package sql

import (
	"bytes"
	"context"
	"database/sql"
	"errors"
	"fmt"
	"io"
	"net/url"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/fnproject/fn/api/common"
	"github.com/fnproject/fn/api/datastore/sql/migrations"
	"github.com/fnproject/fn/api/models"
	"github.com/go-sql-driver/mysql"
	_ "github.com/go-sql-driver/mysql"
	"github.com/jmoiron/sqlx"
	"github.com/lib/pq"
	_ "github.com/lib/pq"
	"github.com/mattn/go-sqlite3"
	_ "github.com/mattn/go-sqlite3"
	"github.com/rdallman/migrate"
	_ "github.com/rdallman/migrate/database/mysql"
	_ "github.com/rdallman/migrate/database/postgres"
	_ "github.com/rdallman/migrate/database/sqlite3"
	"github.com/rdallman/migrate/source"
	"github.com/rdallman/migrate/source/go-bindata"
	"github.com/sirupsen/logrus"
)

// this aims to be an ANSI-SQL compliant package that uses only question
// mark syntax for var placement, leaning on sqlx to make compatible all
// queries to the actual underlying datastore.
//
// currently tested and working are postgres, mysql and sqlite3.

// TODO routes.created_at should be varchar(256), mysql will store 'text'
// fields not contiguous with other fields and this field is a fixed size,
// we'll get better locality with varchar. it's not terribly easy to do this
// with migrations (sadly, need complex transaction)

var tables = [...]string{`CREATE TABLE IF NOT EXISTS routes (
	app_name varchar(256) NOT NULL,
	path varchar(256) NOT NULL,
	image varchar(256) NOT NULL,
	format varchar(16) NOT NULL,
	memory int NOT NULL,
	timeout int NOT NULL,
	idle_timeout int NOT NULL,
	type varchar(16) NOT NULL,
	headers text NOT NULL,
	config text NOT NULL,
	created_at text,
	updated_at varchar(256),
	PRIMARY KEY (app_name, path)
);`,

	`CREATE TABLE IF NOT EXISTS apps (
	name varchar(256) NOT NULL PRIMARY KEY,
	config text NOT NULL,
	created_at varchar(256),
	updated_at varchar(256)
);`,

	`CREATE TABLE IF NOT EXISTS calls (
	created_at varchar(256) NOT NULL,
	started_at varchar(256) NOT NULL,
	completed_at varchar(256) NOT NULL,
	status varchar(256) NOT NULL,
	id varchar(256) NOT NULL,
	app_name varchar(256) NOT NULL,
	path varchar(256) NOT NULL,
	stats text,
	error text,
	PRIMARY KEY (id)
);`,

	`CREATE TABLE IF NOT EXISTS logs (
	id varchar(256) NOT NULL PRIMARY KEY,
	app_name varchar(256) NOT NULL,
	log text NOT NULL
);`,
}

const (
	routeSelector = `SELECT app_name, path, image, format, memory, type, timeout, idle_timeout, headers, config, created_at, updated_at FROM routes`
	callSelector  = `SELECT id, created_at, started_at, completed_at, status, app_name, path, stats, error FROM calls`
)

type sqlStore struct {
	db *sqlx.DB
}

// New will open the db specified by url, create any tables necessary
// and return a models.Datastore safe for concurrent usage.
func New(ctx context.Context, url *url.URL) (models.Datastore, error) {
	return newDS(ctx, url)
}

// for test methods, return concrete type, but don't expose
func newDS(ctx context.Context, url *url.URL) (*sqlStore, error) {
	driver := url.Scheme

	log := common.Logger(ctx)
	// driver must be one of these for sqlx to work, double check:
	switch driver {
	case "postgres", "pgx", "mysql", "sqlite3":
	default:
		return nil, errors.New("invalid db driver, refer to the code")
	}

	if driver == "sqlite3" {
		// make all the dirs so we can make the file..
		dir := filepath.Dir(url.Path)
		err := os.MkdirAll(dir, 0755)
		if err != nil {
			return nil, err
		}
	}

	uri := url.String()
	if driver != "postgres" {
		// postgres seems to need this as a prefix in lib/pq, everyone else wants it stripped of scheme
		uri = strings.TrimPrefix(url.String(), url.Scheme+"://")
	}

	sqldb, err := sql.Open(driver, uri)
	if err != nil {
		log.WithFields(logrus.Fields{"url": uri}).WithError(err).Error("couldn't open db")
		return nil, err
	}

