/**
 *       _  ___   Another      
 *      / |/ (_)______ __ _____
 *     /    / / __(_-</ // (_-<
 *    /_/|_/_/\__/___/\_, /___/ 
 *                   /___/     
 *       production !
 * 
 * Licensed under the MIT License: 
 * This code is free to use and modify, 
 * as long as the copyright notice and license are kept.
 */

class BZgraflow extends Buildoz{
    dirVect = {
        n: { x:  0, y: -1 },
        s: { x:  0, y:  1 },
        e: { x:  1, y:  0 },
        w: { x: -1, y:  0 },
    }
    static _loadedNodeStyles = new Set() // Allow multi instances or re-loadNodes, but avoid reinjecting same styles !

    constructor(){
        super()
        this.defaultAttrs = { tension: 100 }
        this.stagedNodes = { }
        this.stagedWires = { }
        this.arrowDefs = null
    }

    connectedCallback() { 
        super.connectedCallback()
        const flowUrl = this.getBZAttribute('flow')
        if(!flowUrl) {
            console.warn('BZgraflow: No flow URL !?')
            return
        }
        // If attribute "isolated" is present, render inside a shadow root.
        // Otherwise, render in light DOM (no shadow DOM).
        this.hostContainer  = document.createElement('div')
        this.hostContainer.classList.add('bzgf-main-container')
        this.mainContainer = this.hasAttribute('isolated')
            ? this.hostContainer.attachShadow({ mode: 'open' })
            : this.hostContainer
        const style = document.createElement('style')
        //TODO kick this wart somewhere under a carpet
        style.textContent = `
            @import '/app/assets/styles/icons.css';
            .bzgf-wires-container,
            .bzgf-nodes-container{ position: absolute; inset: 0; width: 100%; height: 100%; }
            .bzgf-nodes-container .bzgf-node{ position:absolute; }
            .bzgf-nodes-container .bzgf-fake-node{
                position: absolute;
                width: 5px;
                height: 5px;
                backgrround: transparent;
                border-style: none;
            }
            .bzgf-nodes-container button.bzgf-zoom-in{
                width: 2em;
                height: 2em;
                z-index: 999;
                position: absolute;
                top: -1em;
                right: -1em;
                color: #A00;      
            }
        `
        this.mainContainer.appendChild(style)
        this.nodesContainer = document.createElement('div')
        this.nodesContainer.classList.add('bzgf-nodes-container')
        this.wiresContainer = document.createElementNS('http://www.w3.org/2000/svg', 'svg') 
        this.wiresContainer.setAttribute('overflow','visible')
        this.wiresContainer.classList.add('bzgf-wires-container')
        this.mainContainer.append(this.wiresContainer)
        this.mainContainer.append(this.nodesContainer)
        this.append(this.hostContainer)
        this.loadFlow(flowUrl) // Let it load async 
    }
    
    error(msg, err){
        this.innerHTML = `<div style="background:red;color:black;margin: auto;width: fit-content;">${msg}</div>`
        if(err) console.error(msg, err)
        else console.error(msg)
    }

    async loadFlow(url){
        const res = await fetch(url+'?'+crypto.randomUUID())
        const buf = await res.text()
        let flowObj
        try{
            flowObj = JSON.parse(buf)
        } catch(err){
            this.error('Could not parse flow JSON!?', err)

            return
        }
        if(!flowObj.nodesFile){
            this.error('No nodesFile in JSON!?')
            return
        }
        await this.loadNodes(flowObj.nodesFile)
        this.flow = flowObj.flow
        this.refresh()
    }

    async loadNodes(url) {
        const res = await fetch(url+'?'+crypto.randomUUID())
        const html = await res.text()

        // Get nodes
        const doc = new DOMParser().parseFromString(html, 'text/html')
        this.nodesRegistry = {}
        for(const tpl of doc.querySelectorAll('template')){
            if(tpl.id=='svg-arrows'){
                this.arrowDefs = tpl.querySelector('defs').cloneNode(true)
                this.wiresContainer.appendChild(this.arrowDefs)
            } else {
                const rootEl = tpl.content.querySelector('.bzgf-node')
                if(!rootEl) continue
                this.nodesRegistry[rootEl.dataset.nodetype] = rootEl
            }
        }

