package chatd

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"strings"
	"time"

	"github.com/google/uuid"
	"golang.org/x/xerrors"

	"github.com/coder/coder/v2/coderd/database"
	"github.com/coder/coder/v2/coderd/database/db2sdk"
	coderdpubsub "github.com/coder/coder/v2/coderd/pubsub"
	"github.com/coder/coder/v2/coderd/x/chatd/chatdebug"
	"github.com/coder/coder/v2/coderd/x/chatd/chatprompt"
	"github.com/coder/coder/v2/coderd/x/chatd/chatstate"
	"github.com/coder/coder/v2/coderd/x/chatd/messagepartbuffer"
	"github.com/coder/coder/v2/codersdk"
	"github.com/coder/quartz"
)

const postCommitWatchPublishTimeout = 10 * time.Second

var (
	errTaskExpectedExit = xerrors.New("chatworker task expected exit")
	errTaskRetryable    = xerrors.New("chatworker task retryable error")
)

type taskRetryableError struct {
	err error
}

func (e taskRetryableError) Error() string {
	if e.err == nil {
		return errTaskRetryable.Error()
	}
	return e.err.Error()
}

func (e taskRetryableError) Unwrap() error {
	if e.err == nil {
		return errTaskRetryable
	}
	return errors.Join(errTaskRetryable, e.err)
}

type retryWrapperOptions struct {
	clock        quartz.Clock
	initialDelay time.Duration
	maxDelay     time.Duration
}

func runTaskWithRetry(
	ctx context.Context,
	opts retryWrapperOptions,
	kind taskKind,
	fn func(context.Context) error,
) error {
	if opts.clock == nil {
		opts.clock = quartz.NewReal()
	}
	if opts.initialDelay <= 0 {
		opts.initialDelay = defaultTaskRetryInitialBackoff
	}
	if opts.maxDelay <= 0 {
		opts.maxDelay = defaultTaskRetryMaxBackoff
	}
	if opts.maxDelay < opts.initialDelay {
		opts.maxDelay = opts.initialDelay
	}

	delay := opts.initialDelay
	for {
		err := executeTaskSafely(ctx, fn)
		switch {
		case err == nil:
			return nil
		case errors.Is(err, errTaskExpectedExit):
			return nil
		case ctx.Err() != nil:
			return nil
		}

		timer := opts.clock.NewTimer(delay, "chatworker", "task-retry-"+string(kind))
		select {
		case <-timer.C:
		case <-ctx.Done():
			timer.Stop()
			return nil
		}
		timer.Stop()
		if delay < opts.maxDelay {
			delay *= 2
			if delay > opts.maxDelay {
				delay = opts.maxDelay
			}
		}
	}
}

func executeTaskSafely(ctx context.Context, fn func(context.Context) error) (err error) {
	defer func() {
		if recovered := recover(); recovered != nil {
			err = xerrors.Errorf("chatworker task panic: %v", recovered)
		}
	}()
	return fn(ctx)
}

type interruptionOutcome struct {
	Chat           database.Chat
	Kind           runnerActionKind
	WatchEventKind codersdk.ChatWatchEventKind
}

type taskStarter struct {
	server                   *Server
	opts                     chatWorkerOptions
	routeStateHint           func(context.Context, runnerStateUpdate)
	requestCleanup           func(context.Context, runnerKey)
	afterInterruptionOutcome func(context.Context, interruptionOutcome) error
}

func newTaskStarter(
	server *Server,
	opts chatWorkerOptions,
	routeStateHint func(context.Context, runnerStateUpdate),
	requestCleanup func(context.Context, runnerKey),
) (*taskStarter, error) {
	if opts.Store == nil {
		return nil, xerrors.New("chatworker: task store is required")
	}
	if opts.Pubsub == nil {
		return nil, xerrors.New("chatworker: task pubsub is required")
	}
	if opts.MessagePartBuffer == nil {
		return nil, xerrors.New("chatworker: message part buffer is required")
	}
	if opts.Clock == nil {
		opts.Clock = quartz.NewReal()
	}
	if opts.TaskRetryInitialBackoff <= 0 {
		opts.TaskRetryInitialBackoff = defaultTaskRetryInitialBackoff
	}
	if opts.TaskRetryMaxBackoff <= 0 {
		opts.TaskRetryMaxBackoff = defaultTaskRetryMaxBackoff
	}
	if opts.TaskRetryMaxBackoff < opts.TaskRetryInitialBackoff {
		opts.TaskRetryMaxBackoff = opts.TaskRetryInitialBackoff
	}
	if routeStateHint == nil {
		return nil, xerrors.New("chatworker: route state hint callback is required")
	}
	if requestCleanup == nil {
		return nil, xerrors.New("chatworker: cleanup callback is required")
	}
	return &taskStarter{
		server:         server,
		opts:           opts,
		routeStateHint: routeStateHint,
		requestCleanup: requestCleanup,
	}, nil
}

