package engine

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

type sequenceCombinationContext struct {
	destination Path
}

type sequenceItemProjection struct {
	inputIndex  int
	outputIndex int
}

type sequenceItemReplacement struct {
	lowerIndex  int
	higherIndex int
	outputIndex int
}

type sequenceCombinationResult struct {
	value          *document.Node
	lowerItems     []sequenceItemProjection
	higherItems    []sequenceItemProjection
	replacements   []sequenceItemReplacement
	appendedHigher []int
}

func combineSequence(
	lower, higher *document.Node,
	policy collectionPolicyResolution,
	context sequenceCombinationContext,
) (sequenceCombinationResult, []Diagnostic) {
	if higher == nil {
		return unchangedSequenceValue(lower), nil
	}
	switch policy.operation {
	case sequenceModeReplace:
		return replaceSequence(higher, policy.effectiveIdentityFields, context)
	case sequenceModeAppend, sequenceModeUpsert:
		return combineIdentifiedSequences(lower, higher, policy.operation, policy.effectiveIdentityFields, context)
	default:
		return sequenceCombinationResult{}, []Diagnostic{sequenceCombinationDiagnostic(
			context.destination, "sequence operation is invalid", higher,
		)}
	}
}

func unchangedSequenceValue(lower *document.Node) sequenceCombinationResult {
	result := sequenceCombinationResult{value: document.Clone(lower)}
	if lower != nil && lower.Kind == document.Sequence {
		result.lowerItems = sequenceItemProjections(len(lower.Sequence), 0)
	}
	return result
}

func replaceSequence(
	higher *document.Node,
	identityFields []string,
	context sequenceCombinationContext,
) (sequenceCombinationResult, []Diagnostic) {
	if higher.Kind == document.Sequence && len(identityFields) != 0 {
		if _, diagnostics := validateSequenceIdentity(higher, context.destination, identityFields, sequenceCombinationIdentityCodes); len(diagnostics) != 0 {
			return sequenceCombinationResult{}, diagnostics
		}
	}
	result := sequenceCombinationResult{value: document.Clone(higher)}
	if higher.Kind == document.Sequence {
		result.higherItems = sequenceItemProjections(len(higher.Sequence), 0)
	}
	return result, nil
}

func combineIdentifiedSequences(
	lower, higher *document.Node,
	operation sequenceMode,
	identityFields []string,
	context sequenceCombinationContext,
) (sequenceCombinationResult, []Diagnostic) {
	if higher.Kind != document.Sequence {
		return sequenceCombinationResult{}, []Diagnostic{sequenceCombinationDiagnostic(
			context.destination, "append and upsert require a sequence contribution", higher,
		)}
	}
	if lower != nil && lower.Kind != document.Sequence {
		return sequenceCombinationResult{}, []Diagnostic{sequenceCombinationDiagnostic(
			context.destination, "append and upsert require a lower sequence or an absent lower value", lower,
		)}
	}
	if len(identityFields) == 0 {
		return sequenceCombinationResult{}, []Diagnostic{sequenceCombinationDiagnostic(
			context.destination, "append and upsert require an identity definition", higher,
		)}
	}

	higherIndex, diagnostics := validateSequenceIdentity(higher, context.destination, identityFields, sequenceCombinationIdentityCodes)
	if len(diagnostics) != 0 {
		return sequenceCombinationResult{}, diagnostics
	}
	var lowerIndex map[string]sequenceIdentityRecord
	if lower != nil {
		lowerIndex, diagnostics = validateSequenceIdentity(lower, context.destination, identityFields, sequenceCombinationIdentityCodes)
		if len(diagnostics) != 0 {
			return sequenceCombinationResult{}, diagnostics
		}
	}
	if operation == sequenceModeAppend {
		if duplicate := duplicateAcrossSequenceContributions(lowerIndex, higherIndex, context.destination); duplicate != nil {
			return sequenceCombinationResult{}, []Diagnostic{*duplicate}
		}
	}

	if operation == sequenceModeAppend {
		return appendSequenceItems(lower, higher), nil
	}
	if operation == sequenceModeUpsert {
		return upsertSequenceItems(lower, higher, lowerIndex, higherIndex), nil
	}
	return sequenceCombinationResult{}, []Diagnostic{sequenceCombinationDiagnostic(
		context.destination, "sequence operation is invalid", higher,
	)}
}

