// Package provisions is the contract of the seat mesh-provisioner's records (novox/hq ADR 0570 clauses 1, 2 and 5; issue
// 1954): every provision one key of the state `provisions`, holding a reference and never a value, and every handed
// module's provisioning plan one key of the state `plans`. The module mesh-provisioner alone writes both; the vault,
// each node's provisioner client and every provider read them through `reads`.
package provisions

import (
	"bytes"
	"encoding/json"
	"fmt"
	"regexp"
	"sort"
	"strings"
	"time"

	"git.novox.be/novox/mesh-sdk/go/catalogue"
)

// The seat, its holder and its two states, and the names a reader declares in its `reads`.
const (
	Seat            = "mesh-provisioner"
	Module          = "mesh-provisioner"
	ProvisionsState = "provisions"
	PlansState      = "plans"
	ProvisionsRead  = Module + "." + ProvisionsState
	PlansRead       = Module + "." + PlansState
	// ProvisionsBucket and PlansBucket are the states' buckets.
	ProvisionsBucket = Module + "_" + ProvisionsState
	PlansBucket      = Module + "_" + PlansState
)

// The states of a provision (clause 1).
const (
	// Asked is a provision its consumer needs that its provider has not answered yet, or whose dependencies are not
	// all provided (clause 3).
	Asked = "asked"
	// Provided is a provision the provider said it made: set only from the provider's outcome (clause 3).
	Provided = "provided"
	// Waits is a provision only a person can give, naming what is awaited (clause 7).
	Waits = "waits"
	// Failed is a provision the provider could not make, with why.
	Failed = "failed"
	// Retiring is a provision no want needs, asked of the operator before its credential goes (clause 5).
	Retiring = "retiring"
)

// States is every state a provision may be in.
var States = []string{Asked, Provided, Waits, Failed, Retiring}

// Version is the version of the records' layout.
const Version = 1

// token is one part of a key: what a bucket's key takes, no dot.
var token = regexp.MustCompile(`^[A-Za-z0-9_-]+$`)

// Key is a provision's key: `<node>.<consumer>.<provision>`, and `.<local>` where the consumer keeps several values of
// one provision (ADR 0094). The same key the provider's own entry for that consumer has (provider.Entry.Key).
func Key(node, consumer, provision, local string) (string, error) {
	parts := []string{node, consumer, provision}
	if local != "" {
		parts = append(parts, local)
	}
	for _, p := range parts {
		if !token.MatchString(p) {
			return "", fmt.Errorf("provisions: %q cannot be part of a provision's key", p)
		}
	}
	return strings.Join(parts, "."), nil
}

// ParseKey is the inverse of Key.
func ParseKey(key string) (node, consumer, provision, local string, err error) {
	parts := strings.Split(key, ".")
	if len(parts) < 3 || len(parts) > 4 {
		return "", "", "", "", fmt.Errorf("provisions: %q is not <node>.<consumer>.<provision>[.<local>]", key)
	}
	for _, p := range parts {
		if !token.MatchString(p) {
			return "", "", "", "", fmt.Errorf("provisions: %q is not <node>.<consumer>.<provision>[.<local>]", key)
		}
	}
	if len(parts) == 4 {
		local = parts[3]
	}
	return parts[0], parts[1], parts[2], local, nil
}

// PlanKey is a plan's key in `plans`: `<node>.<module>` (clause 2).
func PlanKey(node, module string) (string, error) {
	if !token.MatchString(node) || !token.MatchString(module) {
		return "", fmt.Errorf("provisions: %s.%s is not a plan's key, <node>.<module>", node, module)
	}
	return node + "." + module, nil
}

// The forms of a provision's credential, as a plan's entry names them (catalogue.PlanProvision.CredentialForm).
const (
	FormPair   = "pair"
	FormShared = "shared"
	FormIssued = "issued"
	FormGiven  = "given"
	// FormNone is an offer whose consumers present no credential (catalogue.CredentialFormNone): the vault mints nothing,
	// and the provision depends on no credential.
	FormNone = "none"
)

