//! The `Slider` method surface — the `CSimpleSlider` widget behavior over the kind tag (factory
//! `0x6eee40`). A value in `[min, max]` with a step and orientation, driving a thumb texture along
//! the track.
//!
//! Grounded in wow-re's byte-verified LoadXML table (RF-28, `rf28-typed-widget-loadxml.md`): the
//! `<ThumbTexture>` sub-element (default layer OVERLAY=3), `minValue`/`maxValue`/`valueStep`/
//! `defaultValue`, the `orientation` shared enum (HORIZONTAL=0/VERTICAL=1, `0x811b00`), and the
//! widget's own `OnValueChanged` script slot (`+0x330`). The **thumb-position** mechanism — the
//! thumb's rect placed at the value fraction along the orientation axis, applied at extract — is
//! faithful to the *documented* widget model, not byte-pinned (same posture as StatusBar's fill and
//! ScrollFrame's scroll; decisions 0112/0250).
//!
//! `SetValue` fires `OnValueChanged` **only on an actual change** ([`SliderState::store_value`]).
//! That is load-bearing, not an optimization: the real scrollbar template wires
//! `OnValueChanged → this:GetParent():SetVerticalScroll(arg1)` and the ScrollFrame's
//! `OnVerticalScroll → scrollbar:SetValue(arg1)` back the other way, so a fire-always `SetValue`
//! would recurse forever (`UIPanelTemplates.xml`). The change-gate breaks the loop after one hop.
//!
//! The methods live in their own registry table, consulted by the frame `__index` dispatcher only
//! for Slider frames — so duck-typing addons (`if frame:GetThumbTexture() then …`) see `nil` on
//! every other kind, exactly as against the client's per-class method sets.

use mlua::{Lua, Table, Value};

use super::object::{draw_layer_from_str, frame_handle_of};
use super::pointer::point_in_rect;
use super::region::region_wrapper;
use super::{event, Model, RegionData};
use crate::layout::Rect;
use crate::order::DrawLayer;
use crate::widget::{FrameHandle, KindState, RegionKind, SliderState};

/// Registry key of the Slider method table (the MAXCSTACK discipline: Lua-side root, named key).
pub(super) const REG_SLIDER_METHODS: &str = "__benilla_slider_methods";

/// Run `f` over a frame's Slider state under one short write borrow. Errors if `this` is not a live
/// Slider (unreachable through the kind dispatcher, but the method table is a plain Lua value — a
/// caller could fish it out and misapply it).
fn with_slider<T>(
    lua: &Lua,
    this: &Table,
    f: impl FnOnce(&mut SliderState) -> T,
) -> mlua::Result<T> {
    let h = frame_handle_of(lua, this)?;
    let mut model = lua.app_data_mut::<Model>().expect("model app_data");
    let frame = model
        .arena
        .frame_mut(h)
        .ok_or_else(|| mlua::Error::runtime("stale frame handle"))?;
    match &mut frame.kind_state {
        KindState::Slider(s) => Ok(f(s)),
        _ => Err(mlua::Error::runtime("not a Slider")),
    }
}

/// Get-or-create the thumb texture region (`SetThumbTexture`/`<ThumbTexture>`); `layer` re-layers an
/// existing thumb. Returns the region's id (for wrapper lookup). The widget default layer is OVERLAY
/// (RF-28 — the Slider's `drawLayer` attr defaults OVERLAY=3, unlike StatusBar's ARTWORK bar).
fn ensure_thumb(lua: &Lua, this: &Table, layer: Option<DrawLayer>) -> mlua::Result<u32> {
    let h = frame_handle_of(lua, this)?;
    let mut model = lua.app_data_mut::<Model>().expect("model app_data");

    let existing = match &model
        .arena
        .frame(h)
        .ok_or_else(|| mlua::Error::runtime("stale frame handle"))?
        .kind_state
    {
        KindState::Slider(s) => s.thumb,
        _ => return Err(mlua::Error::runtime("not a Slider")),
    };

