use crate::gemini_parser::GeminiLine;
use std::path::Path;

/// Renders HTML from a vector of `GeminiLine` elements.
///
/// # Arguments
/// * `lines` - Vector of `GeminiLine` elements to render
///
/// # Returns
/// A String containing the rendered HTML.
///
/// # Examples
/// ```
/// use std::fs::read_to_string;
/// use gema_texto::gemini_parser::parse;
/// use gema_texto::html_renderer::render_html;
///
/// let gemini_source = "\
/// # Hello
/// This is some gemini text!
/// => https://test Go to the test page.
/// ";
///
/// let gemini_lines = parse(&gemini_source);
/// let html_source = render_html(&gemini_lines);
/// println!("{html_source}");
/// ```
#[must_use]
pub fn render_html(lines: &[GeminiLine]) -> String {
    let mut heading_stack = Vec::new();
    let mut last_line: Option<&GeminiLine> = None;
    let mut result = String::new();

    for line in lines {
        result.push_str(&line_preamble(line, last_line, &mut heading_stack));
        result.push_str(&line_content(line));
        result.push('\n');
        last_line = Some(line);
    }

    result.push_str(&finalize_html(&heading_stack, last_line));
    result
}

fn line_preamble(
    line: &GeminiLine,
    last_line: Option<&GeminiLine>,
    heading_stack: &mut Vec<u8>,
) -> String {
    let mut html = String::new();

    if let Some(last_line) = last_line {
        match last_line {
            GeminiLine::ListItem(_) => match line {
                GeminiLine::ListItem(_) => {}
                _ => html.push_str("</ul>\n"),
            },
            GeminiLine::Quote(_) => match line {
                GeminiLine::Quote(_) => {}
                _ => html.push_str("</blockquote>\n"),
            },
            _ => {}
        }
    }

    match line {
        GeminiLine::Heading(level, _) => {
            while let Some(open_heading) = heading_stack.pop() {
                // You just encountered a more important heading.
                // Put it back. Desist.
                if open_heading < *level {
                    heading_stack.push(open_heading);
                    break;
                }

                html.push_str("</section>\n");

                if open_heading == *level {
                    break;
                }
            }
            heading_stack.push(*level);
            html.push_str(&format!("<section class=\"h{level}\">\n"));
        }
        GeminiLine::ListItem(_) => match last_line {
            Some(GeminiLine::ListItem(_)) => {}
            _ => html.push_str("<ul>\n"),
        },
        GeminiLine::Quote(_) => match last_line {
            Some(GeminiLine::Quote(_)) => {}
            _ => html.push_str("<blockquote>\n"),
        },
        _ => {}
    }

    html
}

fn line_content(line: &GeminiLine) -> String {
    match line {
        GeminiLine::Text(content, false) => format!("<p>{content}</p>"),
        GeminiLine::Link(url, text) => {
            let path = Path::new(url);
            let processed_url = if !url.starts_with("gemini:")
                && path
                    .extension()
                    .is_some_and(|extension| extension.eq_ignore_ascii_case("gmi"))
            {
                url.replace(".gmi", ".html")
            } else {
                url.to_string()
            };

            let display = if text.is_empty() {
                &processed_url
            } else {
                text
            };
            format!("<p class=\"a\"><a href=\"{processed_url}\">{display}</a></p>")
        }
        GeminiLine::Heading(level, content) => format!("<h{level}>{content}</h{level}>"),
        GeminiLine::ListItem(content) => format!("<li>{content}</li>"),
        GeminiLine::PreformattedToggle(true, alt_text) => {
            format!("<pre aria-label=\"{alt_text}\">")
        }
        GeminiLine::PreformattedToggle(false, _) => "</pre>".to_string(),
        GeminiLine::Text(content, true) | GeminiLine::Quote(content) => content
            .replace('<', "&lt;")
            .replace('>', "&gt;")
            .to_string(),
    }
}

fn finalize_html(heading_stack: &[u8], last_line: Option<&GeminiLine>) -> String {
    let mut html = String::new();

    match last_line {
        Some(GeminiLine::ListItem(_)) => html.push_str("</ul>\n"),
        Some(GeminiLine::Quote(_)) => html.push_str("</blockquote>\n"),
        _ => {}
    }

    for _ in heading_stack {
        html.push_str("</section>\n");
    }

    html
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_simple_text() {
        let input = vec![GeminiLine::Text("Hello world".to_string(), false)];
        assert_eq!(render_html(&input), "<p>Hello world</p>\n");
    }

