package session

import (
	"fmt"
	"net/http"
	"sort"
	"strings"
	"time"

	"agentu/internal/agent"
	"agentu/pkg/config"
	"agentu/pkg/llm"
)

type Manager struct {
	cfg            *config.Config
	agent          *agent.Agent
	httpClient     *http.Client
	providerName   string
	provider       config.ProviderConfig
	store          *Store
	currentSession *Session
}

func NewManager(cfg *config.Config, assistant *agent.Agent, httpClient *http.Client, store *Store) (*Manager, error) {
	if httpClient == nil {
		httpClient = http.DefaultClient
	}
	providerName := cfg.DefaultProviderName()
	provider, ok := cfg.Providers[providerName]
	if !ok {
		return nil, fmt.Errorf("no provider is configured")
	}
	m := &Manager{
		cfg:          cfg,
		agent:        assistant,
		httpClient:   httpClient,
		providerName: providerName,
		provider:     provider,
		store:        store,
	}
	return m, nil
}

// ResumeLatest loads the most recent session, or creates a new one.
func (m *Manager) ResumeLatest() error {
	if m.store == nil {
		return nil
	}
	metas, err := m.store.List()
	if err != nil {
		return err
	}
	if len(metas) > 0 {
		return m.Resume(metas[0].ID)
	}
	m.newSession()
	return nil
}

// Resume loads a session by ID and restores it into the agent.
func (m *Manager) Resume(id string) error {
	if m.store == nil {
		return fmt.Errorf("session storage is not configured")
	}
	sess, err := m.store.Load(id)
	if err != nil {
		return err
	}
	m.currentSession = sess
	m.agent.SetMessages(sess.Messages)
	m.agent.SetLastUsage(sess.LastUsage)
	return nil
}

// Save persists the current session to disk.
func (m *Manager) Save() error {
	if m.store == nil || m.currentSession == nil {
		return nil
	}
	m.currentSession.Messages = m.agent.Messages()
	m.currentSession.LastUsage = m.agent.LastUsage()
	m.currentSession.Provider = m.providerName
	m.currentSession.Model = m.provider.Model
	// Auto-name if empty
	if m.currentSession.Name == "" {
		m.currentSession.Name = DefaultName(m.currentSession.Messages)
	}
	return m.store.Save(m.currentSession)
}

// Rename changes the current session name and saves.
func (m *Manager) Rename(name string) (string, error) {
	name = strings.TrimSpace(name)
	if name == "" {
		return "", fmt.Errorf("name is required")
	}
	if m.currentSession == nil {
		return "", fmt.Errorf("no active session")
	}
	m.currentSession.Name = name
	if err := m.Save(); err != nil {
		return "", err
	}
	return fmt.Sprintf("Renamed session to %q.", name), nil
}

// Sessions returns a formatted list of all sessions.
func (m *Manager) Sessions() (string, error) {
	if m.store == nil {
		return "", fmt.Errorf("session storage is not configured")
	}
	metas, err := m.store.List()
	if err != nil {
		return "", err
	}
	if len(metas) == 0 {
		return "No saved sessions.", nil
	}
	var b strings.Builder
	b.WriteString("Sessions:\n")
	for _, meta := range metas {
		name := meta.Name
		if name == "" {
			name = "(unnamed)"
		}
		current := ""
		if m.currentSession != nil && meta.ID == m.currentSession.ID {
			current = " (current)"
		}
		ts := meta.UpdatedAt.Local().Format("2006-01-02 15:04")
		fmt.Fprintf(&b, "  %s  %-30s  %s  %d msgs%s\n", meta.ID, fitName(name, 30), ts, meta.MessageCount, current)
	}
	return b.String(), nil
}

// NewSession starts a fresh session, saving the current one first.
func (m *Manager) NewSession() (string, error) {
	// Save current if it has user messages
	if m.currentSession != nil {
		msgs := m.agent.Messages()
		hasUser := false
		for _, msg := range msgs {
			if msg.Role == llm.RoleUser {
				hasUser = true
				break
			}
		}
		if hasUser {
			m.currentSession.Messages = msgs
			m.currentSession.Provider = m.providerName
			m.currentSession.Model = m.provider.Model
			if m.currentSession.Name == "" {
				m.currentSession.Name = DefaultName(msgs)
			}
			if m.store != nil {
				_ = m.store.Save(m.currentSession)
			}
		}
	}
	m.newSession()
	return "Session saved. Starting new session.", nil
}

func (m *Manager) newSession() {
	m.currentSession = &Session{
		ID:        GenerateID(),
		CreatedAt: time.Now().UTC(),
		Provider:  m.providerName,
		Model:     m.provider.Model,
	}
	m.agent.Clear()
}