        // Now load styles (once)
        const isIsolated = this.hasAttribute('isolated')
        if(isIsolated || !BZgraflow._loadedNodeStyles.has(url)) { 
            const styles = doc.querySelectorAll('style')
            styles.forEach(styleEl => {
                const style = document.createElement('style')
                style.textContent = styleEl.textContent
                this.mainContainer.appendChild(style)
            })
            // In non-isolated (light DOM) mode, styles apply globally so we can de-dupe across instances.
            // In isolated (shadow DOM) mode, styles must be injected per instance.
            if(!isIsolated) BZgraflow._loadedNodeStyles.add(url)
        }
    }

    addNode(node){ 
        const id = node.id       
        if(!(node.nodeType in this.nodesRegistry)){ console.warn(`Unknown node type (${node.nodeType})`); return(null)}
        const nodeDef = this.nodesRegistry[node.nodeType]
        this.stagedNodes[id] = nodeDef.cloneNode(true)
        for(const token in node.markup){
                this.stagedNodes[id].innerHTML = this.stagedNodes[id].innerHTML.replace(new RegExp(`\{${token}\}`, 'g'), node.markup[token])
        }
        if(typeof(node.data)=='object') Object.assign(this.stagedNodes[id].dataset, node.data)
        const portEls = this.stagedNodes[id].querySelectorAll('.port')
        this.stagedNodes[id].style.left = (node.coords && node.coords.x) ? `${node.coords.x}px` : '10%'
        this.stagedNodes[id].style.top = (node.coords && node.coords.y) ? `${node.coords.y}px` : '10%'
        this.stagedNodes[id].dataset.id = id
        this.stagedNodes[id].ports = Object.fromEntries(Array.from(portEls).map(item => ([item.dataset.id, { ...item.dataset, el:item }])))
        if(node.subflow) {
            const btnEnterSubflow = document.createElement('button')
            btnEnterSubflow.classList.add('bzgf-zoom-in', 'icon-copy')
            btnEnterSubflow.addEventListener('click', () => {
                this.EnterSubflow(id)
            })
            this.stagedNodes[id].appendChild(btnEnterSubflow)
        }
        this.nodesContainer.append(this.stagedNodes[id])
        return(this.stagedNodes[id])
    }

    EnterSubflow(id){
        const nodeEl = this.stagedNodes[id]
        if(!nodeEl) return

        // Create the child graflow first, place it above (foreground) the current graflow,
        // scaled down so it fits exactly inside the clicked node, then animate it to full size.
        const nodeBB = nodeEl.getBoundingClientRect()
        const parentBB = this.getBoundingClientRect()

        const flowNode = this.flow?.nodes?.find(n => n.id === id)
        const flowUrl = flowNode?.subflow 

        const childEl = document.createElement('bz-graflow')
        childEl.setAttribute('flow', flowUrl)
        childEl.setAttribute('tension', this.getBZAttribute('tension') || '60')
        // Match the clicked node's border so the transition feels like we're "expanding" it.
        const nodeStyle = getComputedStyle(nodeEl)
        childEl.style.border = nodeStyle.border
        childEl.style.borderRadius = nodeStyle.borderRadius

        // Put the child in the exact same viewport rect as the parent (fixed overlay)
        this.Invade(this, childEl)

        // Fade out the current (host) graflow while the child scales up
        this.hostContainer.style.opacity = '1'
        this.hostContainer.style.transition = 'opacity 1000ms ease-in-out'

        // Initial transform so the full-size child "fits" inside the node
        const sx0 = nodeBB.width / parentBB.width
        const sy0 = nodeBB.height / parentBB.height
        const tx0 = nodeBB.left - parentBB.left
        const ty0 = nodeBB.top  - parentBB.top

        // Inline "scaler" (shadow styles don't apply to the child element)
        childEl.style.transformOrigin = 'top left'
        childEl.style.willChange = 'transform'
        childEl.style.transition = 'transform 1000ms ease-in-out'
        childEl.style.transform = 'translate(var(--tx, 0px), var(--ty, 0px)) scale(var(--sx, 1), var(--sy, 1))'
        childEl.style.setProperty('--tx', tx0 + 'px')
        childEl.style.setProperty('--ty', ty0 + 'px')
        childEl.style.setProperty('--sx', sx0)
        childEl.style.setProperty('--sy', sy0)

