package mock

import (
	"context"
	"fmt"
	"hash/fnv"
	"math"
	"math/rand"
	"time"

	"git.avsdev.uk/Go/job-search/internal/mock/findatender/ocds"
)

const ocidPrefix = "ocds-mock-"

// Generator makes new releases from the catalog. About a third of the time it
// moves an existing procedure on (planning -> tender -> award) so the same ocid
// appears in several releases, as it does on the real service.
type Generator struct {
	catalog *Catalog
	store   *Store
	rng     *rand.Rand
	opts    options
}

// NewGenerator returns a generator drawing from catalog and storing releases in
// store. The same seed and store contents give the same releases. It logs to
// slog.Default() unless given WithLogger.
func NewGenerator(
	catalog *Catalog, store *Store, seed int64, opts ...Option,
) *Generator {
	return &Generator{
		catalog: catalog,
		store:   store,
		rng:     rand.New(rand.NewSource(seed)), //nolint:gosec // seeded for repeatable mock data
		opts:    applyOptions(opts),
	}
}

// Make returns a new release with the given date (to the second). About a third
// of the time it moves on a procedure still open from the last 60 days;
// otherwise it starts a new one.
func (g *Generator) Make(date time.Time) ocds.Release {
	date = date.UTC().Truncate(time.Second)
	if g.rng.Float64() < 0.35 {
		if previous, ok := g.store.RandomOpen(g.rng, date.AddDate(0, 0, -60)); ok {
			return g.advance(previous, date)
		}
	}
	return g.newProcedure(date)
}

// newProcedure returns the first release of a new procedure: a tender (or,
// one time in five, a planning notice) from a random catalog buyer and
// subject, using a random procurement method. Values are scaled by a random
// factor, and a tender without lots gets a single lot covering it all.
func (g *Generator) newProcedure(date time.Time) ocds.Release {
	buyer := g.catalog.buyer(g.rng)
	ensurePartyID(&buyer)
	buyer.Roles = []string{"buyer"}
	method := g.catalog.method(g.rng)

	tag, status := "tender", "active"
	if g.rng.Float64() < 0.2 {
		tag, status = "planning", "planned"
	}
	ocid := g.newOCID()

	tender := g.catalog.subject(g.rng)
	tender.ID = ocds.ID(ocid)
	tender.ProcurementMethod = method.Method
	tender.ProcurementMethodDetails = method.Details

	factor := 0.5 + g.rng.Float64()*1.5
	if tender.Value == nil {
		amount := float64((g.rng.Intn(5000) + 10) * 1000)
		tender.Value = &ocds.Value{
			Amount:   &amount,
			Currency: "GBP",
		}
	} else {
		scaleValue(tender.Value, factor)
	}

	for i := range tender.Lots {
		scaleValue(tender.Lots[i].Value, factor)
	}

	if len(tender.Lots) == 0 {
		value := clone(*tender.Value)
		tender.Lots = []ocds.Lot{{
			ID:    "1",
			Title: tender.Title,
			Value: &value,
		}}
	}

	setStatus(&tender, status)
	if status == "active" {
		tender.TenderPeriod = &ocds.Period{
			EndDate: ptr(date.AddDate(0, 0, 30+g.rng.Intn(30))),
		}
	}

	return ocds.Release{
		OCID:           ocid,
		ID:             g.store.NextNoticeID(date.Year()),
		Date:           date,
		Tag:            []string{tag},
		InitiationType: "tender",
		Parties:        []ocds.Organization{buyer},
		Buyer: &ocds.OrganizationReference{
			ID:   ocds.ID(buyer.ID),
			Name: buyer.Name,
		},
		Tender:   &tender,
		Language: "en",
	}
}

// advance returns the next release in previous's procedure: planning moves to
// tender, and a tender either has its deadline extended (tenderUpdate) or is
// awarded to a supplier from the catalog.
func (g *Generator) advance(
	previous ocds.Release, date time.Time,
) ocds.Release {
	release := clone(previous)
	release.ID = g.store.NextNoticeID(date.Year())
	release.Date = date
	release.Awards = nil
	if release.Tender == nil {
		release.Tender = &ocds.Tender{
			ID: ocds.ID(release.OCID),
		}
	}

	next := "award"
	switch previous.Tag[0] {
	case "planning":
		next = "tender"
	case "tender":
		if g.rng.Float64() < 0.25 {
			next = "tenderUpdate"
		}
	}
	release.Tag = []string{next}

