/**
 * Pure state machine + copy helpers for the AI assistant's live generation-status
 * line (Issue #6743, feature 1).
 *
 * The component keeps an `AiGenerationStatus` ref, feeds every `ai-agent-event`
 * into `applyStatusEvent`, and runs a wall-clock whole-second ticker
 * (`createStatusTicker`) that recomputes `now` for
 * `statusText`/`shouldShowLongRunningHint`. Keeping the reducer, the copy
 * selection, and the ticker pure (all inject `now`; i18n `t` is injected into
 * `statusText`) makes the whole feature unit-testable without a DOM harness,
 * matching the existing pattern of `aiConversationLifecycle.ts` /
 * `aiGenerationGuard.ts`.
 *
 * Phase determination is EVENT-DRIVEN, never mode-based: Ask mode also emits
 * `turn_start` and can invoke read-only tools, so `running_tool` is decided purely
 * by `tool_call_start`/`tool_call_end`, not by `assistantMode`.
 */
import type { AgentEvent } from "@/lib/backend/tauri";

export interface AiGenerationStatus {
  /** When `send()` set `isGenerating=true`. Elapsed time is derived from this. */
  startedAt: number;
  /** Most recent event time; `undefined` means no agent event has arrived yet. */
  lastEventAt?: number;
  /** 0-based turn from the latest `turn_start`; display as `turn + 1`. */
  turn?: number;
  /** Active tool between `tool_call_start` and the matching `tool_call_end`. */
  activeTool?: { name: string; startedAt: number };
  /**
   * All outstanding tools for the current turn. The backend emits every start
   * before running read-only tools in parallel, so `activeTool` alone cannot
   * tell whether an earlier completion leaves a later tool still running.
   * `activeTool` remains the newest entry for the compact single-tool UI.
   */
  activeTools?: Array<{ toolCallId: string; name: string; startedAt: number }>;
  /**
   * The reply stream is fully consumed but the run is not yet confirmed
   * successful (entered on `response_complete`). The component hides the line
   * just like `finished`, but keeps listening for the real terminal `agent_end`
   * (success) / `error` (failure).
   */
  phase: "preparing" | "waiting_model" | "generating" | "running_tool" | "cancelling" | "finalizing" | "finished";
  /** When the user explicitly requested cancellation (Stop button). */
  cancelledAt?: number;
}

/** Events silent longer than this switch the copy to "等待此步骤完成 · 最后活动 Ns 前". */
export const STATUS_IDLE_THRESHOLD_MS = 20_000;

/** Generations running longer than this get the gentle "可继续等待或停止" hint. */
export const STATUS_LONG_RUNNING_THRESHOLD_MS = 60_000;

/** vue-i18n `t` surface consumed by `statusText` / `toolLabel` (injected for testability). */
export type AiStatusTranslate = {
  (key: string): string;
  (key: string, named: Record<string, unknown>): string;
};

/** i18n key per agent tool name; unknown tools fall back to the raw snake_case name. */
export const STATUS_TOOL_LABEL_KEYS: Record<string, string> = {
  execute_query: "ai.status.toolLabels.executeQuery",
  execute_sql: "ai.status.toolLabels.executeSql",
  list_tables: "ai.status.toolLabels.listTables",
  get_columns: "ai.status.toolLabels.getColumns",
  get_current_time: "ai.status.toolLabels.getCurrentTime",
  explain_query: "ai.status.toolLabels.explainQuery",
  get_sample_data: "ai.status.toolLabels.getSampleData",
  list_collections: "ai.status.toolLabels.listCollections",
  browse_collection: "ai.status.toolLabels.browseCollection",
};

/** Initial status at `send()` time: `phase=preparing`, `startedAt=now`. */
export function createGenerationStatus(now: number): AiGenerationStatus {
  return { startedAt: now, phase: "preparing" };
}