        // Force style flush, then animate back to identity (full parent size)
        childEl.getBoundingClientRect()
        requestAnimationFrame(() => {
            childEl.style.setProperty('--tx', '0px')
            childEl.style.setProperty('--ty', '0px')
            childEl.style.setProperty('--sx', 1)
            childEl.style.setProperty('--sy', 1)
            this.hostContainer.style.opacity = '0'
        })

        childEl.addEventListener('transitionend', (e) => {
            if(e.propertyName !== 'transform') return
            this.hostContainer.style.visibility = 'hidden'
        }, { once:true })
    }

    Invade(oldEl, newEl){
        const r = oldEl.getBoundingClientRect()
        newEl.style.position = 'fixed'
        newEl.style.left = r.left + 'px'
        newEl.style.top  = r.top  + 'px'
        newEl.style.width  = r.width + 'px'
        newEl.style.height = r.height + 'px'
        newEl.style.display = 'block'
        oldEl.appendChild(newEl)
    }

    Evade(oldEl, newEl){
        oldEl.style.visibility = 'visible'
        oldEl.style.position = 'absolute'
        oldEl.style.left = '0'
        oldEl.style.top = '0'
        oldEl.style.width = '0'
        oldEl.style.height = '0'
        newEl.parentNode.removeChild(newEl)
    }
    
    addFakeNode(nid, x, y, w, h){
        this.stagedNodes[nid] = document.createElement('div')
        this.stagedNodes[nid].classList.add('bzgf-fake-node')
        this.stagedNodes[nid].style.left = `${x}px`
        this.stagedNodes[nid].style.top = `${y}px`
        this.stagedNodes[nid].style.width = `${w}px`
        this.stagedNodes[nid].style.height = `${h}px`
        this.stagedNodes[nid].dataset.id = nid
        this.nodesContainer.append(this.stagedNodes[nid])
        return(this.stagedNodes[nid])
    }

    addWire(link){
        const [idNode1, idPort1] = link.from
        const [idNode2, idPort2] = link.to
        const path = this.bezierNodes(idNode1, idPort1, idNode2, idPort2, this.getBZAttribute('tension'))
        const id  = `${idNode1}_${idNode2}`
        this.stagedWires[id] = document.createElementNS('http://www.w3.org/2000/svg', 'path')
        this.stagedWires[id].setAttribute('d', path)
        this.stagedWires[id].setAttribute('fill', 'none')
        if(this.arrowDefs && link.endArrow) this.stagedWires[id].setAttribute('marker-end','url(#arrow)')
        if(this.arrowDefs && link.startArrow) this.stagedWires[id].setAttribute('marker-start','url(#arrow)')
        this.stagedWires[id].classList.add('bzgf-wire')
        this.stagedWires[id].dataset.id = id
        this.wiresContainer.append(this.stagedWires[id])
        return(this.stagedWires[id])
    }


    clear(){
        this.nodesContainer.innerHTML = ''
        this.wiresContainer.innerHTML = ''
        if(this.arrowDefs) this.wiresContainer.appendChild(this.arrowDefs)
    }

    refresh(){
        this.clear()
        let forceAutoplace = false
        for(const node of this.flow.nodes){
            if((!node.coords) || (!node.coords.x) ||(!node.coords.y)) forceAutoplace=true
            this.addNode(node)
        } 
        for(const link of this.flow.links){
            this.addWire(link)
        }
        
        if(forceAutoplace){
            const bb=this.getBoundingClientRect()
            //TODO compute tensions from ports, height and width
            if(bb.width > bb.height) this.autoPlace('horizontal', 60, 60)
            else this.autoPlace('vertical', 60, 60)    
        } 
    }

