package engine

import (
	"errors"

	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
)

var errDiffInspectionUnavailable = errors.New("configkit: diff inspection unavailable")

type diffRegion struct {
	path  Path
	left  *document.Node
	right *document.Node
}

func prepareDiffRegions(left, right *Inspection) ([]diffRegion, error) {
	if left == nil || left.final == nil || right == nil || right.final == nil {
		return nil, errDiffInspectionUnavailable
	}

	deltas := compareConfigurationValues(left.final, right.final)
	regions := make([]diffRegion, 0, len(deltas))
	for _, delta := range deltas {
		leftNode, leftPresent := documentAtPathWithLookup(left.final, delta.path, left.immutableLookup)
		if !leftPresent {
			leftNode = nil
		}
		rightNode, rightPresent := documentAtPathWithLookup(right.final, delta.path, right.immutableLookup)
		if !rightPresent {
			rightNode = nil
		}
		regions = append(regions, diffRegion{path: delta.path, left: leftNode, right: rightNode})
	}
	return regions, nil
}