import type {
  OrchestrationV2ProviderTurnTokenUsage,
  OrchestrationV2TurnItem,
  ThreadTokenUsageSnapshot,
} from "@t3tools/contracts";
import * as DateTime from "effect/DateTime";

function asFiniteNumber(value: unknown): number | null {
  return typeof value === "number" && Number.isFinite(value) ? value : null;
}

type NullableContextWindowUsage = {
  readonly [Key in keyof ThreadTokenUsageSnapshot]: undefined extends ThreadTokenUsageSnapshot[Key]
    ? Exclude<ThreadTokenUsageSnapshot[Key], undefined> | null
    : ThreadTokenUsageSnapshot[Key];
};

export type ContextWindowSnapshot = NullableContextWindowUsage & {
  readonly remainingTokens: number | null;
  readonly usedPercentage: number | null;
  readonly remainingPercentage: number | null;
  readonly updatedAt: string;
};

/** Prefers the provider's live usage report (#8144); falls back to the last compaction item. */
export function deriveLatestContextWindowSnapshot(
  entries: ReadonlyArray<{
    readonly item: OrchestrationV2TurnItem;
  }>,
  liveUsage?: OrchestrationV2ProviderTurnTokenUsage | null,
): ContextWindowSnapshot | null {
  if (liveUsage != null) {
    const usedTokens = Math.max(0, liveUsage.usedTokens);
    const maxTokens = liveUsage.maxTokens ?? null;
    const usedPercentage =
      maxTokens !== null && maxTokens > 0 ? Math.min(100, (usedTokens / maxTokens) * 100) : null;
    const remainingTokens =
      maxTokens !== null ? Math.max(0, Math.round(maxTokens - usedTokens)) : null;
    const remainingPercentage = usedPercentage !== null ? Math.max(0, 100 - usedPercentage) : null;
    return {
      usedTokens,
      totalProcessedTokens: null,
      maxTokens,
      remainingTokens,
      usedPercentage,
      remainingPercentage,
      inputTokens: liveUsage.inputTokens ?? null,
      cachedInputTokens: liveUsage.cachedInputTokens ?? null,
      outputTokens: liveUsage.outputTokens ?? null,
      reasoningOutputTokens: liveUsage.reasoningOutputTokens ?? null,
      lastUsedTokens: null,
      lastInputTokens: null,
      lastCachedInputTokens: null,
      lastOutputTokens: null,
      lastReasoningOutputTokens: null,
      toolUses: null,
      durationMs: null,
      compactsAutomatically: true,
      autoCompactThreshold: null,
      updatedAt: liveUsage.updatedAt,
    };
  }
  for (let index = entries.length - 1; index >= 0; index -= 1) {
    const entry = entries[index];
    if (!entry || entry.item.type !== "compaction") {
      continue;
    }
    const payload = entry.item;
    const usedTokens = asFiniteNumber(payload.afterTokenCount);
    if (usedTokens === null || usedTokens < 0) {
      continue;
    }

    const maxTokens = null;
    const usedPercentage =
      maxTokens !== null && maxTokens > 0 ? Math.min(100, (usedTokens / maxTokens) * 100) : null;
    const remainingTokens =
      maxTokens !== null ? Math.max(0, Math.round(maxTokens - usedTokens)) : null;
    const remainingPercentage = usedPercentage !== null ? Math.max(0, 100 - usedPercentage) : null;

    return {
      usedTokens,
      totalProcessedTokens: asFiniteNumber(payload.beforeTokenCount),
      maxTokens,
      remainingTokens,
      usedPercentage,
      remainingPercentage,
      inputTokens: null,
      cachedInputTokens: null,
      outputTokens: null,
      reasoningOutputTokens: null,
      lastUsedTokens: null,
      lastInputTokens: null,
      lastCachedInputTokens: null,
      lastOutputTokens: null,
      lastReasoningOutputTokens: null,
      toolUses: null,
      durationMs: null,
      compactsAutomatically: true,
      autoCompactThreshold: null,
      updatedAt: DateTime.formatIso(payload.startedAt ?? payload.updatedAt),
    };
  }

  return null;
}

export function formatContextWindowTokens(value: number | null): string {
  if (value === null || !Number.isFinite(value)) {
    return "0";
  }
  if (value < 1_000) {
    return `${Math.round(value)}`;
  }
  if (value < 10_000) {
    return `${(value / 1_000).toFixed(1).replace(/\.0$/, "")}k`;
  }
  if (value < 1_000_000) {
    return `${Math.round(value / 1_000)}k`;
  }
  return `${(value / 1_000_000).toFixed(1).replace(/\.0$/, "")}m`;
}