    // Convert viewport (client) coordinates to this instance's SVG local coordinates.
    // Required when the whole graflow is CSS-transformed (scale/translate), otherwise wire paths
    // will be computed in the wrong coordinate space.
    clientToSvg(x, y){
        const svg = this.wiresContainer
        const ctm = svg?.getScreenCTM?.()
        if(ctm && ctm.inverse){
            const inv = ctm.inverse()
            if(svg?.createSVGPoint){
                const pt = svg.createSVGPoint()
                pt.x = x
                pt.y = y
                const p = pt.matrixTransform(inv)
                return({ x: p.x, y: p.y })
            }
            if(typeof DOMPoint !== 'undefined'){
                const p = new DOMPoint(x, y).matrixTransform(inv)
                return({ x: p.x, y: p.y })
            }
        }
        // Fallback: approximate using boundingClientRect (works only at scale=1)
        const r = svg.getBoundingClientRect()
        return({ x: x - r.left, y: y - r.top })
    }

    bezierNodes(idNode1, idPort1, idNode2, idPort2, tension=60) {
        tension = parseInt(tension)
        const node1 = this.stagedNodes[idNode1]
        const port1 = node1.ports[idPort1]
        const node2 = this.stagedNodes[idNode2]
        const port2 = node2.ports[idPort2]
        if(!node1 || !node2 || !port1 || !port2) {
            console.warn('Link on bad node / port ', idNode1, idPort1, idNode2, idPort2)
            return('')
        }
        const bb1 = port1.el.getBoundingClientRect()
        const bb2 = port2.el.getBoundingClientRect()
        const p1 = this.clientToSvg(bb1.x + (bb1.width/2), bb1.y + (bb1.height/2))
        const p2 = this.clientToSvg(bb2.x + (bb2.width/2), bb2.y + (bb2.height/2))
        const x1 = Math.floor(p1.x)
        const y1 = Math.floor(p1.y)
        const x2 = Math.floor(p2.x)
        const y2 = Math.floor(p2.y)
        const loop = (idNode1==idNode2) && (idPort1==idPort2)
        const dist = Math.abs(x2 - x1) + Math.abs(y2 - y1)

        let c1x =  Math.floor(x1 + (this.dirVect[port1.direction].x * tension))
        let c1y =  Math.floor(y1 + (this.dirVect[port1.direction].y * tension))
        let c2x =  Math.floor(x2 + (this.dirVect[port2.direction].x * tension))
        let c2y =  Math.floor(y2 + (this.dirVect[port2.direction].y * tension))
        if(loop){ 
            if(['n', 's'].includes(port1.direction)) {
                c1x += tension
                c2x -= tension
            }
            if(['e', 'w'].includes(port1.direction)){
                c1y += 1*tension
                c2y -= 1*tension
            }
        } 
        return(`M ${x1} ${y1} C ${c1x} ${c1y}, ${c2x} ${c2y}, ${x2} ${y2}`)
    }

    bezierInterNodes(idNode1, idPort1, idNode2, idPort2, interNodes, orientation='horizontal', tension=60) {
        tension = parseInt(tension)        
        const node1 = this.stagedNodes[idNode1]
        let port1 = node1.ports[idPort1]

        const makeCubicBezier = (x1, y1, x2, y2, orientation1, orientation2) => {
            const dist = Math.abs(x2 - x1) + Math.abs(y2 - y1)
   
            let c1x, c1y, c2x, c2y       
            if(orientation1=='horizontal'){
                c1x = Math.floor(x1 + tension)
                c1y = y1 
            } else {
                c1x = x1 
                c1y = Math.floor(y1 + tension)
            }                
            if(orientation2=='horizontal'){
                c2x = Math.floor(x2 - tension)
                c2y = y2 
            } else {
                c2x = x2 
                c2y = Math.floor(y2 - tension)                
            }
            return(`C ${c1x} ${c1y}, ${c2x} ${c2y}, ${x2} ${y2}`)
        }
        const directPath = this.bezierNodes(idNode1, idPort1, idNode2, idPort2, tension)
        const startPath = directPath.substring(0,directPath.indexOf('C'))
        const endPath = directPath.substring(directPath.lastIndexOf(',')+1).trim()
        let path = startPath
        let [ , x1, y1] = startPath.split(' ')
        x1 = parseFloat(x1)
        y1 = parseFloat(y1)
        for(const interNode of interNodes){
            const bb = this.stagedNodes[interNode].getBoundingClientRect()
            // Entry/exit points on the placeholder box, converted to SVG coords (handles CSS transforms)
            let entryClient; let exitClient
            if(orientation=='horizontal'){
                entryClient = { x: bb.left,  y: bb.top + (bb.height/2) }
                exitClient  = { x: bb.right, y: bb.top + (bb.height/2) }
            } else {
                entryClient = { x: bb.left + (bb.width/2), y: bb.top }
                exitClient  = { x: bb.left + (bb.width/2), y: bb.bottom }
            }
            const entry = this.clientToSvg(entryClient.x, entryClient.y)
            const exit  = this.clientToSvg(exitClient.x,  exitClient.y)
            let x2 = Math.floor(entry.x)
            let y2 = Math.floor(entry.y)

