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

package btrfstree

import (
	"fmt"

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

type NodeFile interface {
	diskio.File[btrfsvol.LogicalAddr]
	Superblock() (*Superblock, error)

	// ParentTree, given a tree ID, returns that tree's parent
	// tree, if it has one.
	//
	//  - non-zero, true : the parent tree ID
	//
	//  - 0, true : the tree does not have a parent
	//
	//  - any, false : the tree's parent information could not be
	//    looked up
	ParentTree(btrfsprim.ObjID) (btrfsprim.ObjID, bool)
}

// FSReadNode is a utility function to help with implementing the
// 'NodeSource' interface.
func FSReadNode(
	fs NodeFile,
	path Path,
) (*Node, error) {
	sb, err := fs.Superblock()
	if err != nil {
		return nil, fmt.Errorf("btrfs.FS.ReadNode: %w", err)
	}

	var treeParents []btrfsprim.ObjID
	checkOwner := func(owner btrfsprim.ObjID) error {
		exp := path.Node(-1).FromTree
		for {
			if owner == exp {
				return nil
			}
			treeParents = append(treeParents, exp)
			var ok bool
			exp, ok = fs.ParentTree(exp)
			if !ok {
				// Failed look up parent info; fail open.
				return nil
			}
			if exp == 0 {
				// End of the line.
				return fmt.Errorf("expected owner in %v but claims to have owner=%v",
					treeParents, owner)
			}
		}
	}

	return ReadNode[btrfsvol.LogicalAddr](fs, *sb, path.Node(-1).ToNodeAddr, NodeExpectations{
		LAddr:      containers.OptionalValue(path.Node(-1).ToNodeAddr),
		Level:      containers.OptionalValue(path.Node(-1).ToNodeLevel),
		Generation: containers.OptionalValue(path.Node(-1).ToNodeGeneration),
		Owner:      checkOwner,
		MinItem:    containers.OptionalValue(path.Node(-1).ToKey),
		MaxItem:    containers.OptionalValue(path.Node(-1).ToMaxKey),
	})
}