package delivery

import (
	"encoding/json"
	"fmt"
	"sort"
	"time"
)

// Whether the artifact store still holds what a done key names (novox/hq issue 1937). A build module pushes a bundle or
// an archive as a bare blob (ADR 0498 §1), and the store's nightly collector deletes every blob no manifest names; only
// the controller's take-in and sweep hold one by its manifest. A done key the controller has not taken in can therefore
// name a blob that is gone, and reusing it sends a definition every machine fails on. So the builder asks before it
// reuses a done key, and the controller says when a take-in found a gone blob.
const (
	// HeldVerb is the controller seat's verb the builder asks, as a module's invokes names it: references in, each
	// answered held or gone.
	HeldVerb = "seat:mesh-controller.held"
	// ArtifactsGoneEvent is the controller seat's event said when a take-in is refused because the store does not hold
	// an artifact the key names: as a consumer names it, `mesh-controller.artifacts-gone`.
	ArtifactsGoneEvent = "artifacts-gone"
	// ArtifactsGoneSubject is where it is published (the seat's event subject).
	ArtifactsGoneSubject = "mesh.seat.mesh-controller.event." + ArtifactsGoneEvent
)

// HeldAnswer is the answer of HeldVerb: the references the store holds, and those it answered 404 for. A reference the
// store could not be asked about is in neither, and named in Unknown with why.
type HeldAnswer struct {
	Store   string            `json:"store,omitempty"`
	Held    []string          `json:"held"`
	Gone    []string          `json:"gone"`
	Unknown map[string]string `json:"unknown,omitempty"`
}

// DecodeHeldAnswer reads HeldVerb's answer: the verb answers {output, ok, answer}, the answer being HeldAnswer. A
// reference asked that the answer names in none of held, gone and unknown is an error: an answer that leaves one out
// would let a key with a gone blob be reused.
func DecodeHeldAnswer(raw []byte, asked []string) (HeldAnswer, error) {
	var wrapped struct {
		Output string          `json:"output"`
		OK     bool            `json:"ok"`
		Answer json.RawMessage `json:"answer"`
	}
	if err := json.Unmarshal(raw, &wrapped); err != nil {
		return HeldAnswer{}, fmt.Errorf("the answer of %s is not {output, ok, answer}: %w", HeldVerb, err)
	}
	if !wrapped.OK || len(wrapped.Answer) == 0 {
		return HeldAnswer{}, fmt.Errorf("%s did not answer: %s", HeldVerb, wrapped.Output)
	}
	var a HeldAnswer
	if err := json.Unmarshal(wrapped.Answer, &a); err != nil {
		return HeldAnswer{}, fmt.Errorf("the answer of %s is not {held, gone}: %w", HeldVerb, err)
	}
	named := map[string]bool{}
	for _, r := range a.Held {
		named[r] = true
	}
	for _, r := range a.Gone {
		named[r] = true
	}
	for r := range a.Unknown {
		named[r] = true
	}
	for _, r := range asked {
		if !named[r] {
			return HeldAnswer{}, fmt.Errorf("the answer of %s names nothing of %s", HeldVerb, r)
		}
	}
	return a, nil
}

// ArtifactsGone is the body of ArtifactsGoneEvent: the module whose builder's key the controller would not take in,
// the key and its fingerprint, and every reference of it the store does not hold.
type ArtifactsGone struct {
	Event       string    `json:"event"`
	Module      string    `json:"module"`
	Key         string    `json:"key"`
	Fingerprint string    `json:"fingerprint"`
	Gone        []string  `json:"gone"`
	At          time.Time `json:"at"`
}

// EncodeArtifactsGone is the event's body, the references sorted.
func EncodeArtifactsGone(e ArtifactsGone) ([]byte, error) {
	e.Event = ArtifactsGoneEvent
	e.Gone = append([]string(nil), e.Gone...)
	sort.Strings(e.Gone)
	if e.Module == "" || e.Fingerprint == "" || len(e.Gone) == 0 {
		return nil, fmt.Errorf("delivery: %s names a module, a fingerprint and at least one gone reference", ArtifactsGoneEvent)
	}
	return json.Marshal(e)
}

// DecodeArtifactsGone reads the event's body, refusing one that names no module, fingerprint or reference.
func DecodeArtifactsGone(raw []byte) (ArtifactsGone, error) {
	var e ArtifactsGone
	if err := json.Unmarshal(raw, &e); err != nil {
		return ArtifactsGone{}, fmt.Errorf("delivery: %s is not one: %w", ArtifactsGoneEvent, err)
	}
	if e.Event != ArtifactsGoneEvent || e.Module == "" || e.Fingerprint == "" || len(e.Gone) == 0 {
		return ArtifactsGone{}, fmt.Errorf("delivery: %s names no module, fingerprint or gone reference: %s", ArtifactsGoneEvent, raw)
	}
	return e, nil
}