package controller

import (
	"bufio"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os/exec"
	"strings"
	"sync"
	"time"

	"github.com/kandev/kandev/internal/agent/agents"
	"github.com/kandev/kandev/internal/agent/hostutility"
	"github.com/kandev/kandev/internal/agent/managedruntime"
	"github.com/kandev/kandev/internal/agent/settings/dto"
)

var (
	ErrRuntimeUpdateUnsupported    = errors.New("agent runtime update unsupported")
	ErrRuntimeUpdaterUnavailable   = errors.New("agent runtime updater unavailable")
	ErrRuntimeUpdatePreviewFailed  = errors.New("agent runtime update preview failed")
	ErrRuntimeUpdateTargetRequired = errors.New("managed runtime target version is required")
	ErrRuntimeUpdateTargetInvalid  = errors.New("managed runtime target version is invalid")
	ErrRuntimeUpdateTargetMissing  = errors.New("managed runtime target version is not published")
)

// PreviewAgentUpdate resolves the trusted built-in update recipe without
// claiming maintenance state, creating a job, or running the command.
func (c *Controller) PreviewAgentUpdate(
	ctx context.Context,
	name string,
	targetVersions ...string,
) (*dto.AgentUpdatePreviewDTO, error) {
	target := ""
	if len(targetVersions) > 0 {
		target = strings.TrimSpace(targetVersions[0])
	}
	return c.previewAgentUpdate(ctx, name, target, false)
}

// PreviewAgentUpdateUseDefault previews returning to the reviewed Kandev
// default without claiming maintenance state or running a candidate.
func (c *Controller) PreviewAgentUpdateUseDefault(
	ctx context.Context,
	name string,
) (*dto.AgentUpdatePreviewDTO, error) {
	return c.previewAgentUpdate(ctx, name, "", true)
}

func (c *Controller) previewAgentUpdate(
	ctx context.Context,
	name string,
	targetVersion string,
	useDefault bool,
) (*dto.AgentUpdatePreviewDTO, error) {
	if c.runtimeUpdater == nil {
		return nil, ErrRuntimeUpdaterUnavailable
	}
	ag, ok := c.agentRegistry.Get(name)
	if !ok {
		return nil, ErrAgentNotFound
	}
	managed, ok := ag.(agents.ManagedNPMRuntimeAgent)
	if !ok {
		return nil, ErrRuntimeUpdateUnsupported
	}
	spec := managed.ManagedNPMRuntime()
	if strings.TrimSpace(spec.Package) == "" {
		return nil, ErrRuntimeUpdateUnsupported
	}

	current := ""
	if caps, found := c.runtimeUpdater.CurrentCapabilities(name); found {
		current = caps.AgentVersion
	}
	active, effective, defaultVersion, err := c.runtimeVersions(ctx, name, spec)
	if err != nil {
		return nil, fmt.Errorf("%w: %v", ErrRuntimeUpdatePreviewFailed, err)
	}
	catalogue, exactCatalogue, err := c.resolveRuntimeCatalogue(
		ctx, spec.Package, active, current, effective, defaultVersion,
	)
	if err != nil {
		return nil, fmt.Errorf("%w: %v", ErrRuntimeUpdatePreviewFailed, err)
	}
	target, err := resolvePreviewTarget(
		catalogue,
		exactCatalogue,
		targetVersion,
		defaultVersion,
		useDefault,
	)
	if err != nil {
		return nil, err
	}
	operation, err := managedruntime.ClassifyEffectiveOperation(
		useDefault, active, effective, current, target, defaultVersion,
	)
	if err != nil {
		return nil, fmt.Errorf("%w: %v", ErrRuntimeUpdateTargetInvalid, err)
	}
	command := spec.CacheUpdateCommand(target).Args()
	if !exactCatalogue && targetVersion == "" && !useDefault {
		// Keep the compatibility preview for embedders that provide only the
		// legacy latest-version seam. Production uses the catalogue resolver and
		// always previews an exact package@version command.
		command = spec.CacheUpdateCommand().Args()
	}
	return &dto.AgentUpdatePreviewDTO{
		AgentName:         name,
		Package:           spec.Package,
		CurrentVersion:    current,
		DefaultVersion:    defaultVersion,
		ActiveVersion:     active,
		EffectiveVersion:  effective,
		TargetVersion:     target,
		Operation:         string(operation),
		AvailableVersions: runtimeVersionDTOs(catalogue),
		Command:           command,
		CommandString:     buildCommandString(command),
	}, nil
}