            if(port1){
                path += makeCubicBezier(x1, y1, x2, y2, ['w','e'].includes(port1.direction) ? 'horizontal' : 'vertical', orientation)
                port1 = false
            } else {
                path += makeCubicBezier(x1, y1, x2, y2, orientation, orientation)
            }

            const x3 = Math.floor(exit.x)
            const y3 = Math.floor(exit.y)
            path += ` L ${x3} ${y3} `

            x1 = x3
            y1 = y3
        }
        let [x2, y2] = endPath.split(' ')
        x2 = parseFloat(x2)
        y2 = parseFloat(y2)
        path += ' '+makeCubicBezier(x1, y1, x2, y2, orientation, orientation)
        return(path)
    }

    autoPlace(orientation = 'horizontal', gapx = 80, gapy = 80, tween=500, align='center'){
        // Loops create infinite recursion in dfs for getting parents & adjacency lists: Remove them !
        let linksWithoutBackEdges
        if(this.hasAnyLoop(this.flow.nodes, this.flow.links)){
            const backEdges = this.findBackEdges(this.flow.nodes, this.flow.links)
            linksWithoutBackEdges = this.flow.links.filter((link, idx) => (!backEdges.includes(idx)) && (link.from[0] != link.to[0]))
        } else {
            linksWithoutBackEdges = this.flow.links
        }
        const { parents, adj } = this.buildGraphStructures(this.flow.nodes, linksWithoutBackEdges)

        const layers = this.computeLayers(this.flow.nodes, parents)

        // Compute indexes for each layer (int part) & add sub-index for ports
        // Also compute max width/height for each layer
        let maxHeight = 0; let maxWidth = 0
        const layerHeights = []; const layerWidths = []; 
        const indexes = {} // indexes[nid] = { base: <int>, ports: { [portId]: <float in [0,1)> } }
        for(const layer of layers){
            let totHeight = 0; let totWidth = 0
            for(const [idx, nid] of layer.entries()){
                // Use offset* (not impacted by CSS transforms) to keep autoPlace stable during zoom animations.
                const bb = this.stagedNodes[nid].getBoundingClientRect()
                const h = this.stagedNodes[nid].offsetHeight || bb.height
                const w = this.stagedNodes[nid].offsetWidth  || bb.width
                totHeight += h + gapy
                totWidth += w + gapx
                indexes[nid] = { base: idx, ports: this.computePortOffsets(nid, orientation) }
            }
            if(totHeight>maxHeight) maxHeight = totHeight
            layerHeights.push(totHeight)
            if(totWidth>maxWidth) maxWidth = totWidth
            layerWidths.push(totWidth)
        }

        
        // If any long-links, create placeholders for skipped layers
        this._virtualLinks = new Map()
        this.flow.longLinks = this.findLongLinks(this.flow.links)
        for(const llink of this.flow.longLinks){
            let fakeParent = llink.link.from[0]
            for(const layerIdx of llink.skippedLayers){ 
                const nid = `longLinkPlaceHolder_${crypto.randomUUID()}`
                layers[layerIdx].push(nid)
                llink.interNodes.push(nid)
                // Placeholders are added after initial index computation; give them an index
                // so reorderLayers() can take them into account (otherwise they default to base=0).
                indexes[nid] = { base: layers[layerIdx].length - 1, ports: {} }
                // Virtual link: treat placeholder as receiving the same "from port" as the original long-link.
                // (Child port doesn't matter for placeholders since they have no ports.)
                this._virtualLinks.set(`${fakeParent}__${nid}`, {
                    from: [fakeParent, llink.link.from[1]],
                    to:   [nid,       llink.link.to[1]],
                })
                parents[nid] = [fakeParent]
                fakeParent = nid
            }
        }

