diff --git a/.bazelrc b/.bazelrc
index e824c02..e6dc119 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -1,5 +1,5 @@
 test --test_output=errors
 
 # To enable flake8 on all build steps, uncomment this -
-build --aspects="//tools/flake8:flake8.bzl%flake8_aspect" --output_groups=flake8_checks
-build --aspects="//tools/black:black.bzl%black_aspect" --output_groups=black_checks
+test --aspects="//tools/flake8:flake8.bzl%flake8_aspect" --output_groups=flake8_checks
+test --aspects="//tools/black:black.bzl%black_aspect" --output_groups=black_checks
diff --git a/projects/archiver/BUILD b/projects/archiver/BUILD
index fe7ef5c..d60c6a2 100644
--- a/projects/archiver/BUILD
+++ b/projects/archiver/BUILD
@@ -1,11 +1,17 @@
 zapp_binary(
     name = "hash_copy",
     main = "hash_copy.py",
+    srcs = [
+        "util.py"
+    ],
 )
 
 zapp_binary(
     name = "org_photos",
     main = "org_photos.py",
+    srcs = [
+        "util.py"
+    ],
     deps = [
         py_requirement("ExifRead"),
     ]
diff --git a/projects/archiver/hash_copy.py b/projects/archiver/hash_copy.py
index ad273e7..7fc439e 100644
--- a/projects/archiver/hash_copy.py
+++ b/projects/archiver/hash_copy.py
@@ -3,38 +3,16 @@ A tree deduplicator and archiver tool.
 """
 
 import argparse
-from hashlib import sha256
 from pathlib import Path
 from shutil import copy2 as copyfile
 
+from .util import *
 
 parser = argparse.ArgumentParser()
 parser.add_argument("from_dir", type=Path)
 parser.add_argument("to_dir", type=Path)
 
 
-def checksum(p: Path, sum=sha256) -> str:
-    """Compute block-wise checksums of a file.
-
-    Inspired by the Dropbox content-hashing interface -
-
-    https://www.dropbox.com/developers/reference/content-hash
-
-    """
-
-    def iter_chunks(fp):
-        yield from iter(lambda: fp.read(4096), b"")
-
-    def _helper():
-        with open(p, "rb") as fp:
-            for chunk in iter_chunks(fp):
-                digest = sum()
-                digest.update(chunk)
-                yield digest.hexdigest()
-
-    return list(_helper())
-
-
 def main():
     opts, args = parser.parse_known_args()
 
