// Package apitoken issues and verifies the tokens non-browser clients use.
//
// Jellyfin clients send `X-Emby-Token` (or `api_key=`); Subsonic clients send
// `t=md5(key+salt)`. Neither speaks the web app's session cookie, so these
// tokens are a second, revocable way to be a user. They do not weaken the cookie
// model: a token resolves to the same auth.User and every caller still goes
// through the same grant chokepoint.
//
// Two storage shapes, deliberately:
//
//   - A Jellyfin token is a bearer value, so only its hash is stored — the same
//     reasoning as session tokens. A stolen database yields nothing usable.
//   - A Subsonic key must be recoverable, because verifying `t` means computing
//     md5(key + salt) server-side. So Subsonic keys are stored in the clear.
//     That is the Navidrome approach, and it is why the key is a generated
//     random secret rather than anything derived from the user's password.
package apitoken

import (
	"context"
	"crypto/rand"
	"crypto/sha256"
	"database/sql"
	"encoding/hex"
	"errors"
	"fmt"

	"github.com/mithral/vellum/internal/core"
)

// Kinds of token. A client family, not a permission.
const (
	KindJellyfin = "jellyfin"
	KindSubsonic = "subsonic"
)

// ErrNotFound means no token matched.
var ErrNotFound = errors.New("apitoken: not found")

// Token is one issued credential. It never carries the secret itself.
type Token struct {
	ID         int64
	UserID     int64
	Kind       string
	Label      string
	CreatedAt  string
	LastUsedAt string
	ExpiresAt  string
}

// Mint issues a new token for a user and returns the secret exactly once.
//
// The caller must show it to the user immediately; it is not recoverable for
// Jellyfin afterwards (only its hash is kept). For Subsonic it is recoverable,
// because that protocol requires it — see the package comment.
func Mint(ctx context.Context, db *sql.DB, userID int64, kind, label string) (string, error) {
	if kind != KindJellyfin && kind != KindSubsonic {
		return "", fmt.Errorf("apitoken: unknown kind %q", kind)
	}

	var raw [32]byte
	if _, err := rand.Read(raw[:]); err != nil {
		return "", fmt.Errorf("apitoken: read random: %w", err)
	}
	secret := hex.EncodeToString(raw[:])

	plain := ""
	if kind == KindSubsonic {
		// Recoverable by necessity: verifying `t` needs the key itself.
		plain = secret
	}

	_, err := db.ExecContext(ctx, `
		INSERT INTO api_tokens (user_id, kind, label, token_hash, token_plain, created_at)
		VALUES (?, ?, ?, ?, ?, ?)`,
		userID, kind, label, Hash(secret), plain, core.Now())
	if err != nil {
		return "", fmt.Errorf("apitoken: insert: %w", err)
	}
	return secret, nil
}

// Hash is the lookup digest for a token. Exported so the Jellyfin layer can
// resolve a bearer value without duplicating the scheme.
func Hash(secret string) string {
	sum := sha256.Sum256([]byte(secret))
	return hex.EncodeToString(sum[:])
}

// Resolve finds the user a token belongs to, and records the use.
//
// An empty or unknown token is ErrNotFound; the caller turns that into a 401.
// An expired token is also ErrNotFound, so callers cannot accidentally treat an
// expired credential as valid by checking only the error's absence.
func Resolve(ctx context.Context, db *sql.DB, secret string) (int64, error) {
	if secret == "" {
		return 0, ErrNotFound
	}
	var (
		id      int64
		userID  int64
		expires string
	)
	err := db.QueryRowContext(ctx,
		`SELECT id, user_id, expires_at FROM api_tokens WHERE token_hash = ?`,
		Hash(secret)).Scan(&id, &userID, &expires)
	if errors.Is(err, sql.ErrNoRows) {
		return 0, ErrNotFound
	}
	if err != nil {
		return 0, fmt.Errorf("apitoken: resolve: %w", err)
	}
	if expires != "" && expires < core.Now() {
		return 0, ErrNotFound
	}

	// Best-effort: a failed touch must not fail the request.
	_, _ = db.ExecContext(ctx, `UPDATE api_tokens SET last_used_at = ? WHERE id = ?`, core.Now(), id)
	return userID, nil
}

// Plain returns the recoverable secret for a Subsonic token. Jellyfin tokens
// have none by design, so this returns ErrNotFound for them.
func Plain(ctx context.Context, db *sql.DB, userID int64) (string, error) {
	var plain string
	err := db.QueryRowContext(ctx,
		`SELECT token_plain FROM api_tokens
		 WHERE user_id = ? AND kind = ? AND token_plain != ''
		 ORDER BY id LIMIT 1`,
		userID, KindSubsonic).Scan(&plain)
	if errors.Is(err, sql.ErrNoRows) {
		return "", ErrNotFound
	}
	if err != nil {
		return "", fmt.Errorf("apitoken: plain: %w", err)
	}
	return plain, nil
}

// ForUser lists a user's tokens, newest first.
func ForUser(ctx context.Context, db *sql.DB, userID int64) ([]Token, error) {
	rows, err := db.QueryContext(ctx, `
		SELECT id, user_id, kind, label, created_at, last_used_at, expires_at
		FROM api_tokens WHERE user_id = ? ORDER BY id DESC`, userID)
	if err != nil {
		return nil, fmt.Errorf("apitoken: list: %w", err)
	}
	defer rows.Close()

	out := []Token{}
	for rows.Next() {
		var t Token
		if err := rows.Scan(&t.ID, &t.UserID, &t.Kind, &t.Label,
			&t.CreatedAt, &t.LastUsedAt, &t.ExpiresAt); err != nil {
			return nil, err
		}
		out = append(out, t)
	}
	return out, rows.Err()
}

// Revoke deletes a token, scoped to its owner so one user cannot revoke
// another's. Reports whether anything was removed.
func Revoke(ctx context.Context, db *sql.DB, userID, tokenID int64) (bool, error) {
	res, err := db.ExecContext(ctx,
		`DELETE FROM api_tokens WHERE id = ? AND user_id = ?`, tokenID, userID)
	if err != nil {
		return false, fmt.Errorf("apitoken: revoke: %w", err)
	}
	n, err := res.RowsAffected()
	return n > 0, err
}