	db := sqlx.NewDb(sqldb, driver)
	// force a connection and test that it worked
	err = pingWithRetry(ctx, 10, time.Second*1, db)
	if err != nil {
		log.WithFields(logrus.Fields{"url": uri}).WithError(err).Error("couldn't ping db")
		return nil, err
	}

	maxIdleConns := 256 // TODO we need to strip this out of the URL probably
	db.SetMaxIdleConns(maxIdleConns)
	log.WithFields(logrus.Fields{"max_idle_connections": maxIdleConns, "datastore": driver}).Info("datastore dialed")

	err = runMigrations(url.String(), checkExistence(db)) // original url string
	if err != nil {
		log.WithError(err).Error("error running migrations")
		return nil, err
	}

	switch driver {
	case "sqlite3":
		db.SetMaxOpenConns(1)
	}
	for _, v := range tables {
		_, err = db.ExecContext(ctx, v)
		if err != nil {
			return nil, err
		}
	}

	return &sqlStore{db: db}, nil
}

func pingWithRetry(ctx context.Context, attempts int, sleep time.Duration, db *sqlx.DB) (err error) {
	for i := 0; i < attempts; i++ {
		err = db.PingContext(ctx)
		if err == nil {
			return nil
		}
		time.Sleep(sleep)
	}
	return err
}

// checkExistence checks if tables have been created yet, it is not concerned
// about the existence of the schema migration version (since migrations were
// added to existing dbs, we need to know whether the db exists without migrations
// or if it's brand new).
func checkExistence(db *sqlx.DB) bool {
	query := db.Rebind(`SELECT name FROM apps LIMIT 1`)
	row := db.QueryRow(query)

	var dummy string
	err := row.Scan(&dummy)
	if err != nil && err != sql.ErrNoRows {
		// TODO we should probably ensure this is a certain 'no such table' error
		// and if it's not that or err no rows, we should probably block start up.
		// if we return false here spuriously, then migrations could be skipped,
		// which would be bad.
		return false
	}
	return true
}

// check if the db already existed, if the db is brand new then we can skip
// over all the migrations BUT we must be sure to set the right migration
// number so that only current migrations are skipped, not any future ones.
func runMigrations(url string, exists bool) error {
	m, err := migrator(url)
	if err != nil {
		return err
	}
	defer m.Close()

	if !exists {
		// set to highest and bail
		return m.Force(latestVersion(migrations.AssetNames()))
	}

	// run any migrations needed to get to latest, if any
	err = m.Up()
	if err == migrate.ErrNoChange { // we don't care, but want other errors
		err = nil
	}
	return err
}

func migrator(url string) (*migrate.Migrate, error) {
	s := bindata.Resource(migrations.AssetNames(),
		func(name string) ([]byte, error) {
			return migrations.Asset(name)
		})

	d, err := bindata.WithInstance(s)
	if err != nil {
		return nil, err
	}

	return migrate.NewWithSourceInstance("go-bindata", d, url)
}

// latest version will find the latest version from a list of migration
// names (not from the db)
func latestVersion(migs []string) int {
	var highest uint
	for _, m := range migs {
		mig, _ := source.Parse(m)
		if mig.Version > highest {
			highest = mig.Version
		}
	}

	return int(highest)
}

// clear is for tests only, be careful, it deletes all records.
func (ds *sqlStore) clear() error {
	return ds.Tx(func(tx *sqlx.Tx) error {
		query := tx.Rebind(`DELETE FROM routes`)
		_, err := tx.Exec(query)
		if err != nil {
			return err
		}

		query = tx.Rebind(`DELETE FROM calls`)
		_, err = tx.Exec(query)
		if err != nil {
			return err
		}

		query = tx.Rebind(`DELETE FROM apps`)
		_, err = tx.Exec(query)
		if err != nil {
			return err
		}

		query = tx.Rebind(`DELETE FROM logs`)
		_, err = tx.Exec(query)
		return err
	})
}

func (ds *sqlStore) InsertApp(ctx context.Context, app *models.App) (*models.App, error) {
	query := ds.db.Rebind(`INSERT INTO apps (
		name,
		config,
		created_at,
		updated_at
	)
	VALUES (
		:name,
		:config,
		:created_at,
		:updated_at
	);`)
	_, err := ds.db.NamedExecContext(ctx, query, app)
	if err != nil {
		switch err := err.(type) {
		case *mysql.MySQLError:
			if err.Number == 1062 {
				return nil, models.ErrAppsAlreadyExists
			}
		case *pq.Error:
			if err.Code == "23505" {
				return nil, models.ErrAppsAlreadyExists
			}
		case sqlite3.Error:
			if err.ExtendedCode == sqlite3.ErrConstraintUnique || err.ExtendedCode == sqlite3.ErrConstraintPrimaryKey {
				return nil, models.ErrAppsAlreadyExists
			}
		}
		return nil, err
	}

