<?php
/**
 * AgentPass core library — HTTP Message Signatures (RFC 9421) with Ed25519,
 * Web Bot Auth profile (draft-meunier-web-bot-auth-architecture).
 * Pure PHP 8 + ext-sodium. No other dependencies.
 */
namespace AgentPass;

const DIRECTORY_URL = 'https://agentpass.semalt.ai';
const DEFAULT_COMPONENTS = ['@method', '@authority', '@path', 'signature-agent'];

function b64u_enc(string $b): string { return rtrim(strtr(base64_encode($b), '+/', '-_'), '='); }
function b64u_dec(string $s): string|false {
    $s = strtr($s, '-_', '+/');
    return base64_decode($s . str_repeat('=', (4 - strlen($s) % 4) % 4), true);
}

/** RFC 7638 JWK thumbprint of an Ed25519 OKP key (members in lexicographic order). */
function jwk_thumbprint(string $x_b64u): string {
    return b64u_enc(hash('sha256', '{"crv":"Ed25519","kty":"OKP","x":"' . $x_b64u . '"}', true));
}

/** @return array{seed:string,x:string,kid:string} all base64url */
function keygen(): array {
    $kp = sodium_crypto_sign_keypair();
    $sk = sodium_crypto_sign_secretkey($kp);
    $pk = sodium_crypto_sign_publickey($kp);
    $x  = b64u_enc($pk);
    return ['seed' => b64u_enc(substr($sk, 0, 32)), 'x' => $x, 'kid' => jwk_thumbprint($x)];
}

/** Accepts raw 32-byte key as base64url / base64 / hex, or PEM SPKI. Returns raw bytes or null. */
function parse_pubkey(string $in): ?string {
    $in = trim($in);
    if ($in === '') return null;
    if (str_contains($in, 'BEGIN')) {
        $der = base64_decode(preg_replace('/-----[^-]+-----|\s+/', '', $in) ?? '', true);
        if ($der !== false && strlen($der) === 44 && substr($der, 0, 12) === hex2bin('302a300506032b6570032100')) return substr($der, 12);
        return null;
    }
    if (preg_match('/^[0-9a-f]{64}$/i', $in)) return hex2bin($in);
    $b = b64u_dec($in); if ($b !== false && strlen($b) === 32) return $b;
    $b = base64_decode($in, true); if ($b !== false && strlen($b) === 32) return $b;
    return null;
}

/**
 * Message context: ['method'=>'GET','authority'=>'host','path'=>'/x','query'=>'?a=b',
 *   'scheme'=>'https','target_uri'=>'https://host/x?a=b','headers'=>['lower-name'=>'value']]
 */
function component_value(string $id, array $ctx): ?string {
    switch ($id) {
        case '@method':         return strtoupper($ctx['method'] ?? '');
        case '@authority':      return strtolower($ctx['authority'] ?? '');
        case '@path':           return ($ctx['path'] ?? '') === '' ? '/' : $ctx['path'];
        case '@query':          return ($ctx['query'] ?? '') === '' ? '?' : $ctx['query'];
        case '@scheme':         return strtolower($ctx['scheme'] ?? 'https');
        case '@target-uri':     return $ctx['target_uri'] ?? (($ctx['scheme'] ?? 'https') . '://' . ($ctx['authority'] ?? '') . ($ctx['path'] ?? '/') . ($ctx['query'] ?? ''));
        case '@request-target': return (($ctx['path'] ?? '') === '' ? '/' : $ctx['path']) . ($ctx['query'] ?? '');
        default:
            if ($id === '' || $id[0] === '@') return null;
            $v = $ctx['headers'][strtolower($id)] ?? null;
            if ($v === null) return null;
            if (is_array($v)) $v = implode(', ', array_map('trim', $v));
            return trim(preg_replace('/[ \t]*\r?\n[ \t]+/', ' ', $v));
    }
}

/** Build the RFC 9421 signature base. $params = everything after "label=" in Signature-Input. */
function signature_base(array $components, string $params, array $ctx): ?string {
    $lines = [];
    foreach ($components as $c) {
        $v = component_value($c, $ctx);
        if ($v === null) return null;
        $lines[] = '"' . $c . '": ' . $v;
    }
    $lines[] = '"@signature-params": ' . $params;
    return implode("\n", $lines);
}

