// Package launch contains the core-only, fail-closed application startup use
// case. Platform process, compatibility and process-creation capabilities are
// supplied by the caller.
package launch

import (
	"errors"
	"fmt"
	"os"
	"regexp"

	"softbox.local/core/internal/safepath"
	"softbox.local/core/storage"
)

var (
	ErrLaunchConfig       = errors.New("invalid launch service configuration")
	ErrLaunchRequest      = errors.New("invalid launch request")
	ErrAppNotInstalled    = errors.New("app is not installed")
	ErrLaunchMetadata     = errors.New("installed launch metadata is invalid")
	ErrLaunchTargetUnsafe = errors.New("installed launch target is unsafe")
	ErrEntrypointMissing  = errors.New("installed entrypoint is missing")
	ErrCompatibilityCheck = errors.New("system compatibility check failed")
	ErrAppIncompatible    = errors.New("installed app is incompatible with this system")
	ErrAuthorizationCheck = errors.New("launch authorization check failed")
	ErrLaunchUnauthorized = errors.New("launch is not authorized")
	ErrTargetStateCheck   = errors.New("launch target state check failed")
	ErrAppRunning         = errors.New("installed app is already running")
	ErrProcessStart       = errors.New("start installed app")
	launchAppIDPattern    = regexp.MustCompile(`^[a-z0-9-]+$`)
)

// FailureCode is the stable, non-localized result of a launch attempt.
type FailureCode string

const (
	FailureCodeNotInstalled             FailureCode = "not_installed"
	FailureCodeLaunchMetadataInvalid    FailureCode = "launch_metadata_invalid"
	FailureCodeLaunchTargetUnsafe       FailureCode = "launch_target_unsafe"
	FailureCodeEntrypointMissing        FailureCode = "entrypoint_missing"
	FailureCodeCompatibilityUnavailable FailureCode = "compatibility_unavailable"
	FailureCodeAppIncompatible          FailureCode = "app_incompatible"
	FailureCodeAuthorizationFailed      FailureCode = "authorization_unavailable"
	FailureCodeLaunchUnauthorized       FailureCode = "not_authorized"
	FailureCodeAppRunning               FailureCode = "app_running"
	FailureCodeTargetStateUnavailable   FailureCode = "target_state_unavailable"
	FailureCodeLaunchFailed             FailureCode = "launch_failed"
)

// Error preserves a stable launch code and the diagnostic cause.
type Error struct {
	Code FailureCode
	Err  error
}

func (err *Error) Error() string {
	return fmt.Sprintf("launch (%s): %v", err.Code, err.Err)
}

func (err *Error) Unwrap() error {
	return err.Err
}

// Request names the installed app to start. The caller cannot supply a path,
// arguments or working directory.
type Request struct {
	AppID string
}

// Command contains only paths resolved from verified installed metadata.
type Command struct {
	Entrypoint       string
	WorkingDirectory string
	RequiresAdmin    bool
}

// Result is returned only after the platform accepted the process start.
type Result struct {
	AppID string
	PID   int
}

// InstalledAppResolver returns an installed record paired with a validated
// real current directory.
type InstalledAppResolver interface {
	ResolveCurrent(appID string) (storage.InstalledApp, string, error)
}

// CompatibilityChecker reports whether a recorded min_os may run here.
type CompatibilityChecker interface {
	IsCompatible(minOS string) (bool, error)
}

// AuthorizationChecker decides whether the user may launch one app. It is a
// required boundary; license policy is implemented by the later licensing task.
type AuthorizationChecker interface {
	IsAuthorized(appID string) (bool, error)
}

// TargetStateChecker reports whether this precise entrypoint is running.
type TargetStateChecker interface {
	IsRunning(appID string, entrypointPath string) (bool, error)
}

// ProcessLauncher starts one verified command without accepting shell input.
type ProcessLauncher interface {
	Start(command Command) (int, error)
}