	return app, nil
}

func (ds *sqlStore) UpdateApp(ctx context.Context, newapp *models.App) (*models.App, error) {
	app := &models.App{Name: newapp.Name}
	err := ds.Tx(func(tx *sqlx.Tx) error {
		// NOTE: must query whole object since we're returning app, Update logic
		// must only modify modifiable fields (as seen here). need to fix brittle..
		query := tx.Rebind(`SELECT name, config, created_at, updated_at FROM apps WHERE name=?`)
		row := tx.QueryRowxContext(ctx, query, app.Name)

		err := row.StructScan(app)
		if err == sql.ErrNoRows {
			return models.ErrAppsNotFound
		} else if err != nil {
			return err
		}

		app.Update(newapp)

		query = tx.Rebind(`UPDATE apps SET config=:config, updated_at=:updated_at WHERE name=:name`)
		res, err := tx.NamedExecContext(ctx, query, app)
		if err != nil {
			return err
		}

		if n, err := res.RowsAffected(); err != nil {
			return err
		} else if n == 0 {
			// inside of the transaction, we are querying for the app, so we know that it exists
			return nil
		}
		return nil
	})

	if err != nil {
		return nil, err
	}

	return app, nil
}

func (ds *sqlStore) RemoveApp(ctx context.Context, appName string) error {
	return ds.Tx(func(tx *sqlx.Tx) error {
		res, err := tx.ExecContext(ctx, tx.Rebind(`DELETE FROM apps WHERE name=?`), appName)
		if err != nil {
			return err
		}
		n, err := res.RowsAffected()
		if err != nil {
			return err
		}
		if n == 0 {
			return models.ErrAppsNotFound
		}

		deletes := []string{
			`DELETE FROM logs WHERE app_name=?`,
			`DELETE FROM calls WHERE app_name=?`,
			`DELETE FROM routes WHERE app_name=?`,
		}

		for _, stmt := range deletes {
			_, err := tx.ExecContext(ctx, tx.Rebind(stmt), appName)
			if err != nil {
				return err
			}
		}
		return nil
	})
}

func (ds *sqlStore) GetApp(ctx context.Context, name string) (*models.App, error) {
	query := ds.db.Rebind(`SELECT name, config, created_at, updated_at FROM apps WHERE name=?`)
	row := ds.db.QueryRowxContext(ctx, query, name)

	var res models.App
	err := row.StructScan(&res)
	if err == sql.ErrNoRows {
		return nil, models.ErrAppsNotFound
	} else if err != nil {
		return nil, err
	}
	return &res, nil
}

// GetApps retrieves an array of apps according to a specific filter.
func (ds *sqlStore) GetApps(ctx context.Context, filter *models.AppFilter) ([]*models.App, error) {
	res := []*models.App{}
	if filter.NameIn != nil && len(filter.NameIn) == 0 { // this basically makes sure it doesn't return ALL apps
		return res, nil
	}
	query, args, err := buildFilterAppQuery(filter)
	if err != nil {
		return nil, err
	}
	query = ds.db.Rebind(fmt.Sprintf("SELECT DISTINCT name, config, created_at, updated_at FROM apps %s", query))
	rows, err := ds.db.QueryxContext(ctx, query, args...)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	for rows.Next() {
		var app models.App
		err := rows.StructScan(&app)
		if err != nil {
			if err == sql.ErrNoRows {
				return res, nil
			}
			return res, err
		}
		res = append(res, &app)
	}

	if err := rows.Err(); err != nil {
		return res, err
	}
	return res, nil
}

func (ds *sqlStore) InsertRoute(ctx context.Context, route *models.Route) (*models.Route, error) {
	err := ds.Tx(func(tx *sqlx.Tx) error {
		query := tx.Rebind(`SELECT 1 FROM apps WHERE name=?`)
		r := tx.QueryRowContext(ctx, query, route.AppName)
		if err := r.Scan(new(int)); err != nil {
			if err == sql.ErrNoRows {
				return models.ErrAppsNotFound
			}
		}
		query = tx.Rebind(`SELECT 1 FROM routes WHERE app_name=? AND path=?`)
		same, err := tx.QueryContext(ctx, query, route.AppName, route.Path)
		if err != nil {
			return err
		}
		defer same.Close()
		if same.Next() {
			return models.ErrRoutesAlreadyExists
		}

