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
132
133
134
135
136

use crate::util::{read_u32le, read_u8};
use crate::RpnExpr;
use std::convert::TryInto;
use std::fmt::{self, Display, Formatter};
use std::io::{self, Read};

/// A section patch.
/// Patches are bytes (or groups of bytes) whose computation was deferred to the linker.
#[derive(Debug)]
pub struct Patch {
    source_file_id: u32,
    line_no: u32,
    offset: u32,
    pc_section_id: u32,
    pc_offset: u32,
    patch_type: PatchType,
    expr: RpnExpr,
}
impl Patch {
    pub(crate) fn read_from(mut input: impl Read) -> Result<Self, io::Error> {
        let source_file_id = read_u32le(&mut input)?;
        let line_no = read_u32le(&mut input)?;
        let offset = read_u32le(&mut input)?;
        let pc_section_id = read_u32le(&mut input)?;
        let pc_offset = read_u32le(&mut input)?;
        let patch_type = PatchType::try_from(read_u8(&mut input)?)?;

        let expr_size = read_u32le(&mut input)?.try_into().unwrap();
        let mut expr = vec![0; expr_size];
        input.read_exact(&mut expr)?;
        let expr = RpnExpr::from_bytes(expr);

        Ok(Self {
            source_file_id,
            line_no,
            offset,
            pc_section_id,
            pc_offset,
            patch_type,
            expr,
        })
    }

    /// Where the patch was defined.
    /// That is, the [file stack node][crate::Node] ID, and the line number.
    pub fn source(&self) -> (u32, u32) {
        (self.source_file_id, self.line_no)
    }

    /// The offset within the [section][crate::Section]'s data where the patch will be written.
    pub fn offset(&self) -> u32 {
        self.offset
    }

    /// The patch's type, which notably determines its size.
    pub fn patch_type(&self) -> PatchType {
        self.patch_type
    }

    /// The ID of the expression's PC section. See [`pc_offset`][Self::pc_offset] for more info.
    pub fn pc_section_id(&self) -> u32 {
        self.pc_section_id
    }

    /// The expression's PC offset.
    ///
    /// This is separate from the [offset][Self::offset], because PC (`@`) may not point to the
    /// byte being written, and, in the case of [`LOAD` blocks], may be in a different section
    /// entirely!
    ///
    /// [`LOAD` blocks]: https://rgbds.gbdev.io/docs/v0.5.1/rgbasm.5.html#RAM_Code
    pub fn pc_offset(&self) -> u32 {
        self.pc_offset
    }

    /// The patch's RPN expression.
    pub fn expr(&self) -> &RpnExpr {
        &self.expr
    }
}

/// A patch's type.
#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub enum PatchType {
    Byte,
    Word,
    Long,
    JrOfs,
}
impl PatchType {
    fn try_from(byte: u8) -> Result<Self, io::Error> {
        use PatchType::*;

        Ok(match byte {
            0 => Byte,
            1 => Word,
            2 => Long,
            3 => JrOfs,
            _ => {
                return Err(io::Error::new(
                    io::ErrorKind::InvalidData,
                    "Invalid patch type",
                ))
            }
        })
    }

    /// The patch type's name.
    pub fn name(&self) -> &'static str {
        use PatchType::*;

        match self {
            Byte => "byte",
            Word => "word",
            Long => "long",
            JrOfs => "jr",
        }
    }

    /// How many bytes this patch type modifies.
    pub fn size(&self) -> u8 {
        use PatchType::*;

        match self {
            Byte => 1,
            Word => 2,
            Long => 4,
            JrOfs => 1,
        }
    }
}
impl Display for PatchType {
    fn fmt(&self, fmt: &mut Formatter) -> Result<(), fmt::Error> {
        write!(fmt, "{}", self.name())
    }
}