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    //! Minimal, flexible command-line parser
    //!
    //! As opposed to a declarative parser, this processes arguments as a stream of tokens.  As lexing
    //! a command-line is not context-free, we rely on the caller to decide how to interpret the
    //! arguments.
    //!
    //! # Examples
    //!
    //! ```rust
    //! # use std::path::PathBuf;
    //! # type BoxedError = Box<dyn std::error::Error + Send + Sync>;
    //! #[derive(Debug)]
    //! struct Args {
    //!     paths: Vec<PathBuf>,
    //!     color: Color,
    //!     verbosity: usize,
    //! }
    //!
    //! #[derive(Debug)]
    //! enum Color {
    //!     Always,
    //!     Auto,
    //!     Never,
    //! }
    //!
    //! impl Color {
    //!     fn parse(s: Option<&clap_lex::RawOsStr>) -> Result<Self, BoxedError> {
    //!         let s = s.map(|s| s.to_str().ok_or(s));
    //!         match s {
    //!             Some(Ok("always")) | Some(Ok("")) | None => {
    //!                 Ok(Color::Always)
    //!             }
    //!             Some(Ok("auto")) => {
    //!                 Ok(Color::Auto)
    //!             }
    //!             Some(Ok("never")) => {
    //!                 Ok(Color::Never)
    //!             }
    //!             Some(invalid) => {
    //!                 Err(format!("Invalid value for `--color`, {:?}", invalid).into())
    //!             }
    //!         }
    //!     }
    //! }
    //!
    //! fn parse_args(
    //!     raw: impl IntoIterator<Item=impl Into<std::ffi::OsString>>
    //! ) -> Result<Args, BoxedError> {
    //!     let mut args = Args {
    //!         paths: Vec::new(),
    //!         color: Color::Auto,
    //!         verbosity: 0,
    //!     };
    //!
    //!     let raw = clap_lex::RawArgs::new(raw);
    //!     let mut cursor = raw.cursor();
    //!     raw.next(&mut cursor);  // Skip the bin
    //!     while let Some(arg) = raw.next(&mut cursor) {
    //!         if arg.is_escape() {
    //!             args.paths.extend(raw.remaining(&mut cursor).map(PathBuf::from));
    //!         } else if arg.is_stdio() {
    //!             args.paths.push(PathBuf::from("-"));
    //!         } else if let Some((long, value)) = arg.to_long() {
    //!             match long {
    //!                 Ok("verbose") => {
    //!                     if let Some(value) = value {
    //!                         return Err(format!("`--verbose` does not take a value, got `{:?}`", value).into());
    //!                     }
    //!                     args.verbosity += 1;
    //!                 }
    //!                 Ok("color") => {
    //!                     args.color = Color::parse(value)?;
    //!                 }
    //!                 _ => {
    //!                     return Err(
    //!                         format!("Unexpected flag: --{}", arg.display()).into()
    //!                     );
    //!                 }
    //!             }
    //!         } else if let Some(mut shorts) = arg.to_short() {
    //!             while let Some(short) = shorts.next_flag() {
    //!                 match short {
    //!                     Ok('v') => {
    //!                         args.verbosity += 1;
    //!                     }
    //!                     Ok('c') => {
    //!                         let value = shorts.next_value_os();
    //!                         args.color = Color::parse(value)?;
    //!                     }
    //!                     Ok(c) => {
    //!                         return Err(format!("Unexpected flag: -{}", c).into());
    //!                     }
    //!                     Err(e) => {
    //!                         return Err(format!("Unexpected flag: -{}", e.to_str_lossy()).into());
    //!                     }
    //!                 }
    //!             }
    //!         } else {
    //!             args.paths.push(PathBuf::from(arg.to_value_os().to_os_str().into_owned()));
    //!         }
    //!     }
    //!
    //!     Ok(args)
    //! }
    //!
    //! let args = parse_args(["bin", "--hello", "world"]);
    //! println!("{:?}", args);
    //! ```

    use std::ffi::OsStr;
    use std::ffi::OsString;

    pub use std::io::SeekFrom;

    pub use os_str_bytes::RawOsStr;
    pub use os_str_bytes::RawOsString;

