// A JSON storage strategy for Go Again
// SQL would be a better choice, but... meh
//
// Note that we use mutexes instead of channels
// because everything is both synchronous and
// sequential. Meh.
package jsondb

import (
	"crypto/rand"
	"crypto/subtle"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"net/url"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"sync"
	"time"

	"git.rootprojects.org/root/go-again"
)

type JSONDB struct {
	dburl string
	path  string
	json  *dbjson
	mux   sync.Mutex
	fmux  sync.Mutex
}

type dbjson struct {
	Schedules []Schedule `json:"schedules"`
}

func Connect(dburl string) (*JSONDB, error) {
	u, err := url.Parse(dburl)
	if nil != err {
		return nil, err
	}

	// json:/abspath/to/db.json
	path := u.Opaque
	if "" == path {
		// json:///abspath/to/db.json
		path = u.Path
		if "" == path {
			// json:relpath/to/db.json
			// json://relpath/to/db.json
			path = strings.TrimSuffix(u.Host+"/"+u.Path, "/")
		}
	}

	f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0700)
	if nil != err {
		return nil, fmt.Errorf("Couldn't open %q: %s", path, err)
	}

	stat, err := f.Stat()
	if 0 == stat.Size() {
		_, err := f.Write([]byte(`{"schedules":[]}`))
		f.Close()
		if nil != err {
			return nil, err
		}

		f, err = os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0700)
		if nil != err {
			return nil, err
		}
	}

	decoder := json.NewDecoder(f)
	db := &dbjson{}
	err = decoder.Decode(db)
	f.Close()
	if nil != err {
		return nil, fmt.Errorf("Couldn't parse %q as JSON: %s", path, err)
	}

	wd, _ := os.Getwd()
	fmt.Println("jsondb:", filepath.Join(wd, path))
	return &JSONDB{
		dburl: dburl,
		path:  path,
		json:  db,
		mux:   sync.Mutex{},
		fmux:  sync.Mutex{},
	}, nil
}

// A copy of again.Schedule, but with access_id json-able
type Schedule struct {
	ID        string          `json:"id" db:"id"`
	AccessID  string          `json:"access_id" db:"access_id"`
	Date      string          `json:"date" db:"date"`
	Time      string          `json:"time" db:"time"`
	TZ        string          `json:"tz" db:"tz"`
	NextRunAt time.Time       `json:"next_run_at" db:"next_run_at"`
	Disabled  bool            `json:"disabled" db:"disabled"`
	Webhooks  []again.Webhook `json:"webhooks" db"webhooks"`
}

func (db *JSONDB) List(accessID string) ([]*again.Schedule, error) {
	nowish := time.Now().Add(time.Duration(30) * time.Second)
	schedules := []*again.Schedule{}
	for i := range db.json.Schedules {
		s := db.json.Schedules[i]
		if !s.Disabled && ctcmp(accessID, s.AccessID) && s.NextRunAt.Sub(nowish) > 0 {
			schedules = append(schedules, &again.Schedule{
				ID:        s.ID,
				AccessID:  s.AccessID,
				Date:      s.Date,
				Time:      s.Time,
				TZ:        s.TZ,
				NextRunAt: s.NextRunAt,
				Webhooks:  s.Webhooks,
			})
		}
	}
	return schedules, nil
}

func (db *JSONDB) Set(s again.Schedule) (*again.Schedule, error) {
	exists := false
	index := -1
	if "" == s.ID {
		id, err := genID(16)
		if nil != err {
			return nil, err
		}
		s.ID = id
	} else {
		i, old := db.get(s.ID)
		index = i
		exists = nil != old
		// TODO constant time bail
		if !exists || !ctcmp(old.AccessID, s.AccessID) {
			return nil, fmt.Errorf("invalid id")
		}
	}

