rivet-transcoder 0.1.4

//! ABR ladder computation — derive a sensible set of [`Rung`]s from a source
//! resolution.
//!
//! Callers who want full control build [`Rung`]s by hand and skip this module
//! entirely. [`standard_ladder`] is the convenience path: it snaps to standard
//! short-side quantizations (2160/1440/1080/720/480/360/240), preserves the
//! source aspect ratio, even-aligns every dimension, and caps the top rung.

use crate::spec::{Quality, Rung};

/// Standard short-side quantizations, descending. The "p" number always refers
/// to the **short** side of the frame regardless of orientation.
const STANDARD_SHORT_SIDES: &[u32] = &[2160, 1440, 1080, 720, 480, 360, 240];

/// Default cap on the short side of any rung. Sources above this have their
/// top rung clamped down (aspect preserved); rungs above it never appear.
pub const DEFAULT_MAX_SHORT_SIDE: u32 = 1080;

/// Smallest allowed dimension on a ladder rung (excluding the source rung).
const MIN_DIMENSION: u32 = 200;

/// Build a standard ladder for a source clip, every rung at default quality.
///
/// Pass `max_short_side = None` for the default cap (1080). Lifting the cap
/// unlocks the corresponding higher rungs (1440 → QHD, 2160 → 4K).
pub fn standard_ladder(src_width: u32, src_height: u32, max_short_side: Option<u32>) -> Vec<Rung> {
    dims_for(src_width, src_height, max_short_side)
        .into_iter()
        .map(|(w, h)| Rung::new(w, h))
        .collect()
}

/// Same as [`standard_ladder`] but stamps every rung with `quality`.
pub fn standard_ladder_with_quality(
    src_width: u32,
    src_height: u32,
    max_short_side: Option<u32>,
    quality: Quality,
) -> Vec<Rung> {
    dims_for(src_width, src_height, max_short_side)
        .into_iter()
        .map(|(w, h)| Rung::new(w, h).with_quality(quality.clone()))
        .collect()
}

/// Core algorithm: source-aspect-preserving, even-aligned, capped rung dims.
fn dims_for(src_width: u32, src_height: u32, max_short_side: Option<u32>) -> Vec<(u32, u32)> {
    let cap = max_short_side.unwrap_or(DEFAULT_MAX_SHORT_SIDE);
    if src_width == 0 || src_height == 0 {
        return Vec::new();
    }

    let is_landscape = src_width >= src_height;
    let src_short = src_width.min(src_height);
    let src_long = src_width.max(src_height);
    let src_aspect = src_long as f64 / src_short as f64;

    // Source rung — clamp the short side to `cap`, scale the long side
    // proportionally, even-align both axes.
    let (top_short, top_long) = if src_short > cap {
        let s = cap;
        let l = ((s as f64 * src_aspect).round() as u32) & !1;
        (s & !1, l)
    } else {
        (src_short & !1, src_long & !1)
    };
    let (top_w, top_h) = if is_landscape {
        (top_long, top_short)
    } else {
        (top_short, top_long)
    };

    let mut out: Vec<(u32, u32)> = vec![(top_w, top_h)];

    for &short in STANDARD_SHORT_SIDES {
        if short >= top_short || short > cap {
            continue;
        }
        let long = ((short as f64 * src_aspect).round() as u32) & !1;
        let short_even = short & !1;
        if short_even < MIN_DIMENSION || long < MIN_DIMENSION {
            continue;
        }
        let (w, h) = if is_landscape {
            (long, short_even)
        } else {
            (short_even, long)
        };
        if !out.iter().any(|&(pw, ph)| pw == w && ph == h) {
            out.push((w, h));
        }
    }

    out
}

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

    fn dims(rungs: &[Rung]) -> Vec<(u32, u32)> {
        rungs.iter().map(|r| (r.width, r.height)).collect()
    }

    #[test]
    fn ladder_16_9_1080p_source() {
        let v = standard_ladder(1920, 1080, None);
        assert_eq!(
            dims(&v),
            vec![(1920, 1080), (1280, 720), (852, 480), (640, 360), (426, 240)]
        );
    }

    #[test]
    fn ladder_4k_clamps_to_1080p_by_default() {
        let v = standard_ladder(3840, 2160, None);
        assert_eq!(v.first().map(|r| (r.width, r.height)), Some((1920, 1080)));
    }

    #[test]
    fn ladder_4k_with_2160_cap_keeps_full_quality() {
        let v = standard_ladder(3840, 2160, Some(2160));
        assert_eq!(v.first().map(|r| (r.width, r.height)), Some((3840, 2160)));
        assert_eq!(v.len(), 7);
    }

    #[test]
    fn ladder_portrait_short_side_labels() {
        let v = standard_ladder(1080, 1920, None);
        assert_eq!(dims(&v), vec![(1080, 1920), (720, 1280), (480, 852), (360, 640), (240, 426)]);
        assert_eq!(v[0].label, "1080p");
        assert_eq!(v[1].label, "720p");
    }

    #[test]
    fn ladder_below_floor_keeps_only_source() {
        assert_eq!(dims(&standard_ladder(320, 240, None)), vec![(320, 240)]);
    }

    #[test]
    fn ladder_zero_dims_empty() {
        assert!(standard_ladder(0, 1080, None).is_empty());
    }

    #[test]
    fn every_rung_is_even() {
        for r in standard_ladder(1921, 1081, None) {
            assert_eq!(r.width % 2, 0);
            assert_eq!(r.height % 2, 0);
        }
    }
}