//! HTML renderer.
//!
//! Walks a `DocumentNode` and writes HTML5 fragments. The renderer is
//! configured with a link resolver (callback that turns a `LinkTarget` into
//! a URL string) and, optionally, an enclosing template with `{{title}}` /
//! `{{content}}` placeholders (SPEC.md §6.8).
//!
//! Without a template the output is just the body markup, so callers are
//! free to embed it in their own page shell. With a template the rendered
//! body replaces `{{content}}` and the document's `metadata.title`
//! replaces `{{title}}`.

use std::io::{self, Write};
use std::sync::Arc;

use crate::ast::{
    BlockNode, BlockquoteNode, BoldItalicNode, BoldNode, CheckboxState, CodeNode, ColorNode,
    CommentNode, DefinitionItemNode, DefinitionListNode, DocumentNode, ErrorNode, ExternalLinkNode,
    HeadingNode, HorizontalRuleNode, InlineNode, ItalicNode, Keyword, KeywordNode, LinkKind,
    LinkTarget, ListItemNode, ListNode, MathBlockNode, MathInlineNode, ParagraphNode,
    PreformattedNode, RawUrlNode, StrikethroughNode, SubscriptNode, SuperscriptNode, TableCellNode,
    TableNode, TableRowNode, TextNode, TransclusionNode, WikiLinkNode,
};

use super::Renderer;

/// Boxed link-resolution callback. Held in an `Arc` so the renderer is
/// cheap to clone and stays `Send + Sync`.
pub type LinkResolver = Arc<dyn Fn(&LinkTarget) -> String + Send + Sync>;

#[derive(Clone)]
pub struct HtmlRenderer {
    link_resolver: LinkResolver,
    template: Option<String>,
}

impl Default for HtmlRenderer {
    fn default() -> Self {
        Self::new()
    }
}

impl HtmlRenderer {
    pub fn new() -> Self {
        Self {
            link_resolver: Arc::new(default_link_resolver),
            template: None,
        }
    }

    /// Override the link resolver. The callback is invoked for every
    /// wikilink and is expected to return a URL string.
    pub fn with_link_resolver<F>(mut self, f: F) -> Self
    where
        F: Fn(&LinkTarget) -> String + Send + Sync + 'static,
    {
        self.link_resolver = Arc::new(f);
        self
    }

    /// Wrap the rendered body in a template. `{{title}}` and `{{content}}`
    /// are substituted; everything else passes through verbatim.
    pub fn with_template(mut self, template: impl Into<String>) -> Self {
        self.template = Some(template.into());
        self
    }
}

impl Renderer for HtmlRenderer {
    fn render(&self, doc: &DocumentNode, w: &mut dyn Write) -> io::Result<()> {
        if let Some(template) = &self.template {
            let mut body = Vec::new();
            self.render_body(doc, &mut body)?;
            let body_str = std::str::from_utf8(&body)
                .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
            let title = doc.metadata.title.as_deref().unwrap_or("");
            // Replace `{{content}}` first so its substituted body, which may
            // legitimately contain the literal `{{title}}`, isn't itself
            // rewritten in the next pass.
            let with_content = template.replace("{{content}}", body_str);
            let final_doc = with_content.replace("{{title}}", title);
            w.write_all(final_doc.as_bytes())?;
        } else {
            self.render_body(doc, w)?;
        }
        Ok(())
    }
}

impl HtmlRenderer {
    fn render_body(&self, doc: &DocumentNode, w: &mut dyn Write) -> io::Result<()> {
        for block in &doc.children {
            self.render_block(block, w)?;
        }
        Ok(())
    }

