# A create-only projects namespace operation. The registry's topology mode
# holds its metadata mutex and checks lexical/physical source owners before
# calling create. Neither mode repairs ownership or replaces an existing path.
set -eu
[ "$#" -eq 3 ] || exit 73
mode=$1
canonical=$2
alias=$3
case "$mode" in check|create) ;; *) exit 73 ;; esac

namespace_refuse() {
    printf 'RCH: source namespace: %s\n' "$1" >&2
    exit 73
}

namespace_realpath() {
    # Preserve the trailing delimiter and refuse an ambiguous symlink target.
    # Command substitution alone would silently remove embedded final newlines.
    if command -v grealpath >/dev/null 2>&1; then
        physical=$(grealpath -m -- "$1" && printf '.') || return 1
    else
        physical=$(realpath -m -- "$1" && printf '.') || return 1
    fi
    physical=${physical%.}
    newline='
'
    carriage_return=$(printf '\r')
    case "$physical" in *"$newline") ;; *) return 1 ;; esac
    physical=${physical%"$newline"}
    case "$physical" in ''|*"$newline"*|*"$carriage_return"*) return 1 ;; esac
    printf '%s\n' "$physical"
}

namespace_matches() {
    [ -d "$canonical" ] && [ -d "$alias" ] || return 1
    canonical_physical=$(namespace_realpath "$canonical") || return 1
    alias_physical=$(namespace_realpath "$alias") || return 1
    [ "$canonical_physical" = "$alias_physical" ]
}

if [ "$mode" = check ]; then
    namespace_matches
    exit $?
fi

# Refuse a conflicting existing alias before even creating the canonical base.
# A dangling but correctly targeted alias may become valid once that base exists.
if [ -e "$alias" ] || [ -L "$alias" ]; then
    canonical_physical=$(namespace_realpath "$canonical") || namespace_refuse 'unresolvable canonical base'
    alias_physical=$(namespace_realpath "$alias") || namespace_refuse 'unresolvable alias base'
    [ "$canonical_physical" = "$alias_physical" ] || namespace_refuse 'conflicting alias base'
fi
if [ ! -e "$canonical" ] && [ ! -L "$canonical" ]; then
    mkdir -p -- "$canonical" || namespace_refuse 'cannot create canonical base'
fi
[ -d "$canonical" ] || namespace_refuse 'canonical base is not a directory'
if [ ! -e "$alias" ] && [ ! -L "$alias" ]; then
    # No overwrite and no implicit directory target. A competing initializer
    # may win only by establishing the exact same mapping, checked below.
    if command -v gln >/dev/null 2>&1; then
        gln -sT -- "$canonical" "$alias" 2>/dev/null || namespace_matches \
            || namespace_refuse 'cannot create alias base'
    else
        ln -sT -- "$canonical" "$alias" 2>/dev/null || namespace_matches \
            || namespace_refuse 'cannot create alias base'
    fi
fi
namespace_matches || namespace_refuse 'namespace changed during initialization'
# Only the registry may emit readiness, after postcondition and durability checks.