@@ -62,8 +40,8 @@ def main():
                 ):
                     pass
 
-                elif (src_checksum := checksum(abs_src_path)) != (
-                    dest_checksum := checksum(abs_dest_path)
+                elif (src_checksum := checksum_path(abs_src_path)) != (
+                    dest_checksum := checksum_path(abs_dest_path)
                 ):
                     print(
                         f"file conflict (src {src_checksum}, dest {dest_checksum}), correcting..."
diff --git a/projects/archiver/notes.md b/projects/archiver/notes.md
new file mode 100644
index 0000000..8eab1a1
--- /dev/null
+++ b/projects/archiver/notes.md
@@ -0,0 +1,288 @@
+# EXIF tags dataset (exifread edition)
+
+- 'EXIF ApertureValue'
+- 'EXIF BodySerialNumber'
+- 'EXIF BrightnessValue'
+- 'EXIF CVAPattern'
+- 'EXIF CameraOwnerName'
+- 'EXIF ColorSpace'
+- 'EXIF ComponentsConfiguration'
+- 'EXIF CompressedBitsPerPixel'
+- 'EXIF Contrast'
+- 'EXIF CustomRendered'
+- 'EXIF DateTimeDigitized'
+- 'EXIF DateTimeOriginal'
+- 'EXIF DeviceSettingDescription'
+- 'EXIF DigitalZoomRatio'
+- 'EXIF ExifImageLength'
+- 'EXIF ExifImageWidth'
+- 'EXIF ExifVersion'
+- 'EXIF ExposureBiasValue'
+- 'EXIF ExposureIndex'
+- 'EXIF ExposureMode'
+- 'EXIF ExposureProgram'
+- 'EXIF ExposureTime'
+- 'EXIF FNumber'
+- 'EXIF FileSource'
+- 'EXIF Flash'
+- 'EXIF FlashEnergy'
+- 'EXIF FlashPixVersion'
+- 'EXIF FocalLength'
+- 'EXIF FocalLengthIn35mmFilm'
+- 'EXIF FocalPlaneResolutionUnit'
+- 'EXIF FocalPlaneXResolution'
+- 'EXIF FocalPlaneYResolution'
+- 'EXIF GainControl'
+- 'EXIF ISOSpeedRatings'
+- 'EXIF ImageUniqueID'
+- 'EXIF InteroperabilityOffset'
+- 'EXIF JPEGInterchangeFormat'
+- 'EXIF JPEGInterchangeFormatLength'
+- 'EXIF LensMake'
+- 'EXIF LensModel'
+- 'EXIF LensSerialNumber'
+- 'EXIF LensSpecification'
+- 'EXIF LightSource'
+- 'EXIF MakerNote'
+- 'EXIF MaxApertureValue'
+- 'EXIF MeteringMode'
+- 'EXIF OffsetSchema'
+- 'EXIF OffsetTime'
+- 'EXIF OffsetTimeDigitized'
+- 'EXIF OffsetTimeOriginal'
+- 'EXIF Padding'
+- 'EXIF RecommendedExposureIndex'
+- 'EXIF Saturation'
+- 'EXIF SceneCaptureType'
+- 'EXIF SceneType'
+- 'EXIF SensingMethod'
+- 'EXIF SensitivityType'
+- 'EXIF Sharpness'
+- 'EXIF ShutterSpeedValue'
+- 'EXIF SubSecTime'
+- 'EXIF SubSecTimeDigitized'
+- 'EXIF SubSecTimeOriginal'
+- 'EXIF SubjectArea'
+- 'EXIF SubjectDistance'
+- 'EXIF SubjectDistanceRange'
+- 'EXIF UserComment'
+- 'EXIF WhiteBalance'
+- 'GPS GPSAltitude'
+- 'GPS GPSAltitudeRef'
+- 'GPS GPSDOP'
+- 'GPS GPSDate'
+- 'GPS GPSImgDirection'
+- 'GPS GPSImgDirectionRef'
+- 'GPS GPSLatitude'
+- 'GPS GPSLatitudeRef'
+- 'GPS GPSLongitude'
+- 'GPS GPSLongitudeRef'
+- 'GPS GPSMapDatum'
+- 'GPS GPSMeasureMode'
+- 'GPS GPSProcessingMethod'
+- 'GPS GPSTimeStamp'
+- 'GPS GPSVersionID'
+- 'GPS Tag 0xEA1C'
+- 'Image Artist'
+- 'Image BitsPerSample'
+- 'Image Copyright'
+- 'Image DateTime'
+- 'Image DateTimeDigitized'
