package engine

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

const historyNodeLimit = 4_000_000

// History applications borrow immutable policy-validated input trees. Metadata
// records answer presence and origin queries; replay reconstructs value changes.
// Replay reconciles with canonical decoding before domain resolution so both
// contracts agree on the effective result without retaining a tree per field.
type historyApplication struct {
	layer  Layer
	path   Path
	value  *document.Node
	origin Origin
}

func cloneHistoryApplications(values []historyApplication) []historyApplication {
	if values == nil {
		return nil
	}
	cloned := make([]historyApplication, len(values))
	for index, value := range values {
		cloned[index] = historyApplication{
			layer: value.layer, path: value.path.clone(), value: value.value,
			origin: cloneOrigin(value.origin),
		}
	}
	return cloned
}

func applicationOperationPath(application historyApplication, query Path) (Path, bool) {
	if !application.path.valid() || application.value == nil {
		return Path{}, false
	}
	if application.path.String() != "" {
		if pathsIntersect(application.path, query) {
			return application.path.clone(), true
		}
		return Path{}, false
	}
	if len(query.segments) == 0 {
		return Path{}, true
	}
	for length := 1; length <= len(query.segments); length++ {
		prefix := Path{segments: clonePathSegments(query.segments[:length], 0)}
		node, present := documentAtPath(application.value, prefix)
		if !present {
			return Path{}, false
		}
		if length == len(query.segments) || node.Kind != document.Mapping {
			return prefix, true
		}
	}
	return Path{}, false
}

func historyApplicationOrigin(application historyApplication, operationPath Path) Origin {
	if application.origin.Layer != "" {
		return cloneOrigin(application.origin)
	}
	origin := Origin{Layer: application.layer}
	relative, ok := relativeHistoryPath(application.path, operationPath)
	if !ok {
		return origin
	}
	if node, present := documentAtPath(application.value, relative); present {
		origin.Locations = []Location{publicLocation(node.Location)}
	}
	return origin
}

func relativeHistoryPath(root, path Path) (Path, bool) {
	if !pathContains(root, path) {
		return Path{}, false
	}
	return Path{segments: clonePathSegments(path.segments[len(root.segments):], 0)}, true
}

func pathsIntersect(left, right Path) bool {
	return pathContains(left, right) || pathContains(right, left)
}

func applyHistoryApplication(root **document.Node, application historyApplication) {
	if application.path.String() == "" {
		mergeHistoryDocument(root, application.value)
		return
	}
	mergeHistoryAtPath(root, application.path, application.value)
}

func mergeHistoryDocument(target **document.Node, incoming *document.Node) {
	if incoming == nil {
		return
	}
	if *target == nil || (*target).Kind != document.Mapping || incoming.Kind != document.Mapping {
		*target = document.Clone(incoming)
		return
	}
	for _, entry := range incoming.Mapping {
		position := documentEntryIndex((*target).Mapping, entry.Key)
		if position < 0 {
			cloned := entry
			cloned.Value = document.Clone(entry.Value)
			(*target).Mapping = append((*target).Mapping, cloned)
			continue
		}
		mergeHistoryDocument(&(*target).Mapping[position].Value, entry.Value)
	}
}

func mergeHistoryAtPath(root **document.Node, path Path, incoming *document.Node) {
	if root == nil || *root == nil || len(path.segments) == 0 {
		mergeHistoryDocument(root, incoming)
		return
	}
	current := *root
	for index, segment := range path.segments {
		if current.Kind != document.Mapping || segment.kind == pathSegmentIndex {
			return
		}
		position := documentEntryIndex(current.Mapping, segment.key)
		if index == len(path.segments)-1 {
			if position < 0 {
				current.Mapping = append(current.Mapping, document.Entry{Key: segment.key, Value: document.Clone(incoming)})
			} else {
				mergeHistoryDocument(&current.Mapping[position].Value, incoming)
			}
			return
		}
		if position < 0 {
			child := &document.Node{Kind: document.Mapping}
			current.Mapping = append(current.Mapping, document.Entry{Key: segment.key, Value: child})
			current = child
		} else {
			current = current.Mapping[position].Value
		}
	}
}

