwrap();
    let path = dir.path().join("seek.txt");
    std::fs::write(&path, "hello world\n").unwrap();
    let _g = TestGuard::new();

    test_input(format!("exec 9<> {}", path.display())).unwrap();
    test_input("seek 9 6").unwrap();
    test_input("echo -n 'WORLD' >&9").unwrap();

    let contents = std::fs::read_to_string(&path).unwrap();
    assert_eq!(contents, "hello WORLD\n");
  }

  #[test]
  fn seek_rewind_full_read() {
    let dir = tempfile::TempDir::new().unwrap();
    let path = dir.path().join("seek.txt");
    std::fs::write(&path, "abc\n").unwrap();
    let g = TestGuard::new();

    test_input(format!("exec 9<> {}", path.display())).unwrap();
    // Read moves cursor to EOF
    test_input("read line <&9").unwrap();
    // Rewind
    test_input("seek 9 0").unwrap();
    // Clear output from seek
    g.read_output();
    // Read again from beginning
    test_input("read line <&9").unwrap();

    let val = crate::state::read_vars(|v| v.get_var("line"));
    assert_eq!(val, "abc");
  }

  #[test]
  fn seek_bad_fd() {
    let _g = TestGuard::new();

    let result = test_input("seek 99 0");
    assert!(result.is_err());
  }

  #[test]
  fn seek_missing_args() {
    let _g = TestGuard::new();

    let result = test_input("seek");
    assert!(result.is_err());

    let result = test_input("seek 9");
    assert!(result.is_err());
  }
}