cn0 split stats.source.sh into aggregate/render/filter-album modules

Pure code move: split the ~1248-line stats.source.sh (SRP+SoC) into three
cohesive modules, all functions and STATS_* constants/globals moved verbatim:

- stats-aggregate.source.sh: EXIF parsing, bucketing, _stats_tally,
  reset/collect_photo_exif_stats and the STATS_* maps.
- stats-render.source.sh: stats overview page (sections, bars, leaderboard,
  render_stats_page, _stats_build_body, _stats_filter_link, background pickers).
- stats-filter-album.source.sh: per-filter mini-albums (render_filter_pages,
  gallery/view/thumbnail builders, _stats_enqueue_filter_album).

Updated LIB_SOURCES accordingly. No logic change (verified: all 55 functions and
top-level globals preserved; full suite, shellcheck, check-generated, diff all
pass). The SoC point (HTML built in bash rather than templates) is left for a
follow-up (nn0/qn0).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

6 files changed, 1284 insertions, 1250 deletions

diff --git a/Justfile b/Justfile
index de200c8..da16ed3 100644
--- a/Justfile
+++ b/Justfile
@@ -7,7 +7,7 @@ PREFIX := env_var_or_default("PREFIX", "/usr")
 BINDIR := env_var_or_default("BINDIR", PREFIX + "/bin")
 DATADIR := env_var_or_default("DATADIR", PREFIX + "/share")
 SYSCONFDIR := env_var_or_default("SYSCONFDIR", "/etc/default")
-LIB_SOURCES := "src/lib/bootstrap.source.sh src/lib/imagemagick.source.sh src/lib/process.source.sh src/lib/archive.source.sh src/lib/template.source.sh src/lib/job-pool.source.sh src/lib/image.source.sh src/lib/random.source.sh src/lib/image-pipeline.source.sh src/lib/album-metadata.source.sh src/lib/album-render.source.sh src/lib/album.source.sh src/lib/stats.source.sh src/lib/config.source.sh src/lib/config.print.source.sh src/lib/config.sync.source.sh src/lib/config.staging.source.sh src/lib/config.validate.source.sh src/lib/config.cli.source.sh src/lib/action.source.sh"
+LIB_SOURCES := "src/lib/bootstrap.source.sh src/lib/imagemagick.source.sh src/lib/process.source.sh src/lib/archive.source.sh src/lib/template.source.sh src/lib/job-pool.source.sh src/lib/image.source.sh src/lib/random.source.sh src/lib/image-pipeline.source.sh src/lib/album-metadata.source.sh src/lib/album-render.source.sh src/lib/album.source.sh src/lib/stats-aggregate.source.sh src/lib/stats-render.source.sh src/lib/stats-filter-album.source.sh src/lib/config.source.sh src/lib/config.print.source.sh src/lib/config.sync.source.sh src/lib/config.staging.source.sh src/lib/config.validate.source.sh src/lib/config.cli.source.sh src/lib/action.source.sh"
 
 default: build
 
diff --git a/bin/shuriken b/bin/shuriken
index 729e693..49d49a6 100755
--- a/bin/shuriken
+++ b/bin/shuriken
@@ -3084,7 +3084,7 @@ refresh_splash() {
     log_info "Refreshed splash page $(_display_path "$DIST_DIR/index.html")"
 }
 
-# Inlined from src/lib/stats.source.sh
+# Inlined from src/lib/stats-aggregate.source.sh
 # Stats aggregation for the album stats page (feature plan:
 # /home/paul/.pi/plans/shuriken-stats-site.md, field audit:
 # docs/stats-exif-audit.md). This module turns the per-photo
@@ -3688,6 +3688,16 @@ collect_photo_exif_stats() {
     done < <(incoming_image_files)
 }
 
+# Inlined from src/lib/stats-render.source.sh
+# Stats overview page rendering. Split out of stats.source.sh (task cn0) so the
+# HTML/layout concern lives apart from the EXIF aggregation/bucketing (now in
+# stats-aggregate.source.sh) and the per-filter mini-albums (now in
+# stats-filter-album.source.sh). This module reads the STATS_* globals filled by
+# collect_photo_exif_stats and turns them into the static stats overview page
+# (bar charts, sections, camera leaderboard). All libs are sourced before run,
+# so the STATS_* maps and the STATS_*_DIR constants defined in the sibling
+# modules are available here at runtime.
+
 # ----------------------------------------------------------------------------
 # Rendering (task pm0)
 # ----------------------------------------------------------------------------
@@ -4076,6 +4086,15 @@ render_stats_page() {
         tarball_name ''
 }
 
+# Inlined from src/lib/stats-filter-album.source.sh
+# Per-filter mini-album page rendering. Split out of stats.source.sh (task cn0)
+# so this concern is separate from the EXIF aggregation (stats-aggregate.source.sh)
+# and the stats overview page (stats-render.source.sh). Every tallied bucket
+# becomes a clickable mini album under dist/stats/<pagebase>/. This module reads
+# the STATS_FILTER_* globals filled by collect_photo_exif_stats plus the
+# album-side ALBUM_VIEW_PAGE_BY_PHOTO map at runtime; all libs are sourced before
+# run so cross-module references resolve.
