package main

import (
    "bytes"
    "encoding/json"
    "fmt"
    "io/ioutil"
    "net/http"
    "os/exec"
    "strings"
    "time"
)

type inbound struct {
    Language string    `json:"language"`
    Source   string    `json:"source"`
    Args     []string  `json:"args"`
}

type problem struct {
    Code    string  `json:"code"`
    Message string  `json:"message"`
}

type outbound struct {
    Ran       bool    `json:"ran"`
    Output    string  `json:"output"`
}

var instance int

func main() {
    port := 2000

    fmt.Println("starting api on port", port)

    http.HandleFunc("/execute", Execute)
    http.ListenAndServe(fmt.Sprintf("0.0.0.0:%d", port), nil)
}

func Execute(res http.ResponseWriter, req *http.Request) {
    res.Header().Set("Content-Type", "application/json")

    // get json
    inbound := inbound{}
    message := json.NewDecoder(req.Body)
    message.Decode(&inbound)

    whitelist := []string{
        "c",
        "cpp", "c++",
        "c#", "csharp", "cs",
        "go",
        "java",
        "nasm", "asm",
        "javascript", "js", "node",
        "php",
        "python", "python2", "python3",
        "r",
        "ruby",
        "swift",
        "brainfuck", "bf",
    }

    // check if the supplied language is supported
    // now calls function and returns
    for _, lang := range whitelist {
        if lang == inbound.Language {
            launch(inbound, res)
            return
        }
    }

    // now only called when the language is not supported
    problem := problem{
        Code: "unsupported_language",
        Message: inbound.Language + " is not supported by Piston",
    }

    pres, _ := json.Marshal(problem)

    res.Write(pres)
}

func launch(request inbound, res http.ResponseWriter) {
    stamp := time.Now().UnixNano()

    // write the code to temp dir
    srcfile := fmt.Sprintf("/tmp/%d.code", stamp)

    ioutil.WriteFile(srcfile, []byte(request.Source), 0644)

    // set up the arguments to send to the execute command
    var args []string

    args = append(args, request.Language)
    args = append(args, srcfile)

    args = append(args, strings.Join(request.Args, "\n"))

    // set up the execution
    cmd := exec.Command("../lxc/execute", args...)

    // capture out/err
    var stdout, stderr bytes.Buffer
    cmd.Stdout = &stdout
    cmd.Stderr = &stderr

    err := cmd.Run()

    // prepare response
    outbound := outbound{
        Ran: err == nil,
        Output: strings.TrimSpace(stdout.String()),
    }

    response, _ := json.Marshal(outbound)

    res.Write(response)
}