// Package packageseats is the forge module's holding of the two package seats, `npm-package-registry` and
// `go-package-registry` (novox/hq design 51 *The four registry seats*, ADR 0605, ADR 0611). A build module publishes
// a package through `publish` and `publish-part`: the package's one file lands in the forge module's own object store
// `incoming`, is hashed, checked against the builder's numbering and then uploaded into the forge's package registry
// with the module's own write side. The receiving side is mesh-sdk's seat-neutral parts.Receiver and the caller list
// mesh-sdk's VerbCallers (ADR 0627 §2): this package binds both to the two seats and to the forge.
package packageseats

import (
	"errors"
	"fmt"
	"strings"
	"time"

	"git.novox.be/novox/mesh-contracts/health-and-repair/go/clients/meshhandactsclient"
	"git.novox.be/novox/mesh-delivery/sdk/parts"
	stdio "git.novox.be/novox/mesh-sdk/go"
)

// The seats the forge module holds.
const (
	NpmSeat = "npm-package-registry"
	GoSeat  = "go-package-registry"
)

// Seats are the package seats, each with the forge's own package type behind it.
var Seats = map[string]string{NpmSeat: "npm", GoSeat: "go"}

// The verbs both seats serve (design 51 *One contract*).
const (
	VerbPublish     = "publish"
	VerbPublishPart = "publish-part"
	VerbVersions    = "versions"
	VerbRemove      = "remove"
)

// Verbs are the verbs of both seats, in order.
var Verbs = []string{VerbPublish, VerbPublishPart, VerbRemove, VerbVersions}

// The events of both seats.
const (
	EventPublished = "published"
	EventRefused   = "refused"
	EventRemoved   = "removed"
)

// The bounds of incoming (design 51 *Publishing*, ADR 0611): a chunk at most 1 MiB, a transfer with no chunk for 24
// hours dropped, a finding past 80 % of the cap. The cap is the one incoming's binding carries; IncomingCap is the
// manifest's 2 GiB (a package is one file, far smaller than an image), said only where no binding is read.
const (
	MaxChunk        = 1 << 20
	IncomingCap     = 2 << 30
	TransferIdle    = 24 * time.Hour
	IncomingFullPct = 80
	IncomingObjects = "incoming"
	TransfersState  = "transfers"
	// IdleState is the state of one key per open transfer with its own time to live (a state declared key-ttl): its
	// end is the event that drops a transfer left with no chunk for TransferIdle, never a timer.
	IdleState = "idle"
	// KindPackage is the one kind a package seat holds.
	KindPackage = "package"
	// Self is the forge module, the holder every outcome names.
	Self = "gitea"
	// ReasonRetention is the reason of the forge's own retention removing a version nothing keeps.
	ReasonRetention = "retention"
)

// Callers is the trusted config value `callers`, read as mesh-sdk's list per verb.
type Callers = stdio.VerbCallers

// DefaultCallers is design 51's list for the package seats: publish and publish-part the two build modules that
// publish packages; remove the builder (a tagged version whose branch ended); versions anyone on the mesh, as the
// registry's reads are anonymous.
func DefaultCallers() Callers {
	builds := []string{"mesh-build-go", "mesh-build-node"}
	return Callers{VerbPublish: builds, VerbPublishPart: builds, VerbRemove: {"mesh-delivery-builder"},
		VerbVersions: {stdio.AnyCaller}}
}

// ConfiguredCallers is the config value `callers` as mesh-config resolved it; unset is DefaultCallers.
func ConfiguredCallers() (Callers, error) {
	return stdio.ConfiguredVerbCallers("callers", Verbs, DefaultCallers())
}

// Publish is a publish as the seats' contract names it (mesh-contracts npmpackageregistry and gopackageregistry share
// one shape): what the tools bundle reads from either seat's PublishInput.
type Publish struct {
	Transfer    string       `json:"transfer"`
	Name        string       `json:"name"`
	Version     string       `json:"version,omitempty"`
	Tag         string       `json:"tag,omitempty"`
	Kind        string       `json:"kind"`
	Fingerprint string       `json:"fingerprint,omitempty"`
	Commit      string       `json:"commit,omitempty"`
	Digest      string       `json:"digest"`
	Parts       []parts.Want `json:"parts,omitempty"`
}

// Opening is what the holder keeps of a publish beside the receiving side's own fields.
type Opening struct {
	Publish
	Seat string `json:"seat"`
}

// Transfer is one open publish in the state transfers.
type Transfer = parts.Transfer[Opening]

// Outcome is the body of published, refused and removed, as the contract's Outcome names it.
type Outcome struct {
	Name, Version, Kind, Tag, Digest, Fingerprint, Commit, Transfer, Reference, Reason string
	// Module is the Go module path a Go package is fetched under; empty on the npm seat.
	Module string
}