/**
 * Event-driven reducer. Returns a NEW status object (never mutates the input).
 *
 * - Any event refreshes `lastEventAt`.
 * - `turn_start` records the 0-based turn.
 * - `tool_call_start` enters `running_tool` and tracks the tool by call ID.
 * - `tool_call_end` removes only its matching tool. The phase falls back to
 *   `generating` only after the last outstanding tool has completed.
 * - `text_delta` / `reasoning_delta` with no active tool enter `generating`.
 * - `write_sql_confirmation_required` / `production_write_blocked` /
 *   `context_compacted` only refresh `lastEventAt`, they never change the phase.
 * - `agent_end` / `error` are terminal: they enter `finished` (preserving
 *   `startedAt`/`turn`, clearing `activeTool`) so the component can hide the line
 *   the instant the reply completes instead of resetting the counter to 0.
 * - `response_complete` (non-terminal) enters `finalizing`: the reply stream is
 *   fully consumed but the process is not yet confirmed successful. It hides the
 *   line like `finished`, but only `agent_end` / `error` may advance the phase
 *   from `finalizing` — a late `text_delta` must not flip it back to `generating`.
 * - Once the user requested cancellation (`cancelling`) OR the generation has
 *   terminated (`finished`) OR the stream is `finalizing`, later non-terminal
 *   agent events must not overwrite the phase — only the component ticker keeps
 *   running until `send()`'s `finally`/abandon path resets the per-request status.
 */
export function applyStatusEvent(status: AiGenerationStatus, event: AgentEvent, now: number): AiGenerationStatus {
  if (
    status.phase === "cancelling" ||
    status.phase === "finished" ||
    // `finalizing` blocks everything except the real terminal events.
    (status.phase === "finalizing" && event.type !== "agent_end" && event.type !== "error")
  ) {
    return { ...status, lastEventAt: now };
  }
  const next: AiGenerationStatus = { ...status, lastEventAt: now };
  switch (event.type) {
    case "turn_start":
      next.turn = event.turn;
      break;
    case "tool_call_start":
      // `agent_loop` emits all starts before concurrently executing read-only
      // tools. Keep the latest tool as the displayed one, while retaining the
      // earlier calls so their completion cannot clear this status prematurely.
      next.activeTools = (next.activeTools ?? []).filter((tool) => tool.toolCallId !== event.tool_call_id);
      next.activeTools.push({ toolCallId: event.tool_call_id, name: event.tool_name, startedAt: now });
      next.phase = "running_tool";
      next.activeTool = { name: event.tool_name, startedAt: now };
      break;
    case "tool_call_end": {
      const activeTools = next.activeTools;
      if (!activeTools) {
        // Preserve the safe fallback for streams that deliver an end without a
        // corresponding start (older or incomplete provider event streams).
        next.activeTool = undefined;
        next.phase = "generating";
        break;
      }
      const remainingTools = activeTools.filter((tool) => tool.toolCallId !== event.tool_call_id);
      next.activeTools = remainingTools.length ? remainingTools : undefined;
      const newestActiveTool = remainingTools[remainingTools.length - 1];
      if (newestActiveTool) {
        next.activeTool = { name: newestActiveTool.name, startedAt: newestActiveTool.startedAt };
        next.phase = "running_tool";
      } else {
        next.activeTool = undefined;
        next.phase = "generating";
      }
      break;
    }
    case "text_delta":
    case "reasoning_delta":
      if (!next.activeTool) next.phase = "generating";
      break;
    case "write_sql_confirmation_required":
    case "production_write_blocked":
    case "context_compacted":
      // Only refresh lastEventAt above; do NOT change phase.
      break;
    case "agent_end":
    case "error":
      // Terminal: preserve startedAt (the elapsed counter must not reset to 0),
      // clear the active tool, and let the component hide the line via `finished`.
      next.phase = "finished";
      next.activeTool = undefined;
      next.activeTools = undefined;
      break;
    case "response_complete":
      // Non-terminal stream-complete marker: the reply is fully consumed but the
      // run is not yet confirmed successful (the CLI may still exit non-zero or
      // hang after closing stdout). Hide the line like `finished`, but keep the
      // listener alive for the real `agent_end` / `error`.
      next.phase = "finalizing";
      next.activeTool = undefined;
      next.activeTools = undefined;
      break;
    default:
      break;
  }
  return next;
}

