package link

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"

	"git.novox.be/novox/mesh-sdk/go/delivery"
	"github.com/nats-io/nats.go"
)

// ---- the packages this node's compositions declare, in the bus's own storage (novox/hq ADR 0565 §6) ---------------

// PackagesBucket is the node-engine's declared state packages, created by the grants part from the engine's manifest as
// its states health and data are: one key, the node's name, written by that node's engine alone, read by pacman as
// mesh-host.packages (delivery.EnginePackagesRead).
const PackagesBucket = "mesh-host_" + delivery.EnginePackagesState

// packagesStore binds PackagesBucket over the link open now: bound, never created.
func (l *natsLink) packagesStore() (nats.KeyValue, error) {
	kv, err := l.js.KeyValue(PackagesBucket)
	if err != nil {
		return nil, fmt.Errorf("the node-engine's state %s cannot be bound (it is created from the node-engine's "+
			"manifest; written again at the next composition that changes, or by the node seat's packages with write): %w",
			PackagesBucket, err)
	}
	return kv, nil
}

// packagesStore binds PackagesBucket over a link made of a connection the caller holds (OverNATS), as natsLink does.
func (b OverNATS) packagesStore() (nats.KeyValue, error) {
	kv, err := b.JS.KeyValue(PackagesBucket)
	if err != nil {
		return nil, fmt.Errorf("the node-engine's state %s cannot be bound: %w", PackagesBucket, err)
	}
	return kv, nil
}

// EnginePackages is this node's key of PackagesBucket over whichever link the session has open
// (selfcompose.PackagesStore); with none open every read and write is refused, and nothing is kept anywhere else.
type EnginePackages struct{ Session *Session }

func (p EnginePackages) kv() (nats.KeyValue, error) {
	p.Session.init()
	p.Session.mu.Lock()
	bus := p.Session.bus
	p.Session.mu.Unlock()
	l, ok := bus.(interface{ packagesStore() (nats.KeyValue, error) })
	if bus == nil || !ok {
		return nil, ErrNoLink
	}
	return l.packagesStore()
}

// Get is the key's value, nil when it has none.
func (p EnginePackages) Get(_ context.Context, key string) ([]byte, error) {
	kv, err := p.kv()
	if err != nil {
		return nil, err
	}
	e, err := kv.Get(key)
	if errors.Is(err, nats.ErrKeyNotFound) {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	return e.Value(), nil
}

// Put writes the key.
func (p EnginePackages) Put(_ context.Context, key string, value []byte) error {
	kv, err := p.kv()
	if err != nil {
		return err
	}
	_, err = kv.Put(key, value)
	return err
}

// PackagesView is the node seat's verb packages' answer (ADR 0565 §6): this node's key of the engine's state packages.
// The controller's mirror it was once compared with ended with the controller (issue 1126).
type PackagesView struct {
	Node string `json:"node"`
	// Key is the node's key as the bus holds it (Source); null when the engine has written none.
	Source   string                     `json:"source"`
	Key      *delivery.DeclaredPackages `json:"key"`
	KeyError string                     `json:"key_error,omitempty"`
	// Wrote says, for write, whether the key was written again (false: it already held what the engine composed).
	Wrote *bool  `json:"wrote,omitempty"`
	Note  string `json:"note,omitempty"`
}

// PackagesAnswer is the verb's answer from the key as read (nil: no key), with its read's error.
func PackagesAnswer(node string, key []byte, keyErr error) PackagesView {
	v := PackagesView{Node: node, Source: delivery.EnginePackagesRead}
	if keyErr == nil && key != nil {
		var d delivery.DeclaredPackages
		if keyErr = json.Unmarshal(key, &d); keyErr == nil {
			v.Key = &d
		}
	}
	switch {
	case keyErr != nil:
		v.KeyError = keyErr.Error()
	case v.Key == nil:
		v.Note = "the engine has written no key for this node yet"
	}
	return v
}