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package document
import (
"fmt"
"os"
"unsafe"
"reflect"
"math"
"runtime"
"sync"
"crypto/hmac"
"crypto/sha256"
"github.com/scrotadamus/ghligh/go-poppler"
)
var ghlighKey = []byte("ghligh-pdf-doc")
var bufPool = sync.Pool{
New: func() interface{} {
return make([]byte, 0, os.Getpagesize())
},
}
type pageResult struct {
index int
buf []byte
}
func sqrtInt(n int) int{
return int(math.Sqrt(float64(n)))
}
func continueAt(i, n int) bool {
// Very unlikely to edit a pdf and add a page in the center
return i < sqrtInt(n)/2 || i > n - sqrtInt(n)/2
}
// generate identifier from document based on document text (use layout instead)
func (d *GhlighDoc) HashDoc() string {
nPages := d.doc.GetNPages()
hmacHash := hmac.New(sha256.New, ghlighKey)
resultsCh := make(chan pageResult, nPages)
var wg sync.WaitGroup
maxWorkers := runtime.NumCPU() + 1
sem := make(chan struct{}, maxWorkers)
for i := 0; continueAt(i, nPages); i++ {
wg.Add(1)
sem <- struct{}{}
go func(i int) {
defer wg.Done()
defer func() { <-sem }()
page := d.doc.GetPage(i)
text := page.Text()
page.Close()
buf := bufPool.Get().([]byte)
buf = buf[:0]
buf = append(buf, []byte(text)...)
resultsCh <- pageResult{index: i, buf: buf}
}(i)
}
wg.Wait()
close(resultsCh)
results := make([][]byte, nPages)
for res := range resultsCh {
results[res.index] = res.buf
}
for i := 0; continueAt(i, nPages); i++ {
hmacHash.Write(results[i])
hmacHash.Write([]byte{byte(i)})
bufPool.Put(results[i])
}
hmacHash.Write([]byte{byte(nPages)})
return fmt.Sprintf("%x", hmacHash.Sum(nil))
}
func rectToBytes(r *poppler.Rectangle) []byte {
size := int(unsafe.Sizeof(*r))
var sliceHeader reflect.SliceHeader
sliceHeader.Data = uintptr(unsafe.Pointer(r))
sliceHeader.Len = size
sliceHeader.Cap = size
return *(*[]byte)(unsafe.Pointer(&sliceHeader))
}
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