package nativebackendexecutor

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"sync"
	"time"

	"yms-daemon/internal/filestore"
	"yms-daemon/internal/healthcheck"
	"yms-daemon/internal/systemd"
	"yms-daemon/internal/transaction"
)

type installJarOperation struct {
	store       *filestore.Store
	sourcePath  string
	releasePath string
	identity    filestore.Identity
}

func (o *installJarOperation) Apply(context.Context) error {
	source, err := os.Open(o.sourcePath)
	if err != nil {
		return fmt.Errorf("open native backend JAR: %w", err)
	}
	defer source.Close()
	_, err = o.store.Commit(o.releasePath, source, o.identity)
	return err
}

func (o *installJarOperation) Inspect(context.Context) (transaction.Inspection, error) {
	file, found, err := o.store.Inspect(o.releasePath, o.identity)
	if errors.Is(err, filestore.ErrDestinationConflict) {
		return transaction.Inspection{Status: transaction.InspectionUnknown}, nil
	}
	if err != nil {
		return transaction.Inspection{}, err
	}
	if !found {
		return transaction.Inspection{Status: transaction.InspectionNotApplied}, nil
	}
	return transaction.Inspection{Status: transaction.InspectionApplied, Result: resultJSON(file)}, nil
}

type slotLinkOperation struct {
	path           string
	desiredTarget  string
	previousTarget string
}

func (o *slotLinkOperation) Apply(ctx context.Context) error {
	inspection, err := o.Inspect(ctx)
	if err != nil {
		return err
	}
	switch inspection.Status {
	case transaction.InspectionApplied:
		return nil
	case transaction.InspectionNotApplied:
	case transaction.InspectionUnknown:
		return fmt.Errorf("native backend slot link %s does not match the recorded previous target", o.path)
	default:
		return fmt.Errorf("native backend slot link %s returned invalid inspection status %q", o.path, inspection.Status)
	}

	parent := filepath.Dir(o.path)
	parentInfo, err := os.Lstat(parent)
	if err != nil {
		return fmt.Errorf("inspect native backend slot directory %s: %w", parent, err)
	}
	if !parentInfo.IsDir() || parentInfo.Mode()&os.ModeSymlink != 0 {
		return fmt.Errorf("native backend slot parent is not a direct directory: %s", parent)
	}
	if o.desiredTarget == "" {
		if err := os.Remove(o.path); err != nil {
			return fmt.Errorf("remove native backend slot link %s: %w", o.path, err)
		}
		return syncDirectory(parent)
	}
	targetInfo, err := os.Lstat(o.desiredTarget)
	if err != nil {
		return fmt.Errorf("inspect native backend slot target %s: %w", o.desiredTarget, err)
	}
	if !targetInfo.Mode().IsRegular() || targetInfo.Mode()&os.ModeSymlink != 0 {
		return fmt.Errorf("native backend slot target is not a regular file: %s", o.desiredTarget)
	}

	temporary, err := os.CreateTemp(parent, ".slot-link-*")
	if err != nil {
		return fmt.Errorf("reserve native backend slot link path: %w", err)
	}
	temporaryPath := temporary.Name()
	if err := temporary.Close(); err != nil {
		_ = os.Remove(temporaryPath)
		return fmt.Errorf("close native backend slot link reservation: %w", err)
	}
	if err := os.Remove(temporaryPath); err != nil {
		return fmt.Errorf("remove native backend slot link reservation: %w", err)
	}
	committed := false
	defer func() {
		if !committed {
			_ = os.Remove(temporaryPath)
		}
	}()
	if err := os.Symlink(o.desiredTarget, temporaryPath); err != nil {
		return fmt.Errorf("create native backend slot link: %w", err)
	}
	if err := os.Rename(temporaryPath, o.path); err != nil {
		return fmt.Errorf("replace native backend slot link %s: %w", o.path, err)
	}
	committed = true
	return syncDirectory(parent)
}

func (o *slotLinkOperation) Inspect(context.Context) (transaction.Inspection, error) {
	info, err := os.Lstat(o.path)
	if errors.Is(err, os.ErrNotExist) {
		if o.desiredTarget == "" {
			if err := syncDirectory(filepath.Dir(o.path)); err != nil {
				return transaction.Inspection{}, err
			}
			return transaction.Inspection{Status: transaction.InspectionApplied, Result: linkResult(o.path, "")}, nil
		}
		if o.previousTarget == "" {
			return transaction.Inspection{Status: transaction.InspectionNotApplied}, nil
		}
		return transaction.Inspection{Status: transaction.InspectionUnknown}, nil
	}
	if err != nil {
		return transaction.Inspection{}, err
	}
	if info.Mode()&os.ModeSymlink == 0 {
		return transaction.Inspection{Status: transaction.InspectionUnknown}, nil
	}
	target, err := os.Readlink(o.path)
	if err != nil {
		return transaction.Inspection{}, err
	}
	result := linkResult(o.path, target)
	if target == o.desiredTarget {
		if err := syncDirectory(filepath.Dir(o.path)); err != nil {
			return transaction.Inspection{}, err
		}
		return transaction.Inspection{Status: transaction.InspectionApplied, Result: result}, nil
	}
	if target == o.previousTarget {
		return transaction.Inspection{Status: transaction.InspectionNotApplied, Result: result}, nil
	}
	return transaction.Inspection{Status: transaction.InspectionUnknown, Result: result}, nil
}

