//! Source paint dispatch produces checked immutable commands. One read-only VM
//! resumable call sequences all overrides, sharing one instruction/frame budget.
use crate::{
    document::{Frame, RenderCommand},
    layout::{self, Size},
    mount::Mount,
    object_list,
    ui_bridge::{MAX_DIMENSION, UiNode, attach_desktop_type},
};
use anyhow::{Result, bail};
use endor_core::{
    ContextNativeFunction, NativeCallable, NativeContext, NativeResult, ObjectRef, ObjectStore,
    Value, Vm, VmError, WeakObjectRef,
};
use std::{
    collections::{BTreeMap, HashMap},
    sync::{Arc, Mutex},
};

fn invalid(message: &'static str) -> VmError {
    VmError::InvalidArgument(message)
}
fn object(value: Value) -> Result<ObjectRef, VmError> {
    if let Value::Object(object) = value {
        Ok(object)
    } else {
        Err(invalid("paint must return managed objects"))
    }
}
fn text(store: &ObjectStore, object: ObjectRef, name: &str) -> Result<String, VmError> {
    if let Value::Text(value) = store.get_attr(object, name)? {
        Ok(value)
    } else {
        Err(invalid("paint field must be text"))
    }
}
fn number(store: &ObjectStore, object: ObjectRef, name: &str) -> Result<f32, VmError> {
    let Value::Number(value) = store.get_attr(object, name)? else {
        return Err(invalid("paint field must be a Number"));
    };
    let value = value
        .to_string()
        .parse::<f32>()
        .map_err(|_| invalid("invalid paint number"))?;
    if !value.is_finite()
        || value.abs() > MAX_DIMENSION as f32
        || (!matches!(name, "x" | "y") && value < 0.0)
    {
        return Err(invalid("paint number exceeds bounds"));
    }
    Ok(value)
}
fn named_type(store: &ObjectStore, desktop: ObjectRef, name: &str) -> Result<ObjectRef, VmError> {
    let registry = object(store.get_attr(desktop, "types")?)?;
    object(
        store
            .dict_get(registry, &Value::Text(name.into()))?
            .ok_or(invalid("missing paint type"))?,
    )
}
fn decode(
    store: &ObjectStore,
    command: ObjectRef,
    expected: ObjectRef,
) -> Result<RenderCommand, VmError> {
    if !store.is_instance(command, expected)? {
        return Err(invalid("paint commands must be PaintCommand instances"));
    }
    let x = number(store, command, "x")?;
    let y = number(store, command, "y")?;
    let color = text(store, command, "color")?;
    let kind = text(store, command, "kind")?;
    let result = match kind.as_str() {
        "roundedRect" | "strokeRoundedRect" => {
            let width = number(store, command, "width")?;
            let height = number(store, command, "height")?;
            let radius = number(store, command, "radius")?;
            if x + width > MAX_DIMENSION as f32 || y + height > MAX_DIMENSION as f32 {
                return Err(invalid("paint rectangle exceeds bounds"));
            }
            if kind == "roundedRect" {
                RenderCommand::RoundedRect {
                    x,
                    y,
                    width,
                    height,
                    radius,
                    color,
                }
            } else {
                RenderCommand::StrokeRoundedRect {
                    x,
                    y,
                    width,
                    height,
                    radius,
                    color,
                    stroke_width: number(store, command, "strokeWidth")?,
                }
            }
        }
        "text" => {
            let size = number(store, command, "size")?;
            if size.fract() != 0.0 || !(1.0..=8.0).contains(&size) {
                return Err(invalid("paint text size must be an integer from 1 to 8"));
            }
            let wrap_bounds = match (
                store.get_attr(command, "wrapWidth"),
                store.get_attr(command, "wrapHeight"),
            ) {
                (Err(VmError::AttributeNotFound(_)), Err(VmError::AttributeNotFound(_))) => None,
                (Ok(_), Ok(_)) => Some([
                    number(store, command, "wrapWidth")?,
                    number(store, command, "wrapHeight")?,
                ]),
                (Err(error), _) | (_, Err(error)) => return Err(error),
            };
            RenderCommand::Text {
                x,
                y,
                value: text(store, command, "text")?,
                size: size as u32,
                color,
                wrap_bounds,
            }
        }
        _ => return Err(invalid("unsupported paint command kind")),
    };
    result
        .validate()
        .map_err(|_| invalid("invalid paint command geometry, text or color"))?;
    Ok(result)
}