+
 # ----------------------------------------------------------------------------
 # Filter mini-album pages
 # ----------------------------------------------------------------------------
diff --git a/src/lib/stats-aggregate.source.sh b/src/lib/stats-aggregate.source.sh
new file mode 100644
index 0000000..ebb75cf
--- /dev/null
+++ b/src/lib/stats-aggregate.source.sh
@@ -0,0 +1,602 @@
+# Stats aggregation for the album stats page (feature plan:
+# /home/paul/.pi/plans/shuriken-stats-site.md, field audit:
+# docs/stats-exif-audit.md). This module turns the per-photo
+# `identify -verbose` output that album.source.sh already caches into
+# aggregated, photographer-friendly counters.
+#
+# Scope: aggregation only. Rendering (stats.tmpl / camera.tmpl) lives in the
+# sibling tasks pm0/rm0/um0; this module just fills the data structures they
+# read.
+#
+# ----------------------------------------------------------------------------
+# Public API / handoff contract
+# ----------------------------------------------------------------------------
+# collect_photo_exif_stats iterates the album's photos and fills these globals
+# (all declared with `declare -gA` so the render tasks can read them after the
+# call without namerefs):
+#
+#   STATS_CAMERAS[<camera label>]      = count          (camera leaderboard)
+#   STATS_LENSES[<lens model>]         = count           (sparse; may be empty)
+#   STATS_YEARS[<YYYY>]                = count
+#   STATS_MONTHS[<01..12>]             = count
+#   STATS_APERTURE[<bucket>]           = count           (e.g. "f/2.8")
+#   STATS_SHUTTER[<bucket>]            = count           (e.g. "1/250s")
+#   STATS_ISO[<bucket>]                = count           (e.g. "400")
+#   STATS_FOCAL[<bucket>]              = count           (e.g. "35-70mm")
+#   STATS_MEGAPIXELS[<bucket>]         = count           (e.g. "10-20MP")
+#   STATS_ASPECT[<bucket>]             = count           (e.g. "3:2")
+#   STATS_ORIENTATION[<bucket>]        = count           (Landscape/Portrait/Square)
+#   STATS_FORMAT[<bucket>]             = count           (JPEG/PNG/WEBP/GIF)
+#   STATS_EXPOSURE_PROGRAM[<label>]    = count           (decoded enum)
+#   STATS_METERING[<label>]            = count           (decoded enum)
+#   STATS_WHITE_BALANCE[<label>]       = count           (Auto/Manual)
+#   STATS_FLASH[<label>]               = count           (Fired/Did not fire; sparse)
+#   STATS_TOTALS[photos]               = number of photos seen
+#
+# It also fills the filter mini-album maps (see reset_photo_exif_stats):
+# STATS_FILTER_PHOTOS / STATS_FILTER_TITLE keyed by a unique "pagebase", and
+# STATS_FILTER_PAGEBASE mapping "<prefix>\x1f<label>" -> pagebase so the stats
+# rows can link to each bucket's mini-album.
+#
+# The render side should treat every per-category array as possibly empty
+# (sparse data) and only render a section when it has entries. STATS_TOTALS
+# gives the denominator for percentages.
+
+# Reset every stats global to an empty associative array. Called at the start of
+# collect_photo_exif_stats so repeated invocations (e.g. tests, --refresh) do
+# not accumulate stale counts.
+reset_photo_exif_stats() {
+    declare -gA STATS_CAMERAS=()
+    declare -gA STATS_LENSES=()
+    declare -gA STATS_YEARS=()
+    declare -gA STATS_MONTHS=()
+    declare -gA STATS_APERTURE=()
+    declare -gA STATS_SHUTTER=()
+    declare -gA STATS_ISO=()
+    declare -gA STATS_FOCAL=()
+    declare -gA STATS_MEGAPIXELS=()
+    declare -gA STATS_ASPECT=()
+    declare -gA STATS_ORIENTATION=()
+    declare -gA STATS_FORMAT=()
+    declare -gA STATS_EXPOSURE_PROGRAM=()
+    declare -gA STATS_METERING=()
+    declare -gA STATS_WHITE_BALANCE=()
+    declare -gA STATS_FLASH=()
+    declare -gA STATS_TOTALS=()
+    STATS_TOTALS[photos]=0
+    # Every tallied bucket (across all categories) becomes a clickable filter
+    # mini-album. These map a unique, filename-safe "pagebase" (e.g. iso-400,
+    # camera-canon-eos-r5, year-2023) to that bucket's data:
+    #   STATS_FILTER_PHOTOS[pagebase]   = newline-separated photo list
+    #   STATS_FILTER_TITLE[pagebase]    = human heading for the gallery page
+    #   STATS_FILTER_OWNER[pagebase]    = catkey owning the pagebase (collisions)
+    #   STATS_FILTER_PAGEBASE[catkey]   = pagebase for a "<prefix>\x1f<label>"
+    # so the bar rows can link to the matching mini-album.
+    declare -gA STATS_FILTER_PHOTOS=()
+    declare -gA STATS_FILTER_TITLE=()
+    declare -gA STATS_FILTER_OWNER=()
+    declare -gA STATS_FILTER_PAGEBASE=()
+    # Cached background photo list (filled lazily by _stats_random_background);
+    # cleared so a fresh generation rescans the (possibly changed) photos dir.
+    declare -ga STATS_BG_PHOTOS=()
+    STATS_BG_PHOTOS_LOADED=''
+}
+
+# Decode an EXIF rational ("num/den") to a decimal with `scale` digits.
+# Guards den == 0 and tolerates plain decimals (some tools write "0.5"). Prints
+# nothing for unparseable input so callers can skip it. The audit lists this as
+# shared work for FNumber/FocalLength/ExposureTime.
