import React from 'react';
import { Text, Box } from 'ink';

/**
 * A utility class to render a subset of Markdown into Ink components.
 * Handles H1-H4, Lists (ul/ol, no nesting), Code Blocks,
 * and inline styles (bold, italic, strikethrough, code, links).
 */
export class MarkdownRenderer {

    /**
     * Renders INLINE markdown elements using an iterative approach.
     * Supports: **bold**, *italic*, _italic_, ~~strike~~, [link](url), `code`, ``code``, <u>underline</u>
     * @param text The string segment to parse for inline styles.
     * @returns An array of React nodes (Text components or strings).
     */
    private static _renderInline(text: string): React.ReactNode[] {
        const nodes: React.ReactNode[] = [];
        let lastIndex = 0;
        // UPDATED Regex: Added <u>.*?<\/u> pattern
        const inlineRegex = /(\*\*.*?\*\*|\*.*?\*|_.*?_|~~.*?~~|\[.*?\]\(.*?\)|`+.+?`+|<u>.*?<\/u>)/g;
        let match;

        while ((match = inlineRegex.exec(text)) !== null) {
            // 1. Add plain text before the match
            if (match.index > lastIndex) {
                nodes.push(<Text key={`t-${lastIndex}`}>{text.slice(lastIndex, match.index)}</Text>);
            }

            const fullMatch = match[0];
            let renderedNode: React.ReactNode = null;
            const key = `m-${match.index}`; // Base key for matched part

            // 2. Determine type of match and render accordingly
            try {
                if (fullMatch.startsWith('**') && fullMatch.endsWith('**') && fullMatch.length > 4) {
                    renderedNode = <Text key={key} bold>{fullMatch.slice(2, -2)}</Text>;
                } else if (((fullMatch.startsWith('*') && fullMatch.endsWith('*')) || (fullMatch.startsWith('_') && fullMatch.endsWith('_'))) && fullMatch.length > 2) {
                    renderedNode = <Text key={key} italic>{fullMatch.slice(1, -1)}</Text>;
                } else if (fullMatch.startsWith('~~') && fullMatch.endsWith('~~') && fullMatch.length > 4) {
                    // Strikethrough as gray text
                    renderedNode = <Text key={key} strikethrough>{fullMatch.slice(2, -2)}</Text>;
                } else if (fullMatch.startsWith('`') && fullMatch.endsWith('`') && fullMatch.length > 1) {
                    // Code: Try to match varying numbers of backticks
                    const codeMatch = fullMatch.match(/^(`+)(.+?)\1$/s);
                    if (codeMatch && codeMatch[2]) {
                        renderedNode = <Text key={key} color="yellow">{codeMatch[2]}</Text>;
                    } else { // Fallback for simple or non-matching cases
                        renderedNode = <Text key={key} color="yellow">{fullMatch.slice(1, -1)}</Text>;
                    }
                } else if (fullMatch.startsWith('[') && fullMatch.includes('](') && fullMatch.endsWith(')')) {
                    // Link: Extract text and URL
                    const linkMatch = fullMatch.match(/\[(.*?)\]\((.*?)\)/);
                    if (linkMatch) {
                        const linkText = linkMatch[1];
                        const url = linkMatch[2];
                        // Render link text then URL slightly dimmed/colored
                        renderedNode = (
                            <Text key={key}>
                                {linkText}
                                <Text color="blue"> ({url})</Text>
                            </Text>
                        );
                    }
                } else if (fullMatch.startsWith('<u>') && fullMatch.endsWith('</u>') && fullMatch.length > 6) {
                    // ***** NEW: Handle underline tag *****
                    // Use slice(3, -4) to remove <u> and </u>
                    renderedNode = <Text key={key} underline>{fullMatch.slice(3, -4)}</Text>;
                }
            } catch (e) {
                // In case of regex or slicing errors, fallback to literal rendering
                console.error("Error parsing inline markdown part:", fullMatch, e);
                renderedNode = null; // Ensure fallback below is used
            }


            // 3. Add the rendered node or the literal text if parsing failed
            nodes.push(renderedNode ?? <Text key={key}>{fullMatch}</Text>);
            lastIndex = inlineRegex.lastIndex; // Move index past the current match
        }

        // 4. Add any remaining plain text after the last match
        if (lastIndex < text.length) {
            nodes.push(<Text key={`t-${lastIndex}`}>{text.slice(lastIndex)}</Text>);
        }

        // Filter out potential nulls if any error occurred without fallback
        return nodes.filter(node => node !== null);
    }

    /**
     * Helper to render a code block.
     */
    private static _renderCodeBlock(key: string, content: string[], lang: string | null): React.ReactNode {
        // Basic styling for code block
        return (
            <Box key={key} borderStyle="round" paddingX={1} borderColor="gray" flexDirection="column">
                {lang && <Text dimColor> {lang}</Text>}
                {/* Render each line preserving whitespace (within Text component) */}
                {content.map((line, idx) => (
                    <Text key={idx}>{line}</Text>
                ))}
            </Box>
        );
    }

    /**
     * Helper to render a list item (ordered or unordered).
     */
    private static _renderListItem(key: string, text: string, type: 'ul' | 'ol', marker: string): React.ReactNode {
        const renderedText = MarkdownRenderer._renderInline(text); // Allow inline styles in list items
        const prefix = type === 'ol' ? `${marker} ` : `${marker} `; // e.g., "1. " or "* "
        const prefixWidth = prefix.length;

        return (
            <Box key={key} paddingLeft={1} flexDirection="row">
                <Box width={prefixWidth}>
                    <Text>{prefix}</Text>
                </Box>
                <Box flexGrow={1}>
                    <Text wrap="wrap">{renderedText}</Text>
                </Box>
            </Box>
        );
    }


