'use strict';

const fs = require('fs');
const path = require('path');
const process = require('process');
const express = require('express');
const app = express();
const bodyParser = require('body-parser');
const morgan = require('morgan');
const argv = require('minimist')(process.argv.slice(1));// Command line opts

if (!argv.port) {
    argv.port = 8888;
}

// To catch unhandled exceptions thrown by user code async callbacks,
// these exceptions cannot be catched by try-catch in user function invocation code below
process.on('uncaughtException', (err) => {
    console.error(`Caught exception: ${err}`);
});

// User function.  Starts out undefined.
let userFunction;

function loadFunction(modulepath, funcname) {
    // Read and load the code. It's placed there securely by the fission runtime.
    try {
        let startTime = process.hrtime();
        // support v1 codepath and v2 entrypoint like 'foo', '', 'index.hello'
        let userFunction = funcname ? require(modulepath)[funcname] : require(modulepath);
        let elapsed = process.hrtime(startTime);
        console.log(`user code loaded in ${elapsed[0]}sec ${elapsed[1]/1000000}ms`);
        return userFunction;
    } catch(e) {
        console.error(`user code load error: ${e}`);
        return e;
    }
}

function withEnsureGeneric(func) {
    return function(req, res) {
        // Make sure we're a generic container.  (No reuse of containers.
        // Once specialized, the container remains specialized.)
        if (userFunction) {
            res.status(400).send("Not a generic container");
            return;
        }

        func(req, res);
    }
}

function isFunction(func) {
    return func && func.constructor && func.call && func.apply;
}

function specializeV2(req, res) {
    // for V2 entrypoint, 'filename.funcname' => ['filename', 'funcname']
    const entrypoint = req.body.functionName ? req.body.functionName.split('.') : [];
    // for V2, filepath is dynamic path
    const modulepath = path.join(req.body.filepath, entrypoint[0] || '');
    const result = loadFunction(modulepath, entrypoint[1]);

    if(isFunction(result)){
        userFunction = result;
        res.status(202).send();
    } else {
        res.status(500).send(JSON.stringify(result));
    }
}

function specialize(req, res) {
    // Specialize this server to a given user function.  The user function
    // is read from argv.codepath; it's expected to be placed there by the
    // fission runtime.
    //
    const modulepath = argv.codepath || '/userfunc/user';

    // Node resolves module paths according to a file's location. We load
    // the file from argv.codepath, but tell users to put dependencies in
    // the server's package.json; this means the function's dependencies
    // are in /usr/src/app/node_modules.  We could be smarter and have the
    // function deps in the right place in argv.codepath; b ut for now we
    // just symlink the function's node_modules to the server's
    // node_modules.
    fs.symlinkSync('/usr/src/app/node_modules', `${path.dirname(modulepath)}/node_modules`);

    const result = loadFunction(modulepath);

    if(isFunction(result)){
        userFunction = result;
        res.status(202).send();
    } else {
        res.status(500).send(JSON.stringify(result));
    }
}


// Request logger
app.use(morgan('combined'));

let bodyParserLimit = process.env.BODY_PARSER_LIMIT || '1mb';

app.use(bodyParser.urlencoded({ extended: false, limit: bodyParserLimit}));
app.use(bodyParser.json({limit: bodyParserLimit}));
app.use(bodyParser.raw({limit: bodyParserLimit}));
app.use(bodyParser.text({ type : "text/*", limit: bodyParserLimit }));

app.post('/specialize', withEnsureGeneric(specialize));
app.post('/v2/specialize', withEnsureGeneric(specializeV2));

// Generic route -- all http requests go to the user function.
app.all('/', function (req, res) {
    if (!userFunction) {
        res.status(500).send("Generic container: no requests supported");
        return;
    }

    const context = {
        request: req,
        response: res
        // TODO: context should also have: URL template params, query string
    };

    function callback(status, body, headers) {
        if (!status)
            return;
        if (headers) {
            for (let name of Object.keys(headers)) {
                res.set(name, headers[name]);
            }
        }
        res.status(status).send(body);
    }

    //
    // Customizing the request context
    //
    // If you want to modify the context to add anything to it,
    // you can do that here by adding properties to the context.
    //

    if (userFunction.length <= 1) { // One or zero argument (context)
        let result;
        // Make sure their function returns a promise
        if (userFunction.length === 0) {
            result = Promise.resolve(userFunction())
        } else {
            result = Promise.resolve(userFunction(context))
        }
        result.then(function({status, body, headers}) {
            callback(status, body, headers);
        }).catch(function(err) {
            console.log(`Function error: ${err}`);
            callback(500, "Internal server error");
        });
    } else { // 2 arguments (context, callback)
        try {
            userFunction(context, callback);
        } catch (err) {
            console.log(`Function error: ${err}`);
            callback(500, "Internal server error");
        }
    }

});

app.listen(argv.port);