//! Layer render cache.
//!
//! The processed pixels of a layer (source → masks → effects, in layer space) depend only on the
//! layer's own non-transform properties, its source item and the render options — not on its
//! transform, opacity, blend mode or anything below it. [`LayerCache`] keeps those buffers keyed
//! by a content hash of exactly those inputs, *evaluated at the frame time*, so:
//!
//! * a static layer (or one whose only animation is in Transform) renders once and is reused on
//!   every frame while scrubbing or playing;
//! * editing one layer re-renders only that layer — every other layer's cached pixels stay valid
//!   because their keys do not change;
//! * any change to a property value, keyframe, expression result, effect, mask, switch or source
//!   item changes the key, so stale pixels are never returned.
//!
//! Layers whose pixels depend on time in ways the property values do not capture (time-based
//! effects such as Noise or Wave Warp, Wiggle Paths, footage, precomps) either fold the layer
//! time into the key or are not cached.

use std::collections::HashMap;
use std::hash::{Hash, Hasher};
use std::sync::{Arc, Mutex};

use effectcraft_effects::Buf;
use effectcraft_project::{ItemKind, Layer, LayerSource, Node, PropGroup};

use crate::eval::EvalCtx;

/// Thread-safe, memory-budgeted cache of processed layer buffers.
pub struct LayerCache {
    inner: Mutex<Inner>,
}

struct Entry {
    buf: Arc<Buf>,
    bytes: usize,
    last_use: u64,
}

struct Inner {
    map: HashMap<u64, Entry>,
    bytes: usize,
    budget: usize,
    clock: u64,
    hits: u64,
    misses: u64,
}

/// Hit/miss counters and memory use (for perf readouts and tests).
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct CacheStats {
    pub entries: usize,
    pub bytes: usize,
    pub hits: u64,
    pub misses: u64,
}

impl Default for LayerCache {
    fn default() -> Self {
        LayerCache::new(1 << 30)
    }
}

impl LayerCache {
    /// A cache holding at most `budget` bytes of pixels.
    pub fn new(budget: usize) -> LayerCache {
        LayerCache { inner: Mutex::new(Inner { map: HashMap::new(), bytes: 0, budget, clock: 0, hits: 0, misses: 0 }) }
    }

    pub fn get(&self, key: u64) -> Option<Arc<Buf>> {
        let mut g = self.inner.lock().ok()?;
        g.clock += 1;
        let now = g.clock;
        match g.map.get_mut(&key) {
            Some(e) => {
                e.last_use = now;
                let b = e.buf.clone();
                g.hits += 1;
                Some(b)
            }
            None => {
                g.misses += 1;
                None
            }
        }
    }

    pub fn insert(&self, key: u64, buf: Arc<Buf>) {
        let bytes = buf.img.data.len() * std::mem::size_of::<effectcraft_raster::Px>();
        let Ok(mut g) = self.inner.lock() else { return };
        if bytes > g.budget / 4 {
            return;
        }
        g.clock += 1;
        let now = g.clock;
        if let Some(old) = g.map.insert(key, Entry { buf, bytes, last_use: now }) {
            g.bytes -= old.bytes;
        }
        g.bytes += bytes;
        if g.bytes > g.budget {
            // Evict least-recently used entries down to 3/4 of the budget.
            let target = g.budget / 4 * 3;
            let mut by_age: Vec<(u64, u64)> = g.map.iter().map(|(k, e)| (e.last_use, *k)).collect();
            by_age.sort_unstable();
            for (_, k) in by_age {
                if g.bytes <= target {
                    break;
                }
                if let Some(e) = g.map.remove(&k) {
                    g.bytes -= e.bytes;
                }
            }
        }
    }

    pub fn clear(&self) {
        if let Ok(mut g) = self.inner.lock() {
            g.map.clear();
            g.bytes = 0;
        }
    }

    pub fn stats(&self) -> CacheStats {
        self.inner.lock().map(|g| CacheStats { entries: g.map.len(), bytes: g.bytes, hits: g.hits, misses: g.misses }).unwrap_or_default()
    }
}

/// FNV-1a style 64-bit hasher fed by `Debug` output (exact float formatting) and raw values.
struct KeyHasher(u64);

impl Hasher for KeyHasher {
    fn finish(&self) -> u64 {
        self.0
    }
    fn write(&mut self, bytes: &[u8]) {
        for &b in bytes {
            self.0 ^= b as u64;
            self.0 = self.0.wrapping_mul(0x0100_0000_01b3);
        }
    }
}

impl std::fmt::Write for KeyHasher {
    fn write_str(&mut self, s: &str) -> std::fmt::Result {
        Hasher::write(self, s.as_bytes());
        Ok(())
    }
}

fn hash_debug(h: &mut KeyHasher, v: &impl std::fmt::Debug) {
    use std::fmt::Write;
    let _ = write!(h, "{v:?}");
    Hasher::write_u8(h, 0xff);
}

