package partman

import (
	"context"
	"fmt"
	"strconv"
	"strings"
	"time"

	"dynatron.me/x/stillbox/pkg/config"
	"dynatron.me/x/stillbox/pkg/database"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgtype"
	"github.com/rs/zerolog/log"
)

const (
	callsTable = "calls"

	preProvisionDefault = 1
)

/*
 * Partition scheme names:
 * daily: calls_p_2024_11_28
 * weekly: calls_p_2024_w48
 * monthly: calls_p_2024_11
 * quarterly: calls_p_2024_q4
 * yearly: calls_p_2024
 */

type PartitionError string

func (pe PartitionError) Error() string {
	return fmt.Sprintf("bad partition '%s'", string(pe))
}

type ErrInvalidInterval string

func (in ErrInvalidInterval) Error() string {
	return fmt.Sprintf("invalid interval '%s'", string(in))
}

type Interval string

const (
	Daily     Interval = "daily"
	Weekly    Interval = "weekly"
	Monthly   Interval = "monthly"
	Quarterly Interval = "quarterly"
	Yearly    Interval = "yearly"
)

func (p Interval) IsValid() bool {
	switch p {
	case Daily, Weekly, Monthly, Quarterly, Yearly:
		return true
	}

	return false
}

type PartitionManager interface {
	Go(ctx context.Context)
	Check(ctx context.Context, now time.Time) error
}

type partman struct {
	db   database.Store
	cfg  config.Partition
	intv Interval
}

type partition interface {
	PartitionName() string
	Next(i int) partition
	Prev(i int) partition
	Range() (time.Time, time.Time)
}

type monthlyPartition struct {
	t time.Time
}

func (d monthlyPartition) PartitionName() string {
	return fmt.Sprintf("calls_p_%d_%02d", d.t.Year(), d.t.Month())
}

func (d monthlyPartition) Next(i int) partition {
	return d.next(i)
}

func (d monthlyPartition) Prev(i int) partition {
	return d.prev(i)
}

func (d monthlyPartition) Range() (start, end time.Time) {
	start = time.Date(d.t.Year(), d.t.Month(), 1, 0, 0, 0, 0, time.UTC)
	end = start.AddDate(0, 1, 0)

	return
}

func (d monthlyPartition) next(i int) monthlyPartition {
	year, month, _ := d.t.Date()

	return monthlyPartition{
		t: time.Date(year, month+time.Month(i), 1, 0, 0, 0, 0, time.UTC),
	}
}

func (d monthlyPartition) prev(i int) monthlyPartition {
	year, month, _ := d.t.Date()

	return monthlyPartition{
		t: time.Date(year, month-time.Month(i), 1, 0, 0, 0, 0, d.t.Location()),
	}
}

func New(db database.Store, cfg config.Partition) (*partman, error) {
	pm := &partman{
		cfg:  cfg,
		db:   db,
		intv: Interval(cfg.Interval),
	}

	if !pm.intv.IsValid() {
		return nil, ErrInvalidInterval(pm.intv)
	}

	return pm, nil
}

var _ PartitionManager = (*partman)(nil)

func (pm *partman) Go(ctx context.Context) {
	go func(ctx context.Context) {
		tick := time.NewTicker(60 * time.Minute)

		select {
		case now := <-tick.C:
			err := pm.Check(ctx, now)
			if err != nil {
				log.Error().Err(err).Msg("partman check failed")
			}
		case <-ctx.Done():
			return
		}
	}(ctx)
}

func (pm *partman) newPartition(t time.Time) partition {
	switch pm.intv {
	case Monthly:
		return monthlyPartition{t}
	}

	return nil
}

func (pm *partman) retentionPartitions(cur partition) []partition {
	partitions := make([]partition, 0, pm.cfg.Retain)
	for i := 1; i <= pm.cfg.Retain; i++ {
		prev := cur.Prev(i)
		partitions = append(partitions, prev)
	}

	return partitions
}

func (pm *partman) futurePartitions(cur partition) []partition {
	preProv := preProvisionDefault
	if pm.cfg.PreProvision != nil {
		preProv = *pm.cfg.PreProvision
	}

	partitions := make([]partition, 0, pm.cfg.Retain)
	for i := 1; i <= preProv; i++ {
		next := cur.Next(i)
		partitions = append(partitions, next)
	}

	return partitions
}

func (pm *partman) expectedPartitions(now time.Time) []partition {
	curPart := pm.newPartition(now)

	retain := pm.retentionPartitions(curPart)

	future := pm.futurePartitions(curPart)

	shouldExist := append(retain, curPart)
	shouldExist = append(shouldExist, future...)

