package chat

import (
	"fmt"
	"maps"
	"strings"
	"sync"

	"eq2emu/internal/database"
)

// MasterList is a specialized chat channel master list optimized for:
// - Fast ID-based lookups (O(1))
// - Fast channel type filtering (O(1))
// - Fast name-based searching (indexed)
// - Fast member count filtering
// - Efficient channel compatibility queries
type MasterList struct {
	// Core storage
	channels map[int32]*Channel // ID -> Channel
	mutex    sync.RWMutex

	// Specialized indices for O(1) lookups
	byType       map[int][]*Channel        // ChannelType -> channels
	byMemberCt   map[int][]*Channel        // Member count -> channels (active/empty)
	byNameLower  map[string]*Channel       // Lowercase name -> channel
	byRestrict   map[int32][]*Channel      // Restriction level -> channels

	// Cached metadata
	memberCounts []int  // Unique member counts (cached)
	typeStats    map[int]int  // Channel type -> count
	metaStale    bool   // Whether metadata cache needs refresh
}

// NewMasterList creates a new specialized chat channel master list
func NewMasterList() *MasterList {
	return &MasterList{
		channels:     make(map[int32]*Channel),
		byType:       make(map[int][]*Channel),
		byMemberCt:   make(map[int][]*Channel),
		byNameLower:  make(map[string]*Channel),
		byRestrict:   make(map[int32][]*Channel),
		typeStats:    make(map[int]int),
		metaStale:    true,
	}
}

// refreshMetaCache updates the member counts cache and type stats
func (ml *MasterList) refreshMetaCache() {
	if !ml.metaStale {
		return
	}

	// Clear and rebuild type stats
	ml.typeStats = make(map[int]int)
	memberCountSet := make(map[int]struct{})

	// Collect unique member counts and type stats
	for _, channel := range ml.channels {
		ml.typeStats[channel.GetType()]++
		memberCount := channel.GetNumClients()
		memberCountSet[memberCount] = struct{}{}
	}

	// Clear and rebuild member counts cache
	ml.memberCounts = ml.memberCounts[:0]
	for count := range memberCountSet {
		ml.memberCounts = append(ml.memberCounts, count)
	}

	ml.metaStale = false
}

// updateChannelIndices updates all indices for a channel
func (ml *MasterList) updateChannelIndices(channel *Channel, add bool) {
	if add {
		// Add to type index
		ml.byType[channel.GetType()] = append(ml.byType[channel.GetType()], channel)

		// Add to member count index
		memberCount := channel.GetNumClients()
		ml.byMemberCt[memberCount] = append(ml.byMemberCt[memberCount], channel)

		// Add to name index
		ml.byNameLower[strings.ToLower(channel.GetName())] = channel

		// Add to restriction index
		ml.byRestrict[channel.LevelRestriction] = append(ml.byRestrict[channel.LevelRestriction], channel)
	} else {
		// Remove from type index
		typeChannels := ml.byType[channel.GetType()]
		for i, ch := range typeChannels {
			if ch.ID == channel.ID {
				ml.byType[channel.GetType()] = append(typeChannels[:i], typeChannels[i+1:]...)
				break
			}
		}

		// Remove from member count index
		memberCount := channel.GetNumClients()
		memberChannels := ml.byMemberCt[memberCount]
		for i, ch := range memberChannels {
			if ch.ID == channel.ID {
				ml.byMemberCt[memberCount] = append(memberChannels[:i], memberChannels[i+1:]...)
				break
			}
		}

		// Remove from name index
		delete(ml.byNameLower, strings.ToLower(channel.GetName()))

		// Remove from restriction index
		restrChannels := ml.byRestrict[channel.LevelRestriction]
		for i, ch := range restrChannels {
			if ch.ID == channel.ID {
				ml.byRestrict[channel.LevelRestriction] = append(restrChannels[:i], restrChannels[i+1:]...)
				break
			}
		}
	}
}

// RefreshChannelIndices refreshes the indices for a channel (used when member count changes)
func (ml *MasterList) RefreshChannelIndices(channel *Channel, oldMemberCount int) {
	ml.mutex.Lock()
	defer ml.mutex.Unlock()