    /**
     * Renders a full markdown string, handling block elements (headers, lists, code blocks)
     * and applying inline styles. This is the main public static method.
     * @param text The full markdown string to render.
     * @returns An array of React nodes representing markdown blocks.
     */
    public static render(text: string): React.ReactNode[] {
        if (!text) return [];

        const lines = text.split('\n');
        // Regexes for block elements
        const headerRegex = /^ *(#{1,4}) +(.*)/;
        const codeFenceRegex = /^ *(`{3,}|~{3,}) *(\S*?) *$/; // ```lang or ``` or ~~~
        const ulItemRegex = /^ *([-*+]) +(.*)/; // Unordered list item, captures bullet and text
        const olItemRegex = /^ *(\d+)\. +(.*)/; // Ordered list item, captures number and text
        const hrRegex = /^ *([-*_] *){3,} *$/; // Horizontal rule

        const contentBlocks: React.ReactNode[] = [];
        // State for parsing across lines
        let inCodeBlock = false;
        let codeBlockContent: string[] = [];
        let codeBlockLang: string | null = null;
        let codeBlockFence = ''; // Store the type of fence used (``` or ~~~)
        let inListType: 'ul' | 'ol' | null = null; // Track current list type to group items

        lines.forEach((line, index) => {
            const key = `line-${index}`;

            // --- State 1: Inside a Code Block ---
            if (inCodeBlock) {
                const fenceMatch = line.match(codeFenceRegex);
                // Check for closing fence, matching the opening one and length
                if (fenceMatch && fenceMatch[1].startsWith(codeBlockFence[0]) && fenceMatch[1].length >= codeBlockFence.length) {
                    // End of code block - render it
                    contentBlocks.push(MarkdownRenderer._renderCodeBlock(key, codeBlockContent, codeBlockLang));
                    // Reset state
                    inCodeBlock = false;
                    codeBlockContent = [];
                    codeBlockLang = null;
                    codeBlockFence = '';
                    inListType = null; // Ensure list context is reset
                } else {
                    // Add line to current code block content
                    codeBlockContent.push(line);
                }
                return; // Process next line
            }

            // --- State 2: Not Inside a Code Block ---
            // Check for block element starts in rough order of precedence/commonness
            const codeFenceMatch = line.match(codeFenceRegex);
            const headerMatch = line.match(headerRegex);
            const ulMatch = line.match(ulItemRegex);
            const olMatch = line.match(olItemRegex);
            const hrMatch = line.match(hrRegex);

            if (codeFenceMatch) {
                inCodeBlock = true;
                codeBlockFence = codeFenceMatch[1];
                codeBlockLang = codeFenceMatch[2] || null;
                inListType = null; // Starting code block breaks list
            } else if (hrMatch) {
                // Render Horizontal Rule (simple dashed line)
                // Use box with height and border character, or just Text with dashes
                contentBlocks.push(<Box key={key}><Text dimColor>---</Text></Box>);
                inListType = null; // HR breaks list
            } else if (headerMatch) {
                const level = headerMatch[1].length;
                const headerText = headerMatch[2];
                const renderedHeaderText = MarkdownRenderer._renderInline(headerText);
                let headerNode: React.ReactNode = null;
                switch (level) { /* ... (header styling as before) ... */
                    case 1: headerNode = <Text bold color="cyan">{renderedHeaderText}</Text>; break;
                    case 2: headerNode = <Text bold color="blue">{renderedHeaderText}</Text>; break;
                    case 3: headerNode = <Text bold>{renderedHeaderText}</Text>; break;
                    case 4: headerNode = <Text italic color="gray">{renderedHeaderText}</Text>; break;
                }
                if (headerNode) contentBlocks.push(<Box key={key}>{headerNode}</Box>);
                inListType = null; // Header breaks list
            } else if (ulMatch) {
                const marker = ulMatch[1]; // *, -, or +
                const itemText = ulMatch[2];
                // If previous line was not UL, maybe add spacing? For now, just render item.
                contentBlocks.push(MarkdownRenderer._renderListItem(key, itemText, 'ul', marker));
                inListType = 'ul'; // Set/maintain list context
            } else if (olMatch) {
                const marker = olMatch[1]; // The number
                const itemText = olMatch[2];
                contentBlocks.push(MarkdownRenderer._renderListItem(key, itemText, 'ol', marker));
                inListType = 'ol'; // Set/maintain list context
            } else {
                // --- Regular line (Paragraph or Empty line) ---
                inListType = null; // Any non-list line breaks the list sequence

                // Render line content if it's not blank, applying inline styles
                const renderedLine = MarkdownRenderer._renderInline(line);
                if (renderedLine.length > 0 || line.length > 0) { // Render lines with content or only whitespace
                    contentBlocks.push(
                        <Box key={key}>
                            <Text wrap="wrap">{renderedLine}</Text>
                        </Box>
                    );
                } else if (line.trim().length === 0) { // Handle specifically empty lines
                    // Add minimal space for blank lines between paragraphs/blocks
                    if (contentBlocks.length > 0 && !inCodeBlock) { // Avoid adding space inside code block state (handled above)
                        const previousBlock = contentBlocks[contentBlocks.length - 1];
                        // Avoid adding multiple blank lines consecutively easily - check if previous was also blank?
                        // For now, add a minimal spacer for any blank line outside code blocks.
                        contentBlocks.push(<Box key={key} height={1} />);
                    }
                }
            }
        });

        // Handle unclosed code block at the end of the input
        if (inCodeBlock) {
            contentBlocks.push(MarkdownRenderer._renderCodeBlock(`line-eof`, codeBlockContent, codeBlockLang));
        }

        return contentBlocks;
    }
}