import { useMemo, useState } from "react";
import { Lock, X } from "lucide-react";
import { cn } from "@/lib/utils";
import { Badge } from "@/components/ui/badge";
import { Input } from "@/components/ui/input";
import {
  Select,
  SelectContent,
  SelectItem,
  SelectTrigger,
  SelectValue,
} from "@/components/ui/select";
import { ScrollArea } from "@/components/ui/scroll-area";
import {
  Tooltip,
  TooltipContent,
  TooltipTrigger,
} from "@/components/ui/tooltip";
import { Button } from "@/components/ui/button";
import { TaskCard } from "./TaskCard";
import { buildTreeByNode, filterTasks, phaseToNode } from "../taskFilters";
import type { Stage, StateResponse, TaskView, Topology } from "../api";

interface Props {
  state: StateResponse | null;
  topology: Topology | null;
  selectedId: string | null;
  nodeFilter: string | null;
  onSelect: (threadId: string) => void;
  onClearNodeFilter: () => void;
}

const STATUS_OPTIONS = [
  { value: "all", label: "All statuses" },
  { value: "active", label: "Active" },
  { value: "waiting_human", label: "Waiting human" },
  { value: "parked", label: "Parked" },
  { value: "done", label: "Done" },
  { value: "failed", label: "Failed" },
];

/** Derive ordered stages from topology node order when state.stages is absent. */
function deriveStages(tasks: TaskView[], topology: Topology | null): Stage[] {
  // Build node order from topology; fall back to natural insertion order.
  const nodeOrder: string[] = topology?.nodes.map((n) => n.id) ?? [];

  const grouped = new Map<string, TaskView[]>();
  for (const t of tasks) {
    const node = phaseToNode(t.current_phase);
    if (!grouped.has(node)) grouped.set(node, []);
    grouped.get(node)!.push(t);
  }

  // Sort by topology order; unknown nodes go at end.
  const nodeIds = [...grouped.keys()].sort((a, b) => {
    const ai = nodeOrder.indexOf(a);
    const bi = nodeOrder.indexOf(b);
    if (ai === -1 && bi === -1) return 0;
    if (ai === -1) return 1;
    if (bi === -1) return -1;
    return ai - bi;
  });

  return nodeIds.map((nodeId) => {
    const topoNode = topology?.nodes.find((n) => n.id === nodeId);
    const stageTasks = grouped.get(nodeId) ?? [];
    return {
      key: nodeId,
      label: topoNode?.label ?? nodeId,
      agent: topoNode?.agent ?? "",
      phases: [nodeId],
      gated: topoNode?.gated ?? false,
      role_node: false,
      state: "idle" as const,
      count: stageTasks.length,
      tasks: stageTasks,
    };
  });
}

/**
 * A human-decision gate — distinct from `stage.gated`, which means the stage is
 * INERT (a disabled/not-yet-wired P3 node like build/verify/dispatch). A gate is
 * the "gate" stage or a topology node of kind "gate" (e.g. clarify).
 */
function isGate(stage: Stage, topology: Topology | null): boolean {
  if (stage.key === "gate") return true;
  const topoNode = topology?.nodes.find((n) => n.id === stage.key);
  return topoNode?.kind === "gate";
}

export function Board({
  state,
  topology,
  selectedId,
  nodeFilter,
  onSelect,
  onClearNodeFilter,
}: Props) {
  const [query, setQuery] = useState("");
  const [status, setStatus] = useState("all");
  const [tree, setTree] = useState("all");

  const treeByNode = useMemo(() => buildTreeByNode(topology), [topology]);

  // Use backend-provided stages or fall back to derived grouping.
  const allStages: Stage[] = useMemo(() => {
    if (!state) return [];
    if (state.stages && state.stages.length > 0) return state.stages;
    return deriveStages(state.tasks ?? [], topology);
  }, [state, topology]);

  // Filter each stage's tasks by the toolbar + nodeFilter params.
  const filteredStages = useMemo(() => {
    return allStages.map((stage) => {
      const filtered = filterTasks(stage.tasks, {
        query,
        status,
        tree,
        nodeFilter,
        treeByNode,
      });
      return { ...stage, tasks: filtered, count: filtered.length };
    });
  }, [allStages, query, status, tree, nodeFilter, treeByNode]);

  if (!state) {
    return (
      <div className="flex items-center justify-center h-32 text-sm text-muted-foreground">
        Loading…
      </div>
    );
  }

  return (
    <div className="flex flex-col gap-2 h-full min-h-0">
      {/* Toolbar */}
      <div
        className="flex flex-wrap items-center gap-2 px-1"
        role="toolbar"
        aria-label="board filters"
      >
        <Input
          type="search"
          placeholder="Search tasks…"
          aria-label="Search tasks"
          value={query}
          onChange={(e) => setQuery(e.target.value)}
          className="h-8 w-48 text-sm"
        />

