package agent

import (
	"context"
	"errors"
	"fmt"
	"strings"
	"sync"
	"time"

	"github.com/opencode-ai/opencode/internal/config"
	"github.com/opencode-ai/opencode/internal/llm/models"
	"github.com/opencode-ai/opencode/internal/llm/prompt"
	"github.com/opencode-ai/opencode/internal/llm/provider"
	"github.com/opencode-ai/opencode/internal/llm/tools"
	"github.com/opencode-ai/opencode/internal/logging"
	"github.com/opencode-ai/opencode/internal/message"
	"github.com/opencode-ai/opencode/internal/permission"
	"github.com/opencode-ai/opencode/internal/pubsub"
	"github.com/opencode-ai/opencode/internal/session"
)

// Common errors
var (
	ErrRequestCancelled = errors.New("request cancelled by user")
	ErrSessionBusy      = errors.New("session is currently processing another request")
)

type AgentEventType string

const (
	AgentEventTypeError     AgentEventType = "error"
	AgentEventTypeResponse  AgentEventType = "response"
	AgentEventTypeSummarize AgentEventType = "summarize"
)

type AgentEvent struct {
	Type    AgentEventType
	Message message.Message
	Error   error

	// When summarizing
	SessionID string
	Progress  string
	Done      bool
}

type Service interface {
	pubsub.Suscriber[AgentEvent]
	Model() models.Model
	Run(ctx context.Context, sessionID string, content string, attachments ...message.Attachment) (<-chan AgentEvent, error)
	Cancel(sessionID string)
	IsSessionBusy(sessionID string) bool
	IsBusy() bool
	Update(agentName config.AgentName, modelID models.ModelID) (models.Model, error)
	Summarize(ctx context.Context, sessionID string) error
}

type agent struct {
	*pubsub.Broker[AgentEvent]
	sessions session.Service
	messages message.Service

	tools    []tools.BaseTool
	provider provider.Provider

	titleProvider     provider.Provider
	summarizeProvider provider.Provider

	activeRequests sync.Map
}

func NewAgent(
	agentName config.AgentName,
	sessions session.Service,
	messages message.Service,
	agentTools []tools.BaseTool,
) (Service, error) {
	agentProvider, err := createAgentProvider(agentName)
	if err != nil {
		return nil, err
	}
	var titleProvider provider.Provider
	// Only generate titles for the coder agent
	if agentName == config.AgentCoder {
		titleProvider, err = createAgentProvider(config.AgentTitle)
		if err != nil {
			return nil, err
		}
	}
	var summarizeProvider provider.Provider
	if agentName == config.AgentCoder {
		summarizeProvider, err = createAgentProvider(config.AgentSummarizer)
		if err != nil {
			return nil, err
		}
	}

	agent := &agent{
		Broker:            pubsub.NewBroker[AgentEvent](),
		provider:          agentProvider,
		messages:          messages,
		sessions:          sessions,
		tools:             agentTools,
		titleProvider:     titleProvider,
		summarizeProvider: summarizeProvider,
		activeRequests:    sync.Map{},
	}

	return agent, nil
}

func (a *agent) Model() models.Model {
	return a.provider.Model()
}

func (a *agent) Cancel(sessionID string) {
	// Cancel regular requests
	if cancelFunc, exists := a.activeRequests.LoadAndDelete(sessionID); exists {
		if cancel, ok := cancelFunc.(context.CancelFunc); ok {
			logging.InfoPersist(fmt.Sprintf("Request cancellation initiated for session: %s", sessionID))
			cancel()
		}
	}

	// Also check for summarize requests
	if cancelFunc, exists := a.activeRequests.LoadAndDelete(sessionID + "-summarize"); exists {
		if cancel, ok := cancelFunc.(context.CancelFunc); ok {
			logging.InfoPersist(fmt.Sprintf("Summarize cancellation initiated for session: %s", sessionID))
			cancel()
		}
	}
}

func (a *agent) IsBusy() bool {
	busy := false
	a.activeRequests.Range(func(key, value interface{}) bool {
		if cancelFunc, ok := value.(context.CancelFunc); ok {
			if cancelFunc != nil {
				busy = true
				return false // Stop iterating
			}
		}
		return true // Continue iterating
	})
	return busy
}

