import type {
    Blockquote,
    Heading,
    List,
    ListItem,
    Paragraph,
    Root,
    RootContent,
    ThematicBreak,
} from "mdast";
import { toMarkdown } from "mdast-util-to-markdown";
import { absoluteUrl } from "./url.js";
import type {
    CitableSection,
    FaqItem,
    JsonLdNode,
    LlmsSiteConfig,
    SiteSeoConfig,
} from "./types.js";
import { faqJsonLd } from "./jsonld.js";

function heading(depth: 1 | 2 | 3, value: string): Heading {
    return { type: "heading", depth, children: [{ type: "text", value }] };
}

function paragraph(value: string): Paragraph {
    return { type: "paragraph", children: [{ type: "text", value }] };
}

function bullets(items: string[]): List {
    return {
        type: "list",
        ordered: false,
        spread: false,
        children: items.map(
            (item): ListItem => ({
                type: "listItem",
                spread: false,
                children: [paragraph(item)],
            }),
        ),
    };
}

function quote(value: string): Blockquote {
    return { type: "blockquote", children: [paragraph(value)] };
}

function hr(): ThematicBreak {
    return { type: "thematicBreak" };
}

function linkList(pages: NonNullable<LlmsSiteConfig["pages"]>, siteUrl: string): List {
    return {
        type: "list",
        ordered: false,
        spread: false,
        children: pages.map((p): ListItem => {
            const url = absoluteUrl(siteUrl, p.path);
            const children: NonNullable<ListItem["children"]> = [
                {
                    type: "paragraph",
                    children: [
                        { type: "link", url, children: [{ type: "text", value: p.title }] },
                        ...(p.description
                            ? [{ type: "text" as const, value: ` — ${p.description}` }]
                            : []),
                    ],
                },
            ];
            return { type: "listItem", spread: false, children };
        }),
    };
}

function render(children: RootContent[]): string {
    const tree: Root = { type: "root", children };
    return toMarkdown(tree, { bullet: "-", rule: "-", ruleRepetition: 3, fences: true });
}

/**
 * 生成 llms.txt（GEO）：面向 LLM 的站点地图式说明。
 * 规格参考：https://llmstxt.org（约定式，非正式标准）。
 */
export function buildLlmsTxt(site: SiteSeoConfig): string {
    const cfg: LlmsSiteConfig = site.llms ?? { summary: site.description };
    const children: RootContent[] = [heading(1, site.name), quote(cfg.summary)];

    if (cfg.details?.length) {
        for (const d of cfg.details) children.push(paragraph(d));
    }

    if (cfg.pages?.length) {
        children.push(heading(2, "页面"), linkList(cfg.pages, site.siteUrl));
    }

    if (cfg.discouraged?.length) {
        children.push(
            heading(2, "可选"),
            paragraph("以下内容通常无需纳入回答依据："),
            bullets(cfg.discouraged),
        );
    }

    children.push(
        hr(),
        paragraph(`站点: ${absoluteUrl(site.siteUrl, "/")}`),
        paragraph(`完整内容索引: ${absoluteUrl(site.siteUrl, "/llms-full.txt")}`),
    );
    return render(children);
}

/**
 * 生成 llms-full.txt：把可引用章节 + FAQ 拼成整站长文，
 * 供需要全文上下文的抓取方一次拉取。
 */
export function buildLlmsFullTxt(
    site: SiteSeoConfig,
    input: {
        title?: string;
        sections?: Array<CitableSection & { path?: string }>;
        faqs?: FaqItem[];
        extraMarkdown?: string;
    },
): string {
    const children: RootContent[] = [
        heading(1, input.title ?? site.name),
        paragraph(site.description),
    ];

    if (input.sections?.length) {
        for (const s of input.sections) {
            children.push(heading(2, s.heading), paragraph(s.summary));
            if (s.points?.length) children.push(bullets(s.points));
            if (s.path) {
                children.push(paragraph(`来源: ${absoluteUrl(site.siteUrl, s.path)}`));
            }
        }
    }

    if (input.faqs?.length) {
        children.push(heading(2, "常见问题"));
        for (const f of input.faqs) {
            children.push(heading(3, f.question), paragraph(f.answer));
        }
    }

    if (input.extraMarkdown) {
        children.push(paragraph(input.extraMarkdown.trim()));
    }

    children.push(
        hr(),
        paragraph(`由 ${site.name} 提供 · ${absoluteUrl(site.siteUrl, "/llms.txt")}`),
    );
    return render(children);
}

/** FAQ 同时产出 JSON-LD（SEO）与 Markdown 片段（GEO）。 */
export function faqToJsonLdAndMarkdown(faqs: FaqItem[]): {
    jsonLd: JsonLdNode;
    markdown: string;
} {
    const children: RootContent[] = [];
    for (const f of faqs) {
        children.push(
            {
                type: "paragraph",
                children: [
                    {
                        type: "strong",
                        children: [{ type: "text", value: `Q: ${f.question}` }],
                    },
                ],
            },
            paragraph(f.answer),
        );
    }
    return {
        jsonLd: faqJsonLd(faqs),
        markdown: render(children),
    };
}

/** 将可引用章节渲染为紧凑 Markdown（嵌入文章底部利于摘录）。 */
export function citableSectionMarkdown(section: CitableSection): string {
    const children: RootContent[] = [heading(2, section.heading), paragraph(section.summary)];
    if (section.points?.length) children.push(bullets(section.points));
    return render(children);
}