// Package holder is distribution's holding of the two image seats, `container-image-registry` and
// `oci-artifact-registry`, and of the old seat `mesh-artifact-store` until its window closes (novox/hq design 51 *The
// four registry seats*, ADR 0605, ADR 0611, ADR 0617 §2). A build module publishes into a seat through `publish` and
// `publish-part`: the parts land in distribution's own object store `incoming`, are hashed, checked against the
// builder's `builder_versions` and stored in the artifact store, which listens on its node's loopback; the store's port
// is the program's, reads open, writes from its own process alone (front.go).
package holder

import (
	"encoding/json"
	"fmt"
	"slices"
	"sort"
	"strings"
)

// The seats distribution holds, and the old one it holds until its window closes.
const (
	ImageSeat    = "container-image-registry"
	ArtifactSeat = "oci-artifact-registry"
	OldSeat      = "mesh-artifact-store"
)

// The verbs of the seats (design 26 *A seat's definition*; design 51 *One contract*).
const (
	VerbPublish     = "publish"
	VerbPublishPart = "publish-part"
	VerbVersions    = "versions"
	VerbRemove      = "remove"
	VerbMirror      = "mirror"
	VerbTags        = "tags"
	VerbHold        = "hold"
	VerbRelease     = "release"
)

// Seats are the seats distribution answers verbs on.
var Seats = []string{ImageSeat, ArtifactSeat}

// VerbsOf are a seat's verbs: mirror and tags on the image seat alone; hold and release on both of distribution's.
func VerbsOf(seat string) []string {
	v := []string{VerbPublish, VerbPublishPart, VerbVersions, VerbRemove, VerbHold, VerbRelease}
	if seat == ImageSeat {
		v = append(v, VerbMirror, VerbTags)
	}
	sort.Strings(v)
	return v
}

// Callers is the holder's trusted config value `callers` (the form ADR 0363 gives a restricted family): per verb, the
// modules that may call it. The holder checks the caller the tool runner proved and stamped on the request (design 25
// § 12.4), never a name in the request's body.
type Callers map[string][]string

// DefaultCallers is the list design 51 *Who may call which verb* names: publish and publish-part the build modules;
// mirror mesh-build-image; remove the builder (a tagged version) and the artifact sweep's holder (retention); hold the
// artifact sweep's holder alone; release that holder, and the operator's session only through registry_holds (Operator
// below). versions is read by anyone on the mesh, as the store's reads are.
func DefaultCallers() Callers {
	builds := []string{"mesh-build-go", "mesh-build-image", "mesh-build-node"}
	return Callers{
		VerbPublish:     builds,
		VerbPublishPart: builds,
		VerbMirror:      {"mesh-build-image"},
		VerbRemove:      {"mesh-delivery-builder", SweepHolder},
		VerbHold:        {SweepHolder},
		VerbRelease:     {SweepHolder, Operator},
		VerbVersions:    {Anyone},
		VerbTags:        {Anyone},
	}
}

// SweepHolder is the module holding the seat `mesh-artifact-sweep`, the artifact sweep.
const SweepHolder = "artifact-store-tools"

// Anyone on a verb's list lets every proved caller call it.
const Anyone = "*"

// Operator on a list stands for the operator's session, the caller the tool runner proves as `person.<name>` (ADR 0386
// §7): a release by hand through registry_holds carries it on, never distribution's own account.
const Operator = "operator"

// Unproven is the caller the runtime names for a call it could not prove (mesh-sdk stdio.Unproven).
const Unproven = "unproven"

// Self is distribution's own account: never on release's list, so registry_holds cannot release in its own name.
const Self = "distribution"

// ParseCallers reads the config value; an empty value is DefaultCallers. A verb no seat has is refused, and Self on
// release's list is refused (design 51).
func ParseCallers(raw string) (Callers, error) {
	if strings.TrimSpace(raw) == "" {
		return DefaultCallers(), nil
	}
	var c Callers
	if err := json.Unmarshal([]byte(raw), &c); err != nil {
		return nil, fmt.Errorf("callers is not a JSON object of verb to modules: %w", err)
	}
	known := VerbsOf(ImageSeat)
	for verb, mods := range c {
		if !slices.Contains(known, verb) {
			return nil, fmt.Errorf("callers names the verb %q, which no seat of distribution's has", verb)
		}
		if verb == VerbRelease && slices.Contains(mods, Self) {
			return nil, fmt.Errorf("callers puts %s on release's list: registry_holds would release in its own name", Self)
		}
	}
	return c, nil
}

// Allowed answers nil when caller may call verb, else the refusal naming the verb and the caller.
func (c Callers) Allowed(verb, caller string) error {
	if caller == "" || caller == Unproven {
		return fmt.Errorf("%s: refused: the request carries no caller the tool runner proved", verb)
	}
	person := strings.HasPrefix(caller, "person.")
	for _, m := range c[verb] {
		switch {
		case m == Anyone, m == Operator && person, !person && m == CallerModule(caller):
			return nil
		}
	}
	return fmt.Errorf("%s: refused for %s: not on the holder's caller list for %s", verb, caller, verb)
}

// CallerModule is the module of a proved module caller, which the runtime stamps `<node>.<module>`.
func CallerModule(proved string) string {
	if i := strings.LastIndexByte(proved, '.'); i >= 0 {
		return proved[i+1:]
	}
	return proved
}