        // Reorder layers to avoid crossings thanks to indexes
        this.reorderLayers(layers, parents, indexes, orientation)
        delete this._virtualLinks

        // Finally place everything
        if(orientation=='horizontal'){
            const fakeNodeHeight = 10
            let x = gapx
            for(const [idx, layer] of layers.entries()){
                let wMax = this.getMaxWidth(layer)
                let y = 0
                switch(align){
                    case'center':
                        y = ((maxHeight - layerHeights[idx]) / 2) + gapy
                        break
                    case'first':
                        y = gapy
                        break
                    case'last':
                        y = maxHeight - layerHeights[idx] + gapy
                        break
                    case 'auto':
                        //TODO
                        y = ((maxHeight - layerHeights[idx]) / 2) + gapy
                        break
                }
                for(const nid of layer){
                    if(!nid.startsWith('longLinkPlaceHolder_')) {
                        const bb =  this.stagedNodes[nid].getBoundingClientRect()
                        this.moveNode(nid, x, y, orientation, tween)
                        y +=  gapy + (this.stagedNodes[nid].offsetHeight || bb.height)
                    } else {
                        this.addFakeNode(nid, x, y, wMax*0.75, fakeNodeHeight)
                        this.moveNode(nid, x, y, orientation, tween)
                        y +=  gapy + fakeNodeHeight 
                    }
                }
                x += wMax + gapx
            }
        } else if(orientation=='vertical'){
            const fakeNodeWidth = 10
            let y = gapy
            for(const [idx, layer] of layers.entries()){
                let hMax = this.getMaxHeight(layer)
                let x = ((maxWidth - layerWidths[idx]) / 2) + gapx
                for(const nid of layer){
                    if(!nid.startsWith('longLinkPlaceHolder_')){
                        const bb = this.stagedNodes[nid].getBoundingClientRect()
                        this.moveNode(nid, x, y, orientation, tween)
                        x +=  gapx + (this.stagedNodes[nid].offsetWidth || bb.width)
                    } else {
                        this.addFakeNode(nid, x, y, fakeNodeWidth, hMax*0.75)
                        this.moveNode(nid, x, y, orientation, tween)
                        x +=  gapx + fakeNodeWidth 
                    }
                }
                y += hMax + gapy
            }            
        }
    }

    getMaxWidth(layer){
        return(layer.filter(nid => 
            !nid.startsWith('longLinkPlaceHolder_'))
            // Use offsetWidth (not impacted by CSS transforms) to keep autoPlace stable during zoom animations.
            .map(nid => (this.stagedNodes[nid].offsetWidth || this.stagedNodes[nid].getBoundingClientRect().width))
            .reduce((a, b) => a > b ? a : b, 0)
        )
    }

    getMaxHeight(layer){
        return(layer.filter(nid => 
            !nid.startsWith('longLinkPlaceHolder_'))
            // Use offsetHeight (not impacted by CSS transforms) to keep autoPlace stable during zoom animations.
            .map(nid => (this.stagedNodes[nid].offsetHeight || this.stagedNodes[nid].getBoundingClientRect().height))
            .reduce((a, b) => a > b ? a : b, 0)
        )
    }

    computePortOffsets(nid, orientation = 'horizontal'){
        const node = this.stagedNodes[nid]
        if(!node || !node.ports) return({})
        const nodeRect = node.getBoundingClientRect()
        const ports = Object.entries(node.ports)
            .map(([pid, p]) => {
                const r = p.el.getBoundingClientRect()
                const pos = (orientation == 'vertical')
                    ? (r.left + (r.width / 2) - nodeRect.left)
                    : (r.top  + (r.height / 2) - nodeRect.top)
                return({ pid, pos })
            })
            .sort((a, b) => a.pos - b.pos) // smaller pos => "higher/left" => smaller offset

        const denom = ports.length + 1
        const offsets = {}
        for(const [rank, item] of ports.entries()){
            offsets[item.pid] = rank / denom // always < 1
        }
        return(offsets)
    }