// Answer is what publish and publish-part answer: the transfer, the parts lacked, and whether it ended.
type Answer struct {
	Transfer string
	Lacks    []string
	Ended    bool
}

// Version is one version a seat holds of a name.
type Version struct {
	Version   string
	Digest    string
	Published time.Time
}

// Builder answers whether the builder numbered a version with a digest (the builder package's builds.BuilderVersions).
type Builder interface {
	Recorded(name, version, digest string) (ok bool, why string, err error)
}

// Store is the forge's package registry, written with the module's own write side alone.
type Store interface {
	// Held is the sha256 digest of name@version's file when the registry holds it.
	Held(seat, name, version string) (digest string, ok bool, err error)
	// Put uploads the package's file and answers the Go module path (empty for npm).
	Put(seat string, p Publish, file []byte) (module string, err error)
	// Versions is every version of name, newest first.
	Versions(seat, name string) ([]Version, error)
	// Remove deletes name@version.
	Remove(seat, name, version string) error
}

// Holder answers the verbs of both seats.
type Holder struct {
	Callers   Callers
	Objects   parts.Objects
	Transfers parts.Transfers[Opening]
	Builder   Builder
	Store     Store
	// Say says an event on a seat's family.
	Say func(seat, event string, o Outcome) error
	// Finding writes (raised) or clears the module's finding of a kind for a subject.
	Finding func(kind, subject, words string, raised bool)
	Now     func() time.Time
	// Cap reads incoming's cap from its binding (parts.BusCap); IncomingCap when nil or when the binding names none.
	Cap func() (uint64, error)
	// Record records a hand act through the seat mesh-hand-acts (meshhandactsclient.Recorder); a drop by hand is refused
	// without it.
	Record func(meshhandactsclient.Request) error
	// Idle writes a transfer's idle key with its own time to live, once (parts.BusArm over IdleState); the receiver
	// arms it on each open that leaves a transfer open. Nil arms nothing.
	Idle func(key string, ttl time.Duration) error
}

// CapNow is incoming's cap as its binding carries it.
func (h *Holder) CapNow() uint64 { return h.receiver().CapNow() }

func (h *Holder) now() time.Time {
	if h.Now != nil {
		return h.Now().UTC()
	}
	return time.Now().UTC()
}

// Reference is the seat's answer for a package: <name>@<version> (ADR 0605 §9).
func Reference(name, version string) string { return name + "@" + version }

// key is a transfer's key: the caller's own name under its seat, so the two seats' transfers never meet.
func key(seat, transfer string) string { return seat + "_" + transfer }

func (h *Holder) receiver() *parts.Receiver[Opening] {
	return &parts.Receiver[Opening]{Objects: h.Objects, Transfers: h.Transfers, Cap: IncomingCap, Bound: h.Cap,
		MaxChunk: MaxChunk, Idle: TransferIdle, Arm: h.Idle, Full: IncomingFullPct, Now: h.now,
		// The builder's numbering is asked before anything is uploaded (ADR 0605 §4).
		Check: func(t Transfer) error {
			ok, why, err := h.Builder.Recorded(t.Shape.Name, t.Shape.Version, t.Shape.Digest)
			if err != nil {
				return errors.New("builder_versions did not answer, so nothing is stored: " + err.Error())
			}
			if !ok {
				return errors.New("the builder did not number it: " + why)
			}
			return nil
		},
		Store: func(t Transfer, held map[string][]byte) error {
			file := held[t.Shape.Digest]
			module, err := h.Store.Put(t.Shape.Seat, t.Shape.Publish, file)
			if err != nil {
				reason := "the forge did not take it: " + err.Error()
				return errors.Join(errors.New("refused: "+reason), h.refused(t, reason))
			}
			h.Finding("publish-refused", t.Shape.Name+"@"+t.Shape.Version, "", false)
			h.Finding("publish-refused", IncomingObjects, "", false)
			o := outcomeOf(t.Shape.Publish, "")
			o.Reference, o.Module = Reference(t.Shape.Name, t.Shape.Version), module
			return h.Say(t.Shape.Seat, EventPublished, o)
		},
		Refuse: h.refused,
		Filled: func(used, cap uint64, full bool) {
			h.Finding("incoming-full", IncomingObjects, fmt.Sprintf("incoming holds %d of its %d bytes (%d %%)", used, cap, used*100/cap), full)
		}}
}

func (h *Holder) refused(t Transfer, reason string) error {
	subject := t.Shape.Name + "@" + t.Shape.Version
	if parts.RefusedAtCap(reason) {
		subject = IncomingObjects
	}
	h.Finding("publish-refused", subject, reason, true)
	return h.Say(t.Shape.Seat, EventRefused, outcomeOf(t.Shape.Publish, reason))
}

func outcomeOf(p Publish, reason string) Outcome {
	return Outcome{Name: p.Name, Version: p.Version, Kind: p.Kind, Tag: p.Tag, Digest: p.Digest, Fingerprint: p.Fingerprint,
		Commit: p.Commit, Transfer: p.Transfer, Reason: reason}
}

func (h *Holder) answer(transfer string, r parts.Received) Answer {
	return Answer{Transfer: transfer, Lacks: r.Lacks, Ended: r.Ended}
}