    let rh = match existing {
        Some(rh) => {
            if let (Some(l), Some(region)) = (layer, model.arena.region_mut(rh)) {
                region.draw_layer = l;
            }
            rh
        }
        None => {
            let rh = model
                .arena
                .create_region(
                    h,
                    RegionKind::Texture,
                    layer.unwrap_or(DrawLayer::Overlay),
                    0,
                )
                .ok_or_else(|| mlua::Error::runtime("stale frame handle"))?;
            model.region_data.insert(rh, RegionData::default());
            model.touch_layout(); // a region entered the layout gate's read set (decision 0740)
            if let Some(frame) = model.arena.frame_mut(h) {
                if let KindState::Slider(s) = &mut frame.kind_state {
                    s.thumb = Some(rh);
                }
            }
            rh
        }
    };
    Ok(model.region_id(rh))
}

pub(super) fn install(lua: &Lua) -> mlua::Result<()> {
    let m = lua.create_table()?;

    m.set(
        "SetMinMaxValues",
        lua.create_function(|lua, (this, min, max): (Table, f32, f32)| {
            // Unlike StatusBar, a reversed pair is NOT swapped (the Slider LoadXML stores min +
            // (max−min) and does no swap, RF-28). The held value re-clamps into the new range; a
            // move fires OnValueChanged — a value change the caller didn't set explicitly is still a
            // change (the store_value clamp guards a degenerate max<min range).
            let changed = with_slider(lua, &this, |s| {
                (s.min, s.max) = (min, max);
                s.store_value(s.value)
            })?;
            fire_value_changed(lua, &this, changed)
        })?,
    )?;
    m.set(
        "GetMinMaxValues",
        lua.create_function(|lua, this: Table| with_slider(lua, &this, |s| (s.min, s.max)))?,
    )?;
    m.set(
        "SetValue",
        lua.create_function(|lua, (this, v): (Table, f32)| {
            let changed = with_slider(lua, &this, |s| s.store_value(v))?;
            fire_value_changed(lua, &this, changed)
        })?,
    )?;
    m.set(
        "GetValue",
        lua.create_function(|lua, this: Table| with_slider(lua, &this, |s| s.value))?,
    )?;
    m.set(
        "SetValueStep",
        lua.create_function(|lua, (this, step): (Table, f32)| {
            with_slider(lua, &this, |s| s.step = step)
        })?,
    )?;
    m.set(
        "GetValueStep",
        lua.create_function(|lua, this: Table| with_slider(lua, &this, |s| s.step))?,
    )?;
    m.set(
        "SetOrientation",
        lua.create_function(|lua, (this, o): (Table, String)| {
            let vertical = match o.to_ascii_uppercase().as_str() {
                "HORIZONTAL" => false,
                "VERTICAL" => true,
                _ => {
                    return Err(mlua::Error::runtime(format!(
                        "SetOrientation: unknown orientation '{o}'"
                    )))
                }
            };
            with_slider(lua, &this, |s| s.vertical = vertical)
        })?,
    )?;
    m.set(
        "GetOrientation",
        lua.create_function(|lua, this: Table| {
            let v = with_slider(lua, &this, |s| s.vertical)?;
            Ok(if v { "VERTICAL" } else { "HORIZONTAL" }.to_string())
        })?,
    )?;

    // Enable/Disable/IsEnabled — a disabled slider ignores thumb drag (gated in the pointer path).
    m.set(
        "Enable",
        lua.create_function(|lua, this: Table| with_slider(lua, &this, |s| s.enabled = true))?,
    )?;
    m.set(
        "Disable",
        lua.create_function(|lua, this: Table| with_slider(lua, &this, |s| s.enabled = false))?,
    )?;
    m.set(
        "IsEnabled",
        // 1.12 returns 1/nil; the house API target is the Era boolean (decision 0068) — every
        // transcribed `if slider:IsEnabled()` reads both identically.
        lua.create_function(|lua, this: Table| with_slider(lua, &this, |s| s.enabled))?,
    )?;