        <Select value={status} onValueChange={setStatus}>
          <SelectTrigger
            className="h-8 w-40 text-sm"
            aria-label="Filter by status"
          >
            <SelectValue placeholder="All statuses" />
          </SelectTrigger>
          <SelectContent>
            {STATUS_OPTIONS.map((opt) => (
              <SelectItem key={opt.value} value={opt.value} className="text-sm">
                {opt.label}
              </SelectItem>
            ))}
          </SelectContent>
        </Select>

        <Select value={tree} onValueChange={setTree}>
          <SelectTrigger
            className="h-8 w-36 text-sm"
            aria-label="Filter by tree"
          >
            <SelectValue placeholder="All trees" />
          </SelectTrigger>
          <SelectContent>
            <SelectItem value="all" className="text-sm">
              All trees
            </SelectItem>
            {(topology?.trees ?? []).map((t) => (
              <SelectItem key={t.id} value={t.id} className="text-sm">
                {t.label}
              </SelectItem>
            ))}
          </SelectContent>
        </Select>

        {/* Node filter chip */}
        {nodeFilter && (
          <Button
            variant="secondary"
            size="sm"
            className="h-8 gap-1 text-xs"
            onClick={onClearNodeFilter}
            aria-label={`Clear node filter: ${nodeFilter}`}
          >
            node: {nodeFilter}
            <X className="h-3 w-3" />
          </Button>
        )}
      </div>

      {/* Kanban columns — horizontal scroll. Each column is its own listbox of
          task cards (valid ARIA nesting), so this row is just a labelled list. */}
      <div
        className="flex gap-3 overflow-x-auto pb-2 flex-1 min-h-0 px-1"
        role="list"
        aria-label="pipeline stages"
      >
        {filteredStages.map((stage) => (
          <KanbanColumn
            key={stage.key}
            stage={stage}
            topology={topology}
            selectedId={selectedId}
            onSelect={onSelect}
          />
        ))}

        {filteredStages.length === 0 && (
          <div className="flex items-center justify-center flex-1 text-sm text-muted-foreground">
            No stages available.
          </div>
        )}
      </div>
    </div>
  );
}

interface ColumnProps {
  stage: Stage;
  topology: Topology | null;
  selectedId: string | null;
  onSelect: (threadId: string) => void;
}

function KanbanColumn({ stage, topology, selectedId, onSelect }: ColumnProps) {
  const gate = isGate(stage, topology);

  // NOTE: we intentionally do NOT dim stages from the backend `stage.gated`
  // flag. In the live deployment build/verify/dispatch are wired and active even
  // though they're still flagged gated, so that flag is a stale "P3 opt-in" hint,
  // not a real "inactive" signal. Activity is conveyed by live task counts/status.

  return (
    <div
      className={cn(
        "flex h-full min-h-0 w-52 shrink-0 flex-col gap-1.5 rounded-lg border border-border bg-muted/40 p-2",
      )}
      role="listitem"
      aria-label={`Stage: ${stage.label}`}
    >
      {/* Column header */}
      <div className="flex items-center justify-between gap-1 mb-0.5">
        <span className="flex items-center gap-1 truncate text-xs font-semibold text-foreground">
          {stage.label}
        </span>
        <div className="flex items-center gap-1 shrink-0">
          <Badge variant="outline" className="px-1.5 py-0 text-xs">
            {stage.count}
          </Badge>
          {gate && (
            <Tooltip>
              <TooltipTrigger asChild>
                <Lock
                  className="h-3 w-3 text-muted-foreground"
                  aria-label="human gate"
                />
              </TooltipTrigger>
              <TooltipContent>human gate</TooltipContent>
            </Tooltip>
          )}
        </div>
      </div>

      {/* Task cards — scrollable vertically. flex-1 + min-h-0 lets the list cap
          at the real column height (no magic viewport math). */}
      <ScrollArea className="min-h-0 flex-1">
        <div
          className="flex flex-col gap-1.5 pr-1"
          role="listbox"
          aria-label={`${stage.label} tasks`}
        >
          {stage.tasks.length === 0 ? (
            <p className="text-xs text-muted-foreground py-3 text-center">—</p>
          ) : (
            stage.tasks.map((t) => (
              <TaskCard
                key={t.thread_id}
                task={t}
                selected={t.thread_id === selectedId}
                onSelect={onSelect}
              />
            ))
          )}
        </div>
      </ScrollArea>
    </div>
  );
}