#!/usr/bin/env bash
set -euo pipefail
# POS: media sync — Incremental Music → USB sync (mp3/mp4, add/update only)
# POS_FLAGS: --mp3 --mp4 --source --dry-run

source "$(dirname "$0")/../lib/common.sh" 2>/dev/null || source "$(dirname "$0")/common.sh"
source "$(dirname "$0")/../lib/notify.sh" 2>/dev/null || source "$(dirname "$0")/notify.sh"
source "$(dirname "$0")/../lib/usb-lib.sh" 2>/dev/null || source "$(dirname "$0")/usb-lib.sh"

load_system_env

# Deps guards sit before -h|--help (help also errors on a box missing the deps).
command -v lsblk &>/dev/null || err "lsblk not found (util-linux) — needed to detect USB storage"
command -v jq    &>/dev/null || err "jq not found — needed to detect USB storage (sudo apt install jq)"

SRC="${MEDIA_SYNC_SOURCE:-$HOME/Music}"
DEST_DIR="${MEDIA_SYNC_DEST:-Music}"
MP3=0
MP4=0
DRY_RUN=0

usage() {
    cat <<EOF
Usage: pos media sync [options]

Incrementally copy your music onto a USB stick. Add/update only — files on
the stick that are no longer in the source are left alone, never deleted.
USB storage is detected like \`pos system backup\` (lsblk TRAN + lsusb/by-id
corroboration; unmounted sticks get a mount offer first) and you pick which
one to sync to. The source tree is mirrored under <usb>/$DEST_DIR.

Options:
  --mp3               Sync only *.mp3 files
  --mp4               Sync only *.mp4 files
  --source <dir>      Source folder (default: $SRC)
  --dry-run           Preview what would be copied (copies nothing)
  -h, --help          This help

Examples:
  pos media sync
  pos media sync --mp3
  pos media sync --mp4 --dry-run
  pos media sync --source /data/Music

Environment:
  MEDIA_SYNC_SOURCE   Source folder (default: \$HOME/Music)
  MEDIA_SYNC_DEST     Subfolder on the USB stick (default: Music)
  USB_MOUNT_BASE      Where to mount an unmounted stick (default: /media)
  USB_BYID            by-id dir used to corroborate USB detection
                      (default: /dev/disk/by-id)
  (loaded from ~/.config/linux_post_install/system.env unless exported)
EOF
    exit 0
}

while [[ $# -gt 0 ]]; do
    case "$1" in
        -h|--help) usage ;;
        --mp3) MP3=1; shift ;;
        --mp4) MP4=1; shift ;;
        --dry-run) DRY_RUN=1; shift ;;
        --source)
            [ $# -ge 2 ] || err "--source needs a value: pos media sync --source <dir>"
            SRC="$2"; shift 2 ;;
        --source=*) SRC="${1#--source=}"; shift ;;
        -*) err "Unknown option: $1 (see --help)" ;;
        *) err "Unexpected argument: $1 (see --help)" ;;
    esac
done
[ "$MP3" -eq 1 ] || [ "$MP4" -eq 1 ] || { MP3=1; MP4=1; }

# Normalize trailing slashes on the source: GNU find normalizes ONE trailing
# slash on the starting point (find -H /x/ -type f emits /x/a.mp3) but keeps
# a doubled one (find -H /x// -type f emits /x//a.mp3), so with SRC=/x// the
# rel prefix "${f#"$SRC/"}" never matches and files would nest under
# <stick>/Music//x/... instead of mirroring the tree. Strip ALL trailing
# slashes — a lone "/" or "//" ends up empty and hits the guard below.
# Covers both --source /x// and MEDIA_SYNC_SOURCE=...//.
while [[ "$SRC" == */ ]]; do SRC="${SRC%/}"; done
[ -n "$SRC" ] || err "Source path is empty"

[ -d "$SRC" ] || err "Source not found: $SRC"

# find -H follows only the command-line source symlink; symlinks INSIDE the
# tree are never followed, so their targets silently never sync. Count them
# (mindepth 1: a symlink source itself IS followed and must not count) and
# surface the skip instead of leaving a partial mirror unexplained.
inner_links="$(find -H "$SRC" -mindepth 1 -type l 2>/dev/null | wc -l)" || true
inner_links="${inner_links// }"
if [ "$inner_links" -gt 0 ]; then
    warn "${inner_links} symlink(s) inside the source are not followed (find -H) — their targets will not be synced"
fi

trap 'notify_send "Music sync FAILED"' ERR

section "Music sync"
echo "Source : $SRC"
if [ "$MP3" -eq 1 ] && [ "$MP4" -eq 1 ]; then
    echo "Filter : mp3 + mp4"
    find_expr=(-type f \( -iname '*.mp3' -o -iname '*.mp4' \))
elif [ "$MP3" -eq 1 ]; then
    echo "Filter : mp3 only"
    find_expr=(-type f -iname '*.mp3')
else
    echo "Filter : mp4 only"
    find_expr=(-type f -iname '*.mp4')
fi

usb_pick_root "Sync to" "$DEST_DIR" "no sync performed" || {
    log "Skipped — no sync performed"
    exit 0
}
dest_root="${USB_ROOT%/}/$DEST_DIR"
echo "Target : $dest_root"

