import { useEffect, useState } from "react";

const SEOUL_DISTRICTS = [
    "강남구","강동구","강북구","강서구","관악구",
    "광진구","구로구","금천구","노원구","도봉구",
    "동대문구","동작구","마포구","서대문구","서초구",
    "성동구","성북구","송파구","양천구","영등포구",
    "용산구","은평구","종로구","중구","중랑구",
];

const TIERS = [
    { key: "S", label: "S", weight: "100%" },
    { key: "A", label: "A", weight: "80%"  },
    { key: "B", label: "B", weight: "60%"  },
    { key: "C", label: "C", weight: "40%"  },
    { key: "D", label: "D", weight: "20%"  },
];

const EMPTY_TIERS = { S: [], A: [], B: [], C: [], D: [] };

function useIsDesktop() {
    const [isDesktop, setIsDesktop] = useState(
        typeof window !== "undefined" && window.matchMedia("(min-width: 768px)").matches
    );
    useEffect(() => {
        if (typeof window === "undefined") return;
        const mq = window.matchMedia("(min-width: 768px)");
        const handler = (e) => setIsDesktop(e.matches);
        mq.addEventListener("change", handler);
        return () => mq.removeEventListener("change", handler);
    }, []);
    return isDesktop;
}

export default function DistrictTierEditor({ value, onChange }) {
    const isDesktop = useIsDesktop();
    const [dragOver, setDragOver] = useState(null); // 현재 hover 중인 zone key

    const current = value && Object.keys(value).length > 0 ? value : EMPTY_TIERS;

    const unassigned = SEOUL_DISTRICTS.filter(
        d => !TIERS.some(t => (current[t.key] || []).includes(d))
    );

    const moveDistrict = (district, targetTier /* null = 미할당 */) => {
        const next = { S: [], A: [], B: [], C: [], D: [] };
        for (const t of Object.keys(next)) {
            next[t] = (current[t] || []).filter(d => d !== district);
        }
        if (targetTier) {
            next[targetTier] = [...next[targetTier], district];
        }
        onChange(next);
    };

    const onDragStart = (e, district) => {
        e.dataTransfer.setData("text/district", district);
        e.dataTransfer.effectAllowed = "move";
    };
    const onDragOver = (e, key) => {
        e.preventDefault();
        e.dataTransfer.dropEffect = "move";
        if (dragOver !== key) setDragOver(key);
    };
    const onDragLeave = (e) => {
        if (e.currentTarget.contains(e.relatedTarget)) return;
        setDragOver(null);
    };
    const onDrop = (e, targetTier /* null = 미할당 */) => {
        e.preventDefault();
        const district = e.dataTransfer.getData("text/district");
        setDragOver(null);
        if (district) moveDistrict(district, targetTier);
    };

    if (!isDesktop) {
        return (
            <div className="sub-panel">
                <div className="sub-panel__head">
                    <p className="sub-panel__eyebrow">자치구 우선순위</p>
                    <h3>지역 5티어</h3>
                </div>
                <div className="sub-panel__body" style={{ display: "grid", gap: 10 }}>
                    {TIERS.map(t => (
                        <div key={t.key} className="dte-row dte-row--readonly">
                            <span className={`sub-chip sub-chip--tier sub-chip--tier-${t.key}`}>
                                {t.label} {t.weight}
                            </span>
                            <span className="dte-row__list">
                                {(current[t.key] || []).length === 0
                                    ? <span className="dte-empty">(없음)</span>
                                    : (current[t.key] || []).join(", ")}
                            </span>
                        </div>
                    ))}
                    <p className="dte-mobile-hint">✏️ 자치구 분류는 PC에서 편집할 수 있어요</p>
                </div>
            </div>
        );
    }

    return (
        <div className="sub-panel">
            <div className="sub-panel__head">
                <p className="sub-panel__eyebrow">자치구 우선순위</p>
                <h3>지역 5티어 (드래그해서 분류)</h3>
            </div>
            <div className="sub-panel__body" style={{ display: "grid", gap: 12 }}>
                {/* 미할당 풀 */}
                <div
                    className={`dte-pool ${dragOver === "_unassigned" ? "dte-pool--over" : ""}`}
                    onDragOver={(e) => onDragOver(e, "_unassigned")}
                    onDragLeave={onDragLeave}
                    onDrop={(e) => onDrop(e, null)}
                >
                    <p className="dte-pool__title">미할당 ({unassigned.length})</p>
                    <div className="dte-chips">
                        {unassigned.map(d => (
                            <span
                                key={d}
                                draggable
                                onDragStart={(e) => onDragStart(e, d)}
                                className="sub-chip sub-chip--district dte-chip"
                            >
                                {d}
                            </span>
                        ))}
                    </div>
                </div>

                {/* 5티어 그리드 */}
                <div className="dte-grid">
                    {TIERS.map(t => (
                        <div
                            key={t.key}
                            className={`dte-zone ${dragOver === t.key ? "dte-zone--over" : ""}`}
                            onDragOver={(e) => onDragOver(e, t.key)}
                            onDragLeave={onDragLeave}
                            onDrop={(e) => onDrop(e, t.key)}
                        >
                            <div className={`dte-zone__head sub-chip--tier-${t.key}`}>
                                {t.label} <span className="dte-zone__weight">{t.weight}</span>
                            </div>
                            <div className="dte-zone__chips">
                                {(current[t.key] || []).map(d => (
                                    <span
                                        key={d}
                                        draggable
                                        onDragStart={(e) => onDragStart(e, d)}
                                        className="sub-chip sub-chip--district dte-chip"
                                    >
                                        {d}
                                        <button
                                            type="button"
                                            className="dte-chip__remove"
                                            onClick={() => moveDistrict(d, null)}
                                            aria-label={`${d} 미할당으로`}
                                        >
                                            ×
                                        </button>
                                    </span>
                                ))}
                            </div>
                        </div>
                    ))}
                </div>
            </div>
        </div>
    );
}