package d2dagrelayout

import (
	"context"
	_ "embed"
	"encoding/json"
	"fmt"
	"math"
	"regexp"
	"strings"

	"cdr.dev/slog"
	"github.com/dop251/goja"

	"oss.terrastruct.com/util-go/xdefer"

	"oss.terrastruct.com/util-go/go2"

	"oss.terrastruct.com/d2/d2graph"
	"oss.terrastruct.com/d2/d2target"
	"oss.terrastruct.com/d2/lib/geo"
	"oss.terrastruct.com/d2/lib/label"
	"oss.terrastruct.com/d2/lib/log"
	"oss.terrastruct.com/d2/lib/shape"
)

//go:embed setup.js
var setupJS string

//go:embed dagre.js
var dagreJS string

const (
	MIN_SEGMENT_LEN = 10
	MIN_RANK_SEP    = 60
	EDGE_LABEL_GAP  = 20
)

type ConfigurableOpts struct {
	NodeSep int `json:"nodesep"`
	EdgeSep int `json:"edgesep"`
}

var DefaultOpts = ConfigurableOpts{
	NodeSep: 60,
	EdgeSep: 20,
}

type DagreNode struct {
	ID     string  `json:"id"`
	X      float64 `json:"x"`
	Y      float64 `json:"y"`
	Width  float64 `json:"width"`
	Height float64 `json:"height"`
}

type DagreEdge struct {
	Points []*geo.Point `json:"points"`
}

type dagreOpts struct {
	// for a top to bottom graph: ranksep is y spacing, nodesep is x spacing, edgesep is x spacing
	ranksep int
	// graph direction: tb (top to bottom)| bt | lr | rl
	rankdir string

	ConfigurableOpts
}

func DefaultLayout(ctx context.Context, g *d2graph.Graph) (err error) {
	return Layout(ctx, g, nil)
}

func Layout(ctx context.Context, g *d2graph.Graph, opts *ConfigurableOpts) (err error) {
	if opts == nil {
		opts = &DefaultOpts
	}
	defer xdefer.Errorf(&err, "failed to dagre layout")

	debugJS := false
	vm := goja.New()
	if _, err := vm.RunString(dagreJS); err != nil {
		return err
	}
	if _, err := vm.RunString(setupJS); err != nil {
		return err
	}

	rootAttrs := dagreOpts{
		ConfigurableOpts: ConfigurableOpts{
			EdgeSep: opts.EdgeSep,
			NodeSep: opts.NodeSep,
		},
	}
	isHorizontal := false
	switch g.Root.Direction.Value {
	case "down":
		rootAttrs.rankdir = "TB"
	case "right":
		rootAttrs.rankdir = "LR"
		isHorizontal = true
	case "left":
		rootAttrs.rankdir = "RL"
		isHorizontal = true
	case "up":
		rootAttrs.rankdir = "BT"
	default:
		rootAttrs.rankdir = "TB"
	}

	maxContainerLabelHeight := 0
	for _, obj := range g.Objects {
		// TODO count root level container label sizes for ranksep
		if len(obj.ChildrenArray) == 0 || obj.Parent == g.Root {
			continue
		}
		if obj.HasLabel() {
			maxContainerLabelHeight = go2.Max(maxContainerLabelHeight, obj.LabelDimensions.Height+label.PADDING)
		}

		if obj.Icon != nil && obj.Shape.Value != d2target.ShapeImage {
			s := obj.ToShape()
			iconSize := d2target.GetIconSize(s.GetInnerBox(), string(label.InsideTopLeft))
			// Since dagre container labels are pushed up, we don't want a child container to collide
			maxContainerLabelHeight = go2.Max(maxContainerLabelHeight, (iconSize+label.PADDING*2)*2)
		}
	}

	maxLabelWidth := 0
	maxLabelHeight := 0
	for _, edge := range g.Edges {
		width := edge.LabelDimensions.Width
		height := edge.LabelDimensions.Height
		maxLabelWidth = go2.Max(maxLabelWidth, width)
		maxLabelHeight = go2.Max(maxLabelHeight, height)
	}

