package client

import (
	"archive/tar"
	"context"
	"fmt"
	"io"
	"log"
	"os"
	"path/filepath"
	"time"

	"github.com/hashicorp/consul/lib"
	nomadapi "github.com/hashicorp/nomad/api"
	"github.com/hashicorp/nomad/client/allocdir"
	"github.com/hashicorp/nomad/client/config"
	cstructs "github.com/hashicorp/nomad/client/structs"
	"github.com/hashicorp/nomad/nomad/structs"
)

type rpcer interface {
	// RPC allows retrieving remote allocs.
	RPC(method string, args interface{}, reply interface{}) error
}

type prevAllocWatcher interface {
	// Wait for previous alloc to terminate
	Wait(context.Context) error

	// Migrate data from previous alloc
	Migrate(ctx context.Context, dest *allocdir.AllocDir) error
}

// newAllocWatcher creates a prevAllocWatcher appropriate for whether this
// allocs previous allocation was local or remote. If this alloc has no
// previous alloc then a noop implementation is returned.
func newAllocWatcher(alloc *structs.Allocation, prevAR *AllocRunner, rpc rpcer, config *config.Config, l *log.Logger) prevAllocWatcher {
	if alloc.PreviousAllocation == "" {
		// No previous allocation, use noop transitioner
		return noopPrevAlloc{}
	}

	tg := alloc.Job.LookupTaskGroup(alloc.TaskGroup)

	if prevAR != nil {
		// Previous allocation is local, use local transitioner
		return &localPrevAlloc{
			allocID:      alloc.ID,
			prevAllocID:  alloc.PreviousAllocation,
			tasks:        tg.Tasks,
			sticky:       tg.EphemeralDisk != nil && tg.EphemeralDisk.Sticky,
			prevAllocDir: prevAR.GetAllocDir(),
			prevListener: prevAR.GetListener(),
			prevWaitCh:   prevAR.WaitCh(),
			logger:       l,
		}
	}

	return &remotePrevAlloc{
		allocID:     alloc.ID,
		prevAllocID: alloc.PreviousAllocation,
		tasks:       tg.Tasks,
		config:      config,
		migrate:     tg.EphemeralDisk != nil && tg.EphemeralDisk.Migrate,
		rpc:         rpc,
		logger:      l,
	}
}

// localPrevAlloc is a prevAllocWatcher for previous allocations on the same
// node as an updated allocation.
type localPrevAlloc struct {
	allocID     string
	prevAllocID string
	tasks       []*structs.Task

	sticky       bool
	prevAllocDir *allocdir.AllocDir
	prevListener *cstructs.AllocListener
	prevWaitCh   <-chan struct{}

	logger *log.Logger
}

// Wait on a local alloc to become terminal, exit, or the context to be done.
func (p *localPrevAlloc) Wait(ctx context.Context) error {
	defer p.prevListener.Close()
	p.logger.Printf("[DEBUG] client: alloc %q waiting for previous alloc %q to terminate", p.allocID, p.prevAllocID)
	for {
		select {
		case prevAlloc := <-p.prevListener.Ch:
			if prevAlloc.Terminated() {
				return nil
			}
		case <-p.prevWaitCh:
			return nil
		case <-ctx.Done():
			return ctx.Err()
		}
	}
}

// Migrate from previous local alloc dir to destination alloc dir.
func (p *localPrevAlloc) Migrate(ctx context.Context, dest *allocdir.AllocDir) error {
	if !p.sticky {
		// Not a sticky volume, nothing to migrate
		return nil
	}
	p.logger.Printf("[DEBUG] client: alloc %q copying previous alloc %q", p.allocID, p.prevAllocID)

	if err := dest.Move(p.prevAllocDir, p.tasks); err != nil {
		p.logger.Printf("[ERR] client: failed to move previous alloc dir %q: %v", p.prevAllocDir.AllocDir, err)
	}
	if err := p.prevAllocDir.Destroy(); err != nil {
		p.logger.Printf("[ERR] client: error destroying allocdir %v: %v", p.prevAllocDir.AllocDir, err)
	}
	return nil
}

