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

package btrfsutil

import (
	"context"
	"fmt"
	"sync"

	"github.com/datawire/dlib/derror"
	"github.com/datawire/dlib/dlog"

	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs"
	"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"
)

type oldRebuiltTree struct {
	RootErr error
	Items   *containers.RBTree[oldRebuiltTreeValue]
	Errors  *containers.IntervalTree[btrfsprim.Key, oldRebuiltTreeError]
}

type oldRebuiltTreeError struct {
	Min btrfsprim.Key
	Max btrfsprim.Key
	Err error
}

func (e oldRebuiltTreeError) Error() string {
	return fmt.Sprintf("keys %v-%v: %v", e.Min, e.Max, e.Err)
}

func (e oldRebuiltTreeError) Unwrap() error {
	return e.Err
}

type oldRebuiltTreeValue struct {
	Key      btrfsprim.Key
	ItemSize uint32

	Node nodeInfo
	Slot int
}

type nodeInfo struct {
	LAddr      btrfsvol.LogicalAddr
	Level      uint8
	Generation btrfsprim.Generation
	Owner      btrfsprim.ObjID
	MinItem    btrfsprim.Key
	MaxItem    btrfsprim.Key
}

// Compare implements containers.Ordered.
func (a oldRebuiltTreeValue) Compare(b oldRebuiltTreeValue) int {
	return a.Key.Compare(b.Key)
}

func newOldRebuiltTree() oldRebuiltTree {
	return oldRebuiltTree{
		Items: new(containers.RBTree[oldRebuiltTreeValue]),
		Errors: &containers.IntervalTree[btrfsprim.Key, oldRebuiltTreeError]{
			MinFn: func(err oldRebuiltTreeError) btrfsprim.Key {
				return err.Min
			},
			MaxFn: func(err oldRebuiltTreeError) btrfsprim.Key {
				return err.Max
			},
		},
	}
}

type OldRebuiltForrest struct {
	ctx   context.Context //nolint:containedctx // don't have an option while keeping the same API
	inner *btrfs.FS

	// btrfsprim.ROOT_TREE_OBJECTID
	rootTreeMu sync.Mutex
	rootTree   *oldRebuiltTree
	// for all other trees
	treesMu sync.Mutex
	trees   map[btrfsprim.ObjID]oldRebuiltTree
}

var _ btrfstree.TreeOperator = (*OldRebuiltForrest)(nil)

// NewOldRebuiltForrest wraps a *btrfs.FS to support looking up
// information from broken trees.
//
// Of the btrfstree.TreeOperator methods:
//
//   - TreeWalk works on broken trees
//   - TreeLookup relies on the tree being properly ordered (which a
//     broken tree might not be).
//   - TreeSearch relies on the tree being properly ordered (which a
//     broken tree might not be).
//   - TreeSearchAll relies on the tree being properly ordered (which a
//     broken tree might not be), and a bad node may cause it to not
//     return a truncated list of results.
//
// NewOldRebuiltForrest attempts to remedy these deficiencies by using
// .TreeWalk to build an out-of-FS index of all of the items in the
// tree, and re-implements TreeLookup, TreeSearch, and TreeSearchAll
// using that index.
func NewOldRebuiltForrest(ctx context.Context, inner *btrfs.FS) *OldRebuiltForrest {
	return &OldRebuiltForrest{
		ctx:   ctx,
		inner: inner,
	}
}

func (bt *OldRebuiltForrest) RebuiltTree(ctx context.Context, treeID btrfsprim.ObjID) oldRebuiltTree {
	if treeID == btrfsprim.ROOT_TREE_OBJECTID {
		bt.rootTreeMu.Lock()
		defer bt.rootTreeMu.Unlock()
		if bt.rootTree != nil {
			return *bt.rootTree
		}
	} else {
		bt.treesMu.Lock()
		defer bt.treesMu.Unlock()
		if bt.trees == nil {
			bt.trees = make(map[btrfsprim.ObjID]oldRebuiltTree)
		}
		if cacheEntry, exists := bt.trees[treeID]; exists {
			return cacheEntry
		}
	}

	cacheEntry := newOldRebuiltTree()
	dlog.Infof(ctx, "indexing tree %v...", treeID)
	bt.rawTreeWalk(ctx, treeID, &cacheEntry)
	dlog.Infof(ctx, "... done indexing tree %v", treeID)

	if treeID == btrfsprim.ROOT_TREE_OBJECTID {
		bt.rootTree = &cacheEntry
	} else {
		bt.trees[treeID] = cacheEntry
	}
	return cacheEntry
}

