#!/usr/bin/env bash

usage() {
    cat <<EOF
Usage: $0 -s </path/to/wdl> [-t </path/to/wdl-mount>] [-o <max-ring-overworld>] [-n <max-ring-nether>] [-e <max-ring-end>] [-r </path/to/ring-mount>] [-u]

Options:
  -s </path/to/wdl>         Path to directory containing overworld, nether, and end directories (required)
  -t </path/to/wdl-mount>   Mount point for the final merged directory (default: /mnt/wdl)
  -o <max-ring-overworld>   Maximum ring for overworld (default: 33, set to 0 for none)
  -n <max-ring-nether>      Maximum ring for nether (default: 23, set to 0 for none)
  -e <max-ring-end>         Maximum ring for end (default: 8, set to 0 for none)
  -r </path/to/ring-mount>  Mount point for individual rings (default: /mnt/ring)
  -u                        Use FUSE-based tools (squashfuse + mergerfs) instead of kernel (squashfs + overlayfs)
  -h                        Show this help message
EOF
    exit 1
}

SRC=""
MNT="/mnt/wdl"
MAX_RING_OVERWORLD=33
MAX_RING_NETHER=23
MAX_RING_END=8
RING_MOUNT="/mnt/ring"
USE_FUSE=0

while getopts "s:t:o:n:e:r:uh" opt; do
    case "$opt" in
        s) SRC="$OPTARG" ;;
        t) MNT="$OPTARG" ;;
        o) MAX_RING_OVERWORLD="$OPTARG" ;;
        n) MAX_RING_NETHER="$OPTARG" ;;
        e) MAX_RING_END="$OPTARG" ;;
        r) RING_MOUNT="$OPTARG" ;;
        u) USE_FUSE=1 ;;
        h) usage ;;
        *) usage ;;
    esac
done

if [[ -z "$SRC" ]]; then
    echo "Error: -s </path/to/wdl> is required." >&2
    usage
fi

[[ -d "$SRC" ]] || {
    echo "Error: $SRC is not a directory." >&2
    exit 1
}

if [[ $USE_FUSE -eq 1 ]]; then
    command -v mergerfs >/dev/null || {
        echo "Error: mergerfs is not installed or is not in PATH. Did you mean to enable FUSE-mode (-u)?" >&2
        exit 1
    }
    command -v squashfuse >/dev/null || {
        echo "Error: squashfuse is not installed or is not in PATH. Did you mean to enable FUSE-mode (-u)?" >&2
        exit 1
    }
fi

validate_ring() {
    local arg="$1"
    local value="$2"

    if [[ ! "$value" =~ ^[0-9]+$ ]]; then
        echo "Error: -$arg expects a non-negative integer." >&2
        exit 1
    fi
}

validate_ring "o" "$MAX_RING_OVERWORLD"
validate_ring "n" "$MAX_RING_NETHER"
validate_ring "e" "$MAX_RING_END"

exit_code=0
cleanup() {
    umount "$MNT" 2>/dev/null
    for d in "$RING_MOUNT/"*; do
        [[ -d "$d" ]] && umount "$d" 2>/dev/null
    done
    exit "$exit_code"
}

trap 'exit_code=$?; cleanup' ERR INT TERM

# Mount all rings at $RING_MOUNT/*
# Each ring will be named with the first letter of its dimension, followed by its radius.
# It is recommended to not change this naming scheme if you are using the kernel module for overlayfs, as there
# seems to be a limited number of characters for the `lowerdir` argument, with no workaround aside from writing a program
# that uses fsconfig syscalls to incrementally add more directories. there seems to be no configuration available to
# change the limit, and it can only be changed by recompiling the kernel.

# To get around this, we made the names as short as possible, and pass them to the `lowerdir` argument by relative path.
# This limitation does not exist when using mergerfs (uses FUSE internally).
LOWERS=()

mount_ring() {
    local max=$1
    local prefix=$2
    local dim=$3

    for ((r=1; r<=max; r++)); do
        local img="$SRC/$dim/ring$r.squashfs"
        if [[ ! -f "$img" ]]; then
            echo "Skipping missing ring $img"
            continue
        fi
        local mnt_dir="$RING_MOUNT/$prefix$r"
        mkdir -p "$mnt_dir"

        if [[ $USE_FUSE -eq 1 ]]; then
            squashfuse "$img" "$mnt_dir"
        else
            mount -t squashfs "$img" "$mnt_dir"
        fi || {
            echo "Mount failed for $dim ring$r. Check permissions, filesystem support, or try toggling FUSE-mode (-u)" >&2
            exit_code=1
            cleanup
        }
        LOWERS+=("$prefix$r")
    done
}

mount_ring "$MAX_RING_OVERWORLD" "o" "overworld"
mount_ring "$MAX_RING_NETHER" "n" "nether"
mount_ring "$MAX_RING_END" "e" "end"

if ((${#LOWERS[@]} == 0)); then
    echo "No rings were mounted." >&2
    exit 1
fi

FINAL_LOWER=$(IFS=:; echo "${LOWERS[*]}")

mkdir -p "$MNT"
cd "$RING_MOUNT" || exit 1

if [[ $USE_FUSE -eq 1 ]]; then
    mergerfs -o ro "$FINAL_LOWER" "$MNT"
else
    mount -t overlay overlay -o "lowerdir=$FINAL_LOWER,ro" "$MNT"
fi || {
    echo "Mount failed for final merge at $MNT. Check permissions, filesystem support, or try toggling FUSE-mode (-u)" >&2
    exit_code=1
    cleanup
}