//! Per-occurrence scroll state and a single geometry/clip projection shared by
//! native paint, source paint and input. No business object is copied.
use crate::{
    document::Frame,
    geometry::Point,
    layout::{self, Size},
    mount::{Mount, MountTable},
    ui_bridge::{UiKind, UiNode},
};
use anyhow::{Result, bail};
use endor_core::{NativeContext, ObjectRef, Value, Vm, VmError, WeakObjectRef};
use std::collections::HashMap;

fn intersection(a: [f32; 4], b: [f32; 4]) -> [f32; 4] {
    let x = a[0].max(b[0]);
    let y = a[1].max(b[1]);
    [
        x,
        y,
        (a[0] + a[2]).min(b[0] + b[2]).max(x) - x,
        (a[1] + a[3]).min(b[1] + b[3]).max(y) - y,
    ]
}
pub fn project(vm: &mut Vm, table: &MountTable, root: &UiNode, frame: &mut Frame) -> Result<()> {
    let mut nodes = HashMap::new();
    let mut work = vec![root];
    while let Some(node) = work.pop() {
        nodes.insert(node.block_id.as_str(), node);
        work.extend(node.children().iter().map(|node| node.as_ref()));
    }
    let indices: HashMap<_, _> = frame
        .mounts
        .iter()
        .enumerate()
        .map(|(i, m)| (m.id, i))
        .collect();
    let scrolling: Vec<_> = frame
        .mounts
        .iter()
        .map(|m| matches!(nodes[m.block_id.as_str()].kind, UiKind::Scroll { .. }))
        .collect();
    let mut extent: Vec<_> = frame
        .mounts
        .iter()
        .map(|m| {
            let padding = match nodes[m.block_id.as_str()].kind {
                UiKind::Scroll { padding, .. } => padding,
                _ => 0.0,
            };
            (m.x + m.width - padding, m.y + m.height - padding)
        })
        .collect();
    for i in (0..frame.mounts.len()).rev() {
        let m = &frame.mounts[i];
        if let Some(parent) = m.parent {
            let parent = indices[&parent];
            let e = if scrolling[i] {
                (m.x + m.width, m.y + m.height)
            } else {
                extent[i]
            };
            extent[parent].0 = extent[parent].0.max(e.0);
            extent[parent].1 = extent[parent].1.max(e.1);
        }
    }
    let mut contexts = HashMap::<u64, (f32, f32, Option<[f32; 4]>)>::new();
    frame.commands.clear();
    frame.command_clips.clear();
    for (i, m) in frame.mounts.iter_mut().enumerate() {
        let (dx, dy, clip) = m
            .parent
            .and_then(|id| contexts.get(&id).copied())
            .unwrap_or_default();
        let padding = match nodes[m.block_id.as_str()].kind {
            UiKind::Scroll { padding, .. } => padding,
            _ => 0.0,
        };
        let limits = [
            (extent[i].0 + padding - m.x - m.width).max(0.0),
            (extent[i].1 + padding - m.y - m.height).max(0.0),
        ];
        m.x -= dx;
        m.y -= dy;
        m.clip = clip;
        let mut child = (dx, dy, clip);
        if scrolling[i] {
            let weak = table
                .active
                .get(&m.id)
                .ok_or_else(|| anyhow::anyhow!("missing scroll Mount"))?;
            let owner = vm
                .upgrade(*weak)?
