package engine

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

// composedDocument is the private handoff between source assembly and later
// precedence layers. Claims remain ordered by source and declaration traversal;
// origins retain every source that contributes to a composite mapping.
type composedDocument struct {
	root         *document.Node
	claims       []compositionClaim
	origins      map[string]Origin
	overlays     []overlayRecord
	applications []historyApplication
	inputBytes   int64
	inputNodes   int
}

// assemblyAccumulator owns one mutable working document. Acquired trees held by
// history applications are separate from its root and remain unchanged.
type assemblyAccumulator struct {
	current *composedDocument
	index   mappingIndex
}

func newAssemblyAccumulator(owned *composedDocument) *assemblyAccumulator {
	return &assemblyAccumulator{current: owned}
}

// cloneComposedDocument detaches mutable composition and provenance state;
// history application trees are immutable and retain their existing sharing.
func cloneComposedDocument(base *composedDocument) *composedDocument {
	return &composedDocument{
		root: document.Clone(base.root), claims: cloneCompositionClaims(base.claims),
		origins: cloneOriginIndex(base.origins), overlays: cloneOverlayRecords(base.overlays),
		applications: cloneHistoryApplications(base.applications),
		inputBytes:   base.inputBytes, inputNodes: base.inputNodes,
	}
}

type compositionClaim struct {
	path     Path
	kind     document.Kind
	location Location
}

type compositionClaims struct {
	ordered []compositionClaim
	byPath  map[string][]compositionClaim
}

// composeDocuments recursively joins disjoint mapping entries. Source order
// controls only output traversal and diagnostics: every non-mapping overlap is
// rejected before a result is assembled.
func composeDocuments(inputs ...*document.Node) (*composedDocument, []Diagnostic) {
	if len(inputs) == 0 {
		return nil, []Diagnostic{compositionInvalidDiagnostic("strict composition requires at least one document", nil)}
	}

	collected := compositionClaims{byPath: make(map[string][]compositionClaim)}
	for _, input := range inputs {
		if input == nil || input.Kind != document.Mapping {
			var location *Location
			if input != nil {
				converted := publicLocation(input.Location)
				location = &converted
			}
			return nil, []Diagnostic{compositionInvalidDiagnostic("strict composition requires mapping document roots", location)}
		}
		collected.append(input, Path{})
	}

	checked := make(map[string]struct{}, len(collected.byPath))
	for _, claim := range collected.ordered {
		pointer := claim.path.String()
		if _, seen := checked[pointer]; seen {
			continue
		}
		checked[pointer] = struct{}{}
		claims := collected.byPath[pointer]
		if len(claims) < 2 || allMappingClaims(claims) {
			continue
		}
		return nil, []Diagnostic{compositionConflictDiagnostic(claim.path, claims)}
	}

	root := document.Clone(inputs[0])
	index := new(mappingIndex)
	for _, input := range inputs[1:] {
		mergeDisjointMappings(root, input, index)
	}
	applications := make([]historyApplication, 0, len(inputs))
	for _, input := range inputs {
		applications = append(applications, historyApplication{layer: LayerBase, value: input})
	}
	return &composedDocument{
		root:         root,
		claims:       cloneCompositionClaims(collected.ordered),
		origins:      compositionOrigins(collected.ordered),
		applications: applications,
	}, nil
}

func (c *compositionClaims) append(node *document.Node, path Path) {
	claim := compositionClaim{
		path:     path.clone(),
		kind:     node.Kind,
		location: publicLocation(node.Location),
	}
	c.ordered = append(c.ordered, claim)
	pointer := path.String()
	c.byPath[pointer] = append(c.byPath[pointer], claim)

	if node.Kind != document.Mapping {
		return
	}
	for _, entry := range node.Mapping {
		c.append(entry.Value, path.Key(entry.Key))
	}
}

func allMappingClaims(claims []compositionClaim) bool {
	for _, claim := range claims {
		if claim.kind != document.Mapping {
			return false
		}
	}
	return true
}

func mergeDisjointMappings(target, incoming *document.Node, index *mappingIndex) {
	for _, incomingEntry := range incoming.Mapping {
		position := index.find(target, incomingEntry.Key)
		if position < 0 {
			cloned := incomingEntry
			cloned.Value = document.Clone(incomingEntry.Value)
			index.append(target, cloned)
			continue
		}
		// Claim validation guarantees that the only remaining overlap is a
		// mapping pair. Empty mappings naturally contribute no child entries.
		mergeDisjointMappings(target.Mapping[position].Value, incomingEntry.Value, index)
	}
}

func documentEntryIndex(entries []document.Entry, key string) int {
	for index := range entries {
		if entries[index].Key == key {
			return index
		}
	}
	return -1
}

func compositionOrigins(claims []compositionClaim) map[string]Origin {
	origins := make(map[string]Origin, len(claims))
	for _, claim := range claims {
		pointer := claim.path.String()
		origin := origins[pointer]
		origin.Layer = LayerBase
		origin.Locations = append(origin.Locations, claim.location)
		origins[pointer] = origin
	}
	return origins
}

func applyCompositionOrigins(decoded *decodedConfiguration, origins map[string]Origin) {
	for pointer, origin := range origins {
		if _, present := decoded.presence[pointer]; present {
			decoded.origins[pointer] = cloneOrigin(origin)
		}
	}
}

func cloneCompositionClaims(claims []compositionClaim) []compositionClaim {
	cloned := make([]compositionClaim, len(claims))
	for index, claim := range claims {
		cloned[index] = claim
		cloned[index].path = claim.path.clone()
	}
	return cloned
}

func compositionInvalidDiagnostic(message string, location *Location) Diagnostic {
	return Diagnostic{
		Code: CodeComposeInvalid, Severity: SeverityError, Message: message,
		Primary: cloneLocation(location),
	}
}

func compositionConflictDiagnostic(path Path, claims []compositionClaim) Diagnostic {
	primary := claims[0].location
	related := make([]Location, 0, len(claims)-1)
	for _, claim := range claims[1:] {
		related = append(related, claim.location)
	}
	return Diagnostic{
		Code:     CodeComposeConflict,
		Severity: SeverityError,
		Path:     path.clone(),
		Message:  "configuration path is defined by multiple sources",
		Primary:  &primary,
		Related:  related,
	}
}

func publicLocation(location document.Location) Location {
	return Location{SourceID: location.SourceID, Line: location.Line, Column: location.Column}
}