"""
arma_modlist_tools.reporter
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Build and persist a report of mods that are required by the modlists but
absent from the file server.

The report includes a ``group`` field per missing mod so downstream tools
(``sync_missing.py``) know exactly where to place it when it becomes
available on the server, without needing to re-read ``comparison.json``.

Typical usage::

    from arma_modlist_tools.reporter import build_missing_report, save_missing_report

    report = build_missing_report(comparison, server_index)
    save_missing_report(report, cfg.missing_report)
"""

from __future__ import annotations

import json
from datetime import datetime, timezone
from pathlib import Path


def build_missing_report(comparison: dict, server_index: dict) -> dict:
    """
    Cross-reference every mod in *comparison* against *server_index* and
    return a report of mods that are not on the server.

    :param comparison:    Dict as returned by :func:`~arma_modlist_tools.compare.compare_presets`.
    :param server_index:  Dict as returned by :func:`~arma_modlist_tools.fetcher.build_server_index`.
    :returns: Report dict::

        {
          "generated_at": "2026-04-07T12:00:00+00:00",
          "total_mods":   80,
          "on_server":    2,
          "missing":      78,
          "missing_mods": [
            {
              "name":     "CBA_A3",
              "steam_id": "450814997",
              "url":      "https://steamcommunity.com/...",
              "group":    "shared"
            },
            ...
          ]
        }
    """
    by_steam_id: dict = server_index.get("by_steam_id", {})
    by_name:     dict = server_index.get("by_name", {})

    from .fetcher import _normalize_name  # reuse existing helper

    def _on_server(mod: dict) -> bool:
        if mod.get("steam_id") and mod["steam_id"] in by_steam_id:
            return True
        return _normalize_name(mod.get("name", "")) in by_name

    # Flatten all mods with their group label
    all_mods: list[tuple[dict, str]] = []
    for mod in comparison["shared"]["mods"]:
        all_mods.append((mod, "shared"))
    for preset_name, data in comparison["unique"].items():
        for mod in data["mods"]:
            all_mods.append((mod, preset_name))

    missing_mods = []
    on_server_count = 0

    for mod, group in all_mods:
        if _on_server(mod):
            on_server_count += 1
        else:
            missing_mods.append({
                "name":     mod["name"],
                "steam_id": mod.get("steam_id"),
                "url":      mod.get("url"),
                "group":    group,
            })

    return {
        "generated_at": datetime.now(timezone.utc).isoformat(),
        "total_mods":   len(all_mods),
        "on_server":    on_server_count,
        "missing":      len(missing_mods),
        "missing_mods": missing_mods,
    }


def save_missing_report(report: dict, path: Path) -> None:
    """Write *report* as indented JSON to *path*, creating parent dirs as needed."""
    path.parent.mkdir(parents=True, exist_ok=True)
    path.write_text(json.dumps(report, indent=2, ensure_ascii=False), encoding="utf-8")