    /// Command-line arguments
    #[derive(Default, Clone, Debug, PartialEq, Eq)]
    pub struct RawArgs {
        items: Vec<OsString>,
    }

    impl RawArgs {
        //// Create an argument list to parse
        ///
        /// **NOTE:** The argument returned will be the current binary.
        ///
        /// # Example
        ///
        /// ```rust,no_run
        /// # use std::path::PathBuf;
        /// let raw = clap_lex::RawArgs::from_args();
        /// let mut cursor = raw.cursor();
        /// let _bin = raw.next_os(&mut cursor);
        ///
        /// let mut paths = raw.remaining(&mut cursor).map(PathBuf::from).collect::<Vec<_>>();
        /// println!("{:?}", paths);
        /// ```
        pub fn from_args() -> Self {
            Self::new(std::env::args_os())
        }

        //// Create an argument list to parse
        ///
        /// # Example
        ///
        /// ```rust,no_run
        /// # use std::path::PathBuf;
        /// let raw = clap_lex::RawArgs::new(["bin", "foo.txt"]);
        /// let mut cursor = raw.cursor();
        /// let _bin = raw.next_os(&mut cursor);
        ///
        /// let mut paths = raw.remaining(&mut cursor).map(PathBuf::from).collect::<Vec<_>>();
        /// println!("{:?}", paths);
        /// ```
        pub fn new(iter: impl IntoIterator<Item = impl Into<std::ffi::OsString>>) -> Self {
            let iter = iter.into_iter();
            Self::from(iter)
        }

        /// Create a cursor for walking the arguments
        ///
        /// # Example
        ///
        /// ```rust,no_run
        /// # use std::path::PathBuf;
        /// let raw = clap_lex::RawArgs::new(["bin", "foo.txt"]);
        /// let mut cursor = raw.cursor();
        /// let _bin = raw.next_os(&mut cursor);
        ///
        /// let mut paths = raw.remaining(&mut cursor).map(PathBuf::from).collect::<Vec<_>>();
        /// println!("{:?}", paths);
        /// ```
        pub fn cursor(&self) -> ArgCursor {
            ArgCursor::new()
        }

        /// Advance the cursor, returning the next [`ParsedArg`]
        pub fn next(&self, cursor: &mut ArgCursor) -> Option<ParsedArg<'_>> {
            self.next_os(cursor).map(ParsedArg::new)
        }

        /// Advance the cursor, returning a raw argument value.
        pub fn next_os(&self, cursor: &mut ArgCursor) -> Option<&OsStr> {
            let next = self.items.get(cursor.cursor).map(|s| s.as_os_str());
            cursor.cursor = cursor.cursor.saturating_add(1);
            next
        }

        /// Return the next [`ParsedArg`]
        pub fn peek(&self, cursor: &ArgCursor) -> Option<ParsedArg<'_>> {
            self.peek_os(cursor).map(ParsedArg::new)
        }

        /// Return a raw argument value.
        pub fn peek_os(&self, cursor: &ArgCursor) -> Option<&OsStr> {
            self.items.get(cursor.cursor).map(|s| s.as_os_str())
        }

        /// Return all remaining raw arguments, advancing the cursor to the end
        ///
        /// # Example
        ///
        /// ```rust,no_run
        /// # use std::path::PathBuf;
        /// let raw = clap_lex::RawArgs::new(["bin", "foo.txt"]);
        /// let mut cursor = raw.cursor();
        /// let _bin = raw.next_os(&mut cursor);
        ///
        /// let mut paths = raw.remaining(&mut cursor).map(PathBuf::from).collect::<Vec<_>>();
        /// println!("{:?}", paths);
        /// ```
        pub fn remaining(&self, cursor: &mut ArgCursor) -> impl Iterator<Item = &OsStr> {
            let remaining = self.items[cursor.cursor..].iter().map(|s| s.as_os_str());
            cursor.cursor = self.items.len();
            remaining
        }