type unitStartOperation struct {
	units systemd.Manager
	name  string
}

func (o *unitStartOperation) Apply(ctx context.Context) error {
	return o.units.Start(ctx, o.name)
}

func (o *unitStartOperation) Inspect(ctx context.Context) (transaction.Inspection, error) {
	unit, err := o.units.Inspect(ctx, o.name)
	if err != nil {
		return transaction.Inspection{}, err
	}
	result := unitResult(unit)
	switch unit.ActiveState {
	case activeState:
		return transaction.Inspection{Status: transaction.InspectionApplied, Result: result}, nil
	case inactiveState, failedState:
		return transaction.Inspection{Status: transaction.InspectionNotApplied, Result: result}, nil
	default:
		return transaction.Inspection{Status: transaction.InspectionUnknown, Result: result}, nil
	}
}

type unitStopOperation struct {
	units systemd.Manager
	name  string
}

func (o *unitStopOperation) Apply(ctx context.Context) error {
	return o.units.Stop(ctx, o.name)
}

func (o *unitStopOperation) Inspect(ctx context.Context) (transaction.Inspection, error) {
	unit, err := o.units.Inspect(ctx, o.name)
	if err != nil {
		return transaction.Inspection{}, err
	}
	result := unitResult(unit)
	switch unit.ActiveState {
	case inactiveState, failedState:
		return transaction.Inspection{Status: transaction.InspectionApplied, Result: result}, nil
	case activeState:
		return transaction.Inspection{Status: transaction.InspectionNotApplied, Result: result}, nil
	default:
		return transaction.Inspection{Status: transaction.InspectionUnknown, Result: result}, nil
	}
}

type healthOperation struct {
	units    systemd.Manager
	checker  actuatorChecker
	unitName string
	endpoint string
	timeout  time.Duration

	mu              sync.Mutex
	confirmedReport healthcheck.ActuatorReport
	confirmed       bool
}

func (o *healthOperation) Apply(ctx context.Context) error {
	report, err := o.checker.Wait(ctx, o.endpoint, o.timeout, o.running)
	if err != nil {
		return err
	}
	o.mu.Lock()
	o.confirmedReport = report
	o.confirmed = true
	o.mu.Unlock()
	return nil
}

func (o *healthOperation) Inspect(ctx context.Context) (transaction.Inspection, error) {
	o.mu.Lock()
	if o.confirmed {
		report := o.confirmedReport
		o.mu.Unlock()
		return healthInspection(report, true, nil)
	}
	o.mu.Unlock()
	report, ready, err := o.checker.Check(ctx, o.endpoint, o.running)
	return healthInspection(report, ready, err)
}

func (o *healthOperation) running(ctx context.Context) (bool, error) {
	unit, err := o.units.Inspect(ctx, o.unitName)
	if errors.Is(err, systemd.ErrUnitNotFound) {
		return false, nil
	}
	if err != nil {
		return false, err
	}
	return unit.ActiveState == activeState, nil
}

func healthInspection(report healthcheck.ActuatorReport, ready bool, err error) (transaction.Inspection, error) {
	result := resultJSON(report)
	if errors.Is(err, healthcheck.ErrWorkloadStopped) {
		return transaction.Inspection{Status: transaction.InspectionNotApplied, Result: result}, nil
	}
	if err != nil || !ready {
		return transaction.Inspection{Status: transaction.InspectionNotApplied, Result: result}, nil
	}
	return transaction.Inspection{Status: transaction.InspectionApplied, Result: result}, nil
}

func linkResult(path, target string) json.RawMessage {
	return resultJSON(struct {
		Path   string `json:"path"`
		Target string `json:"target"`
	}{path, target})
}

func unitResult(unit systemd.Unit) json.RawMessage {
	return resultJSON(struct {
		Name        string `json:"name"`
		LoadState   string `json:"loadState"`
		ActiveState string `json:"activeState"`
		SubState    string `json:"subState"`
	}{unit.Name, unit.LoadState, unit.ActiveState, unit.SubState})
}

func resultJSON(value any) json.RawMessage {
	payload, err := json.Marshal(value)
	if err != nil {
		panic(fmt.Sprintf("marshal internal step result: %v", err))
	}
	return payload
}

func syncDirectory(path string) error {
	directory, err := os.Open(path)
	if err != nil {
		return fmt.Errorf("open directory for flush: %w", err)
	}
	syncErr := directory.Sync()
	closeErr := directory.Close()
	if err := errors.Join(syncErr, closeErr); err != nil {
		return fmt.Errorf("flush directory: %w", err)
	}
	return nil
}

var _ transaction.Operation = (*installJarOperation)(nil)
var _ transaction.Operation = (*slotLinkOperation)(nil)
var _ transaction.Operation = (*unitStartOperation)(nil)
var _ transaction.Operation = (*unitStopOperation)(nil)
var _ transaction.Operation = (*healthOperation)(nil)