	schedule := Schedule{
		ID:        s.ID,
		AccessID:  s.AccessID,
		Date:      s.Date,
		Time:      s.Time,
		TZ:        s.TZ,
		NextRunAt: s.NextRunAt,
		Webhooks:  s.Webhooks,
	}

	if exists {
		db.mux.Lock()
		db.json.Schedules[index] = schedule
		db.mux.Unlock()
	} else {
		db.mux.Lock()
		db.json.Schedules = append(db.json.Schedules, schedule)
		db.mux.Unlock()
	}

	err := db.save(s.AccessID)
	if nil != err {
		return nil, err
	}

	return &s, nil
}

func (db *JSONDB) Delete(accessID string, id string) (*again.Schedule, error) {
	_, old := db.get(id)
	exists := nil != old
	// TODO constant time bail
	if !exists || !ctcmp(old.AccessID, accessID) {
		return nil, fmt.Errorf("invalid id")
	}

	// Copy everything we keep into its own array
	newSchedules := []Schedule{}
	for i := range db.json.Schedules {
		schedule := db.json.Schedules[i]
		if old.ID != schedule.ID {
			newSchedules = append(newSchedules, schedule)
		}
	}
	db.mux.Lock()
	db.json.Schedules = newSchedules
	db.mux.Unlock()

	err := db.save(accessID)
	if nil != err {
		return nil, err
	}

	return &again.Schedule{
		ID:        old.ID,
		AccessID:  old.AccessID,
		Date:      old.Date,
		Time:      old.Time,
		TZ:        old.TZ,
		NextRunAt: old.NextRunAt,
		Webhooks:  old.Webhooks,
	}, nil
}

func (db *JSONDB) Upcoming(min time.Time, max time.Time) ([]*again.Schedule, error) {
	schedules := []*again.Schedule{}
	for i := range db.json.Schedules {
		s := db.json.Schedules[i]
		if !s.Disabled && s.NextRunAt.Sub(min) > 0 && max.Sub(s.NextRunAt) > 0 {
			schedules = append(schedules, &again.Schedule{
				ID:        s.ID,
				AccessID:  s.AccessID,
				Date:      s.Date,
				Time:      s.Time,
				TZ:        s.TZ,
				NextRunAt: s.NextRunAt,
				Webhooks:  s.Webhooks,
			})
		}
	}
	sort.Sort(again.Schedules(schedules))
	return []*again.Schedule(schedules), nil
}

func ctcmp(x string, y string) bool {
	return 1 == subtle.ConstantTimeCompare([]byte(x), []byte(y))
}

func (db *JSONDB) get(id string) (int, *Schedule) {
	db.mux.Lock()
	scheds := db.json.Schedules
	db.mux.Unlock()
	for i := range scheds {
		schedule := scheds[i]
		if ctcmp(id, schedule.ID) {
			return i, &schedule
		}
	}
	return -1, nil
}

func genID(n int) (string, error) {
	b := make([]byte, n)
	_, err := rand.Read(b)
	if nil != err {
		return "", err
	}
	return hex.EncodeToString(b), nil
}

func (db *JSONDB) save(accessID string) error {
	// TODO per-user files, maybe
	// or probably better to spend that time building the postgres adapter
	rnd, err := genID(4)
	tmppath := db.path + "." + rnd + ".tmp"
	bakpath := db.path + ".bak"

	os.Remove(tmppath) // ignore error
	f, err := os.OpenFile(tmppath, os.O_RDWR|os.O_CREATE, 0700)
	if nil != err {
		return err
	}

	encoder := json.NewEncoder(f)
	err = encoder.Encode(db.json)
	f.Close()
	if nil != err {
		return err
	}

	// TODO could make async and debounce...
	// or spend that time on something useful
	db.fmux.Lock()
	defer db.fmux.Unlock()
	os.Remove(bakpath) // ignore error
	err = os.Rename(db.path, bakpath)
	if nil != err {
		return err
	}
	err = os.Rename(tmppath, db.path)
	if nil != err {
		return err
	}

	return nil
}