/**
 * turnProgress.ts — pure reduction of @cline/sdk Agent runtime events into a
 * small UI-facing progress snapshot (#60, spec coauthoring-live-progress.md §3.2).
 *
 * INV-43: vscode-free. INV-46: a pure function — no vscode, no SDK runtime
 * dependency (`AgentRuntimeEvent` is imported TYPE-only, so it is erased at
 * compile and never pulls the ESM SDK into the bundle). All event→state logic
 * lives here so it is unit-tested in isolation; the UI call sites only format and
 * relay snapshots.
 */
import type { AgentRuntimeEvent } from "@cline/shared";

export type TurnPhase = "thinking" | "writing" | "tool";

export interface TurnProgressSnapshot {
  phase: TurnPhase;
  /** present iff phase === "tool" — the running tool's name. */
  tool?: string;
  /** accumulated assistant-text length so far. */
  chars: number;
  /** running total tokens (input+output); undefined until the first usage event. */
  tokens?: number;
  /** the new assistant-text chunk since the last snapshot (for the OutputChannel). */
  textDelta?: string;
}

export interface TurnProgressState {
  phase: TurnPhase;
  chars: number;
  tokens?: number;
  /** stack of tool names currently running (depth-tracked for overlap). */
  activeTools: string[];
  /** true once any assistant text has streamed (tool-finish then reverts to writing). */
  sawText: boolean;
}

export function createTurnProgressState(): TurnProgressState {
  return { phase: "thinking", chars: 0, tokens: undefined, activeTools: [], sawText: false };
}

function restingPhase(state: TurnProgressState): TurnPhase {
  if (state.activeTools.length) return "tool";
  return state.sawText ? "writing" : "thinking";
}

function toSnapshot(state: TurnProgressState, textDelta?: string): TurnProgressSnapshot {
  return {
    phase: state.phase,
    tool: state.phase === "tool" ? state.activeTools[state.activeTools.length - 1] : undefined,
    chars: state.chars,
    tokens: state.tokens,
    textDelta,
  };
}

/**
 * Fold one SDK event into the state, returning the next state and the snapshot to
 * emit (snapshot undefined for events that don't change the surface).
 */
export function reduceTurnProgress(
  state: TurnProgressState,
  event: AgentRuntimeEvent,
): { state: TurnProgressState; snapshot?: TurnProgressSnapshot } {
  switch (event.type) {
    case "run-started":
    case "turn-started": {
      const next: TurnProgressState = { ...state, phase: restingPhase(state) };
      return { state: next, snapshot: toSnapshot(next) };
    }
    case "assistant-text-delta": {
      const next: TurnProgressState = {
        ...state,
        phase: state.activeTools.length ? "tool" : "writing",
        chars: event.accumulatedText.length,
        sawText: true,
      };
      return { state: next, snapshot: toSnapshot(next, event.text) };
    }
    case "assistant-reasoning-delta": {
      // Reasoning TEXT is not surfaced (operator fork); collapse to motion only.
      const next: TurnProgressState = { ...state, phase: state.activeTools.length ? "tool" : "thinking" };
      return { state: next, snapshot: toSnapshot(next) };
    }
    case "tool-started": {
      const activeTools = [...state.activeTools, event.toolCall.toolName];
      const next: TurnProgressState = { ...state, phase: "tool", activeTools };
      return { state: next, snapshot: toSnapshot(next) };
    }
    case "tool-updated": {
      const next: TurnProgressState = { ...state, phase: "tool" };
      return { state: next, snapshot: toSnapshot(next) };
    }
    case "tool-finished": {
      const name = event.toolCall.toolName;
      const idx = state.activeTools.lastIndexOf(name);
      const activeTools = idx >= 0 ? state.activeTools.filter((_, i) => i !== idx) : state.activeTools.slice(0, -1);
      const next: TurnProgressState = { ...state, activeTools, phase: "thinking" };
      next.phase = restingPhase(next);
      return { state: next, snapshot: toSnapshot(next) };
    }
    case "usage-updated": {
      const tokens = event.usage.inputTokens + event.usage.outputTokens || undefined;
      const next: TurnProgressState = { ...state, tokens };
      return { state: next, snapshot: toSnapshot(next) };
    }
    default:
      return { state };
  }
}

/** Render the notification activity line from a snapshot (pure; spec §2.1). */
export function formatProgressLine(s: TurnProgressSnapshot): string {
  let head: string;
  if (s.phase === "tool") head = `running ${s.tool ?? "tool"}…`;
  else if (s.phase === "writing") head = `writing… (${s.chars} chars)`;
  else head = "thinking…";
  return s.tokens ? `${head} · ${formatTokens(s.tokens)} tokens` : head;
}

export function formatTokens(n: number): string {
  return n >= 1000 ? `${(n / 1000).toFixed(1)}k` : String(n);
}