		query = tx.Rebind(`INSERT INTO routes (
			app_name,
			path,
			image,
			format,
			memory,
			type,
			timeout,
			idle_timeout,
			headers,
			config,
			created_at,
			updated_at
		)
		VALUES (
			:app_name,
			:path,
			:image,
			:format,
			:memory,
			:type,
			:timeout,
			:idle_timeout,
			:headers,
			:config,
			:created_at,
			:updated_at
		);`)

		_, err = tx.NamedExecContext(ctx, query, route)

		return err
	})

	return route, err
}

func (ds *sqlStore) UpdateRoute(ctx context.Context, newroute *models.Route) (*models.Route, error) {
	var route models.Route
	err := ds.Tx(func(tx *sqlx.Tx) error {
		query := tx.Rebind(fmt.Sprintf("%s WHERE app_name=? AND path=?", routeSelector))
		row := tx.QueryRowxContext(ctx, query, newroute.AppName, newroute.Path)

		err := row.StructScan(&route)
		if err == sql.ErrNoRows {
			return models.ErrRoutesNotFound
		} else if err != nil {
			return err
		}

		route.Update(newroute)
		err = route.Validate()
		if err != nil {
			return err
		}

		query = tx.Rebind(`UPDATE routes SET
			image = :image,
			format = :format,
			memory = :memory,
			type = :type,
			timeout = :timeout,
			idle_timeout = :idle_timeout,
			headers = :headers,
			config = :config,
			updated_at = :updated_at
		WHERE app_name=:app_name AND path=:path;`)

		res, err := tx.NamedExecContext(ctx, query, &route)
		if err != nil {
			return err
		}

		if n, err := res.RowsAffected(); err != nil {
			return err
		} else if n == 0 {
			// inside of the transaction, we are querying for the row, so we know that it exists
			return nil
		}

		return nil
	})

	if err != nil {
		return nil, err
	}
	return &route, nil
}

func (ds *sqlStore) RemoveRoute(ctx context.Context, appName, routePath string) error {
	query := ds.db.Rebind(`DELETE FROM routes WHERE path = ? AND app_name = ?`)
	res, err := ds.db.ExecContext(ctx, query, routePath, appName)
	if err != nil {
		return err
	}

	n, err := res.RowsAffected()
	if err != nil {
		return err
	}

	if n == 0 {
		return models.ErrRoutesNotFound
	}

	return nil
}

func (ds *sqlStore) GetRoute(ctx context.Context, appName, routePath string) (*models.Route, error) {
	rSelectCondition := "%s WHERE app_name=? AND path=?"
	query := ds.db.Rebind(fmt.Sprintf(rSelectCondition, routeSelector))
	row := ds.db.QueryRowxContext(ctx, query, appName, routePath)

	var route models.Route
	err := row.StructScan(&route)
	if err == sql.ErrNoRows {
		return nil, models.ErrRoutesNotFound
	} else if err != nil {
		return nil, err
	}
	return &route, nil
}

// GetRoutesByApp retrieves a route with a specific app name.
func (ds *sqlStore) GetRoutesByApp(ctx context.Context, appName string, filter *models.RouteFilter) ([]*models.Route, error) {
	res := []*models.Route{}
	if filter == nil {
		filter = new(models.RouteFilter)
	}

	filter.AppName = appName
	filterQuery, args := buildFilterRouteQuery(filter)

	query := fmt.Sprintf("%s %s", routeSelector, filterQuery)
	query = ds.db.Rebind(query)
	rows, err := ds.db.QueryxContext(ctx, query, args...)
	if err != nil {
		if err == sql.ErrNoRows {
			return res, nil // no error for empty list
		}
		return nil, err
	}
	defer rows.Close()

	for rows.Next() {
		var route models.Route
		err := rows.StructScan(&route)
		if err != nil {
			continue
		}
		res = append(res, &route)
	}
	if err := rows.Err(); err != nil {
		if err == sql.ErrNoRows {
			return res, nil // no error for empty list
		}
	}

	return res, nil
}

func (ds *sqlStore) Tx(f func(*sqlx.Tx) error) error {
	tx, err := ds.db.Beginx()
	if err != nil {
		return err
	}
	err = f(tx)
	if err != nil {
		tx.Rollback()
		return err
	}
	return tx.Commit()
}

func (ds *sqlStore) InsertCall(ctx context.Context, call *models.Call) error {
	query := ds.db.Rebind(`INSERT INTO calls (
		id,
		created_at,
		started_at,
		completed_at,
		status,
		app_name,
		path,
		stats,
		error
	)
	VALUES (
		:id,
		:created_at,
		:started_at,
		:completed_at,
		:status,
		:app_name,
		:path,
		:stats,
		:error
	);`)

