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

package btrfs

import (
	"fmt"

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

// A TreeRoot is more-or-less a btrfsitem.Root, but simpler; returned by
// LookupTreeRoot.
type TreeRoot struct {
	TreeID     ObjID
	RootNode   btrfsvol.LogicalAddr
	Level      uint8
	Generation Generation
}

// LookupTreeRoot is a utility function to help with implementing the 'Trees'
// interface.
func LookupTreeRoot(fs Trees, treeID ObjID) (*TreeRoot, error) {
	sb, err := fs.Superblock()
	if err != nil {
		return nil, err
	}
	switch treeID {
	case ROOT_TREE_OBJECTID:
		return &TreeRoot{
			TreeID:     treeID,
			RootNode:   sb.RootTree,
			Level:      sb.RootLevel,
			Generation: sb.Generation, // XXX: same generation as LOG_TREE?
		}, nil
	case CHUNK_TREE_OBJECTID:
		return &TreeRoot{
			TreeID:     treeID,
			RootNode:   sb.ChunkTree,
			Level:      sb.ChunkLevel,
			Generation: sb.ChunkRootGeneration,
		}, nil
	case TREE_LOG_OBJECTID:
		return &TreeRoot{
			TreeID:     treeID,
			RootNode:   sb.LogTree,
			Level:      sb.LogLevel,
			Generation: sb.Generation, // XXX: same generation as ROOT_TREE?
		}, nil
	case BLOCK_GROUP_TREE_OBJECTID:
		return &TreeRoot{
			TreeID:     treeID,
			RootNode:   sb.BlockGroupRoot,
			Level:      sb.BlockGroupRootLevel,
			Generation: sb.BlockGroupRootGeneration,
		}, nil
	default:
		rootItem, err := fs.TreeSearch(ROOT_TREE_OBJECTID, func(key Key, _ uint32) int {
			if key.ObjectID == treeID && key.ItemType == btrfsitem.ROOT_ITEM_KEY {
				return 0
			}
			return Key{
				ObjectID: treeID,
				ItemType: btrfsitem.ROOT_ITEM_KEY,
				Offset:   0,
			}.Cmp(key)
		})
		if err != nil {
			return nil, err
		}
		rootItemBody, ok := rootItem.Body.(btrfsitem.Root)
		if !ok {
			return nil, fmt.Errorf("malformed ROOT_ITEM for tree %v", treeID)
		}
		return &TreeRoot{
			TreeID:     treeID,
			RootNode:   rootItemBody.ByteNr,
			Level:      rootItemBody.Level,
			Generation: rootItemBody.Generation,
		}, nil
	}
}