+- 'Image ExifOffset'
+- 'Image ExposureMode'
+- 'Image ExposureProgram'
+- 'Image ExposureTime'
+- 'Image FNumber'
+- 'Image Flash'
+- 'Image FocalLength'
+- 'Image GPSInfo'
+- 'Image ISOSpeedRatings'
+- 'Image ImageDescription'
+- 'Image ImageLength'
+- 'Image ImageWidth'
+- 'Image JPEGInterchangeFormat'
+- 'Image JPEGInterchangeFormatLength'
+- 'Image LightSource'
+- 'Image Make'
+- 'Image MeteringMode'
+- 'Image Model'
+- 'Image Orientation'
+- 'Image Padding'
+- 'Image PhotometricInterpretation'
+- 'Image PrintIM'
+- 'Image ResolutionUnit'
+- 'Image SamplesPerPixel'
+- 'Image Software'
+- 'Image UserComment'
+- 'Image WhiteBalance'
+- 'Image XPComment'
+- 'Image XPKeywords'
+- 'Image XPTitle'
+- 'Image XResolution'
+- 'Image YCbCrPositioning'
+- 'Image YResolution'
+- 'Interoperability InteroperabilityIndex'
+- 'Interoperability InteroperabilityVersion'
+- 'JPEGThumbnail'
+- 'MakerNote AEBracketCompensationApplied'
+- 'MakerNote AESetting'
+- 'MakerNote AFAreaMode'
+- 'MakerNote AFInfo2'
+- 'MakerNote AFPointSelected'
+- 'MakerNote AFPointUsed'
+- 'MakerNote ActiveDLighting'
+- 'MakerNote AspectInfo'
+- 'MakerNote AutoBracketRelease'
+- 'MakerNote AutoFlashMode'
+- 'MakerNote BracketMode'
+- 'MakerNote BracketShotNumber'
+- 'MakerNote BracketValue'
+- 'MakerNote BracketingMode'
+- 'MakerNote CanonImageWidth'
+- 'MakerNote ColorBalance'
+- 'MakerNote ColorSpace'
+- 'MakerNote ContinuousDriveMode'
+- 'MakerNote Contrast'
+- 'MakerNote CropHiSpeed'
+- 'MakerNote CropInfo'
+- 'MakerNote DigitalVariProgram'
+- 'MakerNote DigitalZoom'
+- 'MakerNote DustRemovalData'
+- 'MakerNote EasyShootingMode'
+- 'MakerNote ExposureDifference'
+- 'MakerNote ExposureMode'
+- 'MakerNote ExposureTuning'
+- 'MakerNote ExternalFlashExposureComp'
+- 'MakerNote FileInfo'
+- 'MakerNote FileNumber'
+- 'MakerNote FilterEffect'
+- 'MakerNote FirmwareVersion'
+- 'MakerNote FlashActivity'
+- 'MakerNote FlashBias'
+- 'MakerNote FlashBracketCompensationApplied'
+- 'MakerNote FlashCompensation'
+- 'MakerNote FlashDetails'
+- 'MakerNote FlashExposureLock'
+- 'MakerNote FlashInfo'
+- 'MakerNote FlashMode'
+- 'MakerNote FlashSetting'
+- 'MakerNote FocalLength'
+- 'MakerNote FocalType'
+- 'MakerNote FocalUnitsPerMM'
+- 'MakerNote FocusMode'
+- 'MakerNote FocusType'
+- 'MakerNote HDRImageType'
+- 'MakerNote HighISONoiseReduction'
+- 'MakerNote ISO'
+- 'MakerNote ISOInfo'
+- 'MakerNote ISOSetting'
+- 'MakerNote ISOSpeedRequested'
+- 'MakerNote ImageDataSize'
+- 'MakerNote ImageSize'
+- 'MakerNote ImageStabilization'
+- 'MakerNote ImageType'
+- 'MakerNote InternalSerialNumber'
+- 'MakerNote LensData'
+- 'MakerNote LensFStops'
+- 'MakerNote LensMinMaxFocalMaxAperture'
+- 'MakerNote LensModel'
+- 'MakerNote LensType'
+- 'MakerNote LiveViewShooting'
+- 'MakerNote LongExposureNoiseReduction2'
+- 'MakerNote LongFocalLengthOfLensInFocalUnits'
+- 'MakerNote MacroMagnification'
+- 'MakerNote Macromode'
