/**
 * AGENTS.md Injector
 * Safely merges generated indexes into AGENTS.md while preserving user content
 */

import { readFile, writeFile } from 'fs/promises';
import { existsSync } from 'fs';

const BEGIN_MARKER = '<!-- BEGIN SKILL-COMPILER MANAGED SECTION -->';
const END_MARKER = '<!-- END SKILL-COMPILER MANAGED SECTION -->';

/**
 * Inject indexes into AGENTS.md, preserving user content
 */
export async function injectAgentsMd(outPath: string, indexes: string[]): Promise<void> {
    let existingContent = '';

    // Read existing file if it exists
    if (existsSync(outPath)) {
        existingContent = await readFile(outPath, 'utf-8');
    }

    // Generate managed section
    const managedSection = generateManagedSection(indexes);

    // Merge with existing content
    const newContent = mergeContent(existingContent, managedSection);

    // Write back
    await writeFile(outPath, newContent, 'utf-8');
}

/**
 * Generate the managed section with all indexes
 */
function generateManagedSection(indexes: string[]): string {
    const lines = [
        BEGIN_MARKER,
        '<!-- DO NOT EDIT THIS SECTION MANUALLY - Generated by skill-compiler -->',
        '',
        '## Framework Documentation Indexes',
        '',
    ];

    for (const index of indexes) {
        lines.push(index);
        lines.push('');
    }

    lines.push(END_MARKER);

    return lines.join('\n');
}

/**
 * Merge managed section with existing content
 */
function mergeContent(existing: string, managedSection: string): string {
    // If no existing content, just return managed section with a header
    if (!existing.trim()) {
        return `# Project Guidelines\n\n${managedSection}\n`;
    }

    // Check if managed section already exists
    const beginIndex = existing.indexOf(BEGIN_MARKER);
    const endIndex = existing.indexOf(END_MARKER);

    if (beginIndex !== -1 && endIndex !== -1) {
        // Replace existing managed section
        const before = existing.slice(0, beginIndex);
        const after = existing.slice(endIndex + END_MARKER.length);
        return `${before}${managedSection}${after}`;
    }

    // Append managed section to end
    return `${existing.trimEnd()}\n\n${managedSection}\n`;
}

/**
 * Remove managed section from AGENTS.md
 */
export async function removeManagedSection(outPath: string): Promise<void> {
    if (!existsSync(outPath)) return;

    const content = await readFile(outPath, 'utf-8');
    const beginIndex = content.indexOf(BEGIN_MARKER);
    const endIndex = content.indexOf(END_MARKER);

    if (beginIndex !== -1 && endIndex !== -1) {
        const before = content.slice(0, beginIndex);
        const after = content.slice(endIndex + END_MARKER.length);
        const newContent = (before + after).trim();

        if (newContent) {
            await writeFile(outPath, newContent + '\n', 'utf-8');
        }
    }
}

/**
 * Check if AGENTS.md has a managed section
 */
export async function hasManagedSection(outPath: string): Promise<boolean> {
    if (!existsSync(outPath)) return false;

    const content = await readFile(outPath, 'utf-8');
    return content.includes(BEGIN_MARKER) && content.includes(END_MARKER);
}

/**
 * Get just the user content (excluding managed section)
 */
export async function getUserContent(outPath: string): Promise<string> {
    if (!existsSync(outPath)) return '';

    const content = await readFile(outPath, 'utf-8');
    const beginIndex = content.indexOf(BEGIN_MARKER);
    const endIndex = content.indexOf(END_MARKER);

    if (beginIndex !== -1 && endIndex !== -1) {
        const before = content.slice(0, beginIndex);
        const after = content.slice(endIndex + END_MARKER.length);
        return (before + after).trim();
    }

    return content;
}