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
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168

#![warn(clippy::cargo, clippy::nursery, clippy::pedantic)]

//! A Rust library that allows a user to extract an arbitrary number of lines of "front-matter" from the start of any
//! multiline string.
//!
//! Note that absolutely no parsing of extracted front-matter is performed; this is designed to output its results for
//! another library to then parse.
//!
//! See [`Extractor`] for how to use this library.
pub mod config;

mod extraction;
mod modification;

use crate::config::{Modifier, Splitter};
use crate::extraction::{extract_by_delimiter_line, extract_by_line_index, extract_by_line_prefix};
use crate::modification::{strip_first_line, strip_last_line, strip_prefix, trim_whitespace};
use std::borrow::Cow;

/// Holds configuration for how front-matter and data should be extracted from a string.
///
/// 1. Instantiate using [`Extractor::new()`] with the desired [`Splitter`]
/// 2. (Optional) Call [`.with_modifier()`] with a desired [`Modifier`]; repeat as necessary
/// 3. Call [`.extract()`] with a string to get back a tuple of front-matter and data
///
/// [`.with_modifier()`]: Self::with_modifier
/// [`.extract()`]: Self::extract
///
/// # Usage
///
/// ## Example 1 (Markdown with TOML)
///
/// Input:
///
/// ```md
/// [meta]
/// field_one = 10
/// field_two = [2, 4]
/// +++
///
/// ## Markdown example
///
/// This is an example markdown document that contains the following TOML front-matter:
///
///     [meta]
///     field_one = 10
///     field_two = [2, 4]
/// ```
///
/// Code:
///
/// ```rust
/// # use extract_frontmatter::config::Splitter;
/// # use extract_frontmatter::Extractor;
/// # let input = include_str!("../resources/examples/example1.md");
/// let (front_matter, data) = Extractor::new(Splitter::DelimiterLine(String::from("+++")))
///     .extract(input);
/// # assert_eq!(front_matter.trim(), include_str!("../resources/examples/example1-meta.toml").trim());
/// # assert_eq!(data.trim(), include_str!("../resources/examples/example1-data.md").trim());
/// ```
///
/// Front-matter output:
///
/// ```toml
/// [meta]
/// field_one = 10
/// field_two = [2, 4]
/// ```
///
/// Data output:
///
/// ```md
/// ## Markdown example
///
/// This is an example markdown document that contains the following TOML front-matter:
///
///     [meta]
///     field_one = 10
///     field_two = [2, 4]
/// ```
///
/// ## Example 2 (SQL with YAML)
///
/// Input:
///
/// ```sql
/// -- meta:
/// --   field_one: 10
/// --   field_two:
/// --     - 2
/// --     - 4
/// SELECT version();
/// ```
///
/// Code:
///
/// ```rust
/// # use extract_frontmatter::config::{Modifier, Splitter};
/// # use extract_frontmatter::Extractor;
/// # let input = include_str!("../resources/examples/example2.sql");
/// let (front_matter, data) = Extractor::new(Splitter::LinePrefix(String::from("-- ")))
///     .with_modifier(Modifier::StripPrefix(String::from("-- ")))
///     .extract(input);
/// # assert_eq!(front_matter.trim(), include_str!("../resources/examples/example2-meta.yml").trim());
/// # assert_eq!(data.trim(), include_str!("../resources/examples/example2-data.sql").trim());
/// ```
///
/// Front-matter output:
///
/// ```yaml
/// meta:
///   field_one: 10
///   field_two:
///     - 2
///     - 4
/// ```
///
/// Data output:
///
/// ```sql
/// SELECT version();
/// ```
#[derive(Debug)]
pub struct Extractor {
    splitter: Splitter,
    modifiers: Vec<Modifier>,
}

impl Extractor {
    /// Instantiate a new [`Extractor`] config.
    #[must_use]
    pub const fn new(splitter: Splitter) -> Self {
        Self { splitter, modifiers: Vec::new() }
    }

    /// Add a modifier to the front-matter returned by [`.extract()`](Self::extract).
    pub fn with_modifier(&mut self, modifier: Modifier) -> &mut Self {
        self.modifiers.push(modifier);

        self
    }

    /// Split the given input string into a tuple of front-matter and data, applying any modifiers specified with
    /// [`.with_modifier()`].
    ///
    /// [`.with_modifier()`]:Self::with_modifier
    #[must_use]
    pub fn extract<'input>(&self, input: &'input str) -> (Cow<'input, str>, &'input str) {
        let (meta, data) = match self.splitter {
            Splitter::LineIndex(index) => extract_by_line_index(input, index),
            Splitter::DelimiterLine(ref delim) => extract_by_delimiter_line(input, delim),
            Splitter::LinePrefix(ref prefix) => extract_by_line_prefix(input, prefix),
        };

        let mut meta = Cow::from(meta);

        for modifier in &self.modifiers {
            meta = Cow::from(match modifier {
                Modifier::StripPrefix(prefix) => strip_prefix(&meta, prefix),
                Modifier::TrimWhitespace => trim_whitespace(&meta),
                Modifier::StripFirstLine => strip_first_line(&meta),
                Modifier::StripLastLine => strip_last_line(&meta),
            });
        }

        (meta, data)
    }
}