    #[test]
    fn test_heading_nesting() {
        let input = vec![
            GeminiLine::Heading(1, "Top".to_string()),
            GeminiLine::Heading(2, "Sub".to_string()),
            GeminiLine::Heading(3, "SubSub".to_string()),
            GeminiLine::Heading(2, "Another Sub".to_string()),
        ];
        assert_eq!(
            render_html(&input),
            "<section class=\"h1\">\n\
             <h1>Top</h1>\n\
             <section class=\"h2\">\n\
             <h2>Sub</h2>\n\
             <section class=\"h3\">\n\
             <h3>SubSub</h3>\n\
             </section>\n\
             </section>\n\
             <section class=\"h2\">\n\
             <h2>Another Sub</h2>\n\
             </section>\n\
             </section>\n"
        );
    }

    #[test]
    fn test_list_transitions() {
        let input = vec![
            GeminiLine::ListItem("First".to_string()),
            GeminiLine::ListItem("Second".to_string()),
            GeminiLine::Text("Break".to_string(), false),
            GeminiLine::ListItem("New list".to_string()),
        ];
        assert_eq!(
            render_html(&input),
            "<ul>\n\
             <li>First</li>\n\
             <li>Second</li>\n\
             </ul>\n\
             <p>Break</p>\n\
             <ul>\n\
             <li>New list</li>\n\
             </ul>\n"
        );
    }

    #[test]
    fn test_quote_transitions() {
        let input = vec![
            GeminiLine::Quote("First quote".to_string()),
            GeminiLine::Quote("Still quoting".to_string()),
            GeminiLine::Text("Normal text".to_string(), false),
            GeminiLine::Quote("New quote".to_string()),
        ];
        assert_eq!(
            render_html(&input),
            "<blockquote>\n\
             First quote\n\
             Still quoting\n\
             </blockquote>\n\
             <p>Normal text</p>\n\
             <blockquote>\n\
             New quote\n\
             </blockquote>\n"
        );
    }

    #[test]
    fn test_preformatted() {
        let input = vec![
            GeminiLine::PreformattedToggle(true, "code".to_string()),
            GeminiLine::Text("let x = 42;".to_string(), true),
            GeminiLine::PreformattedToggle(false, String::new()),
        ];
        assert_eq!(
            render_html(&input),
            "<pre aria-label=\"code\">\n\
             let x = 42;\n\
             </pre>\n"
        );
    }

    #[test]
    fn test_links() {
        let input = vec![
            GeminiLine::Link("gemini://hi.gmi".to_string(), "Example".to_string()),
            GeminiLine::Link("/hi.gmi/kidding".to_string(), "Example".to_string()),
            GeminiLine::Link("/hi.gmi".to_string(), "Example".to_string()),
            GeminiLine::Link("https://example.com".to_string(), "Example".to_string()),
            GeminiLine::Link("https://rust-lang.org".to_string(), String::new()),
        ];
        assert_eq!(
            render_html(&input),
            "<p class=\"a\"><a href=\"gemini://hi.gmi\">Example</a></p>\n\
             <p class=\"a\"><a href=\"/hi.gmi/kidding\">Example</a></p>\n\
             <p class=\"a\"><a href=\"/hi.html\">Example</a></p>\n\
             <p class=\"a\"><a href=\"https://example.com\">Example</a></p>\n\
             <p class=\"a\"><a href=\"https://rust-lang.org\">https://rust-lang.org</a></p>\n"
        );
    }

    #[test]
    fn test_complex_nesting() {
        let input = vec![
            GeminiLine::Heading(1, "Title".to_string()),
            GeminiLine::Text("Intro".to_string(), false),
            GeminiLine::Heading(2, "Section".to_string()),
            GeminiLine::ListItem("Point 1".to_string()),
            GeminiLine::ListItem("Point 2".to_string()),
            GeminiLine::Quote("Important quote".to_string()),
            GeminiLine::Heading(2, "Another Section".to_string()),
        ];
        assert_eq!(
            render_html(&input),
            "<section class=\"h1\">\n\
             <h1>Title</h1>\n\
             <p>Intro</p>\n\
             <section class=\"h2\">\n\
             <h2>Section</h2>\n\
             <ul>\n\
             <li>Point 1</li>\n\
             <li>Point 2</li>\n\
             </ul>\n\
             <blockquote>\n\
             Important quote\n\
             </blockquote>\n\
             </section>\n\
             <section class=\"h2\">\n\
             <h2>Another Section</h2>\n\
             </section>\n\
             </section>\n"
        );
    }

    #[test]
    fn test_empty_input() {
        let input = Vec::new();
        assert_eq!(render_html(&input), "");
    }
}