package feed

import (
  "encoding/json"
  "fmt"
  "regexp"
  "strconv"
)

// CVE ID
type CveId uint32

var cveIdRe = regexp.MustCompile("\\ACVE-(\\d{4})-(\\d{1,8})\\z")

// parse year component of CVE ID
func parseCveIdYear(s string) (uint16, error) {
  // parse year, check for error
  year, err := strconv.ParseUint(s, 10, 16)
  if err != nil {
    return 0, err
  }

  // check bounds
  if year < 1999 || year > 2126 {
    return 0, fmt.Errorf("year out of bounds: %s", s)
  }

  // return value
  return uint16(year), nil
}

// parse number component of CVE ID
func parseCveIdNum(s string) (uint32, error) {
  // parse number, check for error
  num, err := strconv.ParseUint(s, 10, 32)
  if err != nil {
    return 0, err
  }

  // check bounds
  if num > 0x01ffffff {
    return 0, fmt.Errorf("number out of bounds: %d", num)
  }

  // return value
  return uint32(num), nil
}

// Encode CVE ID as uint32.  
func encodeCveId(year uint16, num uint32) uint32 {
  return uint32((uint32((year - 1999) & 0x7f) << 25) | (num & 0x01ffffff))
}

// Create CVE ID from string.
func NewCveId(s string) (CveId, error) {
  // match components, check for error
  md := cveIdRe.FindStringSubmatch(s)
  if len(md) != 3 {
    return CveId(0), fmt.Errorf("invalid CVE ID: %s", s)
  }

  // parse year, check for error
  year, err := parseCveIdYear(md[1])
  if err != nil {
    return CveId(0), err
  }

  // parse number, check for error
  num, err := parseCveIdNum(md[2])
  if err != nil {
    return CveId(0), err
  }

  // encode and return result
  return CveId(encodeCveId(year, num)), nil
}

// Marshal CVE ID to JSON.
func (me CveId) MarshalJSON() ([]byte, error) {
  return json.Marshal(me.String())
}

// Unmarshal CVE ID from JSON.
func (me *CveId) UnmarshalJSON(b []byte) error {
  // decode string, check for error
  var s string
  if err := json.Unmarshal(b, &s); err != nil {
    return err
  }

  // parse year, check for error
  r, err := NewCveId(s)
  if err != nil {
    return err
  }

  // serialize ID
  *me = r

  // return success
  return nil
}

// Get year component.
func (me CveId) Year() uint16 {
  return uint16((uint32(me) >> 25) & 0x7f) + 1999
}

// Get number component.
func (me CveId) Number() uint32 {
  return (uint32(me) & 0x01ffffff)
}

// Return string representation of CVE ID.
func (me CveId) String() string {
  return fmt.Sprintf("CVE-%04d-%04d", me.Year(), me.Number())
}