    fn render_block(&self, block: &BlockNode, w: &mut dyn Write) -> io::Result<()> {
        match block {
            BlockNode::Heading(n) => self.render_heading(n, w),
            BlockNode::Paragraph(n) => self.render_paragraph(n, w),
            BlockNode::HorizontalRule(n) => self.render_hr(n, w),
            BlockNode::Blockquote(n) => self.render_blockquote(n, w),
            BlockNode::Preformatted(n) => self.render_preformatted(n, w),
            BlockNode::MathBlock(n) => self.render_math_block(n, w),
            BlockNode::List(n) => self.render_list(n, w),
            BlockNode::DefinitionList(n) => self.render_definition_list(n, w),
            BlockNode::Table(n) => self.render_table(n, w),
            BlockNode::Comment(n) => self.render_comment(n, w),
            BlockNode::Error(n) => self.render_error(n, w),
        }
    }

    fn render_heading(&self, n: &HeadingNode, w: &mut dyn Write) -> io::Result<()> {
        let level = n.level.clamp(1, 6);
        let class = if n.centered {
            " class=\"centered\""
        } else {
            ""
        };
        write!(w, "<h{level}{class}>")?;
        self.render_inlines(&n.children, w)?;
        writeln!(w, "</h{level}>")
    }

    fn render_paragraph(&self, n: &ParagraphNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<p>")?;
        self.render_inlines(&n.children, w)?;
        w.write_all(b"</p>\n")
    }

    fn render_hr(&self, _n: &HorizontalRuleNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<hr>\n")
    }

    fn render_blockquote(&self, n: &BlockquoteNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<blockquote>\n")?;
        for child in &n.children {
            self.render_block(child, w)?;
        }
        w.write_all(b"</blockquote>\n")
    }

    fn render_preformatted(&self, n: &PreformattedNode, w: &mut dyn Write) -> io::Result<()> {
        match &n.language {
            Some(lang) => {
                w.write_all(b"<pre><code class=\"language-")?;
                write_escaped(lang, w)?;
                w.write_all(b"\">")?;
            }
            None => w.write_all(b"<pre><code>")?,
        }
        write_escaped(&n.content, w)?;
        w.write_all(b"</code></pre>\n")
    }

    fn render_math_block(&self, n: &MathBlockNode, w: &mut dyn Write) -> io::Result<()> {
        // No actual TeX rendering — caller is expected to run MathJax / KaTeX
        // over the wrapped node. The delimiters match vimwiki convention.
        match &n.environment {
            Some(env) => writeln!(
                w,
                "<div class=\"math-block\" data-env=\"{}\">\\begin{{{env}}}",
                escape(env)
            )?,
            None => w.write_all(b"<div class=\"math-block\">\\[\n")?,
        }
        write_escaped(&n.content, w)?;
        match &n.environment {
            Some(env) => write!(w, "\n\\end{{{env}}}</div>\n", env = escape(env))?,
            None => w.write_all(b"\n\\]</div>\n")?,
        }
        Ok(())
    }

    fn render_list(&self, n: &ListNode, w: &mut dyn Write) -> io::Result<()> {
        let tag = if n.ordered { "ol" } else { "ul" };
        writeln!(w, "<{tag}>")?;
        for item in &n.items {
            self.render_list_item(item, w)?;
        }
        writeln!(w, "</{tag}>")
    }

    fn render_list_item(&self, n: &ListItemNode, w: &mut dyn Write) -> io::Result<()> {
        match n.checkbox {
            Some(state) => {
                let (checked, class) = match state {
                    CheckboxState::Empty => ("", "task-empty"),
                    CheckboxState::Quarter => ("", "task-quarter"),
                    CheckboxState::Half => ("", "task-half"),
                    CheckboxState::ThreeQuarters => ("", "task-three-quarters"),
                    CheckboxState::Done => (" checked", "task-done"),
                    CheckboxState::Rejected => ("", "task-rejected"),
                };
                write!(
                    w,
                    "<li class=\"{class}\"><input type=\"checkbox\" disabled{checked}> "
                )?;
            }
            None => w.write_all(b"<li>")?,
        }
        self.render_inlines(&n.children, w)?;
        if let Some(sublist) = &n.sublist {
            w.write_all(b"\n")?;
            self.render_list(sublist, w)?;
        }
        w.write_all(b"</li>\n")
    }

    fn render_definition_list(&self, n: &DefinitionListNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<dl>\n")?;
        for item in &n.items {
            self.render_definition_item(item, w)?;
        }
        w.write_all(b"</dl>\n")
    }