+_stats_rational_to_decimal() {
+    local -r value="$1"; shift
+    local -r scale="${1:-2}"
+
+    if [[ "$value" =~ ^([0-9]+)/([0-9]+)$ ]]; then
+        local -r num="${BASH_REMATCH[1]}"
+        local -r den="${BASH_REMATCH[2]}"
+        if (( den == 0 )); then
+            return
+        fi
+        awk -v n="$num" -v d="$den" -v s="$scale" \
+            'BEGIN { printf "%.*f", s, n / d }'
+        return
+    fi
+    # Already a bare decimal/integer: echo it back so buckets can use it.
+    if [[ "$value" =~ ^[0-9]+([.][0-9]+)?$ ]]; then
+        printf '%s' "$value"
+    fi
+}
+
+# Bucket an f-number (decimal) to the nearest standard aperture stop, matching
+# the boundaries in the plan (≤f/1.8 ... ≥f/22). The decimal is compared with
+# awk so we avoid bash integer-only math on fractional stops.
+_stats_aperture_bucket() {
+    local -r fnum="$1"; shift
+
+    awk -v f="$fnum" 'BEGIN {
+        if (f <= 1.8) { print "f/1.8 or wider"; }
+        else if (f <= 2.2) { print "f/2"; }
+        else if (f <= 3.2) { print "f/2.8"; }
+        else if (f <= 4.5) { print "f/4"; }
+        else if (f <= 6.7) { print "f/5.6"; }
+        else if (f <= 9.5) { print "f/8"; }
+        else if (f <= 13) { print "f/11"; }
+        else if (f <= 19) { print "f/16"; }
+        else { print "f/22 or narrower"; }
+    }'
+}
+
+# Bucket a shutter speed (already normalized to seconds) into the plan's ranges.
+# Faster shutters are smaller numbers, so the ladder runs from short to long.
+_stats_shutter_bucket() {
+    local -r seconds="$1"; shift
+
+    awk -v s="$seconds" 'BEGIN {
+        if (s <= 1/4000) { print "1/4000s or faster"; }
+        else if (s <= 1/2000) { print "1/2000s"; }
+        else if (s <= 1/1000) { print "1/1000s"; }
+        else if (s <= 1/500) { print "1/500s"; }
+        else if (s <= 1/250) { print "1/250s"; }
+        else if (s <= 1/125) { print "1/125s"; }
+        else if (s <= 1/60) { print "1/60s"; }
+        else if (s <= 1/30) { print "1/30s"; }
+        else if (s <= 1/15) { print "1/15s"; }
+        else if (s <= 1/8) { print "1/8s"; }
+        else if (s <= 1/4) { print "1/4s"; }
+        else if (s <= 1/2) { print "1/2s"; }
+        else if (s <= 1) { print "1s"; }
+        else { print "longer than 1s"; }
+    }'
+}
+
+# Bucket an integer ISO to the next standard value at or above it. Plain integer
+# per the audit; uses bash arithmetic since ISO is always an integer.
+_stats_iso_bucket() {
+    local -ri iso="$1"
+
+    if (( iso <= 50 )); then printf '50'
+    elif (( iso <= 100 )); then printf '100'
+    elif (( iso <= 200 )); then printf '200'
+    elif (( iso <= 400 )); then printf '400'
+    elif (( iso <= 800 )); then printf '800'
+    elif (( iso <= 1600 )); then printf '1600'
+    elif (( iso <= 3200 )); then printf '3200'
+    elif (( iso <= 6400 )); then printf '6400'
+    elif (( iso <= 12800 )); then printf '12800'
+    elif (( iso <= 25600 )); then printf '25600'
+    else printf 'over 25600'
+    fi
+}
+
+# Bucket a focal length (decimal mm) by the plan's lens ranges. Labelled as
+# physical focal length, not 35mm-equivalent, per the audit.
+_stats_focal_bucket() {
+    local -r mm="$1"; shift
+
+    awk -v m="$mm" 'BEGIN {
+        if (m < 24) { print "under 24mm"; }
+        else if (m < 35) { print "24-35mm"; }
+        else if (m < 70) { print "35-70mm"; }
+        else if (m < 135) { print "70-135mm"; }
+        else if (m <= 200) { print "135-200mm"; }
+        else { print "over 200mm"; }
+    }'
+}
+
+# Bucket megapixels (W*H/1e6) by the plan's ranges.
+_stats_megapixels_bucket() {
+    local -r mp="$1"; shift
+
+    awk -v p="$mp" 'BEGIN {
+        if (p < 2) { print "under 2MP"; }
+        else if (p < 5) { print "2-5MP"; }
+        else if (p < 10) { print "5-10MP"; }
+        else if (p < 20) { print "10-20MP"; }
+        else if (p < 40) { print "20-40MP"; }
+        else if (p <= 80) { print "40-80MP"; }
+        else { print "over 80MP"; }
+    }'
+}
+
+# Reduce W:H by GCD and match common photographic aspect ratios. The audit
+# recommends deriving this from Geometry rather than EXIF.
