package engine

import (
	"reflect"
	"strings"

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

// decodedOverrideResult keeps the typed pre-CLI projection and raw CLI
// contributions alongside the effective typed value and its inspection data.
type decodedOverrideResult struct {
	value     reflect.Value
	preCLI    *document.Node
	final     *document.Node
	presence  map[string]inputPresence
	origins   map[string]Origin
	overrides []preparedOverride
}

// applyDecodedOverrides assigns prepared CLI values to a detached, decoded
// configuration. Each sparse mapping is decoded against the current typed
// value, preserving omitted mapping fields while replacing supplied sequences.
func applyDecodedOverrides(
	schema *schemaDescriptor,
	decoded decodedConfiguration,
	batch preparedOverrideBatch,
	context decodeContext,
) (decodedOverrideResult, []decodeIssue) {
	if schema == nil || schema.root == nil || !decoded.value.IsValid() || decoded.value.Type() != schema.root.typeOf || decoded.final == nil {
		return decodedOverrideResult{}, []decodeIssue{{code: CodeSchemaUnsupportedType, message: "decoded configuration does not match the schema"}}
	}

	preCLI := document.Clone(decoded.final)
	working, cloneIssue := cloneConfiguration(schema, decoded.value, defaultProjectionLimits())
	if cloneIssue != nil {
		return decodedOverrideResult{}, []decodeIssue{decodeIssueFromProjection(cloneIssue)}
	}
	presence := cloneInputPresence(decoded.presence)
	origins := cloneOrigins(decoded.origins)
	currentProjection := document.Clone(decoded.final)

	for _, override := range batch.overrides {
		if len(override.path.segments) == 0 {
			return decodedOverrideResult{}, []decodeIssue{{code: CodeOverrideInvalidPath, message: "configuration override path is invalid", location: document.Location{SourceID: override.source.ID}}}
		}
		input, issue := decodedOverrideInput(override)
		if issue != nil {
			return decodedOverrideResult{}, []decodeIssue{*issue}
		}
		updated, issues := decodeValue(input, working, schema.root, Path{}, schema, context)
		if len(issues) != 0 {
			return decodedOverrideResult{}, issues
		}
		working = updated

		location := document.Location{SourceID: override.source.ID}
		recordOverrideAncestors(presence, origins, override.path, location)
		updateOverridePresence(presence, currentProjection, override.value, override.path, location)
		updateOverrideOrigins(origins, currentProjection, override.value, override.path, location)
	}
	final, projectionIssue := projectConfiguration(schema, working, defaultProjectionLimits())
	if projectionIssue != nil {
		return decodedOverrideResult{}, []decodeIssue{decodeIssueFromProjection(projectionIssue)}
	}

	// New fields created by decoding a partial mapping into a previously nil
	// pointer have no input origin. Fill those gaps as defaults while retaining
	// all surviving source and CLI contributions already in the origin map.
	fillDefaultOrigins(final, Path{}, origins)

	return decodedOverrideResult{
		value:     working,
		preCLI:    preCLI,
		final:     final,
		presence:  presence,
		origins:   origins,
		overrides: clonePreparedOverrides(batch.overrides),
	}, nil
}

func recordOverrideAncestors(presence map[string]inputPresence, origins map[string]Origin, path Path, location document.Location) {
	mergeOverlayOrigin(origins, Path{}, location, LayerCLI)
	prefix := Path{}
	for index, segment := range path.segments {
		prefix = prefix.Key(segment.key)
		if index == len(path.segments)-1 {
			break
		}
		pointer := prefix.String()
		if _, exists := presence[pointer]; !exists {
			presence[pointer] = inputPresence{location: location}
		}
		mergeOverlayOrigin(origins, prefix, location, LayerCLI)
	}
}

