package agent

import (
	"context"
	"crypto/rand"
	"errors"
	"fmt"
	"math/big"
	"time"

	rvboxv1 "github.com/rvbox/rvbox/gen/go/rvbox/v1"
	"github.com/rvbox/rvbox/internal/agentproto"
	"github.com/rvbox/rvbox/internal/client/spool"
	"github.com/rvbox/rvbox/internal/domain"
	"google.golang.org/protobuf/proto"
	"google.golang.org/protobuf/types/known/timestamppb"
)

// RunnerOptions contains the replaceable network edge and the durable client
// state used by one daemon. The supervisor is deliberately a callback here:
// process execution can outlive a network session and is owned by the caller.
type RunnerOptions struct {
	Store  *spool.Store
	Dial   func(context.Context) (Transport, error)
	Hello  *rvboxv1.ClientHello
	Limits agentproto.Limits

	Backoff BackoffOptions
	Jitter  Jitter
	Now     func() time.Time

	OnDispatch    func(context.Context, Session, *rvboxv1.CommandDispatch) error
	OnStdin       func(context.Context, Session, *rvboxv1.StdinWrite) error
	OnCloseStdin  func(context.Context, Session, *rvboxv1.CloseStdin) error
	OnSignal      func(context.Context, Session, *rvboxv1.SignalCommand) error
	OnScriptReady func(context.Context, Session, domain.UUID) error
	OnTerminate   func(context.Context, domain.UUID) error
	// OnSessionError observes one failed dial, handshake, protocol, or active
	// transport session before normal reconnect backoff. It must not block; the
	// durable spool and retry policy remain owned by Run.
	OnSessionError func(error)
	// EventReady wakes the active session after a supervisor worker appends a
	// durable event. The network loop remains the sole writer; a reconnect can
	// safely ignore a stale notification because replay reads the spool again.
	EventReady <-chan domain.UUID
}

// BackoffOptions and Jitter are kept at the agent boundary so callers do not
// need to depend on the internal session-machine implementation.
type BackoffOptions struct {
	Initial     time.Duration
	Maximum     time.Duration
	StableReset time.Duration
}

func (options BackoffOptions) Validate() error {
	if options.Initial <= 0 || options.Maximum < options.Initial || options.StableReset <= 0 {
		return errors.New("invalid client reconnect backoff options")
	}
	return nil
}

type Jitter func(time.Duration) time.Duration

func (options RunnerOptions) validate() error {
	if options.Store == nil || options.Dial == nil || options.Hello == nil {
		return errors.New("client runner requires store, dialer, and hello")
	}
	if options.Limits.MaxEnvelopeBytes == 0 {
		options.Limits = agentproto.DefaultLimits()
	}
	if options.Backoff.Initial == 0 {
		options.Backoff = BackoffOptions{Initial: time.Second, Maximum: time.Minute, StableReset: time.Minute}
	}
	if err := options.Backoff.Validate(); err != nil {
		return err
	}
	if options.Jitter == nil {
		return errors.New("client runner jitter is required")
	}
	if options.Now == nil {
		return errors.New("client runner clock is required")
	}
	return nil
}

// Run reconnects until ctx is cancelled. A failed handshake or transport is
// treated as a normal network failure; durable commands and their spool remain
// untouched. The first failure uses the configured initial backoff and a
// successful session resets the exponential history only after StableReset.
func Run(ctx context.Context, options RunnerOptions) error {
	if err := options.validate(); err != nil {
		return err
	}
	delay := time.Duration(0)
	failures := uint32(0)
	for {
		if err := waitUntil(ctx, delay); err != nil {
			return nil
		}
		sessionStarted := options.Now()
		sessionErr := runOnce(ctx, options)
		if ctx.Err() != nil {
			return nil
		}
		if sessionErr != nil && options.OnSessionError != nil {
			options.OnSessionError(sessionErr)
		}
		if options.Now().Sub(sessionStarted) >= options.Backoff.StableReset {
			failures = 0
		}
		if failures < ^uint32(0) {
			failures++
		}
		cap := options.Backoff.Initial
		for index := uint32(1); index < failures && cap < options.Backoff.Maximum; index++ {
			if cap > options.Backoff.Maximum/2 {
				cap = options.Backoff.Maximum
				break
			}
			cap *= 2
		}
		if cap > options.Backoff.Maximum {
			cap = options.Backoff.Maximum
		}
		delay = options.Jitter(cap)
		if delay < 0 {
			delay = 0
		}
		if delay > cap {
			delay = cap
		}
	}
}

func waitUntil(ctx context.Context, delay time.Duration) error {
	if delay <= 0 {
		return nil
	}
	timer := time.NewTimer(delay)
	defer timer.Stop()
	select {
	case <-ctx.Done():
		return ctx.Err()
	case <-timer.C:
		return nil
	}
}

