ribbit/src/ts/hopdown.ts

/*
 * hopdown.ts — configurable markdown↔HTML converter.
 *
 * Usage:
 *   const converter = new HopDown();
 *   const converter = new HopDown({ exclude: ['table'] });
 *   const converter = new HopDown({ tags: { ...defaultTags, 'DEL,S,STRIKE': strikethrough } });
 *
 *   converter.toHTML('**bold**');
 *   converter.toMarkdown('<strong>bold</strong>');
 */

import type { Converter, MatchContext, Tag } from './types';
import { defaultBlockTags, defaultInlineTags, defaultTags, escapeHtml, parseListBlock } from './tags';

export type TagMap = Record<string, Tag>;

export interface HopDownOptions {
    tags?: TagMap;
    exclude?: string[];
}

/**
 * A configurable markdown↔HTML converter.
 *
 * By default includes all standard tags. Pass options to customize:
 *   - tags: a mapping of HTML selectors to Tag definitions
 *   - exclude: remove specific tags by name from the defaults
 */
export class HopDown {
    private blockTags: Tag[];
    private inlineTags: Tag[];
    private tags: Map<string, Tag>;

    constructor(options: HopDownOptions = {}) {
        let tagMap: TagMap;

        if (options.tags) {
            tagMap = options.tags;
        } else if (options.exclude) {
            const excluded = new Set(options.exclude);
            tagMap = Object.fromEntries(
                Object.entries(defaultTags).filter(([, tag]) => !excluded.has(tag.name))
            );
        } else {
            tagMap = defaultTags;
        }

        const allTags = Object.values(tagMap);
        const defaultBlockNames = new Set(Object.values(defaultBlockTags).map(t => t.name));
        const defaultInlineNames = new Set(Object.values(defaultInlineTags).map(t => t.name));

        this.blockTags = allTags.filter(tag =>
            defaultBlockNames.has(tag.name) ||
            (!defaultInlineNames.has(tag.name) && !(tag as any).pattern)
        );
        this.inlineTags = allTags.filter(tag =>
            defaultInlineNames.has(tag.name) || (tag as any).pattern
        );

        this.tags = new Map();
        for (const [selector, tag] of Object.entries(tagMap)) {
            for (const sel of selector.split(',').map(s => s.trim()).filter(Boolean)) {
                if (sel.startsWith('_')) {
                    continue;
                }
                const existing = this.tags.get(sel);
                if (existing && existing !== tag) {
                    throw new Error(
                        `HTML tag "${sel}" is claimed by both "${existing.name}" and "${tag.name}". ` +
                        `Use the exclude option to remove one before adding the other.`
                    );
                }
                this.tags.set(sel, tag);
            }
        }

        this.validateInlineTags();
    }

    /**
     * Verify that no two inline tags have colliding delimiters without
     * correct precedence ordering. If delimiter A is a prefix of delimiter B,
     * B must have lower (earlier) precedence so the longer match wins.
     */
    private validateInlineTags(): void {
        const withDelimiters = this.inlineTags
            .filter(tag => (tag as any).delimiter)
            .map(tag => ({
                name: tag.name,
                delimiter: (tag as any).delimiter as string,
                precedence: (tag as any).precedence as number ?? 50,
            }));

        for (let i = 0; i < withDelimiters.length; i++) {
            for (let j = i + 1; j < withDelimiters.length; j++) {
                const a = withDelimiters[i];
                const b = withDelimiters[j];
                const aPrefix = b.delimiter.startsWith(a.delimiter);
                const bPrefix = a.delimiter.startsWith(b.delimiter);
                if (!aPrefix && !bPrefix) {
                    continue;
                }
                const longer = a.delimiter.length > b.delimiter.length ? a : b;
                const shorter = a.delimiter.length > b.delimiter.length ? b : a;
                if (longer.precedence >= shorter.precedence) {
                    throw new Error(
                        `Inline tag "${longer.name}" (delimiter "${longer.delimiter}") must have ` +
                        `lower precedence than "${shorter.name}" (delimiter "${shorter.delimiter}") ` +
                        `because its delimiter is a prefix match. ` +
                        `Got ${longer.name}=${longer.precedence}, ${shorter.name}=${shorter.precedence}.`
                    );
                }
            }
        }
    }

    /**
     * Convert a markdown string to HTML.
     */
    toHTML(md: string): string {
        return this.processBlocks(md);
    }