	// Remove from old member count index
	oldMemberChannels := ml.byMemberCt[oldMemberCount]
	for i, ch := range oldMemberChannels {
		if ch.ID == channel.ID {
			ml.byMemberCt[oldMemberCount] = append(oldMemberChannels[:i], oldMemberChannels[i+1:]...)
			break
		}
	}

	// Add to new member count index
	newMemberCount := channel.GetNumClients()
	ml.byMemberCt[newMemberCount] = append(ml.byMemberCt[newMemberCount], channel)

	// Invalidate metadata cache
	ml.metaStale = true
}

// AddChannel adds a channel with full indexing
func (ml *MasterList) AddChannel(channel *Channel) bool {
	if channel == nil {
		return false
	}

	ml.mutex.Lock()
	defer ml.mutex.Unlock()

	// Check if exists
	if _, exists := ml.channels[channel.ID]; exists {
		return false
	}

	// Add to core storage
	ml.channels[channel.ID] = channel

	// Update all indices
	ml.updateChannelIndices(channel, true)

	// Invalidate metadata cache
	ml.metaStale = true

	return true
}

// GetChannel retrieves by ID (O(1))
func (ml *MasterList) GetChannel(id int32) *Channel {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()
	return ml.channels[id]
}

// GetChannelSafe retrieves a channel by ID with existence check
func (ml *MasterList) GetChannelSafe(id int32) (*Channel, bool) {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()
	channel, exists := ml.channels[id]
	return channel, exists
}

// HasChannel checks if a channel exists by ID
func (ml *MasterList) HasChannel(id int32) bool {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()
	_, exists := ml.channels[id]
	return exists
}

// RemoveChannel removes a channel and updates all indices
func (ml *MasterList) RemoveChannel(id int32) bool {
	ml.mutex.Lock()
	defer ml.mutex.Unlock()

	channel, exists := ml.channels[id]
	if !exists {
		return false
	}

	// Remove from core storage
	delete(ml.channels, id)

	// Update all indices
	ml.updateChannelIndices(channel, false)

	// Invalidate metadata cache
	ml.metaStale = true

	return true
}

// GetAllChannels returns a copy of all channels map
func (ml *MasterList) GetAllChannels() map[int32]*Channel {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()

	// Return a copy to prevent external modification
	result := make(map[int32]*Channel, len(ml.channels))
	maps.Copy(result, ml.channels)
	return result
}

// GetAllChannelsList returns all channels as a slice
func (ml *MasterList) GetAllChannelsList() []*Channel {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()

	result := make([]*Channel, 0, len(ml.channels))
	for _, channel := range ml.channels {
		result = append(result, channel)
	}
	return result
}

// GetChannelCount returns the number of channels
func (ml *MasterList) GetChannelCount() int {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()
	return len(ml.channels)
}

// Size returns the total number of channels
func (ml *MasterList) Size() int {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()
	return len(ml.channels)
}

// IsEmpty returns true if the master list is empty
func (ml *MasterList) IsEmpty() bool {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()
	return len(ml.channels) == 0
}

// ClearChannels removes all channels from the list
func (ml *MasterList) ClearChannels() {
	ml.mutex.Lock()
	defer ml.mutex.Unlock()

	// Clear all maps
	ml.channels = make(map[int32]*Channel)
	ml.byType = make(map[int][]*Channel)
	ml.byMemberCt = make(map[int][]*Channel)
	ml.byNameLower = make(map[string]*Channel)
	ml.byRestrict = make(map[int32][]*Channel)

	// Clear cached metadata
	ml.memberCounts = ml.memberCounts[:0]
	ml.typeStats = make(map[int]int)
	ml.metaStale = true
}

// Clear removes all channels from the master list
func (ml *MasterList) Clear() {
	ml.ClearChannels()
}

// FindChannelsByName finds channels containing the given name substring (optimized)
func (ml *MasterList) FindChannelsByName(nameSubstring string) []*Channel {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()

	searchKey := strings.ToLower(nameSubstring)

	// Try exact match first for full channel names
	if exactChannel := ml.byNameLower[searchKey]; exactChannel != nil {
		return []*Channel{exactChannel}
	}

