lib/common/plugin/FileWriter.js

var exec = require('cordova/exec'),
    FileError = require('cordova/plugin/FileError'),
    ProgressEvent = require('cordova/plugin/ProgressEvent');

/**
 * This class writes to the mobile device file system.
 *
 * For Android:
 *      The root directory is the root of the file system.
 *      To write to the SD card, the file name is "sdcard/my_file.txt"
 *
 * @constructor
 * @param file {File} File object containing file properties
 * @param append if true write to the end of the file, otherwise overwrite the file
 */
var FileWriter = function(file) {
    this.fileName = "";
    this.length = 0;
    if (file) {
        this.fileName = file.fullPath || file;
        this.length = file.size || 0;
    }
    // default is to write at the beginning of the file
    this.position = 0;

    this.readyState = 0; // EMPTY

    this.result = null;

    // Error
    this.error = null;

    // Event handlers
    this.onwritestart = null;   // When writing starts
    this.onprogress = null;     // While writing the file, and reporting partial file data
    this.onwrite = null;        // When the write has successfully completed.
    this.onwriteend = null;     // When the request has completed (either in success or failure).
    this.onabort = null;        // When the write has been aborted. For instance, by invoking the abort() method.
    this.onerror = null;        // When the write has failed (see errors).
};

// States
FileWriter.INIT = 0;
FileWriter.WRITING = 1;
FileWriter.DONE = 2;

/**
 * Abort writing file.
 */
FileWriter.prototype.abort = function() {
    // check for invalid state
    if (this.readyState === FileWriter.DONE || this.readyState === FileWriter.INIT) {
        throw new FileError(FileError.INVALID_STATE_ERR);
    }

    // set error
    this.error = new FileError(FileError.ABORT_ERR);

    this.readyState = FileWriter.DONE;

    // If abort callback
    if (typeof this.onabort === "function") {
        this.onabort(new ProgressEvent("abort", {"target":this}));
    }

    // If write end callback
    if (typeof this.onwriteend === "function") {
        this.onwriteend(new ProgressEvent("writeend", {"target":this}));
    }
};

/**
 * Writes data to the file
 *
 * @param text to be written
 */
FileWriter.prototype.write = function(text) {
    // Throw an exception if we are already writing a file
    if (this.readyState === FileWriter.WRITING) {
        throw new FileError(FileError.INVALID_STATE_ERR);
    }

    // WRITING state
    this.readyState = FileWriter.WRITING;

    var me = this;

    // If onwritestart callback
    if (typeof me.onwritestart === "function") {
        me.onwritestart(new ProgressEvent("writestart", {"target":me}));
    }

    // Write file
    exec(
        // Success callback
        function(r) {
            // If DONE (cancelled), then don't do anything
            if (me.readyState === FileWriter.DONE) {
                return;
            }

            // position always increases by bytes written because file would be extended
            me.position += r;
            // The length of the file is now where we are done writing.

            me.length = me.position;

            // DONE state
            me.readyState = FileWriter.DONE;

            // If onwrite callback
            if (typeof me.onwrite === "function") {
                me.onwrite(new ProgressEvent("write", {"target":me}));
            }

            // If onwriteend callback
            if (typeof me.onwriteend === "function") {
                me.onwriteend(new ProgressEvent("writeend", {"target":me}));
            }
        },
        // Error callback
        function(e) {
            // If DONE (cancelled), then don't do anything
            if (me.readyState === FileWriter.DONE) {
                return;
            }

            // DONE state
            me.readyState = FileWriter.DONE;

            // Save error
            me.error = new FileError(e);

            // If onerror callback
            if (typeof me.onerror === "function") {
                me.onerror(new ProgressEvent("error", {"target":me}));
            }

            // If onwriteend callback
            if (typeof me.onwriteend === "function") {
                me.onwriteend(new ProgressEvent("writeend", {"target":me}));
            }
        }, "File", "write", [this.fileName, text, this.position]);
};

/**
 * Moves the file pointer to the location specified.
 *
 * If the offset is a negative number the position of the file
 * pointer is rewound.  If the offset is greater than the file
 * size the position is set to the end of the file.
 *
 * @param offset is the location to move the file pointer to.
 */
FileWriter.prototype.seek = function(offset) {
    // Throw an exception if we are already writing a file
    if (this.readyState === FileWriter.WRITING) {
        throw new FileError(FileError.INVALID_STATE_ERR);
    }

    if (!offset && offset !== 0) {
        return;
    }

    // See back from end of file.
    if (offset < 0) {
        this.position = Math.max(offset + this.length, 0);
    }
    // Offset is bigger then file size so set position
    // to the end of the file.
    else if (offset > this.length) {
        this.position = this.length;
    }
    // Offset is between 0 and file size so set the position
    // to start writing.
    else {
        this.position = offset;
    }
};

/**
 * Truncates the file to the size specified.
 *
 * @param size to chop the file at.
 */
FileWriter.prototype.truncate = function(size) {
    // Throw an exception if we are already writing a file
    if (this.readyState === FileWriter.WRITING) {
        throw new FileError(FileError.INVALID_STATE_ERR);
    }

    // WRITING state
    this.readyState = FileWriter.WRITING;

    var me = this;

    // If onwritestart callback
    if (typeof me.onwritestart === "function") {
        me.onwritestart(new ProgressEvent("writestart", {"target":this}));
    }

    // Write file
    exec(
        // Success callback
        function(r) {
            // If DONE (cancelled), then don't do anything
            if (me.readyState === FileWriter.DONE) {
                return;
            }

            // DONE state
            me.readyState = FileWriter.DONE;

            // Update the length of the file
            me.length = r;
            me.position = Math.min(me.position, r);

            // If onwrite callback
            if (typeof me.onwrite === "function") {
                me.onwrite(new ProgressEvent("write", {"target":me}));
            }

            // If onwriteend callback
            if (typeof me.onwriteend === "function") {
                me.onwriteend(new ProgressEvent("writeend", {"target":me}));
            }
        },
        // Error callback
        function(e) {
            // If DONE (cancelled), then don't do anything
            if (me.readyState === FileWriter.DONE) {
                return;
            }

            // DONE state
            me.readyState = FileWriter.DONE;

            // Save error
            me.error = new FileError(e);

            // If onerror callback
            if (typeof me.onerror === "function") {
                me.onerror(new ProgressEvent("error", {"target":me}));
            }

            // If onwriteend callback
            if (typeof me.onwriteend === "function") {
                me.onwriteend(new ProgressEvent("writeend", {"target":me}));
            }
        }, "File", "truncate", [this.fileName, size]);
};

module.exports = FileWriter;