import re


def format_tcl(src: str, indent_str="    ") -> str:
    """
    Simple Tcl formatter with special handling for:
    1) Single-line 'if {cond} {action}' blocks remain on one line.
    2) Combined closing-and-opening lines like '} else {' dedent then re-indent.
    3) Lines like '} Tag' stay on the same line: '} Tag'.
    4) Standard multi-line blocks for 'if', 'elseif', 'else', '{', '}'.
    """
    level = 0
    out_lines = []

    for raw_line in src.splitlines():
        stripped = raw_line.strip()

        # Comments are ignored
        if stripped.startswith("#"):
            out_lines.append(indent_str * level + stripped)
            continue

        # Single-line 'if {cond} {action}' → no indent change
        if re.match(r"^(if|elseif)\s*\{[^}]+\}\s*\{[^}]+\}$", stripped):
            out_lines.append(indent_str * level + stripped)
            continue

        # Combined '} else {' → dedent, print, then indent
        if re.match(r"^\}\s*(elseif|else)\b.*\{$", stripped):
            level = max(level - 1, 0)
            out_lines.append(indent_str * level + stripped)
            level += 1
            continue

        # SPECIAL: closing brace plus tag on same line: '} Tag'
        m = re.match(r"^\}\s+(.+)", stripped)
        if m and not stripped.startswith("#"):
            # close one block
            level = max(level - 1, 0)
            # stay on one line: "} Tag"
            out_lines.append(f"{indent_str * level}}} {m.group(1)}")
            continue

        # Pure '}' → dedent then print
        if stripped == "}":
            level = max(level - 1, 0)
            out_lines.append(f"{indent_str * level}{stripped}")
            continue

        # 'elseif' or 'else' alone → align with matching 'if'
        if re.match(r"^(elseif|else)\b(?!.*\{)", stripped):
            level = max(level - 1, 0)
            out_lines.append(f"{indent_str * level}{stripped}")
            continue

        # Default: print at current indent
        out_lines.append(f"{indent_str * level}{stripped}")

        # Open a new block on lines ending with '{'
        if re.match(r"^(if|elseif)\b.*\{$", stripped) or stripped.endswith("{"):
            level += 1

    return "\n".join(out_lines)