// RunOnce performs one complete session and returns when the transport is
// lost or a protocol/storage error makes that session unusable.
func RunOnce(ctx context.Context, options RunnerOptions) error {
	if err := options.validate(); err != nil {
		return err
	}
	return runOnce(ctx, options)
}

func runOnce(ctx context.Context, options RunnerOptions) (resultErr error) {
	transport, err := options.Dial(ctx)
	if err != nil {
		return err
	}
	defer func() {
		if closeErr := transport.Close(); resultErr == nil && closeErr != nil {
			resultErr = closeErr
		}
	}()

	limits := options.Limits
	if limits.MaxEnvelopeBytes == 0 {
		limits = agentproto.DefaultLimits()
	}
	session, err := Handshake(ctx, transport, options.Hello, limits)
	if err != nil {
		return err
	}
	snapshot, err := options.Store.ReconcileSnapshot(ctx)
	if err != nil {
		return fmt.Errorf("build client reconciliation snapshot: %w", err)
	}
	result, err := Reconcile(ctx, transport, session, snapshot, limits)
	if err != nil {
		return err
	}
	terminated, err := ApplyReconcileResult(ctx, options.Store, result, options.Now())
	if err != nil {
		return fmt.Errorf("apply server reconciliation: %w", err)
	}
	for _, issue := range terminated {
		if options.OnTerminate != nil {
			if err := options.OnTerminate(ctx, issue); err != nil {
				return err
			}
		}
	}
	sentEvents := make(map[domain.UUID]uint64)
	if err := replayEvents(ctx, transport, options.Store, session, snapshot, limits, sentEvents); err != nil {
		return err
	}
	if err := sendCapacity(ctx, transport, session, options.Hello, snapshot, limits); err != nil {
		return err
	}
	return serveActive(ctx, transport, options, session, sentEvents)
}

func replayEvents(ctx context.Context, transport Transport, store *spool.Store, session Session, snapshot *rvboxv1.ReconcileSnapshot, limits agentproto.Limits, sent map[domain.UUID]uint64) error {
	for _, retained := range snapshot.GetRetainedCommands() {
		if retained == nil || retained.GetTombstoned() {
			continue
		}
		issue, err := domain.ParseUUIDv7(retained.GetIssueUuid())
		if err != nil {
			return err
		}
		if _, err := store.AssignSendWindow(ctx, issue, 128, 1<<20); err != nil {
			return err
		}
		events, err := store.PendingEvents(ctx, issue)
		if err != nil {
			return err
		}
		for _, event := range events {
			if err := SendStoredEvent(ctx, transport, session, event, limits); err != nil {
				return err
			}
			if event.EventSeq > sent[issue] {
				sent[issue] = event.EventSeq
			}
		}
	}
	return nil
}

// SendStoredEvent converts the compact local representation back to a
// canonical CommandEvent. Output rows store only their typed OutputChunk to
// avoid duplicating the envelope; metadata rows may store a full event.
func SendStoredEvent(ctx context.Context, transport Transport, session Session, event spool.Event, limits agentproto.Limits) error {
	commandEvent, err := commandEventFromStored(event)
	if err != nil {
		return err
	}
	commandEvent.IssueUuid = event.IssueUUID.String()
	commandEvent.EventSeq = event.EventSeq
	commandEvent.ObservedAt = timestamppb.New(event.CreatedAt)
	return SendCommandEvent(ctx, transport, session, commandEvent, limits)
}

