var eos = require(‘end-of-stream‘);

eos(readableStream, function(err) {
  // this will be set to the stream instance
    if (err) return console.log(‘stream had an error or closed early‘);
    console.log(‘stream has ended‘, this === readableStream);//readableStream关闭可读是end，上下文环境this即readableStream
});

eos(writableStream, function(err) {
    if (err) return console.log(‘stream had an error or closed early‘);
    console.log(‘stream has finished‘, this === writableStream);//writableStream关闭可写是finish
});

eos(duplexStream, function(err) {
    if (err) return console.log(‘stream had an error or closed early‘);
    console.log(‘stream has ended and finished‘, this === duplexStream);//duplexStream关闭要end和finish
});

eos(duplexStream, {readable:false}, function(err) {
    if (err) return console.log(‘stream had an error or closed early‘);
    console.log(‘stream has finished but might still be readable‘);//{readable:false}即不end，该duplexStream可能还能读
});

eos(duplexStream, {writable:false}, function(err) {
    if (err) return console.log(‘stream had an error or closed early‘);
    console.log(‘stream has ended but might still be writable‘);//{writable:false}即不finish，该duplexStream可能还能写
});

eos(readableStream, {error:false}, function(err) {
    // do not treat emit(‘error‘, err) as a end-of-stream
});

var once = require(‘once‘);

var noop = function() {};

var isRequest = function(stream) {
    return stream.setHeader && typeof stream.abort === ‘function‘;
};

var isChildProcess = function(stream) {
    return stream.stdio && Array.isArray(stream.stdio) && stream.stdio.length === 3
};

var eos = function(stream, opts, callback) {
    if (typeof opts === ‘function‘) return eos(stream, null, opts);
    if (!opts) opts = {};

    callback = once(callback || noop);

    var ws = stream._writableState;
    var rs = stream._readableState;
    var readable = opts.readable || (opts.readable !== false && stream.readable);
    var writable = opts.writable || (opts.writable !== false && stream.writable);

    var onlegacyfinish = function() {
        if (!stream.writable) onfinish();
    };

    var onfinish = function() {
        writable = false;
        if (!readable) callback.call(stream);
    };

    var onend = function() {
        readable = false;
        if (!writable) callback.call(stream);
    };

    var onexit = function(exitCode) {
        callback.call(stream, exitCode ? new Error(‘exited with error code: ‘ + exitCode) : null);
    };

    var onerror = function(err) {
        callback.call(stream, err);
    };

    var onclose = function() {
        if (readable && !(rs && rs.ended)) return callback.call(stream, new Error(‘premature close‘));
        if (writable && !(ws && ws.ended)) return callback.call(stream, new Error(‘premature close‘));
    };

    var onrequest = function() {
        stream.req.on(‘finish‘, onfinish);
    };

    if (isRequest(stream)) {
        stream.on(‘complete‘, onfinish);
        stream.on(‘abort‘, onclose);
        if (stream.req) onrequest();
        else stream.on(‘request‘, onrequest);
    } else if (writable && !ws) { // legacy streams
        stream.on(‘end‘, onlegacyfinish);
        stream.on(‘close‘, onlegacyfinish);
    }

    if (isChildProcess(stream)) stream.on(‘exit‘, onexit);
    
    //三类事件的监听
    stream.on(‘end‘, onend);
    stream.on(‘finish‘, onfinish);
    if (opts.error !== false) stream.on(‘error‘, onerror);
    stream.on(‘close‘, onclose);

    return function() {
        stream.removeListener(‘complete‘, onfinish);//移除改事件并调用onfinish函数
        stream.removeListener(‘abort‘, onclose);
        stream.removeListener(‘request‘, onrequest);
        if (stream.req) stream.req.removeListener(‘finish‘, onfinish);
        stream.removeListener(‘end‘, onlegacyfinish);
        stream.removeListener(‘close‘, onlegacyfinish);
        stream.removeListener(‘finish‘, onfinish);
        stream.removeListener(‘exit‘, onexit);
        stream.removeListener(‘end‘, onend);
        stream.removeListener(‘error‘, onerror);
        stream.removeListener(‘close‘, onclose);
    };
};

module.exports = eos;