func (a *agent) IsSessionBusy(sessionID string) bool {
	_, busy := a.activeRequests.Load(sessionID)
	return busy
}

func (a *agent) generateTitle(ctx context.Context, sessionID string, content string) error {
	if content == "" {
		return nil
	}
	if a.titleProvider == nil {
		return nil
	}
	session, err := a.sessions.Get(ctx, sessionID)
	if err != nil {
		return err
	}
	parts := []message.ContentPart{message.TextContent{Text: content}}
	response, err := a.titleProvider.SendMessages(
		ctx,
		[]message.Message{
			{
				Role:  message.User,
				Parts: parts,
			},
		},
		make([]tools.BaseTool, 0),
	)
	if err != nil {
		return err
	}

	title := strings.TrimSpace(strings.ReplaceAll(response.Content, "\n", " "))
	if title == "" {
		return nil
	}

	session.Title = title
	_, err = a.sessions.Save(ctx, session)
	return err
}

func (a *agent) err(err error) AgentEvent {
	return AgentEvent{
		Type:  AgentEventTypeError,
		Error: err,
	}
}

func (a *agent) Run(ctx context.Context, sessionID string, content string, attachments ...message.Attachment) (<-chan AgentEvent, error) {
	if !a.provider.Model().SupportsAttachments && attachments != nil {
		attachments = nil
	}
	events := make(chan AgentEvent)
	if a.IsSessionBusy(sessionID) {
		return nil, ErrSessionBusy
	}

	genCtx, cancel := context.WithCancel(ctx)

	a.activeRequests.Store(sessionID, cancel)
	go func() {
		logging.Debug("Request started", "sessionID", sessionID)
		defer logging.RecoverPanic("agent.Run", func() {
			events <- a.err(fmt.Errorf("panic while running the agent"))
		})
		var attachmentParts []message.ContentPart
		for _, attachment := range attachments {
			attachmentParts = append(attachmentParts, message.BinaryContent{Path: attachment.FilePath, MIMEType: attachment.MimeType, Data: attachment.Content})
		}
		result := a.processGeneration(genCtx, sessionID, content, attachmentParts)
		if result.Error != nil && !errors.Is(result.Error, ErrRequestCancelled) && !errors.Is(result.Error, context.Canceled) {
			logging.ErrorPersist(result.Error.Error())
		}
		logging.Debug("Request completed", "sessionID", sessionID)
		a.activeRequests.Delete(sessionID)
		cancel()
		a.Publish(pubsub.CreatedEvent, result)
		events <- result
		close(events)
	}()
	return events, nil
}

func (a *agent) processGeneration(ctx context.Context, sessionID, content string, attachmentParts []message.ContentPart) AgentEvent {
	// List existing messages; if none, start title generation asynchronously.
	msgs, err := a.messages.List(ctx, sessionID)
	if err != nil {
		return a.err(fmt.Errorf("failed to list messages: %w", err))
	}
	if len(msgs) == 0 {
		go func() {
			defer logging.RecoverPanic("agent.Run", func() {
				logging.ErrorPersist("panic while generating title")
			})
			titleErr := a.generateTitle(context.Background(), sessionID, content)
			if titleErr != nil {
				logging.ErrorPersist(fmt.Sprintf("failed to generate title: %v", titleErr))
			}
		}()
	}
	session, err := a.sessions.Get(ctx, sessionID)
	if err != nil {
		return a.err(fmt.Errorf("failed to get session: %w", err))
	}
	if session.SummaryMessageID != "" {
		summaryMsgInex := -1
		for i, msg := range msgs {
			if msg.ID == session.SummaryMessageID {
				summaryMsgInex = i
				break
			}
		}
		if summaryMsgInex != -1 {
			msgs = msgs[summaryMsgInex:]
			msgs[0].Role = message.User
		}
	}

	userMsg, err := a.createUserMessage(ctx, sessionID, content, attachmentParts)
	if err != nil {
		return a.err(fmt.Errorf("failed to create user message: %w", err))
	}
	// Append the new user message to the conversation history.
	msgHistory := append(msgs, userMsg)

