import { useEffect, useState } from "react";
import { useNavigate, useParams } from "react-router-dom";
import { ArrowLeft, House, Tag, ShieldCheck, Plus, Trash2, Loader2 } from "lucide-react";
import { DateTimePicker } from "@/components/ui/date-time-picker";
import { toast } from "sonner";
import AppBreadcrumb from "@/components/generic/Breadcrumb/AppBreadcrumb";
import { Button }    from "@/components/ui/button";
import { Input }     from "@/components/ui/input";
import { Label }     from "@/components/ui/label";
import { Switch }    from "@/components/ui/switch";
import { Badge }     from "@/components/ui/badge";
import { Separator } from "@/components/ui/separator";
import { Skeleton }  from "@/components/ui/skeleton";
import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from "@/components/ui/select";
import { PageMeta }  from "@/contexts/MetadataContext";
import { useTiers }  from "@/contexts/AdminTiersContext";
import api from "@/utils/api.util";

// ─── Helpers ──────────────────────────────────────────────────────────────────

function SectionCard({ icon: Icon, title, description, children }) {
  return (
    <div className="rounded-lg border bg-card p-5 space-y-4">
      <div>
        <div className="flex items-center gap-2">
          {Icon && <Icon className="h-4 w-4 text-muted-foreground" />}
          <h2 className="text-sm font-semibold">{title}</h2>
        </div>
        {description && <p className="text-xs text-muted-foreground mt-0.5 ml-6">{description}</p>}
      </div>
      <Separator />
      {children}
    </div>
  );
}

const EMPTY_PROMO = {
  code: "", type: "flat", value: "", currency: "USD",
  max_discount: "", max_uses: "", expires_at: "", min_amount: "",
};

const WINDOW_UNITS = ["minutes", "hours", "days"];

// ─── Page ─────────────────────────────────────────────────────────────────────

export default function PaymentPolicy() {
  const navigate = useNavigate();
  const { planId } = useParams();
  const { fetchPlan, plan, loading: planLoading } = useTiers();

  const [policy,        setPolicy]        = useState(null);
  const [policyLoading, setPolicyLoading] = useState(true);
  const [saving,        setSaving]        = useState(false);

  // ── Refund policy fields
  const [refundAllowed,       setRefundAllowed]       = useState(true);
  const [refundWindowValue,   setRefundWindowValue]   = useState(5);
  const [refundWindowUnit,    setRefundWindowUnit]    = useState("minutes");
  const [refundReasonReqd,    setRefundReasonReqd]    = useState(false);

  // ── Promo rules
  const [promoRules,      setPromoRules]      = useState([]);
  const [addForm,         setAddForm]         = useState(EMPTY_PROMO);
  const [showAdd,         setShowAdd]         = useState(false);

  // ─── Load ────────────────────────────────────────────────────────────────────

  useEffect(() => {
    fetchPlan(planId);
    setPolicyLoading(true);
    api.get(`/admin/tier-policies/plans/${planId}/payment-policy`)
      .then(({ data }) => {
        const p = data.data;
        if (p) {
          setPolicy(p);
          const rp = p.refund_policy ?? {};
          setRefundAllowed(rp.allowed ?? true);
          setRefundWindowValue(rp.window_value ?? 5);
          setRefundWindowUnit(rp.window_unit ?? "minutes");
          setRefundReasonReqd(rp.reason_required ?? false);
          setPromoRules(p.promo_rules ?? []);
        }
      })
      .catch(() => {})
      .finally(() => setPolicyLoading(false));

  }, [planId]);

  // ─── Save ────────────────────────────────────────────────────────────────────

  const handleSave = async () => {
    setSaving(true);
    try {
      await api.put(`/admin/tier-policies/plans/${planId}/payment-policy`, {
        refund_policy: {
          allowed:         refundAllowed,
          window_value:    Number(refundWindowValue),
          window_unit:     refundWindowUnit,
          reason_required: refundReasonReqd,
        },
        promo_rules: promoRules,
      });
      toast("Payment policy saved.");
      navigate("/admin/tiers/plans");
    } catch (err) {
      toast(err?.response?.data?.message ?? "Could not save payment policy.");
    } finally {
      setSaving(false);
    }
  };