	_, err := ds.db.NamedExecContext(ctx, query, call)
	return err
}

// This equivalence only makes sense in the context of the datastore, so it's
// not in the model.
func equivalentCalls(expected *models.Call, actual *models.Call) bool {
	equivalentFields := expected.ID == actual.ID &&
		time.Time(expected.CreatedAt).Unix() == time.Time(actual.CreatedAt).Unix() &&
		time.Time(expected.StartedAt).Unix() == time.Time(actual.StartedAt).Unix() &&
		time.Time(expected.CompletedAt).Unix() == time.Time(actual.CompletedAt).Unix() &&
		expected.Status == actual.Status &&
		expected.AppName == actual.AppName &&
		expected.Path == actual.Path &&
		expected.Error == actual.Error &&
		len(expected.Stats) == len(actual.Stats)
	// TODO: We don't do comparisons of individual Stats. We probably should.
	return equivalentFields
}

func (ds *sqlStore) UpdateCall(ctx context.Context, from *models.Call, to *models.Call) error {
	// Assert that from and to are supposed to be the same call
	if from.ID != to.ID || from.AppName != to.AppName {
		return errors.New("assertion error: 'from' and 'to' calls refer to different app/ID")
	}

	// Atomic update
	err := ds.Tx(func(tx *sqlx.Tx) error {
		var call models.Call
		query := tx.Rebind(fmt.Sprintf(`%s WHERE id=? AND app_name=?`, callSelector))
		row := tx.QueryRowxContext(ctx, query, from.ID, from.AppName)

		err := row.StructScan(&call)
		if err == sql.ErrNoRows {
			return models.ErrCallNotFound
		} else if err != nil {
			return err
		}

		// Only do the update if the existing call is exactly what we expect.
		// If something has modified it in the meantime, we must fail the
		// transaction.
		if !equivalentCalls(from, &call) {
			return models.ErrDatastoreCannotUpdateCall
		}

		query = tx.Rebind(`UPDATE calls SET
			id = :id,
			created_at = :created_at,
			started_at = :started_at,
			completed_at = :completed_at,
			status = :status,
			app_name = :app_name,
			path = :path,
			stats = :stats,
			error = :error
		WHERE id=:id AND app_name=:app_name;`)

		res, err := tx.NamedExecContext(ctx, query, to)
		if err != nil {
			return err
		}

		if n, err := res.RowsAffected(); err != nil {
			return err
		} else if n == 0 {
			// inside of the transaction, we are querying for the row, so we know that it exists
			return nil
		}

		return nil
	})

	if err != nil {
		return err
	}
	return nil
}

func (ds *sqlStore) GetCall(ctx context.Context, appName, callID string) (*models.Call, error) {
	query := fmt.Sprintf(`%s WHERE id=? AND app_name=?`, callSelector)
	query = ds.db.Rebind(query)
	row := ds.db.QueryRowxContext(ctx, query, callID, appName)

	var call models.Call
	err := row.StructScan(&call)
	if err != nil {
		if err == sql.ErrNoRows {
			return nil, models.ErrCallNotFound
		}
		return nil, err
	}
	return &call, nil
}

func (ds *sqlStore) GetCalls(ctx context.Context, filter *models.CallFilter) ([]*models.Call, error) {
	res := []*models.Call{}
	query, args := buildFilterCallQuery(filter)
	query = fmt.Sprintf("%s %s", callSelector, query)
	query = ds.db.Rebind(query)
	rows, err := ds.db.QueryxContext(ctx, query, args...)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	for rows.Next() {
		var call models.Call
		err := rows.StructScan(&call)
		if err != nil {
			continue
		}
		res = append(res, &call)
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}
	return res, nil
}

