package mock

import (
	"context"
	"fmt"
	"hash/fnv"
	"log"
	"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 {
	cat   *Catalog
	store *Store
	rnd   *rand.Rand
}

// NewGenerator returns a generator drawing from cat and storing releases in
// store. The same seed and store contents give the same releases.
func NewGenerator(cat *Catalog, store *Store, seed int64) *Generator {
	return &Generator{
		cat:   cat,
		store: store,
		rnd:   rand.New(rand.NewSource(seed)), //nolint:gosec // seeded for repeatable mock data
	}
}

// Make returns a new release dated at (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(at time.Time) ocds.Release {
	at = at.UTC().Truncate(time.Second)
	if g.rnd.Float64() < 0.35 {
		if prev, ok := g.store.RandomOpen(g.rnd, at.AddDate(0, 0, -60)); ok {
			return g.advance(prev, at)
		}
	}
	return g.newProcedure(at)
}

// 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(at time.Time) ocds.Release {
	buyer := g.cat.buyer(g.rnd)
	ensurePartyID(&buyer)
	buyer.Roles = []string{"buyer"}
	m := g.cat.method(g.rnd)

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

	t := g.cat.subject(g.rnd)
	t.ID = ocds.ID(ocid)
	t.ProcurementMethod = m.Method
	t.ProcurementMethodDetails = m.Details

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

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

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

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

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

// advance returns the next release in prev'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(prev ocds.Release, at time.Time) ocds.Release {
	r := clone(prev)
	r.ID = g.store.NextNoticeID(at.Year())
	r.Date = at
	r.Awards = nil
	if r.Tender == nil {
		r.Tender = &ocds.Tender{
			ID: ocds.ID(r.OCID),
		}
	}

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

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

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

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

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

	return r
}

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

// gap returns a random duration from min to max inclusive, or min if max is
// not larger.
func (g *Generator) gap(min, max time.Duration) time.Duration {
	if max <= min {
		return min
	}
	return min + time.Duration(g.rnd.Int63n(int64(max-min)+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, min, max time.Duration,
) (int, error) {
	start := now.Add(-backfill)
	if last, ok := g.store.Last(); ok && last.After(start) {
		start = last
	}

	n := 0
	for t := start.Add(g.gap(min, max)); !t.After(now); t = t.Add(g.gap(min, max)) {
		if err := g.store.AppendNoSync(g.Make(t)); err != nil {
			return n, err
		}
		n++
	}

	return n, g.store.Sync()
}

// Run publishes a new release after a random gap between min and max until ctx ends.
func (g *Generator) Run(ctx context.Context, min, max time.Duration) {
	for {
		d := g.gap(min, max)
		log.Printf("generator: next release in %s", d.Round(time.Second))

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

		r := g.Make(time.Now())
		if err := g.store.Append(r); err != nil {
			log.Printf("generator: storing release: %v", err)
			continue
		}

		log.Printf("generator: published %s (%s) %s", r.ID, r.Tag[0], r.OCID)
	}
}

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

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

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

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

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