func resolvePreviewTarget(
	catalogue managedruntime.Catalogue,
	exactCatalogue bool,
	targetVersion string,
	defaultVersion string,
	useDefault bool,
) (string, error) {
	target := catalogue.Latest
	switch {
	case useDefault:
		target = defaultVersion
	case targetVersion != "":
		target = targetVersion
	default:
		return target, nil
	}
	if _, err := managedruntime.ParseStableVersion(target); err != nil {
		return "", fmt.Errorf("%w: %v", ErrRuntimeUpdateTargetInvalid, err)
	}
	if exactCatalogue && !catalogue.Has(target) {
		return "", fmt.Errorf("%w: %s", ErrRuntimeUpdateTargetMissing, target)
	}
	return target, nil
}

func (c *Controller) resolveRuntimeCatalogue(
	ctx context.Context,
	packageName string,
	extras ...string,
) (managedruntime.Catalogue, bool, error) {
	if resolver, ok := c.runtimeUpdater.(RuntimeVersionResolver); ok {
		metadata, err := resolver.ResolveVersions(ctx, packageName)
		if err != nil {
			return managedruntime.Catalogue{}, true, err
		}
		catalogue, err := managedruntime.BuildCatalogue(metadata.Versions, metadata.Latest, extras...)
		return catalogue, true, err
	}
	target, err := c.runtimeUpdater.ResolveTarget(ctx, packageName)
	if err != nil {
		return managedruntime.Catalogue{}, false, err
	}
	catalogue, err := managedruntime.BuildCatalogue([]string{target}, target)
	return catalogue, false, err
}

func runtimeVersionDTOs(catalogue managedruntime.Catalogue) []dto.AgentUpdateVersionDTO {
	versions := make([]dto.AgentUpdateVersionDTO, 0, len(catalogue.Versions))
	for _, version := range catalogue.Versions {
		versions = append(versions, dto.AgentUpdateVersionDTO{
			Version: version.Version,
			Latest:  version.Latest,
		})
	}
	return versions
}

func (c *Controller) activeRuntimeVersion(
	ctx context.Context,
	agentName string,
	packageName string,
) (string, error) {
	if c.managedRuntimeSelections == nil {
		return "", nil
	}
	selection, found, err := c.managedRuntimeSelections.Get(ctx, agentName, packageName)
	if err != nil {
		return "", fmt.Errorf("read active runtime version: %w", err)
	}
	if !found {
		return "", nil
	}
	return selection.Version, nil
}

func (c *Controller) runtimeVersions(
	ctx context.Context,
	agentName string,
	spec agents.ManagedNPMRuntimeSpec,
) (active, effective, defaultVersion string, err error) {
	defaultVersion = spec.DefaultVersionOrPinned()
	active, err = c.activeRuntimeVersion(ctx, agentName, spec.Package)
	if err != nil {
		return "", "", defaultVersion, err
	}
	effective = defaultVersion
	if active != "" {
		effective = active
	}
	return active, effective, defaultVersion, nil
}

// RuntimeUpdater is the external-process and host-probe boundary used by
// managed runtime jobs. Implementations must execute commands as direct argv.
type RuntimeUpdater interface {
	CurrentCapabilities(agentName string) (hostutility.AgentCapabilities, bool)
	ResolveTarget(ctx context.Context, packageName string) (string, error)
	RunUpdate(ctx context.Context, command agents.Command, onChunk func(string)) error
	InvalidateExecutionCache(ctx context.Context, packageName string) error
	Refresh(
		ctx context.Context,
		agentName string,
		command agents.Command,
	) (hostutility.AgentCapabilities, error)
}

