// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
//
// SPDX-License-Identifier: GPL-2.0-or-later

package btrfsutil

import (
	"context"
	"fmt"
	"reflect"
	"time"

	"github.com/datawire/dlib/dlog"

	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsitem"
	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsprim"
	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfstree"
	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsvol"
	"git.lukeshu.com/btrfs-progs-ng/lib/containers"
	"git.lukeshu.com/btrfs-progs-ng/lib/diskio"
	"git.lukeshu.com/btrfs-progs-ng/lib/maps"
	"git.lukeshu.com/btrfs-progs-ng/lib/slices"
	"git.lukeshu.com/btrfs-progs-ng/lib/textui"
)

type Node struct {
	Level      uint8
	Generation btrfsprim.Generation
	Owner      btrfsprim.ObjID
	NumItems   uint32
	MinItem    btrfsprim.Key
	MaxItem    btrfsprim.Key
	Items      []btrfsprim.Key
}

func (n Node) String() string {
	if reflect.ValueOf(n).IsZero() {
		return "{}"
	}
	return fmt.Sprintf(`{lvl:%v, gen:%v, tree:%v, cnt:%v, min:(%v,%v,%v), max:(%v,%v,%v)}`,
		n.Level, n.Generation, n.Owner, n.NumItems,
		n.MinItem.ObjectID, n.MinItem.ItemType, n.MinItem.Offset,
		n.MaxItem.ObjectID, n.MaxItem.ItemType, n.MaxItem.Offset)
}

type Edge struct {
	// It is invalid for both 'FromRoot' and 'FromNode' to be
	// non-zero.  If both are zero, then the Edge is from the
	// superblock.
	FromRoot btrfsvol.LogicalAddr
	FromNode btrfsvol.LogicalAddr
	FromItem int // only valid if one of FromRoot or FromNode is non-zero

	FromTree btrfsprim.ObjID

	ToNode       btrfsvol.LogicalAddr
	ToLevel      uint8
	ToKey        btrfsprim.Key
	ToGeneration btrfsprim.Generation
}

func (kp Edge) String() string {
	var from string
	switch {
	case kp.FromRoot != 0:
		from = fmt.Sprintf("root@%v[%d]:%v",
			kp.FromRoot, kp.FromItem, kp.FromTree)
	case kp.FromNode != 0:
		from = fmt.Sprintf("{node:%v, tree:%v}[%d]",
			kp.FromNode, kp.FromTree, kp.FromItem)
	default:
		from = fmt.Sprintf("superblock:%v", kp.FromTree)
	}
	return fmt.Sprintf(`%s -> {n:%v,l:%v,g:%v,k:(%v,%v,%v)}`,
		from,
		kp.ToNode, kp.ToLevel, kp.ToGeneration,
		kp.ToKey.ObjectID,
		kp.ToKey.ItemType,
		kp.ToKey.Offset)
}

type Graph struct {
	Nodes     map[btrfsvol.LogicalAddr]Node
	BadNodes  map[btrfsvol.LogicalAddr]error
	EdgesFrom map[btrfsvol.LogicalAddr][]*Edge
	EdgesTo   map[btrfsvol.LogicalAddr][]*Edge
}

func (g Graph) insertEdge(ptr *Edge) {
	if ptr.ToNode == 0 {
		panic("kp.ToNode should not be zero")
	}
	if ptr.FromRoot != 0 && ptr.FromNode != 0 {
		panic("kp.FromRoot and kp.FromNode should not both be set")
	}
	if (ptr.FromRoot == 0 && ptr.FromNode == 0) && ptr.FromItem != 0 {
		panic("kp.FromItem should only be set if either kp.FromRoot or kp.FromItem is set")
	}
	g.EdgesFrom[ptr.FromNode] = append(g.EdgesFrom[ptr.FromNode], ptr)
	g.EdgesTo[ptr.ToNode] = append(g.EdgesTo[ptr.ToNode], ptr)
}

func (g Graph) insertTreeRoot(sb btrfstree.Superblock, treeID btrfsprim.ObjID) {
	treeInfo, err := btrfstree.LookupTreeRoot(nil, sb, treeID)
	if err != nil {
		// This shouldn't ever happen for treeIDs that are
		// mentioned directly in the superblock; which are the
		// only trees for which we should call
		// .insertTreeRoot().
		panic(fmt.Errorf("LookupTreeRoot(%v): %w", treeID, err))
	}
	if treeInfo.RootNode == 0 {
		return
	}
	g.insertEdge(&Edge{
		FromTree:     treeID,
		ToNode:       treeInfo.RootNode,
		ToLevel:      treeInfo.Level,
		ToGeneration: treeInfo.Generation,
	})
}

func NewGraph(sb btrfstree.Superblock) *Graph {
	g := &Graph{
		Nodes:     make(map[btrfsvol.LogicalAddr]Node),
		BadNodes:  make(map[btrfsvol.LogicalAddr]error),
		EdgesFrom: make(map[btrfsvol.LogicalAddr][]*Edge),
		EdgesTo:   make(map[btrfsvol.LogicalAddr][]*Edge),
	}

