// mirror files from upstream NVD source
package nvdmirror

import (
  "fmt"
  "github.com/rs/zerolog/log"
  "io"
  "net/http"
  "net/url"
  "os"
  "path/filepath"
  "time"
)

// default user agent (FIXME: make configurable)
var defaultUserAgent = "cvez/0.1.0"

// Sync() configuration.
type SyncConfig struct {
  // CVE 1.1 Base URL.  The full meta and JSON URLs are constructed by
  // appending the file name to this base.
  Cve11BaseUrl string

  // CPE 1.0 base URL.  The full meta and JSON URLs are constructed by
  // appending the file name to this base.
  Cpe10MatchBaseUrl string

  // CPE 2.3 dictionary URL.
  Cpe23DictUrl string

  // User agent string.  Set to "" for default user agent string.
  UserAgent string

  // Maximum number of idle connections.
	MaxIdleConns int

  // Idle connection timeout.
	IdleConnTimeout time.Duration
}

// Get user agent string.
func (me SyncConfig) GetUserAgent() string {
  if len(me.UserAgent) > 0 {
    return me.UserAgent
  } else {
    return defaultUserAgent
  }
}

// NVD URLs
var DefaultConfig = SyncConfig {
  Cve11BaseUrl: "https://nvd.nist.gov/feeds/json/cve/1.1",
  Cpe10MatchBaseUrl: "https://nvd.nist.gov/feeds/json/cpematch/1.0",
  Cpe23DictUrl: "https://nvd.nist.gov/feeds/xml/cpe/dictionary/official-cpe-dictionary_v2.3.xml.gz",
}

var extraFiles = []string {
  "nvdcve-1.1-modified",
  "nvdcve-1.1-recent",
}

// fetch result
type fetchResult struct {
  src string // source URL
  err error // fetch result
  modified bool // was the result modified?
  lastModified string // last modified response header
  etag string // etag response header
}

// base CVE year
const baseYear = 2002

func fetch(ch chan fetchResult, config SyncConfig, cache Cache, client *http.Client, srcUrl string, dstDir string) {
  // parse source url
  src, err := url.Parse(srcUrl)
  if err != nil {
    ch <- fetchResult { src: srcUrl, err: err }
    return
  }

  // build destination path
  path := filepath.Join(dstDir, filepath.Base(src.Path))
  log.Debug().Str("url", srcUrl).Str("path", path).Send()

  // create temporary output file
  f, err := os.CreateTemp(filepath.Dir(path), "")
  if err != nil {
    ch <- fetchResult { src: srcUrl, err: err }
    return
  }
  defer os.Remove(f.Name())

  // create request
  req, err := http.NewRequest("GET", srcUrl, nil)
  if err != nil {
    ch <- fetchResult { src: srcUrl, err: err }
    return
  }

  // add request headers
  req.Header.Add("user-agent", config.GetUserAgent())
  if headers, ok := cache.Get(srcUrl); ok {
    for k, v := range(headers) {
      req.Header.Add(k, v)
    }
  }

  // send request
  resp, err := client.Do(req)
  if err != nil {
    ch <- fetchResult { src: srcUrl, err: err }
    return
  }
  defer resp.Body.Close()

  switch resp.StatusCode {
  case 200:
    // copy body to result
    if size, err := io.Copy(f, resp.Body); err != nil {
      // copy failed
      ch <- fetchResult { src: srcUrl, err: err, modified: false }
    } else if err = os.Rename(f.Name(), path); err != nil {
      // rename failed
      ch <- fetchResult { src: srcUrl, err: err, modified: false }
    } else {
      log.Debug().Str("url", srcUrl).Int64("size", size).Send()
      ch <- fetchResult {
        src: srcUrl,
        modified: true,
        lastModified: resp.Header.Get("last-modified"),
        etag: resp.Header.Get("etag"),
      }
    }
  case 304:
    ch <- fetchResult { src: srcUrl, modified: false }
  default:
    code := resp.StatusCode
    err := fmt.Errorf("%d: %s", code, http.StatusText(code))
    ch <- fetchResult { src: srcUrl, err: err }
  }
}

func Sync(config SyncConfig, cache Cache, dstDir string) error {
  log.Debug().Str("dstDir", dstDir).Msg("Sync")

  // create fetch result channel
  ch := make(chan fetchResult)

  // create shared transport and client
  tr := &http.Transport{
	  MaxIdleConns:     config.MaxIdleConns,
	  IdleConnTimeout:  config.IdleConnTimeout,
  }
  client := &http.Client{Transport: tr}

  // calculate total number of years
  numYears := time.Now().Year() - baseYear + 1

  // fetch cve feed metas
  for year := baseYear; year < baseYear + numYears; year++ {
    // build url
    url := fmt.Sprintf("%s/nvdcve-1.1-%04d.meta", config.Cve11BaseUrl, year)
    log.Debug().Int("year", year).Str("url", url).Send()
    go fetch(ch, config, cache, client, url, dstDir)
  }

  // fetch cve extra file metas
  for _, s := range(extraFiles) {
    url := fmt.Sprintf("%s/%s.meta", config.Cve11BaseUrl, s)
    log.Debug().Str("file", s).Str("url", url).Send()
    go fetch(ch, config, cache, client, url, dstDir)
  }

  // read results
  for i := 0; i < numYears + len(extraFiles); i++ {
    if r := <-ch; r.err != nil {
      log.Error().Str("url", r.src).Err(r.err).Send()
      // FIXME: errs = append(errs, r)
    } else {
      log.Info().Str("url", r.src).Str("etag", r.etag).Msg("ok")

      if r.modified {
        // build request headers
        headers := map[string]string {
          "if-none-match": r.etag,
          "if-modified-since": r.lastModified,
        }

        // save headers to cache
        if err := cache.Set(r.src, headers); err != nil {
          log.Error().Str("url", r.src).Err(r.err).Msg("Set")
          return err
        }
      }
    }
  }

  // TODO: fetch cpe dictionary
  // TODO: fetch cpematch
  // "nvdcpematch-1.0.{meta,json}",

  // return success
  return nil
}