package inventory

import (
	"context"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"errors"
	"fmt"
	"strings"
	"time"

	"github.com/jackc/pgx/v5"
	"github.com/novox/mesh-control/internal/store"
)

// Inventory is this context, holding the store it exclusively owns.
type Inventory struct{ store *store.Store }

// Open connects to the inventory store.
func Open(ctx context.Context) (*Inventory, error) {
	s, err := store.Open(ctx, Name)
	if err != nil {
		return nil, err
	}
	return &Inventory{store: s}, nil
}

func (i *Inventory) Close() { i.store.Close() }

// Ready waits for the database to answer.
func (i *Inventory) Ready(ctx context.Context, within time.Duration) error {
	return i.store.Ready(ctx, within)
}

// Node is a machine the mesh knows about.
type Node struct {
	ID      string
	Name    string
	Created time.Time
}

// ErrNoSuchNode is returned when a name matches no record.
var ErrNoSuchNode = errors.New("no node of that name")

// ErrNameTaken is returned when a node of that name already exists.
//
// Its own error rather than the driver's, because "that name is taken" is an ordinary answer a
// person can act on, and a unique-violation from PostgreSQL is not.
var ErrNameTaken = errors.New("a node of that name already exists")

// AddNode creates a node record.
//
// The record comes first and the machine second: a token is issued *for* a node record
// (novox/hq 09-the-node-lifecycle), so the record is what a token binds to and must exist before
// there is anything to join.
func (i *Inventory) AddNode(ctx context.Context, name string) (Node, error) {
	name = strings.TrimSpace(name)
	if name == "" {
		return Node{}, errors.New("a node needs a name: it is how a token is issued for it")
	}

	var n Node
	err := i.store.Pool().QueryRow(ctx,
		`insert into node (name) values ($1) returning id, name, created`,
		name).Scan(&n.ID, &n.Name, &n.Created)
	if err != nil {
		if strings.Contains(err.Error(), "node_name_key") {
			return Node{}, fmt.Errorf("%w: %s", ErrNameTaken, name)
		}
		return Node{}, err
	}
	return n, nil
}

// Nodes are every node record, oldest first.
func (i *Inventory) Nodes(ctx context.Context) ([]Node, error) {
	rows, err := i.store.Pool().Query(ctx,
		`select id, name, created from node order by created, name`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var nodes []Node
	for rows.Next() {
		var n Node
		if err := rows.Scan(&n.ID, &n.Name, &n.Created); err != nil {
			return nil, err
		}
		nodes = append(nodes, n)
	}
	return nodes, rows.Err()
}

// NodeByName finds one node record.
func (i *Inventory) NodeByName(ctx context.Context, name string) (Node, error) {
	var n Node
	err := i.store.Pool().QueryRow(ctx,
		`select id, name, created from node where name = $1`, name).Scan(&n.ID, &n.Name, &n.Created)
	if errors.Is(err, pgx.ErrNoRows) {
		return Node{}, fmt.Errorf("%w: %s", ErrNoSuchNode, name)
	}
	return n, err
}

// Issued is a token that has just been made. The secret is in it exactly once.
type Issued struct {
	Node    Node
	Secret  string
	Expires time.Time
}

// hashSecret is what gets stored in place of the secret.
//
// SHA-256 rather than a password hash, and that is deliberate rather than a shortcut. bcrypt and
// its relatives are slow on purpose because a password is low-entropy and guessable; this secret
// is 256 bits from the system's random source, so there is nothing to guess and the slowness would
// buy nothing while making every redemption expensive.
func hashSecret(secret string) string {
	sum := sha256.Sum256([]byte(secret))
	return hex.EncodeToString(sum[:])
}

// IssueToken mints a one-time right to join, for a node record.
//
// The secret is returned once and never again. What is stored is its hash, so a copy of this
// database is not a set of working credentials.
//
// Any outstanding token for the same node is expired first. Two live tokens for one node record
// are two machines able to join as the same node, and nothing downstream could tell which was
// meant — novox/hq ADR 0004's stolen-laptop case arriving before enrolment rather than after.
func (i *Inventory) IssueToken(ctx context.Context, nodeName string, validFor time.Duration) (Issued, error) {
	if validFor <= 0 {
		return Issued{}, errors.New("a token needs a lifetime: one that never expires is a " +
			"permanent credential, which is the thing this is designed not to be")
	}

	node, err := i.NodeByName(ctx, nodeName)
	if err != nil {
		return Issued{}, err
	}

	raw := make([]byte, 32)
	if _, err := rand.Read(raw); err != nil {
		return Issued{}, fmt.Errorf("cannot generate a token secret: %w", err)
	}
	secret := base64.RawURLEncoding.EncodeToString(raw)
	expires := time.Now().Add(validFor)

	tx, err := i.store.Pool().Begin(ctx)
	if err != nil {
		return Issued{}, err
	}
	defer func() { _ = tx.Rollback(context.WithoutCancel(ctx)) }()

	// Expired rather than deleted: what was issued and then withdrawn is worth being able to see.
	if _, err := tx.Exec(ctx,
		`update enrolment_token set expires = now()
		  where node = $1 and redeemed is null and expires > now()`, node.ID); err != nil {
		return Issued{}, err
	}
	if _, err := tx.Exec(ctx,
		`insert into enrolment_token (node, secret, expires) values ($1, $2, $3)`,
		node.ID, hashSecret(secret), expires); err != nil {
		return Issued{}, err
	}
	if err := tx.Commit(ctx); err != nil {
		return Issued{}, err
	}

	return Issued{Node: node, Secret: secret, Expires: expires}, nil
}

// ErrTokenRefused is what redemption returns for anything that is not a live token.
//
// One error for every reason — unknown, already used, expired — and deliberately so. Whoever is
// presenting a token that does not work is either a machine whose operator can be told out of
// band, or somebody guessing, and the second must not learn which of their guesses was a real
// token that had expired.
var ErrTokenRefused = errors.New("that token cannot be used")

// Redeem spends a token and reports which node it was for.
//
// It does not issue an identity. What a node presents afterwards to prove it is that node is not
// decided anywhere (novox/hq ADR 0004 names the property, not the mechanism), and guessing at it
// in a migration is the most expensive guess available here.
//
// The update is the check: one statement that both finds a live token and marks it used, so two
// simultaneous redemptions of one secret cannot both succeed. Reading first and writing second
// would leave exactly that gap.
func (i *Inventory) Redeem(ctx context.Context, secret string) (Node, error) {
	var id string
	err := i.store.Pool().QueryRow(ctx,
		`update enrolment_token set redeemed = now()
		  where secret = $1 and redeemed is null and expires > now()
		  returning node`, hashSecret(secret)).Scan(&id)
	if errors.Is(err, pgx.ErrNoRows) {
		return Node{}, ErrTokenRefused
	}
	if err != nil {
		return Node{}, err
	}

	var n Node
	err = i.store.Pool().QueryRow(ctx,
		`select id, name, created from node where id = $1`, id).Scan(&n.ID, &n.Name, &n.Created)
	return n, err
}