    fn render_definition_item(&self, n: &DefinitionItemNode, w: &mut dyn Write) -> io::Result<()> {
        if let Some(term) = &n.term {
            w.write_all(b"<dt>")?;
            self.render_inlines(term, w)?;
            w.write_all(b"</dt>\n")?;
        }
        for def in &n.definitions {
            w.write_all(b"<dd>")?;
            self.render_inlines(def, w)?;
            w.write_all(b"</dd>\n")?;
        }
        Ok(())
    }

    fn render_table(&self, n: &TableNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<table>\n")?;
        let mut in_thead = false;
        let mut in_tbody = false;
        for row in &n.rows {
            if row.is_header {
                if !in_thead {
                    w.write_all(b"<thead>\n")?;
                    in_thead = true;
                }
            } else {
                if in_thead {
                    w.write_all(b"</thead>\n")?;
                    in_thead = false;
                }
                if !in_tbody {
                    w.write_all(b"<tbody>\n")?;
                    in_tbody = true;
                }
            }
            self.render_table_row(row, w)?;
        }
        if in_thead {
            w.write_all(b"</thead>\n")?;
        }
        if in_tbody {
            w.write_all(b"</tbody>\n")?;
        }
        w.write_all(b"</table>\n")
    }

    fn render_table_row(&self, n: &TableRowNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<tr>")?;
        for cell in &n.cells {
            // col_span / row_span here are *spec flags* meaning "this cell is
            // a continuation marker", which HTML expresses via the *previous*
            // cell's colspan/rowspan attrs. Computing those attrs requires
            // forward state on the renderer side; for now we emit class
            // markers so styling can show the span visually.
            self.render_table_cell(cell, n.is_header, w)?;
        }
        w.write_all(b"</tr>\n")
    }

    fn render_table_cell(
        &self,
        n: &TableCellNode,
        is_header: bool,
        w: &mut dyn Write,
    ) -> io::Result<()> {
        let tag = if is_header { "th" } else { "td" };
        let class = match (n.col_span, n.row_span) {
            (true, _) => " class=\"col-span\"",
            (_, true) => " class=\"row-span\"",
            _ => "",
        };
        write!(w, "<{tag}{class}>")?;
        self.render_inlines(&n.children, w)?;
        write!(w, "</{tag}>")
    }

    fn render_comment(&self, n: &CommentNode, w: &mut dyn Write) -> io::Result<()> {
        // Emit as an HTML comment so it survives round-trips through view-source
        // but isn't rendered to the reader. `--` inside a comment is illegal
        // in HTML, so collapse runs.
        let safe = n.content.replace("--", "- -");
        writeln!(w, "<!--{safe}-->")
    }

    fn render_error(&self, n: &ErrorNode, w: &mut dyn Write) -> io::Result<()> {
        write!(w, "<span class=\"parse-error\" title=\"")?;
        write_escaped(&n.message, w)?;
        w.write_all(b"\">")?;
        write_escaped(&n.raw, w)?;
        w.write_all(b"</span>")
    }

    // ===== Inline =====

    fn render_inlines(&self, nodes: &[InlineNode], w: &mut dyn Write) -> io::Result<()> {
        for n in nodes {
            self.render_inline(n, w)?;
        }
        Ok(())
    }

    fn render_inline(&self, n: &InlineNode, w: &mut dyn Write) -> io::Result<()> {
        match n {
            InlineNode::Text(t) => self.render_text(t, w),
            InlineNode::Bold(t) => self.render_bold(t, w),
            InlineNode::Italic(t) => self.render_italic(t, w),
            InlineNode::BoldItalic(t) => self.render_bold_italic(t, w),
            InlineNode::Strikethrough(t) => self.render_strikethrough(t, w),
            InlineNode::Code(t) => self.render_code(t, w),
            InlineNode::Superscript(t) => self.render_superscript(t, w),
            InlineNode::Subscript(t) => self.render_subscript(t, w),
            InlineNode::MathInline(t) => self.render_math_inline(t, w),
            InlineNode::Keyword(t) => self.render_keyword(t, w),
            InlineNode::Color(t) => self.render_color(t, w),
            InlineNode::WikiLink(t) => self.render_wikilink(t, w),
            InlineNode::ExternalLink(t) => self.render_external_link(t, w),
            InlineNode::Transclusion(t) => self.render_transclusion(t, w),
            InlineNode::RawUrl(t) => self.render_raw_url(t, w),
        }
    }