	if !isHorizontal {
		rootAttrs.ranksep = go2.Max(go2.Max(100, maxLabelHeight+40), maxContainerLabelHeight)
	} else {
		rootAttrs.ranksep = go2.Max(100, maxLabelWidth+40)
		// use existing config
		rootAttrs.NodeSep = rootAttrs.EdgeSep
		// configure vertical padding
		rootAttrs.EdgeSep = go2.Max(maxLabelHeight+40, maxContainerLabelHeight)
		// Note: non-containers have both of these as padding (rootAttrs.NodeSep + rootAttrs.EdgeSep)
	}

	configJS := setGraphAttrs(rootAttrs)
	if _, err := vm.RunString(configJS); err != nil {
		return err
	}

	loadScript := ""
	idToObj := make(map[string]*d2graph.Object)
	for _, obj := range g.Objects {
		id := obj.AbsID()
		idToObj[id] = obj

		width, height := obj.Width, obj.Height
		if obj.HasLabel() {
			if obj.HasOutsideBottomLabel() || obj.Icon != nil {
				height += float64(obj.LabelDimensions.Height) + label.PADDING
			}
			if len(obj.ChildrenArray) > 0 {
				height += float64(obj.LabelDimensions.Height) + label.PADDING
			}
		}
		// reserve extra space for 3d/multiple by providing dagre the larger dimensions
		dx, dy := obj.GetModifierElementAdjustments()
		width += dx
		height += dy

		loadScript += generateAddNodeLine(id, int(width), int(height))
		if obj.Parent != g.Root {
			loadScript += generateAddParentLine(id, obj.Parent.AbsID())
		}
	}
	for _, edge := range g.Edges {
		src, dst := getEdgeEndpoints(g, edge)

		width := edge.LabelDimensions.Width
		height := edge.LabelDimensions.Height

		numEdges := 0
		for _, e := range g.Edges {
			otherSrc, otherDst := getEdgeEndpoints(g, e)
			if (otherSrc == src && otherDst == dst) || (otherSrc == dst && otherDst == src) {
				numEdges++
			}
		}

		// We want to leave some gap between multiple edges
		if numEdges > 1 {
			switch g.Root.Direction.Value {
			case "down", "up", "":
				width += EDGE_LABEL_GAP
			case "left", "right":
				height += EDGE_LABEL_GAP
			}
		}

		loadScript += generateAddEdgeLine(src.AbsID(), dst.AbsID(), edge.AbsID(), width, height)
	}

	if debugJS {
		log.Debug(ctx, "script", slog.F("all", setupJS+configJS+loadScript))
	}

	if _, err := vm.RunString(loadScript); err != nil {
		return err
	}

	if _, err := vm.RunString(`dagre.layout(g)`); err != nil {
		if debugJS {
			log.Warn(ctx, "layout error", slog.F("err", err))
		}
		return err
	}

	for i := range g.Objects {
		val, err := vm.RunString(fmt.Sprintf("JSON.stringify(g.node(g.nodes()[%d]))", i))
		if err != nil {
			return err
		}
		var dn DagreNode
		if err := json.Unmarshal([]byte(val.String()), &dn); err != nil {
			return err
		}
		if debugJS {
			log.Debug(ctx, "graph", slog.F("json", dn))
		}

		obj := idToObj[dn.ID]

		// dagre gives center of node
		obj.TopLeft = geo.NewPoint(math.Round(dn.X-dn.Width/2), math.Round(dn.Y-dn.Height/2))
		obj.Width = math.Ceil(dn.Width)
		obj.Height = math.Ceil(dn.Height)

		if obj.HasLabel() {
			if len(obj.ChildrenArray) > 0 {
				obj.LabelPosition = go2.Pointer(string(label.OutsideTopCenter))
			} else if obj.HasOutsideBottomLabel() {
				obj.LabelPosition = go2.Pointer(string(label.OutsideBottomCenter))
				// remove the extra height we added to the node when passing to dagre
				obj.Height -= float64(obj.LabelDimensions.Height) + label.PADDING
			} else if obj.Icon != nil {
				obj.LabelPosition = go2.Pointer(string(label.InsideTopCenter))
			} else {
				obj.LabelPosition = go2.Pointer(string(label.InsideMiddleCenter))
			}
		}
		if obj.Icon != nil {
			if len(obj.ChildrenArray) > 0 {
				obj.IconPosition = go2.Pointer(string(label.OutsideTopLeft))
				obj.LabelPosition = go2.Pointer(string(label.OutsideTopRight))
			} else {
				obj.IconPosition = go2.Pointer(string(label.InsideMiddleCenter))
			}
		}
	}