+_stats_aspect_bucket() {
+    local -ri width="$1"; shift
+    local -ri height="$1"; shift
+    local -i a="$width"
+    local -i b="$height"
+    local -i t
+
+    if (( width <= 0 || height <= 0 )); then
+        return
+    fi
+    while (( b != 0 )); do
+        t=$b
+        b=$(( a % b ))
+        a=$t
+    done
+    case "$(( width / a )):$(( height / a ))" in
+        3:2|2:3) printf '3:2' ;;
+        4:3|3:4) printf '4:3' ;;
+        16:9|9:16) printf '16:9' ;;
+        1:1) printf '1:1' ;;
+        5:4|4:5) printf '5:4' ;;
+        *) printf 'other' ;;
+    esac
+}
+
+# Orientation from width vs height. The audit prefers this over the native
+# Orientation rotation flag, which is frequently absent or already baked in.
+_stats_orientation_bucket() {
+    local -ri width="$1"; shift
+    local -ri height="$1"; shift
+
+    if (( width > height )); then printf 'Landscape'
+    elif (( height > width )); then printf 'Portrait'
+    else printf 'Square'
+    fi
+}
+
+# Decode the ExposureProgram enum (0-8) to a friendly label. ImageMagick emits
+# the bare integer; the audit supplies this map.
+_stats_exposure_program_label() {
+    case "$1" in
+        1) printf 'Manual' ;;
+        2) printf 'Program AE' ;;
+        3) printf 'Aperture priority' ;;
+        4) printf 'Shutter priority' ;;
+        5) printf 'Creative' ;;
+        6) printf 'Action' ;;
+        7) printf 'Portrait' ;;
+        8) printf 'Landscape' ;;
+        *) printf 'Not defined' ;;
+    esac
+}
+
+# Decode the MeteringMode enum to a friendly label per the audit's map.
+_stats_metering_label() {
+    case "$1" in
+        1) printf 'Average' ;;
+        2) printf 'Center-weighted' ;;
+        3) printf 'Spot' ;;
+        4) printf 'Multi-spot' ;;
+        5) printf 'Multi-segment' ;;
+        6) printf 'Partial' ;;
+        255) printf 'Other' ;;
+        *) printf 'Unknown' ;;
+    esac
+}
+
+# Standard EXIF WhiteBalance is only a 2-value enum (0 Auto, 1 Manual); the
+# richer presets live in MakerNotes and are not exposed by identify (audit).
+_stats_white_balance_label() {
+    case "$1" in
+        0) printf 'Auto' ;;
+        1) printf 'Manual' ;;
+        *) return ;;
+    esac
+}
+
+# Decode the EXIF Flash bitmask: bit 0 indicates the flash fired. The audit
+# warns this tag is frequently missing, so callers must tolerate absence.
+_stats_flash_label() {
+    local -ri flash="$1"
+
+    if (( flash & 1 )); then printf 'Flash fired'
+    else printf 'No flash'
+    fi
+}
+
+# Build a filename-safe slug for camera-<slug>.html. Lowercase, non-alphanumeric
+# runs collapsed to a single dash, leading/trailing dashes trimmed.
+_stats_slug() {
+    local slug="${1,,}"
+
+    slug="${slug//[^a-z0-9]/-}"
+    while [[ "$slug" == *--* ]]; do
+        slug="${slug//--/-}"
+    done
+    slug="${slug#-}"
+    slug="${slug%-}"
+    printf '%s' "$slug"
+}
+
+# Join Make + Model into a single camera label, reusing the same dedup logic as
+# album.source.sh's tooltip builder (handles "Model already includes Make").
+_stats_camera_label() {
+    local -r make="$1"; shift
+    local -r model="$1"; shift
+
+    if [ -z "$model" ]; then
+        printf '%s' "$make"
+        return
+    fi
+    if [ -z "$make" ]; then
+        printf '%s' "$model"
+        return
+    fi
+    case "$model" in
+        "$make"|"$make "*) printf '%s' "$model" ;;
+        *) printf '%s %s' "$make" "$model" ;;
+    esac
+}
+
+# Tally a photo's camera (Make+Model) and, when present, its lens into their
+# leaderboard counts and filter mini-albums. Skips photos with no Make/Model.
+_stats_record_camera() {
+    local -n values_ref="$1"; shift
+    local -r photo="$1"; shift
+    local label
+
+    label=$(_stats_camera_label "${values_ref[Make]:-}" "${values_ref[Model]:-}")
+    _stats_tally STATS_CAMERAS camera "$label" "$label" "$photo"
+    if [ -n "${values_ref[LensModel]:-}" ]; then
+        _stats_tally STATS_LENSES lens \
+            "${values_ref[LensModel]}" "Lens ${values_ref[LensModel]}" "$photo"
+    fi
+}
+
+# Record year and month counters from DateTimeOriginal ("YYYY:MM:DD HH:MM:SS").
+# Parsed by substring per the audit: the colons in the date part are not
+# standard, so this must not be fed to `date -d`. Falls back to the digitized /
+# plain DateTime tags.
+_stats_record_datetime() {
+    local -n values_ref="$1"; shift
+    local -r photo="$1"; shift
+    local raw=''
+    local key
+    local -ra month_names=( '' January February March April May June July
+        August September October November December )
+
+    for key in DateTimeOriginal DateTimeDigitized DateTime; do
+        if [ -n "${values_ref[$key]:-}" ]; then
+            raw="${values_ref[$key]}"
+            break
+        fi
+    done
+    if [[ ! "$raw" =~ ^([0-9]{4}):([0-9]{2}): ]]; then
+        return
+    fi
+    local -r year="${BASH_REMATCH[1]}"
+    local -r month="${BASH_REMATCH[2]}"
+    _stats_tally STATS_YEARS year "$year" "Year $year" "$photo"
+    _stats_tally STATS_MONTHS month "$month" \
+        "${month_names[10#$month]:-Month $month}" "$photo"
+}
+
+# Record the aperture, shutter, ISO and focal-length histograms. Each uses the
+# fallback tag order the audit recommends and the rational decoder for the
+# fiddly fields. Missing/unparseable values are simply skipped.
