// Package companionopening selects short, local conversation openings.
// It does not retrieve memories, generate summaries, or call external services.
package companionopening

import (
	"crypto/sha256"
	"encoding/binary"
	"sort"
	"strings"
	"time"
	_ "time/tzdata"
	"unicode"
)

const recentLimit = 5

type Input struct {
	Now                 time.Time
	Timezone            string
	SessionID           string
	AuthorizedInterests []string
	AvoidedTopics       []string
	Recent              []RecentOpening
}

// RecentOpening describes one earlier call. Both subtitle flags must come
// from retained, real provider subtitles rather than a successful start.
type RecentOpening struct {
	ID                   string
	TopicKey             string
	StartedAt            time.Time
	EndedAt              time.Time
	HasUserSubtitle      bool
	HasAssistantSubtitle bool
}

// Selection records only an opening and its routing metadata, never a copy
// of personal facts. ID and TopicKey are stable, non-personal template keys.
type Selection struct {
	Text     string
	ID       string
	TopicKey string
	Category string
}

// Select is deterministic for the supplied input. Only known interest aliases
// influence selection; arbitrary profile text is never copied into an opening.
func Select(in Input) Selection {
	recent := recentCalls(in.Recent)
	blocked, uncertain := avoided(in.AvoidedTopics)
	seed := selectionSeed(in)
	greeting, period := localGreeting(in.Now, in.Timezone)

	if !uncertain && len(recent) > 0 {
		last := recent[0]
		distance := in.Now.Sub(last.EndedAt)
		if !in.Now.IsZero() && !last.EndedAt.IsZero() && distance >= 0 && distance < 10*time.Minute && last.HasUserSubtitle && last.HasAssistantSubtitle {
			return chooseByID(reopenTemplates, recent, seed)
		}
	}

	if uncertain {
		chosen := chooseNeutral(recent, seed)
		return withGreeting(chosen, greeting, len(recent) == 0)
	}

	interests := knownTopics(in.AuthorizedInterests)
	interestCandidates := []Selection{}
	for _, candidate := range interestTemplates {
		if interests[candidate.TopicKey] && allowedTemplate(candidate, blocked) {
			interestCandidates = append(interestCandidates, candidate)
		}
	}
	if chosen, ok := choose(interestCandidates, recent, seed); ok {
		return withGreeting(chosen, greeting, len(recent) == 0)
	}

	candidates := []Selection{}
	for _, candidate := range periodTemplates[period] {
		if allowedTemplate(candidate, blocked) {
			candidates = append(candidates, candidate)
		}
	}
	for _, candidate := range lightTemplates {
		if allowedTemplate(candidate, blocked) {
			candidates = append(candidates, candidate)
		}
	}
	if len(candidates) > 0 {
		// Everyday greetings can share a neutral topic. Avoid recent wording,
		// without forcing a different activity just to rotate topic metadata.
		return withGreeting(chooseByID(candidates, recent, seed), greeting, len(recent) == 0)
	}
	return withGreeting(chooseNeutral(recent, seed), greeting, len(recent) == 0)
}

func recentCalls(input []RecentOpening) []RecentOpening {
	recent := append([]RecentOpening(nil), input...)
	sort.SliceStable(recent, func(i, j int) bool {
		return recentTime(recent[i]).After(recentTime(recent[j]))
	})
	if len(recent) > recentLimit {
		recent = recent[:recentLimit]
	}
	return recent
}

func recentTime(call RecentOpening) time.Time {
	if !call.EndedAt.IsZero() {
		return call.EndedAt
	}
	return call.StartedAt
}

func selectionSeed(in Input) uint64 {
	sum := sha256.Sum256([]byte(in.SessionID + "|" + in.Now.UTC().Format(time.RFC3339Nano)))
	return binary.BigEndian.Uint64(sum[:8])
}

func choose(candidates []Selection, recent []RecentOpening, seed uint64) (Selection, bool) {
	usedIDs, usedTopics := map[string]bool{}, map[string]bool{}
	for _, call := range recent {
		usedIDs[call.ID] = call.ID != ""
		usedTopics[call.TopicKey] = call.TopicKey != ""
	}
	eligible := []Selection{}
	for _, candidate := range candidates {
		if !usedIDs[candidate.ID] && !usedTopics[candidate.TopicKey] {
			eligible = append(eligible, candidate)
		}
	}
	if len(eligible) == 0 {
		return Selection{}, false
	}
	return eligible[seed%uint64(len(eligible))], true
}

func chooseNeutral(recent []RecentOpening, seed uint64) Selection {
	// When every content topic is excluded, do not relax those exclusions.
	// Neutral topics may repeat, but prefer a new sentence over the last five.
	return chooseByID(neutralTemplates, recent, seed)
}