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

func (bt *OldRebuiltForrest) rawTreeWalk(ctx context.Context, treeID btrfsprim.ObjID, cacheEntry *oldRebuiltTree) {
	sb, err := bt.inner.Superblock()
	if err != nil {
		cacheEntry.RootErr = err
		return
	}
	root, err := btrfstree.LookupTreeRoot(ctx, bt, *sb, treeID)
	if err != nil {
		cacheEntry.RootErr = err
		return
	}

	errHandle := func(err *btrfstree.TreeError) {
		if len(err.Path) > 0 && err.Path.Node(-1).ToNodeAddr == 0 {
			// This is a panic because on the filesystems I'm working with it more likely
			// indicates a bug in my item parser than a problem with the filesystem.
			panic(fmt.Errorf("TODO: error parsing item: %w", err))
		}
		cacheEntry.Errors.Insert(oldRebuiltTreeError{
			Min: err.Path.Node(-1).ToKey,
			Max: err.Path.Node(-1).ToMaxKey,
			Err: err.Err,
		})
	}

	var curNode nodeInfo
	cbs := btrfstree.TreeWalkHandler{
		BadNode: func(path btrfstree.Path, node *btrfstree.Node, err error) error {
			if node != nil {
				curNode = nodeInfo{
					LAddr:      path.Node(-1).ToNodeAddr,
					Level:      node.Head.Level,
					Generation: node.Head.Generation,
					Owner:      node.Head.Owner,
					MinItem:    discardOK(node.MinItem()),
					MaxItem:    discardOK(node.MaxItem()),
				}
			}
			return err
		},
		Node: func(path btrfstree.Path, node *btrfstree.Node) error {
			curNode = nodeInfo{
				LAddr:      path.Node(-1).ToNodeAddr,
				Level:      node.Head.Level,
				Generation: node.Head.Generation,
				Owner:      node.Head.Owner,
				MinItem:    discardOK(node.MinItem()),
				MaxItem:    discardOK(node.MaxItem()),
			}
			return nil
		},
		Item: func(path btrfstree.Path, item btrfstree.Item) error {
			if cacheEntry.Items.Search(func(v oldRebuiltTreeValue) int { return item.Key.Compare(v.Key) }) != nil {
				// This is a panic because I'm not really sure what the best way to
				// handle this is, and so if this happens I want the program to crash
				// and force me to figure out how to handle it.
				panic(fmt.Errorf("dup key=%v in tree=%v", item.Key, treeID))
			}
			cacheEntry.Items.Insert(oldRebuiltTreeValue{
				Key:      item.Key,
				ItemSize: item.BodySize,

				Node: curNode,
				Slot: path.Node(-1).FromItemSlot,
			})
			return nil
		},
	}

	btrfstree.TreeOperatorImpl{NodeSource: bt.inner}.RawTreeWalk(ctx, *root, errHandle, cbs)
}

func (bt *OldRebuiltForrest) TreeLookup(treeID btrfsprim.ObjID, key btrfsprim.Key) (btrfstree.Item, error) {
	return bt.TreeSearch(treeID, btrfstree.SearchExactKey(key))
}

func (tree oldRebuiltTree) addErrs(fn func(btrfsprim.Key, uint32) int, err error) error {
	var errs derror.MultiError
	tree.Errors.Subrange(
		func(k btrfsprim.Key) int { return fn(k, 0) },
		func(v oldRebuiltTreeError) bool {
			errs = append(errs, v)
			return true
		})
	if len(errs) == 0 {
		return err
	}
	if err != nil {
		errs = append(errs, err)
	}
	return errs
}

func (bt *OldRebuiltForrest) readNode(nodeInfo nodeInfo) *btrfstree.Node {
	sb, err := bt.inner.Superblock()
	if err != nil {
		panic(fmt.Errorf("should not happen: i/o error: %w", err))
	}

	node, err := btrfstree.ReadNode[btrfsvol.LogicalAddr](bt.inner, *sb, nodeInfo.LAddr, btrfstree.NodeExpectations{
		LAddr:      containers.OptionalValue(nodeInfo.LAddr),
		Level:      containers.OptionalValue(nodeInfo.Level),
		Generation: containers.OptionalValue(nodeInfo.Generation),
		Owner: func(treeID btrfsprim.ObjID) error {
			if treeID != nodeInfo.Owner {
				return fmt.Errorf("expected owner=%v but claims to have owner=%v",
					nodeInfo.Owner, treeID)
			}
			return nil
		},
		MinItem: containers.OptionalValue(nodeInfo.MinItem),
		MaxItem: containers.OptionalValue(nodeInfo.MaxItem),
	})
	if err != nil {
		panic(fmt.Errorf("should not happen: i/o error: %w", err))
	}