func (o chatWorkerOptions) retryOptions() retryWrapperOptions {
	return retryWrapperOptions{
		clock:        o.Clock,
		initialDelay: o.TaskRetryInitialBackoff,
		maxDelay:     o.TaskRetryMaxBackoff,
	}
}

func (s *taskStarter) StartInterrupt(ctx context.Context, input chatWorkerTaskStartInput) error {
	machine := chatstate.NewChatMachine(s.opts.Store, s.opts.Pubsub, input.ChatID)
	var chat database.Chat
	err := machine.ReadLock(ctx, func(store database.Store) error {
		locked, err := store.GetChatByID(ctx, input.ChatID)
		if errors.Is(err, sql.ErrNoRows) {
			return errTaskExpectedExit
		}
		if err != nil {
			return xerrors.Errorf("load locked chat: %w", err)
		}
		if err := verifyTaskFence(locked, input, database.ChatStatusInterrupting, taskFenceOptions{requireHistory: true}); err != nil {
			return err
		}
		chat = locked
		return nil
	})
	if err != nil {
		return normalizeTaskInfrastructureError(err, "lock chat for interrupt")
	}

	key := messagepartbuffer.Key{
		ChatID:            input.ChatID,
		HistoryVersion:    input.HistoryVersion,
		GenerationAttempt: chat.GenerationAttempt,
	}
	if err := s.opts.MessagePartBuffer.CloseEpisode(key); err != nil {
		if ctx.Err() != nil {
			return errTaskExpectedExit
		}
		return taskRetryableError{err: xerrors.Errorf("close message part episode: %w", err)}
	}
	parts, err := s.opts.MessagePartBuffer.GetParts(key)
	if errors.Is(err, messagepartbuffer.ErrEpisodeNotFound) {
		parts = nil
		err = nil
	}
	if err != nil {
		if ctx.Err() != nil {
			return errTaskExpectedExit
		}
		return taskRetryableError{err: xerrors.Errorf("get message part episode: %w", err)}
	}
	partialMessages, err := bufferedPartsToPartialMessages(bufferedPartsToPartialMessagesInput{
		parts:          parts,
		modelConfigID:  chat.LastModelConfigID,
		contentVersion: chatprompt.CurrentContentVersion,
		logger:         s.opts.Logger,
		interruptedAt:  s.opts.Clock.Now("chatworker", "interrupt"),
	})
	if err != nil {
		return xerrors.Errorf("convert buffered parts: %w", err)
	}

	var committed database.Chat
	err = machine.Update(ctx, func(tx *chatstate.Tx, store database.Store) error {
		locked, err := store.GetChatByID(ctx, input.ChatID)
		if errors.Is(err, sql.ErrNoRows) {
			return errTaskExpectedExit
		}
		if err != nil {
			return xerrors.Errorf("load chat: %w", err)
		}
		if err := verifyTaskFence(locked, input, database.ChatStatusInterrupting, taskFenceOptions{requireHistory: true}); err != nil {
			return err
		}
		messages := partialMessages
		committedCancels, err := committedPendingLocalToolCancellationMessages(ctx, store, locked, s.opts.Clock.Now("chatworker", "interrupt"))
		if err != nil {
			return err
		}
		if len(committedCancels) > 0 {
			messages = append(append([]chatstate.Message{}, partialMessages...), committedCancels...)
		}
		if _, err := tx.FinishInterruption(chatstate.FinishInterruptionInput{PartialMessages: messages}); err != nil {
			return err
		}
		committed, err = store.GetChatByID(ctx, input.ChatID)
		if err != nil {
			return xerrors.Errorf("load committed chat: %w", err)
		}
		return nil
	})
	if err != nil {
		if current, ok := s.committedStateAfterUpdateError(ctx, committed); ok {
			return s.publishWatchAndRoute(ctx, current, codersdk.ChatWatchEventKindStatusChange)
		}
		return normalizeTaskTransitionError(err, "finish interruption")
	}
	input.DebugTurn.RecordOutcome(chatdebug.StatusInterrupted)
	if err := s.publishWatchAndRoute(ctx, committed, codersdk.ChatWatchEventKindStatusChange); err != nil {
		return err
	}
	return s.runAfterInterruptionOutcome(ctx, interruptionOutcome{
		Chat:           committed,
		Kind:           runnerActionKindFinishInterruption,
		WatchEventKind: codersdk.ChatWatchEventKindStatusChange,
	})
}

