1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112

use std::fmt;
use std::iter;

pub trait Formatter: fmt::Write {
    /// Forcibly create a new line.
    fn new_line(&mut self) -> fmt::Result;

    /// Create a new line unless the current line is empty.
    fn new_line_unless_empty(&mut self) -> fmt::Result;

    /// Indent the formatter.
    fn indent(&mut self);

    /// Unindent the formatter.
    fn unindent(&mut self);
}

/// Formatter implementation for write types.
pub struct WriteFormatter<'write, W>
where
    W: fmt::Write + 'write,
{
    write: &'write mut W,
    /// if last line was empty.
    last_line_empty: bool,
    /// Current indentation level.
    indent: usize,
    /// Holds the current indentation level as a string.
    indent_buffer: String,
}

impl<'write, W> WriteFormatter<'write, W>
where
    W: fmt::Write,
{
    /// Create a new write formatter.
    pub fn new(write: &mut W) -> WriteFormatter<W> {
        WriteFormatter {
            write: write,
            last_line_empty: true,
            indent: 0usize,
            indent_buffer: String::from("  "),
        }
    }

    fn check_indent(&mut self) -> fmt::Result {
        if self.last_line_empty {
            self.write.write_str(
                &self.indent_buffer[0..self.indent * 2],
            )?;
        }

        self.last_line_empty = false;
        Ok(())
    }
}

impl<'write, W> fmt::Write for WriteFormatter<'write, W>
where
    W: fmt::Write,
{
    fn write_str(&mut self, s: &str) -> fmt::Result {
        self.check_indent()?;
        self.write.write_str(s)
    }

    fn write_char(&mut self, c: char) -> fmt::Result {
        self.check_indent()?;
        self.write.write_char(c)
    }

    fn write_fmt(&mut self, args: fmt::Arguments) -> fmt::Result {
        self.check_indent()?;
        self.write.write_fmt(args)
    }
}

impl<'write, W> Formatter for WriteFormatter<'write, W>
where
    W: fmt::Write,
{
    fn new_line(&mut self) -> fmt::Result {
        self.write.write_char('\n')?;
        self.last_line_empty = true;
        Ok(())
    }

    fn new_line_unless_empty(&mut self) -> fmt::Result {
        if !self.last_line_empty {
            self.write.write_char('\n')?;
            self.last_line_empty = true;
        }

        Ok(())
    }

    fn indent(&mut self) {
        self.indent += 1;

        // check that buffer contains the current indentation.
        if self.indent_buffer.len() < self.indent * 2 {
            // double the buffer
            for c in iter::repeat(' ').take(self.indent_buffer.len()) {
                self.indent_buffer.push(c);
            }
        }
    }

    fn unindent(&mut self) {
        self.indent = self.indent.saturating_sub(1);
    }
}