import { ToolOutputPruningState } from "./tool-output-pruning/state.js";
import type {
	CompactionMode,
	CompactionTelemetry,
	TelemetryPersistenceIssue,
} from "./types.js";

/**
 * Encapsulates all mutable state for Compact+.
 * Replaces scattered module-level `let` variables with a single instance.
 */
export class CompactionState {
	selectedMode: CompactionMode | null = null;
	lastCompactTime = 0;
	isCompacting = false;
	lastTriggerAuto = false;
	lastCompactTokens = 0;
	lastModelKey: string | null = null;
	lastCompactTurnIndex = -1;
	lastCompaction: CompactionTelemetry | null = null;
	pendingCompaction: CompactionTelemetry | null = null;
	lastFallbackReason: string | null = null;
	lastInjectedEcho: string | null = null;
	telemetryPersistenceIssues: TelemetryPersistenceIssue[] = [];
	echoInjected = false;
	toolOutputPruning = new ToolOutputPruningState();

	/** Reset all state to initial values. */
	reset(): void {
		this.selectedMode = null;
		this.lastCompactTime = 0;
		this.isCompacting = false;
		this.lastTriggerAuto = false;
		this.lastCompactTokens = 0;
		this.lastModelKey = null;
		this.lastCompactTurnIndex = -1;
		this.lastCompaction = null;
		this.pendingCompaction = null;
		this.lastFallbackReason = null;
		this.lastInjectedEcho = null;
		this.telemetryPersistenceIssues = [];
		this.echoInjected = false;
		this.toolOutputPruning.reset();
	}

	/**
	 * Reset state when the model changes.
	 * @returns true if the model key changed (state was reset or initialized).
	 */
	resetOnModelChange(key: string): boolean {
		if (key === this.lastModelKey) {
			return false;
		}
		if (this.lastModelKey !== null) {
			// True model change: reset model-scoped state
			this.lastCompactTime = 0;
			this.selectedMode = null;
			this.lastTriggerAuto = false;
			this.lastCompactTokens = 0;
			this.lastCompactTurnIndex = -1;
			this.lastCompaction = null;
			this.pendingCompaction = null;
			this.lastFallbackReason = null;
			this.lastInjectedEcho = null;
			this.echoInjected = false;
			this.toolOutputPruning.reset();
		}
		this.lastModelKey = key;
		return true;
	}

	recordTelemetryPersistenceIssue(
		issue: TelemetryPersistenceIssue | null,
	): void {
		if (!issue) return;
		this.telemetryPersistenceIssues = [
			issue,
			...this.telemetryPersistenceIssues,
		].slice(0, 5);
	}

	clearPendingCompaction(): void {
		this.pendingCompaction = null;
	}

	// ── Guard helpers ────────────────────────────────────────────────

	/** Check if we're still in the cooldown window since last compaction. */
	isOnCooldown(cooldownMs: number): boolean {
		return Date.now() - this.lastCompactTime < cooldownMs;
	}

	/** Check if token usage hasn't grown enough since last compaction. */
	isRegrowthBelowThreshold(
		currentTokens: number,
		regrowthTokens: number,
	): boolean {
		return (
			this.lastCompactTokens > 0 &&
			currentTokens - this.lastCompactTokens < regrowthTokens
		);
	}

	/** Check if the given turn index matches the last compaction turn. */
	isSameTurn(turnIndex?: number): boolean {
		return turnIndex !== undefined && turnIndex === this.lastCompactTurnIndex;
	}
}