func (s *taskStarter) runAfterInterruptionOutcome(ctx context.Context, outcome interruptionOutcome) error {
	afterOutcome := s.afterInterruptionOutcome
	if afterOutcome == nil && s.server != nil {
		afterOutcome = s.server.afterInterruptionOutcome
	}
	if afterOutcome == nil {
		return nil
	}
	if err := afterOutcome(ctx, outcome); err != nil {
		return taskRetryableError{err: xerrors.Errorf("interruption post-outcome side effects: %w", err)}
	}
	return nil
}

func (s *taskStarter) StartRequiresActionTimeout(ctx context.Context, input chatWorkerTaskStartInput) error {
	machine := chatstate.NewChatMachine(s.opts.Store, s.opts.Pubsub, input.ChatID)
	for {
		decision, err := decideRequiresActionTimeout(ctx, machine, input)
		if err != nil {
			return err
		}
		if decision.cancel {
			return s.cancelRequiresAction(ctx, machine, input, decision.reason)
		}
		if !decision.waitUntil.Valid {
			return errTaskExpectedExit
		}
		if err := s.waitUntil(ctx, decision.waitUntil.Time); err != nil {
			return err
		}
	}
}

type requiresActionTimeoutDecision struct {
	cancel    bool
	reason    string
	waitUntil sql.NullTime
}

func decideRequiresActionTimeout(
	ctx context.Context,
	machine *chatstate.ChatMachine,
	input chatWorkerTaskStartInput,
) (requiresActionTimeoutDecision, error) {
	var decision requiresActionTimeoutDecision
	err := machine.ReadLock(ctx, func(store database.Store) error {
		locked, err := store.GetChatByID(ctx, input.ChatID)
		if errors.Is(err, sql.ErrNoRows) {
			return errTaskExpectedExit
		}
		if err != nil {
			return xerrors.Errorf("load locked chat: %w", err)
		}
		if err := verifyTaskFence(locked, input, database.ChatStatusRequiresAction, taskFenceOptions{requireHistory: true}); err != nil {
			return err
		}
		if !locked.RequiresActionDeadlineAt.Valid {
			decision.cancel = true
			decision.reason = "Tool execution canceled because the action deadline was missing"
			return nil
		}
		now, err := store.GetDatabaseNow(ctx)
		if err != nil {
			return xerrors.Errorf("get database time: %w", err)
		}
		if now.Before(locked.RequiresActionDeadlineAt.Time) {
			decision.waitUntil = locked.RequiresActionDeadlineAt
			return nil
		}
		decision.cancel = true
		decision.reason = "Tool execution timed out"
		return nil
	})
	if err != nil {
		return requiresActionTimeoutDecision{}, normalizeTaskInfrastructureError(err, "lock chat for requires action timeout")
	}
	return decision, nil
}

func (s *taskStarter) waitUntil(ctx context.Context, deadline time.Time) error {
	now := s.opts.Clock.Now("chatworker", "requires-action-timeout")
	if !now.Before(deadline) {
		return nil
	}
	timer := s.opts.Clock.NewTimer(deadline.Sub(now), "chatworker", "requires-action-timeout")
	defer timer.Stop()
	select {
	case <-timer.C:
		return nil
	case <-ctx.Done():
		return errTaskExpectedExit
	}
}

func (s *taskStarter) cancelRequiresAction(
	ctx context.Context,
	machine *chatstate.ChatMachine,
	input chatWorkerTaskStartInput,
	reason string,
) error {
	var committed database.Chat
	err := machine.Update(ctx, func(tx *chatstate.Tx, store database.Store) error {
		locked, err := store.GetChatByID(ctx, input.ChatID)
		if errors.Is(err, sql.ErrNoRows) {
			return errTaskExpectedExit
		}
		if err != nil {
			return xerrors.Errorf("load chat: %w", err)
		}
		if err := verifyTaskFence(locked, input, database.ChatStatusRequiresAction, taskFenceOptions{requireHistory: true}); err != nil {
			return err
		}
		if locked.RequiresActionDeadlineAt.Valid {
			now, err := store.GetDatabaseNow(ctx)
			if err != nil {
				return xerrors.Errorf("get database time: %w", err)
			}
			if now.Before(locked.RequiresActionDeadlineAt.Time) {
				return errTaskExpectedExit
			}
		}
		if _, err := tx.CancelRequiresAction(chatstate.CancelRequiresActionInput{Reason: reason}); err != nil {
			return err
		}
		committed, err = store.GetChatByID(ctx, input.ChatID)
		if err != nil {
			return xerrors.Errorf("load committed chat: %w", err)
		}
		return nil
	})
	if err != nil {
		if current, ok := s.committedStateAfterUpdateError(ctx, committed); ok {
			return s.publishWatchAndRoute(ctx, current, codersdk.ChatWatchEventKindStatusChange)
		}
		return normalizeTaskTransitionError(err, "cancel requires action")
	}
	return s.publishWatchAndRoute(ctx, committed, codersdk.ChatWatchEventKindStatusChange)
}

