//! This module contains functions for editing syntax trees. As the trees are
//! immutable, all function here return a fresh copy of the tree, instead of
//! doing an in-place modification.
use std::{iter, ops::RangeInclusive};

use arrayvec::ArrayVec;

use crate::{
    algo,
    ast::{
        self,
        make::{self, tokens},
        AstNode,
    },
    AstToken, InsertPosition, SmolStr, SyntaxElement,
    SyntaxKind::{ATTR, COMMENT, WHITESPACE},
    SyntaxNode, T,
};

impl ast::FnDef {
    #[must_use]
    pub fn with_body(&self, body: ast::Block) -> ast::FnDef {
        let mut to_insert: ArrayVec<[SyntaxElement; 2]> = ArrayVec::new();
        let old_body_or_semi: SyntaxElement = if let Some(old_body) = self.body() {
            old_body.syntax().clone().into()
        } else if let Some(semi) = self.semicolon_token() {
            to_insert.push(make::tokens::single_space().into());
            semi.into()
        } else {
            to_insert.push(make::tokens::single_space().into());
            to_insert.push(body.syntax().clone().into());
            return insert_children(self, InsertPosition::Last, to_insert.into_iter());
        };
        to_insert.push(body.syntax().clone().into());
        let replace_range = RangeInclusive::new(old_body_or_semi.clone(), old_body_or_semi);
        replace_children(self, replace_range, to_insert.into_iter())
    }
}

impl ast::ItemList {
    #[must_use]
    pub fn append_items(&self, items: impl Iterator<Item = ast::ImplItem>) -> ast::ItemList {
        let mut res = self.clone();
        if !self.syntax().text().contains_char('\n') {
            res = res.make_multiline();
        }
        items.for_each(|it| res = res.append_item(it));
        res
    }

    #[must_use]
    pub fn append_item(&self, item: ast::ImplItem) -> ast::ItemList {
        let (indent, position) = match self.impl_items().last() {
            Some(it) => (
                leading_indent(it.syntax()).unwrap_or_default().to_string(),
                InsertPosition::After(it.syntax().clone().into()),
            ),
            None => match self.l_curly() {
                Some(it) => (
                    "    ".to_string() + &leading_indent(self.syntax()).unwrap_or_default(),
                    InsertPosition::After(it),
                ),
                None => return self.clone(),
            },
        };
        let ws = tokens::WsBuilder::new(&format!("\n{}", indent));
        let to_insert: ArrayVec<[SyntaxElement; 2]> =
            [ws.ws().into(), item.syntax().clone().into()].into();
        insert_children(self, position, to_insert.into_iter())
    }

    fn l_curly(&self) -> Option<SyntaxElement> {
        self.syntax().children_with_tokens().find(|it| it.kind() == T!['{'])
    }

    fn make_multiline(&self) -> ast::ItemList {
        let l_curly = match self.syntax().children_with_tokens().find(|it| it.kind() == T!['{']) {
            Some(it) => it,
            None => return self.clone(),
        };
        let sibling = match l_curly.next_sibling_or_token() {
            Some(it) => it,
            None => return self.clone(),
        };
        let existing_ws = match sibling.as_token() {
            None => None,
            Some(tok) if tok.kind() != WHITESPACE => None,
            Some(ws) => {
                if ws.text().contains('\n') {
                    return self.clone();
                }
                Some(ws.clone())
            }
        };

        let indent = leading_indent(self.syntax()).unwrap_or("".into());
        let ws = tokens::WsBuilder::new(&format!("\n{}", indent));
        let to_insert = iter::once(ws.ws().into());
        match existing_ws {
            None => insert_children(self, InsertPosition::After(l_curly), to_insert),
            Some(ws) => {
                replace_children(self, RangeInclusive::new(ws.clone().into(), ws.into()), to_insert)
            }
        }
    }
}

pub fn strip_attrs_and_docs<N: ast::AttrsOwner>(node: N) -> N {
    N::cast(strip_attrs_and_docs_inner(node.syntax().clone())).unwrap()
}

fn strip_attrs_and_docs_inner(mut node: SyntaxNode) -> SyntaxNode {
    while let Some(start) =
        node.children_with_tokens().find(|it| it.kind() == ATTR || it.kind() == COMMENT)
    {
        let end = match &start.next_sibling_or_token() {
            Some(el) if el.kind() == WHITESPACE => el.clone(),
            Some(_) | None => start.clone(),
        };
        node = algo::replace_children(&node, RangeInclusive::new(start, end), &mut iter::empty());
    }
    node
}

// Note this is copy-pasted from fmt. It seems like fmt should be a separate
// crate, but basic tree building should be this crate. However, tree building
// might want to call into fmt...
fn leading_indent(node: &SyntaxNode) -> Option<SmolStr> {
    let prev_tokens = std::iter::successors(node.first_token(), |token| token.prev_token());
    for token in prev_tokens {
        if let Some(ws) = ast::Whitespace::cast(token.clone()) {
            let ws_text = ws.text();
            if let Some(pos) = ws_text.rfind('\n') {
                return Some(ws_text[pos + 1..].into());
            }
        }
        if token.text().contains('\n') {
            break;
        }
    }
    None
}

#[must_use]
fn insert_children<N: AstNode>(
    parent: &N,
    position: InsertPosition<SyntaxElement>,
    mut to_insert: impl Iterator<Item = SyntaxElement>,
) -> N {
    let new_syntax = algo::insert_children(parent.syntax(), position, &mut to_insert);
    N::cast(new_syntax).unwrap()
}

#[must_use]
fn replace_children<N: AstNode>(
    parent: &N,
    to_replace: RangeInclusive<SyntaxElement>,
    mut to_insert: impl Iterator<Item = SyntaxElement>,
) -> N {
    let new_syntax = algo::replace_children(parent.syntax(), to_replace, &mut to_insert);
    N::cast(new_syntax).unwrap()
}