// Copyright (c) 2020 Google LLC All rights reserved.

// Use of this source code is governed by a BSD-style

// license that can be found in the LICENSE file.

//! Shared functionality between argh_derive and the argh runtime.

//!

//! This library is intended only for internal use by these two crates.

/// Information about a particular command used for output.

pub struct CommandInfo<'a> {

    /// The name of the command.

    pub name: &'a str,

    /// A short description of the command's functionality.

    pub description: &'a str,

}

pub const INDENT: &str = "  ";

const DESCRIPTION_INDENT: usize = 20;

const WRAP_WIDTH: usize = 80;

/// Write command names and descriptions to an output string.

pub fn write_description(out: &mut String, cmd: &CommandInfo<'_>) {

    let mut current_line = INDENT.to_string();

    current_line.push_str(cmd.name);

    if cmd.description.is_empty() {

        new_line(&mut current_line, out);

        return;

    }

    if !indent_description(&mut current_line) {

        // Start the description on a new line if the flag names already

        // add up to more than DESCRIPTION_INDENT.

        new_line(&mut current_line, out);

    }

    let mut words = cmd.description.split(' ').peekable();

    while let Some(first_word) = words.next() {

        indent_description(&mut current_line);

        current_line.push_str(first_word);

        'inner: while let Some(&word) = words.peek() {

            if (char_len(&current_line) + char_len(word) + 1) > WRAP_WIDTH {

                new_line(&mut current_line, out);

                break 'inner;

            } else {

                // advance the iterator

                let _ = words.next();

                current_line.push(' ');

                current_line.push_str(word);

            }

        }

    }

    new_line(&mut current_line, out);

}

// Indent the current line in to DESCRIPTION_INDENT chars.

// Returns a boolean indicating whether or not spacing was added.

fn indent_description(line: &mut String) -> bool {

    let cur_len = char_len(line);

    if cur_len < DESCRIPTION_INDENT {

        let num_spaces = DESCRIPTION_INDENT - cur_len;

        line.extend(std::iter::repeat(' ').take(num_spaces));

        true

    } else {

        false

    }

}

fn char_len(s: &str) -> usize {

    s.chars().count()

}

// Append a newline and the current line to the output,

// clearing the current line.

fn new_line(current_line: &mut String, out: &mut String) {

    out.push('\n');

    out.push_str(current_line);

    current_line.truncate(0);

}