use std::rc::Rc;

use orchid_base::{fmt, is, mk_errv, sym};
use orchid_extension::gen_expr::{call, new_atom};
use orchid_extension::tree::{GenMember, comments, fun, prefix};
use orchid_extension::{Expr, ForeignAtom, exec, get_arg};
use unicode_segmentation::UnicodeSegmentation;

use super::str_atom::StrAtom;
use crate::std::protocol::types::{get_impl, proto};
use crate::std::string::to_string::ToStringMethod;
use crate::{Int, OrcOpt, OrcString, Tpl};

pub fn gen_str_lib() -> Vec<GenMember> {
	prefix("std", [comments(
		["There are two string types, IntStr and Str. Literals are always IntStr, which are quick to \
			equality-compare but may leak, so you can't generally create them at runtime.\n\n\
			All functions here operate on Unicode graphemes. This essentially means that letters with \
			added diacritics and Mandarin multi-codepoint characters are treated as a single character."],
		prefix("string", [
			comments(
				["Concatenate two strings", "|type: Str -> Str -> Str|"],
				fun(true, "concat", async |left: OrcString, right: OrcString| {
					new_atom(StrAtom::new(Rc::new(
						left.get_string().await.to_string() + &right.get_string().await,
					)))
				}),
			),
			comments(
				[
					"Find the size of a string in bytes. Strings are stored in UTF-8. \
					This should be used to determine the computational resource utilization of strings. \
					It should not be used to determine whether to truncate text.",
					"|type: Str -> Int|",
				],
				fun(true, "size", async |s: OrcString| Int(s.get_string().await.len().try_into().unwrap())),
			),
			comments(
				[
					"Find the number of characters in a string. This can be used for example to \
					truncate text. It should not be used to limit the size of messages for security purposes.",
					"|type: Str -> Int|",
				],
				fun(true, "len", async |s: OrcString| {
					Int(s.get_string().await.graphemes(true).count().try_into().unwrap())
				}),
			),
			comments(
				[
					"Takes a string, a start and a length in graphemes. \
					Slices out the specified subsection of the string.",
					"|type: Str -> Int -> Int -> Str|",
				],
				fun(true, "slice", async |s: OrcString, Int(start): Int, Int(len): Int| {
					let str = s.get_string().await;
					if len <= 0 {
						return Ok(new_atom(StrAtom::new(Rc::default())));
					}
					let mut substr_iter = str.graphemes(true).skip(start.try_into().unwrap());
					let new_str: String =
						substr_iter.by_ref().take(usize::try_from(len).unwrap() - 1).collect();
					let Some(s) = substr_iter.next() else {
						let str_len = str.graphemes(true).count();
						return Err(mk_errv(
							is("Index out of bounds").await,
							format!("Tried to select grapheme {start}+{len} from string that only has {str_len}"),
							[get_arg(0).pos().await, get_arg(1).pos().await, get_arg(2).pos().await],
						));
					};
					Ok(new_atom(StrAtom::new(Rc::new(new_str + s))))
				}),
			),
			comments(
				[
					"If the first string contains the second then returns the index.",
					"|type: Str -> Str -> std::option Int|",
				],
				fun(true, "find", async |haystack: OrcString, needle: OrcString| {
					let haystack_str = haystack.get_string().await;
					let needle_str = needle.get_string().await;
					let mut haystack_graphs = haystack_str.graphemes(true);
					let mut index = 0;
					loop {
						let mut needle_graphs = needle_str.graphemes(true);
						// check that all chars are equal
						if haystack_graphs.clone().zip(needle_graphs.by_ref()).all(|(l, r)| l == r) {
							// if we exhausted the haystack but not the needle, we can't succeed
							if needle_graphs.next().is_some() {
								break;
							}
							return OrcOpt(Some(Int(index)));
						}
						if haystack_graphs.next().is_none() {
							break;
						}
						index += 1;
					}
					OrcOpt(None)
				}),
			),
			comments(
				[
					"Splits the string into two substrings at the nth grapheme.",
					"|type: Str -> Int -> std::tuple Str Str|",
				],
				fun(true, "split", async |s: OrcString, i: Int| {
					let str = s.get_string().await;
					let Some((i, _)) = str.grapheme_indices(true).nth(i.0.try_into().unwrap()) else {
						let len = str.graphemes(true).count();
						return Err(mk_errv(
							is("Index out of bounds").await,
							format!("Tried to split string at {}, it only has {} graphemes", i.0, len),
							[get_arg(0).pos().await, get_arg(1).pos().await],
						));
					};
					let (left, right) = str.split_at(i);
					Ok(Tpl((
						new_atom(StrAtom::new(Rc::new(left.to_string()))),
						new_atom(StrAtom::new(Rc::new(right.to_string()))),
					)))
				}),
			),
			comments(
				["Returns the nth grapheme.", "|type: Str -> Int -> Str|"],
				fun(true, "char_at", async |s: OrcString, i: Int| {
					let str = s.get_string().await;
					let Some(s) = str.graphemes(true).nth(i.0.try_into().unwrap()) else {
						let len = str.graphemes(true).count();
						return Err(mk_errv(
							is("Index out of bounds").await,
							format!("Tried to read grapheme {} from string, it only has {}", i.0, len),
							[get_arg(0).pos().await, get_arg(1).pos().await],
						));
					};
					Ok(new_atom(StrAtom::new(Rc::new(s.to_string()))))
				}),
			),
			comments(
				[
					"Converts a value to string. This function is used in interpolation. \
					It supports the std::string::to_string protocol in Orchid, \
					the std::string::to_string request in Rust, \
					and expression debug printing as a fallback (print_atom for Atomic implementors in Rust).\n\n\
					This function is infallible.",
					"|type: any -> Str|",
				],
				fun(true, "to_str", async |input: Expr| {
					exec(async move |mut h| {
						if let Ok(atom) = h.exec::<ForeignAtom>(input.clone()).await {
							if let Some(str) = atom.call(ToStringMethod).await {
								return new_atom(StrAtom::new(Rc::new(str)));
							}
							let proto_ref = sym!(std::string::to_string::__protocol_tag__);
							let proto = h.exec(proto_ref).await.expect("This protocol is defined in this system");
							if let Ok(cb) = get_impl(atom.clone(), proto).await {
								return call(cb, atom).await;
							}
						}
						return new_atom(StrAtom::new(Rc::new(fmt(&input).await)));
					})
					.await
				}),
			),
			proto(true, "to_string").finish(),
		]),
	)])
}