import { useState, useRef, useEffect } from "react";
import type { StudentReport } from "../../App";

interface ReportViewerProps {
  reports: StudentReport[];
  isGenerating: boolean;
  onBack: () => void;
  onExportAllHtml: () => void;
  onSaveToDb?: () => Promise<{ students_saved: number }>;
}

export function ReportViewer({
  reports,
  isGenerating,
  onBack,
  onExportAllHtml,
  onSaveToDb,
}: ReportViewerProps) {
  const [activeIndex, setActiveIndex] = useState(0);
  const [saveState, setSaveState] = useState<"idle" | "saving" | "saved" | "error">("idle");
  const [saveMsg, setSaveMsg] = useState("");
  const iframeRef = useRef<HTMLIFrameElement>(null);

  const handleSaveToDb = async () => {
    if (!onSaveToDb) return;
    setSaveState("saving");
    setSaveMsg("");
    try {
      const res = await onSaveToDb();
      setSaveState("saved");
      setSaveMsg(`已儲存 ${res.students_saved} 位學生成績`);
    } catch (e) {
      setSaveState("error");
      setSaveMsg(e instanceof Error ? e.message : "儲存失敗");
    }
  };

  // Auto-switch to the report currently being generated
  useEffect(() => {
    const generatingIdx = reports.findIndex((r) => r.status === "generating");
    if (generatingIdx >= 0) {
      setActiveIndex(generatingIdx);
    } else {
      // When generation finishes, show the last completed one
      let lastDone = -1;
      for (let j = reports.length - 1; j >= 0; j--) {
        if (reports[j].status === "done") { lastDone = j; break; }
      }
      if (lastDone >= 0) setActiveIndex(lastDone);
    }
  }, [reports]);

  const activeReport = reports[activeIndex];
  const doneCount = reports.filter((r) => r.status === "done").length;
  const errorCount = reports.filter((r) => r.status === "error").length;

  const handleDownloadSingle = () => {
    if (!activeReport?.html) return;
    const blob = new Blob([activeReport.html], { type: "text/html" });
    const url = URL.createObjectURL(blob);
    const a = document.createElement("a");
    a.href = url;
    a.download = `classlens-${activeReport.studentName}.html`;
    a.click();
    URL.revokeObjectURL(url);
  };

  return (
    <div className="space-y-4">
      {/* Progress bar */}
      {isGenerating && (
        <div className="card p-4">
          <div className="flex items-center justify-between mb-2">
            <span className="text-sm font-semibold text-[var(--color-text)]">
              生成進度
            </span>
            <span className="text-sm text-[var(--color-text-muted)]">
              {doneCount + errorCount} / {reports.length}
            </span>
          </div>
          <div className="w-full h-2 bg-[var(--color-border)] rounded-full overflow-hidden">
            <div
              className="h-full bg-gradient-to-r from-[var(--color-primary)] to-[var(--color-success)] transition-all duration-500"
              style={{
                width: `${((doneCount + errorCount) / reports.length) * 100}%`,
              }}
            />
          </div>
        </div>
      )}

      {/* Action bar */}
      <div className="flex flex-wrap items-center gap-3">
        <button onClick={onBack} className="btn btn-outline text-sm">
          ← 返回選擇學生
        </button>
        <div className="flex-1" />
        {activeReport?.status === "done" && (
          <button onClick={handleDownloadSingle} className="btn btn-outline text-sm">
            下載此報告
          </button>
        )}
        {doneCount > 1 && (
          <button onClick={onExportAllHtml} className="btn btn-outline text-sm">
            下載全部報告
          </button>
        )}
        {onSaveToDb && !isGenerating && doneCount > 0 && (
          <button
            onClick={handleSaveToDb}
            disabled={saveState === "saving" || saveState === "saved"}
            className="btn btn-primary text-sm disabled:opacity-60"
          >
            {saveState === "saving" && "儲存中..."}
            {saveState === "saved" && "✅ 已儲存"}
            {(saveState === "idle" || saveState === "error") && "儲存至資料庫"}
          </button>
        )}
      </div>
      {saveMsg && (
        <p
          className={`text-sm text-right ${
            saveState === "error" ? "text-red-400" : "text-[var(--color-success)]"
          }`}
        >
          {saveMsg}
        </p>
      )}

      {/* Student tabs */}
      <div className="flex gap-2 overflow-x-auto pb-2">
        {reports.map((r, i) => (
          <button
            key={r.studentIndex}
            onClick={() => setActiveIndex(i)}
            className={`shrink-0 px-4 py-2 rounded-xl text-sm font-semibold transition-all ${
              i === activeIndex
                ? "bg-[var(--color-primary)] text-white shadow-md"
                : "bg-[var(--color-surface)] text-[var(--color-text-muted)] hover:text-[var(--color-text)] border border-[var(--color-border)]"
            }`}
          >
            <span className="mr-1.5">
              {r.status === "done" && "✅"}
              {r.status === "generating" && "⏳"}
              {r.status === "pending" && "⬜"}
              {r.status === "error" && "❌"}
            </span>
            {r.studentName}
          </button>
        ))}
      </div>

      {/* Report content */}
      <div className="card overflow-hidden" style={{ height: "70vh" }}>
        {activeReport?.status === "done" && (
          <iframe
            ref={iframeRef}
            srcDoc={activeReport.html}
            title={`Report - ${activeReport.studentName}`}
            className="w-full h-full border-0"
            sandbox="allow-scripts allow-same-origin"
          />
        )}

        {activeReport?.status === "generating" && (
          <div className="w-full h-full flex flex-col items-center justify-center gap-4">
            <div className="w-10 h-10 border-3 border-[var(--color-primary)] border-t-transparent rounded-full animate-spin" />
            <p className="text-[var(--color-text-muted)] text-lg">
              正在為 <strong className="text-[var(--color-text)]">{activeReport.studentName}</strong> 生成報告...
            </p>
          </div>
        )}

        {activeReport?.status === "pending" && (
          <div className="w-full h-full flex items-center justify-center">
            <p className="text-[var(--color-text-muted)]">
              等待生成...
            </p>
          </div>
        )}

        {activeReport?.status === "error" && (
          <div className="w-full h-full flex flex-col items-center justify-center gap-3">
            <span className="text-4xl">❌</span>
            <p className="text-[var(--color-text)] font-semibold">
              {activeReport.studentName} 報告生成失敗
            </p>
            <p className="text-sm text-[var(--color-text-muted)] max-w-md text-center">
              {activeReport.error}
            </p>
          </div>
        )}
      </div>
    </div>
  );
}