//! Dragging mesh points and their handles on the canvas, shared by the Mesh tool and Direct
//! Selection: gradient meshes and mesh envelopes alike (`object.mesh.movePoint`). Clicking a
//! point focuses it: its handles show and can be dragged too, and on a gradient mesh a solid fill
//! colour recolours it (the tool's `meshPoint` option).

use std::borrow::Cow;

use serde_json::{Value, json};
use vectorcraft_doc::live::{GradientMesh, envelope_grid};
use vectorcraft_doc::{EnvelopeKind, Node, NodeId, NodeKind};
use vectorcraft_geom::Point;

use crate::{Action, Overlay, ToolContext};

const FEEDBACK: [u8; 3] = [0x4f, 0x9d, 0xff];

/// The editable grid of `n`: a gradient mesh, or a mesh envelope's grid (not while its contents
/// are being edited).
pub fn grid_of(n: &Node) -> Option<Cow<'_, GradientMesh>> {
    match &n.kind {
        NodeKind::Mesh(m) => Some(Cow::Borrowed(m)),
        NodeKind::Envelope { kind: EnvelopeKind::Mesh { rows, cols, points, handles }, editing: false, .. } => {
            envelope_grid(*rows, *cols, points, handles).map(Cow::Owned)
        }
        _ => None,
    }
}

/// What a press on a mesh grabs: the mesh, the point and (on the focused point) a handle.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct MeshGrab {
    pub id: NodeId,
    pub index: usize,
    pub handle: Option<usize>,
}

/// Point and handle drags on meshes.
#[derive(Default)]
pub struct MeshEdit {
    /// The point last clicked: its handles show and can be dragged.
    focus: Option<(NodeId, usize)>,
    drag: Option<MeshGrab>,
}

impl MeshEdit {
    /// The handle of the focused point, else the mesh point, under `p` among the meshes `ids`
    /// (editable ones, in order).
    pub fn hit(&self, cx: &ToolContext, ids: &[NodeId], p: Point) -> Option<MeshGrab> {
        let tol = cx.tol(5.0);
        if let Some((id, index)) = self.focus
            && ids.contains(&id)
            && let Some(grid) = cx.doc.node(id).and_then(grid_of)
            && let Some(q) = grid.points.get(index)
            && let Some(h) = (0..4).find(|h| q.handles[*h].hypot() > 1e-6 && (q.p + q.handles[*h]).distance(p) <= tol)
        {
            return Some(MeshGrab { id, index, handle: Some(h) });
        }
        ids.iter().filter(|id| cx.doc.is_editable(**id)).find_map(|id| {
            let index = grid_of(cx.doc.node(*id)?)?.point_near(p, tol)?;
            Some(MeshGrab { id: *id, index, handle: None })
        })
    }

    /// Start dragging `grab` (its point takes the focus).
    pub fn press(&mut self, grab: MeshGrab) -> Vec<Action> {
        self.focus = Some((grab.id, grab.index));
        self.drag = Some(grab);
        vec![Action::Begin("Move Mesh Point".into())]
    }

    /// The preview of a drag to `p` (`None` when nothing is being dragged).
    pub fn drag_to(&self, p: Point) -> Option<Vec<Action>> {
        let g = self.drag?;
        let mut params = json!({"id": g.id.0, "index": g.index, "x": p.x, "y": p.y});
        if let Some(h) = g.handle {
            params["handle"] = json!(h);
        }
        Some(vec![Action::Preview("object.mesh.movePoint".into(), params)])
    }

    /// End a drag (`None` when nothing was being dragged).
    pub fn release(&mut self) -> Option<Vec<Action>> {
        self.drag.take().map(|_| vec![Action::Commit])
    }

    pub fn dragging(&self) -> bool {
        self.drag.is_some()
    }

    /// Forget the focused point.
    pub fn unfocus(&mut self) {
        self.focus = None;
    }

    /// `{meshPoint: {id, index}|null}`: the focused point, which a solid fill colour recolours
    /// (`paint.setFill` on a gradient mesh).
    pub fn options(&self) -> Value {
        json!({"meshPoint": self.focus.map(|(id, index)| json!({"id": id.0, "index": index}))})
    }

    /// The focused point's handles (lines and ends).
    pub fn overlays(&self, cx: &ToolContext) -> Vec<Overlay> {
        let Some((id, index)) = self.focus else { return vec![] };
        let Some(grid) = cx.doc.node(id).and_then(grid_of) else { return vec![] };
        let Some(q) = grid.points.get(index) else { return vec![] };
        let mut out = vec![Overlay::Anchor { p: q.p, color: FEEDBACK, filled: true, size: 5.0 }];
        for h in q.handles.iter().filter(|h| h.hypot() > 1e-6) {
            out.push(Overlay::Line { a: q.p, b: q.p + *h, color: FEEDBACK, dashed: false });
            out.push(Overlay::Handle { p: q.p + *h, color: FEEDBACK });
        }
        out
    }
}