# Does the destination need this file copied? Missing, or size/mtime differs.
needs_copy() {
    local src="$1" dst="$2" ss="" ds="" sm="" dm=""
    [ -f "$dst" ] || return 0
    ss="$(stat -c %s "$src" 2>/dev/null)" || { return 0; }
    ds="$(stat -c %s "$dst" 2>/dev/null || printf 0)"
    sm="$(stat -c %Y "$src" 2>/dev/null)" || { return 0; }
    dm="$(stat -c %Y "$dst" 2>/dev/null || printf 0)"
    [ "$ss" = "$ds" ] && [ "$sm" -le "$dm" ] && return 1
    return 0
}

# Pre-flight: fail early on "won't fit" instead of a mid-copy ENOSPC that
# leaves a half-written target. Measures exactly what needs_copy would copy.
space_path="$USB_ROOT"
if [ "$DRY_RUN" -eq 0 ]; then
    mkdir -p "$dest_root"
    space_path="$dest_root"
fi
# One find pass into a temp list, sorted once, shared by the space scan and
# the copy loop so both see the identical file set (the old double find is
# gone). The old process substitution swallowed find's exit code and stderr
# (invisible to set -e / pipefail): an unreadable subdir made find exit 1
# with "Permission denied" yet the tool still announced a false "Sync
# complete" on a partial tree. Capture both and surface them explicitly
# instead of continuing silently.
find_list="$(mktemp)"
find_err="$(mktemp)"
trap 'rm -f "$find_list" "$find_err"' EXIT
find_rc=0
find -H "$SRC" "${find_expr[@]}" >"$find_list" 2>"$find_err" || find_rc=$?
sort -o "$find_list" "$find_list"
# One "find reported problems" condition, computed once here and reused at the
# final success messages (below) so a partial tree is never announced as fully
# synced.
find_ok=1
if [ "$find_rc" -ne 0 ] || [ -s "$find_err" ]; then
    find_ok=0
    warn "find of the source reported problems — results may be incomplete:"
    if [ -s "$find_err" ]; then
        sed 's/^/    /' "$find_err"
    fi
fi

need_kb=0
while IFS= read -r f; do
    rel="${f#"$SRC/"}"
    if needs_copy "$f" "$dest_root/$rel"; then
        sz="$(stat -c %s "$f" 2>/dev/null || printf 0)"
        need_kb=$((need_kb + (sz + 1023) / 1024))
    fi
done < "$find_list"
have_kb="$(df -Pk "$space_path" 2>/dev/null | awk 'NR==2 {print $4}')"
have_kb="${have_kb:-0}"
if [ "$need_kb" -gt "$have_kb" ]; then
    msg="Not enough free space on ${USB_ROOT%/}: need ~${need_kb}K, have ${have_kb}K"
    if [ "$DRY_RUN" -eq 1 ]; then
        warn "$msg"
    else
        err "$msg"
    fi
fi

added=0
updated=0
unchanged=0
while IFS= read -r f; do
    rel="${f#"$SRC/"}"
    dest="$dest_root/$rel"

    if needs_copy "$f" "$dest"; then
        if [ -f "$dest" ]; then
            updated=$((updated + 1))
        else
            added=$((added + 1))
        fi
        if [ "$DRY_RUN" -eq 1 ]; then
            log "would copy  $rel"
        else
            mkdir -p "$(dirname "$dest")"
            cp --preserve=timestamps "$f" "$dest"
            echo "  + $rel"
        fi
    else
        unchanged=$((unchanged + 1))
    fi
done < "$find_list"

# Mark the success line + notification as partial when find reported
# problems, so the success signal can't contradict the warning above.
partial_suffix=""
[ "$find_ok" -eq 0 ] && partial_suffix=" (partial — find reported problems)"
if [ "$DRY_RUN" -eq 1 ]; then
    echo "DRY RUN — nothing copied. Would sync: ${added} new, ${updated} updated, ${unchanged} unchanged → $dest_root"
else
    ok "Sync complete: ${added} added, ${updated} updated, ${unchanged} unchanged → $dest_root$partial_suffix"
    notify_send "Music sync completed: ${added} added, ${updated} updated → $dest_root$partial_suffix"
fi