"""Build a target library tree preview from an execution plan."""

from __future__ import annotations

from collections import defaultdict
from pathlib import Path

from vlm.models import ExecutionPlan
from vlm.review_display import display_path


def build_structure_preview_lines(
    plan: ExecutionPlan,
    library_root: Path,
    *,
    max_titles: int = 40,
    max_paths_per_title: int = 8,
) -> list[str]:
    """Return ASCII lines showing where move/rename operations will place files."""
    by_title: dict[str, list[str]] = defaultdict(list)

    for op in plan.operations:
        if op.operation_type not in ("move", "rename") or not op.destination_path:
            continue
        ctx = op.review_context if isinstance(op.review_context, dict) else {}
        title = str(ctx.get("title") or op.destination_path.parent.parent.name)
        rel = display_path(op.destination_path, library_root)
        by_title[title].append(rel)

    lines = [
        "Target library structure preview (move/rename destinations)",
        f"Library root: {library_root}",
        "",
    ]
    if not by_title:
        lines.append("(no move/rename destinations)")
        return lines

    sorted_titles = sorted(by_title.keys())[:max_titles]
    for title in sorted_titles:
        paths = sorted(set(by_title[title]))[:max_paths_per_title]
        lines.append(f"{title}/")
        for p in paths:
            lines.append(f"  {p}")
        remaining = len(by_title[title]) - len(paths)
        if remaining > 0:
            lines.append(f"  ... +{remaining} more path(s)")
        lines.append("")

    if len(by_title) > max_titles:
        lines.append(f"... +{len(by_title) - max_titles} more title(s)")

    return lines


def write_structure_preview(
    plan: ExecutionPlan,
    library_root: Path,
    output_path: Path,
) -> None:
    """Write structure preview text to a file."""
    lines = build_structure_preview_lines(plan, library_root)
    output_path.parent.mkdir(parents=True, exist_ok=True)
    output_path.write_text("\n".join(lines) + "\n", encoding="utf-8")