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// Copyright 2014-2016 Johannes Köster, Martin Larralde.
// Licensed under the MIT license (http://opensource.org/licenses/MIT)
// This file may not be copied, modified, or distributed
// except according to those terms.

//! GC counter over an `IntoTextIterator` object.

//! Complexity: o(n)

use utils::IntoTextIterator;

/// Base gc content counter
fn gcn_content<'a, I: IntoTextIterator<'a>>(sequence: I, step: usize) -> f32 {
    let mut l = 0f32;
    let mut count = 0.0;
    for (i, &n) in sequence.into_iter().enumerate() {
        if i % step == 0 {
            count += match n {
                b'c' | b'g' | b'G' | b'C' => 1f32, // G or C
                _ => 0f32,
            };
        }
        l = i as f32;
    }
    count / (l + 1f32)
}

/// gc content counter for every nucleotide
pub fn gc_content<'a, I: IntoTextIterator<'a>>(sequence: I) -> f32 {
    gcn_content(sequence, 1usize)
}

/// gc content counter for the nucleotide in 3rd position
pub fn gc3_content<'a, I: IntoTextIterator<'a>>(sequence: I) -> f32 {
    gcn_content(sequence, 3usize)
}