    reorderLayers(layers, parents, indexes, orientation = 'horizontal'){
        const swap = (vect, todo) => {
            for(const s of todo){
                [vect[s[0]], vect[s[1]]] = [vect[s[1]], vect[s[0]]]
            }
        }
        const adjIndex = (nid, portId) => {
            const info = indexes?.[nid]
            const base = (info && info.base !== undefined) ? info.base : 0
            const off = (portId && info?.ports?.[portId] !== undefined) ? info.ports[portId] : 0
            return(base + off)
        }
        for(const [lidx, layer] of layers.entries()){
            if(lidx==0) continue
            const toSwap = []
            for(let i=0; i<layer.length; i++){
                const nid1 = layer[i]
                // some parents can be in far layers, but at least one is in the prev layer (by definition of layer)
                const pnid1 = parents[nid1].find((nid => layers[lidx-1].includes(nid)))
                for(let j=i+1; j<layer.length; j++){
                    const nid2 = layer[j]
                    const pnid2 = parents[nid2].find((nid => layers[lidx-1].includes(nid)))
                    const link1 = (pnid1) ? this.getLink(pnid1, nid1) : null
                    const link2 = (pnid2) ? this.getLink(pnid2, nid2) : null
                    const p1 = adjIndex(pnid1, link1?.from?.[1])
                    const p2 = adjIndex(pnid2, link2?.from?.[1])
                    const c1 = adjIndex(nid1,  link1?.to?.[1])
                    const c2 = adjIndex(nid2,  link2?.to?.[1])

                    if(((p1 - p2) * (c1 - c2)) < 0) { // crossing (now refined by per-port ordering)
                        toSwap.push([i, j])
                    }
                }
            }
            swap(layer, toSwap)
            // Keep bases in sync with the new order so later layers use the updated positions
            for(const [idx, nid] of layer.entries()){
                if(!indexes[nid]) indexes[nid] = { base: idx, ports: {} }
                else indexes[nid].base = idx
            }
        }
    }

    moveNode(nid, destx, desty, orientation, duration = 200, cb) {
        const t0 = performance.now()
        const bb = this.stagedNodes[nid].getBoundingClientRect()
        const parentbb = this.stagedNodes[nid].parentElement.getBoundingClientRect()
        const x0=bb.x - parentbb.x
        const y0 = bb.y - parentbb.y
        function frame(t) {
            const p = Math.min((t - t0) / duration, 1)
            const k = p * p * (3 - 2 * p) // smoothstep            
            const x = x0 + (destx - x0) * k
            const y = y0 + (desty - y0) * k            
            this.stagedNodes[nid].style.left = `${x}px`
            this.stagedNodes[nid].style.top = `${y}px`
            this.updateWires(nid, orientation)
            
            if(p < 1) requestAnimationFrame(frame.bind(this))
        }    
        requestAnimationFrame(frame.bind(this))
    }

    updateWires(nid, orientation){        
        const wires = Object.keys(this.stagedWires)
            .filter(id => (id.startsWith(nid+'_')||id.endsWith('_'+nid)))
            .map(id => this.stagedWires[id])
        for(const wire of wires){
            const [nid1, nid2] = wire.dataset.id.split('_')
            const lnk = this.getLink(nid1, nid2)
            const longLink = this.flow.longLinks.find(item => (item.link.from[0] == lnk.from[0] && item.link.from[1] == lnk.from[1] && item.link.to[0] == lnk.to[0] && item.link.to[1] == lnk.to[1]))
            if(longLink) {
                const path = this.bezierInterNodes(nid1, lnk.from[1], nid2, lnk.to[1], longLink.interNodes, orientation, this.getBZAttribute('tension')) 
                wire.setAttribute('d', path)
            } else {
                const path = this.bezierNodes(nid1, lnk.from[1], nid2, lnk.to[1], this.getBZAttribute('tension'))
                wire.setAttribute('d', path)
            }
        }
    }


    
    getLink(nid1, nid2){
        const real = this.flow.links.find(item => ((item.from[0]==nid1) && (item.to[0]==nid2)))
        if(real) return(real)
        const v = this._virtualLinks?.get(`${nid1}__${nid2}`)
        if(v) return(v)
        return(null)
    }

