package api

import (
	"context"
	"errors"
	"slices"
	"sync"

	"github.com/google/uuid"
	"reichard.io/aethera/internal/store"
	"reichard.io/aethera/internal/types"
)

var errGenerationActive = errors.New("generation already active")

type generationManager struct {
	mu          sync.RWMutex
	generations map[uuid.UUID]*generation
}

type generation struct {
	mu          sync.RWMutex
	ctx         context.Context
	cancel      context.CancelFunc
	subscribers map[chan *MessageChunk]struct{}
	done        chan struct{}
	closed      bool
}

func newGenerationManager() *generationManager {
	return &generationManager{generations: make(map[uuid.UUID]*generation)}
}

func (m *generationManager) start(chatID uuid.UUID, prepare func(*generation) error, run func(*generation)) error {
	m.mu.Lock()
	if _, found := m.generations[chatID]; found {
		m.mu.Unlock()
		return errGenerationActive
	}

	// Reserve Generation
	ctx, cancel := context.WithCancel(context.Background())
	gen := &generation{
		ctx:         ctx,
		cancel:      cancel,
		subscribers: make(map[chan *MessageChunk]struct{}),
		done:        make(chan struct{}),
	}
	m.generations[chatID] = gen
	m.mu.Unlock()

	// Prepare Generation - This runs while the generation is reserved so a
	// concurrent request cannot persist duplicate user/assistant messages.
	if err := prepare(gen); err != nil {
		gen.close()
		m.mu.Lock()
		delete(m.generations, chatID)
		m.mu.Unlock()
		return err
	}

	// Run Generation
	go func() {
		defer func() {
			gen.close()
			m.mu.Lock()
			delete(m.generations, chatID)
			m.mu.Unlock()
		}()
		run(gen)
	}()

	return nil
}

func (m *generationManager) subscribe(chatID uuid.UUID) (<-chan *MessageChunk, func(), bool) {
	m.mu.RLock()
	gen, found := m.generations[chatID]
	m.mu.RUnlock()
	if !found {
		return nil, func() {}, false
	}

	ch := gen.subscribe()
	return ch, func() { gen.unsubscribe(ch) }, true
}

func (m *generationManager) stop(chatID uuid.UUID) bool {
	m.mu.RLock()
	gen, found := m.generations[chatID]
	m.mu.RUnlock()
	if !found {
		return false
	}

	// Cancel Generation
	gen.cancel()
	return true
}

func (g *generation) subscribe() chan *MessageChunk {
	ch := make(chan *MessageChunk, 64)

	// Add Subscriber
	g.mu.Lock()
	if g.closed {
		close(ch)
	} else {
		g.subscribers[ch] = struct{}{}
	}
	g.mu.Unlock()

	return ch
}

func (g *generation) unsubscribe(ch chan *MessageChunk) {
	// Remove Subscriber
	g.mu.Lock()
	if _, found := g.subscribers[ch]; found {
		delete(g.subscribers, ch)
		close(ch)
	}
	g.mu.Unlock()
}

func (g *generation) broadcast(chunk *MessageChunk) {
	g.mu.RLock()
	defer g.mu.RUnlock()

	// Broadcast Chunk
	for subscriber := range g.subscribers {
		select {
		case subscriber <- cloneMessageChunk(chunk):
		default:
		}
	}
}

func (g *generation) close() {
	g.mu.Lock()
	defer g.mu.Unlock()

	// Close Subscribers
	if g.closed {
		return
	}
	g.closed = true
	g.cancel()
	close(g.done)
	for subscriber := range g.subscribers {
		close(subscriber)
		delete(g.subscribers, subscriber)
	}
}

func cloneMessageChunk(chunk *MessageChunk) *MessageChunk {
	if chunk == nil {
		return nil
	}

	// Clone Chunk
	cloned := &MessageChunk{
		Chat:             chunk.Chat,
		UserMessage:      cloneStoreMessage(chunk.UserMessage),
		AssistantMessage: cloneStoreMessage(chunk.AssistantMessage),
	}
	return cloned
}

func cloneStoreMessage(msg *store.Message) *store.Message {
	if msg == nil {
		return nil
	}

	// Clone Message
	cloned := *msg
	cloned.Images = slices.Clone(msg.Images)
	if msg.Stats != nil {
		stats := *msg.Stats
		cloned.Stats = &stats
		cloneMessageStatsPointers(msg.Stats, cloned.Stats)
	}
	return &cloned
}

func cloneMessageStatsPointers(src, dst *types.MessageStats) {
	// Clone Pointer Fields
	if src.EndTime != nil {
		v := *src.EndTime
		dst.EndTime = &v
	}
	if src.PromptTokens != nil {
		v := *src.PromptTokens
		dst.PromptTokens = &v
	}
	if src.GeneratedTokens != nil {
		v := *src.GeneratedTokens
		dst.GeneratedTokens = &v
	}
	if src.PromptPerSec != nil {
		v := *src.PromptPerSec
		dst.PromptPerSec = &v
	}
	if src.GeneratedPerSec != nil {
		v := *src.GeneratedPerSec
		dst.GeneratedPerSec = &v
	}
	if src.TimeToFirstToken != nil {
		v := *src.TimeToFirstToken
		dst.TimeToFirstToken = &v
	}
	if src.TimeToLastToken != nil {
		v := *src.TimeToLastToken
		dst.TimeToLastToken = &v
	}
}