///| HTML Renderer

///| Renders markdown AST to HTML

///|
/// Render a document to HTML
pub fn render_html(doc : Document, autolink? : Bool = true) -> String {
  let buf = StringBuilder::new()
  for block in doc.children {
    render_block_html(block, buf, autolink~)
  }
  buf.to_string()
}

///|
/// Render a block element to HTML
fn render_block_html(
  block : Block,
  buf : StringBuilder,
  autolink? : Bool = true,
) -> Unit {
  match block {
    Block::Paragraph(children~, ..) => {
      buf.write_string("
")
      render_inlines_html(children, buf, autolink~)
      buf.write_string("
\n")
    }
    Block::Heading(level~, children~, ..) => {
      buf.write_string("')
      render_inlines_html(children, buf, autolink~)
      buf.write_string("\n")
    }
    Block::ThematicBreak(..) => buf.write_string("
\n")
    Block::FencedCode(info~, code~, ..) => {
      if info.is_empty() {
        buf.write_string("
")
      } else {
        // Extract language from info string (first word)
        let parts = info.split(" ").collect()
        let lang = if parts.length() > 0 { parts[0].to_owned() } else { info }
        buf.write_string("
")
      }
      buf.write_string(escape_html(code))
      buf.write_string("
\n")
    }
    Block::IndentedCode(code~, ..) => {
      buf.write_string("
")
      buf.write_string(escape_html(code))
      buf.write_string("
\n")
    }
    Block::Blockquote(children~, ..) => {
      buf.write_string("
\n")
      for child in children {
        render_block_html(child, buf, autolink~)
      }
      buf.write_string("
\n")
    }
    Block::BulletList(items~, tight~, ..) => {
      // Check if this list contains task items
      let has_task = items.iter().any(fn(item) { !(item.checked is None) })
      if has_task {
        buf.write_string("
\n")
      } else {
        buf.write_string("
\n")
      }
      for item in items {
        render_list_item_html(item, buf, tight, has_task, autolink~)
      }
      buf.write_string("
\n")
    }
    Block::OrderedList(items~, start~, tight~, ..) => {
      let has_task = items.iter().any(fn(item) { !(item.checked is None) })
      if start == 1 {
        if has_task {
          buf.write_string("
\n")
        } else {
          buf.write_string("
\n")
        }
      } else {
        if has_task {
          buf.write_string("
\n")
      }
      for item in items {
        render_list_item_html(item, buf, tight, has_task, autolink~)
      }
      buf.write_string("
\n")
    }
    Block::HtmlBlock(html~, ..) => {
      buf.write_string(html)
      if !html.has_suffix("\n") {
        buf.write_char('\n')
      }
    }
    Block::Table(header~, alignments~, rows~, ..) => {
      buf.write_string("\n\n\n")
      for i, cell in header {
        let align = if i < alignments.length() {
          alignments[i]
        } else {
          TableAlign::None
        }
        render_table_cell_html(cell, buf, "th", align, autolink~)
      }
      buf.write_string("\n\n")
      if rows.length() > 0 {
        buf.write_string("\n")
        for row in rows {
          buf.write_string("\n")
          for i, cell in row {
            let align = if i < alignments.length() {
              alignments[i]
            } else {
              TableAlign::None
            }
            render_table_cell_html(cell, buf, "td", align, autolink~)
          }
          buf.write_string("\n")
        }
        buf.write_string("\n")
      }
      buf.write_string("\n")
    }
    Block::BlankLines(..) => () // Blank lines don't produce HTML output
    Block::FootnoteDefinition(label~, children~, ..) => {
      buf.write_string("
\n")
      for child in children {
        render_block_html(child, buf, autolink~)
      }
      buf.write_string("
\n")
    }
  }
}

///|
/// Render a list item to HTML
fn render_list_item_html(
  item : ListItem,
  buf : StringBuilder,
  tight : Bool,
  is_task_list : Bool,
  autolink? : Bool = true,
) -> Unit {
  // Task list items get a special class
  if is_task_list && !(item.checked is None) {
    buf.write_string("
")
  } else {
    buf.write_string("
")
  }

  // Task list checkbox
  match item.checked {
    Some(true) =>
      buf.write_string(" ")
    Some(false) => buf.write_string(" ")
    None => ()
  }
  if tight {
    // Tight list: render inline content without 
 wrapper
    for child in item.children {
      match child {
        Paragraph(children~, ..) =>
          render_inlines_html(children, buf, autolink~)
        _ => render_block_html(child, buf, autolink~)
      }
    }
  } else {
    // Loose list: render blocks normally
    buf.write_char('\n')
    for child in item.children {
      render_block_html(child, buf, autolink~)
    }
  }
  buf.write_string("
\n")
}

///|
/// Render a table cell to HTML
fn render_table_cell_html(
  cell : TableCell,
  buf : StringBuilder,
  tag : String,
  align : TableAlign,
  autolink? : Bool = true,
) -> Unit {
  buf.write_char('<')
  buf.write_string(tag)
  match align {
    TableAlign::Left => buf.write_string(" align=\"left\"")
    TableAlign::Center => buf.write_string(" align=\"center\"")
    TableAlign::Right => buf.write_string(" align=\"right\"")
    TableAlign::None => ()
  }
  buf.write_char('>')
  render_inlines_html(cell.children, buf, autolink~)
  buf.write_string("\n")
}

///|
/// Render inline elements to HTML
fn render_inlines_html(
  inlines : Array[Inline],
  buf : StringBuilder,
  autolink? : Bool = true,
) -> Unit {
  for inline in inlines {
    render_inline_html(inline, buf, autolink~)
  }
}

