package webui

import (
	"strconv"

	"kjol/vdom"
	"kjol/wasmruntime"
)

// Floating is the live controller for one floating panel — the Go answer to the
// TSX kit's Solid context (which Go has no equivalent of). Tooltips, popovers,
// menus, submenus and the date picker's dropdown are all built on it.
//
// The dance it performs, and why each step exists:
//
//  1. Show() flips a signal, which schedules a render. The panel is rendered
//     PORTALED to document.body (so an ancestor's overflow:hidden or transform
//     cannot clip it or re-root its `position: fixed`) and laid out but INVISIBLE
//     (`visibility: hidden` — which still takes up layout, unlike `display: none`).
//  2. AfterRender fires once the DOM exists. Only now can the panel be measured:
//     you cannot know where to put a panel until you know how big it is.
//  3. ComputePosition does the math; the result is written with SetStyle —
//     imperatively, straight to the DOM node. NOT through a signal: a signal write
//     re-renders the entire app, and this runs on every scroll frame.
//  4. The panel is revealed. It never paints at 0,0.
//
// Create one per floating element, alongside your signals — NOT inside a render
// function, which would rebuild it (and its refs) every frame:
//
//	menu := webui.NewFloating(webui.FloatingOptions{Placement: webui.PlacementBottomEnd})
//	return func() *vdom.VNode {
//	    return Div(
//	        menu.Trigger(webui.FloatingTriggerProps{}, Text("Actions")),
//	        menu.Panel(webui.FloatingPanelProps{}, items...),
//	    )
//	}
type Floating struct {
	id   string
	opts FloatingOptions

	open     *vdom.Signal[bool]
	resolved *vdom.Signal[string] // placement after flipping; the arrow's side depends on it

	triggerRef *vdom.Ref
	panelRef   *vdom.Ref
	arrowRef   *vdom.Ref

	unsubs     []wasmruntime.Unsub
	hoverTimer int
}

// FloatingOptions configures a Floating. The zero value is usable: bottom-start,
// 4px offset, flip + shift on, closes on outside click and Escape.
type FloatingOptions struct {
	Placement string
	Offset    float64
	Padding   float64
	NoFlip    bool // inverted so the zero value means "flip", which is what you want
	NoShift   bool

	// ArrowSize is the arrow's width/height in px. Zero means no arrow.
	ArrowSize    float64
	ArrowPadding float64

	// Standalone opts out of the single-open manager: opening this panel will not
	// close others, and others will not close it. Nested floatings (a submenu
	// inside a menu, a select inside a popover) must set it, or opening the child
	// would close its own parent.
	Standalone bool

	KeepOnOutsideClick bool // inverted: by default an outside mousedown closes
	KeepOnEscape       bool // inverted: by default Escape closes the topmost

	// ConstrainToViewport caps the panel's size on the main axis to the room
	// actually available, so a long menu scrolls instead of running off screen.
	ConstrainToViewport bool

	// OpenOnHover turns the trigger into a hover target. HoverDelay is how long the
	// cursor must rest before opening; HoverCloseDelay is the grace period after
	// leaving — the "bridge" that lets the cursor cross the gap onto the panel
	// without it vanishing. Defaults: 0 and 150ms.
	OpenOnHover     bool
	HoverDelay      int
	HoverCloseDelay int

	OnOpenChange func(bool)
}

var floatingSeq int

// NewFloating creates a floating controller. Call it once per panel, outside the
// render function.
func NewFloating(o FloatingOptions) *Floating {
	floatingSeq++
	if o.Placement == "" {
		o.Placement = PlacementBottomStart
	}
	if o.Offset == 0 {
		o.Offset = 4
	}
	if o.Padding == 0 {
		o.Padding = 8
	}
	if o.ArrowPadding == 0 {
		o.ArrowPadding = 4
	}
	if o.HoverCloseDelay == 0 {
		o.HoverCloseDelay = 150
	}
	return &Floating{
		id:         "floating-" + strconv.Itoa(floatingSeq),
		opts:       o,
		open:       vdom.NewSignal(false),
		resolved:   vdom.NewSignal(o.Placement),
		triggerRef: vdom.NewRef(),
		panelRef:   vdom.NewRef(),
		arrowRef:   vdom.NewRef(),
	}
}

// IsOpen reports the current state. Safe to read during render.
func (f *Floating) IsOpen() bool { return f.open.Get() }

// Placement is the resolved placement — after any flip. Read it during render to
// decide which side an arrow or a transition origin belongs on.
func (f *Floating) Placement() string { return f.resolved.Get() }