                .ok_or_else(|| anyhow::anyhow!("expired scroll Mount"))?;
            let offset = vm
                .payload::<Mount>(owner, "Mount")
                .map(|mount| mount.scroll_offset);
            vm.release(owner)?;
            let offset = offset?;
            let x = offset[0].clamp(0.0, limits[0]);
            let y = offset[1].clamp(0.0, limits[1]);
            m.scroll = Some([x, y, limits[0], limits[1]]);
            let viewport = [m.x, m.y, m.width, m.height];
            child = (
                dx + x,
                dy + y,
                Some(
                    clip.map(|clip| intersection(clip, viewport))
                        .unwrap_or(viewport),
                ),
            );
        }
        contexts.insert(m.id, child);
        if let Some(command) = layout::paint_native(
            nodes[m.block_id.as_str()],
            m.x,
            m.y,
            Size {
                width: m.width,
                height: m.height,
            },
        ) {
            frame.commands.push(command);
            frame.command_clips.push(m.clip);
        }
    }
    if frame.commands.len() > 10_000 {
        bail!("scroll paint command budget exceeded");
    }
    Ok(())
}

pub fn coordinate(value: &Value) -> Result<f32, VmError> {
    let Value::Number(value) = value else {
        return Err(VmError::InvalidArgument(
            "scroll coordinates must be numbers",
        ));
    };
    let n = value
        .to_string()
        .parse::<f32>()
        .map_err(|_| VmError::InvalidArgument("invalid scroll coordinate"))?;
    if !n.is_finite() || n.abs() > 1_000_000.0 {
        return Err(VmError::InvalidArgument("scroll coordinate exceeds limits"));
    }
    Ok(n)
}
pub fn set(
    cx: &mut NativeContext<'_>,
    owner: ObjectRef,
    desktop: WeakObjectRef,
    point: [f32; 2],
    relative: bool,
) -> Result<(), VmError> {
    let mut mount = cx.store().payload::<Mount>(owner, "Mount")?.clone();
    if !mount.mounted || mount.layout.is_some() {
        return Err(VmError::InvalidArgument(
            "scroll requires committed attached Mount",
        ));
    }
    let bounds = mount
        .geometry
        .scroll
        .ok_or(VmError::InvalidArgument("Mount is not scrollable"))?;
    let next = if relative {
        [
            mount.scroll_offset[0] + point[0],
            mount.scroll_offset[1] + point[1],
        ]
    } else {
        point
    };
    mount.scroll_offset = [next[0].clamp(0.0, bounds[2]), next[1].clamp(0.0, bounds[3])];
    let desktop = cx
        .upgrade(desktop)?
        .ok_or(VmError::InvalidArgument("Mount window expired"))?;
    // Check the normal mutation barrier even when the clamped result is equal.
    cx.replace_payload(owner, mount)?;
    cx.set_attr(desktop, "scrollRequested", Value::Bool(true))
}
pub fn into_view(
    cx: &mut NativeContext<'_>,
    owner: ObjectRef,
    desktop: WeakObjectRef,
) -> Result<(), VmError> {
    let mount = cx.store().payload::<Mount>(owner, "Mount")?.clone();
    if !mount.mounted || mount.layout.is_some() {
        return Err(VmError::InvalidArgument(
            "scrollIntoView requires committed attached Mount",
        ));
    }
    let mut rect = [
        mount.geometry.x,
        mount.geometry.y,
        mount.geometry.width,
        mount.geometry.height,
    ];
    let mut parent = mount.parent;
    while let Some(weak) = parent {
        let Some(owner) = cx.upgrade(weak)? else {
            break;
        };
        let mount = cx.store().payload::<Mount>(owner, "Mount")?.clone();
        parent = mount.parent;
        if let Some(offset) = mount.geometry.scroll {
            let delta = |start: f32, length: f32, viewport: f32, size: f32| {
                if start < viewport {
                    start - viewport
                } else {
                    (start + length - viewport - size).max(0.0)
                }
            };
            let dx = delta(rect[0], rect[2], mount.geometry.x, mount.geometry.width);
            let dy = delta(rect[1], rect[3], mount.geometry.y, mount.geometry.height);
            let x = (offset[0] + dx).clamp(0.0, offset[2]);
            let y = (offset[1] + dy).clamp(0.0, offset[3]);
            rect[0] -= x - offset[0];
            rect[1] -= y - offset[1];
            if x != offset[0] || y != offset[1] {
                set(cx, owner, desktop, [x, y], false)?;
            }
        }
    }
    Ok(())
}
pub fn wheel_target(frame: &Frame, point: Point, delta: [f32; 2]) -> Option<u64> {
    let indices: HashMap<_, _> = frame.mounts.iter().map(|mount| (mount.id, mount)).collect();
    let mut current = frame
        .mounts
        .iter()
        .rev()
        .find(|mount| mount.contains(point));
    while let Some(mount) = current {
        if mount.scroll.is_some_and(|s| {
            (s[0] + delta[0]).clamp(0.0, s[2]) != s[0] || (s[1] + delta[1]).clamp(0.0, s[3]) != s[1]
        }) {
            return Some(mount.id);
        }
        current = mount.parent.and_then(|id| indices.get(&id).copied());
    }
    None
}