// Publish is `publish` on seat for the proved caller: a package is one file, its digest the file's sha256.
func (h *Holder) Publish(seat, caller string, p Publish) (Answer, error) {
	if err := h.Callers.Allowed(VerbPublish, caller); err != nil {
		return Answer{}, err
	}
	if err := checkPublish(seat, p); err != nil {
		return Answer{}, err
	}
	// A rebuild of a published version answers it held and uploads nothing; the same version with other content is
	// refused, as the registry would refuse it.
	if d, ok, err := h.Store.Held(seat, p.Name, p.Version); err != nil {
		return Answer{}, fmt.Errorf("publish: the forge cannot say whether it holds %s@%s: %w", p.Name, p.Version, err)
	} else if ok {
		if d != p.Digest {
			reason := fmt.Sprintf("%s@%s is published with %s, not %s", p.Name, p.Version, d, p.Digest)
			return Answer{Transfer: p.Transfer, Ended: true}, h.refused(Transfer{Shape: Opening{Publish: p, Seat: seat}}, reason)
		}
		o := outcomeOf(p, "")
		o.Reference = Reference(p.Name, p.Version)
		return Answer{Transfer: p.Transfer, Ended: true}, h.Say(seat, EventPublished, o)
	}
	// The transfer's name is the caller's own (the seat's contract): none would open the seat's one nameless transfer,
	// which key() still makes a valid id.
	if strings.TrimSpace(p.Transfer) == "" {
		return Answer{}, errors.New("publish: no transfer named; the caller names its own")
	}
	got, err := h.receiver().Open(key(seat, p.Transfer), caller, p.Parts, Opening{Publish: p, Seat: seat})
	if err != nil {
		return h.answer(p.Transfer, got), fmt.Errorf("publish: %w", err)
	}
	return h.answer(p.Transfer, got), nil
}

// PublishPart is `publish-part`: one chunk, from the caller that opened the transfer alone.
func (h *Holder) PublishPart(seat, caller, transfer, part string, sequence int, last bool, data []byte) (Answer, error) {
	if err := h.Callers.Allowed(VerbPublishPart, caller); err != nil {
		return Answer{}, err
	}
	got, err := h.receiver().Take(key(seat, transfer), caller, part, sequence, last, data, func(t Transfer) error {
		if t.Shape.Seat != seat {
			return fmt.Errorf("transfer %s is %s's, not %s's", transfer, t.Shape.Seat, seat)
		}
		return nil
	})
	if err != nil {
		return h.answer(transfer, got), fmt.Errorf("publish-part: %w", err)
	}
	return h.answer(transfer, got), nil
}

// Versions is `versions`: every version the seat holds of name, newest first.
func (h *Holder) Versions(seat, caller, name string) ([]Version, error) {
	if err := h.Callers.Allowed(VerbVersions, caller); err != nil {
		return nil, err
	}
	if _, ok := Seats[seat]; !ok {
		return nil, fmt.Errorf("versions: the forge holds no seat %s", seat)
	}
	if strings.TrimSpace(name) == "" {
		return nil, errors.New("versions: no name")
	}
	v, err := h.Store.Versions(seat, name)
	if err != nil {
		return nil, fmt.Errorf("versions: the forge cannot list %s: %w", name, err)
	}
	return v, nil
}

// Remove is `remove`: the builder removes a tagged version (its branch ended); an untagged version goes only by the
// forge's own retention, never by a call. A version already gone is said removed all the same, so a retry ends.
func (h *Holder) Remove(seat, caller, name, version, reason string) (Outcome, error) {
	if err := h.Callers.Allowed(VerbRemove, caller); err != nil {
		return Outcome{}, err
	}
	if _, ok := Seats[seat]; !ok {
		return Outcome{}, fmt.Errorf("remove: the forge holds no seat %s", seat)
	}
	if strings.TrimSpace(name) == "" || strings.TrimSpace(reason) == "" {
		return Outcome{}, errors.New("remove: a name and a reason are required")
	}
	if !strings.Contains(version, "-") {
		return Outcome{}, fmt.Errorf("remove: refused: %s@%s has no tag; only a tagged version is removed, an untagged one by retention alone", name, version)
	}
	d, held, err := h.Store.Held(seat, name, version)
	if err != nil {
		return Outcome{}, fmt.Errorf("remove: the forge cannot read %s@%s: %w", name, version, err)
	}
	if held {
		if err := h.Store.Remove(seat, name, version); err != nil {
			return Outcome{}, fmt.Errorf("remove: the forge did not remove %s@%s: %w", name, version, err)
		}
	}
	o := Outcome{Name: name, Version: version, Kind: KindPackage, Digest: d, Reason: reason}
	return o, h.Say(seat, EventRemoved, o)
}