	// These 4 trees are mentioned directly in the superblock, so
	// they are always seen.
	g.insertTreeRoot(sb, btrfsprim.ROOT_TREE_OBJECTID)
	g.insertTreeRoot(sb, btrfsprim.CHUNK_TREE_OBJECTID)
	g.insertTreeRoot(sb, btrfsprim.TREE_LOG_OBJECTID)
	g.insertTreeRoot(sb, btrfsprim.BLOCK_GROUP_TREE_OBJECTID)

	return g
}

func (g Graph) InsertNode(nodeRef *diskio.Ref[btrfsvol.LogicalAddr, btrfstree.Node]) {
	nodeData := Node{
		Level:      nodeRef.Data.Head.Level,
		Generation: nodeRef.Data.Head.Generation,
		Owner:      nodeRef.Data.Head.Owner,
		NumItems:   nodeRef.Data.Head.NumItems,
		MinItem:    discardOK(nodeRef.Data.MinItem()),
		MaxItem:    discardOK(nodeRef.Data.MaxItem()),
	}

	if nodeRef.Data.Head.Level == 0 {
		cnt := 0
		for _, item := range nodeRef.Data.BodyLeaf {
			if _, ok := item.Body.(*btrfsitem.Root); ok {
				cnt++
			}
		}
		kps := make([]Edge, 0, cnt)
		keys := make([]btrfsprim.Key, len(nodeRef.Data.BodyLeaf))
		nodeData.Items = keys
		g.Nodes[nodeRef.Addr] = nodeData
		for i, item := range nodeRef.Data.BodyLeaf {
			keys[i] = item.Key
			if itemBody, ok := item.Body.(*btrfsitem.Root); ok {
				kps = append(kps, Edge{
					FromRoot:     nodeRef.Addr,
					FromItem:     i,
					FromTree:     item.Key.ObjectID,
					ToNode:       itemBody.ByteNr,
					ToLevel:      itemBody.Level,
					ToGeneration: itemBody.Generation,
				})
				g.insertEdge(&kps[len(kps)-1])
			}
		}
	} else {
		g.Nodes[nodeRef.Addr] = nodeData
		kps := make([]Edge, len(nodeRef.Data.BodyInternal))
		for i, kp := range nodeRef.Data.BodyInternal {
			kps[i] = Edge{
				FromNode:     nodeRef.Addr,
				FromItem:     i,
				FromTree:     nodeRef.Data.Head.Owner,
				ToNode:       kp.BlockPtr,
				ToLevel:      nodeRef.Data.Head.Level - 1,
				ToKey:        kp.Key,
				ToGeneration: kp.Generation,
			}
			g.insertEdge(&kps[i])
		}
	}
}

func (g Graph) FinalCheck(ctx context.Context, fs diskio.File[btrfsvol.LogicalAddr], sb btrfstree.Superblock) error {
	var stats textui.Portion[int]
	_ctx := ctx

	ctx = dlog.WithField(_ctx, "btrfsinspect.rebuild-nodes.read.substep", "check-keypointers")
	dlog.Info(_ctx, "Checking keypointers for dead-ends...")
	progressWriter := textui.NewProgress[textui.Portion[int]](ctx, dlog.LogLevelInfo, textui.Tunable(1*time.Second))
	stats.D = len(g.EdgesTo)
	progressWriter.Set(stats)
	for laddr := range g.EdgesTo {
		if _, ok := g.Nodes[laddr]; !ok {
			_, err := btrfstree.ReadNode[btrfsvol.LogicalAddr](fs, sb, laddr, btrfstree.NodeExpectations{
				LAddr: containers.Optional[btrfsvol.LogicalAddr]{OK: true, Val: laddr},
			})
			if err == nil {
				progressWriter.Done()
				return fmt.Errorf("node@%v exists but was not in node scan results", laddr)
			}
			g.BadNodes[laddr] = err
		}
		stats.N++
		progressWriter.Set(stats)
	}
	progressWriter.Done()
	dlog.Info(ctx, "... done checking keypointers")

	ctx = dlog.WithField(_ctx, "btrfsinspect.rebuild-nodes.read.substep", "check-for-loops")
	dlog.Info(_ctx, "Checking for btree loops...")
	stats.D = len(g.Nodes)
	stats.N = 0
	progressWriter = textui.NewProgress[textui.Portion[int]](ctx, dlog.LogLevelInfo, textui.Tunable(1*time.Second))
	progressWriter.Set(stats)
	visited := make(containers.Set[btrfsvol.LogicalAddr], len(g.Nodes))
	numLoops := 0
	var checkNode func(node btrfsvol.LogicalAddr, stack []btrfsvol.LogicalAddr)
	checkNode = func(node btrfsvol.LogicalAddr, stack []btrfsvol.LogicalAddr) {
		defer func() {
			stats.N = len(visited)
			progressWriter.Set(stats)
		}()
		if visited.Has(node) {
			return
		}
		if slices.Contains(node, stack) {
			numLoops++
			dlog.Error(ctx, "loop:")
			for _, line := range g.renderLoop(append(stack, node)) {
				dlog.Errorf(ctx, "    %s", line)
			}
			return
		}
		stack = append(stack, node)
		for _, kp := range g.EdgesTo[node] {
			checkNode(kp.FromNode, stack)
		}
		visited.Insert(node)
	}
	for _, node := range maps.SortedKeys(g.Nodes) {
		checkNode(node, nil)
	}
	progressWriter.Done()
	if numLoops > 0 {
		return fmt.Errorf("%d btree loops", numLoops)
	}
	dlog.Info(_ctx, "... done checking for loops")

	return nil
}

func discardOK[T any](val T, _ bool) T {
	return val
}