/// Time-based layer content: does any part of the source/effects read the clock directly
/// (rather than through property values)?
fn time_dependent(layer: &Layer) -> bool {
    if layer.switches.effects
        && let Some(fx) = layer.effects()
    {
        for g in fx.groups() {
            if let effectcraft_project::GroupKind::Effect { effect } = &g.kind
                && g.enabled
                && effectcraft_effects::is_time_dependent(effect)
            {
                return true;
            }
        }
    }
    if matches!(layer.source, LayerSource::Shape)
        && let Some(c) = layer.props.sub("contents")
    {
        return group_has(c, "wiggle");
    }
    false
}

fn group_has(g: &PropGroup, match_id: &str) -> bool {
    g.children.iter().any(|c| match c {
        Node::Group(sub) => sub.match_id == match_id || group_has(sub, match_id),
        Node::Prop(_) => false,
    })
}

/// Feed every property of `g` that can change over time (keyframes or expression) as its value
/// at the context time. The static structure is hashed separately.
fn hash_values(h: &mut KeyHasher, ctx: &EvalCtx, layer: &Layer, g: &PropGroup) {
    for c in &g.children {
        match c {
            Node::Prop(p) => {
                if !p.keys.is_empty() || p.has_expression() {
                    p.uid.hash(h);
                    hash_debug(h, &ctx.value(layer, p));
                }
            }
            Node::Group(sub) => hash_values(h, ctx, layer, sub),
        }
    }
}

/// Cache key for the processed (source → masks → effects) buffer of `layer` at the context
/// time, or `None` when the layer must not be cached (footage, precomps, cameras, adjustment
/// layers…).
pub fn layer_key(ctx: &EvalCtx, layer: &Layer, scale: f64, draft: bool) -> Option<u64> {
    if layer.switches.adjustment {
        return None;
    }
    let mut h = KeyHasher(0xcbf2_9ce4_8422_2325);
    match &layer.source {
        LayerSource::Solid { item } => {
            let it = ctx.project.item(*item)?;
            let ItemKind::Solid(s) = &it.kind else { return None };
            hash_debug(&mut h, s);
        }
        LayerSource::Text | LayerSource::Shape => {}
        _ => return None,
    }
    ctx.comp_id.hash(&mut h);
    ctx.comp.width.hash(&mut h);
    ctx.comp.height.hash(&mut h);
    scale.to_bits().hash(&mut h);
    draft.hash(&mut h);
    layer.id.hash(&mut h);
    hash_debug(&mut h, &layer.source);
    hash_debug(&mut h, &layer.switches);
    for c in &layer.props.children {
        // Transform is applied later; Layer Styles are keyed separately (see [`styles_key`]).
        if let Node::Group(g) = c
            && (g.match_id == "transform" || g.match_id == effectcraft_project::styles::GROUP)
        {
            continue;
        }
        // Static structure: values, keyframes, expressions, enabled flags, effect ids, modes.
        hash_debug(&mut h, c);
        if let Node::Group(g) = c {
            hash_values(&mut h, ctx, layer, g);
        }
    }
    if time_dependent(layer) {
        layer.layer_time(ctx.time).0.hash(&mut h);
        // Effects also see the layer's time mapping.
        layer.start_time.0.hash(&mut h);
        layer.stretch.to_bits().hash(&mut h);
    }
    Some(h.finish())
}

/// Cache key for the styled layer (content key + the Layer Styles group: structure, eye
/// switches, values, keyframes, expressions and their values at the context time — Global Light
/// included, as every layer mirrors it in its Blending Options).
pub fn styles_key(ctx: &EvalCtx, layer: &Layer, content_key: u64) -> u64 {
    let mut h = KeyHasher(content_key ^ 0x9e37_79b9_7f4a_7c15);
    if let Some(g) = layer.layer_styles() {
        hash_debug(&mut h, g);
        hash_values(&mut h, ctx, layer, g);
    }
    h.finish()
}

/// A sub-key of `key` (styled layer passes, flattened buffer).
pub fn derive(key: u64, i: u64) -> u64 {
    let mut h = KeyHasher(key);
    i.hash(&mut h);
    h.finish()
}