/*
Copyright 2011 Google Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package main

// Package cgi implements a CGI (Common Gateway Interface) HTTP handler as specified
// in RFC 3875.  Using CGI isn't usually incredibly efficient and this package
// is intended primarily for compatibility.

import (
	"camli/encoding/line"
	"exec"
	"fmt"
	"http"
	"io"
	"log"
	"os"
	"regexp"
	"strconv"
	"strings"
)

var trailingPort = regexp.MustCompile(`:([0-9]+)$`)

type CgiHandler struct {
	ExecutablePath string
	Root           string // empty is "/"; otherwise must start with "/"
	Environ        []string
	// TODO: custom log.Logger
}

func (h *CgiHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
	pathInfo := req.URL.RawPath
	if strings.HasPrefix(pathInfo, h.Root) {
		pathInfo = pathInfo[len(h.Root):]
	}

	port := "80"
	if matches := trailingPort.FindStringSubmatch(req.Host); len(matches) != 0 {
		port = matches[1]
	}

	env := []string{
		"SERVER_SOFTWARE=golang",
		"SERVER_NAME=" + req.Host,
		"HTTP_HOST=" + req.Host,
		"GATEWAY_INTERFACE=CGI/1.1",
		"REQUEST_METHOD=" + req.Method,
		"QUERY_STRING=" + req.URL.RawQuery,
		"REQUEST_URI=" + req.URL.RawPath,
		"PATH_INFO=" + pathInfo,
		"SCRIPT_NAME=" + h.Root,
		"SCRIPT_FILENAME=" + h.ExecutablePath,
		"REMOTE_ADDR=0.0.0.0", // TODO
		"REMOTE_HOST=",        // TODO
		"SERVER_PORT=" + port,
	}

	for k, v := range req.Header {
		k = strings.Map(upperCaseAndUnderscore, k)
		env = append(env, "HTTP_"+k+"="+v)
	}

	if req.ContentLength > 0 {
		env = append(env, fmt.Sprintf("CONTENT_LENGTH=%d", req.ContentLength))
	}
	if ctype, ok := req.Header["Content-Type"]; ok {
		env = append(env, "CONTENT_TYPE="+ctype)
	}

	if h.Environ != nil {
		env = append(env, h.Environ...)
	}

	cwd := h.ExecutablePath
	if slash := strings.LastIndex(cwd, "/"); slash != -1 {
		cwd = cwd[0:slash]
	}
	if !strings.HasPrefix(cwd, "/") {
		cwd = "."
	}

	cmd, err := exec.Run(
		h.ExecutablePath,
		[]string{h.ExecutablePath},
		env,
		cwd,
		exec.Pipe,        // stdin
		exec.Pipe,        // stdout
		exec.PassThrough, // stderr (for now)
	)
	if err != nil {
		rw.WriteHeader(http.StatusInternalServerError)
		log.Printf("CGI error: %v", err)
		return
	}
	defer func() {
		cmd.Stdin.Close()
		cmd.Stdout.Close()
		cmd.Wait(0)  // no zombies
	}()

	if req.ContentLength != 0 {
		go func() {
			io.Copy(cmd.Stdin, req.Body)
		}()
	}

	linebody := line.NewReader(cmd.Stdout, 1024)
	headers := make(map[string]string)
	statusCode := http.StatusOK
	for {
		line, isPrefix, err := linebody.ReadLine()
		if isPrefix {
			rw.WriteHeader(http.StatusInternalServerError)
			log.Printf("CGI: long header line from subprocess.")
			return
		}
		if err == os.EOF {
			break
		}
		if err != nil {
			rw.WriteHeader(http.StatusInternalServerError)
			log.Printf("CGI: error reading headers: %v", err)
			return
		}
		if len(line) == 0 {
			break
		}
		parts := strings.Split(string(line), ":", 2)
		if len(parts) < 2 {
			log.Printf("CGI: bogus header line: %s", string(line))
			continue
		}
		h, v := parts[0], parts[1]
		h = strings.TrimSpace(h)
		v = strings.TrimSpace(v)
		switch {
		case h == "Status":
			if len(v) < 3 {
				log.Printf("CGI: bogus status (short): %q", v)
				return
			}
			code, err := strconv.Atoi(v[0:3])
			if err != nil {
				log.Printf("CGI: bogus status: %q", v)
				log.Printf("CGI: line was %q", line)
				return
			}
			statusCode = code
		default:
			headers[h] = v
		}
	}
	for h, v := range headers {
		rw.SetHeader(h, v)
	}
	rw.WriteHeader(statusCode)

	_, err = io.Copy(rw, linebody)
	if err != nil {
		log.Printf("CGI: copy error: %v", err)
	}
}

func upperCaseAndUnderscore(rune int) int {
	switch {
	case rune >= 'a' && rune <= 'z':
		return rune - ('a' - 'A')
	case rune == '-':
		return '_'
	}
	return rune
}