+_stats_record_exposure() {
+    local -n values_ref="$1"; shift
+    local -r photo="$1"; shift
+    local decimal raw bucket
+
+    raw="${values_ref[FNumber]:-}"
+    decimal=$(_stats_rational_to_decimal "$raw")
+    if [ -n "$decimal" ]; then
+        bucket=$(_stats_aperture_bucket "$decimal")
+        _stats_tally STATS_APERTURE aperture "$bucket" "Aperture $bucket" "$photo"
+    fi
+
+    raw="${values_ref[ExposureTime]:-}"
+    decimal=$(_stats_rational_to_decimal "$raw" 6)
+    if [ -n "$decimal" ]; then
+        bucket=$(_stats_shutter_bucket "$decimal")
+        _stats_tally STATS_SHUTTER shutter "$bucket" "Shutter $bucket" "$photo"
+    fi
+
+    # ISO fallback order mirrors album.source.sh's tooltip builder
+    # (ISOSpeedRatings -> PhotographicSensitivity -> ISO) so a photo carrying
+    # several ISO tags buckets the same value it shows in its tooltip.
+    raw="${values_ref[ISOSpeedRatings]:-${values_ref[PhotographicSensitivity]:-${values_ref[ISO]:-}}}"
+    if [[ "$raw" =~ ^[0-9]+$ ]]; then
+        bucket=$(_stats_iso_bucket "$raw")
+        _stats_tally STATS_ISO iso "$bucket" "ISO $bucket" "$photo"
+    fi
+
+    raw="${values_ref[FocalLength]:-}"
+    decimal=$(_stats_rational_to_decimal "$raw")
+    if [ -n "$decimal" ]; then
+        bucket=$(_stats_focal_bucket "$decimal")
+        _stats_tally STATS_FOCAL focal "$bucket" "Focal length $bucket" "$photo"
+    fi
+}
+
+# Record the decoded enum stats (exposure program, metering, white balance,
+# flash). Each is skipped when the tag is absent or decodes to nothing (empty
+# labels are dropped by _stats_tally).
+_stats_record_enums() {
+    local -n values_ref="$1"; shift
+    local -r photo="$1"; shift
+    local label
+
+    if [ -n "${values_ref[ExposureProgram]:-}" ]; then
+        label=$(_stats_exposure_program_label "${values_ref[ExposureProgram]}")
+        _stats_tally STATS_EXPOSURE_PROGRAM exposure-program \
+            "$label" "Exposure program $label" "$photo"
+    fi
+    if [ -n "${values_ref[MeteringMode]:-}" ]; then
+        label=$(_stats_metering_label "${values_ref[MeteringMode]}")
+        _stats_tally STATS_METERING metering "$label" "Metering $label" "$photo"
+    fi
+    if [ -n "${values_ref[WhiteBalance]:-}" ]; then
+        label=$(_stats_white_balance_label "${values_ref[WhiteBalance]}")
+        _stats_tally STATS_WHITE_BALANCE white-balance \
+            "$label" "White balance $label" "$photo"
+    fi
+    if [[ "${values_ref[Flash]:-}" =~ ^[0-9]+$ ]]; then
+        label=$(_stats_flash_label "${values_ref[Flash]}")
+        _stats_tally STATS_FLASH flash "$label" "Flash $label" "$photo"
+    fi
+}
+
+# Record dimension stats (megapixels, aspect ratio, orientation) from the native
+# Geometry field. Geometry is "WxH+x+y"; the leading WxH is what we need. These
+# are native fields, not exif: lines, so they come from the separate native
+# parser path in _stats_parse_identify_stream.
+_stats_record_dimensions() {
+    local -n values_ref="$1"; shift
+    local -r photo="$1"; shift
+    local mp bucket
+
+    if [[ ! "${values_ref[__geometry]:-}" =~ ^([0-9]+)x([0-9]+) ]]; then
+        return
+    fi
+    local -ri width="${BASH_REMATCH[1]}"
+    local -ri height="${BASH_REMATCH[2]}"
+
+    mp=$(awk -v w="$width" -v h="$height" 'BEGIN { printf "%.4f", w * h / 1000000 }')
+    bucket=$(_stats_megapixels_bucket "$mp")
+    _stats_tally STATS_MEGAPIXELS megapixels "$bucket" "Megapixels $bucket" "$photo"
+    bucket=$(_stats_aspect_bucket "$width" "$height")
+    _stats_tally STATS_ASPECT aspect "$bucket" "Aspect ratio $bucket" "$photo"
+    bucket=$(_stats_orientation_bucket "$width" "$height")
+    _stats_tally STATS_ORIENTATION orientation "$bucket" "$bucket" "$photo"
+}
+
+# Record the file-format breakdown. The audit's cheapest path keys off the file
+# extension (no identify parsing), so this maps the extension to a format label.
+# This trusts the extension over actual content: a misnamed file (e.g. a PNG
+# named .jpg) is counted by its name. Unrecognized extensions fall into 'other'.