    fn render_text(&self, n: &TextNode, w: &mut dyn Write) -> io::Result<()> {
        write_escaped(&n.content, w)
    }

    fn render_bold(&self, n: &BoldNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<strong>")?;
        self.render_inlines(&n.children, w)?;
        w.write_all(b"</strong>")
    }

    fn render_italic(&self, n: &ItalicNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<em>")?;
        self.render_inlines(&n.children, w)?;
        w.write_all(b"</em>")
    }

    fn render_bold_italic(&self, n: &BoldItalicNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<strong><em>")?;
        self.render_inlines(&n.children, w)?;
        w.write_all(b"</em></strong>")
    }

    fn render_strikethrough(&self, n: &StrikethroughNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<del>")?;
        self.render_inlines(&n.children, w)?;
        w.write_all(b"</del>")
    }

    fn render_code(&self, n: &CodeNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<code>")?;
        write_escaped(&n.content, w)?;
        w.write_all(b"</code>")
    }

    fn render_superscript(&self, n: &SuperscriptNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<sup>")?;
        self.render_inlines(&n.children, w)?;
        w.write_all(b"</sup>")
    }

    fn render_subscript(&self, n: &SubscriptNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<sub>")?;
        self.render_inlines(&n.children, w)?;
        w.write_all(b"</sub>")
    }

    fn render_math_inline(&self, n: &MathInlineNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<span class=\"math-inline\">\\(")?;
        write_escaped(&n.content, w)?;
        w.write_all(b"\\)</span>")
    }

    fn render_keyword(&self, n: &KeywordNode, w: &mut dyn Write) -> io::Result<()> {
        let (label, class) = match n.keyword {
            Keyword::Todo => ("TODO", "keyword keyword-todo"),
            Keyword::Done => ("DONE", "keyword keyword-done"),
            Keyword::Started => ("STARTED", "keyword keyword-started"),
            Keyword::Fixme => ("FIXME", "keyword keyword-fixme"),
            Keyword::Fixed => ("FIXED", "keyword keyword-fixed"),
            Keyword::Xxx => ("XXX", "keyword keyword-xxx"),
        };
        write!(w, "<span class=\"{class}\">{label}</span>")
    }

    fn render_color(&self, n: &ColorNode, w: &mut dyn Write) -> io::Result<()> {
        write!(w, "<span class=\"color-")?;
        write_escaped(&n.color, w)?;
        w.write_all(b"\">")?;
        self.render_inlines(&n.children, w)?;
        w.write_all(b"</span>")
    }

    fn render_wikilink(&self, n: &WikiLinkNode, w: &mut dyn Write) -> io::Result<()> {
        let href = (self.link_resolver)(&n.target);
        w.write_all(b"<a href=\"")?;
        write_escaped(&href, w)?;
        w.write_all(b"\">")?;
        match &n.description {
            Some(desc) => self.render_inlines(desc, w)?,
            None => {
                let label = n
                    .target
                    .path
                    .clone()
                    .or_else(|| n.target.anchor.clone())
                    .unwrap_or_else(|| href.clone());
                write_escaped(&label, w)?;
            }
        }
        w.write_all(b"</a>")
    }

    fn render_external_link(&self, n: &ExternalLinkNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<a href=\"")?;
        write_escaped(&n.url, w)?;
        w.write_all(b"\">")?;
        match &n.description {
            Some(desc) => self.render_inlines(desc, w)?,
            None => write_escaped(&n.url, w)?,
        }
        w.write_all(b"</a>")
    }