+- 'MakerNote MakernoteVersion'
+- 'MakerNote ManualFlashOutput'
+- 'MakerNote MeteringMode'
+- 'MakerNote ModelID'
+- 'MakerNote MultiExposure'
+- 'MakerNote NikonPreview'
+- 'MakerNote NoiseReduction'
+- 'MakerNote NumAFPoints'
+- 'MakerNote OwnerName'
+- 'MakerNote PhotoCornerCoordinates'
+- 'MakerNote PictureControl'
+- 'MakerNote PowerUpTime'
+- 'MakerNote ProgramShift'
+- 'MakerNote Quality'
+- 'MakerNote RawJpgQuality'
+- 'MakerNote RawJpgSize'
+- 'MakerNote RecordMode'
+- 'MakerNote RetouchHistory'
+- 'MakerNote Saturation'
+- 'MakerNote SelfTimer'
+- 'MakerNote SequenceNumber'
+- 'MakerNote SerialNumber'
+- 'MakerNote Sharpness'
+- 'MakerNote ShortFocalLengthOfLensInFocalUnits'
+- 'MakerNote ShotInfo'
+- 'MakerNote SlowShutter'
+- 'MakerNote SpotMeteringMode'
+- 'MakerNote SubjectDistance'
+- 'MakerNote Tag 0x0001'
+- 'MakerNote Tag 0x0002'
+- 'MakerNote Tag 0x0003'
+- 'MakerNote Tag 0x0004'
+- 'MakerNote Tag 0x0005'
+- 'MakerNote Tag 0x0006'
+- 'MakerNote Tag 0x0007'
+- 'MakerNote Tag 0x0008'
+- 'MakerNote Tag 0x0009'
+- 'MakerNote Tag 0x000E'
+- 'MakerNote Tag 0x0014'
+- 'MakerNote Tag 0x0015'
+- 'MakerNote Tag 0x0019'
+- 'MakerNote Tag 0x002B'
+- 'MakerNote Tag 0x002C'
+- 'MakerNote Tag 0x002D'
+- 'MakerNote Tag 0x0083'
+- 'MakerNote Tag 0x0099'
+- 'MakerNote Tag 0x009D'
+- 'MakerNote Tag 0x00A0'
+- 'MakerNote Tag 0x00A3'
+- 'MakerNote Tag 0x00AA'
+- 'MakerNote Tag 0x00BB'
+- 'MakerNote Tag 0x00D0'
+- 'MakerNote Tag 0x00E0'
+- 'MakerNote Tag 0x4001'
+- 'MakerNote Tag 0x4008'
+- 'MakerNote Tag 0x4009'
+- 'MakerNote Tag 0x4010'
+- 'MakerNote Tag 0x4011'
+- 'MakerNote Tag 0x4012'
+- 'MakerNote Tag 0x4015'
+- 'MakerNote Tag 0x4016'
+- 'MakerNote Tag 0x4017'
+- 'MakerNote Tag 0x4018'
+- 'MakerNote Tag 0x4019'
+- 'MakerNote Tag 0x4020'
+- 'MakerNote ThumbnailImageValidArea'
+- 'MakerNote ToningEffect'
+- 'MakerNote TotalShutterReleases'
+- 'MakerNote Unknown'
+- 'MakerNote VRInfo'
+- 'MakerNote ValidAFPoints'
+- 'MakerNote WBBracketMode'
+- 'MakerNote WBBracketValueAB'
+- 'MakerNote WBBracketValueGM'
+- 'MakerNote WhiteBalance'
+- 'MakerNote WhiteBalanceBias'
+- 'MakerNote WhiteBalanceRBCoeff'
+- 'MakerNote Whitebalance'
+- 'MakerNote WorldTime'
+- 'Thumbnail Compression'
+- 'Thumbnail DateTime'
+- 'Thumbnail ImageDescription'
+- 'Thumbnail ImageLength'
+- 'Thumbnail ImageWidth'
+- 'Thumbnail JPEGInterchangeFormat'
+- 'Thumbnail JPEGInterchangeFormatLength'
+- 'Thumbnail Make'
+- 'Thumbnail Model'
+- 'Thumbnail Orientation'
+- 'Thumbnail ResolutionUnit'
+- 'Thumbnail Software'
+- 'Thumbnail XResolution'
+- 'Thumbnail YCbCrPositioning'
+- 'Thumbnail YResolution'
diff --git a/projects/archiver/org_photos.py b/projects/archiver/org_photos.py
index 38f7a11..8b3007d 100644
--- a/projects/archiver/org_photos.py
+++ b/projects/archiver/org_photos.py
@@ -25,6 +25,8 @@ from shutil import copy2 as copyfile
 import sys
 import typing as t
 
