/**
 * Pure argument validation for the web_search tool — input → output, no I/O.
 *
 * Resolves the operation mode (explicit, or inferred from `query`/`url`),
 * applies per-mode field requirements, clamps `limit`, and defaults `format`.
 * Returns a discriminated union so the tool's dispatch narrows by `mode`.
 */

export const MODES = ["search", "scrape", "crawl", "map"] as const;
export type Mode = (typeof MODES)[number];

export const FORMATS = ["markdown", "text", "html"] as const;
export type Format = (typeof FORMATS)[number];

export const SEARCH_DEFAULT_LIMIT = 7;
export const CRAWL_DEFAULT_LIMIT = 3;
export const MAX_LIMIT = 10;

interface BaseArgs {
	readonly format: Format;
}

export interface SearchArgs extends BaseArgs {
	readonly mode: "search";
	readonly query: string;
	readonly limit: number;
	readonly scrape: boolean;
	readonly lang?: string;
	readonly country?: string;
}

export interface ScrapeArgs extends BaseArgs {
	readonly mode: "scrape";
	readonly url: string;
}

export interface CrawlArgs extends BaseArgs {
	readonly mode: "crawl";
	readonly url: string;
	readonly limit: number;
}

export interface MapArgs extends BaseArgs {
	readonly mode: "map";
	readonly url: string;
}

export type ValidatedArgs = SearchArgs | ScrapeArgs | CrawlArgs | MapArgs;

export type ValidationError = { readonly error: string };

type Result<T> = { readonly value: T } | ValidationError;

function resolveFormat(raw: unknown): Result<Format> {
	if (raw === undefined || raw === null) {
		return { value: "markdown" };
	}
	if (typeof raw === "string" && (FORMATS as readonly string[]).includes(raw)) {
		return { value: raw as Format };
	}
	return {
		error: `Error: Invalid format "${String(raw)}" (must be one of: markdown, text, html).`,
	};
}

function resolveMode(raw: unknown, query: unknown, url: unknown): Result<Mode> {
	if (raw === undefined || raw === null) {
		const hasQuery = typeof query === "string" && query.trim().length > 0;
		const hasUrl = typeof url === "string" && url.trim().length > 0;
		return { value: hasQuery ? "search" : hasUrl ? "scrape" : "search" };
	}
	if (typeof raw === "string" && (MODES as readonly string[]).includes(raw)) {
		return { value: raw as Mode };
	}
	return {
		error: `Error: Invalid mode "${String(raw)}" (must be one of: search, scrape, crawl, map).`,
	};
}

function optionalString(raw: unknown, name: string): Result<string | undefined> {
	if (raw === undefined || raw === null) {
		return { value: undefined };
	}
	if (typeof raw === "string") {
		return { value: raw };
	}
	return { error: `Error: "${name}" must be a string.` };
}

function resolveLimit(raw: unknown, defaultLimit: number): Result<number> {
	if (raw === undefined || raw === null) {
		return { value: defaultLimit };
	}
	const n = Number(raw);
	if (!Number.isFinite(n) || n < 1) {
		return { error: 'Error: "limit" must be a positive number.' };
	}
	return { value: Math.min(Math.floor(n), MAX_LIMIT) };
}

function resolveBoolean(raw: unknown, name: string): Result<boolean> {
	if (raw === undefined || raw === null) {
		return { value: false };
	}
	if (typeof raw === "boolean") {
		return { value: raw };
	}
	return { error: `Error: "${name}" must be a boolean.` };
}

/**
 * Validate raw tool args and resolve a typed, mode-aware `ValidatedArgs`.
 * Returns `{ error }` for invalid input — the tool surfaces it verbatim.
 */
export function validateArgs(args: unknown): ValidatedArgs | ValidationError {
	if (args === null || args === undefined || typeof args !== "object") {
		return { error: "Error: Arguments must be an object." };
	}
	const obj = args as Record<string, unknown>;

	const format = resolveFormat(obj.format);
	if ("error" in format) {
		return format;
	}

	const mode = resolveMode(obj.mode, obj.query, obj.url);
	if ("error" in mode) {
		return mode;
	}

	const query = optionalString(obj.query, "query");
	if ("error" in query) {
		return query;
	}

	const url = optionalString(obj.url, "url");
	if ("error" in url) {
		return url;
	}

	switch (mode.value) {
		case "search": {
			if (query.value === undefined || query.value.trim().length === 0) {
				return { error: "Error: query is required for search mode." };
			}
			const limit = resolveLimit(obj.limit, SEARCH_DEFAULT_LIMIT);
			if ("error" in limit) {
				return limit;
			}
			const scrape = resolveBoolean(obj.scrape, "scrape");
			if ("error" in scrape) {
				return scrape;
			}
			const lang = optionalString(obj.lang, "lang");
			if ("error" in lang) {
				return lang;
			}
			const country = optionalString(obj.country, "country");
			if ("error" in country) {
				return country;
			}
			const result: SearchArgs = {
				mode: "search",
				query: query.value,
				limit: limit.value,
				scrape: scrape.value,
				format: format.value,
				...(lang.value !== undefined ? { lang: lang.value } : {}),
				...(country.value !== undefined ? { country: country.value } : {}),
			};
			return result;
		}
		case "scrape": {
			if (url.value === undefined || url.value.trim().length === 0) {
				return { error: "Error: url is required for scrape mode." };
			}
			const result: ScrapeArgs = {
				mode: "scrape",
				url: url.value,
				format: format.value,
			};
			return result;
		}
		case "crawl": {
			if (url.value === undefined || url.value.trim().length === 0) {
				return { error: "Error: url is required for crawl mode." };
			}
			const limit = resolveLimit(obj.limit, CRAWL_DEFAULT_LIMIT);
			if ("error" in limit) {
				return limit;
			}
			const result: CrawlArgs = {
				mode: "crawl",
				url: url.value,
				limit: limit.value,
				format: format.value,
			};
			return result;
		}
		case "map": {
			if (url.value === undefined || url.value.trim().length === 0) {
				return { error: "Error: url is required for map mode." };
			}
			const result: MapArgs = {
				mode: "map",
				url: url.value,
				format: format.value,
			};
			return result;
		}
	}
}