func appendSequenceItems(lower, higher *document.Node) sequenceCombinationResult {
	lowerCount := 0
	if lower != nil {
		lowerCount = len(lower.Sequence)
	}
	items := make([]*document.Node, 0, lowerCount+len(higher.Sequence))
	if lower != nil {
		items = append(items, lower.Sequence...)
	}
	items = append(items, higher.Sequence...)
	return sequenceCombinationResult{
		value:          cloneSequenceWithItems(higher, items),
		lowerItems:     sequenceItemProjections(lowerCount, 0),
		higherItems:    sequenceItemProjections(len(higher.Sequence), lowerCount),
		appendedHigher: sequenceIndexes(len(higher.Sequence)),
	}
}

func upsertSequenceItems(
	lower, higher *document.Node,
	lowerIndex, higherIndex map[string]sequenceIdentityRecord,
) sequenceCombinationResult {
	lowerCount := 0
	var lowerItems []*document.Node
	if lower != nil {
		lowerCount = len(lower.Sequence)
		lowerItems = lower.Sequence
	}
	matchedLower := make(map[int]sequenceIdentityRecord, len(higherIndex))
	matchedLowerByHigher := make([]int, len(higher.Sequence))
	for index := range matchedLowerByHigher {
		matchedLowerByHigher[index] = -1
	}
	for tuple, incoming := range higherIndex {
		if retained, exists := lowerIndex[tuple]; exists {
			matchedLower[retained.index] = incoming
			matchedLowerByHigher[incoming.index] = retained.index
		}
	}
	items := make([]*document.Node, lowerCount, lowerCount+len(higher.Sequence))
	result := sequenceCombinationResult{
		lowerItems:  make([]sequenceItemProjection, 0, lowerCount-len(matchedLower)),
		higherItems: sequenceItemProjections(len(higher.Sequence), 0),
	}
	for lowerPosition, item := range lowerItems {
		if incoming, replaced := matchedLower[lowerPosition]; replaced {
			items[lowerPosition] = higher.Sequence[incoming.index]
			result.higherItems[incoming.index].outputIndex = lowerPosition
			result.replacements = append(result.replacements, sequenceItemReplacement{
				lowerIndex: lowerPosition, higherIndex: incoming.index, outputIndex: lowerPosition,
			})
			continue
		}
		items[lowerPosition] = item
		result.lowerItems = append(result.lowerItems, sequenceItemProjection{inputIndex: lowerPosition, outputIndex: lowerPosition})
	}
	for higherPosition := range higher.Sequence {
		if matchedLowerByHigher[higherPosition] >= 0 {
			continue
		}
		outputIndex := len(items)
		items = append(items, higher.Sequence[higherPosition])
		result.appendedHigher = append(result.appendedHigher, higherPosition)
		result.higherItems[higherPosition].outputIndex = outputIndex
	}
	result.value = cloneSequenceWithItems(higher, items)
	return result
}

func duplicateAcrossSequenceContributions(
	lowerIndex, higherIndex map[string]sequenceIdentityRecord,
	path Path,
) *Diagnostic {
	higherTuples := make([]string, len(higherIndex))
	for tuple, record := range higherIndex {
		higherTuples[record.index] = tuple
	}
	for _, tuple := range higherTuples {
		if lower, exists := lowerIndex[tuple]; exists {
			higher := higherIndex[tuple]
			primary := publicLocation(lower.location)
			related := publicLocation(higher.location)
			return &Diagnostic{
				Code: CodeSequenceConflict, Severity: SeverityError, Path: path.clone(),
				Message: "sequence contributions contain a duplicate identity",
				Primary: &primary, Related: []Location{related},
			}
		}
	}
	return nil
}

func cloneSequenceWithItems(template *document.Node, items []*document.Node) *document.Node {
	cloned := *template
	cloned.Mapping = nil
	cloned.Sequence = make([]*document.Node, len(items))
	for index, item := range items {
		cloned.Sequence[index] = document.Clone(item)
	}
	return &cloned
}

func sequenceItemProjections(length, outputOffset int) []sequenceItemProjection {
	projections := make([]sequenceItemProjection, length)
	for index := range projections {
		projections[index] = sequenceItemProjection{inputIndex: index, outputIndex: index + outputOffset}
	}
	return projections
}

func sequenceIndexes(length int) []int {
	indexes := make([]int, length)
	for index := range indexes {
		indexes[index] = index
	}
	return indexes
}

func sequenceCombinationDiagnostic(path Path, message string, node *document.Node) Diagnostic {
	var primary *Location
	if node != nil {
		location := publicLocation(node.Location)
		primary = &location
	}
	return Diagnostic{Code: CodeSequenceInvalid, Severity: SeverityError, Path: path.clone(), Message: message, Primary: primary}
}

var sequenceCombinationIdentityCodes = sequenceIdentityDiagnosticCodes{
	invalid: CodeSequenceInvalid, conflict: CodeSequenceConflict,
}