+from .util import *
+
 # FIXME: use piexif, which supports writeback not exifread.
 import exifread
 
@@ -32,351 +34,18 @@ import exifread
 parser = argparse.ArgumentParser()
 parser.add_argument("src_dir", type=Path)
 parser.add_argument("dest_dir", type=Path)
+parser.add_option("destructive", action="store_true", default=False)
 
 
 MODIFIED_ISO_DATE = "%Y:%m:%dT%H:%M:%SF%f"
 
 
-def take(n, iter):
-    """Take the first N items lazily off of an iterable."""
-
-    for _ in range(0, n):
-        try:
-            yield next(iter)
-        except StopIteration:
-            break
-
-
 def exif_tags(p: Path) -> object:
     """Return the EXIF tags on an image."""
     with open(p, "rb") as fp:
         return exifread.process_file(fp)
 
 
-# EXIF tags dataset (exifread edition) -
-#
-# ---
-# - 'EXIF ApertureValue'
-# - 'EXIF BodySerialNumber'
-# - 'EXIF BrightnessValue'
-# - 'EXIF CVAPattern'
-# - 'EXIF CameraOwnerName'
-# - 'EXIF ColorSpace'
-# - 'EXIF ComponentsConfiguration'
-# - 'EXIF CompressedBitsPerPixel'
-# - 'EXIF Contrast'
-# - 'EXIF CustomRendered'
-# - 'EXIF DateTimeDigitized'
-# - 'EXIF DateTimeOriginal'
-# - 'EXIF DeviceSettingDescription'
-# - 'EXIF DigitalZoomRatio'
-# - 'EXIF ExifImageLength'
-# - 'EXIF ExifImageWidth'
-# - 'EXIF ExifVersion'
-# - 'EXIF ExposureBiasValue'
-# - 'EXIF ExposureIndex'
-# - 'EXIF ExposureMode'
-# - 'EXIF ExposureProgram'
-# - 'EXIF ExposureTime'
-# - 'EXIF FNumber'
-# - 'EXIF FileSource'
-# - 'EXIF Flash'
-# - 'EXIF FlashEnergy'
-# - 'EXIF FlashPixVersion'
-# - 'EXIF FocalLength'
-# - 'EXIF FocalLengthIn35mmFilm'
-# - 'EXIF FocalPlaneResolutionUnit'
-# - 'EXIF FocalPlaneXResolution'
-# - 'EXIF FocalPlaneYResolution'
-# - 'EXIF GainControl'
-# - 'EXIF ISOSpeedRatings'
-# - 'EXIF ImageUniqueID'
-# - 'EXIF InteroperabilityOffset'
-# - 'EXIF JPEGInterchangeFormat'
-# - 'EXIF JPEGInterchangeFormatLength'
-# - 'EXIF LensMake'
-# - 'EXIF LensModel'
-# - 'EXIF LensSerialNumber'
-# - 'EXIF LensSpecification'
-# - 'EXIF LightSource'
-# - 'EXIF MakerNote'
-# - 'EXIF MaxApertureValue'
-# - 'EXIF MeteringMode'
-# - 'EXIF OffsetSchema'
-# - 'EXIF OffsetTime'
-# - 'EXIF OffsetTimeDigitized'
-# - 'EXIF OffsetTimeOriginal'
-# - 'EXIF Padding'
-# - 'EXIF RecommendedExposureIndex'
-# - 'EXIF Saturation'
-# - 'EXIF SceneCaptureType'
-# - 'EXIF SceneType'
-# - 'EXIF SensingMethod'
-# - 'EXIF SensitivityType'
-# - 'EXIF Sharpness'
-# - 'EXIF ShutterSpeedValue'
-# - 'EXIF SubSecTime'
-# - 'EXIF SubSecTimeDigitized'
-# - 'EXIF SubSecTimeOriginal'
-# - 'EXIF SubjectArea'
-# - 'EXIF SubjectDistance'
-# - 'EXIF SubjectDistanceRange'
-# - 'EXIF UserComment'
-# - 'EXIF WhiteBalance'
-# - 'GPS GPSAltitude'
-# - 'GPS GPSAltitudeRef'
-# - 'GPS GPSDOP'
-# - 'GPS GPSDate'
-# - 'GPS GPSImgDirection'
-# - 'GPS GPSImgDirectionRef'
-# - 'GPS GPSLatitude'
-# - 'GPS GPSLatitudeRef'
-# - 'GPS GPSLongitude'
-# - 'GPS GPSLongitudeRef'
-# - 'GPS GPSMapDatum'
-# - 'GPS GPSMeasureMode'
-# - 'GPS GPSProcessingMethod'
-# - 'GPS GPSTimeStamp'
-# - 'GPS GPSVersionID'
-# - 'GPS Tag 0xEA1C'
-# - 'Image Artist'
-# - 'Image BitsPerSample'
-# - 'Image Copyright'
-# - 'Image DateTime'
-# - 'Image DateTimeDigitized'
-# - 'Image ExifOffset'
-# - 'Image ExposureMode'
-# - 'Image ExposureProgram'
-# - 'Image ExposureTime'
-# - 'Image FNumber'
-# - 'Image Flash'
-# - 'Image FocalLength'
