use core::fmt;

pub struct Html {
	pub nodes: Vec<Node>,
}

impl Html {
	pub fn parse<S: AsRef<str>>(raw: S) -> Self {
		let mut raw = raw.as_ref();

		let mut nodes = vec![];

		loop {
			let Consumed { node, remaining } = Self::parse_node(raw);
			nodes.push(node);

			match remaining {
				None => break Self { nodes },
				Some(rem) => raw = rem,
			}
		}
	}

	fn parse_node(raw: &str) -> Consumed {
		match Self::is_tag(raw) {
			Some(_) => {
				if let Some(cmt) = Self::parse_comment(raw) {
					cmt
				} else {
					Self::parse_tag(raw)
				}
			}
			None => {
				let cons = Self::parse_text(raw);
				cons
			}
		}
	}

	fn parse_tag(raw: &str) -> Consumed {
		let (root_tag, mut rest) = Self::is_tag(raw).unwrap();

		//println!("- {raw}");
		if root_tag.closing {
			panic!(
				"found closing tag when not expected! {:?}\n{raw}",
				root_tag.name
			)
		} else if root_tag.self_closing {
			return Consumed {
				node: Node::Tag {
					self_closing: true,
					name: root_tag.name.into(),
					children: vec![],
				},
				remaining: rest,
			};
		}

		let mut children = vec![];

		loop {
			// Special case <script> and <style>
			if root_tag.name == "script" || root_tag.name == "style" {
				let special = Self::special_parse(rest.unwrap(), root_tag.name);

				match special {
					None => {
						panic!("found tag '{}' with no end", root_tag.name);
					}
					Some((text, remaining)) => {
						let remaining = if remaining.is_empty() {
							None
						} else {
							Some(remaining)
						};

						return Consumed {
							node: Node::Tag {
								self_closing: false,
								name: root_tag.name.into(),
								children: vec![text!(text)],
							},
							remaining,
						};
					}
				}
			}

			// Find the closing end of out root_tag
			if let Some((parsed, remaining)) = Self::is_tag(rest.unwrap()) {
				if parsed.closing && parsed.name == root_tag.name {
					break Consumed {
						node: Node::Tag {
							self_closing: false,
							name: root_tag.name.to_owned(),
							children,
						},
						remaining,
					};
				}
			}

			// Not our closing root? parse and push
			let cons = Self::parse_node(rest.unwrap());
			rest = cons.remaining;
			children.push(cons.node);
		}
	}

	fn special_parse<'a>(mut raw: &'a str, looking_for_name: &str) -> Option<(&'a str, &'a str)> {
		let close = format!("</{looking_for_name}>");

		let mut offset = 0;
		loop {
			match raw[offset..].find('\n') {
				None => return None,
				Some(nl_idx) => {
					offset += nl_idx + 1;
					match raw[offset..].find(|c: char| !c.is_ascii_whitespace()) {
						None => return None,
						Some(whole_idx) => {
							let whole_start = &raw[offset + whole_idx..];
							if let Some(stripped) = whole_start.strip_prefix(&close) {
								return Some((&raw[..offset + whole_idx], stripped));
							}
						}
					}
				}
			}
		}

		None
	}

	fn parse_comment(raw: &str) -> Option<Consumed> {
		if let Some(after_start) = raw.strip_prefix("<!--") {
			after_start.find("-->").map(|end| Consumed {
				node: Node::Comment(after_start[..end].into()),
				remaining: after_start.get(end + 3..),
			})
		} else {
			None
		}
	}

	/// check if the start of the string is a valid tag
	#[rustfmt::skip]
	fn is_tag(raw: &str) -> Option<(ParsedTag,  Option<&str>)> {
		// Starts '<' and any non-whitespace character
		let starts_right = raw.starts_with('<')
			&& raw.chars().nth(1).map(|c| !c.is_ascii_whitespace()).unwrap_or(false);

		if !starts_right {
			return None;
		}

		match raw.find('>') {
			// not a tag if there's no close
			None => None,
			Some(idx) => {
				let rest = match raw.get(idx+1..) {
					None => None,
					Some("") => None,
					Some(txt) => Some(txt)
				};
				let tag_innards = &raw[1..idx];

				let close = tag_innards.starts_with('/');
				let self_close_idx = {
					let possible = &tag_innards[1..];
					let last_whole_char = possible.rfind(|c: char| !c.is_ascii_whitespace()).map(|n| n + 1);
					let last_slash = possible.rfind('/').map(|n| n + 1);
					match (last_slash, last_whole_char) {
						(Some(slash), Some(whole)) if slash == whole => {
							Some(slash)
						},
						_ => None
					}
				};
				let self_close = self_close_idx.is_some();
				// can't close and self_close
				if close && self_close { return None; }

				// clean the close from the raw string
				let name_raw = if let Some(close_idx) = self_close_idx {
					&tag_innards[..close_idx]
				} else if close {
					&tag_innards[1..]
				} else {
					tag_innards
				};

				let (name, body) = match name_raw.find(|c: char| c.is_ascii_whitespace()){
					None => {
						(name_raw, "")
					},
					Some(idx) => {
						(&name_raw[..idx], &name_raw[idx+1..])
					}
				};

