package gfit

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

	"github.com/octo/gfitsync/app"
	"golang.org/x/oauth2"
	oauth2google "golang.org/x/oauth2/google"
	fitness "google.golang.org/api/fitness/v1"
	"google.golang.org/api/googleapi"
	"google.golang.org/appengine"
	"google.golang.org/appengine/log"
)

const (
	csrfToken = "@CSRFTOKEN@"
	userID    = "me"

	dataTypeNameCalories = "com.google.calories.expended"
	dataTypeNameSteps    = "com.google.step_count.delta"
)

var oauthConfig = &oauth2.Config{
	ClientID:     "@GOOGLE_CLIENT_ID@",
	ClientSecret: "@GOOGLE_CLIENT_SECRET@",
	Endpoint:     oauth2google.Endpoint,
	RedirectURL:  "https://fitbit-gfit-sync.appspot.com/google/grant",
	Scopes: []string{
		fitness.FitnessActivityWriteScope,
		fitness.FitnessBodyWriteScope,
	},
}

func Application(ctx context.Context) *fitness.Application {
	return &fitness.Application{
		Name:       "Fitbit to Google Fit sync",
		Version:    appengine.VersionID(ctx),
		DetailsUrl: "", // optional
	}
}

func AuthURL() string {
	return oauthConfig.AuthCodeURL(csrfToken, oauth2.AccessTypeOffline)
}

func ParseToken(ctx context.Context, r *http.Request, u *app.User) error {
	if state := r.FormValue("state"); state != csrfToken {
		return fmt.Errorf("invalid state parameter: %q", state)
	}

	tok, err := oauthConfig.Exchange(ctx, r.FormValue("code"))
	if err != nil {
		return err
	}

	return u.SetToken(ctx, "Google", tok)
}

type Client struct {
	*fitness.Service
}

func NewClient(ctx context.Context, u *app.User) (*Client, error) {
	c, err := u.OAuthClient(ctx, "Google", oauthConfig)
	if err != nil {
		return nil, err
	}

	service, err := fitness.New(c)
	if err != nil {
		return nil, err
	}

	return &Client{
		Service: service,
	}, nil
}

func DataStreamID(dataSource *fitness.DataSource) string {
	fields := []string{
		dataSource.Type,
		dataSource.DataType.Name,
		"@PROJECT_NUMBER@", // FIXME
	}

	if dev := dataSource.Device; dev != nil {
		if dev.Manufacturer != "" {
			fields = append(fields, dev.Manufacturer)
		}
		if dev.Model != "" {
			fields = append(fields, dev.Model)
		}
		if dev.Uid != "" {
			fields = append(fields, dev.Uid)
		}
	}

	return strings.Join(fields, ":")
}

func (c *Client) DataSourceCreate(ctx context.Context, dataSource *fitness.DataSource) (string, error) {
	res, err := c.Service.Users.DataSources.Create(userID, dataSource).Context(ctx).Do()
	if err != nil {
		if gerr, ok := err.(*googleapi.Error); ok && gerr.Code == http.StatusConflict {
			if dataSource.DataStreamId != "" {
				return dataSource.DataStreamId, nil
			}
			return DataStreamID(dataSource), nil
		}
		log.Errorf(ctx, "c.Service.Users.DataSources.Create() = (%+v, %v)", res, err)
		return "", err
	}
	return res.DataStreamId, nil
}

func (c *Client) DataSetPatch(ctx context.Context, dataSourceID string, points []*fitness.DataPoint) error {
	startTimeNanos, endTimeNanos := int64(-1), int64(-1)
	for _, p := range points {
		if startTimeNanos == -1 || startTimeNanos > p.StartTimeNanos {
			startTimeNanos = p.StartTimeNanos
		}
		if endTimeNanos == -1 || endTimeNanos < p.EndTimeNanos {
			endTimeNanos = p.EndTimeNanos
		}
	}
	datasetID := fmt.Sprintf("%d-%d", startTimeNanos, endTimeNanos)

	dataset := &fitness.Dataset{
		DataSourceId:   dataSourceID,
		MinStartTimeNs: startTimeNanos,
		MaxEndTimeNs:   endTimeNanos,
		Point:          points,
	}

