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
use crate::parser::{FromData, FromSlice, LazyArray16, LazyOffsetArray16, Stream};
use super::{ClassDefinition, Coverage, LookupIndex};

/// A [Contextual Lookup Subtable](
/// https://docs.microsoft.com/en-us/typography/opentype/spec/chapter2#seqctxt1).
#[allow(missing_docs)]
#[derive(Clone, Copy, Debug)]
pub enum ContextLookup<'a> {
    /// Simple glyph contexts.
    Format1 {
        coverage: Coverage<'a>,
        sets: SequenceRuleSets<'a>,
    },
    /// Class-based glyph contexts.
    Format2 {
        coverage: Coverage<'a>,
        classes: ClassDefinition<'a>,
        sets: SequenceRuleSets<'a>,
    },
    /// Coverage-based glyph contexts.
    Format3 {
        coverage: Coverage<'a>,
        coverages: LazyOffsetArray16<'a, Coverage<'a>>,
        lookups: LazyArray16<'a, SequenceLookupRecord>,
    },
}

impl<'a> ContextLookup<'a> {
    pub(crate) fn parse(data: &'a [u8]) -> Option<Self> {
        let mut s = Stream::new(data);
        match s.read::<u16>()? {
            1 => {
                let coverage = Coverage::parse(s.read_at_offset16(data)?)?;
                let count = s.read::<u16>()?;
                let offsets = s.read_array16(count)?;
                Some(Self::Format1 {
                    coverage,
                    sets: SequenceRuleSets::new(data, offsets),
                })
            }
            2 => {
                let coverage = Coverage::parse(s.read_at_offset16(data)?)?;
                let classes = ClassDefinition::parse(s.read_at_offset16(data)?)?;
                let count = s.read::<u16>()?;
                let offsets = s.read_array16(count)?;
                Some(Self::Format2 {
                    coverage,
                    classes,
                    sets: SequenceRuleSets::new(data, offsets),
                })
            }
            3 => {
                let input_count = s.read::<u16>()?;
                let lookup_count = s.read::<u16>()?;
                let coverage = Coverage::parse(s.read_at_offset16(data)?)?;
                let coverages = s.read_array16(input_count.checked_sub(1)?)?;
                let lookups = s.read_array16(lookup_count)?;
                Some(Self::Format3 {
                    coverage,
                    coverages: LazyOffsetArray16::new(data, coverages),
                    lookups,
                })
            }
            _ => None,
        }
    }

    /// Returns the subtable coverage.
    #[inline]
    pub fn coverage(&self) -> Coverage<'a> {
        match self {
            Self::Format1 { coverage, .. } => *coverage,
            Self::Format2 { coverage, .. } => *coverage,
            Self::Format3 { coverage, .. } => *coverage,
        }
    }
}

/// A list of [`SequenceRuleSet`]s.
pub type SequenceRuleSets<'a> = LazyOffsetArray16<'a, SequenceRuleSet<'a>>;

impl<'a> FromSlice<'a> for SequenceRuleSet<'a> {
    fn parse(data: &'a [u8]) -> Option<Self> {
        Self::parse(data)
    }
}

impl<'a> FromSlice<'a> for SequenceRule<'a> {
    fn parse(data: &'a [u8]) -> Option<Self> {
        let mut s = Stream::new(data);
        let input_count = s.read::<u16>()?;
        let lookup_count = s.read::<u16>()?;
        let input = s.read_array16(input_count.checked_sub(1)?)?;
        let lookups = s.read_array16(lookup_count)?;
        Some(Self { input, lookups })
    }
}

/// A set of [`SequenceRule`]s.
pub type SequenceRuleSet<'a> = LazyOffsetArray16<'a, SequenceRule<'a>>;

/// A sequence rule.
#[allow(missing_docs)]
#[derive(Clone, Copy, Debug)]
pub struct SequenceRule<'a> {
    pub input: LazyArray16<'a, u16>,
    pub lookups: LazyArray16<'a, SequenceLookupRecord>,
}

/// A sequence rule record.
#[allow(missing_docs)]
#[derive(Clone, Copy, Debug)]
pub struct SequenceLookupRecord {
    pub sequence_index: u16,
    pub lookup_list_index: LookupIndex,
}

impl FromData for SequenceLookupRecord {
    const SIZE: usize = 4;

    #[inline]
    fn parse(data: &[u8]) -> Option<Self> {
        let mut s = Stream::new(data);
        Some(Self {
            sequence_index: s.read::<u16>()?,
            lookup_list_index: s.read::<LookupIndex>()?,
        })
    }
}