+_stats_record_format() {
+    local -r photo="$1"; shift
+    local extension="${photo##*.}"
+    local label
+
+    if [[ "$photo" != *.* ]]; then
+        return
+    fi
+    case "${extension,,}" in
+        jpg|jpeg) label=JPEG ;;
+        png) label=PNG ;;
+        webp) label=WEBP ;;
+        gif) label=GIF ;;
+        *) label=other ;;
+    esac
+    _stats_tally STATS_FORMAT format "$label" "$label" "$photo"
+}
+
+# Increment a counter in the named global associative array. Centralizes the
+# "create-or-add-one" idiom and skips empty keys so unparseable buckets do not
+# create blank entries.
+_stats_bump() {
+    local -n array_ref="$1"; shift
+    local -r key="$1"; shift
+
+    if [ -z "$key" ]; then
+        return
+    fi
+    array_ref["$key"]=$(( ${array_ref["$key"]:-0} + 1 ))
+}
+
+# Field separator used inside STATS_FILTER_PAGEBASE keys ("<prefix>\x1f<label>").
+# A control char that cannot appear in a prefix or an EXIF label.
+declare -gr STATS_FILTER_KEYSEP=$'\x1f'
+
+# Resolve the unique, filename-safe pagebase for a (prefix, label) filter into
+# the named output variable, caching it so repeated tallies reuse it. Distinct
+# labels in the same category whose slug collides (e.g. two camera models
+# differing only in punctuation) get a numeric suffix. Uses a nameref output --
+# not command substitution -- so the STATS_FILTER_OWNER/PAGEBASE mutations
+# persist in the caller's shell.
+_stats_resolve_filter_pagebase() {
+    local -n pagebase_out_ref="$1"; shift
+    local -r prefix="$1"; shift
+    local -r label="$1"; shift
+    local -r catkey="$prefix$STATS_FILTER_KEYSEP$label"
+    local base slug
+    local -i suffix=2
+
+    if [ -n "${STATS_FILTER_PAGEBASE[$catkey]:-}" ]; then
+        pagebase_out_ref="${STATS_FILTER_PAGEBASE[$catkey]}"
+        return
+    fi
+    slug=$(_stats_slug "$label")
+    if [ -z "$slug" ]; then
+        slug=other
+    fi
+    base="$prefix-$slug"
+    pagebase_out_ref="$base"
+    while [ -n "${STATS_FILTER_OWNER[$pagebase_out_ref]:-}" ] \
+        && [ "${STATS_FILTER_OWNER[$pagebase_out_ref]}" != "$catkey" ]; do
+        pagebase_out_ref="$base-$suffix"
+        (( ++suffix ))
+    done
+    STATS_FILTER_OWNER["$pagebase_out_ref"]="$catkey"
+    STATS_FILTER_PAGEBASE["$catkey"]="$pagebase_out_ref"
+}
+
+# Tally one photo into a bucket: bump the category count AND record the photo on
+# the bucket's filter mini-album (keyed by a unique pagebase). prefix namespaces
+# the pagebase per category, label is the bucket key (also the count-array key),
+# and title is the gallery heading shown for that bucket. Skips empty labels.
+_stats_tally() {
+    local -r count_array="$1"; shift
+    local -r prefix="$1"; shift
+    local -r label="$1"; shift
+    local -r title="$1"; shift
+    local -r photo="$1"; shift
+    local pagebase
+
+    if [ -z "$label" ]; then
+        return
+    fi
+    _stats_bump "$count_array" "$label"
+    _stats_resolve_filter_pagebase pagebase "$prefix" "$label"
+    if [ -n "${STATS_FILTER_PHOTOS[$pagebase]:-}" ]; then
+        STATS_FILTER_PHOTOS["$pagebase"]+=$'\n'"$photo"
+    else
+        STATS_FILTER_PHOTOS["$pagebase"]="$photo"
+        STATS_FILTER_TITLE["$pagebase"]="$title"
+    fi
+}
+
+# Parse one photo's `identify -verbose` stream into an associative array. The
+# current album.source.sh regex only captures exif: lines, but the audit needs
+# the native Geometry field for dimensions, so this adds a second match path
+# storing it under the synthetic key __geometry.
+_stats_parse_identify_stream() {
+    local -n values_ref="$1"; shift
+    local line
+
+    values_ref=()
+    while IFS= read -r line; do
+        if [[ "$line" =~ ^[[:space:]]*exif:([^:]+):[[:space:]]*(.*)$ ]]; then
+            values_ref["${BASH_REMATCH[1]}"]="${BASH_REMATCH[2]}"
+        elif [[ "$line" =~ ^[[:space:]]*Geometry:[[:space:]]*(.*)$ ]]; then
+            values_ref[__geometry]="${BASH_REMATCH[1]}"
+        fi
+    done
+}
+
+# Aggregate a single photo: parse its identify stream (from stdin) and update
+# every counter. Split out from collect_photo_exif_stats so tests can feed a
+# synthetic fixture without stubbing the cache layer.
+accumulate_photo_stats() {
+    local -r photo="$1"; shift
+    # exif_values is filled and read through the nameref helpers below.
+    # shellcheck disable=SC2034
+    local -A exif_values=()
+
+    _stats_parse_identify_stream exif_values
+    STATS_TOTALS[photos]=$(( STATS_TOTALS[photos] + 1 ))
+    _stats_record_camera exif_values "$photo"
+    _stats_record_datetime exif_values "$photo"
+    _stats_record_exposure exif_values "$photo"
+    _stats_record_enums exif_values "$photo"
+    _stats_record_dimensions exif_values "$photo"
+    _stats_record_format "$photo"
+}
+
+# Iterate the album's incoming photos, read each one's cached identify output via
+# album.source.sh's cache helper, and aggregate it into the STATS_* globals.
