// Std
use std::borrow::Cow;
use std::cmp;
use std::fmt::Write as _;
use std::io::{self, Write};
use std::usize;

// Internal
use crate::builder::{display_arg_val, Arg, Command};
use crate::output::{fmt::Colorizer, Usage};
use crate::PossibleValue;

// Third party
use indexmap::IndexSet;
use textwrap::core::display_width;

/// `clap` Help Writer.
///
/// Wraps a writer stream providing different methods to generate help for `clap` objects.
pub(crate) struct Help<'help, 'cmd, 'writer> {
    writer: HelpWriter<'writer>,
    cmd: &'cmd Command<'help>,
    usage: &'cmd Usage<'help, 'cmd>,
    next_line_help: bool,
    term_w: usize,
    use_long: bool,
}

// Public Functions
impl<'help, 'cmd, 'writer> Help<'help, 'cmd, 'writer> {
    #[cfg(feature = "unstable-v4")]
    const DEFAULT_TEMPLATE: &'static str = "\
        {before-help}{name} {version}\n\
        {author-with-newline}{about-with-newline}\n\
        {usage-heading}\n    {usage}\n\
        \n\
        {all-args}{after-help}\
    ";
    #[cfg(not(feature = "unstable-v4"))]
    const DEFAULT_TEMPLATE: &'static str = "\
        {before-help}{bin} {version}\n\
        {author-with-newline}{about-with-newline}\n\
        {usage-heading}\n    {usage}\n\
        \n\
        {all-args}{after-help}\
    ";

    #[cfg(feature = "unstable-v4")]
    const DEFAULT_NO_ARGS_TEMPLATE: &'static str = "\
        {before-help}{name} {version}\n\
        {author-with-newline}{about-with-newline}\n\
        {usage-heading}\n    {usage}{after-help}\
    ";
    #[cfg(not(feature = "unstable-v4"))]
    const DEFAULT_NO_ARGS_TEMPLATE: &'static str = "\
        {before-help}{bin} {version}\n\
        {author-with-newline}{about-with-newline}\n\
        {usage-heading}\n    {usage}{after-help}\
    ";

    /// Create a new `Help` instance.
    pub(crate) fn new(
        writer: HelpWriter<'writer>,
        cmd: &'cmd Command<'help>,
        usage: &'cmd Usage<'help, 'cmd>,
        use_long: bool,
    ) -> Self {
        debug!("Help::new cmd={}, use_long={}", cmd.get_name(), use_long);
        let term_w = match cmd.get_term_width() {
            Some(0) => usize::MAX,
            Some(w) => w,
            None => cmp::min(
                dimensions().map_or(100, |(w, _)| w),
                match cmd.get_max_term_width() {
                    None | Some(0) => usize::MAX,
                    Some(mw) => mw,
                },
            ),
        };
        let next_line_help = cmd.is_next_line_help_set();

        Help {
            writer,
            cmd,
            usage,
            next_line_help,
            term_w,
            use_long,
        }
    }

    /// Writes the parser help to the wrapped stream.
    pub(crate) fn write_help(&mut self) -> io::Result<()> {
        debug!("Help::write_help");

        if let Some(h) = self.cmd.get_override_help() {
            self.none(h)?;
        } else if let Some(tmpl) = self.cmd.get_help_template() {
            self.write_templated_help(tmpl)?;
        } else {
            let pos = self
                .cmd
                .get_positionals()
                .any(|arg| should_show_arg(self.use_long, arg));
            let non_pos = self
                .cmd
                .get_non_positionals()
                .any(|arg| should_show_arg(self.use_long, arg));
            let subcmds = self.cmd.has_visible_subcommands();

            if non_pos || pos || subcmds {
                self.write_templated_help(Self::DEFAULT_TEMPLATE)?;
            } else {
                self.write_templated_help(Self::DEFAULT_NO_ARGS_TEMPLATE)?;
            }
        }

        self.none("\n")?;

        Ok(())
    }
}

macro_rules! write_method {
    ($_self:ident, $msg:ident, $meth:ident) => {
        match &mut $_self.writer {
            HelpWriter::Buffer(c) => {
                c.$meth(($msg).into());
                Ok(())
            }
            HelpWriter::Normal(w) => w.write_all($msg.as_ref()),
        }
    };
}

// Methods to write Arg help.
impl<'help, 'cmd, 'writer> Help<'help, 'cmd, 'writer> {
    #[inline(never)]
    fn good<T: Into<String> + AsRef<[u8]>>(&mut self, msg: T) -> io::Result<()> {
        write_method!(self, msg, good)
    }