	for i, edge := range g.Edges {
		val, err := vm.RunString(fmt.Sprintf("JSON.stringify(g.edge(g.edges()[%d]))", i))
		if err != nil {
			return err
		}
		var de DagreEdge
		if err := json.Unmarshal([]byte(val.String()), &de); err != nil {
			return err
		}
		if debugJS {
			log.Debug(ctx, "graph", slog.F("json", de))
		}

		points := make([]*geo.Point, len(de.Points))
		for i := range de.Points {
			if edge.SrcArrow && !edge.DstArrow {
				points[len(de.Points)-i-1] = de.Points[i].Copy()
			} else {
				points[i] = de.Points[i].Copy()
			}
		}

		startIndex, endIndex := 0, len(points)-1
		start, end := points[startIndex], points[endIndex]

		// chop where edge crosses the source/target boxes since container edges were routed to a descendant
		if edge.Src != edge.Dst {
			for i := 1; i < len(points); i++ {
				segment := *geo.NewSegment(points[i-1], points[i])
				if intersections := edge.Src.Box.Intersections(segment); len(intersections) > 0 {
					start = intersections[0]
					startIndex = i - 1
				}

				if intersections := edge.Dst.Box.Intersections(segment); len(intersections) > 0 {
					end = intersections[0]
					endIndex = i
					break
				}
			}
		}
		points = points[startIndex : endIndex+1]
		points[0] = start
		points[len(points)-1] = end

		edge.Route = points
	}

	for _, obj := range g.Objects {
		if !obj.HasLabel() || len(obj.ChildrenArray) == 0 {
			continue
		}

		// usually you don't want to take away here more than what was added, which is the label height
		// however, if the label height is more than the ranksep/2, we'll have no padding around children anymore
		// so cap the amount taken off at ranksep/2
		subtract := float64(go2.Min(rootAttrs.ranksep/2, obj.LabelDimensions.Height+label.PADDING))

		obj.Height -= subtract

		// If the edge is connected to two descendants that are about to be downshifted, their whole route gets downshifted
		movedEdges := make(map[*d2graph.Edge]struct{})
		for _, e := range g.Edges {
			isSrcDesc := e.Src.IsDescendantOf(obj)
			isDstDesc := e.Dst.IsDescendantOf(obj)

			if isSrcDesc && isDstDesc {
				stepSize := subtract
				if e.Src != obj || e.Dst != obj {
					stepSize /= 2.
				}
				movedEdges[e] = struct{}{}
				for _, p := range e.Route {
					p.Y += stepSize
				}
			}
		}

		q := []*d2graph.Object{obj}
		// Downshift descendants and edges that have one endpoint connected to a descendant
		for len(q) > 0 {
			curr := q[0]
			q = q[1:]

			stepSize := subtract
			// The object itself needs to move down the height it was just subtracted
			// all descendants move half, to maintain vertical padding
			if curr != obj {
				stepSize /= 2.
			}
			curr.TopLeft.Y += stepSize
			almostEqual := func(a, b float64) bool {
				return b-1 <= a && a <= b+1
			}
			shouldMove := func(p *geo.Point) bool {
				if curr != obj {
					return true
				}
				if isHorizontal {
					// Only move horizontal edges if they are connected to the top side of the shrinking container
					return almostEqual(p.Y, obj.TopLeft.Y-stepSize)
				} else {
					// Edge should only move if it's not connected to the bottom side of the shrinking container
					return !almostEqual(p.Y, obj.TopLeft.Y+obj.Height)
				}
			}
			for _, e := range g.Edges {
				if _, ok := movedEdges[e]; ok {
					continue
				}
				moveWholeEdge := false
				if e.Src == curr {
					// Don't move src points on side of container
					if almostEqual(e.Route[0].X, obj.TopLeft.X) || almostEqual(e.Route[0].X, obj.TopLeft.X+obj.Width) {
						// Unless the dst is also on a container
						if !e.Dst.HasLabel() || len(e.Dst.ChildrenArray) <= 0 {
							continue
						}
					}
					if shouldMove(e.Route[0]) {
						if isHorizontal && e.Src.Parent != g.Root && e.Dst.Parent != g.Root {
							moveWholeEdge = true
						} else {
							e.Route[0].Y += stepSize
						}
					}
				}
				if !moveWholeEdge && e.Dst == curr {
					if shouldMove(e.Route[len(e.Route)-1]) {
						if isHorizontal && e.Dst.Parent != g.Root && e.Src.Parent != g.Root {
							moveWholeEdge = true
						} else {
							e.Route[len(e.Route)-1].Y += stepSize
						}
					}
				}