  // ─── Promo helpers ────────────────────────────────────────────────────────────

  const handleAddPromo = () => {
    const code = addForm.code.trim().toUpperCase();
    if (!code) { toast("Code is required."); return; }
    if (!addForm.value || Number(addForm.value) <= 0) { toast("Value must be greater than 0."); return; }
    if (promoRules.some((r) => r.code.toUpperCase() === code)) {
      toast("A rule with this code already exists."); return;
    }

    const rule = {
      code,
      type:  addForm.type,
      value: Number(addForm.value),
      ...(addForm.type === "flat"    && addForm.currency   ? { currency:     addForm.currency.trim().toUpperCase() } : {}),
      ...(addForm.type === "percent" && addForm.max_discount ? { max_discount: Number(addForm.max_discount) } : {}),
      ...(addForm.max_uses  ? { max_uses:  Number(addForm.max_uses)  } : {}),
      ...(addForm.expires_at ? { expires_at: addForm.expires_at }       : {}),
      ...(addForm.min_amount ? { min_amount: Number(addForm.min_amount) } : {}),
    };

    setPromoRules((prev) => [...prev, rule]);
    setAddForm(EMPTY_PROMO);
    setShowAdd(false);
  };

  const handleRemovePromo = (code) =>
    setPromoRules((prev) => prev.filter((r) => r.code !== code));

  // ─── Render ───────────────────────────────────────────────────────────────────

  const isLoading = planLoading || policyLoading;

  return (
    <section className="bg-muted/60 min-h-full">
      <PageMeta title={plan ? `Payment Policy — ${plan.label} - STARR` : "Payment Policy - STARR"} />
      <div className="lg:container lg:mx-auto lg:px-0 flex flex-col items-start px-4 py-10">
        <div className="w-full max-w-2xl mx-auto">

          <div className="flex flex-col gap-2 mb-6">
            <AppBreadcrumb items={[
              { label: "Home",  icon: <House className="size-4" />, to: "/admin" },
              { label: "Plans", to: "/admin/tiers/plans" },
              { label: plan?.label ?? `Plan #${planId}`, to: `/admin/tiers/plans/${planId}/view` },
              { label: "Payment Policy" },
            ]} />
          </div>

          <div className="flex items-center gap-3 mb-6">
            <Button type="button" variant="ghost" size="icon" onClick={() => navigate(`/admin/tiers/plans/${planId}/view`)}>
              <ArrowLeft className="h-4 w-4" />
            </Button>
            <div>
              <h1 className="text-xl font-semibold">Payment Policy</h1>
              <p className="text-sm text-muted-foreground capitalize">
                {plan?.tier} — {plan?.label}
              </p>
            </div>
          </div>

          {isLoading ? (
            <div className="space-y-4">
              {[...Array(3)].map((_, i) => <Skeleton key={i} className="h-32 w-full" />)}
            </div>
          ) : (
            <div className="space-y-5">

              {/* ── Refund Policy ─────────────────────────────────────────── */}
              <SectionCard
                icon={ShieldCheck}
                title="Refund Policy"
                description="Controls whether and how long after purchase a user can request a refund."
              >
                <div className="space-y-4">
                  <div className="flex items-center justify-between rounded-lg border p-4">
                    <div>
                      <p className="text-sm font-medium">Allow Refunds</p>
                      <p className="text-xs text-muted-foreground">Users can request a refund within the window below.</p>
                    </div>
                    <Switch checked={refundAllowed} onCheckedChange={setRefundAllowed} />
                  </div>

                  {refundAllowed && (
                    <>
                      <div className="space-y-1.5">
                        <Label>Refund Window</Label>
                        <div className="flex gap-2">
                          <Input
                            type="number"
                            min={1}
                            className="w-28"
                            value={refundWindowValue}
                            onChange={(e) => setRefundWindowValue(e.target.value)}
                            placeholder="5"
                          />
                          <Select value={refundWindowUnit} onValueChange={setRefundWindowUnit}>
                            <SelectTrigger className="w-36">
                              <SelectValue />
                            </SelectTrigger>
                            <SelectContent>
                              {WINDOW_UNITS.map((u) => (
                                <SelectItem key={u} value={u} className="capitalize">{u}</SelectItem>
                              ))}
                            </SelectContent>
                          </Select>
                        </div>
                        <p className="text-xs text-muted-foreground">
                          Users have {refundWindowValue || "?"} {refundWindowUnit} from payment to request a refund.
                        </p>
                      </div>