func (s *taskStarter) StartAbandon(ctx context.Context, input chatWorkerTaskStartInput) error {
	machine := chatstate.NewChatMachine(s.opts.Store, s.opts.Pubsub, input.ChatID)
	mismatch := false
	err := machine.Update(ctx, func(tx *chatstate.Tx, store database.Store) error {
		locked, err := store.GetChatByID(ctx, input.ChatID)
		if errors.Is(err, sql.ErrNoRows) {
			mismatch = true
			return errTaskExpectedExit
		}
		if err != nil {
			return xerrors.Errorf("load chat: %w", err)
		}
		if !ownedByTask(locked, input) {
			mismatch = true
			return errTaskExpectedExit
		}
		if err := verifyTaskFence(locked, input, input.Status, taskFenceOptions{requireHistory: true, allowArchived: true}); err != nil {
			return err
		}
		if _, err := tx.Abandon(chatstate.AbandonInput{}); err != nil {
			return err
		}
		return nil
	})
	if err != nil {
		if errors.Is(err, errTaskExpectedExit) && mismatch {
			s.requestCleanup(ctx, runnerKey{ChatID: input.ChatID, RunnerID: input.RunnerID})
			return nil
		}
		return normalizeTaskTransitionError(err, "abandon chat")
	}
	s.requestCleanup(ctx, runnerKey{ChatID: input.ChatID, RunnerID: input.RunnerID})
	return nil
}

func (s *taskStarter) committedStateAfterUpdateError(ctx context.Context, committed database.Chat) (database.Chat, bool) {
	if committed.ID == uuid.Nil {
		return database.Chat{}, false
	}
	current, err := s.opts.Store.GetChatByID(ctx, committed.ID)
	if err != nil {
		return database.Chat{}, false
	}
	if current.SnapshotVersion != committed.SnapshotVersion ||
		current.HistoryVersion != committed.HistoryVersion ||
		current.QueueVersion != committed.QueueVersion ||
		current.GenerationAttempt != committed.GenerationAttempt ||
		current.Status != committed.Status ||
		current.Archived != committed.Archived ||
		current.WorkerID != committed.WorkerID ||
		current.RunnerID != committed.RunnerID {
		return database.Chat{}, false
	}
	return current, true
}

func (s *taskStarter) publishWatchAndRoute(
	ctx context.Context,
	chat database.Chat,
	kind codersdk.ChatWatchEventKind,
) error {
	watchCtx, cancel := context.WithTimeout(context.WithoutCancel(ctx), postCommitWatchPublishTimeout)
	defer cancel()
	if err := s.publishWatchWithRetry(watchCtx, chat, kind); err != nil {
		return err
	}
	s.routeStateHint(ctx, stateUpdateFromChat(chat))
	return nil
}

func (s *taskStarter) publishWatchWithRetry(
	ctx context.Context,
	chat database.Chat,
	kind codersdk.ChatWatchEventKind,
) error {
	delay := s.opts.TaskRetryInitialBackoff
	for {
		if err := publishChatWatchEvent(s.opts.Pubsub, chat, kind); err == nil {
			return nil
		} else if ctx.Err() != nil {
			return errTaskExpectedExit
		}
		timer := s.opts.Clock.NewTimer(delay, "chatworker", "watch-publish-retry")
		select {
		case <-timer.C:
		case <-ctx.Done():
			timer.Stop()
			return errTaskExpectedExit
		}
		timer.Stop()
		if delay < s.opts.TaskRetryMaxBackoff {
			delay *= 2
			if delay > s.opts.TaskRetryMaxBackoff {
				delay = s.opts.TaskRetryMaxBackoff
			}
		}
	}
}

func publishChatWatchEvent(pubsub chatWorkerPubsub, chat database.Chat, kind codersdk.ChatWatchEventKind) error {
	event := codersdk.ChatWatchEvent{
		Kind: kind,
		Chat: db2sdk.Chat(chat, nil, nil),
	}
	payload, err := json.Marshal(event)
	if err != nil {
		return xerrors.Errorf("marshal chat watch event: %w", err)
	}
	if err := pubsub.Publish(coderdpubsub.ChatWatchEventChannel(chat.OwnerID), payload); err != nil {
		return xerrors.Errorf("publish chat watch event: %w", err)
	}
	return nil
}

