package chatclient

import (
	"context"
	"sync"
	"time"

	pb "gitea.fe.kaien.ru/kaien/l-ai-chat-proto"
)

// ParticipantCache is a bounded in-memory cache keyed by author_id.
// Callers should prefer BatchGetParticipants over N+1 GetParticipant.
type ParticipantCache struct {
	mu      sync.RWMutex
	byID    map[string]*pb.Participant
	maxSize int
}

// NewParticipantCache creates a cache. maxSize <= 0 defaults to 512.
func NewParticipantCache(maxSize int) *ParticipantCache {
	if maxSize <= 0 {
		maxSize = 512
	}
	return &ParticipantCache{
		byID:    make(map[string]*pb.Participant),
		maxSize: maxSize,
	}
}

// Get returns a cached participant if present.
func (c *ParticipantCache) Get(authorID string) (*pb.Participant, bool) {
	c.mu.RLock()
	defer c.mu.RUnlock()
	p, ok := c.byID[authorID]
	return p, ok
}

// Put stores a participant, preferring newer profile/presence versions.
func (c *ParticipantCache) Put(p *pb.Participant) {
	if p == nil || p.GetAuthorId() == "" {
		return
	}
	c.mu.Lock()
	defer c.mu.Unlock()
	if existing, ok := c.byID[p.GetAuthorId()]; ok {
		if p.GetProfileVersion() < existing.GetProfileVersion() {
			// Keep newer profile fields but allow presence-only updates below.
			merged := cloneParticipant(existing)
			if p.GetPresenceVersion() > existing.GetPresenceVersion() {
				merged.Online = p.GetOnline()
				merged.PresenceVersion = p.GetPresenceVersion()
				merged.LastSeenAt = p.GetLastSeenAt()
			}
			c.byID[p.GetAuthorId()] = merged
			return
		}
		if p.GetProfileVersion() == existing.GetProfileVersion() &&
			p.GetPresenceVersion() < existing.GetPresenceVersion() {
			return
		}
	}
	if len(c.byID) >= c.maxSize {
		// Simple eviction: clear half (bounded cache, not LRU).
		n := 0
		for id := range c.byID {
			delete(c.byID, id)
			n++
			if n >= c.maxSize/2 {
				break
			}
		}
	}
	c.byID[p.GetAuthorId()] = cloneParticipant(p)
}

// PutAll stores many participants.
func (c *ParticipantCache) PutAll(ps []*pb.Participant) {
	for _, p := range ps {
		c.Put(p)
	}
}

// MissingIDs returns author IDs not present in the cache.
func (c *ParticipantCache) MissingIDs(ids []string) []string {
	c.mu.RLock()
	defer c.mu.RUnlock()
	var missing []string
	seen := make(map[string]struct{}, len(ids))
	for _, id := range ids {
		if id == "" {
			continue
		}
		if _, dup := seen[id]; dup {
			continue
		}
		seen[id] = struct{}{}
		if _, ok := c.byID[id]; !ok {
			missing = append(missing, id)
		}
	}
	return missing
}

func cloneParticipant(p *pb.Participant) *pb.Participant {
	if p == nil {
		return nil
	}
	out := &pb.Participant{
		AuthorId:        p.AuthorId,
		AuthorType:      p.AuthorType,
		DisplayName:     p.DisplayName,
		Role:            p.Role,
		Bio:             p.Bio,
		StatusText:      p.StatusText,
		AvatarHash:      p.AvatarHash,
		Online:          p.Online,
		ProfileVersion:  p.ProfileVersion,
		PresenceVersion: p.PresenceVersion,
		AgentId:         p.AgentId,
		CreatedAt:       p.CreatedAt,
		UpdatedAt:       p.UpdatedAt,
		LastSeenAt:      p.LastSeenAt,
	}
	if len(p.Aliases) > 0 {
		out.Aliases = make(map[string]string, len(p.Aliases))
		for k, v := range p.Aliases {
			out.Aliases[k] = v
		}
	}
	return out
}

// EnsureParticipants fetches missing IDs via BatchGetParticipants and caches them.
func (c *Client) EnsureParticipants(ctx context.Context, cache *ParticipantCache, authorIDs []string) error {
	if cache == nil {
		return nil
	}
	missing := cache.MissingIDs(authorIDs)
	if len(missing) == 0 {
		return nil
	}
	ps, err := c.BatchGetParticipants(ctx, missing)
	if err != nil {
		return err
	}
	cache.PutAll(ps)
	return nil
}

// ResolveDisplayName picks a localized alias then falls back to display_name.
// locale examples: "ru-RU", "ru", "en-US".
func ResolveDisplayName(p *pb.Participant, locale string) string {
	if p == nil {
		return ""
	}
	if locale != "" && len(p.Aliases) > 0 {
		if v, ok := p.Aliases[locale]; ok && v != "" {
			return v
		}
		// primary language subtag
		if i := indexByte(locale, '-'); i > 0 {
			lang := locale[:i]
			if v, ok := p.Aliases[lang]; ok && v != "" {
				return v
			}
		}
	}
	if p.DisplayName != "" {
		return p.DisplayName
	}
	return ""
}

func indexByte(s string, c byte) int {
	for i := 0; i < len(s); i++ {
		if s[i] == c {
			return i
		}
	}
	return -1
}

// AvatarUploadNeeded reports whether localHash differs from the server hash
// (empty local means skip; empty server means upload if local present).
func AvatarUploadNeeded(serverHash, localHash string) bool {
	if localHash == "" {
		return false
	}
	return serverHash != localHash
}

// Idle helper kept for callers that want a soft TTL hint (cache itself is version-based).
func CacheSoftTTL() time.Duration { return 5 * time.Minute }