package configkit

import "gitea.maximumdirect.net/eric/ConfigKit/internal/engine"

// Difference describes one canonical changed region between two successful
// loads. Left is the earlier value and Right is the later value. Each snapshot
// is detached; Present distinguishes absence from an explicit null, and
// Redacted reports whether combined sensitivity affected that side. Mappings
// are compared recursively, while sequences are reported as atomic values.
// Records are ordered by canonical JSON pointer. HiddenChanged indicates that
// a value concealed by combined sensitivity changed, without revealing which
// concealed member changed.
type Difference struct {
	Path          Path
	Left          ValueSnapshot
	Right         ValueSnapshot
	HiddenChanged bool
}

// Diff compares the frozen effective values of two successful loads of the
// same configuration type. It does not reread sources, environment variables,
// or rerun defaults or resolvers. Equal values produce no records even when
// their sources, defaults, or resolution histories differ. Credential contents
// are not compared: typed secret references compare by reference name only.
//
// Both results must be non-nil successful loads with inspection state; nil or
// zero results return an error and no records. Load errors are returned by
// Load, so callers must handle those before calling Diff. Snapshots are safe
// for presentation but are not a complete reloadable configuration.
func Diff[T any](left, right *Result[T]) ([]Difference, error) {
	var leftInspection, rightInspection *engine.Inspection
	if left != nil {
		leftInspection = left.inspection
	}
	if right != nil {
		rightInspection = right.inspection
	}

	values, err := engine.Diff(leftInspection, rightInspection)
	if err != nil {
		return nil, err
	}
	differences := make([]Difference, len(values))
	for index, value := range values {
		differences[index] = Difference{
			Path:          fromEnginePath(value.Path),
			Left:          fromEngineValueSnapshot(value.Left),
			Right:         fromEngineValueSnapshot(value.Right),
			HiddenChanged: value.HiddenChanged,
		}
	}
	return differences, nil
}