// Toggle, Show and Hide drive the panel. They are safe to call from event handlers.
func (f *Floating) Toggle() {
	if f.open.Get() {
		f.Hide()
	} else {
		f.Show()
	}
}

func (f *Floating) Show() {
	if f.open.Get() {
		return
	}
	f.cancelHover()
	registerOpen(f)
	f.open.Set(true)
	if f.opts.OnOpenChange != nil {
		f.opts.OnOpenChange(true)
	}
	// The panel does not exist yet — the signal write only *scheduled* a render.
	// Measure once it does.
	wasmruntime.AfterRender(f.mounted)
}

func (f *Floating) Hide() {
	if !f.open.Get() {
		return
	}
	f.cancelHover()
	f.teardown()
	unregisterOpen(f)
	f.open.Set(false)
	if f.opts.OnOpenChange != nil {
		f.opts.OnOpenChange(false)
	}
}

// Dispose closes the panel and removes every listener. Call it if the component
// owning this Floating goes away while the panel might still be open.
func (f *Floating) Dispose() {
	f.cancelHover()
	f.teardown()
	unregisterOpen(f)
	if f.open.Get() {
		f.open.Set(false)
	}
}

// mounted runs once the panel is in the DOM: position it, then start tracking.
func (f *Floating) mounted() {
	f.Reposition()

	// Reposition when anything that feeds the math changes. `scroll` is registered
	// with capture=true because scroll does NOT bubble — capture on window is the
	// only way to hear a scroll inside a nested container (a panel anchored to a row
	// in a scrollable table depends on this).
	f.unsubs = append(f.unsubs,
		wasmruntime.OnWindow(vdom.EVENT_SCROLL, true, func(vdom.Event) { f.Reposition() }),
		wasmruntime.OnWindow(vdom.EVENT_RESIZE, false, func(vdom.Event) { f.Reposition() }),
		// The original kit repositioned only on scroll/resize, so a panel whose own
		// content changed size (an async list, a filtered dropdown) stayed at its
		// stale position. This is the fix.
		wasmruntime.ObserveResize(f.panelRef, f.Reposition),
	)

	if !f.opts.KeepOnOutsideClick {
		// mousedown, not click: it fires before focus moves, so a click that both
		// closes this panel and focuses something else behaves predictably.
		f.unsubs = append(f.unsubs, wasmruntime.OnDocument(vdom.EVENT_MOUSEDOWN, false, f.onOutside))
	}
	if !f.opts.KeepOnEscape {
		f.unsubs = append(f.unsubs, wasmruntime.OnDocument(vdom.EVENT_KEYDOWN, false, f.onKeydown))
	}
}

// Reposition re-runs the math against the live DOM. Cheap enough to call on every
// scroll frame: two measurements, some arithmetic, and a couple of style writes —
// no re-render.
func (f *Floating) Reposition() {
	if !f.open.Get() {
		return
	}
	// Self-heal: if the panel was torn out from under us (a route change re-rendered
	// the page away), stop tracking rather than leaking listeners forever.
	if !f.panelRef.Mounted() {
		f.teardown()
		return
	}

	trigger := wasmruntime.Measure(f.triggerRef)
	panel := wasmruntime.Measure(f.panelRef)
	if trigger.Empty() || panel.Empty() {
		return // not laid out yet; stay hidden rather than paint at 0,0
	}

	pos := ComputePosition(trigger, panel, wasmruntime.Viewport(), f.positionOptions())

	wasmruntime.SetStyle(f.panelRef, "top", px(pos.Top))
	wasmruntime.SetStyle(f.panelRef, "left", px(pos.Left))
	if f.opts.ConstrainToViewport {
		if pos.MaxHeight > 0 {
			wasmruntime.SetStyle(f.panelRef, "max-height", px(pos.MaxHeight))
			wasmruntime.SetStyle(f.panelRef, "overflow-y", "auto")
		}
		if pos.MaxWidth > 0 {
			wasmruntime.SetStyle(f.panelRef, "max-width", px(pos.MaxWidth))
		}
	}
	wasmruntime.SetStyle(f.panelRef, "visibility", "visible")

	if f.opts.ArrowSize > 0 && f.arrowRef.Mounted() {
		base, _ := splitPlacement(pos.Placement)
		if base == "top" || base == "bottom" {
			wasmruntime.SetStyle(f.arrowRef, "left", px(pos.ArrowOffset))
			wasmruntime.RemoveStyle(f.arrowRef, "top")
		} else {
			wasmruntime.SetStyle(f.arrowRef, "top", px(pos.ArrowOffset))
			wasmruntime.RemoveStyle(f.arrowRef, "left")
		}
	}

