const fs = require('fs');
const path = require('path');

/**
 * Current config version. All config JSONs should declare this version.
 * Bump this when the config schema changes.
 */
const CURRENT_CONFIG_VERSION = '1.0.0';

class ConfigManager {
    constructor(relPath = '.') {
        this.configDir = path.resolve(__dirname, relPath);

        /**
         * Migration functions keyed by "fromVersion->toVersion".
         * Each function receives a config object and returns the migrated config.
         *
         * Example:
         *   this.migrations['1.0.0->1.1.0'] = (config) => {
         *       config.newSection = { enabled: false };
         *       return config;
         *   };
         */
        this.migrations = {};
    }

    /**
     * Load a configuration file by name.
     * Automatically checks the config version and migrates if needed.
     * @param {string} configName - Name of the config file (without .json extension)
     * @returns {Object} Parsed configuration object (migrated to current version if necessary)
     */
    getConfig(configName) {
        try {
            const configPath = path.resolve(this.configDir, `${configName}.json`);
            const configData = fs.readFileSync(configPath, 'utf8');
            let config = JSON.parse(configData);

            // Auto-migrate if version is behind current
            const configVersion = config.version || '0.0.0';
            if (configVersion !== CURRENT_CONFIG_VERSION) {
                config = this.migrateConfig(config, configVersion, CURRENT_CONFIG_VERSION);
            }

            return config;
        } catch (error) {
            if (error.message && error.message.startsWith('Failed to load config')) {
                throw error;
            }
            throw new Error(`Failed to load config '${configName}': ${error.message}`);
        }
    }

    /**
     * Get list of available configuration files
     * @returns {Array<string>} Array of config names (without .json extension)
     */
    getAvailableConfigs() {
        try {
            const resolvedDir = path.resolve(this.configDir);
            const files = fs.readdirSync(resolvedDir);
            return files
                .filter(file => file.endsWith('.json'))
                .map(file => path.basename(file, '.json'));
        } catch (error) {
            throw new Error(`Failed to read config directory: ${error.message}`);
        }
    }

    /**
     * Check if a specific config exists
     * @param {string} configName - Name of the config file
     * @returns {boolean} True if config exists
     */
    hasConfig(configName) {
        const configPath = path.resolve(this.configDir, `${configName}.json`);
        return fs.existsSync(configPath);
    }

    /**
     * Build a runtime config by merging base schema + node schema + UI overrides.
     * Eliminates the need for each nodeClass to manually construct general/asset/functionality sections.
     *
     * @param {string} nodeName - Node type name (e.g., 'valve', 'measurement')
     * @param {object} uiConfig - Raw config from Node-RED UI
     * @param {string} nodeId - Node-RED node ID (from node.id)
     * @param {object} [domainConfig={}] - Domain-specific config sections (e.g., { scaling: {...}, smoothing: {...} })
     * @returns {object} Merged runtime config
     *
     * @example
     * const cfgMgr = new ConfigManager();
     * const config = cfgMgr.buildConfig('measurement', uiConfig, node.id, {
     *   scaling: { enabled: uiConfig.scaling, inputMin: uiConfig.i_min, ... },
     *   smoothing: { smoothWindow: uiConfig.count, ... }
     * });
     */
    buildConfig(nodeName, uiConfig, nodeId, domainConfig = {}) {
        // Build base sections from UI config (common to ALL nodes)
        const config = {
            general: {
                name: uiConfig.name || nodeName,
                id: nodeId,
                unit: uiConfig.unit || 'unitless',
                logging: {
                    enabled: uiConfig.enableLog !== undefined ? uiConfig.enableLog : true,
                    logLevel: uiConfig.logLevel || 'info'
                }
            },
            functionality: {
                softwareType: nodeName.toLowerCase(),
                positionVsParent: uiConfig.positionVsParent || 'atEquipment',
                distance: uiConfig.hasDistance ? uiConfig.distance : undefined
            }
        };

        // Add asset section if UI provides asset fields
        if (uiConfig.supplier || uiConfig.category || uiConfig.assetType || uiConfig.model) {
            config.asset = {
                uuid: uiConfig.uuid || uiConfig.assetUuid || null,
                tagCode: uiConfig.tagCode || uiConfig.assetTagCode || null,
                supplier: uiConfig.supplier || 'Unknown',
                category: uiConfig.category || 'sensor',
                type: uiConfig.assetType || 'Unknown',
                model: uiConfig.model || 'Unknown',
                unit: uiConfig.unit || 'unitless'
            };
        }

        // Merge domain-specific sections
        Object.assign(config, domainConfig);

        return config;
    }

    /**
     * Migrate a config object from one version to another by applying
     * registered migration functions in sequence.
     * @param {object} config - The config object to migrate
     * @param {string} fromVersion - Current version of the config
     * @param {string} toVersion - Target version
     * @returns {object} Migrated config with updated version field
     */
    migrateConfig(config, fromVersion, toVersion) {
        const migrationKey = `${fromVersion}->${toVersion}`;
        const migrationFn = this.migrations[migrationKey];

        if (migrationFn) {
            config = migrationFn(config);
        }

        // Stamp the current version so it won't re-migrate
        config.version = toVersion;
        return config;
    }

    /**
     * Get the base config schema (shared across all nodes).
     * @returns {object} Base config schema
     */
    getBaseConfig() {
        return this.getConfig('baseConfig');
    }

    createEndpoint(nodeName) {
        try {
            const config = this.getConfig(nodeName);
            const configJSON = JSON.stringify(config, null, 2);

            return `
                window.EVOLV = window.EVOLV || {};
                window.EVOLV.nodes = window.EVOLV.nodes || {};
                window.EVOLV.nodes.${nodeName} = window.EVOLV.nodes.${nodeName} || {};
                window.EVOLV.nodes.${nodeName}.config = ${configJSON};
                console.log('${nodeName} config loaded and endpoint created');
            `;
        } catch (error) {
            throw new Error(`Failed to create endpoint for '${nodeName}': ${error.message}`);
        }
    }
}

module.exports = ConfigManager;