    #[inline(never)]
    fn warning<T: Into<String> + AsRef<[u8]>>(&mut self, msg: T) -> io::Result<()> {
        write_method!(self, msg, warning)
    }

    #[inline(never)]
    fn none<T: Into<String> + AsRef<[u8]>>(&mut self, msg: T) -> io::Result<()> {
        write_method!(self, msg, none)
    }

    #[inline(never)]
    fn spaces(&mut self, n: usize) -> io::Result<()> {
        // A string with 64 consecutive spaces.
        const SHORT_SPACE: &str =
            "                                                                ";
        if let Some(short) = SHORT_SPACE.get(..n) {
            self.none(short)
        } else {
            self.none(" ".repeat(n))
        }
    }

    /// Writes help for each argument in the order they were declared to the wrapped stream.
    fn write_args_unsorted(&mut self, args: &[&Arg<'help>]) -> io::Result<()> {
        debug!("Help::write_args_unsorted");
        // The shortest an arg can legally be is 2 (i.e. '-x')
        let mut longest = 2;
        let mut arg_v = Vec::with_capacity(10);

        for &arg in args
            .iter()
            .filter(|arg| should_show_arg(self.use_long, *arg))
        {
            if arg.longest_filter() {
                longest = longest.max(display_width(&arg.to_string()));
                debug!(
                    "Help::write_args_unsorted: arg={:?} longest={}",
                    arg.get_id(),
                    longest
                );
            }
            arg_v.push(arg)
        }

        let next_line_help = self.will_args_wrap(args, longest);

        let argc = arg_v.len();
        for (i, arg) in arg_v.iter().enumerate() {
            self.write_arg(arg, i + 1 == argc, next_line_help, longest)?;
        }
        Ok(())
    }

    /// Sorts arguments by length and display order and write their help to the wrapped stream.
    fn write_args(&mut self, args: &[&Arg<'help>], _category: &str) -> io::Result<()> {
        debug!("Help::write_args {}", _category);
        // The shortest an arg can legally be is 2 (i.e. '-x')
        let mut longest = 2;
        let mut ord_v = Vec::new();

        // Determine the longest
        for &arg in args.iter().filter(|arg| {
            // If it's NextLineHelp we don't care to compute how long it is because it may be
            // NextLineHelp on purpose simply *because* it's so long and would throw off all other
            // args alignment
            should_show_arg(self.use_long, *arg)
        }) {
            if arg.longest_filter() {
                longest = longest.max(display_width(&arg.to_string()));
                debug!(
                    "Help::write_args: arg={:?} longest={}",
                    arg.get_id(),
                    longest
                );
            }

            // Formatting key like this to ensure that:
            // 1. Argument has long flags are printed just after short flags.
            // 2. For two args both have short flags like `-c` and `-C`, the
            //    `-C` arg is printed just after the `-c` arg
            // 3. For args without short or long flag, print them at last(sorted
            //    by arg name).
            // Example order: -a, -b, -B, -s, --select-file, --select-folder, -x

            let key = if let Some(x) = arg.short {
                let mut s = x.to_ascii_lowercase().to_string();
                s.push(if x.is_ascii_lowercase() { '0' } else { '1' });
                s
            } else if let Some(x) = arg.long {
                x.to_string()
            } else {
                let mut s = '{'.to_string();
                s.push_str(arg.name);
                s
            };
            ord_v.push((arg.get_display_order(), key, arg));
        }
        ord_v.sort_by(|a, b| (a.0, &a.1).cmp(&(b.0, &b.1)));

        let next_line_help = self.will_args_wrap(args, longest);

        for (i, (_, _, arg)) in ord_v.iter().enumerate() {
            let last_arg = i + 1 == ord_v.len();
            self.write_arg(arg, last_arg, next_line_help, longest)?;
        }
        Ok(())
    }

    /// Writes help for an argument to the wrapped stream.
    fn write_arg(
        &mut self,
        arg: &Arg<'help>,
        last_arg: bool,
        next_line_help: bool,
        longest: usize,
    ) -> io::Result<()> {
        let spec_vals = &self.spec_vals(arg);

        self.short(arg)?;
        self.long(arg)?;
        self.val(arg)?;
        self.align_to_about(arg, next_line_help, longest)?;

        let about = if self.use_long {
            arg.long_help.or(arg.help).unwrap_or("")
        } else {
            arg.help.or(arg.long_help).unwrap_or("")
        };

        self.help(Some(arg), about, spec_vals, next_line_help, longest)?;

        if !last_arg {
            self.none("\n")?;
            if next_line_help {
                self.none("\n")?;
            }
        }
        Ok(())
    }