// RuntimeVersionMetadata is the trusted npm catalogue used to authorize an
// exact target after the browser preview has been shown.
type RuntimeVersionMetadata struct {
	Versions []string
	Latest   string
}

type npmRuntimeMetadata struct {
	Versions []string          `json:"versions"`
	DistTags map[string]string `json:"dist-tags"`
}

// RuntimeVersionResolver obtains package metadata without executing a package.
type RuntimeVersionResolver interface {
	ResolveVersions(context.Context, string) (RuntimeVersionMetadata, error)
}

// RuntimeCandidateUpdater separates validation probes from live capability
// publication. The update job persists the selection between these calls.
type RuntimeCandidateUpdater interface {
	Probe(context.Context, string, agents.Command) (hostutility.AgentCapabilities, error)
	PublishCapabilities(string, hostutility.AgentCapabilities)
}

// ExactRuntimeCacheInvalidator removes only the version-specific npm tree.
type ExactRuntimeCacheInvalidator interface {
	InvalidateExecutionCacheVersion(context.Context, string, string) error
}

// InvalidateExecutionCache delegates the exact managed-runtime cache cleanup
// to the configured host updater. Lifecycle startup recovery uses this
// boundary instead of discovering npm paths itself.
func (c *Controller) InvalidateExecutionCache(ctx context.Context, packageName string) error {
	if c.runtimeUpdater == nil {
		return ErrRuntimeUpdaterUnavailable
	}
	return c.runtimeUpdater.InvalidateExecutionCache(ctx, packageName)
}

// InvalidateExecutionCacheVersion delegates version-specific cleanup when the
// host updater supports the exact-tree contract.
func (c *Controller) InvalidateExecutionCacheVersion(ctx context.Context, packageName, version string) error {
	if c.runtimeUpdater == nil {
		return ErrRuntimeUpdaterUnavailable
	}
	invalidator, ok := c.runtimeUpdater.(ExactRuntimeCacheInvalidator)
	if !ok {
		return ErrRuntimeUpdateUnsupported
	}
	return invalidator.InvalidateExecutionCacheVersion(ctx, packageName, version)
}

type hostRuntimeUpdater struct {
	host     *hostutility.Manager
	executor directCommandExecutor
}

type directCommandExecutor interface {
	Output(ctx context.Context, command agents.Command) (string, error)
	Stream(ctx context.Context, command agents.Command, onChunk func(string)) error
}

type execDirectCommandExecutor struct{}

func (execDirectCommandExecutor) Output(
	ctx context.Context,
	command agents.Command,
) (string, error) {
	return runDirectCommandOutput(ctx, command)
}

func (execDirectCommandExecutor) Stream(
	ctx context.Context,
	command agents.Command,
	onChunk func(string),
) error {
	return runDirectCommand(ctx, command, onChunk)
}

func (u *hostRuntimeUpdater) CurrentCapabilities(agentName string) (hostutility.AgentCapabilities, bool) {
	return u.host.Get(agentName)
}

func (u *hostRuntimeUpdater) ResolveTarget(ctx context.Context, packageName string) (string, error) {
	command := agents.NewCommand("npm", "view", packageName, "dist-tags.latest", "--json")
	output, err := u.executor.Output(ctx, command)
	if err != nil {
		return "", err
	}
	var target string
	if err := json.Unmarshal([]byte(strings.TrimSpace(output)), &target); err != nil {
		return "", fmt.Errorf("parse npm target version: %w", err)
	}
	if strings.TrimSpace(target) == "" {
		return "", errors.New("npm target version is empty")
	}
	target = strings.TrimSpace(target)
	if _, err := managedruntime.ParseStableVersion(target); err != nil {
		return "", fmt.Errorf("npm target version is not stable: %w", err)
	}
	return target, nil
}