        /// Adjust the cursor's position
        pub fn seek(&self, cursor: &mut ArgCursor, pos: SeekFrom) {
            let pos = match pos {
                SeekFrom::Start(pos) => pos,
                SeekFrom::End(pos) => (self.items.len() as i64).saturating_add(pos).max(0) as u64,
                SeekFrom::Current(pos) => (cursor.cursor as i64).saturating_add(pos).max(0) as u64,
            };
            let pos = (pos as usize).min(self.items.len());
            cursor.cursor = pos;
        }

        /// Inject arguments before the [`RawArgs::next`]
        pub fn insert(
            &mut self,
            cursor: &ArgCursor,
            insert_items: impl IntoIterator<Item = impl Into<OsString>>,
        ) {
            self.items.splice(
                cursor.cursor..cursor.cursor,
                insert_items.into_iter().map(Into::into),
            );
        }

        /// Any remaining args?
        pub fn is_end(&self, cursor: &ArgCursor) -> bool {
            self.peek_os(cursor).is_none()
        }
    }

    impl<I, T> From<I> for RawArgs
    where
        I: Iterator<Item = T>,
        T: Into<OsString>,
    {
        fn from(val: I) -> Self {
            Self {
                items: val.map(|x| x.into()).collect(),
            }
        }
    }

    /// Position within [`RawArgs`]
    #[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
    pub struct ArgCursor {
        cursor: usize,
    }

    impl ArgCursor {
        fn new() -> Self {
            Self { cursor: 0 }
        }
    }

    /// Command-line Argument
    #[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
    pub struct ParsedArg<'s> {
        inner: std::borrow::Cow<'s, RawOsStr>,
        utf8: Option<&'s str>,
    }

    impl<'s> ParsedArg<'s> {
        fn new(inner: &'s OsStr) -> Self {
            let utf8 = inner.to_str();
            let inner = RawOsStr::new(inner);
            Self { inner, utf8 }
        }

        /// Argument is length of 0
        pub fn is_empty(&self) -> bool {
            self.inner.as_ref().is_empty()
        }

        /// Does the argument look like a stdio argument (`-`)
        pub fn is_stdio(&self) -> bool {
            self.inner.as_ref() == "-"
        }

        /// Does the argument look like an argument escape (`--`)
        pub fn is_escape(&self) -> bool {
            self.inner.as_ref() == "--"
        }

        /// Does the argument look like a number
        pub fn is_number(&self) -> bool {
            self.to_value()
                .map(|s| s.parse::<f64>().is_ok())
                .unwrap_or_default()
        }

        /// Treat as a long-flag
        pub fn to_long(&self) -> Option<(Result<&str, &RawOsStr>, Option<&RawOsStr>)> {
            if let Some(raw) = self.utf8 {
                let remainder = raw.strip_prefix("--")?;
                if remainder.is_empty() {
                    debug_assert!(self.is_escape());
                    return None;
                }

                let (flag, value) = if let Some((p0, p1)) = remainder.split_once('=') {
                    (p0, Some(p1))
                } else {
                    (remainder, None)
                };
                let flag = Ok(flag);
                let value = value.map(RawOsStr::from_str);
                Some((flag, value))
            } else {
                let raw = self.inner.as_ref();
                let remainder = raw.strip_prefix("--")?;
                if remainder.is_empty() {
                    debug_assert!(self.is_escape());
                    return None;
                }

                let (flag, value) = if let Some((p0, p1)) = remainder.split_once('=') {
                    (p0, Some(p1))
                } else {
                    (remainder, None)
                };
                let flag = flag.to_str().ok_or(flag);
                Some((flag, value))
            }
        }

        /// Can treat as a long-flag
        pub fn is_long(&self) -> bool {
            self.inner.as_ref().starts_with("--") && !self.is_escape()
        }

        /// Treat as a short-flag
        pub fn to_short(&self) -> Option<ShortFlags<'_>> {
            if let Some(remainder_os) = self.inner.as_ref().strip_prefix('-') {
                if remainder_os.starts_with('-') {
                    None
                } else if remainder_os.is_empty() {
                    debug_assert!(self.is_stdio());
                    None
                } else {
                    let remainder = self.utf8.map(|s| &s[1..]);
                    Some(ShortFlags::new(remainder_os, remainder))
                }
            } else {
                None
            }
        }