    /// Writes argument's short command to the wrapped stream.
    fn short(&mut self, arg: &Arg<'help>) -> io::Result<()> {
        debug!("Help::short");

        self.none(TAB)?;

        if let Some(s) = arg.short {
            self.good(format!("-{}", s))
        } else if !arg.is_positional() {
            self.none(TAB)
        } else {
            Ok(())
        }
    }

    /// Writes argument's long command to the wrapped stream.
    fn long(&mut self, arg: &Arg<'help>) -> io::Result<()> {
        debug!("Help::long");
        if let Some(long) = arg.long {
            if arg.short.is_some() {
                self.none(", ")?;
            }
            self.good(format!("--{}", long))?;
        }
        Ok(())
    }

    /// Writes argument's possible values to the wrapped stream.
    fn val(&mut self, arg: &Arg<'help>) -> io::Result<()> {
        debug!("Help::val: arg={}", arg.name);
        let mut need_closing_bracket = false;
        if arg.is_takes_value_set() && !arg.is_positional() {
            let is_optional_val = arg.min_vals == Some(0);
            let sep = if arg.is_require_equals_set() {
                if is_optional_val {
                    need_closing_bracket = true;
                    "[="
                } else {
                    "="
                }
            } else if is_optional_val {
                need_closing_bracket = true;
                " ["
            } else {
                " "
            };
            self.none(sep)?;
        }

        if arg.is_takes_value_set() || arg.is_positional() {
            display_arg_val(
                arg,
                |s, good| if good { self.good(s) } else { self.none(s) },
            )?;
        }

        if need_closing_bracket {
            self.none("]")?;
        }
        Ok(())
    }

    /// Write alignment padding between arg's switches/values and its about message.
    fn align_to_about(
        &mut self,
        arg: &Arg<'help>,
        next_line_help: bool,
        longest: usize,
    ) -> io::Result<()> {
        debug!(
            "Help::align_to_about: arg={}, next_line_help={}, longest={}",
            arg.name, next_line_help, longest
        );
        if self.use_long || next_line_help {
            // long help prints messages on the next line so it doesn't need to align text
            debug!("Help::align_to_about: printing long help so skip alignment");
        } else if !arg.is_positional() {
            let self_len = display_width(&arg.to_string());
            // Since we're writing spaces from the tab point we first need to know if we
            // had a long and short, or just short
            let padding = if arg.long.is_some() {
                // Only account 4 after the val
                4
            } else {
                // Only account for ', --' + 4 after the val
                8
            };
            let spcs = longest + padding - self_len;
            debug!(
                "Help::align_to_about: positional=false arg_len={}, spaces={}",
                self_len, spcs
            );

            self.spaces(spcs)?;
        } else {
            let self_len = display_width(&arg.to_string());
            let padding = 4;
            let spcs = longest + padding - self_len;
            debug!(
                "Help::align_to_about: positional=true arg_len={}, spaces={}",
                self_len, spcs
            );

            self.spaces(spcs)?;
        }
        Ok(())
    }

    fn write_before_help(&mut self) -> io::Result<()> {
        debug!("Help::write_before_help");
        let before_help = if self.use_long {
            self.cmd
                .get_before_long_help()
                .or_else(|| self.cmd.get_before_help())
        } else {
            self.cmd.get_before_help()
        };
        if let Some(output) = before_help {
            self.none(text_wrapper(&output.replace("{n}", "\n"), self.term_w))?;
            self.none("\n\n")?;
        }
        Ok(())
    }

    fn write_after_help(&mut self) -> io::Result<()> {
        debug!("Help::write_after_help");
        let after_help = if self.use_long {
            self.cmd
                .get_after_long_help()
                .or_else(|| self.cmd.get_after_help())
        } else {
            self.cmd.get_after_help()
        };
        if let Some(output) = after_help {
            self.none("\n\n")?;
            self.none(text_wrapper(&output.replace("{n}", "\n"), self.term_w))?;
        }
        Ok(())
    }

