use codemap::Spanned;

use crate::{
    common::Identifier,
    error::SassResult,
    utils::{
        peek_ident_no_interpolation, read_until_closing_paren, read_until_closing_quote,
        read_until_newline,
    },
    value::Value,
    Token,
};

use super::Parser;

#[derive(Debug)]
struct VariableValue {
    value: Spanned<Value>,
    global: bool,
    default: bool,
}

impl VariableValue {
    pub const fn new(value: Spanned<Value>, global: bool, default: bool) -> Self {
        Self {
            value,
            global,
            default,
        }
    }
}

impl<'a> Parser<'a> {
    pub(super) fn parse_variable_declaration(&mut self) -> SassResult<()> {
        assert!(matches!(self.toks.next(), Some(Token { kind: '$', .. })));
        let ident: Identifier = self.parse_identifier_no_interpolation(false)?.node.into();
        self.whitespace();
        if !matches!(self.toks.next(), Some(Token { kind: ':', .. })) {
            return Err(("expected \":\".", self.span_before).into());
        }
        let value = self.parse_variable_value()?;

        if value.global && !value.default {
            self.global_scope
                .insert_var(ident.clone(), value.value.clone())?;
        }

        if value.default {
            if self.at_root && !self.in_control_flow {
                if !self.global_scope.var_exists_no_global(&ident) {
                    self.global_scope.insert_var(ident, value.value)?;
                }
            } else {
                if value.global && !self.global_scope.var_exists_no_global(&ident) {
                    self.global_scope
                        .insert_var(ident.clone(), value.value.clone())?;
                }
                if !self.scopes.last().var_exists_no_global(&ident) {
                    self.scopes.last_mut().insert_var(ident, value.value)?;
                }
            }
        } else if self.at_root {
            if self.in_control_flow {
                if self.global_scope.var_exists_no_global(&ident) {
                    self.global_scope.insert_var(ident, value.value)?;
                } else {
                    self.scopes.last_mut().insert_var(ident, value.value)?;
                }
            } else {
                self.global_scope.insert_var(ident, value.value)?;
            }
        } else {
            let len = self.scopes.len();
            for (_, scope) in self
                .scopes
                .iter_mut()
                .enumerate()
                .filter(|(i, _)| *i != len)
            {
                if scope.var_exists_no_global(&ident) {
                    scope.insert_var(ident.clone(), value.value.clone())?;
                }
            }
            if self.scopes.first().var_exists_no_global(&ident) {
                self.scopes
                    .first_mut()
                    .insert_var(ident.clone(), value.value.clone())?;
            }
            self.scopes.last_mut().insert_var(ident, value.value)?;
        }
        Ok(())
    }

    fn parse_variable_value(&mut self) -> SassResult<VariableValue> {
        let mut default = false;
        let mut global = false;

        let mut val_toks = Vec::new();
        let mut nesting = 0;
        while let Some(tok) = self.toks.peek() {
            match tok.kind {
                ';' => {
                    self.toks.next();
                    break;
                }
                '\\' => {
                    val_toks.push(self.toks.next().unwrap());
                    if self.toks.peek().is_some() {
                        val_toks.push(self.toks.next().unwrap());
                    }
                }
                '"' | '\'' => {
                    let quote = self.toks.next().unwrap();
                    val_toks.push(quote);
                    val_toks.extend(read_until_closing_quote(self.toks, quote.kind)?);
                }
                '#' => {
                    val_toks.push(self.toks.next().unwrap());
                    match self.toks.peek() {
                        Some(Token { kind: '{', .. }) => nesting += 1,
                        Some(Token { kind: ';', .. }) => break,
                        Some(Token { kind: '}', .. }) => {
                            if nesting == 0 {
                                break;
                            } else {
                                nesting -= 1;
                            }
                        }
                        Some(..) | None => {}
                    }
                    if let Some(tok) = self.toks.next() {
                        val_toks.push(tok);
                    }
                }
                '{' => break,
                '}' => {
                    if nesting == 0 {
                        break;
                    } else {
                        nesting -= 1;
                        val_toks.push(self.toks.next().unwrap());
                    }
                }
                '/' => {
                    let next = self.toks.next().unwrap();
                    match self.toks.peek() {
                        Some(Token { kind: '/', .. }) => read_until_newline(self.toks),
                        Some(..) | None => val_toks.push(next),
                    };
                    continue;
                }
                '(' => {
                    val_toks.push(self.toks.next().unwrap());
                    val_toks.extend(read_until_closing_paren(self.toks)?);
                }
                '!' => {
                    let pos = tok.pos();
                    if self.toks.peek_forward(1).is_none() {
                        return Err(("Expected identifier.", pos).into());
                    }
                    // todo: it should not be possible to declare the same flag more than once
                    let mut ident = peek_ident_no_interpolation(self.toks, false, pos)?;
                    ident.node.make_ascii_lowercase();
                    match ident.node.as_str() {
                        "global" => {
                            self.toks.take(7).for_each(drop);
                            global = true;
                        }
                        "default" => {
                            self.toks.take(8).for_each(drop);
                            default = true;
                        }
                        "important" => {
                            self.toks.reset_cursor();
                            val_toks.push(self.toks.next().unwrap());
                            continue;
                        }
                        _ => {
                            return Err(("Invalid flag name.", ident.span).into());
                        }
                    }
                }
                _ => val_toks.push(self.toks.next().unwrap()),
            }
        }
        let val = self.parse_value_from_vec(val_toks)?;
        Ok(VariableValue::new(val, global, default))
    }
}