#!/usr/bin/env bash
# Turn the staging directory into a disk image (boot contract v1):
#   * a raw file of IMAGE_MIB MiB,
#   * a GPT partition table (sfdisk) with one partition at sector 2048,
#   * a FAT32 file system in it (mkfs.vfat), filled with mtools.
# mtools (mmd/mcopy) write straight into the image file, so no root and no
# loop-mounting is needed. This is what the kernel's build.rs does.
#
# Usage: scripts/mkimage.sh STAGING IMAGE MIB LABEL "bin order..."
#   The /bin files are copied in the given order (same as the kernel's
#   build.rs), then any other file in STAGING/bin.
set -euo pipefail
STAGING=$1 IMAGE=$2 MIB=$3 LABEL=$4 ORDER=$5
PATH=$PATH:/usr/sbin:/sbin
export MTOOLS_SKIP_CHECK=1

SECTORS=$((MIB * 1024 * 1024 / 512))
START=2048
PART_SECTORS=$((SECTORS - 2 * START))   # 1 MiB free at the end for the backup GPT
PART=$IMAGE.part
rm -f "$PART" "$IMAGE"

# 1. The FAT32 file system as its own file first. -s 1: one sector per
#    cluster (FAT32 needs >= 65525 clusters). -i: a fixed volume serial
#    number, so two builds of the same tree give the same bytes.
mkfs.vfat -F 32 -s 1 -n "$LABEL" -i 466f6e64 -C "$PART" $((PART_SECTORS / 2)) >/dev/null

# Top-level entries (everything except bin/) in sorted order...
for entry in $(cd "$STAGING" && ls -A | LC_ALL=C sort); do
    [ "$entry" = bin ] && continue
    mcopy -s -i "$PART" "$STAGING/$entry" ::/
done
# ...then the programs.
mmd -i "$PART" ::/bin
done_list=" "
for p in $ORDER; do
    [ -f "$STAGING/bin/$p" ] || { echo "[mkimage] missing $STAGING/bin/$p"; exit 1; }
    mcopy -i "$PART" "$STAGING/bin/$p" "::/bin/$p"
    done_list+="$p "
done
for f in $(cd "$STAGING/bin" && ls | LC_ALL=C sort); do
    case "$done_list" in *" $f "*) ;; *) mcopy -i "$PART" "$STAGING/bin/$f" "::/bin/$f" ;; esac
done

# 2. The whole disk: zeros + GPT, then the FAT32 file system in the partition.
truncate -s $((SECTORS * 512)) "$IMAGE"
printf 'label: gpt\nstart=%d, size=%d, type=EBD0A0A2-B9E5-4433-87C0-68B6B72699C7, name="fat32"\n' \
    $START $PART_SECTORS | sfdisk --quiet "$IMAGE"
dd if="$PART" of="$IMAGE" bs=512 seek=$START conv=notrunc status=none
rm -f "$PART"
echo "[mkimage] $IMAGE: $MIB MiB, GPT + FAT32 '$LABEL', $(ls "$STAGING/bin" | wc -l) programs in /bin"