+# This is the entry point the render tasks call before reading the counters.
+collect_photo_exif_stats() {
+    local photo
+
+    reset_photo_exif_stats
+    while IFS= read -r photo; do
+        accumulate_photo_stats "$photo" \
+            < <(cached_photo_identify_output "$photo" "$INCOMING_DIR/$photo")
+    done < <(incoming_image_files)
+}
diff --git a/src/lib/stats-filter-album.source.sh b/src/lib/stats-filter-album.source.sh
new file mode 100644
index 0000000..2bd6c1b
--- /dev/null
+++ b/src/lib/stats-filter-album.source.sh
@@ -0,0 +1,265 @@
+# Per-filter mini-album page rendering. Split out of stats.source.sh (task cn0)
+# so this concern is separate from the EXIF aggregation (stats-aggregate.source.sh)
+# and the stats overview page (stats-render.source.sh). Every tallied bucket
+# becomes a clickable mini album under dist/stats/<pagebase>/. This module reads
+# the STATS_FILTER_* globals filled by collect_photo_exif_stats plus the
+# album-side ALBUM_VIEW_PAGE_BY_PHOTO map at runtime; all libs are sourced before
+# run so cross-module references resolve.
+
+# ----------------------------------------------------------------------------
+# Filter mini-album pages
+# ----------------------------------------------------------------------------
+# Every tallied bucket (camera, lens, year, month, aperture, ISO, ...) becomes a
+# clickable, self-contained mini album. render_filter_pages turns each pagebase
+# in STATS_FILTER_PHOTOS into a gallery (<pagebase>.html, a thumbnail grid) plus
+# one view page per photo (<pagebase>--<index>.html) whose prev/next cycle only
+# within that filter. The "--<index>" suffix cannot collide with another gallery
+# name because a pagebase never contains "--". All pages reuse the album's shared
+# photos/thumbs/blurs assets (only the HTML differs); view pages link "Details"
+# to the album's own details page via ALBUM_VIEW_PAGE_BY_PHOTO. Pages render in
+# parallel through the shared job pool, throttled to IMAGE_JOBS. The galleries
+# reuse camera.tmpl and the view pages reuse cameraview.tmpl.
+
+# Dist-relative subdirectories holding the shared full-size images, thumbnails
+# and blurred backgrounds, matching the literals generate() passes to
+# render_album_pages so filter pages reuse the same asset files.
+declare -gr STATS_PHOTOS_DIR='photos'
+declare -gr STATS_THUMBS_DIR='thumbs'
+declare -gr STATS_BLURS_DIR='blurs'
+# Everything stats-related lives under this dist subdirectory so the album root
+# only holds the main album: the stats overview is stats/index.html and each
+# filter mini-album is stats/<pagebase>/ (gallery index.html + view pages
+# <index>.html). This keeps the file count in any single directory bounded.
+declare -gr STATS_DIR='stats'
+# Relative path from a filter mini-album page (dist/stats/<pagebase>/...) back to
+# the album root (dist/), used for shared assets and album links.
+declare -gr STATS_FILTER_BACKHREF='../..'
+
+# Emit one thumbnail anchor for a filter gallery: a thumb image (from thumbs/)
+# linking to this filter's view page for that photo (<pagebase>--<index>.html).
+# The photo filename is HTML-escaped; the pagebase and index are filename-safe.
+_stats_filter_thumbnail() {
+    local -r backhref_html="$1"; shift
+    local -ri index="$1"; shift
+    local -r photo="$1"; shift
+    local photo_html
+    local animation_class
+
+    photo_html=$(_html_escape "$photo")
+    # Same seeded animation the album thumbnail uses for this photo.
+    animation_class=$(random_animation_css_class slow "$photo")
+    # The view page sits in the same directory as this gallery, so link to it by
+    # bare index; the thumbnail image lives at the album root via backhref.
+    printf '        <a name="%s" href="%d.html">' "$photo_html" "$index"
+    printf '<img class="thumb %s" src="%s/%s/%s" /></a>\n' \
+        "$animation_class" "$backhref_html" "$STATS_THUMBS_DIR" "$photo_html"
+}
+
+# Build the full thumbnail grid for one filter from its newline-separated photo
+# list, preserving aggregation (encounter) order for deterministic output.
+_stats_build_filter_thumbs() {
+    local -r backhref_html="$1"; shift
+    local -r photos="$1"; shift
+    local photo
+    local -i index=0
+
+    while IFS= read -r photo; do
+        if [ -n "$photo" ]; then
+            (( ++index ))
+            _stats_filter_thumbnail "$backhref_html" "$index" "$photo"
+        fi
+    done <<< "$photos"
+}
+
+# Render a filter gallery page (<pagebase>.html): header + camera.tmpl (heading +
+# pre-built thumbnail grid) + footer. camera.tmpl is reused for every filter; the
+# heading is the bucket's title (camera name, "ISO 400", "Year 2023", ...).
+# Each filter mini-album lives in its own directory stats/<pagebase>/, so the
+# gallery is index.html and the view pages are <index>.html. backhref is fixed
+# (../.. back to the album root). camera.tmpl/cameraview.tmpl are reused.
