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
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131

//! The interface and implementations of LZ77 compression algorithm.
//!
//! LZ77 is a compression algorithm used in [DEFLATE](https://tools.ietf.org/html/rfc1951).
pub use self::default::DefaultLz77Encoder;

mod default;

/// Maximum length of sharable bytes in a pointer.
pub const MAX_LENGTH: u16 = 258;

/// Maximum backward distance of a pointer.
pub const MAX_DISTANCE: u16 = 32_768;

/// Maximum size of a sliding window.
pub const MAX_WINDOW_SIZE: u16 = MAX_DISTANCE;

/// A LZ77 encoded data.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub enum Code {
    /// Literal byte.
    Literal(u8),

    /// Backward pointer to shared data.
    Pointer {
        /// Length of the shared data.
        /// The values must be limited to `MAX_LENGTH`.
        length: u16,

        /// Distance between current position and start position of the shared data.
        /// The values must be limited to `MAX_DISTANCE`.
        backward_distance: u16,
    },
}

/// Compression level.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub enum CompressionLevel {
    /// No compression.
    None,

    /// Best speed.
    Fast,

    /// Balanced between speed and size.
    Balance,

    /// Best compression.
    Best,
}

/// The `Sink` trait represents a consumer of LZ77 encoded data.
pub trait Sink {
    /// Consumes a LZ77 encoded `Code`.
    fn consume(&mut self, code: Code);
}
impl<'a, T> Sink for &'a mut T
where
    T: Sink,
{
    fn consume(&mut self, code: Code) {
        (*self).consume(code);
    }
}

/// The `LZ77Encode` trait defines the interface of LZ77 encoding algorithm.
pub trait Lz77Encode {
    /// Encodes a buffer and writes result LZ77 codes to `sink`.
    fn encode<S>(&mut self, buf: &[u8], sink: S)
    where
        S: Sink;

    /// Flushes the encoder, ensuring that all intermediately buffered codes are consumed by `sink`.
    fn flush<S>(&mut self, sink: S)
    where
        S: Sink;

    /// Returns the compression level of the encoder.
    ///
    /// If the implementation is omitted, `CompressionLevel::Balance` will be returned.
    fn compression_level(&self) -> CompressionLevel {
        CompressionLevel::Balance
    }

    /// Returns the window size of the encoder.
    ///
    /// If the implementation is omitted, `MAX_WINDOW_SIZE` will be returned.
    fn window_size(&self) -> u16 {
        MAX_WINDOW_SIZE
    }
}

/// A no compression implementation of `LZ77Encode` trait.
#[derive(Debug, Default)]
pub struct NoCompressionLz77Encoder;
impl NoCompressionLz77Encoder {
    /// Makes a new encoder instance.
    ///
    /// # Examples
    /// ```
    /// use libflate::deflate;
    /// use libflate::lz77::{Lz77Encode, NoCompressionLz77Encoder, CompressionLevel};
    ///
    /// let lz77 = NoCompressionLz77Encoder::new();
    /// assert_eq!(lz77.compression_level(), CompressionLevel::None);
    ///
    /// let options = deflate::EncodeOptions::with_lz77(lz77);
    /// let _deflate = deflate::Encoder::with_options(Vec::new(), options);
    /// ```
    pub fn new() -> Self {
        NoCompressionLz77Encoder
    }
}
impl Lz77Encode for NoCompressionLz77Encoder {
    fn encode<S>(&mut self, buf: &[u8], mut sink: S)
    where
        S: Sink,
    {
        for c in buf.iter().cloned().map(Code::Literal) {
            sink.consume(c);
        }
    }
    #[allow(unused_variables)]
    fn flush<S>(&mut self, sink: S)
    where
        S: Sink,
    {
    }
    fn compression_level(&self) -> CompressionLevel {
        CompressionLevel::None
    }
}