import { existsSync, mkdirSync, readFileSync, writeFileSync } from "fs";
import path from "path";
import type { BundlerCTXMap, BunextPageLastmodRecord } from "../types";
import grabDirNames from "./grab-dir-names";
import { log } from "./log";

/**
 * # Path of the page last-modified record
 */
export function grabPageLastmodFile(lastmod_file?: string) {
    const { ROOT_DIR, PAGE_LASTMOD_JSON } = grabDirNames();
    const target = lastmod_file || global.BUNEXT_CONFIG?.sitemap?.lastmod_file;

    return target ? path.resolve(ROOT_DIR, target) : PAGE_LASTMOD_JSON;
}

export function readPageLastmodRecord(
    lastmod_file?: string,
): BunextPageLastmodRecord | undefined {
    const file = grabPageLastmodFile(lastmod_file);
    if (!existsSync(file)) return;

    try {
        const record = JSON.parse(readFileSync(file, "utf-8"));
        if (record?.pages && typeof record.pages == "object") return record;
    } catch {}

    log.warn(`Ignoring invalid page lastmod record ${file}`);
}

/**
 * # Record when each page's client bundle last changed
 * A page's bundle hash covers its whole client import graph (including
 * the root layout), so a component edit re-dates every page that uses it.
 * Unchanged pages keep their previous date; removed pages are dropped.
 */
export function updatePageLastmodRecord({
    ctx_map,
    build_date = new Date(),
    lastmod_file,
}: {
    ctx_map: { [local_path: string]: BundlerCTXMap };
    build_date?: Date;
    lastmod_file?: string;
}): BunextPageLastmodRecord {
    const prior = readPageLastmodRecord(lastmod_file);
    const record: BunextPageLastmodRecord = { pages: {} };

    // Sorted so a committed record produces minimal diffs
    const local_paths = Object.keys(ctx_map).sort();

    for (const local_path of local_paths) {
        const artifact = ctx_map[local_path];
        if (!artifact?.hash) continue;

        const fingerprint = `${artifact.hash}:${artifact.css_path || ""}`;
        const prior_page = prior?.pages[local_path];

        record.pages[local_path] =
            prior_page?.fingerprint == fingerprint
                ? prior_page
                : { fingerprint, lastmod: build_date.toISOString() };
    }

    const file = grabPageLastmodFile(lastmod_file);
    mkdirSync(path.dirname(file), { recursive: true });
    writeFileSync(file, JSON.stringify(record, null, 4), "utf-8");

    return record;
}