func (u *hostRuntimeUpdater) ResolveVersions(
	ctx context.Context,
	packageName string,
) (RuntimeVersionMetadata, error) {
	command := agents.NewCommand("npm", "view", packageName, "versions", "dist-tags", "--json")
	output, err := u.executor.Output(ctx, command)
	if err != nil {
		return RuntimeVersionMetadata{}, err
	}
	metadata, err := parseNPMRuntimeMetadata(output)
	if err != nil {
		return RuntimeVersionMetadata{}, err
	}
	latest := ""
	if metadata.DistTags != nil {
		latest = strings.TrimSpace(metadata.DistTags["latest"])
	}
	if latest == "" {
		return RuntimeVersionMetadata{}, errors.New("npm latest runtime version is empty")
	}
	return RuntimeVersionMetadata{Versions: metadata.Versions, Latest: latest}, nil
}

func parseNPMRuntimeMetadata(output string) (npmRuntimeMetadata, error) {
	payload := []byte(strings.TrimSpace(output))
	if len(payload) > 0 && payload[0] == '[' {
		var records []npmRuntimeMetadata
		if err := json.Unmarshal(payload, &records); err != nil {
			return npmRuntimeMetadata{}, fmt.Errorf("parse npm runtime metadata: %w", err)
		}
		if len(records) != 1 {
			return npmRuntimeMetadata{}, errors.New("parse npm runtime metadata: expected one record")
		}
		return records[0], nil
	}

	var metadata npmRuntimeMetadata
	if err := json.Unmarshal(payload, &metadata); err != nil {
		return npmRuntimeMetadata{}, fmt.Errorf("parse npm runtime metadata: %w", err)
	}
	return metadata, nil
}

func runDirectCommandOutput(ctx context.Context, command agents.Command) (string, error) {
	argv := command.Args()
	if len(argv) == 0 {
		return "", errors.New("runtime update command is empty")
	}
	cmd := exec.CommandContext(ctx, argv[0], argv[1:]...)
	cmd.Env = filteredInstallEnv()
	output, err := cmd.Output()
	if err != nil {
		return "", err
	}
	return string(output), nil
}

func (u *hostRuntimeUpdater) RunUpdate(
	ctx context.Context,
	command agents.Command,
	onChunk func(string),
) error {
	return u.executor.Stream(ctx, command, onChunk)
}

func (u *hostRuntimeUpdater) npxCacheRoot(ctx context.Context) (string, error) {
	output, err := u.executor.Output(ctx, agents.NewCommand("npm", "config", "get", "cache"))
	if err != nil {
		return "", fmt.Errorf("resolve npm cache root: %w", err)
	}
	return strings.TrimSpace(output), nil
}

func (u *hostRuntimeUpdater) InvalidateExecutionCache(ctx context.Context, packageName string) error {
	packageName = strings.TrimSpace(packageName)
	if packageName == "" {
		return errors.New("managed runtime package is empty")
	}
	cacheRoot, err := u.npxCacheRoot(ctx)
	if err != nil {
		return err
	}
	// Cache repair must target the same exact package spec used by the managed
	// launch command. Known built-ins therefore invalidate their pinned tree,
	// while unknown packages retain the unversioned compatibility path.
	spec := agents.ManagedNPMRuntimeSpec{Package: packageName}
	return managedruntime.RemoveNpxExecutionTree(cacheRoot, spec.PackageSpec(""))
}

func (u *hostRuntimeUpdater) InvalidateExecutionCacheVersion(
	ctx context.Context,
	packageName string,
	version string,
) error {
	packageName = strings.TrimSpace(packageName)
	version = strings.TrimSpace(version)
	if packageName == "" || version == "" {
		return errors.New("managed runtime package and version are required")
	}
	if _, err := managedruntime.ParseStableVersion(version); err != nil {
		return err
	}
	cacheRoot, err := u.npxCacheRoot(ctx)
	if err != nil {
		return err
	}
	spec := agents.ManagedNPMRuntimeSpec{Package: packageName}
	return managedruntime.RemoveNpxExecutionTree(cacheRoot, spec.PackageSpec(version))
}