	return node
}

func (bt *OldRebuiltForrest) TreeSearch(treeID btrfsprim.ObjID, searcher btrfstree.TreeSearcher) (btrfstree.Item, error) {
	tree := bt.RebuiltTree(bt.ctx, treeID)
	if tree.RootErr != nil {
		return btrfstree.Item{}, tree.RootErr
	}

	indexItem := tree.Items.Search(func(indexItem oldRebuiltTreeValue) int {
		return searcher.Search(indexItem.Key, indexItem.ItemSize)
	})
	if indexItem == nil {
		return btrfstree.Item{}, fmt.Errorf("item with %s: %w", searcher, tree.addErrs(searcher.Search, btrfstree.ErrNoItem))
	}

	node := bt.readNode(indexItem.Value.Node)
	defer node.Free()

	item := node.BodyLeaf[indexItem.Value.Slot]
	item.Body = item.Body.CloneItem()

	// Since we were only asked to return 1 item, it isn't
	// necessary to augment this `nil` with tree.addErrs().
	return item, nil
}

func (bt *OldRebuiltForrest) TreeSearchAll(treeID btrfsprim.ObjID, searcher btrfstree.TreeSearcher) ([]btrfstree.Item, error) {
	tree := bt.RebuiltTree(bt.ctx, treeID)
	if tree.RootErr != nil {
		return nil, tree.RootErr
	}

	var ret []btrfstree.Item
	var node *btrfstree.Node
	tree.Items.Subrange(
		func(indexItem oldRebuiltTreeValue) int {
			return searcher.Search(indexItem.Key, indexItem.ItemSize)
		},
		func(rbNode *containers.RBNode[oldRebuiltTreeValue]) bool {
			if node == nil || node.Head.Addr != rbNode.Value.Node.LAddr {
				node.Free()
				node = bt.readNode(rbNode.Value.Node)
			}
			item := node.BodyLeaf[rbNode.Value.Slot]
			item.Body = item.Body.CloneItem()
			ret = append(ret, item)
			return true
		})
	node.Free()

	var err error
	if len(ret) == 0 {
		err = btrfstree.ErrNoItem
	}
	err = tree.addErrs(searcher.Search, err)
	if err != nil {
		err = fmt.Errorf("items with %s: %w", searcher, err)
	}

	return ret, err
}

func (bt *OldRebuiltForrest) TreeWalk(ctx context.Context, treeID btrfsprim.ObjID, errHandle func(*btrfstree.TreeError), cbs btrfstree.TreeWalkHandler) {
	tree := bt.RebuiltTree(ctx, treeID)
	if tree.RootErr != nil {
		errHandle(&btrfstree.TreeError{
			Path: btrfstree.Path{{
				FromTree: treeID,
				ToMaxKey: btrfsprim.MaxKey,
			}},
			Err: tree.RootErr,
		})
		return
	}
	if cbs.Item == nil {
		return
	}
	var node *btrfstree.Node
	tree.Items.Range(func(indexItem *containers.RBNode[oldRebuiltTreeValue]) bool {
		if ctx.Err() != nil {
			return false
		}
		if bt.ctx.Err() != nil {
			return false
		}
		if node == nil || node.Head.Addr != indexItem.Value.Node.LAddr {
			node.Free()
			node = bt.readNode(indexItem.Value.Node)
		}
		item := node.BodyLeaf[indexItem.Value.Slot]

		itemPath := btrfstree.Path{
			{
				FromTree:         treeID,
				ToNodeAddr:       indexItem.Value.Node.LAddr,
				ToNodeGeneration: indexItem.Value.Node.Generation,
				ToNodeLevel:      indexItem.Value.Node.Level,
				ToKey:            indexItem.Value.Node.MinItem,
				ToMaxKey:         indexItem.Value.Node.MaxItem,
			},
			{
				FromTree:     indexItem.Value.Node.Owner,
				FromItemSlot: indexItem.Value.Slot,
				ToKey:        indexItem.Value.Key,
				ToMaxKey:     indexItem.Value.Key,
			},
		}
		if err := cbs.Item(itemPath, item); err != nil {
			errHandle(&btrfstree.TreeError{Path: itemPath, Err: err})
		}
		return true
	})
	node.Free()
}

func (bt *OldRebuiltForrest) Superblock() (*btrfstree.Superblock, error) {
	return bt.inner.Superblock()
}

func (bt *OldRebuiltForrest) ReadAt(p []byte, off btrfsvol.LogicalAddr) (int, error) {
	return bt.inner.ReadAt(p, off)
}