import { readFileSync } from "node:fs";
import { fileURLToPath } from "node:url";

export interface OverflowSettings {
	enabled: boolean;
	thresholdChars: number;
	headLines: number;
	tailLines: number;
	maxSignalLines: number;
	signalPattern: string;
	signalRegex: RegExp;
	maxLineChars: number;
	exemptTools: string[];
	retentionDays: number;
	maxStoreBytes: number;
	maxEntryBytes: number;
}

export const DEFAULT_SIGNAL_PATTERN =
	"\\b(error|errors|fail|failed|failure|warn|warning|exception|traceback|panic|fatal)\\b";

export const OVERFLOW_DEFAULTS = {
	enabled: true,
	thresholdChars: 24_000,
	headLines: 40,
	tailLines: 120,
	maxSignalLines: 40,
	signalPattern: DEFAULT_SIGNAL_PATTERN,
	maxLineChars: 500,
	exemptTools: ["read", "edit", "write", "overflow_query", "ask_user_question"],
	retentionDays: 7,
	maxStoreBytes: 1_073_741_824,
	maxEntryBytes: 67_108_864,
} as const;

// Bundle-level `config/` is the single source of truth: the extension reads
// `config/pi-overflow.json` from inside the installed bundle (resolved
// relative to this package-root source file), never `settings.json`.
export const OVERFLOW_CONFIG_PATH = fileURLToPath(
	new URL("../config/pi-overflow.json", import.meta.url),
);

function isObject(value: unknown): value is Record<string, unknown> {
	return value !== null && typeof value === "object" && !Array.isArray(value);
}

function bool(value: unknown, fallback: boolean): boolean {
	return typeof value === "boolean" ? value : fallback;
}

function intInRange(value: unknown, fallback: number, min: number, max: number): number {
	return typeof value === "number" && Number.isInteger(value) && value >= min && value <= max
		? value
		: fallback;
}

function compileSignalPattern(value: unknown): { pattern: string; regex: RegExp } {
	const pattern = typeof value === "string" && value.length > 0 ? value : DEFAULT_SIGNAL_PATTERN;
	try {
		return { pattern, regex: new RegExp(pattern, "i") };
	} catch {
		return { pattern: DEFAULT_SIGNAL_PATTERN, regex: new RegExp(DEFAULT_SIGNAL_PATTERN, "i") };
	}
}

function stringList(value: unknown, fallback: readonly string[]): string[] {
	if (!Array.isArray(value)) return [...fallback];
	const list = value.filter((item): item is string => typeof item === "string" && item.length > 0);
	return [...new Set(list)];
}

/**
 * Read `config/pi-overflow.json`. Every field is validated independently and
 * falls back to its bundle default when missing or invalid; an unreadable or
 * non-object file yields all defaults. Tests inject an explicit path.
 */
export function readOverflowSettings(configPath: string = OVERFLOW_CONFIG_PATH): OverflowSettings {
	let parsed: unknown = {};
	try {
		parsed = JSON.parse(readFileSync(configPath, "utf8"));
	} catch {
		parsed = {};
	}
	const config = isObject(parsed) ? parsed : {};
	const signal = compileSignalPattern(config.signalPattern);
	return {
		enabled: bool(config.enabled, OVERFLOW_DEFAULTS.enabled),
		thresholdChars: intInRange(config.thresholdChars, OVERFLOW_DEFAULTS.thresholdChars, 1, 10_000_000),
		headLines: intInRange(config.headLines, OVERFLOW_DEFAULTS.headLines, 0, 10_000),
		tailLines: intInRange(config.tailLines, OVERFLOW_DEFAULTS.tailLines, 0, 10_000),
		maxSignalLines: intInRange(config.maxSignalLines, OVERFLOW_DEFAULTS.maxSignalLines, 0, 1_000),
		signalPattern: signal.pattern,
		signalRegex: signal.regex,
		maxLineChars: intInRange(config.maxLineChars, OVERFLOW_DEFAULTS.maxLineChars, 10, 100_000),
		exemptTools: stringList(config.exemptTools, OVERFLOW_DEFAULTS.exemptTools),
		retentionDays: intInRange(config.retentionDays, OVERFLOW_DEFAULTS.retentionDays, 0, 3_650),
		maxStoreBytes: intInRange(config.maxStoreBytes, OVERFLOW_DEFAULTS.maxStoreBytes, 1_024, 1_099_511_627_776),
		maxEntryBytes: intInRange(config.maxEntryBytes, OVERFLOW_DEFAULTS.maxEntryBytes, 1_024, 1_099_511_627_776),
	};
}