from __future__ import annotations

import json
from copy import deepcopy
from pathlib import Path
from typing import Any


ALLOWED_COMPONENTS = {
    "task-list",
    "overview-summary",
    "task-progress-grid",
    "task-header",
    "today-record",
    "metric-progress",
    "activity-heatmap",
    "task-settings",
}

# 每个组件允许出现的页面与区域。组件在各自区域内必须单例，避免重复 ID
# 与重复事件绑定；跨页/跨区错放（例如把 today-record 放进首页）视为非法布局。
COMPONENT_SCOPES: dict[str, tuple[tuple[str, ...], str]] = {
    "task-list": (("home", "task-detail"), "sidebar"),
    "overview-summary": (("home",), "main"),
    "task-progress-grid": (("home",), "main"),
    "task-header": (("task-detail",), "main"),
    "today-record": (("task-detail",), "main"),
    "metric-progress": (("task-detail",), "main"),
    "activity-heatmap": (("task-detail",), "main"),
    "task-settings": (("task-detail",), "main"),
}

FALLBACKS = {
    "home": {
        "schemaVersion": 1,
        "page": "home",
        "regions": {
            "sidebar": [{"component": "task-list"}],
            "main": [{"component": "overview-summary"}, {"component": "task-progress-grid"}],
        },
    },
    "task-detail": {
        "schemaVersion": 1,
        "page": "task-detail",
        "regions": {
            "sidebar": [{"component": "task-list"}],
            "main": [
                {"component": "task-header"},
                {"component": "today-record"},
                {"component": "metric-progress"},
                {"component": "activity-heatmap"},
                {"component": "task-settings"},
            ],
        },
    },
}


def validate_layout(layout: Any, expected_page: str) -> bool:
    if not isinstance(layout, dict):
        return False
    if layout.get("schemaVersion") != 1 or layout.get("page") != expected_page:
        return False
    regions = layout.get("regions")
    if not isinstance(regions, dict) or set(regions) - {"sidebar", "main"}:
        return False
    for region, items in regions.items():
        if not isinstance(items, list):
            return False
        seen: set[str] = set()
        for item in items:
            if not isinstance(item, dict) or set(item) - {"component", "options"}:
                return False
            component = item.get("component")
            if component not in ALLOWED_COMPONENTS:
                return False
            if "options" in item and not isinstance(item["options"], dict):
                return False
            pages, expected_region = COMPONENT_SCOPES[component]
            if expected_page not in pages or region != expected_region:
                return False
            if component in seen:
                return False
            seen.add(component)
    return True


def load_layout(layout_dir: Path, page: str) -> dict[str, Any]:
    if page not in FALLBACKS:
        raise KeyError(page)
    try:
        with (layout_dir / f"{page}.json").open("r", encoding="utf-8") as handle:
            layout = json.load(handle)
        if validate_layout(layout, page):
            return layout
    except (OSError, json.JSONDecodeError):
        pass
    return deepcopy(FALLBACKS[page])