				if moveWholeEdge {
					for _, p := range e.Route {
						p.Y += stepSize / 2.
					}
					movedEdges[e] = struct{}{}
				}

			}
			q = append(q, curr.ChildrenArray...)
		}
	}

	// remove the extra width/height we added for 3d/multiple after all objects/connections are placed
	// and shift the shapes down accordingly
	for _, obj := range g.Objects {
		dx, dy := obj.GetModifierElementAdjustments()
		if dx != 0 || dy != 0 {
			obj.TopLeft.Y += dy
			obj.ShiftDescendants(0, dy)
			if !obj.IsContainer() {
				obj.Width -= dx
				obj.Height -= dy
			}
		}
	}

	for _, edge := range g.Edges {
		points := edge.Route
		startIndex, endIndex := 0, len(points)-1
		start, end := points[startIndex], points[endIndex]

		// arrowheads can appear broken if segments are very short from dagre routing a point just outside the shape
		// to fix this, we try extending the previous segment into the shape instead of having a very short segment
		if !start.Equals(points[0]) && startIndex+2 < len(points) {
			newStartingSegment := *geo.NewSegment(start, points[startIndex+1])
			if newStartingSegment.Length() < MIN_SEGMENT_LEN {
				// we don't want a very short segment right next to the source because it will mess up the arrowhead
				// instead we want to extend the next segment into the shape border if possible
				nextStart := points[startIndex+1]
				nextEnd := points[startIndex+2]

				// Note: in other direction to extend towards source
				nextSegment := *geo.NewSegment(nextStart, nextEnd)
				v := nextSegment.ToVector()
				extendedStart := nextEnd.ToVector().Add(v.AddLength(MIN_SEGMENT_LEN)).ToPoint()
				extended := *geo.NewSegment(nextEnd, extendedStart)

				if intersections := edge.Src.Box.Intersections(extended); len(intersections) > 0 {
					start = intersections[0]
					startIndex += 1
				}
			}
		}
		if !end.Equals(points[len(points)-1]) && endIndex-2 >= 0 {
			newEndingSegment := *geo.NewSegment(end, points[endIndex-1])
			if newEndingSegment.Length() < MIN_SEGMENT_LEN {
				// extend the prev segment into the shape border if possible
				prevStart := points[endIndex-2]
				prevEnd := points[endIndex-1]

				prevSegment := *geo.NewSegment(prevStart, prevEnd)
				v := prevSegment.ToVector()
				extendedEnd := prevStart.ToVector().Add(v.AddLength(MIN_SEGMENT_LEN)).ToPoint()
				extended := *geo.NewSegment(prevStart, extendedEnd)

				if intersections := edge.Dst.Box.Intersections(extended); len(intersections) > 0 {
					end = intersections[0]
					endIndex -= 1
				}
			}
		}

		var originalSrcTL, originalDstTL *geo.Point
		// if the edge passes through 3d/multiple, use the offset box for tracing to border
		if srcDx, srcDy := edge.Src.GetModifierElementAdjustments(); srcDx != 0 || srcDy != 0 {
			if start.X > edge.Src.TopLeft.X+srcDx &&
				start.Y < edge.Src.TopLeft.Y+edge.Src.Height-srcDy {
				originalSrcTL = edge.Src.TopLeft.Copy()
				edge.Src.TopLeft.X += srcDx
				edge.Src.TopLeft.Y -= srcDy
			}
		}
		if dstDx, dstDy := edge.Dst.GetModifierElementAdjustments(); dstDx != 0 || dstDy != 0 {
			if end.X > edge.Dst.TopLeft.X+dstDx &&
				end.Y < edge.Dst.TopLeft.Y+edge.Dst.Height-dstDy {
				originalDstTL = edge.Dst.TopLeft.Copy()
				edge.Dst.TopLeft.X += dstDx
				edge.Dst.TopLeft.Y -= dstDy
			}
		}

		srcShape := edge.Src.ToShape()
		dstShape := edge.Dst.ToShape()