/** User explicitly requested stop — show the cancelling phase until the generation ends. */
export function markCancelling(status: AiGenerationStatus, now: number): AiGenerationStatus {
  // A generation that already reached the terminal `finished` state (reply
  // complete, send()'s finally still settling) or the `finalizing` state (reply
  // stream fully consumed, process exit pending) must not be flipped back into
  // "正在取消…" — the reply is already done, the line stays hidden.
  if (status.phase === "finished" || status.phase === "finalizing") return status;
  return { ...status, phase: "cancelling", cancelledAt: now, lastEventAt: now };
}

/** Resolve a snake_case tool name through the i18n label map, falling back to the raw name. */
export function toolLabel(toolName: string, t: AiStatusTranslate): string {
  const key = STATUS_TOOL_LABEL_KEYS[toolName];
  return key ? t(key) : toolName;
}

/** Round a duration up to whole seconds, never below 0 (guards a stale timer -1s). */
function secondsUp(milliseconds: number): number {
  return Math.max(0, Math.ceil(milliseconds / 1000));
}

/**
 * Status-line copy, highest priority first:
 *
 * 1. Idle timeout (`lastEventAt` defined AND `now - lastEventAt > 20s`) →
 *    "等待此步骤完成 · 最后活动 {idle}s 前" (+ " · 正在执行 {tool}" when a tool is active).
 * 2. `running_tool` with an active tool → "第 {turn+1} 轮 · 正在执行 {tool} · 已运行 {elapsed}s".
 * 3. `generating` (a delta has arrived) → "正在生成回复 · 已运行 {elapsed}s".
 * 4. `lastEventAt === undefined` (no events yet — e.g. a slow CLI first token) →
 *    "等待模型响应 · 已运行 {elapsed}s". Separate branch: it must NOT hit the idle branch.
 *
 * Cancelling is handled first — once the user clicks Stop the line reads "正在取消…".
 * `finished` is terminal and the component hides the line, so it returns an empty
 * string here (never the waitingModel/idle copy) to keep the pure function total.
 * `finalizing` (reply stream consumed, process exit pending) also returns an
 * empty string — the line is hidden while the real `agent_end`/`error` is still
 * pending.
 * The >60s gentle hint is NOT part of this string; it renders next to the Stop
 * button via `shouldShowLongRunningHint`.
 */
export function statusText(status: AiGenerationStatus, now: number, t: AiStatusTranslate): string {
  // `finished`/`finalizing` must win over BOTH the idle branch and the
  // waitingModel fallthrough, or a completed reply could re-render
  // "等待此步骤完成 · 最后活动 Ns 前"/"0s".
  if (status.phase === "finished" || status.phase === "finalizing") return "";
  const elapsed = secondsUp(now - status.startedAt);
  if (status.phase === "cancelling") {
    return t("ai.status.cancelling");
  }

  if (status.lastEventAt !== undefined && now - status.lastEventAt > STATUS_IDLE_THRESHOLD_MS) {
    const idle = secondsUp(now - status.lastEventAt);
    if (status.activeTool) {
      return t("ai.status.idleWithTool", { idle, tool: toolLabel(status.activeTool.name, t) });
    }
    return t("ai.status.idle", { idle });
  }

  if (status.phase === "running_tool" && status.activeTool) {
    return t("ai.status.runningTool", {
      turn: status.turn !== undefined ? status.turn + 1 : 1,
      tool: toolLabel(status.activeTool.name, t),
      elapsed,
    });
  }

  if (status.phase === "generating") {
    return t("ai.status.generating", { elapsed });
  }