                      <div className="flex items-center justify-between rounded-lg border p-4">
                        <div>
                          <p className="text-sm font-medium">Require Reason</p>
                          <p className="text-xs text-muted-foreground">User must provide a reason when requesting a refund.</p>
                        </div>
                        <Switch checked={refundReasonReqd} onCheckedChange={setRefundReasonReqd} />
                      </div>
                    </>
                  )}
                </div>
              </SectionCard>

              {/* ── Promo Codes ───────────────────────────────────────────── */}
              <SectionCard
                icon={Tag}
                title="Promo Codes"
                description="Define discount codes users can apply at checkout. Flat reduces price by a fixed amount; percent reduces by a percentage."
              >
                {/* Existing rules */}
                {promoRules.length > 0 ? (
                  <div className="space-y-2">
                    {promoRules.map((rule) => (
                      <div
                        key={rule.code}
                        className="flex items-center justify-between gap-3 rounded-lg border bg-muted/30 px-4 py-3"
                      >
                        <div className="flex items-center gap-3 min-w-0 flex-1">
                          <code className="text-sm font-semibold tracking-wide">{rule.code}</code>
                          <Badge variant="outline" className="text-xs capitalize shrink-0">
                            {rule.type}
                          </Badge>
                          <span className="text-sm text-muted-foreground shrink-0">
                            {rule.type === "flat"
                              ? `${rule.currency ?? "USD"} ${Number(rule.value).toFixed(2)} off`
                              : `${rule.value}% off${rule.max_discount ? ` (max ${rule.max_discount})` : ""}`
                            }
                          </span>
                          {rule.max_uses && (
                            <span className="text-xs text-muted-foreground shrink-0">
                              · {rule.max_uses} uses max
                            </span>
                          )}
                          {rule.expires_at && (
                            <span className="text-xs text-muted-foreground shrink-0">
                              · expires {new Date(rule.expires_at).toLocaleString(undefined, { dateStyle: "medium", timeStyle: "short" })}
                            </span>
                          )}
                        </div>
                        <Button
                          variant="ghost"
                          size="icon"
                          className="text-destructive hover:text-destructive shrink-0"
                          onClick={() => handleRemovePromo(rule.code)}
                        >
                          <Trash2 className="h-4 w-4" />
                        </Button>
                      </div>
                    ))}
                  </div>
                ) : (
                  <div className="flex items-center gap-2 rounded-lg border border-dashed p-4 text-sm text-muted-foreground">
                    <Tag className="size-4 shrink-0" />
                    No promo codes configured for this plan.
                  </div>
                )}

                {/* Add form */}
                {showAdd ? (
                  <div className="rounded-lg border bg-muted/20 p-4 space-y-4">
                    <p className="text-sm font-medium">New Promo Code</p>

                    <div className="grid grid-cols-2 gap-3">
                      <div className="space-y-1.5">
                        <Label>Code <span className="text-destructive">*</span></Label>
                        <Input
                          placeholder="e.g. SAVE10"
                          value={addForm.code}
                          onChange={(e) => setAddForm((f) => ({ ...f, code: e.target.value.toUpperCase() }))}
                        />
                      </div>
                      <div className="space-y-1.5">
                        <Label>Type <span className="text-destructive">*</span></Label>
                        <Select value={addForm.type} onValueChange={(v) => setAddForm((f) => ({ ...f, type: v }))}>
                          <SelectTrigger><SelectValue /></SelectTrigger>
                          <SelectContent>
                            <SelectItem value="flat">Flat (fixed amount off)</SelectItem>
                            <SelectItem value="percent">Percent (% off)</SelectItem>
                          </SelectContent>
                        </Select>
                      </div>
                    </div>