// ServiceConfig makes every external launch dependency explicit.
type ServiceConfig struct {
	Records       InstalledAppResolver
	Compatibility CompatibilityChecker
	Authorization AuthorizationChecker
	TargetState   TargetStateChecker
	Launcher      ProcessLauncher
}

// Service executes the safe local launch flow.
type Service struct {
	records       InstalledAppResolver
	compatibility CompatibilityChecker
	authorization AuthorizationChecker
	targetState   TargetStateChecker
	launcher      ProcessLauncher
}

func NewService(config ServiceConfig) (*Service, error) {
	if config.Records == nil {
		return nil, fmt.Errorf("%w: installed app resolver is required", ErrLaunchConfig)
	}
	if config.Compatibility == nil {
		return nil, fmt.Errorf("%w: compatibility checker is required", ErrLaunchConfig)
	}
	if config.Authorization == nil {
		return nil, fmt.Errorf("%w: authorization checker is required", ErrLaunchConfig)
	}
	if config.TargetState == nil {
		return nil, fmt.Errorf("%w: target state checker is required", ErrLaunchConfig)
	}
	if config.Launcher == nil {
		return nil, fmt.Errorf("%w: process launcher is required", ErrLaunchConfig)
	}
	return &Service{
		records:       config.Records,
		compatibility: config.Compatibility,
		authorization: config.Authorization,
		targetState:   config.TargetState,
		launcher:      config.Launcher,
	}, nil
}

// Start validates local metadata and filesystem identity before invoking the
// platform process launcher.
func (service *Service) Start(request Request) (Result, error) {
	if !launchAppIDPattern.MatchString(request.AppID) {
		return Result{}, launchError(ErrLaunchRequest)
	}
	record, current, err := service.records.ResolveCurrent(request.AppID)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return Result{}, launchError(ErrAppNotInstalled)
		}
		if errors.Is(err, storage.ErrStorageLayoutUnsafe) {
			return Result{}, launchError(fmt.Errorf("%w: %w", ErrLaunchTargetUnsafe, err))
		}
		return Result{}, launchError(fmt.Errorf("resolve installed app: %w", err))
	}
	command, err := launchCommand(record, current)
	if err != nil {
		return Result{}, launchError(err)
	}
	compatible, err := service.compatibility.IsCompatible(record.MinOS)
	if err != nil {
		return Result{}, launchError(fmt.Errorf("%w: %w", ErrCompatibilityCheck, err))
	}
	if !compatible {
		return Result{}, launchError(ErrAppIncompatible)
	}
	authorized, err := service.authorization.IsAuthorized(record.ID)
	if err != nil {
		return Result{}, launchError(fmt.Errorf("%w: %w", ErrAuthorizationCheck, err))
	}
	if !authorized {
		return Result{}, launchError(ErrLaunchUnauthorized)
	}
	running, err := service.targetState.IsRunning(record.ID, command.Entrypoint)
	if err != nil {
		return Result{}, launchError(fmt.Errorf("%w: %w", ErrTargetStateCheck, err))
	}
	if running {
		return Result{}, launchError(ErrAppRunning)
	}
	pid, err := service.launcher.Start(command)
	if err != nil {
		return Result{}, launchError(fmt.Errorf("%w: %w", ErrProcessStart, err))
	}
	if pid <= 0 {
		return Result{}, launchError(fmt.Errorf("%w: invalid process ID", ErrProcessStart))
	}
	return Result{AppID: record.ID, PID: pid}, nil
}