	for {
		// Check for cancellation before each iteration
		select {
		case <-ctx.Done():
			return a.err(ctx.Err())
		default:
			// Continue processing
		}
		agentMessage, toolResults, err := a.streamAndHandleEvents(ctx, sessionID, msgHistory)
		if err != nil {
			if errors.Is(err, context.Canceled) {
				agentMessage.AddFinish(message.FinishReasonCanceled)
				a.messages.Update(context.Background(), agentMessage)
				return a.err(ErrRequestCancelled)
			}
			return a.err(fmt.Errorf("failed to process events: %w", err))
		}
		logging.Info("Result", "message", agentMessage.FinishReason(), "toolResults", toolResults)
		if (agentMessage.FinishReason() == message.FinishReasonToolUse) && toolResults != nil {
			// We are not done, we need to respond with the tool response
			msgHistory = append(msgHistory, agentMessage, *toolResults)
			continue
		}
		return AgentEvent{
			Type:    AgentEventTypeResponse,
			Message: agentMessage,
			Done:    true,
		}
	}
}

func (a *agent) createUserMessage(ctx context.Context, sessionID, content string, attachmentParts []message.ContentPart) (message.Message, error) {
	parts := []message.ContentPart{message.TextContent{Text: content}}
	parts = append(parts, attachmentParts...)
	return a.messages.Create(ctx, sessionID, message.CreateMessageParams{
		Role:  message.User,
		Parts: parts,
	})
}

func (a *agent) streamAndHandleEvents(ctx context.Context, sessionID string, msgHistory []message.Message) (message.Message, *message.Message, error) {
	eventChan := a.provider.StreamResponse(ctx, msgHistory, a.tools)

	assistantMsg, err := a.messages.Create(ctx, sessionID, message.CreateMessageParams{
		Role:  message.Assistant,
		Parts: []message.ContentPart{},
		Model: a.provider.Model().ID,
	})
	if err != nil {
		return assistantMsg, nil, fmt.Errorf("failed to create assistant message: %w", err)
	}

	// Add the session and message ID into the context if needed by tools.
	ctx = context.WithValue(ctx, tools.MessageIDContextKey, assistantMsg.ID)
	ctx = context.WithValue(ctx, tools.SessionIDContextKey, sessionID)

	// Process each event in the stream.
	for event := range eventChan {
		if processErr := a.processEvent(ctx, sessionID, &assistantMsg, event); processErr != nil {
			a.finishMessage(ctx, &assistantMsg, message.FinishReasonCanceled)
			return assistantMsg, nil, processErr
		}
		if ctx.Err() != nil {
			a.finishMessage(context.Background(), &assistantMsg, message.FinishReasonCanceled)
			return assistantMsg, nil, ctx.Err()
		}
	}

	toolResults := make([]message.ToolResult, len(assistantMsg.ToolCalls()))
	toolCalls := assistantMsg.ToolCalls()
	for i, toolCall := range toolCalls {
		select {
		case <-ctx.Done():
			a.finishMessage(context.Background(), &assistantMsg, message.FinishReasonCanceled)
			// Make all future tool calls cancelled
			for j := i; j < len(toolCalls); j++ {
				toolResults[j] = message.ToolResult{
					ToolCallID: toolCalls[j].ID,
					Content:    "Tool execution canceled by user",
					IsError:    true,
				}
			}
			goto out
		default:
			// Continue processing
			var tool tools.BaseTool
			for _, availableTools := range a.tools {
				if availableTools.Info().Name == toolCall.Name {
					tool = availableTools
				}
			}

			// Tool not found
			if tool == nil {
				toolResults[i] = message.ToolResult{
					ToolCallID: toolCall.ID,
					Content:    fmt.Sprintf("Tool not found: %s", toolCall.Name),
					IsError:    true,
				}
				continue
			}
			toolResult, toolErr := tool.Run(ctx, tools.ToolCall{
				ID:    toolCall.ID,
				Name:  toolCall.Name,
				Input: toolCall.Input,
			})
			if toolErr != nil {
				if errors.Is(toolErr, permission.ErrorPermissionDenied) {
					toolResults[i] = message.ToolResult{
						ToolCallID: toolCall.ID,
						Content:    "Permission denied",
						IsError:    true,
					}
					for j := i + 1; j < len(toolCalls); j++ {
						toolResults[j] = message.ToolResult{
							ToolCallID: toolCalls[j].ID,
							Content:    "Tool execution canceled by user",
							IsError:    true,
						}
					}
					a.finishMessage(ctx, &assistantMsg, message.FinishReasonPermissionDenied)
					break
				}
			}
			toolResults[i] = message.ToolResult{
				ToolCallID: toolCall.ID,
				Content:    toolResult.Content,
				Metadata:   toolResult.Metadata,
				IsError:    toolResult.IsError,
			}
		}
	}
out:
	if len(toolResults) == 0 {
		return assistantMsg, nil, nil
	}
	parts := make([]message.ContentPart, 0)
	for _, tr := range toolResults {
		parts = append(parts, tr)
	}
	msg, err := a.messages.Create(context.Background(), assistantMsg.SessionID, message.CreateMessageParams{
		Role:  message.Tool,
		Parts: parts,
	})
	if err != nil {
		return assistantMsg, nil, fmt.Errorf("failed to create cancelled tool message: %w", err)
	}

