// Package npcinteractions owns canonical ordering and exact-identity rules for
// D&D NPC interaction artifacts.
package npcinteractions

import (
	"sort"
	"strconv"
	"strings"

	"gitea.maximumdirect.net/eric/notarius/internal/core/source"
	"gitea.maximumdirect.net/eric/notarius/internal/modules/dnd"
	"gitea.maximumdirect.net/eric/notarius/internal/modules/dnd/npcs/identity"
)

// CanonicalizeSourceRefs returns a cloned, document-ordered, de-duplicated
// source-reference list.
func CanonicalizeSourceRefs(doc *source.SourceDocument, input []source.SourceRef) []source.SourceRef {
	if input == nil {
		return nil
	}
	canonical := append([]source.SourceRef(nil), input...)
	sort.SliceStable(canonical, func(left, right int) bool {
		return SourceRefLess(doc, canonical[left], canonical[right])
	})
	unique := make([]source.SourceRef, 0, len(canonical))
	for _, ref := range canonical {
		if len(unique) == 0 || unique[len(unique)-1] != ref {
			unique = append(unique, ref)
		}
	}
	return unique
}

// SourceRefsEqual reports whether two source-reference lists have identical
// representations and values.
func SourceRefsEqual(left, right []source.SourceRef) bool {
	if (left == nil) != (right == nil) || len(left) != len(right) {
		return false
	}
	for index := range left {
		if left[index] != right[index] {
			return false
		}
	}
	return true
}

// SourceRefLess orders references by source identity and then by the source
// document positions of their endpoints. Invalid endpoints sort after valid
// endpoints and fall back to their literal IDs for deterministic diagnostics.
func SourceRefLess(doc *source.SourceDocument, left, right source.SourceRef) bool {
	if left.SourceID != right.SourceID {
		return left.SourceID < right.SourceID
	}
	leftStart, leftStartOK := source.UnitIndex(doc, left.StartUnitID)
	rightStart, rightStartOK := source.UnitIndex(doc, right.StartUnitID)
	if leftStartOK != rightStartOK {
		return leftStartOK
	}
	if leftStartOK && leftStart != rightStart {
		return leftStart < rightStart
	}
	if left.StartUnitID != right.StartUnitID {
		return left.StartUnitID < right.StartUnitID
	}
	leftEnd, leftEndOK := source.UnitIndex(doc, left.EndUnitID)
	rightEnd, rightEndOK := source.UnitIndex(doc, right.EndUnitID)
	if leftEndOK != rightEndOK {
		return leftEndOK
	}
	if leftEndOK && leftEnd != rightEnd {
		return leftEnd < rightEnd
	}
	return left.EndUnitID < right.EndUnitID
}

// Less defines the canonical order for NPC interaction occurrences.
func Less(doc *source.SourceDocument, left, right dnd.NPCInteraction) bool {
	leftPosition, leftHasEvidence := EarliestSourcePosition(doc, left)
	rightPosition, rightHasEvidence := EarliestSourcePosition(doc, right)
	if leftHasEvidence != rightHasEvidence {
		return leftHasEvidence
	}
	if leftHasEvidence && leftPosition != rightPosition {
		return leftPosition < rightPosition
	}
	leftKey := identity.ComparisonKey(left.Name)
	rightKey := identity.ComparisonKey(right.Name)
	if leftKey != rightKey {
		return leftKey < rightKey
	}
	if left.Name != right.Name {
		return left.Name < right.Name
	}
	if left.Kind != right.Kind {
		return left.Kind < right.Kind
	}
	return sourceRefsLess(doc, left.SourceRefs, right.SourceRefs)
}

// EarliestSourcePosition returns the earliest valid cited position.
func EarliestSourcePosition(doc *source.SourceDocument, interaction dnd.NPCInteraction) (int, bool) {
	found := false
	earliest := 0
	for _, ref := range interaction.SourceRefs {
		if source.ValidateRef(doc, ref) != nil {
			continue
		}
		position, ok := source.UnitIndex(doc, ref.StartUnitID)
		if !ok || (found && position >= earliest) {
			continue
		}
		earliest = position
		found = true
	}
	return earliest, found
}

// ValidSourceRefs reports whether an interaction has non-empty, valid
// current-document evidence.
func ValidSourceRefs(doc *source.SourceDocument, refs []source.SourceRef) bool {
	if len(refs) == 0 {
		return false
	}
	for _, ref := range refs {
		if source.ValidateRef(doc, ref) != nil {
			return false
		}
	}
	return true
}

// ExactIdentity returns a collision-safe key over every durable interaction
// field. Callers decide whether the record is eligible for duplicate handling.
func ExactIdentity(interaction dnd.NPCInteraction) string {
	var key strings.Builder
	writeKeyString(&key, interaction.Name)
	writeKeyString(&key, string(interaction.Kind))
	for _, ref := range interaction.SourceRefs {
		writeKeyString(&key, ref.SourceID)
		writeKeyInt(&key, ref.StartUnitID)
		writeKeyInt(&key, ref.EndUnitID)
	}
	return key.String()
}

func sourceRefsLess(doc *source.SourceDocument, left, right []source.SourceRef) bool {
	for index := 0; index < len(left) && index < len(right); index++ {
		if left[index] == right[index] {
			continue
		}
		return SourceRefLess(doc, left[index], right[index])
	}
	return len(left) < len(right)
}

func writeKeyString(builder *strings.Builder, value string) {
	builder.WriteString(strconv.Itoa(len(value)))
	builder.WriteByte(':')
	builder.WriteString(value)
}

func writeKeyInt(builder *strings.Builder, value int) {
	builder.WriteString(strconv.Itoa(value))
	builder.WriteByte(';')
}