/**
 * Pure core for cache-warming — zero I/O, zero ambient state.
 * Every function is input → output; testable without mocks.
 */

import type {
	CustomField,
	NumberField,
	StatField,
	SurfaceSpec,
	ToggleField,
} from "@dispatch/ui-contract";

// --- Types ---

/** Persisted per-conversation settings (storage-facing). */
export interface ConversationSettings {
	readonly enabled: boolean;
	readonly intervalMs: number;
}

/** Full per-conversation runtime state (in-memory, not persisted). */
export interface ConversationState extends ConversationSettings {
	readonly active: boolean;
	readonly lastPct: number | null;
	readonly lastExpectedPct: number | null;
	readonly lastWarmAt: number | null;
	readonly nextWarmAt: number | null;
	readonly token: number;
}

/** Context stored per-conversation from the latest lifecycle event. */
export interface ConversationContext {
	readonly cwd?: string;
	readonly modelName?: string;
}

export const DEFAULT_INTERVAL_MS = 240_000;
export const MIN_INTERVAL_MS = 1000;

// --- Pure functions ---

/**
 * Compute cache-hit percentage from token counts.
 * Returns an integer in [0, 100]. inputTokens ≤ 0 → 0.
 */
export function computeCachePct(inputTokens: number, cacheReadTokens: number): number {
	if (inputTokens <= 0) return 0;
	const ratio = cacheReadTokens / inputTokens;
	const clamped = Math.max(0, Math.min(1, ratio));
	return Math.round(clamped * 100);
}

/**
 * Compute expected cache retention rate from token counts.
 * Of the cacheable prefix the warm touched, how much was still warm (read back)
 * vs. had to be (re)written.
 * Returns an integer in [0, 100]. cacheRead + cacheWrite ≤ 0 → 0.
 */
export function computeExpectedCacheRate(
	cacheReadTokens: number,
	cacheWriteTokens: number,
): number {
	const total = cacheReadTokens + cacheWriteTokens;
	if (total <= 0) return 0;
	return Math.round((cacheReadTokens / total) * 100);
}

/**
 * Decide whether a conversation should be warmed right now.
 * Requires: enabled, idle (not active), and the token is current (not superseded).
 */
export function shouldWarm(state: ConversationState, currentToken: number): boolean {
	return state.enabled && !state.active && state.token === currentToken;
}

/**
 * Check whether a token is still current (not superseded by a newer cancel/fire).
 */
export function isTokenCurrent(current: number, expected: number): boolean {
	return current === expected;
}

const SETTINGS_KEY = "settings";

/**
 * Parse settings from a raw storage string.
 * Returns defaults if null or malformed.
 *
 * Warming defaults to OFF (CR-4a): a new conversation never schedules warms
 * until the user explicitly opts in via the toggle.
 */
export function parseSettings(raw: string | null): ConversationSettings {
	if (raw === null) return { enabled: false, intervalMs: DEFAULT_INTERVAL_MS };
	try {
		const parsed: unknown = JSON.parse(raw);
		if (typeof parsed !== "object" || parsed === null) {
			return { enabled: false, intervalMs: DEFAULT_INTERVAL_MS };
		}
		const obj = parsed as Record<string, unknown>;
		const enabled = typeof obj.enabled === "boolean" ? obj.enabled : false;
		const rawInterval = obj.intervalMs;
		let intervalMs = DEFAULT_INTERVAL_MS;
		if (typeof rawInterval === "number" && Number.isFinite(rawInterval)) {
			intervalMs =
				rawInterval <= 0 ? MIN_INTERVAL_MS : Math.max(MIN_INTERVAL_MS, Math.round(rawInterval));
		}
		return { enabled, intervalMs };
	} catch {
		return { enabled: false, intervalMs: DEFAULT_INTERVAL_MS };
	}
}

/**
 * Serialize settings for storage.
 */
export function serializeSettings(settings: ConversationSettings): string {
	return JSON.stringify(settings);
}

/** The storage key for a conversation's settings. */
export function settingsKey(conversationId: string): string {
	return `${SETTINGS_KEY}:${conversationId}`;
}

// --- Surface spec builders (pure) ---

/** Convert intervalMs to display seconds (rounded). */
export function msToSeconds(intervalMs: number): number {
	return Math.round(intervalMs / 1000);
}

/**
 * Convert seconds (from the UI) to intervalMs, flooring at MIN_INTERVAL_MS.
 * Returns null for NaN / non-positive (caller should ignore).
 */
export function secondsToMs(seconds: number): number | null {
	if (!Number.isFinite(seconds) || seconds <= 0) return null;
	return Math.max(MIN_INTERVAL_MS, Math.round(seconds * 1000));
}

/**
 * Build a per-conversation surface spec with toggle + number(interval) + stat fields.
 * Pure — no I/O.
 */
export function buildConversationSpec(
	enabled: boolean,
	intervalMs: number,
	lastPct: number | null,
	lastExpectedPct: number | null,
	nextWarmAt: number | null,
	lastWarmAt: number | null,
): SurfaceSpec {
	const pctDisplay = lastPct === null ? "—" : `${lastPct}%`;
	const retentionDisplay = lastExpectedPct === null ? "—" : `${lastExpectedPct}%`;
	const toggle: ToggleField = {
		kind: "toggle",
		label: "Enabled",
		value: enabled,
		action: { actionId: "cache-warming/toggle" },
	};
	const interval: NumberField = {
		kind: "number",
		label: "Refresh Interval",
		value: msToSeconds(intervalMs),
		min: 1,
		step: 1,
		unit: "s",
		action: { actionId: "cache-warming/set-interval" },
	};
	const stat: StatField = {
		kind: "stat",
		label: "Last Cache %",
		value: pctDisplay,
	};
	const retentionStat: StatField = {
		kind: "stat",
		label: "Cache retention",
		value: retentionDisplay,
	};
	const timer: CustomField = {
		kind: "custom",
		rendererId: "cache-warming-timer",
		payload: { nextWarmAt, lastWarmAt },
	};
	return {
		id: "cache-warming",
		region: "side",
		title: "Cache Warming",
		fields: [toggle, interval, stat, retentionStat, timer],
	};
}

/**
 * Build a default surface spec when no conversation is in focus.
 * Pure — no I/O.
 */
export function buildDefaultSpec(): SurfaceSpec {
	return {
		id: "cache-warming",
		region: "side",
		title: "Cache Warming",
		fields: [
			{
				kind: "stat",
				label: "Status",
				value: "No conversation focused",
			},
		],
	};
}

/**
 * Parse the payload for a set-interval action.
 * Accepts a bare number OR { value: number }. Returns the seconds value, or
 * null if the payload is invalid (NaN / non-positive / wrong shape).
 */
export function parseIntervalPayload(payload: unknown): number | null {
	if (typeof payload === "number" && Number.isFinite(payload) && payload > 0) {
		return payload;
	}
	if (
		typeof payload === "object" &&
		payload !== null &&
		"value" in payload &&
		typeof (payload as Record<string, unknown>).value === "number"
	) {
		const v = (payload as Record<string, unknown>).value as number;
		if (Number.isFinite(v) && v > 0) return v;
	}
	return null;
}