package validators

import (
	"fmt"
	"regexp"
	"sort"
	"strings"

	"gitea.maximumdirect.net/eric/audita/v3/internal/core/glossary"
)

type protectedTermDef struct {
	identities []glossary.Identity
	canonical  string
}

type protectedOccurrence struct {
	text      string
	identity  glossary.Identity
	canonical string
}

// ProtectedVocabulary is a deterministic glossary-derived protected term set.
type ProtectedVocabulary struct {
	termsByFolded map[string]protectedTermDef
	pattern       *regexp.Regexp
}

// NewProtectedVocabulary prepares the independently selected terms for matching.
func NewProtectedVocabulary(terms []glossary.Term) ProtectedVocabulary {
	termsByFolded := make(map[string]protectedTermDef, len(terms))
	alternatives := make([]string, 0, len(terms))
	for _, term := range terms {
		if !term.Exempt {
			termsByFolded[strings.ToLower(term.Spelling)] = protectedTermDef{identities: term.Identities, canonical: term.Spelling}
		}
		alternatives = append(alternatives, regexp.QuoteMeta(term.Spelling))
	}
	if len(termsByFolded) == 0 {
		return ProtectedVocabulary{}
	}
	sort.SliceStable(alternatives, func(i, j int) bool { return len(alternatives[i]) > len(alternatives[j]) })
	pattern := regexp.MustCompile(`(?i)\b(?:` + strings.Join(alternatives, "|") + `)\b`)
	return ProtectedVocabulary{termsByFolded: termsByFolded, pattern: pattern}
}

// AllowsChange checks a proposed segment against the effective protection view.
// Spoken-word cleanup may reduce repeated mentions while preserving each identity.
func (v ProtectedVocabulary) AllowsChange(before, after string, allowRepetitionCleanup bool) bool {
	if v.violationReason(before, after) == "" {
		return true
	}
	return allowRepetitionCleanup && v.preservesRepeatedIdentities(before, after)
}

func (v ProtectedVocabulary) violationReason(before, after string) string {
	beforeByID := v.occurrencesByIdentity(before)
	afterByID := v.occurrencesByIdentity(after)
	if reason := validateIdentityPreservation(beforeByID, afterByID); reason != "" {
		return reason
	}
	if reason := validateCapitalizationTransitions(beforeByID, afterByID); reason != "" {
		return reason
	}
	return ""
}

func (v ProtectedVocabulary) occurrencesByIdentity(text string) map[glossary.Identity][]protectedOccurrence {
	byID := make(map[glossary.Identity][]protectedOccurrence)
	for _, o := range v.occurrences(text) {
		byID[o.identity] = append(byID[o.identity], o)
	}
	return byID
}

func (v ProtectedVocabulary) occurrences(text string) []protectedOccurrence {
	if v.pattern == nil {
		return nil
	}
	matches := v.pattern.FindAllStringIndex(text, -1)
	if len(matches) == 0 {
		return nil
	}
	out := make([]protectedOccurrence, 0, len(matches))
	for _, idx := range matches {
		matched := text[idx[0]:idx[1]]
		def, ok := v.termsByFolded[strings.ToLower(matched)]
		if !ok {
			continue
		}
		for _, identity := range def.identities {
			out = append(out, protectedOccurrence{text: matched, identity: identity, canonical: def.canonical})
		}
	}
	return out
}

func validateIdentityPreservation(beforeByID, afterByID map[glossary.Identity][]protectedOccurrence) string {
	var selected string
	found := false
	for identity, beforeItems := range beforeByID {
		if len(afterByID[identity]) < len(beforeItems) && len(beforeItems) > 0 {
			if spelling := beforeItems[0].canonical; !found || spelling < selected {
				selected, found = spelling, true
			}
		}
	}
	return protectedSpellingMessage(selected, found)
}

func validateCapitalizationTransitions(beforeByID, afterByID map[glossary.Identity][]protectedOccurrence) string {
	var selected string
	found := false
	for identity, afterItems := range afterByID {
		beforeItems := beforeByID[identity]
		for i, afterItem := range afterItems {
			if i >= len(beforeItems) || afterItem.text == beforeItems[i].text || afterItem.text == afterItem.canonical {
				continue
			}
			if !found || afterItem.canonical < selected {
				selected, found = afterItem.canonical, true
			}
		}
	}
	return protectedSpellingMessage(selected, found)
}

func protectedSpellingMessage(spelling string, found bool) string {
	if !found {
		return ""
	}
	return fmt.Sprintf("proposal may alter protected glossary spelling %q", spelling)
}

// preservesRepeatedIdentities permits a spoken-word proposal to reduce repeated
// mentions, but not remove an identity or replace its surviving spelling.
// Editorial and meaning validators still decide whether the cleanup is warranted.
func (v ProtectedVocabulary) preservesRepeatedIdentities(before, after string) bool {
	original := v.occurrencesByIdentity(before)
	result := v.occurrencesByIdentity(after)
	reduced := false
	for identity, occurrences := range original {
		remaining := result[identity]
		if len(remaining) == 0 {
			return false
		}
		if len(remaining) < len(occurrences) {
			reduced = true
		}
	}
	return reduced && validateCapitalizationTransitions(original, result) == ""
}