/** Sign a request. Returns headers to add: Signature-Agent, Signature-Input, Signature. */
function sign(array $ctx, string $seed_b64u, string $kid, array $components = DEFAULT_COMPONENTS,
              int $ttl = 300, string $tag = 'web-bot-auth', string $signature_agent = DIRECTORY_URL, string $label = 'sig1'): array {
    $seed = b64u_dec($seed_b64u);
    if ($seed === false || strlen($seed) !== 32) throw new \InvalidArgumentException('bad seed');
    $sk = sodium_crypto_sign_secretkey(sodium_crypto_sign_seed_keypair($seed));
    $created = time(); $expires = $created + $ttl; $nonce = b64u_enc(random_bytes(16));
    $out = [];
    if (in_array('signature-agent', $components, true)) {
        $ctx['headers']['signature-agent'] = '"' . $signature_agent . '"';
        $out['Signature-Agent'] = $ctx['headers']['signature-agent'];
    }
    $params = '(' . implode(' ', array_map(fn($c) => '"' . $c . '"', $components)) . ')'
        . ';created=' . $created . ';expires=' . $expires . ';keyid="' . $kid . '";alg="ed25519";tag="' . $tag . '";nonce="' . $nonce . '"';
    $base = signature_base($components, $params, $ctx);
    if ($base === null) throw new \RuntimeException('missing component for signing');
    $out['Signature-Input'] = $label . '=' . $params;
    $out['Signature']       = $label . '=:' . base64_encode(sodium_crypto_sign_detached($base, $sk)) . ':';
    return $out;
}

/** Parse Signature-Input into [label => ['components'=>[], 'params'=>[k=>v], 'raw'=>string]] */
function parse_signature_input(string $si): array {
    $out = [];
    if (!preg_match_all('/([A-Za-z0-9_\-\.\*]+)=(\([^)]*\)(?:;[^,]*)?)/', $si, $m, PREG_SET_ORDER)) return $out;
    foreach ($m as $mm) {
        if (!preg_match('/^\(([^)]*)\)(.*)$/s', $mm[2], $pm)) continue;
        $comps = preg_match_all('/"([^"]+)"/', $pm[1], $cm) ? $cm[1] : [];
        $p = [];
        foreach (explode(';', ltrim(trim($pm[2]), ';')) as $kv) {
            if ($kv === '') continue;
            [$k, $v] = array_pad(explode('=', $kv, 2), 2, null);
            $p[trim($k)] = $v === null ? true : trim(trim($v), '"');
        }
        $out[$mm[1]] = ['components' => $comps, 'params' => $p, 'raw' => trim($mm[2])];
    }
    return $out;
}

/**
 * Verify a request. $ctx as in component_value (headers must include signature, signature-input).
 * $resolver(string $kid): ?string  -> raw 32-byte public key or null.
 * Options: tag (default web-bot-auth; null = any), skew (sec), require_authority (bool), require_expires (bool)
 */
function verify(array $ctx, callable $resolver, array $opt = []): array {
    $tag = array_key_exists('tag', $opt) ? $opt['tag'] : 'web-bot-auth';
    $skew = $opt['skew'] ?? 60;
    $reqAuth = $opt['require_authority'] ?? true;
    $reqExp  = $opt['require_expires'] ?? true;
    $h = [];
    foreach ($ctx['headers'] ?? [] as $k => $v) $h[strtolower($k)] = $v;
    $ctx['headers'] = $h;
    $fail = fn(string $r, array $extra = []) => ['ok' => false, 'reason' => $r] + $extra;

    $si = $h['signature-input'] ?? null; $sg = $h['signature'] ?? null;
    if (!$si || !$sg) return $fail('missing_signature_headers');
    $inputs = parse_signature_input($si);
    if (!$inputs) return $fail('bad_signature_input');