    /// Writes argument's help to the wrapped stream.
    fn help(
        &mut self,
        arg: Option<&Arg<'help>>,
        about: &str,
        spec_vals: &str,
        next_line_help: bool,
        longest: usize,
    ) -> io::Result<()> {
        debug!("Help::help");
        let mut help = String::from(about) + spec_vals;
        debug!("Help::help: Next Line...{:?}", next_line_help);

        let spaces = if next_line_help {
            12 // "tab" * 3
        } else {
            longest + 12
        };

        let too_long = spaces + display_width(&help) >= self.term_w;

        // Is help on next line, if so then indent
        if next_line_help {
            self.none(format!("\n{}{}{}", TAB, TAB, TAB))?;
        }

        debug!("Help::help: Too long...");
        if too_long && spaces <= self.term_w || help.contains("{n}") {
            debug!("Yes");
            debug!("Help::help: help...{}", help);
            debug!("Help::help: help width...{}", display_width(&help));
            // Determine how many newlines we need to insert
            let avail_chars = self.term_w - spaces;
            debug!("Help::help: Usable space...{}", avail_chars);
            help = text_wrapper(&help.replace("{n}", "\n"), avail_chars);
        } else {
            debug!("No");
        }
        if let Some(part) = help.lines().next() {
            self.none(part)?;
        }

        // indent of help
        let spaces = if next_line_help {
            TAB_WIDTH * 3
        } else if let Some(true) = arg.map(|a| a.is_positional()) {
            longest + TAB_WIDTH * 2
        } else {
            longest + TAB_WIDTH * 3
        };

        for part in help.lines().skip(1) {
            self.none("\n")?;
            self.spaces(spaces)?;
            self.none(part)?;
        }

        #[cfg(feature = "unstable-v4")]
        if let Some(arg) = arg {
            const DASH_SPACE: usize = "- ".len();
            const COLON_SPACE: usize = ": ".len();
            let possible_vals = arg.get_possible_values2();
            if self.use_long
                && !arg.is_hide_possible_values_set()
                && possible_vals.iter().any(PossibleValue::should_show_help)
            {
                debug!("Help::help: Found possible vals...{:?}", possible_vals);
                if !help.is_empty() {
                    self.none("\n\n")?;
                    self.spaces(spaces)?;
                }
                self.none("Possible values:")?;
                let longest = possible_vals
                    .iter()
                    .filter_map(|f| f.get_visible_quoted_name().map(|name| display_width(&name)))
                    .max()
                    .expect("Only called with possible value");
                let help_longest = possible_vals
                    .iter()
                    .filter_map(|f| f.get_visible_help().map(display_width))
                    .max()
                    .expect("Only called with possible value with help");
                // should new line
                let taken = longest + spaces + DASH_SPACE;

                let possible_value_new_line =
                    self.term_w >= taken && self.term_w < taken + COLON_SPACE + help_longest;

                let spaces = spaces + TAB_WIDTH - DASH_SPACE;
                let spaces_help = if possible_value_new_line {
                    spaces + DASH_SPACE
                } else {
                    spaces + longest + DASH_SPACE + COLON_SPACE
                };

                for pv in possible_vals.iter().filter(|pv| !pv.is_hide_set()) {
                    self.none("\n")?;
                    self.spaces(spaces)?;
                    self.none("- ")?;
                    self.good(pv.get_name())?;
                    if let Some(help) = pv.get_help() {
                        debug!("Help::help: Possible Value help");

                        if possible_value_new_line {
                            self.none(":\n")?;
                            self.spaces(spaces_help)?;
                        } else {
                            self.none(": ")?;
                            // To align help messages
                            self.spaces(longest - display_width(pv.get_name()))?;
                        }

                        let avail_chars = if self.term_w > spaces_help {
                            self.term_w - spaces_help
                        } else {
                            usize::MAX
                        };

                        let help = text_wrapper(help, avail_chars);
                        let mut help = help.lines();

                        self.none(help.next().unwrap_or_default())?;
                        for part in help {
                            self.none("\n")?;
                            self.spaces(spaces_help)?;
                            self.none(part)?;
                        }
                    }
                }
            }
        }
        Ok(())
    }