	// The arrow's SIDE (which edge it hangs off) is a class, not a style, so a flip
	// has to go through a render. Guarded on change, so this converges after one
	// extra render instead of looping.
	if f.resolved.Get() != pos.Placement {
		f.resolved.Set(pos.Placement)
	}
}

func (f *Floating) positionOptions() PositionOptions {
	return PositionOptions{
		Placement:    f.opts.Placement,
		Offset:       f.opts.Offset,
		Flip:         !f.opts.NoFlip,
		Shift:        !f.opts.NoShift,
		Padding:      f.opts.Padding,
		ArrowSize:    f.opts.ArrowSize,
		ArrowPadding: f.opts.ArrowPadding,
	}
}

func (f *Floating) teardown() {
	for _, un := range f.unsubs {
		un()
	}
	f.unsubs = nil
}

// onOutside closes the panel on a mousedown that landed outside it — unless it
// landed inside a floating that opened LATER, which makes that floating a
// descendant of this one (a submenu of this menu, a select inside this popover).
// Clicking an ANCESTOR still closes this panel, which is what you want.
func (f *Floating) onOutside(ev vdom.Event) {
	target := ev.Target()
	if wasmruntime.Contains(f.panelRef, target) || wasmruntime.Contains(f.triggerRef, target) {
		return
	}
	if id, ok := wasmruntime.ClosestAttr(target, "[data-floating-id]", "data-floating-id"); ok && openedAfter(id, f.id) {
		return
	}
	f.Hide()
}

// onKeydown closes on Escape — but only the topmost panel, so a menu inside a
// popover closes one layer per press instead of collapsing the whole stack.
func (f *Floating) onKeydown(ev vdom.Event) {
	if ev.Key() != vdom.KEY_ESCAPE || !isTopmost(f) {
		return
	}
	ev.PreventDefault()
	f.Hide()
}

// ---- hover bridge ----

// The gap between a trigger and its panel is dead space: without a grace period,
// moving the cursor across it closes the panel before you arrive. Both the trigger
// and the panel cancel the pending close on enter and reschedule it on leave, so
// the cursor can travel between them.

func (f *Floating) hoverEnter() {
	f.cancelHover()
	if f.open.Get() {
		return
	}
	if f.opts.HoverDelay <= 0 {
		f.Show()
		return
	}
	f.hoverTimer = wasmruntime.SetTimeout(f.opts.HoverDelay, func() {
		f.hoverTimer = 0
		f.Show()
	})
}

func (f *Floating) hoverLeave() {
	f.cancelHover()
	f.hoverTimer = wasmruntime.SetTimeout(f.opts.HoverCloseDelay, func() {
		f.hoverTimer = 0
		f.Hide()
	})
}

func (f *Floating) cancelHover() {
	if f.hoverTimer != 0 {
		wasmruntime.ClearTimeout(f.hoverTimer)
		f.hoverTimer = 0
	}
}

// ---- the single-open manager + open-order stack ----

var (
	// floatingStack is every open floating, in the order they opened. Order is what
	// makes "close only the topmost on Escape" and the descendant test above work.
	floatingStack []*Floating
	// currentSingle is the one non-standalone floating allowed open at a time.
	currentSingle *Floating
)

func registerOpen(f *Floating) {
	if !f.opts.Standalone && currentSingle != nil && currentSingle != f {
		currentSingle.Hide()
	}
	floatingStack = append(floatingStack, f)
	if !f.opts.Standalone {
		currentSingle = f
	}
}

func unregisterOpen(f *Floating) {
	for i, o := range floatingStack {
		if o == f {
			floatingStack = append(floatingStack[:i], floatingStack[i+1:]...)
			break
		}
	}
	if currentSingle == f {
		currentSingle = nil
	}
}

func isTopmost(f *Floating) bool {
	return len(floatingStack) > 0 && floatingStack[len(floatingStack)-1] == f
}

// openedAfter reports whether the floating with the given id opened later than
// self — i.e. is nested inside it.
func openedAfter(id, selfID string) bool {
	selfIdx := -1
	for i, o := range floatingStack {
		if o.id == selfID {
			selfIdx = i
			break
		}
	}
	if selfIdx < 0 {
		return false
	}
	for _, o := range floatingStack[selfIdx+1:] {
		if o.id == id {
			return true
		}
	}
	return false
}

// ---- rendering ----

// FloatingTriggerProps configures the element that opens the panel.
type FloatingTriggerProps struct {
	Class        string
	Title        string
	Tag          string // default "button"
	AriaHasPopup string
	// OnClick runs in addition to the toggle (which is suppressed when the trigger
	// opens on hover).
	OnClick func()
}