	// Fallback to substring search
	var result []*Channel
	for _, channel := range ml.channels {
		if contains(strings.ToLower(channel.GetName()), searchKey) {
			result = append(result, channel)
		}
	}

	return result
}

// FindChannelsByType finds channels of a specific type (O(1))
func (ml *MasterList) FindChannelsByType(channelType int) []*Channel {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()
	return ml.byType[channelType]
}

// GetWorldChannels returns all world channels (O(1))
func (ml *MasterList) GetWorldChannels() []*Channel {
	return ml.FindChannelsByType(ChannelTypeWorld)
}

// GetCustomChannels returns all custom channels (O(1))
func (ml *MasterList) GetCustomChannels() []*Channel {
	return ml.FindChannelsByType(ChannelTypeCustom)
}

// GetActiveChannels returns channels that have members
func (ml *MasterList) GetActiveChannels() []*Channel {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()

	var result []*Channel
	for _, channel := range ml.channels {
		if !channel.IsEmpty() {
			result = append(result, channel)
		}
	}

	return result
}

// GetEmptyChannels returns channels that have no members
func (ml *MasterList) GetEmptyChannels() []*Channel {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()

	var result []*Channel
	for _, channel := range ml.channels {
		if channel.IsEmpty() {
			result = append(result, channel)
		}
	}

	return result
}

// GetChannelByName retrieves a channel by name (case-insensitive, O(1))
func (ml *MasterList) GetChannelByName(name string) *Channel {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()
	return ml.byNameLower[strings.ToLower(name)]
}

// HasChannelByName checks if a channel exists by name (case-insensitive, O(1))
func (ml *MasterList) HasChannelByName(name string) bool {
	return ml.GetChannelByName(name) != nil
}

// GetCompatibleChannels returns channels compatible with player restrictions
func (ml *MasterList) GetCompatibleChannels(level, race, class int32) []*Channel {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()

	var result []*Channel
	for _, channel := range ml.channels {
		if channel.CanJoinChannelByLevel(level) &&
			channel.CanJoinChannelByRace(race) &&
			channel.CanJoinChannelByClass(class) {
			result = append(result, channel)
		}
	}

	return result
}

// GetChannelsByMemberCount returns channels with specific member count
func (ml *MasterList) GetChannelsByMemberCount(memberCount int) []*Channel {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()
	return ml.byMemberCt[memberCount]
}

// GetChannelsByLevelRestriction returns channels with specific level restriction
func (ml *MasterList) GetChannelsByLevelRestriction(levelRestriction int32) []*Channel {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()
	return ml.byRestrict[levelRestriction]
}

// UpdateChannel updates an existing channel and refreshes indices
func (ml *MasterList) UpdateChannel(channel *Channel) error {
	if channel == nil {
		return fmt.Errorf("channel cannot be nil")
	}

	ml.mutex.Lock()
	defer ml.mutex.Unlock()

	// Check if exists
	old, exists := ml.channels[channel.ID]
	if !exists {
		return fmt.Errorf("channel %d not found", channel.ID)
	}

	// Remove old channel from indices (but not core storage yet)
	ml.updateChannelIndices(old, false)

	// Update core storage
	ml.channels[channel.ID] = channel

	// Add new channel to indices
	ml.updateChannelIndices(channel, true)

	// Invalidate metadata cache
	ml.metaStale = true

	return nil
}

// ForEach executes a function for each channel
func (ml *MasterList) ForEach(fn func(int32, *Channel)) {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()

	for id, channel := range ml.channels {
		fn(id, channel)
	}
}

// ValidateChannels checks all channels for consistency
func (ml *MasterList) ValidateChannels() []string {
	ml.mutex.RLock()
	defer ml.mutex.RUnlock()

	var issues []string

	for id, channel := range ml.channels {
		if channel == nil {
			issues = append(issues, fmt.Sprintf("Channel ID %d is nil", id))
			continue
		}

		if channel.GetID() != id {
			issues = append(issues, fmt.Sprintf("Channel ID mismatch: map key %d != channel ID %d", id, channel.GetID()))
		}

		if len(channel.GetName()) == 0 {
			issues = append(issues, fmt.Sprintf("Channel ID %d has empty name", id))
		}

