import fs from "node:fs/promises";
import { existsSync } from "node:fs";
import path from "node:path";

/**
 * Lectura directa de los markdown del knowledge base desde el filesystem.
 *
 * Orden de resolucion del directorio de docs:
 *   1. `ACAI_DOCS_DIR` — override explicito por entorno (si esta definido y no vacio).
 *   2. `<ACAI_PROJECT_DIR>/docs` — caso principal: cada proyecto/web tiene su
 *      propio `docs/`. El `.mcp.json` inyecta `ACAI_PROJECT_DIR` (p.ej.
 *      `/opt/acai/webs/<user>/<site>`), funciona tanto en local (VSCode) como
 *      en cloud (agentic).
 *   3. `/app/docs` — fallback final: container `agentic` donde esta horneada la
 *      copia canonica de los .md.
 */

function dirExists(p) {
    try {
        return existsSync(p);
    } catch {
        return false;
    }
}

function resolveDocsDir() {
    // 1. Override explicito
    const override = process.env.ACAI_DOCS_DIR;
    if (override && override.trim() !== "") return override;

    // 2. Docs del proyecto/web
    const projectDir = process.env.ACAI_PROJECT_DIR;
    if (projectDir && projectDir.trim() !== "") {
        const projectDocs = path.join(projectDir, "docs");
        if (dirExists(projectDocs)) return projectDocs;
    }

    // 3. Fallback al container agentic
    return "/app/docs";
}

export async function listDocs() {
    const dir = resolveDocsDir();
    let files;
    try {
        files = await fs.readdir(dir);
    } catch (err) {
        const error = new Error(`No se pudo leer el directorio de docs (${dir}): ${err.message}`);
        error.code = "DOCS_DIR_NOT_FOUND";
        throw error;
    }

    const mdFiles = files.filter((f) => f.endsWith(".md")).sort();
    const docs = [];

    for (const file of mdFiles) {
        const id = file.replace(/\.md$/i, "");
        const filePath = path.join(dir, file);
        const content = await fs.readFile(filePath, "utf8");
        const lines = content.split("\n");
        const titleLine = lines.find((l) => l.trim().startsWith("# ")) || id;
        const title = titleLine.replace(/^#+/, "").trim();

        // Summary: primeras 30 lineas no-heading, capeado a 500 chars
        const summaryLines = [];
        for (const line of lines.slice(0, 30)) {
            const t = line.trim();
            if (t && !t.startsWith("#")) summaryLines.push(t);
            if (summaryLines.join(" ").length > 500) break;
        }
        const summary = summaryLines.join(" ").slice(0, 500);

        docs.push({
            id,
            title,
            summary,
            chars: content.length,
        });
    }
    return docs;
}

export async function readDoc(name, section) {
    const dir = resolveDocsDir();
    const safeName = String(name).replace(/\.md$/i, "").replace(/[\/\\]/g, "");
    const filePath = path.join(dir, `${safeName}.md`);

    let content;
    try {
        content = await fs.readFile(filePath, "utf8");
    } catch (err) {
        const error = new Error(`Doc '${safeName}' no encontrado en ${dir}`);
        error.code = "DOC_NOT_FOUND";
        throw error;
    }

    const titleLine = content.split("\n").find((l) => l.trim().startsWith("# ")) || safeName;
    const title = titleLine.replace(/^#+/, "").trim();
    const availableSections = listSections(content);

    if (section) {
        const sectionContent = extractSection(content, section);
        if (sectionContent === null) {
            return {
                id: safeName,
                title,
                section_requested: section,
                section_found: false,
                available_sections: availableSections,
                chars: 0,
                content: "",
            };
        }
        return {
            id: safeName,
            title,
            section,
            section_found: true,
            chars: sectionContent.length,
            content: sectionContent,
        };
    }

    return {
        id: safeName,
        title,
        section: null,
        section_found: true,
        chars: content.length,
        available_sections: availableSections,
        content,
    };
}

function listSections(content) {
    const sections = [];
    for (const line of content.split("\n")) {
        const t = line.trimStart();
        if (t.startsWith("## ") && !t.startsWith("### ")) {
            sections.push(t.slice(3).trim());
        }
    }
    return sections;
}

function extractSection(content, query) {
    const q = String(query).toLowerCase().trim();
    if (!q) return null;
    const lines = content.split("\n");
    const captured = [];
    let capturing = false;

    for (const line of lines) {
        const t = line.trimStart();
        const isH2 = t.startsWith("## ") && !t.startsWith("### ");

        if (isH2) {
            const heading = t.slice(3).trim();
            if (capturing) break;
            if (heading.toLowerCase().includes(q)) {
                capturing = true;
                captured.push(line);
                continue;
            }
        }

        if (capturing) captured.push(line);
    }

    if (captured.length === 0) return null;
    return captured.join("\n").trimEnd();
}