    buildGraphStructures(nodes, links, includeLinkIndexes = false) {
        const parents = {}
        const adj = {}
        nodes.forEach(n => {
            parents[n.id] = []
            adj[n.id] = []
        })

        links.forEach((link, idx) => {
            const from = link.from[0]
            const to   = link.to[0]
            if(link.from[0] !== link.to[0]) { // Skip self-loops
                parents[to].push(from)
                if(includeLinkIndexes) {
                    adj[from].push({ to, linkIdx: idx })
                } else {
                    adj[from].push(to)
                }
            }
        })
        return({ parents, adj })
    }

    computeLayers(nodes, parents) {
        const layer = {}
        const dfs = (id) => {
            if (layer[id] !== undefined) return(layer[id])
            
            if (parents[id].length === 0) {
                layer[id] = 0
            } else {
                layer[id] = 1 + Math.max(...parents[id].map(dfs))
            }
            return(layer[id])
        }        
        nodes.forEach(n => dfs(n.id))
        const t = []
        for(const nid in layer) { 
            if(!t[layer[nid]]) t[layer[nid]]=[]
            t[layer[nid]].push(nid)
        } 
        return(t)
    }

    hasAnyLoop(nodes, links) {
        if(links.some(l => l.from[0] === l.to[0])) return(true) // self-loops
        
        const { adj } = this.buildGraphStructures(nodes, links) 
        const visiting = new Set(); 
        const visited = new Set()
        const dfs = (nid) => {
            if(visiting.has(nid)) {
                return(true)
            }

            if(visited.has(nid)) return(false)
            visiting.add(nid)
            for(const m of adj[nid]) {
                if(dfs(m)) {
                    return(true)
                }
            }
            visiting.delete(nid)
            visited.add(nid)
            return(false)
        }    
        return(nodes.map(n => n.id).some(dfs))
    }
    
    findBackEdges(nodes, links) {
        const { adj } = this.buildGraphStructures(nodes, links, true)
        const color = {}; nodes.forEach(n => color[n.id] = 'white')        
        const backEdges = []
        
        function dfs(u) {
            color[u] = 'gray'
            for (const neighbor of adj[u]) {
                const v = neighbor.to
                const linkIdx = neighbor.linkIdx
                if (color[v] === 'gray') {
                    backEdges.push(linkIdx)   // 👈 cycle edge - return link index
                } else if (color[v] === 'white') {
                    dfs(v)
                }
            }
            color[u] = 'black'
        }
        
        nodes.forEach(n => {
            if (color[n.id] === 'white') dfs(n.id)
        })
        
        return(backEdges)
    }

    findLongLinks(links) {
        let linksWithoutBackEdges
        if(this.hasAnyLoop(this.flow.nodes, this.flow.links)){
            const backEdges = this.findBackEdges(this.flow.nodes, this.flow.links)
            linksWithoutBackEdges = this.flow.links.filter((link, idx) => (!backEdges.includes(idx)) && (link.from[0] != link.to[0]))
        } else {
            linksWithoutBackEdges = this.flow.links
        }
        /// Yes that means we ignore long & back links !
        const { parents } = this.buildGraphStructures(this.flow.nodes, linksWithoutBackEdges)
        const layers = this.computeLayers(this.flow.nodes, parents)
        const crossLayerLinks = []
        for(const link of links){
            const from = link.from[0]
            const to = link.to[0]
            const idx1 = layers.findIndex(layer => layer.includes(from))
            const idx2 = layers.findIndex(layer => layer.includes(to))
            if(Math.abs(idx1-idx2)>1) {
                const lowerIdx = idx1<idx2 ? idx1 : idx2
                const higherIdx = idx1>idx2 ? idx1 : idx2
                crossLayerLinks.push({
                    link,
                    linkIdx: link.linkIdx,
                    interNodes: [],
                    skippedLayers: Array.from({ length: higherIdx - lowerIdx - 1 }, (_, i) => lowerIdx + i + 1),
                })
            }
        }
        return(crossLayerLinks)
    }
}

Buildoz.define('graflow', BZgraflow)