func commandEventFromStored(event spool.Event) (*rvboxv1.CommandEvent, error) {
	if event.EventSeq == 0 || event.IssueUUID == (domain.UUID{}) || event.CreatedAt.IsZero() {
		return nil, errors.New("stored event lacks assigned sequence or owner")
	}
	if event.Kind == spool.EventKindOutput {
		var output rvboxv1.OutputChunk
		if err := proto.Unmarshal(event.Payload, &output); err != nil {
			return nil, fmt.Errorf("decode stored output event: %w", err)
		}
		return &rvboxv1.CommandEvent{Payload: &rvboxv1.CommandEvent_Output{Output: &output}}, nil
	}
	if event.Kind == spool.EventKindOutputTruncation {
		var marker rvboxv1.OutputTruncation
		if err := proto.Unmarshal(event.Payload, &marker); err != nil {
			return nil, fmt.Errorf("decode stored truncation event: %w", err)
		}
		return &rvboxv1.CommandEvent{Payload: &rvboxv1.CommandEvent_OutputTruncation{OutputTruncation: &marker}}, nil
	}
	var stored rvboxv1.CommandEvent
	if err := proto.Unmarshal(event.Payload, &stored); err != nil || stored.Payload == nil {
		return nil, fmt.Errorf("decode stored command event: %w", err)
	}
	return &stored, nil
}

func sendCapacity(ctx context.Context, transport Transport, session Session, hello *rvboxv1.ClientHello, snapshot *rvboxv1.ReconcileSnapshot, limits agentproto.Limits) error {
	var running, queued uint32
	for _, retained := range snapshot.GetRetainedCommands() {
		if retained == nil || retained.GetTombstoned() {
			continue
		}
		switch retained.GetLifecycle() {
		case rvboxv1.CommandLifecycle_COMMAND_ACCEPTED, rvboxv1.CommandLifecycle_COMMAND_RUNNING:
			running++
		case rvboxv1.CommandLifecycle_COMMAND_QUEUED, rvboxv1.CommandLifecycle_COMMAND_DISPATCHED:
			queued++
		}
	}
	if running > hello.GetMaxRunningCommands() || queued > hello.GetMaxQueuedCommands() {
		return fmt.Errorf("durable client command count exceeds advertised capacity")
	}
	envelope := &rvboxv1.AgentEnvelope{SessionId: session.ID, SessionGeneration: session.Generation, Payload: &rvboxv1.AgentEnvelope_ClientCapacity{ClientCapacity: &rvboxv1.ClientCapacity{RunningCommands: running, QueuedCommands: queued, MaxRunningCommands: hello.GetMaxRunningCommands(), MaxQueuedCommands: hello.GetMaxQueuedCommands()}}}
	if err := agentproto.ValidateEnvelope(envelope, limits, rvboxv1.Platform_PLATFORM_WINDOWS); err != nil {
		return err
	}
	encoded, err := proto.Marshal(envelope)
	if err != nil {
		return err
	}
	return transport.Write(ctx, encoded)
}