///|
/// Build the rendered destination for a wiki link.
fn render_wikilink_destination(target : String, fragment : String) -> String {
  if fragment.is_empty() {
    target
  } else {
    target + "#" + fragment
  }
}

///|
/// Render text content, optionally turning bare http(s) URLs into anchors.
fn render_text_html(
  content : String,
  buf : StringBuilder,
  autolink? : Bool = true,
) -> Unit {
  if !autolink {
    buf.write_string(escape_html(content))
    return
  }
  let len = content.length()
  let mut pos = 0
  while pos < len {
    match find_next_url_start(content, pos) {
      Some(start) => {
        write_escaped_text_range(content, pos, start, buf)
        let raw_end = find_url_raw_end(content, start)
        let url_end = trim_url_end(content, start, raw_end)
        if url_end > start {
          let url = content.unsafe_substring(start~, end=url_end)
          buf.write_string("")
          buf.write_string(escape_html(url))
          buf.write_string("")
          pos = url_end
        } else {
          write_escaped_text_range(content, start, raw_end, buf)
          pos = raw_end
        }
      }
      None => {
        write_escaped_text_range(content, pos, len, buf)
        pos = len
      }
    }
  }
}

///|
fn write_escaped_text_range(
  content : String,
  start : Int,
  end : Int,
  buf : StringBuilder,
) -> Unit {
  if end > start {
    buf.write_string(escape_html(content.unsafe_substring(start~, end~)))
  }
}

///|
/// Render a single inline element to HTML
fn render_inline_html(
  inline : Inline,
  buf : StringBuilder,
  autolink? : Bool = true,
) -> Unit {
  match inline {
    Inline::Text(content~, ..) => render_text_html(content, buf, autolink~)
    Inline::Code(content~, ..) => {
      buf.write_string("")
      buf.write_string(escape_html(content))
      buf.write_string("")
    }
    Inline::WikiLink(target~, label~, fragment~, ..) => {
      let href = render_wikilink_destination(target, fragment)
      let text = if label.is_empty() { href } else { label }
      buf.write_string("")
      buf.write_string(escape_html(text))
      buf.write_string("")
    }
    Inline::Emphasis(children~, ..) => {
      buf.write_string("")
      render_inlines_html(children, buf, autolink~)
      buf.write_string("")
    }
    Inline::Strong(children~, ..) => {
      buf.write_string("")
      render_inlines_html(children, buf, autolink~)
      buf.write_string("")
    }
    Inline::Strikethrough(children~, ..) => {
      buf.write_string("")
      render_inlines_html(children, buf, autolink~)
      buf.write_string("")
    }
    Inline::Link(children~, url~, title~, ..) => {
      buf.write_string("')
      render_inlines_html(children, buf, autolink=false)
      buf.write_string("")
    }
    Inline::RefLink(children~, label~, ..) => {
      // Reference links should be resolved before rendering
      // For now, render as plain text with the label
      buf.write_char('[')
      render_inlines_html(children, buf, autolink=false)
      buf.write_string("][")
      buf.write_string(escape_html(label))
      buf.write_char(']')
    }
    Inline::Autolink(url~, is_email~, ..) => {
      buf.write_string("")
      buf.write_string(escape_html(url))
      buf.write_string("")
    }
    Inline::Image(alt~, url~, title~, ..) => {
      buf.write_string("")
    }
    Inline::RefImage(alt~, label~, ..) => {
      // Reference images should be resolved before rendering
      buf.write_string("![")
      buf.write_string(escape_html(alt))
      buf.write_string("][")
      buf.write_string(escape_html(label))
      buf.write_char(']')
    }
    Inline::HtmlInline(html~, ..) => buf.write_string(html)
    Inline::SoftBreak(..) => buf.write_char('\n')
    Inline::HardBreak(..) => buf.write_string("
\n")
    Inline::FootnoteReference(label~, ..) => {
      buf.write_string("")
      buf.write_string(escape_html(label))
      buf.write_string("")
    }
  }
}

///|
/// Escape HTML special characters in text content.
/// Pass `attr=true` to also escape `'` (for attribute values).
///
/// Most input strings don't contain any HTML-special characters, so a
/// quick scan-pass lets us return the input unchanged in that common
/// case and avoid building a new buffer.
fn escape_html(s : String, attr? : Bool = false) -> String {
  let mut needs_escape = false
  for c in s {
    match c {
      '&' | '<' | '>' | '"' => {
        needs_escape = true
        break
      }
      '\'' if attr => {
        needs_escape = true
        break
      }
      _ => ()
    }
  }
  if !needs_escape {
    return s
  }
  let buf = StringBuilder::new()
  for c in s {
    match c {
      '&' => buf.write_string("&")
      '<' => buf.write_string("<")
      '>' => buf.write_string(">")
      '"' => buf.write_string(""")
      '\'' if attr => buf.write_string("'")
      _ => buf.write_char(c)
    }
  }
  buf.to_string()
}

///|
/// Escape HTML special characters in attribute values
fn escape_html_attr(s : String) -> String {
  escape_html(s, attr=true)
}

///|
/// Parse markdown and render to HTML
pub fn md_to_html(
  source : String,
  wikilinks? : Bool = false,
  autolink? : Bool = true,
) -> String {
  let result = parse(source, wikilinks~)
  render_html(result.document, autolink~)
}

///|
/// Parse markdown and render to HTML (strict mode)
pub fn md_to_html_strict(
  source : String,
  wikilinks? : Bool = false,
  autolink? : Bool = true,
) -> String {
  let result = parse(source, strict=true, wikilinks~)
  render_html(result.document, autolink~)
}