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

use crate::alphabets;
use crate::core::{calculate_confidence, Info, InternalQuery};
use crate::trigrams;
use crate::Lang;

#[derive(Debug)]
pub struct RawOutcome {
    pub scores: Vec<(Lang, f64)>,
    pub alphabet_raw_outcome: alphabets::RawOutcome,
    pub trigram_raw_outcome: trigrams::RawOutcome,
}

pub fn detect(iquery: &InternalQuery) -> Option<Info> {
    let raw_outcome = raw_detect(iquery);

    let count = raw_outcome.trigram_raw_outcome.trigrams_count;
    let mut normalized_scores_iter = raw_outcome.scores.into_iter();

    let opt_lang_score1 = normalized_scores_iter.next();
    let opt_lang_score2 = normalized_scores_iter.next();

    // TODO: Logic is duplicated in alphabets and trigrams. Consider refactoring
    opt_lang_score1.map(|(lang1, score1)| {
        let script = iquery.multi_lang_script.to_script();
        let confidence = if let Some((_, score2)) = opt_lang_score2 {
            calculate_confidence(score1, score2, count)
        } else {
            1.0
        };
        Info::new(script, lang1, confidence)
    })
}

// TODO: optimize!
pub fn raw_detect(iquery: &InternalQuery) -> RawOutcome {
    let alphabet_raw_outcome = alphabets::raw_detect(iquery);
    let trigram_raw_outcome = trigrams::raw_detect(iquery);

    let alphabet_scores = &alphabet_raw_outcome.scores;
    let trigram_scores = &trigram_raw_outcome.scores;

    let mut all_langs: Vec<Lang> = alphabet_scores.iter().map(|x| x.0).collect();
    trigram_scores.iter().for_each(|(lang, _)| {
        if !all_langs.contains(lang) {
            all_langs.push(*lang);
        }
    });

    let count = alphabet_raw_outcome.count;

    let alphabet_weight = calc_alphabet_weight(count);
    let trigram_weight = 1.0 - alphabet_weight;

    let mut scores = vec![];

    for lang in all_langs {
        let a: f64 = alphabet_scores
            .iter()
            .find(|(l, _)| l == &lang)
            .map(|x| x.1)
            .unwrap_or(0.0);
        let t: f64 = trigram_scores
            .iter()
            .find(|(l, _)| l == &lang)
            .map(|x| x.1)
            .unwrap_or(0.0);

        debug_assert!(a >= 0.0);
        debug_assert!(a <= 1.0);
        debug_assert!(t >= 0.0);
        debug_assert!(t <= 1.0);

        let score = a * alphabet_weight + t * trigram_weight;

        debug_assert!(score >= 0.0);
        debug_assert!(score <= 1.0);

        scores.push((lang, score));
    }

    scores.sort_unstable_by(|a, b| b.1.partial_cmp(&a.1).unwrap_or(std::cmp::Ordering::Less));

    RawOutcome {
        scores,
        alphabet_raw_outcome,
        trigram_raw_outcome,
    }
}

// Function that calculates weight of alphabet score depending on number of characters in the given
// text. The longer text the less significant alphabet weight is (and the more significant is
// trigram weight).
//
// y = -(x/300) + 2/3
// where:
//   x - number of characters
//   y = alphabet weight
//
//
//          alphabet weight
//          ^
//          |
//     2/3 -* (0; 2/3)
//          | \_
//          |   \_
//          |     \_
//          |       \_
//          |         \  (100; 1/3)
//     1/3 -|          *------------
//          |
//          +----------|------------> count
//         0          100
//
fn calc_alphabet_weight(count: usize) -> f64 {
    let weight = -(count as f64 / 300.0) + 2.0 / 3.0;
    weight.clamp(1.0 / 3.0, 2.0 / 3.0)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_calc_alphabet_weight() {
        assert_eq!(calc_alphabet_weight(0), 2.0 / 3.0);
        assert_eq!(calc_alphabet_weight(50), 0.5);
        assert_eq!(calc_alphabet_weight(100), 1.0 / 3.0);
        assert_eq!(calc_alphabet_weight(200), 1.0 / 3.0);
    }
}