#[cfg(test)]
mod tests {
    use std::sync::Arc;

    use super::*;
    use crate::testutil::*;
    use crate::{PointerEvent, PointerKind, Tool};
    use vectorcraft_doc::live::{EnvelopeOptions, grid_points};
    use vectorcraft_doc::{Document, Selection};
    use vectorcraft_geom::{Affine, Rect};

    /// The rectangle of [`doc_with_rect`] (100..200 square) in a 1×1 mesh envelope.
    fn doc_with_envelope() -> (Document, NodeId) {
        let (mut d, a) = doc_with_rect();
        let rect = d.node(a).cloned().unwrap();
        d.remove(a).unwrap();
        let id = d.alloc_id();
        let kind = EnvelopeKind::Mesh { rows: 1, cols: 1, points: grid_points(Rect::new(100.0, 100.0, 200.0, 200.0), 1, 1), handles: vec![] };
        let env = NodeKind::Envelope {
            content: vec![Arc::new(rect)],
            kind,
            fidelity: 50.0,
            editing: false,
            options: EnvelopeOptions::NEW,
            frame: Affine::IDENTITY,
        };
        let l = d.layers[0].id;
        d.insert(Some(l), 0, Node::new(id, env)).unwrap();
        (d, id)
    }

    #[test]
    fn the_mesh_tool_drags_envelope_points_and_adds_lines() {
        let (d, e) = doc_with_envelope();
        let (s, p) = (Selection::default(), paint());
        let c = cx(&d, &s, &p);
        let mut t = crate::meshblend::create("mesh").unwrap();
        assert_eq!(t.pointer(&c, &PointerEvent::new(PointerKind::Down, 200.0, 100.0)), vec![Action::Begin("Move Mesh Point".into())]);
        assert_eq!(
            t.pointer(&c, &PointerEvent::new(PointerKind::Drag, 210.0, 90.0)),
            vec![Action::Preview("object.mesh.movePoint".into(), json!({"id": e.0, "index": 1, "x": 210.0, "y": 90.0}))]
        );
        assert_eq!(t.pointer(&c, &PointerEvent::new(PointerKind::Up, 210.0, 90.0)), vec![Action::Commit]);
        // The clicked point shows its handles (the smooth mesh's) and they can be dragged.
        assert!(t.overlays(&c).iter().any(|o| matches!(o, Overlay::Handle { .. })));
        assert_eq!(t.pointer(&c, &PointerEvent::new(PointerKind::Down, 200.0, 133.33333)), vec![Action::Begin("Move Mesh Point".into())]);
        let drag = t.pointer(&c, &PointerEvent::new(PointerKind::Drag, 220.0, 140.0));
        assert!(matches!(&drag[..], [Action::Preview(id, p)] if id == "object.mesh.movePoint" && p["handle"] == json!(2)), "{drag:?}");
        t.pointer(&c, &PointerEvent::new(PointerKind::Up, 220.0, 140.0));
        // Inside the envelope: a new row and column.
        assert_eq!(
            t.pointer(&c, &PointerEvent::new(PointerKind::Down, 150.0, 160.0)),
            vec![Action::Exec("object.mesh.addLine".into(), json!({"id": e.0, "x": 150.0, "y": 160.0}))]
        );
    }

    #[test]
    fn direct_selection_drags_a_selected_envelopes_points() {
        let (d, e) = doc_with_envelope();
        let mut s = Selection::default();
        let p = paint();
        let mut t = crate::direct::DirectSelectionTool::new(false);
        // Not selected: its points aren't handles to grab.
        let c = cx(&d, &s, &p);
        assert_ne!(t.pointer(&c, &PointerEvent::new(PointerKind::Down, 100.0, 200.0)), vec![Action::Begin("Move Mesh Point".into())]);
        t.pointer(&c, &PointerEvent::new(PointerKind::Up, 100.0, 200.0));
        s.set([e]);
        let c = cx(&d, &s, &p);
        assert_eq!(t.pointer(&c, &PointerEvent::new(PointerKind::Down, 100.0, 200.0)), vec![Action::Begin("Move Mesh Point".into())]);
        assert_eq!(
            t.pointer(&c, &PointerEvent::new(PointerKind::Drag, 90.0, 210.0)),
            vec![Action::Preview("object.mesh.movePoint".into(), json!({"id": e.0, "index": 2, "x": 90.0, "y": 210.0}))]
        );
        assert_eq!(t.pointer(&c, &PointerEvent::new(PointerKind::Up, 90.0, 210.0)), vec![Action::Commit]);
    }
}