func serveActive(ctx context.Context, transport Transport, options RunnerOptions, session Session, sent map[domain.UUID]uint64) error {
	limits := options.Limits
	if limits.MaxEnvelopeBytes == 0 {
		limits = agentproto.DefaultLimits()
	}
	readContext, cancelRead := context.WithCancel(ctx)
	defer cancelRead()
	frames := make(chan []byte, 1)
	readErrors := make(chan error, 1)
	go func() {
		for {
			encoded, err := transport.Read(readContext)
			if err != nil {
				select {
				case readErrors <- err:
				case <-readContext.Done():
				}
				return
			}
			select {
			case frames <- encoded:
			case <-readContext.Done():
				return
			}
		}
	}()
	for {
		var encoded []byte
		select {
		case <-ctx.Done():
			return nil
		case err := <-readErrors:
			return err
		case issue := <-options.EventReady:
			if issue == (domain.UUID{}) {
				continue
			}
			if err := flushEvents(ctx, transport, options.Store, session, issue, limits, sent); err != nil {
				return err
			}
			continue
		case encoded = <-frames:
		}
		envelope, err := agentproto.DecodeEnvelope(encoded, limits, rvboxv1.Platform_PLATFORM_WINDOWS)
		if err != nil {
			return err
		}
		if envelope.GetSessionId() != session.ID || envelope.GetSessionGeneration() != session.Generation {
			return ErrProtocolHandshake
		}
		switch {
		case envelope.GetCommandDispatch() != nil:
			if err := handleDispatch(ctx, transport, options, session, envelope.GetCommandDispatch(), limits); err != nil {
				return fmt.Errorf("handle command dispatch %s: %w", envelope.GetCommandDispatch().GetIssueUuid(), err)
			}
			issue, parseErr := domain.ParseUUIDv7(envelope.GetCommandDispatch().GetIssueUuid())
			if parseErr == nil {
				if err := flushEvents(ctx, transport, options.Store, session, issue, limits, sent); err != nil {
					return fmt.Errorf("flush dispatched command %s events: %w", issue, err)
				}
			}
		case envelope.GetEventAck() != nil:
			if err := ApplyEventAck(ctx, options.Store, envelope.GetEventAck()); err != nil {
				return fmt.Errorf("apply event acknowledgement for %s: %w", envelope.GetEventAck().GetIssueUuid(), err)
			}
		case envelope.GetScriptChunk() != nil:
			if err := handleScriptChunk(ctx, transport, options.Store, session, envelope.GetScriptChunk(), limits, options.Now, sent); err != nil {
				return err
			}
		case envelope.GetScriptCommit() != nil:
			if err := handleScriptCommit(ctx, transport, options.Store, session, envelope.GetScriptCommit(), limits, options.Now, sent); err != nil {
				return err
			}
			if options.OnScriptReady != nil {
				issue, err := domain.ParseUUIDv7(envelope.GetScriptCommit().GetIssueUuid())
				if err != nil {
					return err
				}
				if err := options.OnScriptReady(ctx, session, issue); err != nil {
					return err
				}
			}
		case envelope.GetStdinWrite() != nil:
			if options.OnStdin != nil {
				if err := options.OnStdin(ctx, session, envelope.GetStdinWrite()); err != nil {
					return err
				}
			}
			if issue, parseErr := domain.ParseUUIDv7(envelope.GetStdinWrite().GetIssueUuid()); parseErr == nil {
				if err := flushEvents(ctx, transport, options.Store, session, issue, limits, sent); err != nil {
					return err
				}
			}
		case envelope.GetCloseStdin() != nil:
			if options.OnCloseStdin != nil {
				if err := options.OnCloseStdin(ctx, session, envelope.GetCloseStdin()); err != nil {
					return err
				}
			}
			if issue, parseErr := domain.ParseUUIDv7(envelope.GetCloseStdin().GetIssueUuid()); parseErr == nil {
				if err := flushEvents(ctx, transport, options.Store, session, issue, limits, sent); err != nil {
					return err
				}
			}
		case envelope.GetSignalCommand() != nil:
			if options.OnSignal != nil {
				if err := options.OnSignal(ctx, session, envelope.GetSignalCommand()); err != nil {
					return err
				}
			}
			if issue, parseErr := domain.ParseUUIDv7(envelope.GetSignalCommand().GetIssueUuid()); parseErr == nil {
				if err := flushEvents(ctx, transport, options.Store, session, issue, limits, sent); err != nil {
					return err
				}
			}
		case envelope.GetError() != nil:
			if envelope.GetError().GetCloseSession() {
				return fmt.Errorf("server closed agent session: %s", envelope.GetError().GetError().GetMessage())
			}
		case envelope.GetReconcileRequest() != nil:
			// A request is advisory after the snapshot/result barrier. The next
			// reconnect repeats the complete snapshot; never apply partial targets.
		default:
			return ErrUnexpectedMessage
		}
	}
}

func flushEvents(ctx context.Context, transport Transport, store *spool.Store, session Session, issue domain.UUID, limits agentproto.Limits, sent map[domain.UUID]uint64) error {
	if issue == (domain.UUID{}) {
		return nil
	}
	if _, err := store.AssignSendWindow(ctx, issue, 128, 1<<20); err != nil {
		return err
	}
	events, err := store.PendingEvents(ctx, issue)
	if err != nil {
		return err
	}
	for _, event := range events {
		if event.EventSeq == 0 || event.EventSeq <= sent[issue] {
			continue
		}
		if err := SendStoredEvent(ctx, transport, session, event, limits); err != nil {
			return err
		}
		sent[issue] = event.EventSeq
	}
	return nil
}

func handleDispatch(ctx context.Context, transport Transport, options RunnerOptions, session Session, dispatch *rvboxv1.CommandDispatch, limits agentproto.Limits) error {
	acceptance, err := PersistDispatch(ctx, options.Store, session, dispatch, options.Now(), limits)
	accepted := err == nil
	ack := &rvboxv1.CommandAccepted{IssueUuid: dispatch.GetIssueUuid(), CommandRevision: dispatch.GetCommandRevision(), Accepted: accepted}
	if err != nil {
		ack.Rejection = rejectionForError(err, dispatch.GetIssueUuid())
	}
	envelope := &rvboxv1.AgentEnvelope{SessionId: session.ID, SessionGeneration: session.Generation, Payload: &rvboxv1.AgentEnvelope_CommandAccepted{CommandAccepted: ack}}
	if validateErr := agentproto.ValidateEnvelope(envelope, limits, rvboxv1.Platform_PLATFORM_WINDOWS); validateErr != nil {
		return validateErr
	}
	encoded, marshalErr := proto.Marshal(envelope)
	if marshalErr != nil {
		return marshalErr
	}
	if err := transport.Write(ctx, encoded); err != nil {
		return err
	}
	if accepted && options.OnDispatch != nil {
		return options.OnDispatch(ctx, session, dispatch)
	}
	_ = acceptance
	return nil
}