#[derive(Debug, Default)]
struct PaintOutput {
    commands: BTreeMap<u64, Vec<RenderCommand>>,
    count: usize,
}
type Output = Arc<Mutex<PaintOutput>>;
#[derive(Debug)]
struct Collect {
    desktop: ObjectRef,
    mount: u64,
    output: Output,
}
impl NativeCallable for Collect {
    fn arity(&self) -> Option<endor_core::CallArity> {
        Some(endor_core::CallArity::exact(1))
    }

    fn invoke(&self, cx: &mut NativeContext<'_>, args: &[Value]) -> Result<NativeResult, VmError> {
        let [Value::Object(result)] = args else {
            return Err(invalid("paint must return a DisplayList"));
        };
        if !cx.store().is_instance(
            *result,
            named_type(cx.store(), self.desktop, "DisplayList")?,
        )? {
            return Err(invalid("paint must return a DisplayList"));
        }
        let commands = object(cx.store().get_attr(*result, "commands")?)?;
        let expected = named_type(cx.store(), self.desktop, "PaintCommand")?;
        let commands = object_list::items(cx.store(), commands)?
            .iter()
            .map(|command| decode(cx.store(), *command, expected))
            .collect::<Result<Vec<_>, _>>()?;
        let mut output = self
            .output
            .lock()
            .map_err(|_| invalid("paint output poisoned"))?;
        if output.count + commands.len() > 10_000 {
            return Err(invalid("paint command budget exceeded"));
        }
        output.count += commands.len();
        output.commands.insert(self.mount, commands);
        Ok(NativeResult::Return(Value::Nil))
    }
}
#[derive(Debug)]
struct Prepare {
    desktop: ObjectRef,
    mounts: Vec<(u64, WeakObjectRef)>,
    output: Output,
}
impl NativeCallable for Prepare {
    fn arity(&self) -> Option<endor_core::CallArity> {
        Some(endor_core::CallArity::exact(0))
    }

    fn invoke(&self, cx: &mut NativeContext<'_>, _: &[Value]) -> Result<NativeResult, VmError> {
        let advance = cx.allocate(ContextNativeFunction::new(
            "next paint occurrence",
            Advance {
                desktop: self.desktop,
                mounts: self.mounts.clone().into(),
                next: Mutex::new(0),
                output: self.output.clone(),
            },
            vec![self.desktop],
        ))?;
        let function = crate::vm_sequence::repeat_call(cx, advance, "source paint", self.desktop)?;
        Ok(NativeResult::Invoke {
            function,
            arguments: vec![],
        })
    }
}

#[derive(Debug)]
struct Advance {
    desktop: ObjectRef,
    mounts: Arc<[(u64, WeakObjectRef)]>,
    next: Mutex<usize>,
    output: Output,
}
impl NativeCallable for Advance {
    fn arity(&self) -> Option<endor_core::CallArity> {
        Some(endor_core::CallArity::exact(0))
    }
    fn invoke(&self, cx: &mut NativeContext<'_>, _: &[Value]) -> Result<NativeResult, VmError> {
        let occurrence = {
            let mut next = self
                .next
                .lock()
                .map_err(|_| invalid("paint cursor poisoned"))?;
            let occurrence = self.mounts.get(*next).copied();
            *next += usize::from(occurrence.is_some());
            occurrence
        };
        let Some((id, weak)) = occurrence else {
            return Ok(NativeResult::Return(Value::Bool(false)));
        };
        let mount = cx
            .upgrade(weak)?
            .ok_or(invalid("paint Mount has expired"))?;
        let data = cx.store().payload::<Mount>(mount, "Mount")?.clone();
        if !data.mounted {
            return Err(invalid("paint Mount is detached"));
        }
        let definition = cx
            .store()
            .type_of(data.block)?
            .ok_or(invalid("untyped paint target"))?;
        let function = cx
            .store()
            .lookup_method(definition, "paint")?
            .ok_or(invalid("missing paint method"))?;
        if crate::native_visual::is_intrinsic(cx.store(), function, "paint", self.desktop)? {
            return Ok(NativeResult::Return(Value::Bool(true)));
        }
        let bounds = cx.new_object()?;
        attach_desktop_type(cx, bounds, "Bounds", self.desktop)?;
        for (name, value) in [
            ("x", data.geometry.x),
            ("y", data.geometry.y),
            ("width", data.geometry.width),
            ("height", data.geometry.height),
        ] {
            cx.set_attr(bounds, name, Value::Number((value as f64).into()))?;
        }
        let collector = cx.allocate(ContextNativeFunction::new(
            "collect source paint",
            Collect {
                desktop: self.desktop,
                mount: id,
                output: self.output.clone(),
            },
            vec![self.desktop],
        ))?;
        let function = crate::vm_sequence::collect_and_continue(
            cx,
            collector,
            function,
            vec![
                Value::Object(data.block),
                Value::Object(mount),
                Value::Object(bounds),
            ],
            "paint occurrence",
            self.desktop,
        )?;
        Ok(NativeResult::Invoke {
            function,
            arguments: vec![],
        })
    }
}

pub struct Draft {
    pub frame: Frame,
    pub reads: Vec<endor_core::ReadDependency>,
    pub slices: usize,
}