	return assistantMsg, &msg, err
}

func (a *agent) finishMessage(ctx context.Context, msg *message.Message, finishReson message.FinishReason) {
	msg.AddFinish(finishReson)
	_ = a.messages.Update(ctx, *msg)
}

func (a *agent) processEvent(ctx context.Context, sessionID string, assistantMsg *message.Message, event provider.ProviderEvent) error {
	select {
	case <-ctx.Done():
		return ctx.Err()
	default:
		// Continue processing.
	}

	switch event.Type {
	case provider.EventThinkingDelta:
		assistantMsg.AppendReasoningContent(event.Content)
		return a.messages.Update(ctx, *assistantMsg)
	case provider.EventContentDelta:
		assistantMsg.AppendContent(event.Content)
		return a.messages.Update(ctx, *assistantMsg)
	case provider.EventToolUseStart:
		assistantMsg.AddToolCall(*event.ToolCall)
		return a.messages.Update(ctx, *assistantMsg)
	// TODO: see how to handle this
	// case provider.EventToolUseDelta:
	// 	tm := time.Unix(assistantMsg.UpdatedAt, 0)
	// 	assistantMsg.AppendToolCallInput(event.ToolCall.ID, event.ToolCall.Input)
	// 	if time.Since(tm) > 1000*time.Millisecond {
	// 		err := a.messages.Update(ctx, *assistantMsg)
	// 		assistantMsg.UpdatedAt = time.Now().Unix()
	// 		return err
	// 	}
	case provider.EventToolUseStop:
		assistantMsg.FinishToolCall(event.ToolCall.ID)
		return a.messages.Update(ctx, *assistantMsg)
	case provider.EventError:
		if errors.Is(event.Error, context.Canceled) {
			logging.InfoPersist(fmt.Sprintf("Event processing canceled for session: %s", sessionID))
			return context.Canceled
		}
		logging.ErrorPersist(event.Error.Error())
		return event.Error
	case provider.EventComplete:
		assistantMsg.SetToolCalls(event.Response.ToolCalls)
		assistantMsg.AddFinish(event.Response.FinishReason)
		if err := a.messages.Update(ctx, *assistantMsg); err != nil {
			return fmt.Errorf("failed to update message: %w", err)
		}
		return a.TrackUsage(ctx, sessionID, a.provider.Model(), event.Response.Usage)
	}

	return nil
}

func (a *agent) TrackUsage(ctx context.Context, sessionID string, model models.Model, usage provider.TokenUsage) error {
	sess, err := a.sessions.Get(ctx, sessionID)
	if err != nil {
		return fmt.Errorf("failed to get session: %w", err)
	}

	cost := model.CostPer1MInCached/1e6*float64(usage.CacheCreationTokens) +
		model.CostPer1MOutCached/1e6*float64(usage.CacheReadTokens) +
		model.CostPer1MIn/1e6*float64(usage.InputTokens) +
		model.CostPer1MOut/1e6*float64(usage.OutputTokens)

	sess.Cost += cost
	sess.CompletionTokens = usage.OutputTokens + usage.CacheReadTokens
	sess.PromptTokens = usage.InputTokens + usage.CacheCreationTokens