	return shouldExist
}

func (pm *partman) comparePartitions(existingTables, expectedTables []partition) (unexpectedTables, missingTables []partition) {
	existing := make(map[string]partition)
	expectedAndExists := make(map[string]bool)

	for _, t := range existingTables {
		existing[t.PartitionName()] = t
	}

	for _, t := range expectedTables {
		if _, found := existing[t.PartitionName()]; found {
			expectedAndExists[t.PartitionName()] = true
		} else {
			missingTables = append(missingTables, t)
		}
	}

	for _, t := range existingTables {
		if _, found := expectedAndExists[t.PartitionName()]; !found {
			// Only in existingTables and not in both
			unexpectedTables = append(unexpectedTables, t)
		}
	}

	return unexpectedTables, missingTables
}

func (pm *partman) existingPartitions(parts []string) ([]partition, error) {
	existing := make([]partition, 0, len(parts))
	for _, v := range parts {
		p, err := parsePartName(v)
		if err != nil {
			return nil, err
		}

		existing = append(existing, p)
	}
	return existing, nil
}

func (pm *partman) fullTableName(s string) string {
	return fmt.Sprintf("%s.%s", pm.cfg.Schema, s)
}

func (pm *partman) prunePartition(ctx context.Context, tx database.Store, p partition) error {
	s, e := p.Range()
	start := pgtype.Timestamptz{Time: s, Valid: true}
	end := pgtype.Timestamptz{Time: e, Valid: true}
	err := tx.SweepCalls(ctx, start, end)
	if err != nil {
		return err
	}

	err = tx.CleanupSweptCalls(ctx, start, end)
	if err != nil {
		return err
	}

	err = tx.DetachPartition(ctx, pm.fullTableName(p.PartitionName()))
	if err != nil {
		return err
	}

	if pm.cfg.Drop {
		return tx.DropPartition(ctx, pm.fullTableName(p.PartitionName()))
	}

	return nil
}

func (pm *partman) Check(ctx context.Context, now time.Time) error {
	return pm.db.InTx(ctx, func(db database.Store) error {
		// by default, we want to make sure a partition exists for this and next month
		// since we run this at startup, it's safe to do only that.
		partitions, err := db.GetTablePartitions(ctx, pm.cfg.Schema, callsTable)
		if err != nil {
			return err
		}

		existing, err := pm.existingPartitions(partitions)
		if err != nil {
			return err
		}

		expected := pm.expectedPartitions(now)

		unexpected, missing := pm.comparePartitions(existing, expected)

		for _, p := range unexpected {
			err := pm.prunePartition(ctx, db, p)
			if err != nil {
				return err
			}
		}

		for _, p := range missing {
			err := pm.createPartition(ctx, db, p)
			if err != nil {
				return err
			}
		}

		return nil

	}, pgx.TxOptions{})
}

func (pm *partman) createPartition(ctx context.Context, tx database.Store, part partition) error {
	start, end := part.Range()
	return tx.CreatePartition(ctx, callsTable, part.PartitionName(), start, end)
}

func parsePartName(p string) (partition, error) {
	dateAr := strings.Split(p, "calls_p_")
	if len(dateAr) != 2 {
		return nil, PartitionError(p)
	}

	dateAr = strings.Split(dateAr[1], "_")
	if len(dateAr) != 2 {
		return nil, PartitionError(p)
	}

	year, err := strconv.Atoi(dateAr[0])
	if err != nil {
		return nil, PartitionError(p)
	}

	month, err := strconv.Atoi(dateAr[1])
	if err != nil {
		return nil, PartitionError(p)
	}

	r := monthlyPartition{time.Date(year, time.Month(month), 1, 0, 0, 0, 0, time.UTC)}

	return r, nil
}

type partMap map[partition]struct{}

func (pm partMap) exists(dt partition) bool {
	_, ex := pm[dt]

	return ex
}

func partitionsMap(partitions []string, mustExist map[partition]struct{}) (partMap, error) {
	partsDate := make(partMap, len(partitions))

	for _, p := range partitions {
		dt, err := parsePartName(p)
		if err != nil {
			return nil, err
		}

		partsDate[dt] = struct{}{}
	}

	return partsDate, nil
}

func runRetention() {
	// make sure to check if partition was attached first
	// before dropping. don't want to accidentally drop pre-detached partitions.
}

func dropPart() {
	// intx
	// SweepCalls
	// DropPart
}