// remotePrevAlloc is a prevAllcWatcher for previous allocations on remote
// nodes as an updated allocation.
type remotePrevAlloc struct {
	allocID     string
	prevAllocID string
	tasks       []*structs.Task

	config  *config.Config
	migrate bool
	rpc     rpcer

	// nodeID is the node the previous alloc. Set by Wait() for use in
	// Migrate() iff the previous alloc has not already been GC'd.
	nodeID string

	logger *log.Logger
}

func (p *remotePrevAlloc) Wait(ctx context.Context) error {
	p.logger.Printf("[DEBUG] client: alloc %q waiting for remote previous alloc %q to terminate", p.allocID, p.prevAllocID)
	req := structs.AllocSpecificRequest{
		AllocID: p.prevAllocID,
		QueryOptions: structs.QueryOptions{
			Region:     p.config.Region,
			AllowStale: true,
		},
	}

	done := func() bool {
		select {
		case <-ctx.Done():
			return true
		default:
			return false
		}
	}

	for !done() {
		resp := structs.SingleAllocResponse{}
		err := p.rpc.RPC("Alloc.GetAlloc", &req, &resp)
		if err != nil {
			p.logger.Printf("[ERR] client: failed to query previous alloc %q: %v", p.prevAllocID, err)
			retry := getAllocRetryIntv + lib.RandomStagger(getAllocRetryIntv)
			select {
			case <-time.After(retry):
				continue
			case <-ctx.Done():
				return ctx.Err()
			}
		}
		if resp.Alloc == nil {
			p.logger.Printf("[DEBUG] client: blocking alloc %q has been GC'd", p.prevAllocID)
			return nil
		}
		if resp.Alloc.Terminated() {
			// Terminated!
			p.nodeID = resp.Alloc.NodeID
			return nil
		}

		// Update the query index and requery.
		if resp.Index > req.MinQueryIndex {
			req.MinQueryIndex = resp.Index
		}
	}

	if done() {
		return ctx.Err()
	}

	return nil
}

// Migrate alloc data from a remote node if the new alloc has migration enabled
// and the old alloc hasn't been GC'd.
func (p *remotePrevAlloc) Migrate(ctx context.Context, dest *allocdir.AllocDir) error {
	if !p.migrate {
		// Volume wasn't configured to be migrated, return early
		return nil
	}
	p.logger.Printf("[DEBUG] client: alloc %q copying from remote previous alloc %q", p.allocID, p.prevAllocID)

	if p.nodeID == "" {
		// NodeID couldn't be found; likely alloc was GC'd
		p.logger.Printf("[WARN] client: alloc %q couldn't migrate data from previous alloc %q; previous alloc may have been GC'd",
			p.allocID, p.prevAllocID)
		return nil
	}

	addr, err := p.getNodeAddr(ctx, p.nodeID)
	if err != nil {
		return err
	}

	prevAllocDir, err := p.migrateAllocDir(ctx, addr)
	if err != nil {
		return err
	}

	if err := dest.Move(prevAllocDir, p.tasks); err != nil {
		// cleanup on error
		prevAllocDir.Destroy()
		return err
	}

	if err := prevAllocDir.Destroy(); err != nil {
		p.logger.Printf("[ERR] client: error destroying allocdir %q: %v", prevAllocDir.AllocDir, err)
	}
	return nil
}

// getNodeAddr gets the node from the server with the given Node ID
func (p *remotePrevAlloc) getNodeAddr(ctx context.Context, nodeID string) (string, error) {
	req := structs.NodeSpecificRequest{
		NodeID: nodeID,
		QueryOptions: structs.QueryOptions{
			Region:     p.config.Region,
			AllowStale: true,
		},
	}

	resp := structs.SingleNodeResponse{}
	for {
		err := p.rpc.RPC("Node.GetNode", &req, &resp)
		if err != nil {
			p.logger.Printf("[ERR] client: failed to query node info %q: %v", nodeID, err)
			retry := getAllocRetryIntv + lib.RandomStagger(getAllocRetryIntv)
			select {
			case <-time.After(retry):
				continue
			case <-ctx.Done():
				return "", ctx.Err()
			}
		}
		break
	}

	if resp.Node == nil {
		return "", fmt.Errorf("node %q not found", nodeID)
	}

	scheme := "http://"
	if resp.Node.TLSEnabled {
		scheme = "https://"
	}
	return scheme + resp.Node.HTTPAddr, nil
}