	_, err = a.sessions.Save(ctx, sess)
	if err != nil {
		return fmt.Errorf("failed to save session: %w", err)
	}
	return nil
}

func (a *agent) Update(agentName config.AgentName, modelID models.ModelID) (models.Model, error) {
	if a.IsBusy() {
		return models.Model{}, fmt.Errorf("cannot change model while processing requests")
	}

	if err := config.UpdateAgentModel(agentName, modelID); err != nil {
		return models.Model{}, fmt.Errorf("failed to update config: %w", err)
	}

	provider, err := createAgentProvider(agentName)
	if err != nil {
		return models.Model{}, fmt.Errorf("failed to create provider for model %s: %w", modelID, err)
	}

	a.provider = provider

	return a.provider.Model(), nil
}

func (a *agent) Summarize(ctx context.Context, sessionID string) error {
	if a.summarizeProvider == nil {
		return fmt.Errorf("summarize provider not available")
	}

	// Check if session is busy
	if a.IsSessionBusy(sessionID) {
		return ErrSessionBusy
	}

	// Create a new context with cancellation
	summarizeCtx, cancel := context.WithCancel(ctx)

	// Store the cancel function in activeRequests to allow cancellation
	a.activeRequests.Store(sessionID+"-summarize", cancel)

	go func() {
		defer a.activeRequests.Delete(sessionID + "-summarize")
		defer cancel()
		event := AgentEvent{
			Type:     AgentEventTypeSummarize,
			Progress: "Starting summarization...",
		}

		a.Publish(pubsub.CreatedEvent, event)
		// Get all messages from the session
		msgs, err := a.messages.List(summarizeCtx, sessionID)
		if err != nil {
			event = AgentEvent{
				Type:  AgentEventTypeError,
				Error: fmt.Errorf("failed to list messages: %w", err),
				Done:  true,
			}
			a.Publish(pubsub.CreatedEvent, event)
			return
		}

		if len(msgs) == 0 {
			event = AgentEvent{
				Type:  AgentEventTypeError,
				Error: fmt.Errorf("no messages to summarize"),
				Done:  true,
			}
			a.Publish(pubsub.CreatedEvent, event)
			return
		}
		session, err := a.sessions.Get(summarizeCtx, sessionID)
		if err != nil {
			event = AgentEvent{
				Type:  AgentEventTypeError,
				Error: fmt.Errorf("failed to get session: %w", err),
				Done:  true,
			}
			a.Publish(pubsub.CreatedEvent, event)
			return
		}
		if session.SummaryMessageID != "" {
			summaryMsgInex := -1
			for i, msg := range msgs {
				if msg.ID == session.SummaryMessageID {
					summaryMsgInex = i
					break
				}
			}
			if summaryMsgInex != -1 {
				msgs = msgs[summaryMsgInex:]
				msgs[0].Role = message.User
			}
		}

		event = AgentEvent{
			Type:     AgentEventTypeSummarize,
			Progress: "Analyzing conversation...",
		}
		a.Publish(pubsub.CreatedEvent, event)

		// Add a system message to guide the summarization
		summarizePrompt := "Provide a detailed but concise summary of our conversation above. Focus on information that would be helpful for continuing the conversation, including what we did, what we're doing, which files we're working on, and what we're going to do next."

		// Create a new message with the summarize prompt
		promptMsg := message.Message{
			Role:  message.User,
			Parts: []message.ContentPart{message.TextContent{Text: summarizePrompt}},
		}

		// Append the prompt to the messages
		msgsWithPrompt := append(msgs, promptMsg)

		event = AgentEvent{
			Type:     AgentEventTypeSummarize,
			Progress: "Generating summary...",
		}

		a.Publish(pubsub.CreatedEvent, event)

		// Send the messages to the summarize provider
		response, err := a.summarizeProvider.SendMessages(
			summarizeCtx,
			msgsWithPrompt,
			make([]tools.BaseTool, 0),
		)
		if err != nil {
			event = AgentEvent{
				Type:  AgentEventTypeError,
				Error: fmt.Errorf("failed to summarize: %w", err),
				Done:  true,
			}
			a.Publish(pubsub.CreatedEvent, event)
			return
		}

		summary := strings.TrimSpace(response.Content)
		if summary == "" {
			event = AgentEvent{
				Type:  AgentEventTypeError,
				Error: fmt.Errorf("empty summary returned"),
				Done:  true,
			}
			a.Publish(pubsub.CreatedEvent, event)
			return
		}
		event = AgentEvent{
			Type:     AgentEventTypeSummarize,
			Progress: "Creating new session...",
		}