	_, err := c.Service.Users.DataSources.Datasets.Patch(userID, dataSourceID, datasetID, dataset).Context(ctx).Do()
	if err != nil {
		log.Errorf(ctx, "c.Service.Users.DataSources.Datasets.Patch() = %v", err)
		return err
	}
	return nil
}

func (c *Client) SetSteps(ctx context.Context, totalSteps int, startOfDay time.Time) error {
	return c.updateCumulative(ctx,
		&fitness.DataSource{
			Application: Application(ctx),
			DataType: &fitness.DataType{
				Field: []*fitness.DataTypeField{
					&fitness.DataTypeField{
						Name:   "steps",
						Format: "integer",
					},
				},
				Name: dataTypeNameSteps,
			},
			Name: "Step Count",
			Type: "raw",
		},
		&fitness.Value{
			IntVal: int64(totalSteps),
		},
		startOfDay)
}

func (c *Client) SetCalories(ctx context.Context, totalCalories float64, startOfDay time.Time) error {
	return c.updateCumulative(ctx,
		&fitness.DataSource{
			Application: Application(ctx),
			DataType: &fitness.DataType{
				Field: []*fitness.DataTypeField{
					&fitness.DataTypeField{
						Name:   "calories",
						Format: "floatPoint",
					},
				},
				Name: dataTypeNameCalories,
			},
			Name: "Calories expended",
			Type: "raw",
		},
		&fitness.Value{
			FpVal: totalCalories,
		},
		startOfDay)
}

func (c *Client) updateCumulative(ctx context.Context, dataSource *fitness.DataSource, rawValue *fitness.Value, startOfDay time.Time) error {
	switch f := dataSource.DataType.Field[0].Format; f {
	case "integer":
		if rawValue.IntVal == 0 {
			return nil
		}
	case "floatPoint":
		if rawValue.FpVal == 0 {
			return nil
		}
	default:
		return fmt.Errorf("unexpected data type field format %q", f)
	}

	dataSourceID, err := c.DataSourceCreate(ctx, dataSource)
	if err != nil {
		return err
	}
	dataSource.DataStreamId = dataSourceID

	endOfDay := startOfDay.Add(24 * time.Hour).Add(-1 * time.Nanosecond)
	currValue, startTime, err := c.readCumulative(ctx, dataSource, startOfDay, endOfDay)

	var diffValue fitness.Value
	if dataSource.DataType.Field[0].Format == "integer" {
		if rawValue.IntVal == currValue.IntVal {
			return nil
		}
		diffValue.IntVal = rawValue.IntVal - currValue.IntVal
		if diffValue.IntVal < 0 {
			log.Warningf(ctx, "stored value (%d) is larger than new value (%d); assuming count was reset", currValue.IntVal, rawValue.IntVal)
			diffValue.IntVal = rawValue.IntVal
		}
	} else { // if dataSource.DataType.Field[0].Format == "floatPoint"
		if rawValue.FpVal == currValue.FpVal {
			return nil
		}
		diffValue.FpVal = rawValue.FpVal - currValue.FpVal
		if diffValue.FpVal < 0 {
			log.Warningf(ctx, "stored value (%g) is larger than new value (%g); assuming count was reset", currValue.FpVal, rawValue.FpVal)
			diffValue.FpVal = rawValue.FpVal
		}
	}

	endTime := endOfDay
	if now := time.Now().In(startOfDay.Location()); now.Before(endOfDay) {
		endTime = now
	}
	log.Debugf(ctx, "adding cumulative data point: %v-%v %+v", startTime, endTime, diffValue)

	return c.DataSetPatch(ctx, dataSource.DataStreamId, []*fitness.DataPoint{
		&fitness.DataPoint{
			DataTypeName:   dataSource.DataType.Name,
			StartTimeNanos: startTime.UnixNano(),
			EndTimeNanos:   endTime.UnixNano(),
			Value:          []*fitness.Value{&diffValue},
		},
	})
}

func (c *Client) readCumulative(ctx context.Context, dataSource *fitness.DataSource, startTime, endTime time.Time) (*fitness.Value, time.Time, error) {
	datasetID := fmt.Sprintf("%d-%d", startTime.UnixNano(), endTime.UnixNano())

	res, err := c.Service.Users.DataSources.Datasets.Get(userID, dataSource.DataStreamId, datasetID).Context(ctx).Do()
	if err != nil {
		log.Errorf(ctx, "c.Service.Users.DataSources.Datasets.Get(%q, %q) = %v", dataSource.DataStreamId, datasetID, err)
		return nil, time.Time{}, err
	}

	if len(res.Point) == 0 {
		return &fitness.Value{}, startTime, nil
	}

	var sum fitness.Value
	maxEndTime := startTime
	for _, p := range res.Point {
		switch f := dataSource.DataType.Field[0].Format; f {
		case "integer":
			sum.IntVal += p.Value[0].IntVal
		case "floatPoint":
			sum.FpVal += p.Value[0].FpVal
		default:
			return nil, time.Time{}, fmt.Errorf("unexpected data type field format %q", f)
		}

		pointEndTime := time.Unix(0, p.EndTimeNanos).In(startTime.Location())
		if maxEndTime.Before(pointEndTime) {
			maxEndTime = pointEndTime
		}
	}

	log.Debugf(ctx, "read cumulative data %s until %v: %+v", dataSource.DataStreamId, maxEndTime, sum)
	return &sum, maxEndTime, nil
}