#!/usr/bin/env bash

set -euo pipefail

usage() {
  cat <<'EOF'
Usage:
  generate_migration_test_dataset.sh TARGET_DIR

Creates a compact filesystem migration test dataset under TARGET_DIR.
The dataset matches the manifest in migration-test-manifest.md.

Notes:
  - Existing TARGET_DIR contents are left in place unless they collide.
  - ACL and xattr cases are created only if the local tools are available.
  - Sparse files are created with logical size but low physical allocation.
EOF
}

if [[ $# -ne 1 ]]; then
  usage
  exit 1
fi

TARGET_DIR=$1
ROOT=$(realpath -m "$TARGET_DIR")

mkdir -p "$ROOT"

have_setfacl=0
have_setfattr=0

if command -v setfacl >/dev/null 2>&1; then
  have_setfacl=1
fi

if command -v setfattr >/dev/null 2>&1; then
  have_setfattr=1
fi

create_dir() {
  mkdir -p "$ROOT/$1"
}

set_times() {
  local rel=$1
  local stamp=$2
  touch -a -m -t "$stamp" "$ROOT/$rel"
}

write_text() {
  local path=$1
  local mib=$2
  local bytes=$((mib * 1024 * 1024))
  perl -e '
    my ($target, $label) = @ARGV;
    my $chunk = "Migration text payload for $label\n";
    while (length($chunk) < 8192) { $chunk .= $chunk; }
    while ($target > 0) {
      my $part = substr($chunk, 0, $target > length($chunk) ? length($chunk) : $target);
      print $part;
      $target -= length($part);
    }
  ' "$bytes" "$path" >"$ROOT/$path"
}

write_compressible() {
  local path=$1
  local mib=$2
  local bytes=$((mib * 1024 * 1024))
  perl -e '
    my ($target) = @ARGV;
    my $chunk = "A" x 8192;
    while ($target > 0) {
      my $part = substr($chunk, 0, $target > length($chunk) ? length($chunk) : $target);
      print $part;
      $target -= length($part);
    }
  ' "$bytes" >"$ROOT/$path"
}

write_random() {
  local path=$1
  local mib=$2
  dd if=/dev/urandom of="$ROOT/$path" bs=1M count="$mib" status=none
}

write_script() {
  local path=$1
  local mib=$2
  cat >"$ROOT/$path" <<'EOF'
#!/usr/bin/env bash
echo "migration test script"
EOF
  local current_size
  current_size=$(wc -c <"$ROOT/$path")
  local target_size=$((mib * 1024 * 1024))
  if (( current_size < target_size )); then
    dd if=/dev/zero bs=1 count=$((target_size - current_size)) status=none | tr '\0' '#' >>"$ROOT/$path"
  fi
}

write_empty() {
  : >"$ROOT/$1"
}

write_sparse() {
  local path=$1
  local mib=$2
  truncate -s "${mib}M" "$ROOT/$path"
}

apply_mode() {
  chmod "$2" "$ROOT/$1"
}

make_file() {
  local path=$1
  local type=$2
  local mib=$3
  local mode=$4

  create_dir "$(dirname "$path")"

  case "$type" in
    text) write_text "$path" "$mib" ;;
    random) write_random "$path" "$mib" ;;
    compressible) write_compressible "$path" "$mib" ;;
    script) write_script "$path" "$mib" ;;
    empty) write_empty "$path" ;;
    sparse) write_sparse "$path" "$mib" ;;
    *)
      echo "Unknown type: $type" >&2
      exit 1
      ;;
  esac

  apply_mode "$path" "$mode"
}

create_base_dirs() {
  create_dir "regular"
  create_dir "hidden"
  create_dir "spaces in name"
  create_dir "deep/tree/level1/level2/level3"
  create_dir "readonly-dir"
  create_dir "links"
  create_dir "metadata"
  create_dir "empty-dirs/empty_a"
  create_dir "empty-dirs/empty_b"
  create_dir "empty-dirs/.hidden_empty_dir"
  create_dir "readonly-dir/no_write_subdir"
}

create_regular_files() {
  make_file "regular/text_1mb_644.txt" text 1 0644
  make_file "regular/text_3mb_600.txt" text 3 0600
  make_file "regular/text_5mb_755.txt" text 5 0755
  make_file "regular/random_1mb_600.bin" random 1 0600
  make_file "regular/random_3mb_644.bin" random 3 0644
  make_file "regular/random_5mb_755.bin" random 5 0755
  make_file "regular/compressible_1mb_644.log" compressible 1 0644
  make_file "regular/compressible_3mb_600.log" compressible 3 0600
  make_file "regular/compressible_5mb_755.log" compressible 5 0755
  make_file "regular/script_1mb_755.sh" script 1 0755
  make_file "regular/script_3mb_700.sh" script 3 0700
  make_file "regular/script_5mb_755.sh" script 5 0755
  make_file "regular/sparse_1mb_600.img" sparse 1 0600
  make_file "regular/sparse_3mb_600.img" sparse 3 0600
  make_file "regular/sparse_5mb_600.img" sparse 5 0600
  make_file "regular/empty_000_644.txt" empty 0 0644
  make_file "regular/empty_001_600.txt" empty 0 0600
  make_file "regular/empty_002_755.txt" empty 0 0755
}