		a.Publish(pubsub.CreatedEvent, event)
		oldSession, err := a.sessions.Get(summarizeCtx, sessionID)
		if err != nil {
			event = AgentEvent{
				Type:  AgentEventTypeError,
				Error: fmt.Errorf("failed to get session: %w", err),
				Done:  true,
			}

			a.Publish(pubsub.CreatedEvent, event)
			return
		}
		// Create a message in the new session with the summary
		msg, err := a.messages.Create(summarizeCtx, oldSession.ID, message.CreateMessageParams{
			Role: message.Assistant,
			Parts: []message.ContentPart{
				message.TextContent{Text: summary},
				message.Finish{
					Reason: message.FinishReasonEndTurn,
					Time:   time.Now().Unix(),
				},
			},
			Model: a.summarizeProvider.Model().ID,
		})
		if err != nil {
			event = AgentEvent{
				Type:  AgentEventTypeError,
				Error: fmt.Errorf("failed to create summary message: %w", err),
				Done:  true,
			}

			a.Publish(pubsub.CreatedEvent, event)
			return
		}
		oldSession.SummaryMessageID = msg.ID
		oldSession.CompletionTokens = response.Usage.OutputTokens
		oldSession.PromptTokens = 0
		model := a.summarizeProvider.Model()
		usage := response.Usage
		cost := model.CostPer1MInCached/1e6*float64(usage.CacheCreationTokens) +
			model.CostPer1MOutCached/1e6*float64(usage.CacheReadTokens) +
			model.CostPer1MIn/1e6*float64(usage.InputTokens) +
			model.CostPer1MOut/1e6*float64(usage.OutputTokens)
		oldSession.Cost += cost
		_, err = a.sessions.Save(summarizeCtx, oldSession)
		if err != nil {
			event = AgentEvent{
				Type:  AgentEventTypeError,
				Error: fmt.Errorf("failed to save session: %w", err),
				Done:  true,
			}
			a.Publish(pubsub.CreatedEvent, event)
		}

		event = AgentEvent{
			Type:      AgentEventTypeSummarize,
			SessionID: oldSession.ID,
			Progress:  "Summary complete",
			Done:      true,
		}
		a.Publish(pubsub.CreatedEvent, event)
		// Send final success event with the new session ID
	}()

	return nil
}

func createAgentProvider(agentName config.AgentName) (provider.Provider, error) {
	cfg := config.Get()
	agentConfig, ok := cfg.Agents[agentName]
	if !ok {
		return nil, fmt.Errorf("agent %s not found", agentName)
	}
	model, ok := models.SupportedModels[agentConfig.Model]
	if !ok {
		return nil, fmt.Errorf("model %s not supported", agentConfig.Model)
	}

	providerCfg, ok := cfg.Providers[model.Provider]
	if !ok {
		return nil, fmt.Errorf("provider %s not supported", model.Provider)
	}
	if providerCfg.Disabled {
		return nil, fmt.Errorf("provider %s is not enabled", model.Provider)
	}
	maxTokens := model.DefaultMaxTokens
	if agentConfig.MaxTokens > 0 {
		maxTokens = agentConfig.MaxTokens
	}
	opts := []provider.ProviderClientOption{
		provider.WithAPIKey(providerCfg.APIKey),
		provider.WithModel(model),
		provider.WithSystemMessage(prompt.GetAgentPrompt(agentName, model.Provider)),
		provider.WithMaxTokens(maxTokens),
	}
	if model.Provider == models.ProviderOpenAI && model.CanReason {
		opts = append(
			opts,
			provider.WithOpenAIOptions(
				provider.WithReasoningEffort(agentConfig.ReasoningEffort),
			),
		)
	} else if model.Provider == models.ProviderAnthropic && model.CanReason && agentName == config.AgentCoder {
		opts = append(
			opts,
			provider.WithAnthropicOptions(
				provider.WithAnthropicShouldThinkFn(provider.DefaultShouldThinkFn),
			),
		)
	}
	agentProvider, err := provider.NewProvider(
		model.Provider,
		opts...,
	)
	if err != nil {
		return nil, fmt.Errorf("could not create provider: %v", err)
	}

	return agentProvider, nil
}