package api

import (
	"context"
	"errors"
	"io"
	"net/http"
	"os"
	"time"

	"github.com/danielgtaylor/huma/v2"
	"github.com/danielgtaylor/huma/v2/adapters/humago"

	"github.com/v10networks/nmon/internal/vmsup"
)

// ErrBackupRefused means a backup was refused because the disk is below the reserve.
var ErrBackupRefused = errors.New("backup refused")

// BackupFile is a finished backup waiting to be streamed to the caller.
type BackupFile struct {
	Path        string
	KeyIncluded bool
	// Done deletes the file once it has been sent.
	Done func()
}

// BackupRunner runs one online backup into a temporary file.
type BackupRunner interface {
	Create(ctx context.Context, includeKey bool) (BackupFile, error)
}

// StoreRestarter resumes a metric store that gave up after repeated crashes. *vmsup.Supervisor implements it.
type StoreRestarter interface{ Restart(name string) error }

// backupOut streams the archive. KeyIncluded repeats what the archive's manifest says, so a client can print it.
type backupOut struct {
	ContentType string `header:"Content-Type"`
	Disposition string `header:"Content-Disposition"`
	KeyIncluded string `header:"X-Nmon-Key-Included"`
	Body        func(ctx huma.Context)
}

func (s *server) registerAdmin(api huma.API) {
	huma.Register(api, huma.Operation{
		OperationID: "create-backup", Method: http.MethodPost, Path: "/api/v1/admin/backup", Tags: []string{"admin"},
		Summary: "Take a backup and download it",
		Description: "Admin only. Runs nmon's online backup (inventory snapshot, both metric stores' snapshots, config and profiles) " +
			"and streams the tar. The X-Nmon-Key-Included header says whether the encryption key is inside. `nmon backup` is the client.",
		Responses: map[string]*huma.Response{"200": {
			Description: "The backup archive.",
			Content:     map[string]*huma.MediaType{"application/x-tar": {}},
		}},
		Middlewares: huma.Middlewares{noWriteDeadline},
		Errors:      []int{http.StatusInsufficientStorage, http.StatusServiceUnavailable},
	}, s.createBackup)
	huma.Register(api, huma.Operation{
		OperationID: "restart-store", Method: http.MethodPost, Path: "/api/v1/admin/stores/{name}/restart", Tags: []string{"admin"},
		Summary: "Resume a failed metric store", DefaultStatus: http.StatusNoContent,
		Description: "Admin only. After store_failed the supervisor stopped restarting the store; this starts it again. " +
			"A store that has not failed is a 409.",
		Errors: []int{http.StatusNotFound, http.StatusConflict, http.StatusServiceUnavailable},
	}, s.restartStore)
}

// noWriteDeadline lifts the server's write timeout for one request: a backup can take longer than it.
func noWriteDeadline(ctx huma.Context, next func(huma.Context)) {
	if _, w := humago.Unwrap(ctx); w != nil {
		_ = http.NewResponseController(w).SetWriteDeadline(time.Time{}) // unsupported writers keep the default
	}
	next(ctx)
}

func (s *server) createBackup(ctx context.Context, in *struct {
	IncludeKey bool `query:"include_key" doc:"Put the encryption key in the archive. Default false."`
}) (*backupOut, error) {
	if s.Backups == nil {
		return nil, errNotConfigured("backup")
	}
	bf, err := s.Backups.Create(ctx, in.IncludeKey)
	if errors.Is(err, ErrBackupRefused) {
		return nil, huma.NewError(http.StatusInsufficientStorage, trimSentinel(err, ErrBackupRefused))
	}
	if err != nil {
		s.Logger.Error("backup", "err", err)
		return nil, huma.Error500InternalServerError("backup failed; see the log")
	}
	detail := map[string]bool{"key_included": bf.KeyIncluded}
	if err := s.Store.AppendAudit(ctx, actorOf(ctx), "backup.create", "backup", nil, detail); err != nil {
		s.Logger.Warn("audit backup.create", "err", err)
	}
	key := "false"
	if bf.KeyIncluded {
		key = "true"
	}
	return &backupOut{
		ContentType: "application/x-tar", Disposition: `attachment; filename="nmon-backup.tar"`, KeyIncluded: key,
		Body: func(hc huma.Context) { s.streamBackup(hc, bf) },
	}, nil
}

func (s *server) streamBackup(hc huma.Context, bf BackupFile) {
	defer bf.Done()
	f, err := os.Open(bf.Path)
	if err != nil {
		s.Logger.Error("open backup for download", "err", err)
		return
	}
	defer func() { _ = f.Close() }()
	if _, err := io.Copy(hc.BodyWriter(), f); err != nil {
		s.Logger.Warn("stream backup", "err", err)
	}
}

func (s *server) restartStore(ctx context.Context, in *struct {
	Name string `path:"name" enum:"hot,long" doc:"Which metric store."`
}) (*struct{}, error) {
	if s.Stores == nil {
		return nil, errNotConfigured("metric store supervisor")
	}
	err := s.Stores.Restart(in.Name)
	switch {
	case errors.Is(err, vmsup.ErrUnknownStore):
		return nil, huma.Error404NotFound("no such store")
	case errors.Is(err, vmsup.ErrNotFailed), errors.Is(err, vmsup.ErrExternalStore):
		return nil, huma.Error409Conflict(err.Error())
	case err != nil:
		s.Logger.Error("restart store", "err", err)
		return nil, huma.Error500InternalServerError("restart failed; see the log")
	}
	if err := s.Store.AppendAudit(ctx, actorOf(ctx), "store.restart", "store:"+in.Name, nil, nil); err != nil {
		s.Logger.Warn("audit store.restart", "err", err)
	}
	return &struct{}{}, nil
}