// VaultName is the vault's name of a provision's credential in form, as its verb `own` names it and the provider asks
// it: `pair/<provider node>/<provision>/<consumer node>/<module>[/<local>]` for a login of the consumer's own (ADR 0158
// §11), `provision/<provider node>/<provision>` for the provider's one shared value, and `provision/<provider
// node>/<provision>/<consumer node>/<module>` for a holder's own issued or given value. Empty for a form with no
// credential.
func VaultName(form string, p Provision) string {
	switch form {
	case FormPair:
		n := "pair/" + p.Provider.Node + "/" + p.Provision + "/" + p.Consumer.Node + "/" + p.Consumer.Module
		if p.Local != "" {
			n += "/" + p.Local
		}
		return n
	case FormShared:
		return "provision/" + p.Provider.Node + "/" + p.Provision
	case FormIssued, FormGiven:
		return "provision/" + p.Provider.Node + "/" + p.Provision + "/" + p.Consumer.Node + "/" + p.Consumer.Module
	}
	return ""
}

// VaultModule is the provider of every provision's credential (novox/hq ADR 0570 clauses 1, 6).
const VaultModule = "mesh-vault"

// CredentialKey is the key of a provision's credential, itself a provision whose provider is the vault (clause 6; the
// key form the lead settled on 2026-10-29): `<consumer node>.<consumer>.secret-<provision>[.<local>]` for a value of the
// consumer's own (pair, issued, given), and `<provider node>.<provider>.secret-<provision>` for the provider's one
// shared value. False for a form with no vault value, and for a provision the vault itself provides.
func CredentialKey(form string, consumer, provider End, provision, local string) (string, bool) {
	if provider.Module == VaultModule {
		return "", false // the vault's own offer is the value: it has no credential beside it (the lead, 2026-10-29)
	}
	name := catalogue.CredentialProvisionPrefix + provision
	switch form {
	case FormPair, FormIssued, FormGiven:
		k, err := Key(consumer.Node, consumer.Module, name, local)
		return k, err == nil
	case FormShared:
		k, err := Key(provider.Node, provider.Module, name, "")
		return k, err == nil
	}
	return "", false
}

// DependsOn is what a provision waits for before its provider makes it (clause 3): its credential's key, where its form
// has a vault value, and the key of every provision its provider module itself requires on its own node, read from
// the provider's plan there (nil when the provider is not handed and has none). Sorted, none twice.
func DependsOn(consumer End, entry catalogue.PlanProvision, providerPlan *catalogue.Plan) []string {
	seen := map[string]bool{}
	var out []string
	add := func(k string) {
		if k != "" && !seen[k] {
			seen[k] = true
			out = append(out, k)
		}
	}
	provider := End{Module: entry.ProviderModule, Node: entry.Provider}
	if k, ok := CredentialKey(entry.CredentialForm, consumer, provider, entry.Provision, entry.Local); ok {
		add(k)
	}
	if providerPlan != nil {
		for _, own := range providerPlan.Provisions {
			if k, err := Key(provider.Node, provider.Module, own.Provision, own.Local); err == nil {
				add(k)
			}
		}
	}
	sort.Strings(out)
	return out
}

// End is one end of a provision: a module on a node.
type End struct {
	Module string `json:"module"`
	Node   string `json:"node"`
}

// Reference is a value the vault keeps, by its id and the generation of the value: never the value, sealed or not
// (ADR 0349 §7). The holder writes the generation the vault says in its own entry (clause 6). ID is the vault's name of
// the credential exactly as its verb `own` names it (VaultName): the consuming node's engine checks both the name and
// the generation of what it is handed.
type Reference struct {
	ID         string `json:"id"`
	Generation int    `json:"generation"`
}

// Warrant is the operator's answer to a retiring provision's ask, as the holder writes it into the key (clause 5).
type Warrant struct {
	Ask    string    `json:"ask"`
	Option string    `json:"option"`
	By     string    `json:"by"`
	At     time.Time `json:"at"`
}