+_stats_render_filter_gallery() {
+    local -r pagebase="$1"; shift
+    local thumbs
+    local background_image
+    local -r html_dir="$STATS_DIR/$pagebase"
+    local -r backhref="$STATS_FILTER_BACKHREF"
+    local -r backhref_html="$STATS_FILTER_BACKHREF"
+    local -r title="${STATS_FILTER_TITLE[$pagebase]:-}"
+
+    thumbs=$(_stats_build_filter_thumbs \
+        "$backhref_html" "${STATS_FILTER_PHOTOS[$pagebase]}")
+    # Background fits the category: a random photo from this filter's own set,
+    # mirroring how the album preview pages pick a random album photo.
+    background_image=$(_stats_pick_background \
+        "$pagebase" "${STATS_FILTER_PHOTOS[$pagebase]}")
+    template header index.html \
+        html_dir "$html_dir" backhref "$backhref" \
+        blurs_dir "$STATS_BLURS_DIR" background_image "$background_image" \
+        show_header_bar 'yes'
+    template camera index.html \
+        html_dir "$html_dir" backhref "$backhref" \
+        camera_name "$title" camera_thumbs "$thumbs"
+    template footer index.html \
+        html_dir "$html_dir" backhref "$backhref" tarball_name ''
+}
+
+# Render one filter view page (<pagebase>--<index>.html): header + cameraview
+# body + footer, with prev/next cycling within the filter.
+_stats_render_filter_view_page() {
+    local -r pagebase="$1"; shift
+    local -r photo="$1"; shift
+    local -ri index="$1"; shift
+    local -ri prev="$1"; shift
+    local -ri next="$1"; shift
+    local body
+    local background_image
+    local -r html_dir="$STATS_DIR/$pagebase"
+    local -r backhref="$STATS_FILTER_BACKHREF"
+    local -r page="$index.html"
+
+    body=$(_stats_build_filterview_body \
+        "$STATS_FILTER_BACKHREF" "$photo" "$prev" "$next")
+    # The view page's blurred background is the photo it shows, exactly like the
+    # album view pages.
+    background_image="$photo"
+    template header "$page" \
+        html_dir "$html_dir" backhref "$backhref" \
+        blurs_dir "$STATS_BLURS_DIR" background_image "$background_image" \
+        show_header_bar 'no'
+    template cameraview "$page" \
+        html_dir "$html_dir" backhref "$backhref" cameraview_body "$body"
+    template footer "$page" \
+        html_dir "$html_dir" backhref "$backhref" tarball_name ''
+}
+
+# Build a filter view page body: the photo (linked to the filter's next photo)
+# plus a navigator whose prev/next cycle within the filter, a link back to the
+# gallery, an optional Details link to the album's details page, and a direct
+# image link.
+_stats_build_filterview_body() {
+    local -r backhref_html="$1"; shift
+    local -r photo="$1"; shift
+    local -ri prev="$1"; shift
+    local -ri next="$1"; shift
+    local photo_html
+    local animation_class
+    local tooltip
+    local tooltip_attr=''
+    local view_page
+    local details_link=''
+
+    photo_html=$(_html_escape "$photo")
+    animation_class=$(random_animation_css_class fast "$photo")
+    tooltip=$(photo_exif_tooltip_text "$photo" "$INCOMING_DIR/$photo")
+    if [ -n "$tooltip" ]; then
+        tooltip_attr=" title=\"$(_html_escape "$tooltip")\""
+    fi
+    view_page="${ALBUM_VIEW_PAGE_BY_PHOTO[$photo]:-}"
+    if [ -n "$view_page" ]; then
+        details_link=$(printf ' <a href="%s/%s-details.html">Details</a> |' \
+            "$backhref_html" "$view_page")
+    fi
+    _stats_print_filterview_body "$backhref_html" "$photo_html" \
+        "$animation_class" "$tooltip_attr" "$details_link" "$prev" "$next"
+}
+
+# Emit the filter view page markup. Split out so _stats_build_filterview_body
+# stays focused on assembling the pieces.
+# The prev/next/gallery links are same-directory (this view page lives in the
+# filter's own stats/<pagebase>/ dir); the image, details, and direct links go
+# back to the album root via backhref.
+_stats_print_filterview_body() {
+    local -r backhref_html="$1"; shift
+    local -r photo_html="$1"; shift
+    local -r animation_class="$1"; shift
+    local -r tooltip_attr="$1"; shift
+    local -r details_link="$1"; shift
+    local -ri prev="$1"; shift
+    local -ri next="$1"; shift
+
+    cat <<END
+<div class='view'>
+    <a href="$next.html">
+        <img class='view $animation_class' border='0' src='$backhref_html/$STATS_PHOTOS_DIR/$photo_html'$tooltip_attr />
+    </a>
+    <div class="navigator">
+        <a href="$prev.html" class="arrow">&lArr;</a>
+        <a href="index.html">Gallery</a> |$details_link
+        <a href="$backhref_html/$STATS_PHOTOS_DIR/$photo_html">Direct link</a>
+        <a href="$next.html" class="arrow">&rArr;</a>
+    </div>
+</div>
+END
+}
+
+# Enqueue one filter's mini-album (gallery + a view page per photo) onto the
+# shared render job pool, waiting for a free slot (<= IMAGE_JOBS) before each
+# background render so parallelism follows the configured IMAGE_JOBS.
+_stats_enque