<?php
/**
 * PubChem PUG REST API integration for molecular data enrichment.
 *
 * What: Fetches verified molecular data (formula, weight, SMILES, InChI) from PubChem.
 * Who calls it: PSA_AI_Generator::background_generate() during peptide content generation.
 * Dependencies: WordPress HTTP API (wp_remote_get), PSA_Config for cache TTL.
 *
 * @package PeptideSearchAI
 * @see     includes/class-psa-ai-generator.php
 */
declare( strict_types=1 );

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

class PSA_PubChem {

	const API_BASE = 'https://pubchem.ncbi.nlm.nih.gov/rest/pug';

	/**
	 * Look up a peptide/compound by name and return molecular properties.
	 * Results are cached in transients to respect PubChem rate limits.
	 *
	 * @param string $name Peptide or compound name.
	 * @return array|WP_Error|null Array of properties, WP_Error on failure, or null if not found.
	 */
	public static function lookup( string $name ) {
		$options     = get_option( 'psa_settings', array() );
		$use_pubchem = $options['use_pubchem'] ?? '1';

		if ( '1' !== $use_pubchem ) {
			return null;
		}

		// Check cache first (respect PubChem's 5 req/sec limit).
		$cache_key = 'psa_pubchem_' . md5( strtolower( trim( $name ) ) );
		$cached    = get_transient( $cache_key );
		if ( false !== $cached ) {
			// We store 'not_found' string to differentiate from cache miss.
			if ( 'not_found' === $cached ) {
				return null;
			}
			if ( is_wp_error( $cached ) ) {
				return $cached;
			}
			return $cached;
		}

		// Step 1: Get the CID by compound name.
		$cid = self::get_cid_by_name( $name );
		if ( is_wp_error( $cid ) ) {
			set_transient( $cache_key, $cid, 1 * HOUR_IN_SECONDS );
			return $cid;
		}
		if ( ! $cid ) {
			set_transient( $cache_key, 'not_found', 12 * HOUR_IN_SECONDS );
			return null;
		}

		// Step 2: Get properties by CID.
		$properties = self::get_properties( $cid );
		if ( is_wp_error( $properties ) ) {
			set_transient( $cache_key, $properties, 1 * HOUR_IN_SECONDS );
			return $properties;
		}
		if ( ! $properties ) {
			set_transient( $cache_key, 'not_found', 12 * HOUR_IN_SECONDS );
			return null;
		}

		$properties['cid'] = $cid;

		// Cache successful lookups for 7 days.
		$ttl = PSA_Config::PUBCHEM_CACHE_TTL ? PSA_Config::PUBCHEM_CACHE_TTL : 7 * DAY_IN_SECONDS;
		set_transient( $cache_key, $properties, $ttl );

		return $properties;
	}

	/**
	 * Get PubChem Compound ID (CID) by name.
	 *
	 * @param string $name Compound name.
	 * @return int|WP_Error|null CID, WP_Error on API failure, or null if not found.
	 */
	private static function get_cid_by_name( string $name ) {
		$url = self::API_BASE . '/compound/name/' . rawurlencode( $name ) . '/cids/JSON';

		$response = wp_remote_get(
			$url,
			array(
				'timeout' => 15,
				'headers' => array( 'Accept' => 'application/json' ),
			)
		);

		if ( is_wp_error( $response ) ) {
			return new WP_Error( 'pubchem_api_error', 'PubChem API request failed: ' . $response->get_error_message() );
		}

		$code = wp_remote_retrieve_response_code( $response );
		if ( 200 !== $code ) {
			return new WP_Error( 'pubchem_http_error', 'PubChem returned HTTP ' . $code );
		}

		$body = json_decode( wp_remote_retrieve_body( $response ), true );

		return isset( $body['IdentifierList']['CID'][0] )
			? (int) $body['IdentifierList']['CID'][0]
			: null;
	}

	/**
	 * Get molecular properties for a given CID.
	 *
	 * @param int $cid PubChem Compound ID.
	 * @return array|WP_Error|null Properties array, WP_Error on failure, or null if not found.
	 */
	private static function get_properties( int $cid ) {
		$props = 'MolecularFormula,MolecularWeight,IUPACName,CanonicalSMILES,InChI';
		$url   = self::API_BASE . '/compound/cid/' . (int) $cid . '/property/' . $props . '/JSON';

		$response = wp_remote_get(
			$url,
			array(
				'timeout' => 15,
				'headers' => array( 'Accept' => 'application/json' ),
			)
		);

		if ( is_wp_error( $response ) ) {
			return new WP_Error( 'pubchem_api_error', 'PubChem API request failed: ' . $response->get_error_message() );
		}

		$code = wp_remote_retrieve_response_code( $response );
		if ( 200 !== $code ) {
			return new WP_Error( 'pubchem_http_error', 'PubChem returned HTTP ' . $code );
		}

		$body = json_decode( wp_remote_retrieve_body( $response ), true );

		if ( ! isset( $body['PropertyTable']['Properties'][0] ) ) {
			return null;
		}

		$p = $body['PropertyTable']['Properties'][0];

		return array(
			'molecular_formula' => $p['MolecularFormula'] ?? '',
			'molecular_weight'  => isset( $p['MolecularWeight'] ) ? $p['MolecularWeight'] . ' Da' : '',
			'iupac_name'        => $p['IUPACName'] ?? '',
			'smiles'            => $p['CanonicalSMILES'] ?? '',
			'inchi'             => $p['InChI'] ?? '',
		);
	}
}