	switch next {
	case "tender":
		setStatus(release.Tender, "active")
		release.Tender.TenderPeriod = &ocds.Period{
			EndDate: ptr(date.AddDate(0, 0, 30+g.rng.Intn(30))),
		}
	case "tenderUpdate":
		// A typical update: the deadline is extended by two weeks.
		end := date.AddDate(0, 0, 30)
		if period := release.Tender.TenderPeriod; period != nil &&
			period.EndDate != nil {
			end = *period.EndDate
		}
		release.Tender.TenderPeriod = &ocds.Period{
			EndDate: ptr(end.AddDate(0, 0, 14)),
		}
	case "award":
		setStatus(release.Tender, "complete")
		supplier := g.catalog.supplier(g.rng)
		ensurePartyID(&supplier)
		supplier.Roles = []string{"supplier"}
		release.Parties = append(release.Parties, supplier)

		var value *ocds.Value
		if release.Tender.Value != nil {
			scaled := clone(*release.Tender.Value)
			scaleValue(&scaled, 0.8+g.rng.Float64()*0.2)
			value = &scaled
		}

		var lotIDs []string
		for _, lot := range release.Tender.Lots {
			if lot.ID != "" {
				lotIDs = append(lotIDs, lot.ID)
			}
		}

		release.Awards = []ocds.Award{{
			ID:     "1",
			Status: "active",
			Date:   ptr(date),
			Value:  value,
			Suppliers: []ocds.OrganizationReference{
				{
					ID:   ocds.ID(supplier.ID),
					Name: supplier.Name,
				},
			},
			RelatedLots: lotIDs,
		}}
	}

	return release
}

// newOCID returns a random ocid not already in the store.
func (g *Generator) newOCID() string {
	for {
		id := fmt.Sprintf("%s%06x", ocidPrefix, g.rng.Intn(1<<24))
		if !g.store.HasOCID(id) {
			return id
		}
	}
}

// gap returns a random duration from minGap to maxGap inclusive, or minGap if
// maxGap is not larger.
func (g *Generator) gap(minGap, maxGap time.Duration) time.Duration {
	if maxGap <= minGap {
		return minGap
	}
	return minGap + time.Duration(g.rng.Int63n(int64(maxGap-minGap)+1))
}

// CatchUp fills the period since the last stored release (or the last backfill
// period, whichever is shorter) so restarts leave no gap in the timeline.
func (g *Generator) CatchUp(
	now time.Time, backfill, minGap, maxGap time.Duration,
) (int, error) {
	start := now.Add(-backfill)
	if last, ok := g.store.Last(); ok && last.After(start) {
		start = last
	}

	count := 0
	when := start.Add(g.gap(minGap, maxGap))
	for ; !when.After(now); when = when.Add(g.gap(minGap, maxGap)) {
		if err := g.store.AppendNoSync(g.Make(when)); err != nil {
			return count, err
		}
		count++
	}

	return count, g.store.Sync()
}

// Run publishes a new release after a random gap between minGap and maxGap
// until ctx ends.
func (g *Generator) Run(ctx context.Context, minGap, maxGap time.Duration) {
	logger := g.opts.logger("generator")
	for {
		gap := g.gap(minGap, maxGap)
		logger.Info("next release", "in", gap.Round(time.Second))

		timer := time.NewTimer(gap)
		select {
		case <-ctx.Done():
			timer.Stop()
			return
		case <-timer.C:
		}

		release := g.Make(time.Now())
		if err := g.store.Append(release); err != nil {
			logger.Error("storing release failed", "error", err)
			continue
		}

		logger.Info(
			"published release",
			"release_id", release.ID,
			"tag", release.Tag[0],
			"ocid", release.OCID,
		)
	}
}

// ---------- helpers ----------

func ptr[T any](value T) *T { return &value }

func setStatus(tender *ocds.Tender, status string) {
	tender.Status = status
	for i := range tender.Lots {
		tender.Lots[i].Status = status
	}
}

// scaleValue multiplies value's amounts by factor, rounded to the nearest 100.
func scaleValue(value *ocds.Value, factor float64) {
	if value == nil {
		return
	}
	for _, amount := range []**float64{&value.Amount, &value.AmountGross} {
		if *amount != nil {
			*amount = ptr(math.Round(**amount*factor/100) * 100)
		}
	}
}

// ensurePartyID gives party an id derived from its name if it has none, so the
// same organisation always gets the same id.
func ensurePartyID(party *ocds.Organization) {
	if party.ID != "" {
		return
	}
	hasher := fnv.New32a()
	hasher.Write([]byte(party.Name)) //nolint:gosec // never fails
	party.ID = fmt.Sprintf("GB-FTS-%d", hasher.Sum32()%1000000)
}