// Provision is one key of `provisions`.
type Provision struct {
	V         int    `json:"v"`
	Provision string `json:"provision"`
	Local     string `json:"local,omitempty"`
	Consumer  End    `json:"consumer"`
	Provider  End    `json:"provider"`
	// DependsOn are the keys of the provisions this one waits for (clause 3): a database user whose password is the
	// vault's.
	DependsOn []string `json:"depends-on,omitempty"`
	State     string   `json:"state"`
	// Why is the reason for waits, failed and retiring, and for asked when a dependency holds it.
	Why       string     `json:"why,omitempty"`
	Reference *Reference `json:"reference,omitempty"`
	// Ask is a retiring provision's ask of the operator; Warrant the answer, once given.
	Ask     string    `json:"ask,omitempty"`
	Warrant *Warrant  `json:"warrant,omitempty"`
	At      time.Time `json:"at"`
}

// Key is the provision's key.
func (p Provision) Key() (string, error) {
	return Key(p.Consumer.Node, p.Consumer.Module, p.Provision, p.Local)
}

func (p Provision) check() error {
	if _, err := p.Key(); err != nil {
		return err
	}
	if p.Provider.Module == "" || p.Provider.Node == "" {
		return fmt.Errorf("provisions: %s names no provider", p.Provision)
	}
	known := false
	for _, s := range States {
		known = known || s == p.State
	}
	switch {
	case !known:
		return fmt.Errorf("provisions: a provision's state is one of %s, not %q", strings.Join(States, ", "), p.State)
	case (p.State == Waits || p.State == Failed || p.State == Retiring) && strings.TrimSpace(p.Why) == "":
		return fmt.Errorf("provisions: a %s provision says why", p.State)
	case p.Warrant != nil && p.State != Retiring:
		return fmt.Errorf("provisions: only a retiring provision carries the operator's warrant")
	}
	for _, d := range p.DependsOn {
		if _, _, _, _, err := ParseKey(d); err != nil {
			return err
		}
	}
	return nil
}

// Encode is p as JSON at Version; it refuses what a holder may not write.
func Encode(p Provision) ([]byte, error) {
	p.V = Version
	if err := p.check(); err != nil {
		return nil, err
	}
	return json.Marshal(p)
}

// Decode reads a key's value strictly: a field the layout does not name is refused, so no value, sealed or not, rides in
// a provision (clause 1, ADR 0201 §13).
func Decode(data []byte) (Provision, error) {
	var p Provision
	dec := json.NewDecoder(bytes.NewReader(data))
	dec.DisallowUnknownFields()
	if err := dec.Decode(&p); err != nil {
		return Provision{}, fmt.Errorf("provisions: a provision is not readable: %w", err)
	}
	if p.V != Version {
		return Provision{}, fmt.Errorf("provisions: a provision of version %d, and this reads %d", p.V, Version)
	}
	return p, p.check()
}

// Plan is one key of `plans`: a module's provisioning plan on a node, never a value (clause 2).
type Plan struct {
	V      int            `json:"v"`
	Node   string         `json:"node"`
	Module string         `json:"module"`
	Plan   catalogue.Plan `json:"plan"`
}

// EncodePlan is p as JSON at Version.
func EncodePlan(p Plan) ([]byte, error) {
	p.V = Version
	if _, err := PlanKey(p.Node, p.Module); err != nil {
		return nil, err
	}
	return json.Marshal(p)
}

// DecodePlan reads a plan's key.
func DecodePlan(data []byte) (Plan, error) {
	var p Plan
	if err := json.Unmarshal(data, &p); err != nil {
		return Plan{}, fmt.Errorf("provisions: a plan is not readable: %w", err)
	}
	if p.V != Version {
		return Plan{}, fmt.Errorf("provisions: a plan of version %d, and this reads %d", p.V, Version)
	}
	_, err := PlanKey(p.Node, p.Module)
	return p, err
}