    // SetThumbTexture(path [, drawLayer]) | SetThumbTexture(r, g, b [, a]) — the same two forms as a
    // region's SetTexture, targeting the thumb region (created on first use). Mirrors
    // SetStatusBarTexture; the thumb defaults to the OVERLAY layer.
    m.set(
        "SetThumbTexture",
        lua.create_function(
            |lua, (this, a1, a2, a3, a4): (Table, Value, Value, Value, Value)| {
                let layer = match &a2 {
                    Value::String(s) => s.to_str().ok().and_then(|l| draw_layer_from_str(&l)),
                    _ => None,
                };
                let id = ensure_thumb(lua, &this, layer)?;
                let rh = {
                    let model = lua.app_data_ref::<Model>().expect("model app_data");
                    *model.id_to_region.get(&id).expect("thumb region id")
                };
                let mut model = lua.app_data_mut::<Model>().expect("model app_data");
                let data = model.region_data.entry(rh).or_default();
                match &a1 {
                    Value::String(s) => data.texture = Some(s.to_str()?.to_string()),
                    Value::Number(_) | Value::Integer(_) => {
                        data.color = Some([
                            num_f32(&a1),
                            num_f32(&a2),
                            num_f32(&a3),
                            match &a4 {
                                Value::Nil => 1.0,
                                v => num_f32(v),
                            },
                        ]);
                    }
                    _ => {}
                }
                Ok(())
            },
        )?,
    )?;
    m.set(
        "GetThumbTexture",
        lua.create_function(|lua, this: Table| {
            let thumb = with_slider(lua, &this, |s| s.thumb)?;
            let id = {
                let mut model = lua.app_data_mut::<Model>().expect("model app_data");
                thumb.map(|rh| model.region_id(rh))
            };
            match id {
                Some(id) => Ok(Value::Table(region_wrapper(lua, id)?)),
                None => Ok(Value::Nil),
            }
        })?,
    )?;

    lua.set_named_registry_value(REG_SLIDER_METHODS, m)?;
    Ok(())
}

/// Fire `OnValueChanged(self, value)` if `changed` carries the new value (RF-28: the Slider's own
/// script slot `+0x330`). Fired outside any model borrow; errors go to [`Model::errors`].
fn fire_value_changed(lua: &Lua, this: &Table, changed: Option<f32>) -> mlua::Result<()> {
    let Some(value) = changed else { return Ok(()) };
    let id = {
        let h = frame_handle_of(lua, this)?;
        let mut model = lua.app_data_mut::<Model>().expect("model app_data");
        model.frame_id(h)
    };
    if let Err(e) = event::fire_widget_handler(
        lua,
        id,
        "OnValueChanged",
        vec![Value::Number(f64::from(value))],
    ) {
        lua.app_data_mut::<Model>()
            .expect("model app_data")
            .errors
            .push(e.to_string());
    }
    Ok(())
}

/// A Lua number-ish → f32 (nil/other → 0.0), for the color-form arguments.
fn num_f32(v: &Value) -> f32 {
    match v {
        Value::Number(n) => *n as f32,
        Value::Integer(i) => *i as f32,
        _ => 0.0,
    }
}

// ── Thumb geometry + drag (decision 0250 §4/§5) ──────────────────────────────────────────────

/// A Slider's thumb rect: the thumb of size `thumb_size` placed at `fraction` along the slider `r`'s
/// track and centered on the cross-axis. The thumb stays **inset** within the track (travel =
/// trackLen − thumbLen), the way WoW scrollbar knobs visibly do. VERTICAL runs y-up-inverted —
/// `fraction` 0 (value=min) sits the thumb flush at the **top** (a scrollbar at 0 is scrolled to the
/// top), `fraction` 1 flush at the bottom. A thumb with no explicit size fills the slider (zero
/// travel). This is the single geometry source shared by `extract` (render) and [`begin_drag`]
/// (hit-test), so render and input never disagree. Returns a [`Rect`] as `(bottom, left, top, right)`.
pub(super) fn thumb_rect(
    r: Rect,
    thumb_size: Option<(f32, f32)>,
    vertical: bool,
    fraction: f32,
) -> Rect {
    let (tw, th) = thumb_size.unwrap_or((r.width(), r.height()));
    if vertical {
        let travel = (r.height() - th).max(0.0);
        let top = r.top - fraction * travel; // f=0 → track top, f=1 → track bottom
        let cx = (r.left + r.right) * 0.5;
        Rect::new(top - th, cx - tw * 0.5, top, cx + tw * 0.5)
    } else {
        let travel = (r.width() - tw).max(0.0);
        let left = r.left + fraction * travel;
        let cy = (r.bottom + r.top) * 0.5;
        Rect::new(cy - th * 0.5, left, cy + th * 0.5, left + tw)
    }
}