    // choose the label: first one whose tag matches (or first if tag=null)
    $label = null;
    foreach ($inputs as $l => $in) { if ($tag === null || ($in['params']['tag'] ?? null) === $tag) { $label = $l; break; } }
    if ($label === null) return $fail('no_matching_tag', ['labels' => array_keys($inputs)]);
    $in = $inputs[$label]; $p = $in['params'];

    if (!preg_match('/(?:^|,)\s*' . preg_quote($label, '/') . '=:([A-Za-z0-9+\/=]+):/', $sg, $sm)) return $fail('signature_label_missing', ['label' => $label]);
    $sig = base64_decode($sm[1], true);
    if ($sig === false || strlen($sig) !== 64) return $fail('bad_signature_encoding');

    if (isset($p['alg']) && strtolower($p['alg']) !== 'ed25519') return $fail('unsupported_alg', ['alg' => $p['alg']]);
    $kid = $p['keyid'] ?? null;
    if (!$kid) return $fail('missing_keyid');
    $now = time();
    if (isset($p['created']) && (int)$p['created'] > $now + $skew) return $fail('created_in_future');
    if ($reqExp && !isset($p['expires'])) return $fail('missing_expires');
    if (isset($p['expires']) && (int)$p['expires'] < $now - $skew) return $fail('expired');
    if ($reqAuth && !in_array('@authority', $in['components'], true)) return $fail('authority_not_covered');
    $pk = $resolver($kid);
    if ($pk === null) return $fail('unknown_key', ['kid' => $kid]);
    if (strlen($pk) !== 32) return $fail('bad_public_key');
    $base = signature_base($in['components'], $in['raw'], $ctx);
    if ($base === null) return $fail('missing_component');
    $ok = sodium_crypto_sign_verify_detached($sig, $base, $pk);
    return ['ok' => $ok, 'reason' => $ok ? 'valid' : 'bad_signature', 'kid' => $kid, 'label' => $label,
            'components' => $in['components'], 'created' => isset($p['created']) ? (int)$p['created'] : null,
            'expires' => isset($p['expires']) ? (int)$p['expires'] : null, 'nonce' => $p['nonce'] ?? null, 'tag' => $p['tag'] ?? null,
            'signature_agent' => isset($h['signature-agent']) ? trim($h['signature-agent'], '" ') : null];
}

/** Build a message context from the current PHP request (for verifying incoming requests). */
function ctx_from_server(?array $server = null): array {
    $s = $server ?? $_SERVER;
    $headers = [];
    foreach ($s as $k => $v) if (str_starts_with($k, 'HTTP_')) $headers[strtolower(str_replace('_', '-', substr($k, 5)))] = $v;
    if (isset($s['CONTENT_TYPE'])) $headers['content-type'] = $s['CONTENT_TYPE'];
    $uri = $s['REQUEST_URI'] ?? '/';
    $q = strpos($uri, '?'); $path = $q === false ? $uri : substr($uri, 0, $q); $query = $q === false ? '' : substr($uri, $q);
    $scheme = (($s['HTTPS'] ?? '') !== '' && $s['HTTPS'] !== 'off') || (($headers['x-forwarded-proto'] ?? '') === 'https') ? 'https' : 'http';
    $authority = strtolower($headers['host'] ?? ($s['SERVER_NAME'] ?? ''));
    return ['method' => $s['REQUEST_METHOD'] ?? 'GET', 'authority' => $authority, 'path' => $path, 'query' => $query,
            'scheme' => $scheme, 'target_uri' => $scheme . '://' . $authority . $uri, 'headers' => $headers];
}

/** Resolver that fetches keys from the AgentPass directory with a small file cache. */
function directory_resolver(string $directory = DIRECTORY_URL, int $ttl = 300, ?string $cacheFile = null): callable {
    $cacheFile = $cacheFile ?: sys_get_temp_dir() . '/agentpass-dir-' . md5($directory) . '.json';
    return function (string $kid) use ($directory, $ttl, $cacheFile): ?string {
        $keys = null;
        if (is_file($cacheFile) && filemtime($cacheFile) > time() - $ttl) $keys = json_decode((string)file_get_contents($cacheFile), true);
        if (!is_array($keys) || !isset($keys[$kid])) {
            $j = @file_get_contents(rtrim($directory, '/') . '/api/v1/keys/' . rawurlencode($kid), false,
                stream_context_create(['http' => ['timeout' => 5, 'header' => "Accept: application/json\r\n"]]));
            $d = $j ? json_decode($j, true) : null;
            if (!is_array($keys)) $keys = [];
            if (is_array($d) && isset($d['key']['x']) && ($d['agent']['status'] ?? 'active') === 'active') $keys[$kid] = $d['key']['x'];
            @file_put_contents($cacheFile, json_encode($keys), LOCK_EX);
        }
        if (!isset($keys[$kid])) return null;
        $raw = b64u_dec($keys[$kid]);
        return $raw === false ? null : $raw;
    };
}