				Some((ParsedTag{
					closing: close,
					self_closing: self_close,
					name,
					body
				}, rest))
			}
		}
	}

	fn parse_text(raw: &str) -> Consumed {
		let mut end_idx = 0;
		let mut search_from = raw;

		loop {
			match search_from.find('<') {
				// if we ever run out of <'s, the entire string was text
				None => {
					break Consumed {
						node: Node::Text(raw.to_owned()),
						remaining: None,
					}
				}
				Some(idx) => {
					end_idx += idx;

					if Self::is_tag(&search_from[idx..]).is_some() {
						// we've found a new tag, this text node is done
						break Consumed {
							node: Node::Text(raw[..end_idx].to_owned()),
							remaining: Some(&raw[end_idx..]),
						};
					} else {
						// step over the <
						end_idx += 1;
						search_from = &raw[end_idx..];
					}
				}
			}
		}
	}
}

struct Consumed<'a> {
	node: Node,
	remaining: Option<&'a str>,
}

struct ParsedTag<'a> {
	closing: bool,
	name: &'a str,
	// a tag's body is what exists between the end of the name and the end of
	// the tag (including a self-close that may be there and any whitespace)
	body: &'a str,
	self_closing: bool,
}

#[derive(Debug, PartialEq)]
pub enum Node {
	Text(String),
	Tag {
		// for roundtripping
		self_closing: bool,
		name: String,
		children: Vec<Node>,
	},
	Comment(String),
}

#[macro_export]
macro_rules! text {
	($text:expr) => {
		Node::Text(String::from($text))
	};
}

#[macro_export]
macro_rules! comment {
	($text:expr) => {
		Node::Comment(String::from($text))
	};
}

#[cfg(test)]
mod test {
	use crate::{Html, Node};

	macro_rules! text {
		($text:expr) => {
			Node::Text(String::from($text))
		};
	}

	#[test]
	fn parse_text_finds_start_of_tag() {
		let no_tag = "Hello, World!";
		let starts_tag = "<p>Hello, World!";
		let ends_tag = "Hello, World!</p>";

		let no_tag_res = Html::parse_text(no_tag);
		assert_eq!(no_tag_res.node, text!("Hello, World!"));
		assert!(no_tag_res.remaining.is_none());

		let starts_tag_res = Html::parse_text(starts_tag);
		assert_eq!(starts_tag_res.node, text!(""));
		assert_eq!(starts_tag_res.remaining, Some(starts_tag));

		let ends_tag_res = Html::parse_text(ends_tag);
		assert_eq!(ends_tag_res.node, text!("Hello, World!"));
		assert_eq!(ends_tag_res.remaining, Some("</p>"));
	}

	#[test]
	fn parse_text_correctly_ignores_nontags() {
		let sentence = "The condition 2 < 1 should be 1 > 2";
		let weird = "Hello, < p>";
		let no_close = "Hello <p my name is ";

		let sentence_res = Html::parse_text(sentence);
		assert_eq!(sentence_res.node, text!(sentence));
		assert!(sentence_res.remaining.is_none());

		let weird_res = Html::parse_text(weird);
		assert_eq!(weird_res.node, text!(weird));
		assert!(weird_res.remaining.is_none());

		let no_close_res = Html::parse_text(no_close);
		assert_eq!(no_close_res.node, text!(no_close));
		assert!(no_close_res.remaining.is_none());
	}

	#[test]
	fn special_parse_find_tag_end() {
		let basic = "words words\n</script>";
		let special = Html::special_parse(basic, "script");
		assert_eq!(special.unwrap().0, "words words\n");
		assert!(special.unwrap().1.is_empty());
	}

	#[test]
	fn special_parse_correctly_ignore_non_start() {
		let nonstart = "first_line\nlet end = '</script>';\n";
		let special = Html::special_parse(nonstart, "script");
		assert!(special.is_none());
	}

	#[test]
	fn special_parse_correctly_handles_leading_whitespace() {
		let white = "words words\n  \t\t</script>";
		let special = Html::special_parse(white, "script");
		assert_eq!(special.unwrap().0, "words words\n  \t\t");
	}

	#[test]
	fn parse_node_parses_comment() {
		let cmt = "<!-- Comment! -->";

		let node = Html::parse_node(cmt);
		assert_eq!(node.node, comment!(" Comment! "));
	}

	#[test]
	fn parse_node_parses_tag() {
		let basic = "<p>Hello!</p>";

		let hh = Html::parse_node(basic);
		assert_eq!(
			hh.node,
			Node::Tag {
				self_closing: false,
				name: "p".into(),
				children: vec![text!("Hello!")]
			}
		)
	}

	#[test]
	fn parse_node_parses_nested_tags() {
		let nested = "<p><p>Hello!</p></p>";

		let hh = Html::parse_node(nested);
		assert_eq!(
			hh.node,
			Node::Tag {
				self_closing: false,
				name: "p".into(),
				children: vec![Node::Tag {
					self_closing: false,
					name: "p".into(),
					children: vec![text!("Hello!")]
				}]
			}
		)
	}

	#[test]
	fn parse_multiple_toplevel() {
		let nested = "<p>Hello </p><p>World!</p>";

		let hh = Html::parse(nested);
		assert_eq!(
			hh.nodes,
			vec![
				Node::Tag {
					self_closing: false,
					name: "p".into(),
					children: vec![text!("Hello ")]
				},
				Node::Tag {
					self_closing: false,
					name: "p".into(),
					children: vec![text!("World!")]
				}
			]
		)
	}
}