		// trace the edge to the specific shape's border
		points[startIndex] = shape.TraceToShapeBorder(srcShape, start, points[startIndex+1])

		// if an edge to a container runs into its label, stop the edge at the label instead
		overlapsContainerLabel := false
		if edge.Dst.IsContainer() && edge.Dst.Label.Value != "" && !dstShape.Is(shape.TEXT_TYPE) {
			// assumes LabelPosition, LabelWidth, LabelHeight are all set if there is a label
			labelWidth := float64(edge.Dst.LabelDimensions.Width)
			labelHeight := float64(edge.Dst.LabelDimensions.Height)
			labelTL := label.Position(*edge.Dst.LabelPosition).
				GetPointOnBox(edge.Dst.Box, label.PADDING, labelWidth, labelHeight)

			endingSegment := geo.Segment{Start: points[endIndex-1], End: points[endIndex]}
			labelBox := geo.NewBox(labelTL, labelWidth, labelHeight)
			// add left/right padding to box
			labelBox.TopLeft.X -= label.PADDING
			labelBox.Width += 2 * label.PADDING
			if intersections := labelBox.Intersections(endingSegment); len(intersections) > 0 {
				overlapsContainerLabel = true
				// move ending segment to label intersection point
				points[endIndex] = intersections[0]
				endingSegment.End = intersections[0]
				// if the segment becomes too short, just merge it with the previous segment
				if endIndex-1 > 0 && endingSegment.Length() < MIN_SEGMENT_LEN {
					points[endIndex-1] = points[endIndex]
					endIndex--
				}
			}
		}
		if !overlapsContainerLabel {
			points[endIndex] = shape.TraceToShapeBorder(dstShape, end, points[endIndex-1])
		}
		points = points[startIndex : endIndex+1]

		// build a curved path from the dagre route
		vectors := make([]geo.Vector, 0, len(points)-1)
		for i := 1; i < len(points); i++ {
			vectors = append(vectors, points[i-1].VectorTo(points[i]))
		}

		path := make([]*geo.Point, 0)
		path = append(path, points[0])
		if len(vectors) > 1 {
			path = append(path, points[0].AddVector(vectors[0].Multiply(.8)))
			for i := 1; i < len(vectors)-2; i++ {
				p := points[i]
				v := vectors[i]
				path = append(path, p.AddVector(v.Multiply(.2)))
				path = append(path, p.AddVector(v.Multiply(.5)))
				path = append(path, p.AddVector(v.Multiply(.8)))
			}
			path = append(path, points[len(points)-2].AddVector(vectors[len(vectors)-1].Multiply(.2)))
			edge.IsCurve = true
		}
		path = append(path, points[len(points)-1])

		edge.Route = path
		// compile needs to assign edge label positions
		if edge.Label.Value != "" {
			edge.LabelPosition = go2.Pointer(string(label.InsideMiddleCenter))
		}

		// undo 3d/multiple offset
		if originalSrcTL != nil {
			edge.Src.TopLeft.X = originalSrcTL.X
			edge.Src.TopLeft.Y = originalSrcTL.Y
		}
		if originalDstTL != nil {
			edge.Dst.TopLeft.X = originalDstTL.X
			edge.Dst.TopLeft.Y = originalDstTL.Y
		}
	}

	return nil
}

func getEdgeEndpoints(g *d2graph.Graph, edge *d2graph.Edge) (*d2graph.Object, *d2graph.Object) {
	// dagre doesn't work with edges to containers so we connect container edges to their first child instead (going all the way down)
	// we will chop the edge where it intersects the container border so it only shows the edge from the container
	src := edge.Src
	for len(src.Children) > 0 && src.Class == nil && src.SQLTable == nil {
		// We want to get the bottom node of sources, setting its rank higher than all children
		src = getLongestEdgeChainTail(g, src)
	}
	dst := edge.Dst
	for len(dst.Children) > 0 && dst.Class == nil && dst.SQLTable == nil {
		dst = dst.ChildrenArray[0]