// migrate a remote alloc dir to local node
func (p *remotePrevAlloc) migrateAllocDir(ctx context.Context, nodeAddr string) (*allocdir.AllocDir, error) {
	// Create the previous alloc dir
	prevAllocDir := allocdir.NewAllocDir(p.logger, filepath.Join(p.config.AllocDir, p.prevAllocID))
	if err := prevAllocDir.Build(); err != nil {
		return nil, fmt.Errorf("error building alloc dir for previous alloc %q: %v", p.prevAllocID, err)
	}

	// Create an API client
	apiConfig := nomadapi.DefaultConfig()
	apiConfig.Address = nodeAddr
	apiConfig.TLSConfig = &nomadapi.TLSConfig{
		CACert:     p.config.TLSConfig.CAFile,
		ClientCert: p.config.TLSConfig.CertFile,
		ClientKey:  p.config.TLSConfig.KeyFile,
	}
	apiClient, err := nomadapi.NewClient(apiConfig)
	if err != nil {
		return nil, err
	}

	url := fmt.Sprintf("/v1/client/allocation/%v/snapshot", p.prevAllocID)
	resp, err := apiClient.Raw().Response(url, nil)
	if err != nil {
		prevAllocDir.Destroy()
		return nil, fmt.Errorf("error getting snapshot from previous alloc %q: %v", p.prevAllocID, err)
	}

	if err := p.streamAllocDir(ctx, resp, prevAllocDir.AllocDir); err != nil {
		prevAllocDir.Destroy()
		return nil, err
	}

	return prevAllocDir, nil
}

// stream remote alloc to dir to a local path. Caller should cleanup dest on
// error.
func (p *remotePrevAlloc) streamAllocDir(ctx context.Context, resp io.ReadCloser, dest string) error {
	p.logger.Printf("[DEBUG] client: alloc %q streaming snapshot of previous alloc %q to %q", p.allocID, p.prevAllocID, dest)
	tr := tar.NewReader(resp)
	defer resp.Close()

	canceled := func() bool {
		select {
		case <-ctx.Done():
			p.logger.Printf("[INFO] client: stopping migration of previous alloc %q for new alloc: %v",
				p.prevAllocID, p.allocID)
			return true
		default:
			return false
		}
	}

	buf := make([]byte, 1024)
	for !canceled() {
		// Get the next header
		hdr, err := tr.Next()

		// Snapshot has ended
		if err == io.EOF {
			return nil
		}

		if err != nil {
			return fmt.Errorf("error streaming previous alloc %p for new alloc %q: %v",
				p.prevAllocID, p.allocID, err)
		}

		// If the header is for a directory we create the directory
		if hdr.Typeflag == tar.TypeDir {
			os.MkdirAll(filepath.Join(dest, hdr.Name), os.FileMode(hdr.Mode))
			continue
		}
		// If the header is for a symlink we create the symlink
		if hdr.Typeflag == tar.TypeSymlink {
			if err = os.Symlink(hdr.Linkname, filepath.Join(dest, hdr.Name)); err != nil {
				return fmt.Errorf("error creating symlink: %v", err)
			}
			continue
		}
		// If the header is a file, we write to a file
		if hdr.Typeflag == tar.TypeReg {
			f, err := os.Create(filepath.Join(dest, hdr.Name))
			if err != nil {
				return fmt.Errorf("error creating file: %v", err)
			}

			// Setting the permissions of the file as the origin.
			if err := f.Chmod(os.FileMode(hdr.Mode)); err != nil {
				f.Close()
				return fmt.Errorf("error chmoding file %v", err)
			}
			if err := f.Chown(hdr.Uid, hdr.Gid); err != nil {
				f.Close()
				return fmt.Errorf("error chowning file %v", err)
			}

			// We write in chunks so that we can test if the client
			// is still alive
			for !canceled() {
				n, err := tr.Read(buf)
				if err != nil {
					f.Close()
					if err != io.EOF {
						return fmt.Errorf("error reading snapshot: %v", err)
					}
					break
				}
				if _, err := f.Write(buf[:n]); err != nil {
					f.Close()
					return fmt.Errorf("error writing to file %q: %v", f.Name(), err)
				}
			}

		}
	}

	if canceled() {
		return ctx.Err()
	}

	return nil
}

// noopPrevAlloc does not block or migrate on a previous allocation and never
// returns an error.
type noopPrevAlloc struct{}

// Wait returns nil immediately.
func (noopPrevAlloc) Wait(context.Context) error { return nil }

// Migrate returns nil immediately.
func (noopPrevAlloc) Migrate(context.Context, *allocdir.AllocDir) error { return nil }