    /**
     * Convert an HTML string back to markdown.
     */
    toMarkdown(html: string): string {
        const container = document.createElement('div');
        container.innerHTML = html;
        return this.nodeToMd(container).replace(/\n{3,}/g, '\n\n').trim();
    }

    private processBlocks(md: string): string {
        const lines = md.replace(/\r\n/g, '\n').split('\n');
        const output: string[] = [];
        let index = 0;

        while (index < lines.length) {
            if (/^\s*$/.test(lines[index])) {
                index++;
                continue;
            }

            let matched = false;
            for (const tag of this.blockTags) {
                const context: MatchContext = {
                    lines,
                    index,
                    text: '',
                    offset: 0,
                };
                const token = tag.match(context);
                if (!token) continue;

                if (tag.name === 'list') {
                    const result = parseListBlock(lines, index, 0, (source) => this.processInline(source));
                    output.push(result.html);
                    index = result.end;
                } else {
                    output.push(tag.toHTML(token, this.makeConverter()));
                    index += token.consumed;
                }
                matched = true;
                break;
            }

            if (!matched) {
                index++;
            }
        }

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

    private processInline(source: string): string {
        const sorted = [...this.inlineTags].sort((a, b) =>
            ((a as any).precedence ?? 50) - ((b as any).precedence ?? 50)
        );

        const placeholders: string[] = [];
        let text = source;

        // Pass 1: extract links and non-recursive tags into placeholders before escaping
        for (const tag of sorted) {
            const recursive = (tag as any).recursive ?? true;

            if (tag.name === 'link') {
                text = text.replace(/\[([^\]]+)\]\(([^)]+)\)/g, (_, linkText: string, href: string) => {
                    // Process link text: restore earlier placeholders, then run inline on any remaining markdown
                    let inner = linkText;
                    // Check if link text contains placeholders (already-processed content)
                    const hasPlaceholders = /\x00P\d+\x00/.test(inner);
                    if (hasPlaceholders) {
                        inner = inner.replace(/\x00P(\d+)\x00/g, (__, idx: string) => placeholders[parseInt(idx)]);
                    } else {
                        inner = this.processInline(inner);
                    }
                    placeholders.push('<a href="' + escapeHtml(href) + '">' + inner + '</a>');
                    return '\x00P' + (placeholders.length - 1) + '\x00';
                });
            } else if (!recursive && (tag as any).pattern) {
                const globalPattern = (tag as any).pattern as RegExp;
                globalPattern.lastIndex = 0;
                text = text.replace(globalPattern, (_, content: string) => {
                    placeholders.push(tag.toHTML(
                        { content, raw: '', consumed: 0 },
                        this.makeConverter(),
                    ));
                    return '\x00P' + (placeholders.length - 1) + '\x00';
                });
            }
        }

        text = escapeHtml(text);

        // Pass 2: apply recursive tags in precedence order (longest delimiter first).
        // Content matched here is already HTML-escaped and has had earlier
        // passes applied, so we wrap directly without re-processing.
        for (const tag of sorted) {
            const recursive = (tag as any).recursive ?? true;
            if (tag.name === 'link' || !recursive) {
                continue;
            }
            const globalPattern = (tag as any).pattern as RegExp | undefined;
            if (globalPattern) {
                globalPattern.lastIndex = 0;
                text = text.replace(globalPattern, (_, content: string) => {
                    // Restore any placeholders in the captured content
                    const restored = content.replace(/\x00P(\d+)\x00/g, (__, idx: string) => placeholders[parseInt(idx)]);
                    const htmlTag = (tag as any).name === 'boldItalic'
                        ? null
                        : ((tag.selector as string) || '').split(',')[0].toLowerCase();
                    if (tag.name === 'boldItalic') {
                        return '<em><strong>' + restored + '</strong></em>';
                    }
                    return `<${htmlTag}>${restored}</${htmlTag}>`;
                });
            }
        }

        // Restore placeholders
        text = text.replace(/\x00P(\d+)\x00/g, (_, index: string) => placeholders[parseInt(index)]);
        return text;
    }

    private nodeToMd(node: Node): string {
        if (node.nodeType === 3) {
            return node.textContent || '';
        }
        if (node.nodeType !== 1) {
            return '';
        }
        const element = node as HTMLElement;

        const tag = this.tags.get(element.nodeName);
        if (tag) {
            return tag.toMarkdown(element, this.makeConverter());
        }

        return this.childrenToMd(node);
    }

    private childrenToMd(node: Node): string {
        return Array.from(node.childNodes).map(child => this.nodeToMd(child)).join('');
    }

    private makeConverter(): Converter {
        return {
            inline: (source) => this.processInline(source),
            block: (md) => this.processBlocks(md),
            children: (node) => this.childrenToMd(node),
            node: (node) => this.nodeToMd(node),
        };
    }
}

/**
 * A default HopDown instance with all standard tags enabled.
 * Use this for simple cases where no configuration is needed.
 */
const hopdown = new HopDown();

export function toHTML(md: string): string {
    return hopdown.toHTML(md);
}

export function toMarkdown(html: string): string {
    return hopdown.toMarkdown(html);
}

export default hopdown;