    /// Will use next line help on writing args.
    fn will_args_wrap(&self, args: &[&Arg<'help>], longest: usize) -> bool {
        args.iter()
            .filter(|arg| should_show_arg(self.use_long, *arg))
            .any(|arg| {
                let spec_vals = &self.spec_vals(arg);
                self.arg_next_line_help(arg, spec_vals, longest)
            })
    }

    fn arg_next_line_help(&self, arg: &Arg<'help>, spec_vals: &str, longest: usize) -> bool {
        if self.next_line_help || arg.is_next_line_help_set() || self.use_long {
            // setting_next_line
            true
        } else {
            // force_next_line
            let h = arg.help.unwrap_or("");
            let h_w = display_width(h) + display_width(spec_vals);
            let taken = longest + 12;
            self.term_w >= taken
                && (taken as f32 / self.term_w as f32) > 0.40
                && h_w > (self.term_w - taken)
        }
    }

    fn spec_vals(&self, a: &Arg) -> String {
        debug!("Help::spec_vals: a={}", a);
        let mut spec_vals = vec![];
        #[cfg(feature = "env")]
        if let Some(ref env) = a.env {
            if !a.is_hide_env_set() {
                debug!(
                    "Help::spec_vals: Found environment variable...[{:?}:{:?}]",
                    env.0, env.1
                );
                let env_val = if !a.is_hide_env_values_set() {
                    format!(
                        "={}",
                        env.1
                            .as_ref()
                            .map_or(Cow::Borrowed(""), |val| val.to_string_lossy())
                    )
                } else {
                    String::new()
                };
                let env_info = format!("[env: {}{}]", env.0.to_string_lossy(), env_val);
                spec_vals.push(env_info);
            }
        }
        if a.is_takes_value_set() && !a.is_hide_default_value_set() && !a.default_vals.is_empty() {
            debug!(
                "Help::spec_vals: Found default value...[{:?}]",
                a.default_vals
            );

            let pvs = a
                .default_vals
                .iter()
                .map(|&pvs| pvs.to_string_lossy())
                .map(|pvs| {
                    if pvs.contains(char::is_whitespace) {
                        Cow::from(format!("{:?}", pvs))
                    } else {
                        pvs
                    }
                })
                .collect::<Vec<_>>()
                .join(" ");

            spec_vals.push(format!("[default: {}]", pvs));
        }
        if !a.aliases.is_empty() {
            debug!("Help::spec_vals: Found aliases...{:?}", a.aliases);

            let als = a
                .aliases
                .iter()
                .filter(|&als| als.1) // visible
                .map(|&als| als.0) // name
                .collect::<Vec<_>>()
                .join(", ");

            if !als.is_empty() {
                spec_vals.push(format!("[aliases: {}]", als));
            }
        }

        if !a.short_aliases.is_empty() {
            debug!(
                "Help::spec_vals: Found short aliases...{:?}",
                a.short_aliases
            );

            let als = a
                .short_aliases
                .iter()
                .filter(|&als| als.1) // visible
                .map(|&als| als.0.to_string()) // name
                .collect::<Vec<_>>()
                .join(", ");

            if !als.is_empty() {
                spec_vals.push(format!("[short aliases: {}]", als));
            }
        }

        let possible_vals = a.get_possible_values2();
        if !(a.is_hide_possible_values_set()
            || possible_vals.is_empty()
            || cfg!(feature = "unstable-v4")
                && self.use_long
                && possible_vals.iter().any(PossibleValue::should_show_help))
        {
            debug!("Help::spec_vals: Found possible vals...{:?}", possible_vals);

            let pvs = possible_vals
                .iter()
                .filter_map(PossibleValue::get_visible_quoted_name)
                .collect::<Vec<_>>()
                .join(", ");

            spec_vals.push(format!("[possible values: {}]", pvs));
        }
        let connector = if self.use_long { "\n" } else { " " };
        let prefix = if !spec_vals.is_empty() && !a.get_help().unwrap_or("").is_empty() {
            if self.use_long {
                "\n\n"
            } else {
                " "
            }
        } else {
            ""
        };
        prefix.to_string() + &spec_vals.join(connector)
    }

    fn write_about(&mut self, before_new_line: bool, after_new_line: bool) -> io::Result<()> {
        let about = if self.use_long {
            self.cmd.get_long_about().or_else(|| self.cmd.get_about())
        } else {
            self.cmd.get_about()
        };
        if let Some(output) = about {
            if before_new_line {
                self.none("\n")?;
            }
            self.none(text_wrapper(output, self.term_w))?;
            if after_new_line {
                self.none("\n")?;
            }
        }
        Ok(())
    }

    fn write_author(&mut self, before_new_line: bool, after_new_line: bool) -> io::Result<()> {
        if let Some(author) = self.cmd.get_author() {
            if before_new_line {
                self.none("\n")?;
            }
            self.none(text_wrapper(author, self.term_w))?;
            if after_new_line {
                self.none("\n")?;
            }
        }
        Ok(())
    }

    fn write_version(&mut self) -> io::Result<()> {
        let version = self
            .cmd
            .get_version()
            .or_else(|| self.cmd.get_long_version());
        if let Some(output) = version {
            self.none(text_wrapper(output, self.term_w))?;
        }
        Ok(())
    }
}