type taskFenceOptions struct {
	requireHistory bool
	allowArchived  bool
}

func verifyTaskFence(
	chat database.Chat,
	input chatWorkerTaskStartInput,
	status database.ChatStatus,
	opts taskFenceOptions,
) error {
	if !ownedByTask(chat, input) {
		return errTaskExpectedExit
	}
	if chat.Status != status {
		return errTaskExpectedExit
	}
	if !opts.allowArchived && chat.Archived {
		return errTaskExpectedExit
	}
	if opts.requireHistory && chat.HistoryVersion != input.HistoryVersion {
		return errTaskExpectedExit
	}
	return nil
}

func ownedByTask(chat database.Chat, input chatWorkerTaskStartInput) bool {
	return chat.WorkerID.Valid && chat.WorkerID.UUID == input.WorkerID &&
		chat.RunnerID.Valid && chat.RunnerID.UUID == input.RunnerID
}

func normalizeTaskInfrastructureError(err error, action string) error {
	if err == nil {
		return nil
	}
	if errors.Is(err, errTaskExpectedExit) || errors.Is(err, chatstate.ErrChatNotFound) || errors.Is(err, sql.ErrNoRows) || errors.Is(err, context.Canceled) {
		return errTaskExpectedExit
	}
	return taskRetryableError{err: xerrors.Errorf("%s: %w", action, err)}
}

func normalizeTaskTransitionError(err error, action string) error {
	if err == nil {
		return nil
	}
	if errors.Is(err, errTaskExpectedExit) || errors.Is(err, chatstate.ErrChatNotFound) || errors.Is(err, sql.ErrNoRows) || errors.Is(err, context.Canceled) {
		return errTaskExpectedExit
	}
	if errors.Is(err, chatstate.ErrTransitionNotAllowed) || errors.Is(err, chatstate.ErrInvalidState) {
		return xerrors.Errorf("%s: %w", action, err)
	}
	return taskRetryableError{err: xerrors.Errorf("%s: %w", action, err)}
}

func dynamicToolNamesFromChat(chat database.Chat) map[string]bool {
	if !chat.DynamicTools.Valid || len(chat.DynamicTools.RawMessage) == 0 {
		return nil
	}
	var tools []codersdk.DynamicTool
	if err := json.Unmarshal(chat.DynamicTools.RawMessage, &tools); err != nil {
		return nil
	}
	names := make(map[string]bool, len(tools))
	for _, tool := range tools {
		name := strings.TrimSpace(tool.Name)
		if name != "" {
			names[name] = true
		}
	}
	return names
}

func committedPendingLocalToolCancellationMessages(
	ctx context.Context,
	store database.Store,
	chat database.Chat,
	interruptedAt time.Time,
) ([]chatstate.Message, error) {
	messages, err := store.GetChatMessagesByChatID(ctx, database.GetChatMessagesByChatIDParams{
		ChatID:  chat.ID,
		AfterID: 0,
	})
	if err != nil {
		return nil, xerrors.Errorf("load committed messages for interruption: %w", err)
	}
	localCalls, _, err := unresolvedToolCallsFromHistory(messages, dynamicToolNamesFromChat(chat))
	if err != nil {
		return nil, err
	}
	if len(localCalls) == 0 {
		return nil, nil
	}
	result := make([]chatstate.Message, 0, len(localCalls))
	for _, call := range localCalls {
		payload, err := json.Marshal(map[string]string{"error": interruptedToolResultErrorMessage})
		if err != nil {
			return nil, xerrors.Errorf("marshal interrupted tool result: %w", err)
		}
		part := codersdk.ChatMessageToolResult(call.ToolCallID, call.ToolName, payload, true, false)
		if !interruptedAt.IsZero() {
			part.CreatedAt = &interruptedAt
		}
		content, err := chatprompt.MarshalParts([]codersdk.ChatMessagePart{part})
		if err != nil {
			return nil, xerrors.Errorf("marshal interrupted tool result part: %w", err)
		}
		result = append(result, chatstate.Message{
			Role:           database.ChatMessageRoleTool,
			Content:        content,
			Visibility:     database.ChatMessageVisibilityBoth,
			ModelConfigID:  uuid.NullUUID{UUID: chat.LastModelConfigID, Valid: chat.LastModelConfigID != uuid.Nil},
			ContentVersion: chatprompt.CurrentContentVersion,
		})
	}
	return result, nil
}