package strategy

import (
	"context"
	"fmt"
	"net/http"
	"strings"

	"cloud.google.com/go/storage"
	"go.skia.org/infra/go/gcs"
	"go.skia.org/infra/go/git"
	"go.skia.org/infra/go/sklog"
	"go.skia.org/infra/go/vcsinfo"
	"google.golang.org/api/option"
)

const (
	ROLL_STRATEGY_AFDO         = "afdo"
	ROLL_STRATEGY_BATCH        = "batch"
	ROLL_STRATEGY_FUCHSIA_SDK  = "fuchsiaSDK"
	ROLL_STRATEGY_GCS_FILE     = "gcs file"
	ROLL_STRATEGY_REMOTE_BATCH = "remote batch"
	ROLL_STRATEGY_SINGLE       = "single"
)

// NextRollStrategy is an interface for modules which determine what the next roll
// revision should be.
type NextRollStrategy interface {
	// Return the next roll revision, given the list of not-yet-rolled
	// commits in reverse chronological order. Returning the empty string
	// implies that we are up-to-date.
	GetNextRollRev(context.Context, []*vcsinfo.LongCommit) (string, error)
}

// Return the NextRollStrategy indicated by the given string.
func GetNextRollStrategy(ctx context.Context, strategy, branch, upstreamRemote, gsBucket string, gsPathTemplates []string, repo *git.Checkout, authClient *http.Client) (NextRollStrategy, error) {
	switch strategy {
	case ROLL_STRATEGY_AFDO:
		storageClient, err := storage.NewClient(ctx, option.WithHTTPClient(authClient))
		if err != nil {
			return nil, err
		}
		return &AFDOStrategy{
			gcs: gcs.NewGCSClient(storageClient, AFDO_GS_BUCKET),
		}, nil
	case ROLL_STRATEGY_GCS_FILE:
		storageClient, err := storage.NewClient(ctx)
		if err != nil {
			return nil, err
		}
		return StrategyGCSFile(gcs.NewGCSClient(storageClient, gsBucket), gsPathTemplates), nil
	case ROLL_STRATEGY_BATCH:
		return StrategyHead(branch), nil
	case ROLL_STRATEGY_FUCHSIA_SDK:
		return nil, nil // Handled by FuchsiaSDKRepoManager.
	case ROLL_STRATEGY_REMOTE_BATCH:
		return StrategyRemoteHead(branch, upstreamRemote, repo), nil
	case ROLL_STRATEGY_SINGLE:
		return StrategySingle(branch), nil
	default:
		return nil, fmt.Errorf("Unknown roll strategy %q", strategy)
	}
}

// headStrategy is a NextRollStrategy which always rolls to HEAD of a given branch.
type headStrategy struct {
	branch string
}

// See documentation for NextRollStrategy interface.
func (s *headStrategy) GetNextRollRev(ctx context.Context, notRolled []*vcsinfo.LongCommit) (string, error) {
	if len(notRolled) > 0 {
		// Commits are listed in reverse chronological order.
		return notRolled[0].Hash, nil
	}
	return "", nil
}

// StrategyHead returns a NextRollStrategy which always rolls to HEAD of a given branch.
func StrategyHead(branch string) NextRollStrategy {
	return &headStrategy{
		branch: branch,
	}
}

// remoteHeadStrategy is a NextRollStrategy which always rolls to HEAD of a
// given branch, as defined by "git ls-remote".
type remoteHeadStrategy struct {
	branch         string
	repo           *git.Checkout
	upstreamRemote string
}

// See documentation for NextRollStrategy interface.
func (s *remoteHeadStrategy) GetNextRollRev(ctx context.Context, _ []*vcsinfo.LongCommit) (string, error) {
	output, err := s.repo.Git(ctx, "ls-remote", s.upstreamRemote, fmt.Sprintf("refs/heads/%s", s.branch), "-1")
	if err != nil {
		return "", err
	}
	tokens := strings.Split(output, "\t")
	return tokens[0], nil
}

// StrategyRemoteHead returns a NextRollStrategy which always rolls to HEAD of a
// given branch, as defined by "git ls-remote".
func StrategyRemoteHead(branch, upstreamRemote string, repo *git.Checkout) NextRollStrategy {
	return &remoteHeadStrategy{
		branch:         branch,
		repo:           repo,
		upstreamRemote: upstreamRemote,
	}
}

// gcsFileStrategy is a NextRollStrategy which rolls to a hash that has an
// entry in the provided google storage locations.
type gcsFileStrategy struct {
	gcs             gcs.GCSClient
	gsPathTemplates []string
}

// See documentation for NextRollStrategy interface.
func (s *gcsFileStrategy) GetNextRollRev(ctx context.Context, notRolled []*vcsinfo.LongCommit) (string, error) {
	if len(notRolled) > 0 {
		// Commits are listed in reverse chronological order.
		for _, notRolledCommit := range notRolled {
			// Check to see if this commit exists in the gsPath locations.
			missingFile := false
			for _, gsPathTemplate := range s.gsPathTemplates {
				gsPath := fmt.Sprintf(gsPathTemplate, notRolledCommit.Hash)
				fileExists, err := s.gcs.DoesFileExist(ctx, gsPath)
				if err != nil {
					return "", err
				}
				if fileExists {
					sklog.Infof("[gcsFileStrategy] Found %s", gsPath)
					continue
				} else {
					sklog.Infof("[gcsFileStrategy] Could not find %s", gsPath)
					missingFile = true
					break
				}
			}
			if !missingFile {
				sklog.Infof("[gcsFileStrategy] Found all %s paths for %s", s.gsPathTemplates, notRolledCommit.Hash)
				return notRolledCommit.Hash, nil
			}
		}
		// Could not find any hash in Google Storage.
		sklog.Info("[gcsFileStrategy] Could not find any notRolled hashes in storage.")
		return "", nil
	}
	return "", nil
}

// StrategyGCSFile returns a NextRollStrategy which rolls to a hash that has the
// specified entries in the provided google storage location.
func StrategyGCSFile(gcs gcs.GCSClient, gsPathTemplates []string) NextRollStrategy {
	return &gcsFileStrategy{
		gcs:             gcs,
		gsPathTemplates: gsPathTemplates,
	}
}

// singleStrategy is a NextRollStrategy which rolls toward HEAD of a given branch, one
// commit at a time.
type singleStrategy struct {
	*headStrategy
}

// See documentation for NextRollStrategy interface.
func (s *singleStrategy) GetNextRollRev(ctx context.Context, notRolled []*vcsinfo.LongCommit) (string, error) {
	if len(notRolled) > 0 {
		return notRolled[len(notRolled)-1].Hash, nil
	}
	return "", nil
}

// StrategySingle returns a NextRollStrategy which rolls toward HEAD of a given branch,
// one commit at a time.
func StrategySingle(branch string) NextRollStrategy {
	return &singleStrategy{StrategyHead(branch).(*headStrategy)}
}