func (m *Manager) CurrentSessionID() string {
	if m.currentSession == nil {
		return ""
	}
	return m.currentSession.ID
}

func (m *Manager) CurrentSessionName() string {
	if m.currentSession == nil {
		return ""
	}
	if m.currentSession.Name != "" {
		return m.currentSession.Name
	}
	return m.currentSession.ID
}

func (m *Manager) CurrentProvider() string {
	return m.providerName
}

func (m *Manager) CurrentModel() string {
	return m.provider.Model
}

func (m *Manager) CurrentThinking() string {
	if !m.provider.ThinkingConfigured {
		return "unset"
	}
	return m.provider.Thinking
}

func (m *Manager) Info() string {
	var b strings.Builder
	fmt.Fprintf(&b, "provider: %s\n", m.CurrentProvider())
	fmt.Fprintf(&b, "model: %s\n", m.CurrentModel())
	fmt.Fprintf(&b, "thinking: %s\n", m.CurrentThinking())
	fmt.Fprintf(&b, "providers: %s\n", strings.Join(m.providerNames(), ", "))
	fmt.Fprintf(&b, "models: %s\n", strings.Join(m.provider.Models, ", "))
	fmt.Fprintf(&b, "thinking levels: %s\n", strings.Join(config.ThinkingLevels(), ", "))
	b.WriteString("usage: /model provider <name> | /model model <name> | /model thinking <level>")
	return b.String()
}

func (m *Manager) SetProvider(name string) (string, error) {
	provider, ok := m.cfg.Providers[name]
	if !ok {
		return "", fmt.Errorf("unknown provider %q; available: %s", name, strings.Join(m.providerNames(), ", "))
	}
	m.providerName = name
	m.provider = provider
	m.syncAgent(llm.NewOpenAICompatibleClient(provider.BaseURL, provider.APIKey, m.httpClient))
	return "Switched provider.\n" + m.summary(), nil
}

func (m *Manager) SetModel(model string) (string, error) {
	model = strings.TrimSpace(model)
	if model == "" {
		return "", fmt.Errorf("model is required")
	}
	if !contains(m.provider.Models, model) {
		return "", fmt.Errorf("model %q is not configured for provider %q; available: %s", model, m.providerName, strings.Join(m.provider.Models, ", "))
	}
	m.provider = m.provider.WithModel(model)
	m.cfg.Providers[m.providerName] = m.provider
	m.syncAgent(nil)
	return "Switched model.\n" + m.summary(), nil
}

func (m *Manager) SetThinking(level string) (string, error) {
	level = strings.ToLower(strings.TrimSpace(level))
	if !config.IsThinkingLevel(level) {
		return "", fmt.Errorf("thinking must be one of: %s", strings.Join(config.ThinkingLevels(), ", "))
	}
	m.provider.Thinking = level
	m.provider.ThinkingConfigured = true
	if m.provider.ThinkingParam == "" {
		m.provider.ThinkingParam = "thinking"
	}
	m.cfg.Providers[m.providerName] = m.provider
	m.syncAgent(nil)
	return "Updated thinking.\n" + m.summary(), nil
}

func (m *Manager) summary() string {
	return fmt.Sprintf("provider: %s\nmodel: %s\nthinking: %s", m.CurrentProvider(), m.CurrentModel(), m.CurrentThinking())
}

func (m *Manager) maxContextTokens() int {
	if m.cfg != nil && m.cfg.Agent.MaxContextTokens > 0 {
		return m.cfg.Agent.MaxContextTokens
	}
	return m.provider.ContextTokens
}

func (m *Manager) syncAgent(provider llm.Provider) {
	m.agent.SetRuntime(agent.RuntimeOptions{
		Provider:         provider,
		ProviderName:     m.providerName,
		Model:            m.provider.Model,
		Thinking:         m.provider.Thinking,
		ThinkingParam:    m.provider.ThinkingParam,
		ThinkingEnabled:  m.provider.ThinkingConfigured,
		MaxContextTokens: m.maxContextTokens(),
	})
}

func (m *Manager) providerNames() []string {
	names := make([]string, 0, len(m.cfg.Providers))
	for name := range m.cfg.Providers {
		names = append(names, name)
	}
	sort.Strings(names)
	return names
}

func (m *Manager) AvailableModels() []string {
	return append([]string(nil), m.provider.Models...)
}

func contains(values []string, value string) bool {
	for _, v := range values {
		if v == value {
			return true
		}
	}
	return false
}

func fitName(name string, width int) string {
	if len(name) <= width {
		return name
	}
	return name[:width-3] + "..."
}