                    <div className="grid grid-cols-2 gap-3">
                      <div className="space-y-1.5">
                        <Label>
                          {addForm.type === "flat" ? "Amount Off" : "Percent Off"}{" "}
                          <span className="text-destructive">*</span>
                        </Label>
                        <Input
                          type="number"
                          step="0.01"
                          min="0.01"
                          placeholder={addForm.type === "flat" ? "10.00" : "20"}
                          value={addForm.value}
                          onChange={(e) => setAddForm((f) => ({ ...f, value: e.target.value }))}
                        />
                      </div>

                      {addForm.type === "flat" && (
                        <div className="space-y-1.5">
                          <Label>Currency</Label>
                          <Select
                            value={addForm.currency}
                            onValueChange={(v) => setAddForm((f) => ({ ...f, currency: v }))}
                          >
                            <SelectTrigger><SelectValue /></SelectTrigger>
                            <SelectContent>
                              <SelectItem value={plan?.currency ?? "USD"}>
                                {plan?.currency ?? "USD"} — Base price
                              </SelectItem>
                              {localizedPrices.map((p) => (
                                <SelectItem key={p.currency} value={p.currency}>
                                  {p.currency} — Localized price
                                </SelectItem>
                              ))}
                            </SelectContent>
                          </Select>
                          {localizedPrices.length === 0 && (
                            <p className="text-xs text-muted-foreground">
                              No localized prices set — only base currency available.
                            </p>
                          )}
                        </div>
                      )}

                      {addForm.type === "percent" && (
                        <div className="space-y-1.5">
                          <Label>Max Discount Cap</Label>
                          <Input
                            type="number"
                            step="0.01"
                            placeholder="50.00 (optional)"
                            value={addForm.max_discount}
                            onChange={(e) => setAddForm((f) => ({ ...f, max_discount: e.target.value }))}
                          />
                        </div>
                      )}
                    </div>

                    <div className="grid grid-cols-2 gap-3">
                      <div className="space-y-1.5">
                        <Label>Max Uses</Label>
                        <Input
                          type="number"
                          min="1"
                          placeholder="Unlimited"
                          value={addForm.max_uses}
                          onChange={(e) => setAddForm((f) => ({ ...f, max_uses: e.target.value }))}
                        />
                      </div>
                      <div className="space-y-1.5">
                        <Label>Expires At</Label>
                        <DateTimePicker
                          value={addForm.expires_at || null}
                          onChange={(iso) => setAddForm((f) => ({ ...f, expires_at: iso ?? "" }))}
                          placeholder="No expiry"
                        />
                      </div>
                    </div>

                    <div className="space-y-1.5">
                      <Label>Minimum Purchase Amount</Label>
                      <Input
                        type="number"
                        step="0.01"
                        placeholder="No minimum"
                        value={addForm.min_amount}
                        onChange={(e) => setAddForm((f) => ({ ...f, min_amount: e.target.value }))}
                      />
                    </div>

                    <div className="flex gap-2 justify-end pt-1">
                      <Button variant="outline" size="sm" onClick={() => { setShowAdd(false); setAddForm(EMPTY_PROMO); }}>
                        Cancel
                      </Button>
                      <Button size="sm" onClick={handleAddPromo}>
                        <Plus className="h-4 w-4 mr-1" /> Add Code
                      </Button>
                    </div>
                  </div>
                ) : (
                  <Button
                    variant="outline"
                    size="sm"
                    onClick={() => {
                      setAddForm((f) => ({ ...f, currency: plan?.currency ?? "USD" }));
                      setShowAdd(true);
                    }}
                  >
                    <Plus className="h-4 w-4 mr-1" /> Add Promo Code
                  </Button>
                )}
              </SectionCard>

              {/* ── Save ─────────────────────────────────────────────────── */}
              <div className="flex justify-end gap-3 pt-1">
                <Button variant="outline" onClick={() => navigate(`/admin/tiers/plans/${planId}/view`)} disabled={saving}>
                  Cancel
                </Button>
                <Button onClick={handleSave} disabled={saving}>
                  {saving && <Loader2 className="h-4 w-4 mr-2 animate-spin" />}
                  Save Policy
                </Button>
              </div>

            </div>
          )}
        </div>
      </div>
    </section>
  );
}