package asses

import (
	"context"
	"crypto/md5"
	"encoding/base64"
	"fmt"
	"io"
	"log"
	"math/rand"
	"os"
	"path"
	"show-rss/src/slow"
	"time"
)

func One(ctx context.Context, p string) error {
	shortp := path.Join("...", path.Base(path.Dir(p)), path.Base(p))

	last, err := checkLast(ctx, p)
	if err != nil {
		return err
	}

   threshold := 20 + rand.Int()%10
	if daysSince := int(time.Since(last.T).Hours()/24);  daysSince > threshold {
      log.Printf("asses.One(%s) // no modified check as %vd since last check", shortp, daysSince)
	} else if stat, err := os.Stat(p); err != nil {
		return fmt.Errorf("cannot stat %s: %w", p, err)
	} else if stat.ModTime() == last.Modified {
		log.Printf("asses.One(%s) // unmodified since %v", shortp, last.T)
		return nil
	} else {
		log.Printf("asses.One(%s) // modified (%v) is now %v", shortp, last.Modified, stat.ModTime())
   }

	if err := func() error {
		if len(last.Cksum) > 0 {
         if last.Modified.IsZero() {
				log.Printf("asses.One(%s) // assume cksum unchanged given null modified ", shortp)
				return nil
         }

			cksum, err := Cksum(ctx, p)
			if err != nil {
				return err
			}

			if cksum == last.Cksum {
				log.Printf("asses.One(%s) // cksum unchanged since %v", shortp, last.T)
				return nil
			}
		}

		log.Printf("asses.deport(%s)...", shortp)
		if err := deport(ctx, p); err != nil {
			return err
		}

		return nil
	}(); err != nil {
		return err
	}

	cksum, err := Cksum(ctx, p)
	if err != nil {
		return err
	}
	stat, err := os.Stat(p)
	if err != nil {
		return err
	}
	if err := checked(ctx, p, cksum, stat.ModTime()); err != nil {
      log.Printf("failed to mark %s checked: %v", shortp, err)
      return err
   }

   return nil
}

func Cksum(ctx context.Context, p string) (string, error) {
	f, err := os.Open(p)
	if err != nil {
		return "", err
	}
	defer f.Close()

	hasher := md5.New()
	_, err = io.Copy(hasher, slow.NewReader(ctx, 10_000_000, f))
	return base64.StdEncoding.EncodeToString(hasher.Sum(nil)), err
}