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use std::cmp::max;
use crate::interest::{Interest, InterestVector};
/// Calculate score for a piece of categorized content based on a user interest vector.
///
/// This scoring function is of the following properties:
/// - The score ranges from 0.0 to 1.0
/// - The score is monotonically increasing for the accumulated interest count
///
/// Params:
/// - `interest_vector`: a user interest vector that can be fetched via
/// `RelevancyStore::user_interest_vector()`.
/// - `content_categories`: a list of categories (interests) of the give content.
/// Return:
// - A score ranges in [0, 1].
#[uniffi::export]
pub fn score(interest_vector: InterestVector, content_categories: Vec<Interest>) -> f64 {
let n = content_categories
.iter()
.fold(0, |acc, &category| acc + interest_vector[category]);
// Apply base 10 logarithm to the accumulated count so its hyperbolic tangent is more
// evenly distributed in [0, 1]. Note that `max(n, 1)` is used to avoid negative scores.
(max(n, 1) as f64).log10().tanh()
}
#[cfg(test)]
mod test {
use crate::interest::{Interest, InterestVector};
use super::*;
const EPSILON: f64 = 1e-10;
const SUBEPSILON: f64 = 1e-6;
#[test]
fn test_score_lower_bound() {
// Empty interest vector yields score 0.
let s = score(InterestVector::default(), vec![Interest::Food]);
let delta = (s - 0_f64).abs();
assert!(delta < EPSILON);
// No overlap also yields score 0.
let s = score(
InterestVector {
animals: 10,
..InterestVector::default()
},
vec![Interest::Food],
);
let delta = (s - 0_f64).abs();
assert!(delta < EPSILON);
}
#[test]
fn test_score_upper_bound() {
let score = score(
InterestVector {
animals: 1_000_000_000,
..InterestVector::default()
},
vec![Interest::Animals],
);
let delta = (score - 1.0_f64).abs();
// Can get very close to the upper bound 1.0 but not over.
assert!(delta < SUBEPSILON);
}
#[test]
fn test_score_monotonic() {
let l = score(
InterestVector {
animals: 1,
..InterestVector::default()
},
vec![Interest::Animals],
);
let r = score(
InterestVector {
animals: 5,
..InterestVector::default()
},
vec![Interest::Animals],
);
assert!(l < r);
}
#[test]
fn test_score_multi_categories() {
let l = score(
InterestVector {
animals: 100,
food: 100,
..InterestVector::default()
},
vec![Interest::Animals, Interest::Food],
);
let r = score(
InterestVector {
animals: 200,
..InterestVector::default()
},
vec![Interest::Animals],
);
let delta = (l - r).abs();
assert!(delta < EPSILON);
}
}