        /// Can treat as a short-flag
        pub fn is_short(&self) -> bool {
            self.inner.as_ref().starts_with('-')
                && !self.is_stdio()
                && !self.inner.as_ref().starts_with("--")
        }

        /// Treat as a value
        ///
        /// **NOTE:** May return a flag or an escape.
        pub fn to_value_os(&self) -> &RawOsStr {
            self.inner.as_ref()
        }

        /// Treat as a value
        ///
        /// **NOTE:** May return a flag or an escape.
        pub fn to_value(&self) -> Result<&str, &RawOsStr> {
            self.utf8.ok_or_else(|| self.inner.as_ref())
        }

        /// Safely print an argument that may contain non-UTF8 content
        ///
        /// This may perform lossy conversion, depending on the platform. If you would like an implementation which escapes the path please use Debug instead.
        pub fn display(&self) -> impl std::fmt::Display + '_ {
            self.inner.to_str_lossy()
        }
    }

    /// Walk through short flags within a [`ParsedArg`]
    #[derive(Clone, Debug)]
    pub struct ShortFlags<'s> {
        inner: &'s RawOsStr,
        utf8_prefix: std::str::CharIndices<'s>,
        invalid_suffix: Option<&'s RawOsStr>,
    }

    impl<'s> ShortFlags<'s> {
        fn new(inner: &'s RawOsStr, utf8: Option<&'s str>) -> Self {
            let (utf8_prefix, invalid_suffix) = if let Some(utf8) = utf8 {
                (utf8, None)
            } else {
                split_nonutf8_once(inner)
            };
            let utf8_prefix = utf8_prefix.char_indices();
            Self {
                inner,
                utf8_prefix,
                invalid_suffix,
            }
        }

        /// Move the iterator forward by `n` short flags
        pub fn advance_by(&mut self, n: usize) -> Result<(), usize> {
            for i in 0..n {
                self.next().ok_or(i)?.map_err(|_| i)?;
            }
            Ok(())
        }

        /// No short flags left
        pub fn is_empty(&self) -> bool {
            self.invalid_suffix.is_none() && self.utf8_prefix.as_str().is_empty()
        }

        /// Does the short flag look like a number
        ///
        /// Ideally call this before doing any iterator
        pub fn is_number(&self) -> bool {
            self.invalid_suffix.is_none() && self.utf8_prefix.as_str().parse::<f64>().is_ok()
        }

        /// Advance the iterator, returning the next short flag on success
        ///
        /// On error, returns the invalid-UTF8 value
        pub fn next_flag(&mut self) -> Option<Result<char, &'s RawOsStr>> {
            if let Some((_, flag)) = self.utf8_prefix.next() {
                return Some(Ok(flag));
            }

            if let Some(suffix) = self.invalid_suffix {
                self.invalid_suffix = None;
                return Some(Err(suffix));
            }

            None
        }

        /// Advance the iterator, returning everything left as a value
        pub fn next_value_os(&mut self) -> Option<&'s RawOsStr> {
            if let Some((index, _)) = self.utf8_prefix.next() {
                self.utf8_prefix = "".char_indices();
                self.invalid_suffix = None;
                return Some(&self.inner[index..]);
            }

            if let Some(suffix) = self.invalid_suffix {
                self.invalid_suffix = None;
                return Some(suffix);
            }

            None
        }
    }

    impl<'s> Iterator for ShortFlags<'s> {
        type Item = Result<char, &'s RawOsStr>;

        fn next(&mut self) -> Option<Self::Item> {
            self.next_flag()
        }
    }

    fn split_nonutf8_once(b: &RawOsStr) -> (&str, Option<&RawOsStr>) {
        match std::str::from_utf8(b.as_raw_bytes()) {
            Ok(s) => (s, None),
            Err(err) => {
                let (valid, after_valid) = b.split_at(err.valid_up_to());
                let valid = std::str::from_utf8(valid.as_raw_bytes()).unwrap();
                (valid, Some(after_valid))
            }
        }
    }