-# - 'Image GPSInfo'
-# - 'Image ISOSpeedRatings'
-# - 'Image ImageDescription'
-# - 'Image ImageLength'
-# - 'Image ImageWidth'
-# - 'Image JPEGInterchangeFormat'
-# - 'Image JPEGInterchangeFormatLength'
-# - 'Image LightSource'
-# - 'Image Make'
-# - 'Image MeteringMode'
-# - 'Image Model'
-# - 'Image Orientation'
-# - 'Image Padding'
-# - 'Image PhotometricInterpretation'
-# - 'Image PrintIM'
-# - 'Image ResolutionUnit'
-# - 'Image SamplesPerPixel'
-# - 'Image Software'
-# - 'Image UserComment'
-# - 'Image WhiteBalance'
-# - 'Image XPComment'
-# - 'Image XPKeywords'
-# - 'Image XPTitle'
-# - 'Image XResolution'
-# - 'Image YCbCrPositioning'
-# - 'Image YResolution'
-# - 'Interoperability InteroperabilityIndex'
-# - 'Interoperability InteroperabilityVersion'
-# - 'JPEGThumbnail'
-# - 'MakerNote AEBracketCompensationApplied'
-# - 'MakerNote AESetting'
-# - 'MakerNote AFAreaMode'
-# - 'MakerNote AFInfo2'
-# - 'MakerNote AFPointSelected'
-# - 'MakerNote AFPointUsed'
-# - 'MakerNote ActiveDLighting'
-# - 'MakerNote AspectInfo'
-# - 'MakerNote AutoBracketRelease'
-# - 'MakerNote AutoFlashMode'
-# - 'MakerNote BracketMode'
-# - 'MakerNote BracketShotNumber'
-# - 'MakerNote BracketValue'
-# - 'MakerNote BracketingMode'
-# - 'MakerNote CanonImageWidth'
-# - 'MakerNote ColorBalance'
-# - 'MakerNote ColorSpace'
-# - 'MakerNote ContinuousDriveMode'
-# - 'MakerNote Contrast'
-# - 'MakerNote CropHiSpeed'
-# - 'MakerNote CropInfo'
-# - 'MakerNote DigitalVariProgram'
-# - 'MakerNote DigitalZoom'
-# - 'MakerNote DustRemovalData'
-# - 'MakerNote EasyShootingMode'
-# - 'MakerNote ExposureDifference'
-# - 'MakerNote ExposureMode'
-# - 'MakerNote ExposureTuning'
-# - 'MakerNote ExternalFlashExposureComp'
-# - 'MakerNote FileInfo'
-# - 'MakerNote FileNumber'
-# - 'MakerNote FilterEffect'
-# - 'MakerNote FirmwareVersion'
-# - 'MakerNote FlashActivity'
-# - 'MakerNote FlashBias'
-# - 'MakerNote FlashBracketCompensationApplied'
-# - 'MakerNote FlashCompensation'
-# - 'MakerNote FlashDetails'
-# - 'MakerNote FlashExposureLock'
-# - 'MakerNote FlashInfo'
-# - 'MakerNote FlashMode'
-# - 'MakerNote FlashSetting'
-# - 'MakerNote FocalLength'
-# - 'MakerNote FocalType'
-# - 'MakerNote FocalUnitsPerMM'
-# - 'MakerNote FocusMode'
-# - 'MakerNote FocusType'
-# - 'MakerNote HDRImageType'
-# - 'MakerNote HighISONoiseReduction'
-# - 'MakerNote ISO'
-# - 'MakerNote ISOInfo'
-# - 'MakerNote ISOSetting'
-# - 'MakerNote ISOSpeedRequested'
-# - 'MakerNote ImageDataSize'
-# - 'MakerNote ImageSize'
-# - 'MakerNote ImageStabilization'
-# - 'MakerNote ImageType'
-# - 'MakerNote InternalSerialNumber'
-# - 'MakerNote LensData'
-# - 'MakerNote LensFStops'
-# - 'MakerNote LensMinMaxFocalMaxAperture'
-# - 'MakerNote LensModel'
-# - 'MakerNote LensType'
-# - 'MakerNote LiveViewShooting'
-# - 'MakerNote LongExposureNoiseReduction2'
-# - 'MakerNote LongFocalLengthOfLensInFocalUnits'
-# - 'MakerNote MacroMagnification'
-# - 'MakerNote Macromode'
-# - 'MakerNote MakernoteVersion'
-# - 'MakerNote ManualFlashOutput'
-# - 'MakerNote MeteringMode'
-# - 'MakerNote ModelID'
-# - 'MakerNote MultiExposure'
-# - 'MakerNote NikonPreview'
-# - 'MakerNote NoiseReduction'
-# - 'MakerNote NumAFPoints'
-# - 'MakerNote OwnerName'
-# - 'MakerNote PhotoCornerCoordinates'
-# - 'MakerNote PictureControl'
-# - 'MakerNote PowerUpTime'
-# - 'MakerNote ProgramShift'