/// The in-flight thumb drag (decision 0250 §5): the slider being dragged + the grab offset (the
/// cursor's distance from the thumb's leading edge along the axis at grab time), so the thumb tracks
/// the cursor without jumping. Engine C++-equivalent — no Lua, like the real client's scrollbar.
#[derive(Clone, Copy)]
pub(crate) struct SliderDrag {
    pub(crate) slider: FrameHandle,
    /// cursor-along-axis − thumb-leading-edge at grab (VERTICAL: `y − thumb.top`; HORIZONTAL:
    /// `x − thumb.left`).
    pub(crate) grab_offset: f32,
}

/// On a LeftButton press at `(x, y)` whose hit frame is `hit`: if that frame is an **enabled**
/// Slider with a resolved rect and the cursor lies on its thumb, begin a drag capture (records
/// [`Model::slider_drag`]). Returns whether a capture began — the caller needs nothing from it (the
/// press still fires OnMouseDown normally). A press off the thumb (on the track) captures nothing:
/// only the thumb drags, matching the vanilla scrollbar where the arrows do the stepping.
pub(super) fn begin_drag(model: &mut Model, hit: Option<FrameHandle>, x: f32, y: f32) -> bool {
    let Some(h) = hit else { return false };
    let Some(r) = model.resolved.get(&h).copied() else {
        return false;
    };
    let (enabled, vertical, fraction, thumb) = match model.arena.frame(h).map(|f| &f.kind_state) {
        Some(KindState::Slider(s)) => (s.enabled, s.vertical, s.fraction(), s.thumb),
        _ => return false,
    };
    if !enabled {
        return false;
    }
    let size = thumb
        .and_then(|rh| model.region_data.get(&rh))
        .and_then(|d| d.size);
    let trect = thumb_rect(r, size, vertical, fraction);
    if !point_in_rect(trect, x, y) {
        return false;
    }
    let grab_offset = if vertical {
        y - trect.top
    } else {
        x - trect.left
    };
    model.slider_drag = Some(SliderDrag {
        slider: h,
        grab_offset,
    });
    true
}

/// On a pointer move at `(x, y)` while a thumb is captured: recompute the value from the cursor
/// position (absolute, drift-free — the grab offset keeps the same thumb point under the cursor) and
/// store it. Returns `Some((frame id, new value))` if the value actually changed — the caller fires
/// `OnValueChanged` outside the model borrow — else `None` (no capture, no travel, or no change).
pub(super) fn drag_move(model: &mut Model, x: f32, y: f32) -> Option<(u32, f32)> {
    let SliderDrag {
        slider,
        grab_offset,
    } = *model.slider_drag.as_ref()?;
    let r = model.resolved.get(&slider).copied()?;
    let (min, max, vertical, thumb) = match model.arena.frame(slider).map(|f| &f.kind_state) {
        Some(KindState::Slider(s)) => (s.min, s.max, s.vertical, s.thumb),
        _ => return None, // slider destroyed mid-drag
    };
    let (tw, th) = thumb
        .and_then(|rh| model.region_data.get(&rh))
        .and_then(|d| d.size)
        .unwrap_or((r.width(), r.height()));
    let fraction = if vertical {
        let travel = r.height() - th;
        if travel <= 0.0 {
            return None; // nothing to scroll
        }
        ((r.top - (y - grab_offset)) / travel).clamp(0.0, 1.0)
    } else {
        let travel = r.width() - tw;
        if travel <= 0.0 {
            return None;
        }
        (((x - grab_offset) - r.left) / travel).clamp(0.0, 1.0)
    };
    let value = min + fraction * (max - min);
    let changed = match model.arena.frame_mut(slider).map(|f| &mut f.kind_state) {
        Some(KindState::Slider(s)) => s.store_value(value),
        _ => None,
    };
    changed.map(|v| (model.frame_id(slider), v))
}

/// Release any in-flight thumb drag (LeftButton up, or the pointer leaving the window).
pub(super) fn end_drag(model: &mut Model) {
    model.slider_drag = None;
}