func rejectionForError(err error, issue string) *rvboxv1.ControlError {
	code := rvboxv1.ControlError_TRANSIENT
	if errors.Is(err, spool.ErrCommandConflict) || errors.Is(err, spool.ErrAlreadyExecuted) {
		code = rvboxv1.ControlError_CONFLICT
	} else if errors.Is(err, agentproto.ErrInvalidExecutionSpec) || errors.Is(err, ErrProtocolHandshake) {
		code = rvboxv1.ControlError_INVALID_ARGUMENT
	}
	return &rvboxv1.ControlError{Code: code, Message: boundedError(err), Retryable: code == rvboxv1.ControlError_TRANSIENT, IssueUuid: issue}
}

func boundedError(err error) string {
	if err == nil {
		return ""
	}
	message := err.Error()
	if len(message) > 1024 {
		message = message[:1024]
	}
	return message
}

func handleScriptChunk(ctx context.Context, transport Transport, store *spool.Store, session Session, chunk *rvboxv1.ScriptChunk, limits agentproto.Limits, now func() time.Time, sent map[domain.UUID]uint64) error {
	status, err := ApplyScriptChunk(ctx, store, session, chunk, limits)
	if err != nil {
		return err
	}
	return appendAndSendScriptStatus(ctx, transport, store, session, chunk.GetIssueUuid(), status, limits, now, sent)
}

func handleScriptCommit(ctx context.Context, transport Transport, store *spool.Store, session Session, commit *rvboxv1.ScriptCommit, limits agentproto.Limits, now func() time.Time, sent map[domain.UUID]uint64) error {
	status, err := ApplyScriptCommit(ctx, store, session, commit, limits)
	if err != nil {
		return err
	}
	return appendAndSendScriptStatus(ctx, transport, store, session, commit.GetIssueUuid(), status, limits, now, sent)
}

func appendAndSendScriptStatus(ctx context.Context, transport Transport, store *spool.Store, session Session, issueText string, status spool.ScriptStatus, limits agentproto.Limits, now func() time.Time, sent map[domain.UUID]uint64) error {
	issue, err := domain.ParseUUIDv7(issueText)
	if err != nil {
		return err
	}
	if sent == nil {
		sent = make(map[domain.UUID]uint64)
	}
	if now == nil {
		now = func() time.Time { return time.Now().UTC() }
	}
	observedAt := now()
	if observedAt.IsZero() {
		return errors.New("script status clock returned zero")
	}
	event := &rvboxv1.CommandEvent{IssueUuid: issueText, ObservedAt: timestamppb.New(observedAt), Payload: &rvboxv1.CommandEvent_ScriptStatus{ScriptStatus: &rvboxv1.ScriptUploadStatus{ReceivedBytes: status.ReceivedBytes, Complete: status.Committed}}}
	payload, err := proto.MarshalOptions{Deterministic: true}.Marshal(event)
	if err != nil {
		return err
	}
	if _, err := store.AppendEvent(ctx, issue, spool.EventInput{Kind: 9, Compression: 1, RawBytes: uint64(len(payload)), Payload: payload, CreatedAt: event.GetObservedAt().AsTime()}); err != nil {
		return err
	}
	assigned, err := store.AssignSendWindow(ctx, issue, 1, 1<<20)
	if err != nil {
		return err
	}
	for _, item := range assigned {
		if item.EventSeq == 0 || item.EventSeq <= sent[issue] {
			continue
		}
		if err := SendStoredEvent(ctx, transport, session, item, limits); err != nil {
			return err
		}
		sent[issue] = item.EventSeq
	}
	return nil
}

// CryptoJitter returns a full-jitter delay without relying on math/rand's
// process-global state. Tests inject a deterministic jitter instead.
func CryptoJitter(capacity time.Duration) time.Duration {
	if capacity <= 0 {
		return 0
	}
	value, err := rand.Int(rand.Reader, big.NewInt(int64(capacity)+1))
	if err != nil {
		return capacity
	}
	return time.Duration(value.Int64())
}