-# - 'MakerNote Quality'
-# - 'MakerNote RawJpgQuality'
-# - 'MakerNote RawJpgSize'
-# - 'MakerNote RecordMode'
-# - 'MakerNote RetouchHistory'
-# - 'MakerNote Saturation'
-# - 'MakerNote SelfTimer'
-# - 'MakerNote SequenceNumber'
-# - 'MakerNote SerialNumber'
-# - 'MakerNote Sharpness'
-# - 'MakerNote ShortFocalLengthOfLensInFocalUnits'
-# - 'MakerNote ShotInfo'
-# - 'MakerNote SlowShutter'
-# - 'MakerNote SpotMeteringMode'
-# - 'MakerNote SubjectDistance'
-# - 'MakerNote Tag 0x0001'
-# - 'MakerNote Tag 0x0002'
-# - 'MakerNote Tag 0x0003'
-# - 'MakerNote Tag 0x0004'
-# - 'MakerNote Tag 0x0005'
-# - 'MakerNote Tag 0x0006'
-# - 'MakerNote Tag 0x0007'
-# - 'MakerNote Tag 0x0008'
-# - 'MakerNote Tag 0x0009'
-# - 'MakerNote Tag 0x000E'
-# - 'MakerNote Tag 0x0014'
-# - 'MakerNote Tag 0x0015'
-# - 'MakerNote Tag 0x0019'
-# - 'MakerNote Tag 0x002B'
-# - 'MakerNote Tag 0x002C'
-# - 'MakerNote Tag 0x002D'
-# - 'MakerNote Tag 0x0083'
-# - 'MakerNote Tag 0x0099'
-# - 'MakerNote Tag 0x009D'
-# - 'MakerNote Tag 0x00A0'
-# - 'MakerNote Tag 0x00A3'
-# - 'MakerNote Tag 0x00AA'
-# - 'MakerNote Tag 0x00BB'
-# - 'MakerNote Tag 0x00D0'
-# - 'MakerNote Tag 0x00E0'
-# - 'MakerNote Tag 0x4001'
-# - 'MakerNote Tag 0x4008'
-# - 'MakerNote Tag 0x4009'
-# - 'MakerNote Tag 0x4010'
-# - 'MakerNote Tag 0x4011'
-# - 'MakerNote Tag 0x4012'
-# - 'MakerNote Tag 0x4015'
-# - 'MakerNote Tag 0x4016'
-# - 'MakerNote Tag 0x4017'
-# - 'MakerNote Tag 0x4018'
-# - 'MakerNote Tag 0x4019'
-# - 'MakerNote Tag 0x4020'
-# - 'MakerNote ThumbnailImageValidArea'
-# - 'MakerNote ToningEffect'
-# - 'MakerNote TotalShutterReleases'
-# - 'MakerNote Unknown'
-# - 'MakerNote VRInfo'
-# - 'MakerNote ValidAFPoints'
-# - 'MakerNote WBBracketMode'
-# - 'MakerNote WBBracketValueAB'
-# - 'MakerNote WBBracketValueGM'
-# - 'MakerNote WhiteBalance'
-# - 'MakerNote WhiteBalanceBias'
-# - 'MakerNote WhiteBalanceRBCoeff'
-# - 'MakerNote Whitebalance'
-# - 'MakerNote WorldTime'
-# - 'Thumbnail Compression'
-# - 'Thumbnail DateTime'
-# - 'Thumbnail ImageDescription'
-# - 'Thumbnail ImageLength'
-# - 'Thumbnail ImageWidth'
-# - 'Thumbnail JPEGInterchangeFormat'
-# - 'Thumbnail JPEGInterchangeFormatLength'
-# - 'Thumbnail Make'
-# - 'Thumbnail Model'
-# - 'Thumbnail Orientation'
-# - 'Thumbnail ResolutionUnit'
-# - 'Thumbnail Software'
-# - 'Thumbnail XResolution'
-# - 'Thumbnail YCbCrPositioning'
-# - 'Thumbnail YResolution'
-
-
-def checksum(p: Path, sum=sha256) -> str:
-    """Compute a chunked checksum of a file.
-
-    Does not produce individual block checksums.
-    """
-
-    def iter_blocks(fp):
-        yield from iter(lambda: fp.read(4096), b"")
-
-    with open(p, "rb") as fp:
-        digest = sum()
-        for chunk in iter_blocks(fp):
-            digest.update(chunk)
-        return digest.hexdigest()
-
-
-def checksum_list(iter, sum=sha256):
-    """Compute the checksum of a bunch of stuff from an iterable."""
-
-    sum = sum()
-    for i in iter:
-        sum.update(b";")  # Merkle tree salting.
-        if isinstance(i, str):
-            i = str.encode(i, "utf-8")
-        try:
-            sum.update(i)
-        except Exception as e:
-            print(i, type(i))
-            raise e
-
-    return sum.hexdigest()
-
-
 def sanitize(s: str) -> str:
     """Something like b64encode; sanitize a string to a path-friendly version."""
 