func (u *hostRuntimeUpdater) Refresh(
	ctx context.Context,
	agentName string,
	command agents.Command,
) (hostutility.AgentCapabilities, error) {
	return u.host.RefreshWithCommand(ctx, agentName, command)
}

func (u *hostRuntimeUpdater) Probe(
	ctx context.Context,
	agentName string,
	command agents.Command,
) (hostutility.AgentCapabilities, error) {
	return u.host.ProbeWithCommand(ctx, agentName, command)
}

func (u *hostRuntimeUpdater) PublishCapabilities(
	agentName string,
	caps hostutility.AgentCapabilities,
) {
	u.host.PublishCapabilities(agentName, caps)
}

func runDirectCommand(ctx context.Context, command agents.Command, onChunk func(string)) error {
	argv := command.Args()
	if len(argv) == 0 {
		return errors.New("runtime update command is empty")
	}
	cmd := exec.CommandContext(ctx, argv[0], argv[1:]...)
	cmd.Env = filteredInstallEnv()
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return err
	}
	stderr, err := cmd.StderrPipe()
	if err != nil {
		return err
	}
	if err := cmd.Start(); err != nil {
		return err
	}

	errCh := make(chan error, 2)
	var wg sync.WaitGroup
	wg.Add(2)
	go scanCommandOutput(stdout, onChunk, &wg, errCh)
	go scanCommandOutput(stderr, onChunk, &wg, errCh)
	wg.Wait()
	close(errCh)
	if err := cmd.Wait(); err != nil {
		return err
	}
	for scanErr := range errCh {
		if scanErr != nil {
			return scanErr
		}
	}
	return nil
}

func scanCommandOutput(
	reader io.Reader,
	onChunk func(string),
	wg *sync.WaitGroup,
	errCh chan<- error,
) {
	defer wg.Done()
	scanner := bufio.NewScanner(reader)
	scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024)
	for scanner.Scan() {
		onChunk(scanner.Text() + "\n")
	}
	if err := scanner.Err(); err != nil {
		errCh <- err
	}
}

// EnqueueAgentUpdate starts or reuses an update for a built-in managed agent.
func (c *Controller) EnqueueAgentUpdate(
	ctx context.Context,
	name string,
	targetVersion string,
) (*dto.AgentUpdateJobDTO, error) {
	return c.enqueueAgentUpdate(ctx, name, strings.TrimSpace(targetVersion), false)
}

// EnqueueAgentUpdateUseDefault validates and activates the reviewed Kandev
// default, deleting an operator selection only after the candidate probe
// succeeds.
func (c *Controller) EnqueueAgentUpdateUseDefault(
	ctx context.Context,
	name string,
) (*dto.AgentUpdateJobDTO, error) {
	return c.enqueueAgentUpdate(ctx, name, "", true)
}

func (c *Controller) enqueueAgentUpdate(
	ctx context.Context,
	name string,
	targetVersion string,
	useDefault bool,
) (*dto.AgentUpdateJobDTO, error) {
	if c.updateJobStore == nil || c.runtimeUpdater == nil {
		return nil, ErrRuntimeUpdaterUnavailable
	}
	if active, found := c.updateJobStore.GetActive(name); found {
		return active, nil
	}
	ag, ok := c.agentRegistry.Get(name)
	if !ok {
		return nil, ErrAgentNotFound
	}
	managed, ok := ag.(agents.ManagedNPMRuntimeAgent)
	if !ok {
		return nil, ErrRuntimeUpdateUnsupported
	}
	spec := managed.ManagedNPMRuntime()
	if strings.TrimSpace(spec.Package) == "" {
		return nil, ErrRuntimeUpdateUnsupported
	}
	if useDefault {
		targetVersion = spec.DefaultVersionOrPinned()
	}
	targetVersion = strings.TrimSpace(targetVersion)
	if targetVersion == "" {
		return nil, ErrRuntimeUpdateTargetRequired
	}
	if err := c.validateAgentUpdateTarget(ctx, spec, targetVersion); err != nil {
		return nil, err
	}
	if !useDefault {
		if noOp := c.alreadyActiveHealthyUpdate(ctx, name, spec, targetVersion); noOp != nil {
			return noOp, nil
		}
	}
	var job *AgentUpdateJob
	var err error
	if useDefault {
		job, err = c.updateJobStore.EnqueueDefault(name, spec)
	} else {
		job, err = c.updateJobStore.Enqueue(name, spec, targetVersion)
	}
	if err != nil {
		return nil, err
	}
	if snapshot, found := c.updateJobStore.Get(job.ID); found {
		return snapshot, nil
	}
	snapshot := job.snapshot()
	return &snapshot, nil
}