/// Methods to write a single subcommand
impl<'help, 'cmd, 'writer> Help<'help, 'cmd, 'writer> {
    fn write_subcommand(
        &mut self,
        sc_str: &str,
        cmd: &Command<'help>,
        next_line_help: bool,
        longest: usize,
    ) -> io::Result<()> {
        debug!("Help::write_subcommand");

        let spec_vals = &self.sc_spec_vals(cmd);

        let about = cmd
            .get_about()
            .or_else(|| cmd.get_long_about())
            .unwrap_or("");

        self.subcmd(sc_str, next_line_help, longest)?;
        self.help(None, about, spec_vals, next_line_help, longest)
    }

    fn sc_spec_vals(&self, a: &Command) -> String {
        debug!("Help::sc_spec_vals: a={}", a.get_name());
        let mut spec_vals = vec![];
        if 0 < a.get_all_aliases().count() || 0 < a.get_all_short_flag_aliases().count() {
            debug!(
                "Help::spec_vals: Found aliases...{:?}",
                a.get_all_aliases().collect::<Vec<_>>()
            );
            debug!(
                "Help::spec_vals: Found short flag aliases...{:?}",
                a.get_all_short_flag_aliases().collect::<Vec<_>>()
            );

            let mut short_als = a
                .get_visible_short_flag_aliases()
                .map(|a| format!("-{}", a))
                .collect::<Vec<_>>();

            let als = a.get_visible_aliases().map(|s| s.to_string());

            short_als.extend(als);

            let all_als = short_als.join(", ");

            if !all_als.is_empty() {
                spec_vals.push(format!(" [aliases: {}]", all_als));
            }
        }
        spec_vals.join(" ")
    }

    fn subcommand_next_line_help(
        &self,
        cmd: &Command<'help>,
        spec_vals: &str,
        longest: usize,
    ) -> bool {
        if self.next_line_help | self.use_long {
            // setting_next_line
            true
        } else {
            // force_next_line
            let h = cmd.get_about().unwrap_or("");
            let h_w = display_width(h) + display_width(spec_vals);
            let taken = longest + 12;
            self.term_w >= taken
                && (taken as f32 / self.term_w as f32) > 0.40
                && h_w > (self.term_w - taken)
        }
    }

    /// Writes subcommand to the wrapped stream.
    fn subcmd(&mut self, sc_str: &str, next_line_help: bool, longest: usize) -> io::Result<()> {
        self.none(TAB)?;
        self.good(sc_str)?;
        if !next_line_help {
            let width = display_width(sc_str);
            self.spaces(width.max(longest + 4) - width)?;
        }
        Ok(())
    }
}

// Methods to write Parser help.
impl<'help, 'cmd, 'writer> Help<'help, 'cmd, 'writer> {
    /// Writes help for all arguments (options, flags, args, subcommands)
    /// including titles of a Parser Object to the wrapped stream.
    pub(crate) fn write_all_args(&mut self) -> io::Result<()> {
        debug!("Help::write_all_args");
        let pos = self
            .cmd
            .get_positionals_with_no_heading()
            .filter(|arg| should_show_arg(self.use_long, arg))
            .collect::<Vec<_>>();
        let non_pos = self
            .cmd
            .get_non_positionals_with_no_heading()
            .filter(|arg| should_show_arg(self.use_long, arg))
            .collect::<Vec<_>>();
        let subcmds = self.cmd.has_visible_subcommands();

        let custom_headings = self
            .cmd
            .get_arguments()
            .filter_map(|arg| arg.get_help_heading())
            .collect::<IndexSet<_>>();

        let mut first = if !pos.is_empty() {
            // Write positional args if any
            self.warning("ARGS:\n")?;
            self.write_args_unsorted(&pos)?;
            false
        } else {
            true
        };

        if !non_pos.is_empty() {
            if !first {
                self.none("\n\n")?;
            }
            self.warning("OPTIONS:\n")?;
            self.write_args(&non_pos, "OPTIONS")?;
            first = false;
        }
        if !custom_headings.is_empty() {
            for heading in custom_headings {
                let args = self
                    .cmd
                    .get_arguments()
                    .filter(|a| {
                        if let Some(help_heading) = a.get_help_heading() {
                            return help_heading == heading;
                        }
                        false
                    })
                    .filter(|arg| should_show_arg(self.use_long, arg))
                    .collect::<Vec<_>>();