create_named_variants() {
  make_file "hidden/.hidden_text_1mb_644.txt" text 1 0644
  make_file "hidden/.hidden_random_3mb_600.bin" random 3 0600
  make_file "hidden/.hidden_script_1mb_755.sh" script 1 0755
  make_file "hidden/.hidden_empty_644" empty 0 0644
  make_file "hidden/.hidden_sparse_5mb_600.img" sparse 5 0600

  make_file "spaces in name/file with spaces text 1mb 644.txt" text 1 0644
  make_file "spaces in name/file with spaces random 3mb 600.bin" random 3 0600
  make_file "spaces in name/file with spaces script 1mb 755.sh" script 1 0755
  make_file "spaces in name/file with spaces empty 644" empty 0 0644
  make_file "spaces in name/file with spaces sparse 5mb 600.img" sparse 5 0600

  make_file "regular/longname_aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa_text_1mb_644.txt" text 1 0644
  make_file "regular/longname_bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb_random_3mb_600.bin" random 3 0600
  make_file "regular/longname_cccccccccccccccccccccccccccccccc_compressible_5mb_755.log" compressible 5 0755
}

create_deep_and_duplicate_cases() {
  make_file "deep/tree/level1/level2/level3/deep_text_1mb_644.txt" text 1 0644
  make_file "deep/tree/level1/level2/level3/deep_random_3mb_600.bin" random 3 0600
  make_file "deep/tree/level1/level2/level3/deep_script_1mb_755.sh" script 1 0755
  make_file "deep/tree/level1/level2/level3/deep_sparse_5mb_600.img" sparse 5 0600

  make_file "regular/dup_source_text_3mb_644.txt" text 3 0644
  cp "$ROOT/regular/dup_source_text_3mb_644.txt" "$ROOT/regular/dup_copy_a_text_3mb_600.txt"
  cp "$ROOT/regular/dup_source_text_3mb_644.txt" "$ROOT/deep/tree/level1/level2/dup_copy_b_text_3mb_755.txt"
  chmod 0600 "$ROOT/regular/dup_copy_a_text_3mb_600.txt"
  chmod 0755 "$ROOT/deep/tree/level1/level2/dup_copy_b_text_3mb_755.txt"
}

create_time_and_readonly_cases() {
  make_file "regular/old_text_1mb_644.txt" text 1 0644
  make_file "regular/recent_text_1mb_644.txt" text 1 0644
  make_file "regular/futureish_text_1mb_644.txt" text 1 0644
  set_times "regular/old_text_1mb_644.txt" 201801020304
  set_times "regular/recent_text_1mb_644.txt" 202604191530
  set_times "regular/futureish_text_1mb_644.txt" 203001020304

  make_file "readonly-dir/locked_text_1mb_444.txt" text 1 0444
  make_file "readonly-dir/locked_random_3mb_400.bin" random 3 0400
  make_file "readonly-dir/locked_script_1mb_500.sh" script 1 0500
  chmod 0555 "$ROOT/readonly-dir/no_write_subdir"
}

create_links() {
  ln -s ../regular/text_1mb_644.txt "$ROOT/links/symlink_to_text_1mb_644.txt"
  ln -s ../deep/tree/level1/level2/level3/deep_random_3mb_600.bin "$ROOT/links/symlink_to_deep_random_3mb_600.bin"
  ln -s ../hidden/.hidden_text_1mb_644.txt "$ROOT/links/symlink_to_hidden_file"
  ln "$ROOT/regular/random_3mb_644.bin" "$ROOT/links/hardlink_to_random_3mb_644.bin"
  ln "$ROOT/regular/compressible_5mb_755.log" "$ROOT/links/hardlink_to_compressible_5mb_755.log"
}

create_metadata_cases() {
  make_file "metadata/xattr_text_1mb_644.txt" text 1 0644
  make_file "metadata/xattr_random_3mb_600.bin" random 3 0600
  make_file "metadata/acl_text_1mb_644.txt" text 1 0644
  make_file "metadata/acl_script_1mb_755.sh" script 1 0755

  if (( have_setfattr )); then
    setfattr -n user.migration_case -v "xattr-text" "$ROOT/metadata/xattr_text_1mb_644.txt"
    setfattr -n user.migration_case -v "xattr-random" "$ROOT/metadata/xattr_random_3mb_600.bin"
  else
    echo "Skipping xattr assignment: setfattr not available"
  fi

  if (( have_setfacl )); then
    setfacl -m u:nobody:r-- "$ROOT/metadata/acl_text_1mb_644.txt"
    setfacl -m u:nobody:r-x "$ROOT/metadata/acl_script_1mb_755.sh"
  else
    echo "Skipping ACL assignment: setfacl not available"
  fi
}

write_summary() {
  cat >"$ROOT/GENERATION_SUMMARY.txt" <<EOF
Dataset root: $ROOT
Manifest: migration-test-manifest.md

Optional metadata support:
- setfacl available: $have_setfacl
- setfattr available: $have_setfattr

Notes:
- Sparse files have logical size with low physical allocation.
- Hard links share inode data with their source file.
- Read-only files and directories may require elevated privileges to modify later.
EOF
}

create_base_dirs
create_regular_files
create_named_variants
create_deep_and_duplicate_cases
create_time_and_readonly_cases
create_links
create_metadata_cases
write_summary

echo "Created migration test dataset at: $ROOT"