    fn render_transclusion(&self, n: &TransclusionNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<img src=\"")?;
        write_escaped(&n.url, w)?;
        w.write_all(b"\" alt=\"")?;
        write_escaped(n.alt.as_deref().unwrap_or(""), w)?;
        w.write_all(b"\"")?;
        // Emit any extra attrs verbatim; both key and value are escaped.
        let mut keys: Vec<&String> = n.attrs.keys().collect();
        keys.sort();
        for k in keys {
            let v = &n.attrs[k];
            w.write_all(b" ")?;
            write_escaped(k, w)?;
            w.write_all(b"=\"")?;
            write_escaped(v, w)?;
            w.write_all(b"\"")?;
        }
        w.write_all(b">")
    }

    fn render_raw_url(&self, n: &RawUrlNode, w: &mut dyn Write) -> io::Result<()> {
        w.write_all(b"<a href=\"")?;
        write_escaped(&n.url, w)?;
        w.write_all(b"\">")?;
        write_escaped(&n.url, w)?;
        w.write_all(b"</a>")
    }
}

// ===== Default link resolver =====

/// Default `LinkResolver`. Mirrors the conventions in SPEC.md §9:
/// wiki pages become `path.html`; interwiki links land in sibling
/// directories; diary entries land under `diary/`; file/local schemes
/// use their literal path; anchor-only links collapse to a fragment.
pub fn default_link_resolver(target: &LinkTarget) -> String {
    if matches!(target.kind, LinkKind::AnchorOnly) {
        return match &target.anchor {
            Some(a) => format!("#{a}"),
            None => String::new(),
        };
    }

    let path = target.path.as_deref().unwrap_or("");
    let mut out = String::new();

    match target.kind {
        LinkKind::Wiki => {
            if target.is_absolute {
                out.push('/');
            }
            out.push_str(path);
            if target.is_directory {
                out.push('/');
            } else if !path.is_empty() {
                out.push_str(".html");
            }
        }
        LinkKind::Interwiki => {
            if let Some(idx) = target.wiki_index {
                out.push_str(&format!("../wiki{idx}/"));
            } else if let Some(name) = &target.wiki_name {
                out.push_str(&format!("../wn-{name}/"));
            }
            out.push_str(path);
            if !target.is_directory {
                out.push_str(".html");
            }
        }
        LinkKind::Diary => {
            out.push_str("diary/");
            out.push_str(path);
            out.push_str(".html");
        }
        LinkKind::File => {
            out.push_str(path);
        }
        LinkKind::Local => {
            out.push_str("file://");
            if target.is_absolute && !path.starts_with('/') {
                out.push('/');
            }
            out.push_str(path);
        }
        LinkKind::Raw => {
            out.push_str(path);
        }
        LinkKind::AnchorOnly => unreachable!(),
    }

    if let Some(anchor) = &target.anchor {
        out.push('#');
        out.push_str(anchor);
    }
    out
}

// ===== HTML escaping =====

fn write_escaped(s: &str, w: &mut dyn Write) -> io::Result<()> {
    let bytes = s.as_bytes();
    let mut last = 0;
    for (i, &b) in bytes.iter().enumerate() {
        let replacement: &[u8] = match b {
            b'<' => b"&lt;",
            b'>' => b"&gt;",
            b'&' => b"&amp;",
            b'"' => b"&quot;",
            b'\'' => b"&#39;",
            _ => continue,
        };
        if i > last {
            w.write_all(&bytes[last..i])?;
        }
        w.write_all(replacement)?;
        last = i + 1;
    }
    if last < bytes.len() {
        w.write_all(&bytes[last..])?;
    }
    Ok(())
}

fn escape(s: &str) -> String {
    let mut out = String::with_capacity(s.len());
    for c in s.chars() {
        match c {
            '<' => out.push_str("&lt;"),
            '>' => out.push_str("&gt;"),
            '&' => out.push_str("&amp;"),
            '"' => out.push_str("&quot;"),
            '\'' => out.push_str("&#39;"),
            c => out.push(c),
        }
    }
    out
}