// Resolution records describe one before/final transformation, not assignment
// order. A parent already carries its descendants' final values; merge overlapping
// intent into that event rather than replay a child assignment a second time.
func coalescedResolutionSnapshots(snapshots []resolutionSnapshot) []resolutionSnapshot {
	groups := make([]resolutionSnapshot, 0, len(snapshots))
	for _, snapshot := range snapshots {
		merged := false
		for i := range groups {
			if !pathContains(groups[i].change.Path, snapshot.change.Path) {
				continue
			}
			for _, reason := range snapshot.change.Reasons {
				groups[i].change.Reasons = appendUniqueString(groups[i].change.Reasons, reason)
			}
			for _, dependency := range snapshot.change.Dependencies {
				groups[i].change.Dependencies = appendUniquePath(groups[i].change.Dependencies, dependency)
			}
			if snapshot.change.Origin.Operation == ChangeNormalization {
				groups[i].change.Origin.Operation = ChangeNormalization
			}
			merged = true
			break
		}
		if !merged {
			snapshot.change = cloneChange(snapshot.change)
			groups = append(groups, snapshot)
		}
	}
	return groups
}

func replaceHistoryPath(root **document.Node, path Path, replacement *document.Node) {
	if root == nil || *root == nil {
		return
	}
	if len(path.segments) == 0 {
		*root = document.Clone(replacement)
		return
	}
	current := *root
	for index, segment := range path.segments {
		last := index == len(path.segments)-1
		switch current.Kind {
		case document.Mapping:
			if segment.kind == pathSegmentIndex {
				return
			}
			position := documentEntryIndex(current.Mapping, segment.key)
			if position < 0 {
				if replacement == nil {
					return
				}
				child := &document.Node{Kind: document.Mapping}
				if last {
					child = document.Clone(replacement)
				}
				current.Mapping = append(current.Mapping, document.Entry{Key: segment.key, Value: child})
				if last {
					return
				}
				current = child
				continue
			}
			if last {
				if replacement == nil {
					current.Mapping = append(current.Mapping[:position], current.Mapping[position+1:]...)
				} else {
					current.Mapping[position].Value = document.Clone(replacement)
				}
				return
			}
			current = current.Mapping[position].Value
		case document.Sequence:
			position, ok := schemaIndex(segment)
			if !ok || position >= len(current.Sequence) {
				return
			}
			if last {
				if replacement != nil {
					current.Sequence[position] = document.Clone(replacement)
				}
				return
			}
			current = current.Sequence[position]
		default:
			return
		}
	}
}

func historyNodesWithinLimit(baseline, input, final *document.Node, applications []historyApplication, resolutions []resolutionSnapshot) bool {
	return historyNodesWithin(historyNodeLimit, baseline, input, final, applications, resolutions)
}

func historyNodesWithin(limit int, baseline, input, final *document.Node, applications []historyApplication, resolutions []resolutionSnapshot) bool {
	seen := make(map[*document.Node]bool)
	count := 0
	var visit func(*document.Node) bool
	visit = func(node *document.Node) bool {
		if node == nil || seen[node] {
			return true
		}
		seen[node] = true
		count++
		if count > limit {
			return false
		}
		for _, entry := range node.Mapping {
			if !visit(entry.Value) {
				return false
			}
		}
		for _, child := range node.Sequence {
			if !visit(child) {
				return false
			}
		}
		return true
	}
	if !visit(baseline) || !visit(input) || !visit(final) {
		return false
	}
	for _, application := range applications {
		if !visit(application.value) {
			return false
		}
	}
	for _, resolution := range resolutions {
		if !visit(resolution.before) || !visit(resolution.after) {
			return false
		}
	}
	return true
}