#[must_use = "pending paint must be resumed or cancelled on its owning VM"]
pub enum Progress {
    Pending(Box<Work>),
    Complete(Box<Draft>),
}

/// Only unpublished native commands and an owning prepare root cross a pause.
pub struct Work {
    desktop: ObjectRef,
    prepare: ObjectRef,
    output: Output,
    root: Option<Arc<UiNode>>,
    frame: Frame,
    slices: usize,
}

impl Work {
    pub fn resume(mut self, vm: &mut Vm, slice: usize) -> Result<Progress> {
        self.slices += 1;
        let progress = vm.resume_read_only_call(slice);
        self.accept(vm, progress)
    }

    pub fn cancel(self, vm: &mut Vm) -> Result<()> {
        let cancelled = vm.cancel_read_only_call();
        let released = vm.release(self.prepare);
        cancelled?;
        released?;
        Ok(())
    }

    fn accept(
        self,
        vm: &mut Vm,
        progress: Result<endor_core::ExecutionProgress, VmError>,
    ) -> Result<Progress> {
        match progress {
            Ok(endor_core::ExecutionProgress::Pending { .. }) => {
                Ok(Progress::Pending(Box::new(self)))
            }
            Ok(endor_core::ExecutionProgress::Complete {
                value,
                dependencies,
                ..
            }) => {
                vm.release(self.prepare)?;
                vm.release_value(value)?;
                finish(vm, self, dependencies)
            }
            Err(error) => {
                let diagnostic = crate::endor_host::runtime_error(vm, error);
                self.cancel(vm)?;
                Err(diagnostic)
            }
        }
    }
}

pub fn start(
    vm: &mut Vm,
    desktop: ObjectRef,
    mounts: Vec<(u64, WeakObjectRef)>,
    root: Option<Arc<UiNode>>,
    frame: Frame,
    slice: usize,
) -> Result<Progress> {
    anyhow::ensure!(slice > 0, "paint slice must be positive");
    anyhow::ensure!(
        !vm.has_suspended_call() && !vm.object_store().is_read_only(),
        "cannot start paint while another read-only execution is active"
    );
    let output = Arc::new(Mutex::new(PaintOutput::default()));
    let prepare = vm.allocate(ContextNativeFunction::new(
        "prepare source paint",
        Prepare {
            desktop,
            mounts,
            output: output.clone(),
        },
        vec![desktop],
    ))?;
    let work = Work {
        desktop,
        prepare,
        output,
        root,
        frame,
        slices: 1,
    };
    let result = vm.start_read_only_call(
        prepare,
        &[],
        endor_core::ExecutionLimits {
            max_frames: 128,
            max_instructions: 1_000_000,
        },
        slice,
    );
    work.accept(vm, result)
}

fn finish(vm: &mut Vm, mut work: Work, reads: Vec<endor_core::ReadDependency>) -> Result<Progress> {
    let output = work
        .output
        .lock()
        .map_err(|_| anyhow::anyhow!("paint output poisoned"))?;
    if output.commands.is_empty() {
        return Ok(Progress::Complete(Box::new(Draft {
            frame: work.frame,
            reads: Vec::new(),
            slices: work.slices,
        })));
    }
    let root = work.root.as_deref();
    let desktop = work.desktop;
    let frame = &mut work.frame;
    let mut nodes = HashMap::new();
    let mut pending: Vec<_> = root.into_iter().collect();
    while let Some(node) = pending.pop() {
        nodes.insert(node.block_id.as_str(), node);
        pending.extend(node.children().iter().map(|node| node.as_ref()));
    }
    let mut commands = Vec::new();
    let mut clips = Vec::new();
    for mount in &frame.mounts {
        let before = commands.len();
        if let Some(custom) = output.commands.get(&mount.id) {
            commands.extend(custom.iter().cloned());
        } else {
            let node = nodes
                .get(mount.block_id.as_str())
                .ok_or_else(|| anyhow::anyhow!("paint projection has no node"))?;
            if let Some(command) = layout::paint_native(
                node,
                mount.x,
                mount.y,
                Size {
                    width: mount.width,
                    height: mount.height,
                },
            ) {
                commands.push(command);
            }
        }
        clips.extend(std::iter::repeat_n(mount.clip, commands.len() - before));
        if commands.len() > 10_000 {
            bail!("paint command budget exceeded");
        }
    }
    frame.commands = commands;
    frame.command_clips = clips;
    let registry = object(vm.get_attr(desktop, "types")?)?;
    let reads = reads
        .into_iter()
        .filter(|dependency| {
            let object = dependency.object();
            object != desktop
                && object != registry
                && vm
                    .object(object)
                    .is_ok_and(|object| !object.payload().as_any().is::<Mount>())
        })
        .collect();
    Ok(Progress::Complete(Box::new(Draft {
        frame: work.frame,
        reads,
        slices: work.slices,
    })))
}