import { existsSync, readFileSync } from "node:fs";
import { join } from "node:path";
import { CONFIG_DIR } from "./settings.ts";

const TAXONOMY_PATH = join(CONFIG_DIR, "taxonomy.json");

export interface TaxonomyCategory {
	/** Enum key used in classification and log records. */
	key: string;
	/** Human-readable label shown in the report. */
	label: string;
	/** Excluded from the ranked report while still being logged, e.g. mechanical typos. */
	reportable: boolean;
}

/**
 * Coarse, mutually disjoint English error categories. Disjointness is the point: a
 * category an error could plausibly land in twice makes counts incomparable across
 * time, which is the only reason the enum exists.
 */
export const DEFAULT_TAXONOMY: TaxonomyCategory[] = [
	{ key: "subject_verb_agreement", label: "Subject-verb agreement", reportable: true },
	{ key: "article_determiner", label: "Articles and determiners", reportable: true },
	{ key: "preposition", label: "Prepositions", reportable: true },
	{ key: "verb_tense", label: "Verb tense", reportable: true },
	{ key: "verb_form", label: "Verb form", reportable: true },
	{ key: "noun_number", label: "Noun number", reportable: true },
	{ key: "word_form", label: "Word form", reportable: true },
	{ key: "word_choice", label: "Word choice", reportable: true },
	{ key: "word_order", label: "Word order", reportable: true },
	{ key: "pronoun_reference", label: "Pronoun reference", reportable: true },
	{ key: "sentence_structure", label: "Sentence structure", reportable: true },
	{ key: "punctuation", label: "Punctuation", reportable: true },
	{ key: "capitalization", label: "Capitalization", reportable: true },
	{ key: "spelling", label: "Spelling", reportable: false },
];

function isTaxonomyCategory(value: unknown): value is TaxonomyCategory {
	if (!value || typeof value !== "object") return false;
	const r = value as Record<string, unknown>;
	return typeof r.key === "string" && typeof r.label === "string" && typeof r.reportable === "boolean";
}

/**
 * The override file when it yields at least one valid category, the built-in default
 * otherwise. Never returns an empty array — that is the invariant that keeps the
 * extension from being installed but silently inert.
 */
export function loadTaxonomy(): TaxonomyCategory[] {
	if (!existsSync(TAXONOMY_PATH)) return DEFAULT_TAXONOMY;
	try {
		const raw = JSON.parse(readFileSync(TAXONOMY_PATH, "utf8"));
		if (!Array.isArray(raw)) return DEFAULT_TAXONOMY;
		const categories = raw.filter(isTaxonomyCategory);
		return categories.length > 0 ? categories : DEFAULT_TAXONOMY;
	} catch {
		return DEFAULT_TAXONOMY;
	}
}