                if !args.is_empty() {
                    if !first {
                        self.none("\n\n")?;
                    }
                    self.warning(format!("{}:\n", heading))?;
                    self.write_args(&args, heading)?;
                    first = false
                }
            }
        }

        if subcmds {
            if !first {
                self.none("\n\n")?;
            }

            self.warning(
                self.cmd
                    .get_subcommand_help_heading()
                    .unwrap_or("SUBCOMMANDS"),
            )?;
            self.warning(":\n")?;

            self.write_subcommands(self.cmd)?;
        }

        Ok(())
    }

    /// Will use next line help on writing subcommands.
    fn will_subcommands_wrap<'a>(
        &self,
        subcommands: impl IntoIterator<Item = &'a Command<'help>>,
        longest: usize,
    ) -> bool
    where
        'help: 'a,
    {
        subcommands
            .into_iter()
            .filter(|&subcommand| should_show_subcommand(subcommand))
            .any(|subcommand| {
                let spec_vals = &self.sc_spec_vals(subcommand);
                self.subcommand_next_line_help(subcommand, spec_vals, longest)
            })
    }

    /// Writes help for subcommands of a Parser Object to the wrapped stream.
    fn write_subcommands(&mut self, cmd: &Command<'help>) -> io::Result<()> {
        debug!("Help::write_subcommands");
        // The shortest an arg can legally be is 2 (i.e. '-x')
        let mut longest = 2;
        let mut ord_v = Vec::new();
        for subcommand in cmd
            .get_subcommands()
            .filter(|subcommand| should_show_subcommand(subcommand))
        {
            let mut sc_str = String::new();
            sc_str.push_str(subcommand.get_name());
            if let Some(short) = subcommand.get_short_flag() {
                write!(sc_str, " -{}", short).unwrap();
            }
            if let Some(long) = subcommand.get_long_flag() {
                write!(sc_str, " --{}", long).unwrap();
            }
            longest = longest.max(display_width(&sc_str));
            ord_v.push((subcommand.get_display_order(), sc_str, subcommand));
        }
        ord_v.sort_by(|a, b| (a.0, &a.1).cmp(&(b.0, &b.1)));

        debug!("Help::write_subcommands longest = {}", longest);

        let next_line_help = self.will_subcommands_wrap(cmd.get_subcommands(), longest);

        let mut first = true;
        for (_, sc_str, sc) in &ord_v {
            if first {
                first = false;
            } else {
                self.none("\n")?;
            }
            self.write_subcommand(sc_str, sc, next_line_help, longest)?;
        }
        Ok(())
    }

    /// Writes binary name of a Parser Object to the wrapped stream.
    fn write_display_name(&mut self) -> io::Result<()> {
        debug!("Help::write_display_name");

        let display_name = text_wrapper(
            &self
                .cmd
                .get_display_name()
                .unwrap_or_else(|| self.cmd.get_name())
                .replace("{n}", "\n"),
            self.term_w,
        );
        self.good(&display_name)?;
        Ok(())
    }

    /// Writes binary name of a Parser Object to the wrapped stream.
    fn write_bin_name(&mut self) -> io::Result<()> {
        debug!("Help::write_bin_name");

        let bin_name = if let Some(bn) = self.cmd.get_bin_name() {
            if bn.contains(' ') {
                // In case we're dealing with subcommands i.e. git mv is translated to git-mv
                bn.replace(' ', "-")
            } else {
                text_wrapper(&self.cmd.get_name().replace("{n}", "\n"), self.term_w)
            }
        } else {
            text_wrapper(&self.cmd.get_name().replace("{n}", "\n"), self.term_w)
        };
        self.good(&bin_name)?;
        Ok(())
    }
}

// Methods to write Parser help using templates.
impl<'help, 'cmd, 'writer> Help<'help, 'cmd, 'writer> {
    /// Write help to stream for the parser in the format defined by the template.
    ///
    /// For details about the template language see [`Command::help_template`].
    ///
    /// [`Command::help_template`]: Command::help_template()
    fn write_templated_help(&mut self, template: &str) -> io::Result<()> {
        debug!("Help::write_templated_help");

        // The strategy is to copy the template from the reader to wrapped stream
        // until a tag is found. Depending on its value, the appropriate content is copied
        // to the wrapped stream.
        // The copy from template is then resumed, repeating this sequence until reading
        // the complete template.