func (c *Controller) validateAgentUpdateTarget(
	ctx context.Context,
	spec agents.ManagedNPMRuntimeSpec,
	targetVersion string,
) error {
	if _, err := managedruntime.ParseStableVersion(targetVersion); err != nil {
		return fmt.Errorf("%w: %v", ErrRuntimeUpdateTargetInvalid, err)
	}
	resolver, ok := c.runtimeUpdater.(RuntimeVersionResolver)
	if !ok {
		return nil
	}
	metadata, err := resolver.ResolveVersions(ctx, spec.Package)
	if err != nil {
		return fmt.Errorf("%w: %v", ErrRuntimeUpdatePreviewFailed, err)
	}
	catalogue, err := managedruntime.BuildCatalogue(metadata.Versions, metadata.Latest)
	if err != nil {
		return fmt.Errorf("%w: %v", ErrRuntimeUpdatePreviewFailed, err)
	}
	if !catalogue.Has(targetVersion) {
		return fmt.Errorf("%w: %s", ErrRuntimeUpdateTargetMissing, targetVersion)
	}
	return nil
}

// alreadyActiveHealthyUpdate returns a terminal response without retaining a
// job when the requested version is already the exact active healthy runtime.
func (c *Controller) alreadyActiveHealthyUpdate(
	ctx context.Context,
	agentName string,
	spec agents.ManagedNPMRuntimeSpec,
	targetVersion string,
) *dto.AgentUpdateJobDTO {
	if c.managedRuntimeSelections == nil {
		return nil
	}
	caps, found := c.runtimeUpdater.CurrentCapabilities(agentName)
	if !found || caps.Status != hostutility.StatusOK || caps.AgentVersion != targetVersion {
		return nil
	}
	selection, found, err := c.managedRuntimeSelections.Get(ctx, agentName, spec.Package)
	if err != nil || !found || selection.Package != spec.Package || selection.Version != targetVersion {
		return nil
	}
	now := time.Now().UTC()
	defaultVersion := spec.DefaultVersionOrPinned()
	return &dto.AgentUpdateJobDTO{
		AgentName:        agentName,
		Status:           dto.AgentUpdateJobStatusSucceeded,
		Operation:        string(managedruntime.OperationUpToDate),
		CurrentVersion:   caps.AgentVersion,
		DefaultVersion:   defaultVersion,
		ActiveVersion:    selection.Version,
		EffectiveVersion: selection.Version,
		TargetVersion:    targetVersion,
		Output:           "Runtime already up to date.\n",
		StartedAt:        now,
		FinishedAt:       &now,
	}
}

func (c *Controller) ListAgentUpdateJobs() []dto.AgentUpdateJobDTO {
	if c.updateJobStore == nil {
		return nil
	}
	return c.updateJobStore.ListAll()
}

func (c *Controller) GetAgentUpdateJob(id string) (*dto.AgentUpdateJobDTO, bool) {
	if c.updateJobStore == nil {
		return nil, false
	}
	return c.updateJobStore.Get(id)
}