@@ -524,10 +193,10 @@ class ImgInfo(t.NamedTuple):
         return self.file_sha256sum()[: self.shasum_prefix]
 
     def file_sha256sum(self):
-        return checksum(self.file_path, sha256)
+        return checksum_path(self.file_path, sha256)
 
     def file_sha512sum(self):
-        return checksum(self.file_path, sha512)
+        return checksum_path(self.file_path, sha512)
 
 
 def img_info(p: Path) -> ImgInfo:
@@ -620,11 +289,27 @@ def img_info(p: Path) -> ImgInfo:
 def main():
     opts, args = parser.parse_known_args()
 
+    def _copy():
+        print(f"  rename: {target}")
+        try:
+            if not opts.destructive:
+                raise OSError()
+
+            src.rename(target)  # Execute the rename
+        except OSError:  # cross-device move
+            copyfile(src, target)
+
+            if opts.destructive:
+                src.chmod(0o644)
+                src.unlink()
+
     print("---")
     for src in list(opts.src_dir.glob("**/*")):
         if src.is_dir():
             continue
 
+        print(f"{src}:")
+
         info = img_info(src)
         year_dir = Path(opts.dest_dir / str(info.date.year))
         year_dir.mkdir(exist_ok=True)  # Ignore existing and continue
@@ -636,20 +321,20 @@ def main():
             continue  # Just skip fucked up files
         target = Path(year_dir / f"{stable_name}{ext}")
 
-        print(f"{src}:")
-        print(f"  rename: {target}")
         if not target.exists():
-            try:
-                src.rename(target)  # Execute the rename
-            except OSError:
-                copyfile(src, target)
-                target.chmod(0o644)
-                src.unlink()
+            # src & !target => copy
+            _copy()
         elif src == target:
-            pass  # Nothing to do
+            # src == target; skip DO NOT DELETE SRC
+            pass
+        elif checksum_path_blocks(src) == checksum_path_blocks(target):
+            # src != target && id(src) == id(target); delete src
+            if opts.destructive:
+                src.chmod(0o644)
+                src.unlink()
         else:
-            target.chmod(0o644)
-            src.unlink()  # Delete the source
+            # src != target && id(src) != id(target); replace target with src?
+            print(f"  warning: {target} is a content-id collision with a different checksum")
 
 
 if __name__ == "__main__":
diff --git a/projects/archiver/util.py b/projects/archiver/util.py
new file mode 100644
index 0000000..0eaadb9
--- /dev/null
+++ b/projects/archiver/util.py
@@ -0,0 +1,69 @@
+import typing as t
+
+from hashlib import sha256
+from pathlib import Path
+
+
+def iter_chunks(fp):
+    yield from iter(lambda: fp.read(4096), b"")
+
+
+def take(n, iter):
+    """Take the first N items lazily off of an iterable."""
+
+    for _ in range(0, n):
+        try:
+            yield next(iter)
+        except StopIteration:
+            break
+
+
+def checksum_list(iter, sum=sha256, salt=b";"):
+    """Compute the checksum of a bunch of stuff from an iterable."""
+
+    sum = sum()
+    for i in iter:
+        if salt:
+            sum.update(salt)  # Merkle tree salting.
+        if isinstance(i, str):
+            i = str.encode(i, "utf-8")
+        try:
+            sum.update(i)
+        except Exception as e:
+            print(i, type(i))
+            raise e
+
+    return sum.hexdigest()
+
+
+def checksum_path_blocks(p: Path, sum=sha256) -> t.Iterable[str]:
+    """Compute block-wise checksums of a file.
+
+    Inspired by the Dropbox content-hashing interface -
+
+    https://www.dropbox.com/developers/reference/content-hash
+
+    """
+
+    def _helper():
+        with open(p, "rb") as fp:
+            for chunk in iter_chunks(fp):
+                digest = sum()
+                digest.update(chunk)
+                yield digest.hexdigest()
+
+    return list(_helper())
+
+
+def checksum_path(p: Path, sum=sha256) -> str:
+    """Compute 'the' checksum of an entire file.
+
+    Note that this does semi-streaming I/O.
+
+    """
+
+    sum = sum()
+    with open(p, "rb") as fp:
+        for chunk in iter_chunks(fp):
+            sum.update(chunk)
+    return sum.hexdigest()
diff --git a/tools/autoflake/BUILD b/tools/autoflake/BUILD
index 9088820..bf94b18 100644
--- a/tools/autoflake/BUILD
+++ b/tools/autoflake/BUILD
@@ -1,4 +1,4 @@
-py_binary(
+zapp_binary(
     name = "autoflake",
     main = "__main__.py",
     deps = [
diff --git a/tools/fmt.sh b/tools/fmt.sh
index 6e6640f..fac39f9 100755
--- a/tools/fmt.sh
+++ b/tools/fmt.sh
@@ -9,8 +9,7 @@ DIRS=(projects tools)
 function brl() {
     bin="$1"
     shift
-    bazel build "//${bin}"
-    "bazel-bin/${bin}/$(basename ${bin})" "$@"
+    bazel run "//${bin}" -- "$@"
     return "$?"
 }