// Trigger renders the element the panel is anchored to.
func (f *Floating) Trigger(p FloatingTriggerProps, children ...*vdom.VNode) *vdom.VNode {
	expanded := "false"
	if f.open.Get() {
		expanded = "true"
	}
	mods := []vdom.Mod{
		vdom.WithRef(f.triggerRef),
		vdom.Attr("class", p.Class),
		vdom.Attr("aria-expanded", expanded),
		vdom.Attr("aria-haspopup", pick(p.AriaHasPopup, "menu")),
	}
	tag := pick(p.Tag, "button")
	if tag == "button" {
		mods = append(mods, vdom.Attr("type", "button"))
	}
	if p.Title != "" {
		mods = append(mods, vdom.Attr("title", p.Title))
	}

	if f.opts.OpenOnHover {
		mods = append(mods,
			vdom.On(vdom.EVENT_MOUSEENTER, f.hoverEnter),
			vdom.On(vdom.EVENT_MOUSELEAVE, f.hoverLeave),
			// focus opens it too, so the panel is reachable from the keyboard.
			vdom.On(vdom.EVENT_FOCUSIN, f.Show),
			vdom.On(vdom.EVENT_FOCUSOUT, f.hoverLeave),
		)
		if p.OnClick != nil {
			mods = append(mods, vdom.On(vdom.EVENT_CLICK, p.OnClick))
		}
	} else {
		mods = append(mods, vdom.On(vdom.EVENT_CLICK, func() {
			if p.OnClick != nil {
				p.OnClick()
			}
			f.Toggle()
		}))
	}

	// Enter/Space activate a non-button trigger; Escape closes from the trigger.
	mods = append(mods, vdom.OnEvent(vdom.EVENT_KEYDOWN, func(ev vdom.Event) {
		switch ev.Key() {
		case vdom.KEY_ENTER, vdom.KEY_SPACE:
			if tag != "button" { // a real button already fires click on Enter/Space
				ev.PreventDefault()
				f.Toggle()
			}
		case vdom.KEY_ESCAPE:
			f.Hide()
		}
	}))

	return vdom.El(tag, kids(mods, children)...)
}

// FloatingPanelProps configures the floating panel.
type FloatingPanelProps struct {
	Class string
	Role  string // default "menu"
}

// Panel renders the floating content, portaled to document.body.
//
// It is rendered `position: fixed` at 0,0 with `visibility: hidden` — laid out (so
// it can be measured) but not painted. Reposition then writes the real coordinates
// and reveals it. The inline style string is IDENTICAL on every render, which is
// what stops the reconciler's attribute diff from clobbering the imperative
// positions: it only calls setAttribute when the declared value changes.
//
// When closed it renders an EMPTY portal rather than nothing, so its slot in the
// parent's child list never disappears — the reconciler diffs children by index,
// and a vanishing child would shift every sibling after it.
func (f *Floating) Panel(p FloatingPanelProps, children ...*vdom.VNode) *vdom.VNode {
	if !f.open.Get() {
		return vdom.Portal()
	}
	mods := []vdom.Mod{
		vdom.WithRef(f.panelRef),
		vdom.Attr("data-floating-id", f.id),
		vdom.Attr("role", pick(p.Role, "menu")),
		vdom.Attr("class", cx("z-[110]", p.Class)),
		vdom.Attr("style", "position:fixed;top:0;left:0;visibility:hidden"),
	}
	if f.opts.OpenOnHover {
		mods = append(mods,
			vdom.On(vdom.EVENT_MOUSEENTER, f.cancelHover),
			vdom.On(vdom.EVENT_MOUSELEAVE, f.hoverLeave),
		)
	}
	return vdom.Portal(vdom.Div(kids(mods, children)...))
}

// Arrow renders the little triangle that points at the trigger. Its side comes
// from the RESOLVED placement, so it follows the panel through a flip; its offset
// along that side is written imperatively by Reposition, so it keeps pointing at
// the trigger even after the panel has been shifted away from it.
//
// Requires FloatingOptions.ArrowSize to be set.
func (f *Floating) Arrow(class string) *vdom.VNode {
	side := OppositeSide(f.resolved.Get())
	size := px(f.opts.ArrowSize)

	// The arrow is a rotated square pinned to the panel's edge; the translate pulls
	// it half its own size outside, and centres it on the offset Reposition writes.
	var edge, translate string
	switch side {
	case "top":
		edge, translate = "top:0;", "translate(-50%, -50%) rotate(45deg)"
	case "bottom":
		edge, translate = "bottom:0;", "translate(-50%, 50%) rotate(45deg)"
	case "left":
		edge, translate = "left:0;", "translate(-50%, -50%) rotate(45deg)"
	default: // right
		edge, translate = "right:0;", "translate(50%, -50%) rotate(45deg)"
	}
	style := "position:absolute;" + edge +
		"width:" + size + ";height:" + size + ";transform:" + translate + ";"

	return vdom.Div(vdom.WithRef(f.arrowRef),
		vdom.Attr("class", cx("pointer-events-none", class)),
		vdom.Attr("style", style),
	)
}

func px(v float64) string {
	return strconv.FormatFloat(v, 'f', -1, 64) + "px"
}