		if channel.GetType() < ChannelTypeNone || channel.GetType() > ChannelTypeCustom {
			issues = append(issues, fmt.Sprintf("Channel ID %d has invalid type: %d", id, channel.GetType()))
		}

		if len(channel.GetName()) > MaxChannelNameLength {
			issues = append(issues, fmt.Sprintf("Channel ID %d name too long: %d > %d", id, len(channel.GetName()), MaxChannelNameLength))
		}

		if len(channel.Password) > MaxChannelPasswordLength {
			issues = append(issues, fmt.Sprintf("Channel ID %d password too long: %d > %d", id, len(channel.Password), MaxChannelPasswordLength))
		}
	}

	return issues
}

// IsValid returns true if all channels are valid
func (ml *MasterList) IsValid() bool {
	issues := ml.ValidateChannels()
	return len(issues) == 0
}

// GetStatistics returns statistics about the channel collection using cached data
func (ml *MasterList) GetStatistics() map[string]any {
	ml.mutex.Lock() // Need write lock to potentially update cache
	defer ml.mutex.Unlock()

	ml.refreshMetaCache()

	stats := make(map[string]any)
	stats["total_channels"] = len(ml.channels)

	if len(ml.channels) == 0 {
		return stats
	}

	// Use cached type stats
	stats["channels_by_type"] = ml.typeStats
	stats["world_channels"] = ml.typeStats[ChannelTypeWorld]
	stats["custom_channels"] = ml.typeStats[ChannelTypeCustom]

	// Calculate additional stats
	var totalMembers int
	var activeChannels int
	var minID, maxID int32
	first := true

	for id, channel := range ml.channels {
		totalMembers += channel.GetNumClients()

		if !channel.IsEmpty() {
			activeChannels++
		}

		if first {
			minID = id
			maxID = id
			first = false
		} else {
			if id < minID {
				minID = id
			}
			if id > maxID {
				maxID = id
			}
		}
	}

	stats["total_members"] = totalMembers
	stats["active_channels"] = activeChannels
	stats["min_id"] = minID
	stats["max_id"] = maxID
	stats["id_range"] = maxID - minID

	return stats
}

// LoadAllChannels loads all channels from the database into the master list
func (ml *MasterList) LoadAllChannels(db *database.Database) error {
	if db == nil {
		return fmt.Errorf("database connection is nil")
	}

	// Clear existing channels
	ml.Clear()

	query := `SELECT id, name, password, type, level_restriction, race_restriction, class_restriction, discord_enabled, created_at, updated_at FROM channels ORDER BY id`
	rows, err := db.Query(query)
	if err != nil {
		return fmt.Errorf("failed to query channels: %w", err)
	}
	defer rows.Close()

	count := 0
	for rows.Next() {
		channel := &Channel{
			db:      db,
			isNew:   false,
			members: make([]int32, 0),
		}

		err := rows.Scan(&channel.ID, &channel.Name, &channel.Password, &channel.ChannelType,
			&channel.LevelRestriction, &channel.RaceRestriction, &channel.ClassRestriction,
			&channel.DiscordEnabled, &channel.Created, &channel.Updated)
		if err != nil {
			return fmt.Errorf("failed to scan channel: %w", err)
		}

		if !ml.AddChannel(channel) {
			return fmt.Errorf("failed to add channel %d to master list", channel.ID)
		}

		count++
	}

	if err := rows.Err(); err != nil {
		return fmt.Errorf("error iterating channel rows: %w", err)
	}

	return nil
}

// LoadAllChannelsFromDatabase is a convenience function that creates a master list and loads all channels
func LoadAllChannelsFromDatabase(db *database.Database) (*MasterList, error) {
	masterList := NewMasterList()
	err := masterList.LoadAllChannels(db)
	if err != nil {
		return nil, err
	}
	return masterList, nil
}

// contains checks if a string contains a substring (case-sensitive)
func contains(str, substr string) bool {
	if len(substr) == 0 {
		return true
	}
	if len(str) < len(substr) {
		return false
	}

	for i := 0; i <= len(str)-len(substr); i++ {
		if str[i:i+len(substr)] == substr {
			return true
		}
	}

	return false
}