func (ds *sqlStore) InsertLog(ctx context.Context, appName, callID string, logR io.Reader) error {
	// coerce this into a string for sql
	var log string
	if stringer, ok := logR.(fmt.Stringer); ok {
		log = stringer.String()
	} else {
		// TODO we could optimize for Size / buffer pool, but atm we aren't hitting
		// this code path anyway (a fallback)
		var b bytes.Buffer
		io.Copy(&b, logR)
		log = b.String()
	}

	query := ds.db.Rebind(`INSERT INTO logs (id, app_name, log) VALUES (?, ?, ?);`)
	_, err := ds.db.ExecContext(ctx, query, callID, appName, log)
	return err
}

func (ds *sqlStore) GetLog(ctx context.Context, appName, callID string) (io.Reader, error) {
	query := ds.db.Rebind(`SELECT log FROM logs WHERE id=? AND app_name=?`)
	row := ds.db.QueryRowContext(ctx, query, callID, appName)

	var log string
	err := row.Scan(&log)
	if err != nil {
		if err == sql.ErrNoRows {
			return nil, models.ErrCallLogNotFound
		}
		return nil, err
	}

	return strings.NewReader(log), nil
}

func buildFilterRouteQuery(filter *models.RouteFilter) (string, []interface{}) {
	if filter == nil {
		return "", nil
	}
	var b bytes.Buffer
	var args []interface{}

	where := func(colOp, val string) {
		if val != "" {
			args = append(args, val)
			if len(args) == 1 {
				fmt.Fprintf(&b, `WHERE %s`, colOp)
			} else {
				fmt.Fprintf(&b, ` AND %s`, colOp)
			}
		}
	}

	where("app_name=? ", filter.AppName)
	where("image=?", filter.Image)
	where("path>?", filter.Cursor)
	// where("path LIKE ?%", filter.PathPrefix) TODO needs escaping

	fmt.Fprintf(&b, ` ORDER BY path ASC`) // TODO assert this is indexed
	fmt.Fprintf(&b, ` LIMIT ?`)
	args = append(args, filter.PerPage)

	return b.String(), args
}

func buildFilterAppQuery(filter *models.AppFilter) (string, []interface{}, error) {
	var args []interface{}
	if filter == nil {
		return "", args, nil
	}

	var b bytes.Buffer

	// todo: this same thing is in several places in here, DRY it up across this file
	where := func(colOp, val interface{}) {
		if val == nil {
			return
		}
		switch v := val.(type) {
		case string:
			if v == "" {
				return
			}
		case []string:
			if len(v) == 0 {
				return
			}
		}
		args = append(args, val)
		if len(args) == 1 {
			fmt.Fprintf(&b, `WHERE %s`, colOp)
		} else {
			fmt.Fprintf(&b, ` AND %s`, colOp)
		}
	}

	// where("name LIKE ?%", filter.Name) // TODO needs escaping?
	where("name>?", filter.Cursor)
	where("name IN (?)", filter.NameIn)

	fmt.Fprintf(&b, ` ORDER BY name ASC`) // TODO assert this is indexed
	fmt.Fprintf(&b, ` LIMIT ?`)
	args = append(args, filter.PerPage)
	if len(filter.NameIn) > 0 {
		// fmt.Println("about to sqlx.in:", b.String(), args)
		return sqlx.In(b.String(), args...)
	}
	return b.String(), args, nil
}

func buildFilterCallQuery(filter *models.CallFilter) (string, []interface{}) {
	if filter == nil {
		return "", nil
	}
	var b bytes.Buffer
	var args []interface{}

	where := func(colOp, val string) {
		if val != "" {
			args = append(args, val)
			if len(args) == 1 {
				fmt.Fprintf(&b, `WHERE %s?`, colOp)
			} else {
				fmt.Fprintf(&b, ` AND %s?`, colOp)
			}
		}
	}

	where("id<", filter.Cursor)
	if !time.Time(filter.ToTime).IsZero() {
		where("created_at<", filter.ToTime.String())
	}
	if !time.Time(filter.FromTime).IsZero() {
		where("created_at>", filter.FromTime.String())
	}
	where("app_name=", filter.AppName)
	where("path=", filter.Path)

	fmt.Fprintf(&b, ` ORDER BY id DESC`) // TODO assert this is indexed
	fmt.Fprintf(&b, ` LIMIT ?`)
	args = append(args, filter.PerPage)

	return b.String(), args
}

// GetDatabase returns the underlying sqlx database implementation
func (ds *sqlStore) GetDatabase() *sqlx.DB {
	return ds.db
}