func decodedOverrideInput(override preparedOverride) (*document.Node, *decodeIssue) {
	location := document.Location{SourceID: override.source.ID}
	value := document.Clone(override.value)
	if value == nil {
		return nil, &decodeIssue{code: CodeOverrideInvalidPath, path: override.path.clone(), message: "configuration override value is invalid", location: location}
	}
	for index := len(override.path.segments) - 1; index >= 0; index-- {
		segment := override.path.segments[index]
		if segment.kind == pathSegmentIndex {
			return nil, &decodeIssue{code: CodeOverrideInvalidPath, path: override.path.clone(), message: "configuration override path is invalid", location: location}
		}
		value = &document.Node{
			Kind:     document.Mapping,
			Location: location,
			Mapping: []document.Entry{{
				Key: segment.key, KeyLocation: location, ValueLocation: location, Value: value,
			}},
		}
	}
	return value, nil
}

func cloneInputPresence(input map[string]inputPresence) map[string]inputPresence {
	cloned := make(map[string]inputPresence, len(input))
	for path, value := range input {
		cloned[path] = value
	}
	return cloned
}

func cloneOrigins(input map[string]Origin) map[string]Origin {
	cloned := make(map[string]Origin, len(input))
	for path, value := range input {
		cloned[path] = cloneOrigin(value)
	}
	return cloned
}

func clonePreparedOverrides(input []preparedOverride) []preparedOverride {
	cloned := make([]preparedOverride, len(input))
	for index, value := range input {
		cloned[index] = preparedOverride{
			path:   value.path.clone(),
			value:  document.Clone(value.value),
			source: value.source,
			bytes:  value.bytes,
			nodes:  value.nodes,
		}
	}
	return cloned
}

func updateOverridePresence(presence map[string]inputPresence, existing, incoming *document.Node, path Path, location document.Location) {
	if existing != nil && existing.Kind == document.Mapping && incoming.Kind == document.Mapping {
		if _, exists := presence[path.String()]; !exists {
			presence[path.String()] = inputPresence{location: location}
		}
		var index mappingIndex
		for _, entry := range incoming.Mapping {
			childPath := path.Key(entry.Key)
			position := index.find(existing, entry.Key)
			var previous *document.Node
			if position >= 0 {
				previous = existing.Mapping[position].Value
			}
			updateOverridePresence(presence, previous, entry.Value, childPath, location)
		}
		return
	}

	deletePresencePathSubtree(presence, path)
	collectPresence(incoming, path, presence)
}

func deletePresencePathSubtree(presence map[string]inputPresence, path Path) {
	pointer := path.String()
	for candidate := range presence {
		if candidate == pointer || strings.HasPrefix(candidate, pointer+"/") {
			delete(presence, candidate)
		}
	}
}

func updateOverrideOrigins(origins map[string]Origin, existing, incoming *document.Node, path Path, location document.Location) {
	if existing != nil && existing.Kind == document.Mapping && incoming.Kind == document.Mapping {
		mergeOverlayOrigin(origins, path, location, LayerCLI)
		var index mappingIndex
		for _, entry := range incoming.Mapping {
			childPath := path.Key(entry.Key)
			position := index.find(existing, entry.Key)
			var previous *document.Node
			if position >= 0 {
				previous = existing.Mapping[position].Value
			}
			updateOverrideOrigins(origins, previous, entry.Value, childPath, location)
		}
		return
	}

	pointer := path.String()
	for candidate := range origins {
		if candidate == pointer || strings.HasPrefix(candidate, pointer+"/") {
			delete(origins, candidate)
		}
	}
	collectOverlayOrigins(origins, incoming, path, LayerCLI)
}

func fillDefaultOrigins(node *document.Node, path Path, origins map[string]Origin) {
	if _, exists := origins[path.String()]; !exists {
		origins[path.String()] = Origin{Layer: LayerDefault}
	}
	switch node.Kind {
	case document.Mapping:
		for _, entry := range node.Mapping {
			fillDefaultOrigins(entry.Value, path.Key(entry.Key), origins)
		}
	case document.Sequence:
		for index, child := range node.Sequence {
			fillDefaultOrigins(child, path.Index(index), origins)
		}
	}
}