func chooseByID(candidates []Selection, recent []RecentOpening, seed uint64) Selection {
	ids := map[string]bool{}
	for _, call := range recent {
		ids[call.ID] = true
	}
	eligible := []Selection{}
	for _, candidate := range candidates {
		if !ids[candidate.ID] {
			eligible = append(eligible, candidate)
		}
	}
	if len(eligible) == 0 {
		eligible = candidates
	}
	return eligible[seed%uint64(len(eligible))]
}

func allowedTemplate(candidate Selection, blocked map[string]bool) bool {
	if blocked[candidate.TopicKey] {
		return false
	}
	for _, related := range templateTopics[candidate.ID] {
		if blocked[related] {
			return false
		}
	}
	return true
}

func withGreeting(chosen Selection, greeting string, first bool) Selection {
	if first {
		chosen.Text = greeting + "，我是小禾。" + chosen.Text
	} else {
		chosen.Text = greeting + "。" + chosen.Text
	}
	return chosen
}

func localGreeting(now time.Time, timezone string) (string, string) {
	if now.IsZero() {
		return "您好", "unknown"
	}
	zoneName := strings.TrimSpace(timezone)
	zone, err := time.LoadLocation(zoneName)
	if zoneName == "" || strings.EqualFold(zoneName, "Local") || err != nil {
		zone = time.FixedZone("Asia/Shanghai", 8*60*60)
	}
	hour := now.In(zone).Hour()
	switch {
	case hour >= 5 && hour < 11:
		return "早上好", "morning"
	case hour >= 11 && hour < 14:
		return "中午好", "noon"
	case hour >= 14 && hour < 18:
		return "下午好", "afternoon"
	case hour >= 18 && hour < 23:
		return "晚上好", "evening"
	default:
		return "您好", "night"
	}
}

func knownTopics(values []string) map[string]bool {
	topics := map[string]bool{}
	for _, value := range values {
		// A free sentence can negate a listed interest. Accept category labels
		// only, and skip ambiguous negative phrases instead of reversing them.
		if strings.Contains(value, "不") || strings.Contains(value, "别") || matchesAny(value, []string{"not", "no", "never", "don't", "dislike"}) {
			continue
		}
		for _, label := range strings.FieldsFunc(value, func(r rune) bool {
			return r == ',' || r == '，' || r == '、' || r == ';' || r == '；'
		}) {
			label = normalizeLabel(label)
			for key, aliases := range topicAliases {
				for _, alias := range aliases {
					if label == normalizeLabel(alias) {
						topics[key] = true
					}
				}
			}
		}
	}
	return topics
}

func normalizeLabel(value string) string {
	return strings.ToLower(strings.NewReplacer("_", " ", "-", " ").Replace(strings.TrimSpace(value)))
}

func avoided(values []string) (map[string]bool, bool) {
	blocked := map[string]bool{}
	uncertain := false
	for _, value := range values {
		if strings.TrimSpace(value) == "" {
			continue
		}
		matched := false
		for key, aliases := range topicAliases {
			if matchesAny(value, aliases) {
				blocked[key] = true
				matched = true
			}
		}
		if matchesAny(value, []string{"怀旧", "过去", "往事", "回忆", "reminiscence", "nostalgia", "the past"}) {
			blocked["childhood"], blocked["old_objects"] = true, true
			matched = true
		}
		// These known exclusions do not have content templates in this package.
		if matchesAny(value, []string{"健康", "疾病", "医疗", "收入", "金钱", "家庭", "家人", "政治", "宗教", "health", "illness", "medical", "income", "money", "family", "politics", "religion"}) {
			matched = true
		}
		if !matched {
			uncertain = true
		}
	}
	return blocked, uncertain
}

func matchesAny(value string, aliases []string) bool {
	value = strings.ToLower(strings.NewReplacer("_", " ", "-", " ").Replace(strings.TrimSpace(value)))
	for _, alias := range aliases {
		alias = strings.ToLower(alias)
		start := 0
		for start < len(value) {
			found := strings.Index(value[start:], alias)
			if found < 0 {
				break
			}
			found += start
			end := found + len(alias)
			if !asciiWord(alias) || ((found == 0 || !asciiWordByte(value[found-1])) && (end == len(value) || !asciiWordByte(value[end]))) {
				return true
			}
			start = end
		}
	}
	return false
}

func asciiWord(value string) bool {
	for _, r := range value {
		if r > unicode.MaxASCII {
			return false
		}
	}
	return true
}

func asciiWordByte(value byte) bool {
	return value >= 'a' && value <= 'z' || value >= '0' && value <= '9'
}