func launchCommand(record storage.InstalledApp, current string) (Command, error) {
	if record.Entrypoint == "" || record.WorkingDirectory == "" || record.MinOS == "" {
		return Command{}, ErrLaunchMetadata
	}
	if err := safepath.ValidateRelative(record.Entrypoint); err != nil {
		return Command{}, fmt.Errorf("%w: entrypoint: %v", ErrLaunchMetadata, err)
	}
	if record.WorkingDirectory != "." {
		if err := safepath.ValidateRelative(record.WorkingDirectory); err != nil {
			return Command{}, fmt.Errorf("%w: working directory: %v", ErrLaunchMetadata, err)
		}
	}
	if !validMinOS(record.MinOS) {
		return Command{}, ErrLaunchMetadata
	}
	if !containsEntrypoint(record.Files, record.Entrypoint) {
		return Command{}, fmt.Errorf("%w: entrypoint is not in installed files", ErrLaunchMetadata)
	}
	if err := requireRealDirectory(current); err != nil {
		return Command{}, err
	}
	entrypoint, err := safepath.JoinUnder(current, record.Entrypoint)
	if err != nil {
		return Command{}, fmt.Errorf("%w: entrypoint: %v", ErrLaunchTargetUnsafe, err)
	}
	workingDirectory := current
	if record.WorkingDirectory != "." {
		workingDirectory, err = safepath.JoinUnder(current, record.WorkingDirectory)
		if err != nil {
			return Command{}, fmt.Errorf("%w: working directory: %v", ErrLaunchTargetUnsafe, err)
		}
	}
	if err := requireRealDirectory(workingDirectory); err != nil {
		return Command{}, err
	}
	if err := requireRegularFile(entrypoint); err != nil {
		return Command{}, err
	}
	return Command{
		Entrypoint:       entrypoint,
		WorkingDirectory: workingDirectory,
		RequiresAdmin:    record.RequiresAdmin,
	}, nil
}

func containsEntrypoint(files []storage.InstalledFile, entrypoint string) bool {
	for _, file := range files {
		if file.Path == entrypoint {
			return true
		}
	}
	return false
}

func validMinOS(minOS string) bool {
	return minOS == "windows-7-sp1" || minOS == "windows-10" || minOS == "windows-11"
}

func requireRealDirectory(path string) error {
	info, err := os.Lstat(path)
	if os.IsNotExist(err) {
		return fmt.Errorf("%w: %s", ErrLaunchTargetUnsafe, path)
	}
	if err != nil {
		return fmt.Errorf("%w: inspect %s: %w", ErrLaunchTargetUnsafe, path, err)
	}
	if info.Mode()&os.ModeSymlink != 0 || !info.IsDir() {
		return fmt.Errorf("%w: %s is not a real directory", ErrLaunchTargetUnsafe, path)
	}
	return nil
}

func requireRegularFile(path string) error {
	info, err := os.Lstat(path)
	if os.IsNotExist(err) {
		return fmt.Errorf("%w: %s", ErrEntrypointMissing, path)
	}
	if err != nil {
		return fmt.Errorf("%w: inspect %s: %w", ErrLaunchTargetUnsafe, path, err)
	}
	if info.Mode()&os.ModeSymlink != 0 || !info.Mode().IsRegular() {
		return fmt.Errorf("%w: %s is not a regular file", ErrLaunchTargetUnsafe, path)
	}
	return nil
}

func launchError(err error) error {
	return &Error{Code: failureCodeFor(err), Err: err}
}

func failureCodeFor(err error) FailureCode {
	switch {
	case errors.Is(err, ErrAppNotInstalled):
		return FailureCodeNotInstalled
	case errors.Is(err, ErrLaunchMetadata):
		return FailureCodeLaunchMetadataInvalid
	case errors.Is(err, ErrLaunchTargetUnsafe):
		return FailureCodeLaunchTargetUnsafe
	case errors.Is(err, ErrEntrypointMissing):
		return FailureCodeEntrypointMissing
	case errors.Is(err, ErrCompatibilityCheck):
		return FailureCodeCompatibilityUnavailable
	case errors.Is(err, ErrAppIncompatible):
		return FailureCodeAppIncompatible
	case errors.Is(err, ErrAuthorizationCheck):
		return FailureCodeAuthorizationFailed
	case errors.Is(err, ErrLaunchUnauthorized):
		return FailureCodeLaunchUnauthorized
	case errors.Is(err, ErrAppRunning):
		return FailureCodeAppRunning
	case errors.Is(err, ErrTargetStateCheck):
		return FailureCodeTargetStateUnavailable
	default:
		return FailureCodeLaunchFailed
	}
}