/** @module persistence */
/** @hidden */
const fs = require('fs');

import { IConfigurable } from 'pip-services3-commons-node';
import { ConfigParams } from 'pip-services3-commons-node';
import { ConfigException } from 'pip-services3-commons-node';
import { FileException } from 'pip-services3-commons-node';
import { JsonConverter } from 'pip-services3-commons-node';
import { ArrayConverter } from 'pip-services3-commons-node';

import { ILoader } from '../ILoader';
import { ISaver } from '../ISaver';

/**
 * Persistence component that loads and saves data from/to flat file.
 * 
 * It is used by [[FilePersistence]], but can be useful on its own.
 * 
 * ### Configuration parameters ###
 * 
 * - path:          path to the file where data is stored
 * 
 * ### Example ###
 * 
 *     let persister = new JsonFilePersister("./data/data.json");
 *     
 *     persister.save("123", ["A", "B", "C"], (err) => {
 *         ...
 *         persister.load("123", (err, items) => {
 *             console.log(items);                      // Result: ["A", "B", "C"]
 *         });
 *     });
 */
export class JsonFilePersister<T> implements ILoader<T>, ISaver<T>, IConfigurable {
    private _path: string;

    /**
     * Creates a new instance of the persistence.
     * 
     * @param path  (optional) a path to the file where data is stored.
     */
    public constructor(path?: string) {
        this._path = path;
    }

    /**
     * Gets the file path where data is stored.
     * 
     * @returns the file path where data is stored.
     */
    public get path(): string {
        return this._path;
    }

    /**
     * Sets the file path where data is stored.
     * 
     * @param value     the file path where data is stored.
     */
    public set path(value: string) {
        this._path = value;
    }

    /**
     * Configures component by passing configuration parameters.
     * 
     * @param config    configuration parameters to be set.
     */
    public configure(config: ConfigParams): void {
        this._path = config.getAsStringWithDefault("path", this._path);
    }

    /**
     * Loads data items from external JSON file.
     * 
     * @param correlation_id    (optional) transaction id to trace execution through call chain.
     * @param callback          callback function that receives loaded items or error.
     */
    public load(correlation_id: string, callback: (err: any, data: T[]) => void): void {
        if (this._path == null) {
            callback(new ConfigException(null, "NO_PATH", "Data file path is not set"), null);
            return;
        }

        if (!fs.existsSync(this._path)) {
            callback(null, []);
            return;
        }

        try {
            let json: any = fs.readFileSync(this._path, "utf8");
            let list = JsonConverter.toNullableMap(json);
            let arr = ArrayConverter.listToArray(list);

            callback(null, arr);
        } catch (ex) {
            let err = new FileException(correlation_id, "READ_FAILED", "Failed to read data file: " + this._path)
                .withCause(ex);

            callback(err, null);
        }
    }

    /**
     * Saves given data items to external JSON file.
     * 
     * @param correlation_id    (optional) transaction id to trace execution through call chain.
     * @param items             list if data items to save
     * @param callback          callback function that error or null for success.
     */
    public save(correlation_id: string, items: T[], callback?: (err: any) => void): void {
        try {
            let json = JsonConverter.toJson(items);
            fs.writeFileSync(this._path, json);
            if (callback) callback(null);
        } catch (ex) {
            let err = new FileException(correlation_id, "WRITE_FAILED", "Failed to write data file: " + this._path)
                .withCause(ex);

            if (callback) callback(err);
            else throw err;
        }
    }

}