		// We want to get the top node of destinations
		for _, child := range dst.ChildrenArray {
			isHead := true
			for _, e := range g.Edges {
				if inContainer(e.Src, child) != nil && inContainer(e.Dst, dst) != nil {
					isHead = false
					break
				}
			}
			if isHead {
				dst = child
				break
			}
		}
	}
	if edge.SrcArrow && !edge.DstArrow {
		// for `b <- a`, edge.Edge is `a -> b` and we expect this routing result
		src, dst = dst, src
	}
	return src, dst
}

func setGraphAttrs(attrs dagreOpts) string {
	return fmt.Sprintf(`g.setGraph({
  ranksep: %d,
  edgesep: %d,
  nodesep: %d,
  rankdir: "%s",
});
`,
		attrs.ranksep,
		attrs.ConfigurableOpts.EdgeSep,
		attrs.ConfigurableOpts.NodeSep,
		attrs.rankdir,
	)
}

func escapeID(id string) string {
	// fixes \\
	id = strings.ReplaceAll(id, "\\", `\\`)
	// replaces \n with \\n whenever \n is not preceded by \ (does not replace \\n)
	re := regexp.MustCompile(`[^\\]\n`)
	id = re.ReplaceAllString(id, `\\n`)
	// avoid an unescaped \r becoming a \n in the layout result
	id = strings.ReplaceAll(id, "\r", `\r`)
	return id
}

func generateAddNodeLine(id string, width, height int) string {
	id = escapeID(id)
	return fmt.Sprintf("g.setNode(`%s`, { id: `%s`, width: %d, height: %d });\n", id, id, width, height)
}

func generateAddParentLine(childID, parentID string) string {
	return fmt.Sprintf("g.setParent(`%s`, `%s`);\n", escapeID(childID), escapeID(parentID))
}

func generateAddEdgeLine(fromID, toID, edgeID string, width, height int) string {
	return fmt.Sprintf("g.setEdge({v:`%s`, w:`%s`, name:`%s`}, { width:%d, height:%d, labelpos: `c` });\n", escapeID(fromID), escapeID(toID), escapeID(edgeID), width, height)
}

// getLongestEdgeChainTail gets the node at the end of the longest edge chain, because that will be the end of the container
// and is what external connections should connect with
func getLongestEdgeChainTail(g *d2graph.Graph, container *d2graph.Object) *d2graph.Object {
	rank := make(map[*d2graph.Object]int)

	for _, obj := range container.ChildrenArray {
		isHead := true
		for _, e := range g.Edges {
			if inContainer(e.Src, container) != nil && inContainer(e.Dst, obj) != nil {
				isHead = false
				break
			}
		}
		if !isHead {
			continue
		}
		rank[obj] = 1
		// BFS
		queue := []*d2graph.Object{obj}
		visited := make(map[*d2graph.Object]struct{})
		for len(queue) > 0 {
			curr := queue[0]
			queue = queue[1:]
			if _, ok := visited[curr]; ok {
				continue
			}
			visited[curr] = struct{}{}
			for _, e := range g.Edges {
				child := inContainer(e.Dst, container)
				if child == curr {
					continue
				}
				if child != nil && inContainer(e.Src, curr) != nil {
					rank[child] = go2.Max(rank[child], rank[curr]+1)
					queue = append(queue, child)
				}
			}
		}
	}
	max := int(math.MinInt32)
	var tail *d2graph.Object
	for _, obj := range container.ChildrenArray {
		if rank[obj] >= max {
			max = rank[obj]
			tail = obj
		}
	}
	return tail
}

func inContainer(obj, container *d2graph.Object) *d2graph.Object {
	if obj == nil {
		return nil
	}
	if obj == container {
		return obj
	}
	if obj.Parent == container {
		return obj
	}
	return inContainer(obj.Parent, container)
}