// Retained says `removed` for a version the forge's own retention deleted (design 51 *Retention*).
func (h *Holder) Retained(seat, name, version, digest string) error {
	return h.Say(seat, EventRemoved, Outcome{Name: name, Version: version, Kind: KindPackage, Digest: digest, Reason: ReasonRetention})
}

// Drop drops a transfer by hand.
func (h *Holder) Drop(seat, transfer string) (Transfer, error) {
	return h.receiver().Drop(key(seat, transfer))
}

// DropByHand is <type>_incoming's drop: by a person, with why, recorded as a hand act through mesh-hand-acts before
// anything goes; an act not recorded leaves the transfer open.
func (h *Holder) DropByHand(seat, transfer, by, why string) (Transfer, error) {
	if strings.TrimSpace(why) == "" {
		return Transfer{}, errors.New("a drop is a hand act: say why")
	}
	if h.Record == nil {
		return Transfer{}, errors.New("no hand act can be recorded here, so nothing is dropped")
	}
	t, found, err := h.Transfers.Get(key(seat, transfer))
	if err != nil {
		return Transfer{}, fmt.Errorf("transfer %s cannot be read, so nothing is dropped: %w", transfer, err)
	}
	if !found {
		return Transfer{}, fmt.Errorf("transfer %s of %s is not open", transfer, seat)
	}
	what := fmt.Sprintf("dropped the open transfer %s of %s's incoming (%s@%s, opened by %s), by %s", transfer, seat, t.Shape.Name, t.Shape.Version, t.Opener, by)
	if err := h.Record(meshhandactsclient.Request{What: what, Why: why, Cause: Seats[seat] + "_incoming"}); err != nil {
		return Transfer{}, fmt.Errorf("the hand act cannot be recorded, so transfer %s stays open: %w", transfer, err)
	}
	return h.Drop(seat, transfer)
}

// Incoming is what npm_incoming and go_incoming answer of a seat: its open transfers, incoming's fill (both seats
// share the store) and the cap its binding carries.
type Incoming struct {
	Seat      string     `json:"seat"`
	Transfers []Transfer `json:"transfers"`
	Used      uint64     `json:"used"`
	Cap       uint64     `json:"cap"`
}

// IncomingOf reads a seat's open transfers and incoming's fill.
func (h *Holder) IncomingOf(seat string) (Incoming, error) {
	if _, ok := Seats[seat]; !ok {
		return Incoming{}, fmt.Errorf("the forge holds no seat %s", seat)
	}
	all, err := h.Transfers.List()
	if err != nil {
		return Incoming{}, fmt.Errorf("the transfers cannot be read: %w", err)
	}
	out := Incoming{Seat: seat, Transfers: []Transfer{}, Cap: h.CapNow()}
	for _, t := range all {
		if t.Shape.Seat == seat {
			out.Transfers = append(out.Transfers, t)
		}
	}
	if out.Used, err = h.Objects.Used(); err != nil {
		return out, fmt.Errorf("incoming's fill cannot be read: %w", err)
	}
	return out, nil
}

// Expired is told that a transfer's idle key (its key in the state transfers) ended (the bus's marker,
// parts.FollowIdle): the receiver drops a transfer with no chunk for TransferIdle with its chunks, arms one that took a
// chunk since again for the rest, and leaves one gone. It answers whether it dropped it.
func (h *Holder) Expired(id string) (bool, error) { return h.receiver().Expired(id) }

func checkPublish(seat string, p Publish) error {
	switch {
	case Seats[seat] == "":
		return fmt.Errorf("publish: the forge holds no seat %s", seat)
	case strings.TrimSpace(p.Name) == "":
		return errors.New("publish: no name")
	case strings.TrimSpace(p.Version) == "":
		return errors.New("publish: a package is published under the version the builder gave it")
	case p.Kind != KindPackage:
		return fmt.Errorf("publish: %s holds packages, not a %s", seat, p.Kind)
	case !strings.HasPrefix(p.Digest, "sha256:"):
		return fmt.Errorf("publish: digest %q is no sha256 digest", p.Digest)
	case len(p.Parts) != 1 || p.Parts[0].Digest != p.Digest:
		return errors.New("publish: a package is one file, its one part the package's digest")
	}
	return nil
}