  return t("ai.status.waitingModel", { elapsed });
}

/**
 * Screen-reader announcement for the status line (Issue #6743 feature 1, a11y).
 *
 * Rendered inside a `role="status"` (`aria-live="polite"` + `aria-atomic`) live
 * region. Deliberately EXCLUDES the ticking elapsed/idle numerals that
 * `statusText` embeds — a live region whose content changed once per second
 * would re-announce the running timer on every tick and spam screen-reader
 * users. Only discrete state changes are announced: phase transitions, tool
 * start/end, turn, and crossing the 20s idle threshold (the idle cross happens
 * once and the announced string stays stable until the next event).
 */
export function liveAnnouncementText(status: AiGenerationStatus, now: number, t: AiStatusTranslate): string {
  // A completed reply is silent for screen readers too — never re-announce the
  // waitingModel/idle copy under a finished/finalizing generation.
  if (status.phase === "finished" || status.phase === "finalizing") return "";
  if (status.phase === "cancelling") return t("ai.status.cancelling");

  const idle = status.lastEventAt !== undefined && now - status.lastEventAt > STATUS_IDLE_THRESHOLD_MS;
  if (idle) {
    return status.activeTool ? `${t("ai.status.idleLive")} ${t("ai.status.runningToolAction")} ${toolLabel(status.activeTool.name, t)}` : t("ai.status.idleLive");
  }

  if (status.phase === "running_tool" && status.activeTool) {
    const turn = status.turn;
    const badge = turn !== undefined ? t("ai.status.turnBadge", { turn: turn + 1 }) : "";
    return [badge, t("ai.status.runningToolAction"), toolLabel(status.activeTool.name, t)].filter(Boolean).join(" ");
  }

  if (status.phase === "generating") return t("ai.status.generatingLive");

  return t("ai.status.waitingModelLive");
}

/** Whether the gentle "响应时间较长，可继续等待或停止" hint should appear next to Stop. */
export function shouldShowLongRunningHint(status: AiGenerationStatus, now: number): boolean {
  return status.phase !== "finished" && status.phase !== "finalizing" && now - status.startedAt > STATUS_LONG_RUNNING_THRESHOLD_MS;
}

/**
 * Delay (ms) until the next real wall-clock second boundary. Used to align the
 * status ticker to whole-second boundaries so the displayed elapsed/idle rolls
 * +1s exactly when the wall clock does — a fixed `setInterval(1000)` drifts and
 * skips values when a late callback shifts the phase.
 */
export function nextStatusTickDelay(now: number): number {
  return 1000 - (now % 1000);
}

/**
 * Cancellable whole-second ticker for the live generation-status line.
 *
 * Replaces a per-frame `requestAnimationFrame` loop that rescheduled 60+ times
 * per second while only updating displayed state once per second. This ticker
 * runs ONE `setTimeout` per whole-second boundary: it schedules the next tick to
 * the next real wall-clock second (`nextStatusTickDelay`), so a delayed tick
 * re-aligns instead of accumulating drift. Being wall-clock based it also keeps
 * ticking while the document is hidden/occluded (rAF pauses then), so a long
 * request's idle/elapsed display stays live in the background.
 *
 * `start` seeds the callback immediately with `now` (so the line shows a fresh
 * timestamp) and schedules the next boundary tick. `stop` cancels a pending
 * tick and clears the running flag; a tick callback already queued when `stop`
 * runs bails without rescheduling (the `running` guard), so a stopped ticker
 * stays stopped. `start` is idempotent (re-starts from the given `now`).
 */
export interface StatusTicker {
  start(now: number): void;
  stop(): void;
}

export function createStatusTicker(onTick: (now: number) => void): StatusTicker {
  let timer: ReturnType<typeof setTimeout> | null = null;
  let running = false;

  function tick() {
    timer = null;
    // A tick queued before stop() may still fire once after it — bail without
    // rescheduling so a stopped ticker stays stopped.
    if (!running) return;
    const now = Date.now();
    onTick(now);
    timer = setTimeout(tick, nextStatusTickDelay(now));
  }

  function stop() {
    running = false;
    if (timer !== null) {
      clearTimeout(timer);
      timer = null;
    }
  }

  return {
    start(now: number) {
      stop();
      running = true;
      onTick(now);
      timer = setTimeout(tick, nextStatusTickDelay(now));
    },
    stop,
  };
}