        macro_rules! tags {
            (
                match $part:ident {
                    $( $tag:expr => $action:stmt )*
                }
            ) => {
                match $part {
                    $(
                        part if part.starts_with(concat!($tag, "}")) => {
                            $action
                            let rest = &part[$tag.len()+1..];
                            self.none(rest)?;
                        }
                    )*

                    // Unknown tag, write it back.
                    part => {
                        self.none("{")?;
                        self.none(part)?;
                    }
                }
            };
        }

        let mut parts = template.split('{');
        if let Some(first) = parts.next() {
            self.none(first)?;
        }

        for part in parts {
            tags! {
                match part {
                    "name" => {
                        self.write_display_name()?;
                    }
                    "bin" => {
                        self.write_bin_name()?;
                    }
                    "version" => {
                        self.write_version()?;
                    }
                    "author" => {
                        self.write_author(false, false)?;
                    }
                    "author-with-newline" => {
                        self.write_author(false, true)?;
                    }
                    "author-section" => {
                        self.write_author(true, true)?;
                    }
                    "about" => {
                        self.write_about(false, false)?;
                    }
                    "about-with-newline" => {
                        self.write_about(false, true)?;
                    }
                    "about-section" => {
                        self.write_about(true, true)?;
                    }
                    "usage-heading" => {
                        self.warning("USAGE:")?;
                    }
                    "usage" => {
                        self.none(self.usage.create_usage_no_title(&[]))?;
                    }
                    "all-args" => {
                        self.write_all_args()?;
                    }
                    "options" => {
                        // Include even those with a heading as we don't have a good way of
                        // handling help_heading in the template.
                        self.write_args(&self.cmd.get_non_positionals().collect::<Vec<_>>(), "options")?;
                    }
                    "positionals" => {
                        self.write_args(&self.cmd.get_positionals().collect::<Vec<_>>(), "positionals")?;
                    }
                    "subcommands" => {
                        self.write_subcommands(self.cmd)?;
                    }
                    "after-help" => {
                        self.write_after_help()?;
                    }
                    "before-help" => {
                        self.write_before_help()?;
                    }
                }
            }
        }

        Ok(())
    }
}

pub(crate) fn dimensions() -> Option<(usize, usize)> {
    #[cfg(not(feature = "wrap_help"))]
    return None;

    #[cfg(feature = "wrap_help")]
    terminal_size::terminal_size().map(|(w, h)| (w.0.into(), h.0.into()))
}

const TAB: &str = "    ";
const TAB_WIDTH: usize = 4;

pub(crate) enum HelpWriter<'writer> {
    Normal(&'writer mut dyn Write),
    Buffer(&'writer mut Colorizer),
}

fn should_show_arg(use_long: bool, arg: &Arg) -> bool {
    debug!("should_show_arg: use_long={:?}, arg={}", use_long, arg.name);
    if arg.is_hide_set() {
        return false;
    }
    (!arg.is_hide_long_help_set() && use_long)
        || (!arg.is_hide_short_help_set() && !use_long)
        || arg.is_next_line_help_set()
}

fn should_show_subcommand(subcommand: &Command) -> bool {
    !subcommand.is_hide_set()
}

fn text_wrapper(help: &str, width: usize) -> String {
    let wrapper = textwrap::Options::new(width)
        .break_words(false)
        .word_splitter(textwrap::WordSplitter::NoHyphenation);
    help.lines()
        .map(|line| textwrap::fill(line, &wrapper))
        .collect::<Vec<String>>()
        .join("\n")
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn wrap_help_last_word() {
        let help = String::from("foo bar baz");
        assert_eq!(text_wrapper(&help, 5), "foo\nbar\nbaz");
    }

    #[test]
    fn display_width_handles_non_ascii() {
        // Popular Danish tongue-twister, the name of a fruit dessert.
        let text = "rødgrød med fløde";
        assert_eq!(display_width(text), 17);
        // Note that the string width is smaller than the string
        // length. This is due to the precomposed non-ASCII letters:
        assert_eq!(text.len(), 20);
    }

    #[test]
    fn display_width_handles_emojis() {
        let text = "😂";
        // There is a single `char`...
        assert_eq!(text.chars().count(), 1);
        // but it is double-width:
        assert_eq!(display_width(text), 2);
        // This is much less than the byte length:
        assert_eq!(text.len(), 4);
    }
}