use std::iter::Iterator;

use codemap::{Span, Spanned};

use peekmore::PeekMoreIterator;

use crate::common::QuoteKind;
use crate::error::SassResult;
use crate::selector::Selector;
use crate::value::Value;
use crate::{Scope, Token};

use super::{as_hex, hex_char_for, is_name, is_name_start, parse_interpolation};

fn ident_body_no_interpolation<I: Iterator<Item = Token>>(
    toks: &mut PeekMoreIterator<I>,
    unit: bool,
    mut span: Span,
) -> SassResult<Spanned<String>> {
    let mut text = String::new();
    while let Some(tok) = toks.peek() {
        span = span.merge(tok.pos());
        if unit && tok.kind == '-' {
            // Disallow `-` followed by a dot or a digit digit in units.
            let second = match toks.peek_forward(1) {
                Some(v) => *v,
                None => break,
            };

            toks.peek_backward(1).unwrap();

            if second.kind == '.' || second.kind.is_ascii_digit() {
                break;
            }
            toks.next();
            text.push('-');
            text.push(toks.next().unwrap().kind);
        } else if is_name(tok.kind) {
            text.push(toks.next().unwrap().kind);
        } else if tok.kind == '\\' {
            toks.next();
            text.push_str(&escape(toks, false)?);
        } else {
            break;
        }
    }
    Ok(Spanned { node: text, span })
}

fn interpolated_ident_body<I: Iterator<Item = Token>>(
    toks: &mut PeekMoreIterator<I>,
    scope: &Scope,
    super_selector: &Selector,
    mut span: Span,
) -> SassResult<Spanned<String>> {
    let mut buf = String::new();
    while let Some(tok) = toks.peek() {
        if tok.kind == '_'
            || tok.kind.is_alphanumeric()
            || tok.kind == '-'
            || tok.kind as u32 >= 0x0080
        {
            span = span.merge(tok.pos());
            buf.push(toks.next().unwrap().kind);
        } else if tok.kind == '\\' {
            toks.next();
            buf.push_str(&escape(toks, false)?);
        } else if tok.kind == '#' {
            toks.next();
            // TODO: peekmore
            let next = toks.next().unwrap();
            if next.kind == '{' {
                // TODO: if ident, interpolate literally
                let interpolation = parse_interpolation(toks, scope, super_selector)?;
                buf.push_str(&interpolation.node.to_css_string(interpolation.span)?);
            }
        } else {
            break;
        }
    }
    Ok(Spanned { node: buf, span })
}

fn escape<I: Iterator<Item = Token>>(
    toks: &mut PeekMoreIterator<I>,
    identifier_start: bool,
) -> SassResult<String> {
    let mut value = 0;
    let first = match toks.peek() {
        Some(t) => t,
        None => return Ok(String::new()),
    };
    if first.kind == '\n' {
        return Err(("Expected escape sequence.", first.pos()).into());
    } else if first.kind.is_ascii_hexdigit() {
        for _ in 0..6 {
            let next = match toks.peek() {
                Some(t) => t,
                None => break,
            };
            if !next.kind.is_ascii_hexdigit() {
                break;
            }
            value *= 16;
            value += as_hex(toks.next().unwrap().kind as u32)
        }
        if toks.peek().is_some() && toks.peek().unwrap().kind.is_whitespace() {
            toks.next();
        }
    } else {
        value = toks.next().unwrap().kind as u32;
    }

    // tabs are emitted literally
    // TODO: figure out where this check is done
    // in the source dart
    if value == 0x9 {
        return Ok("\\\t".to_string());
    }

    let c = std::char::from_u32(value).unwrap();
    if (identifier_start && is_name_start(c) && !c.is_digit(10))
        || (!identifier_start && is_name(c))
    {
        Ok(c.to_string())
    } else if value <= 0x1F || value == 0x7F || (identifier_start && c.is_digit(10)) {
        let mut buf = String::with_capacity(4);
        buf.push('\\');
        if value > 0xF {
            buf.push(hex_char_for(value >> 4));
        }
        buf.push(hex_char_for(value & 0xF));
        buf.push(' ');
        Ok(buf)
    } else {
        Ok(format!("\\{}", c))
    }
}

pub(crate) fn eat_ident<I: Iterator<Item = Token>>(
    toks: &mut PeekMoreIterator<I>,
    scope: &Scope,
    super_selector: &Selector,
) -> SassResult<Spanned<String>> {
    // TODO: take span as param because we use unwrap here
    let mut span = toks.peek().unwrap().pos();
    let mut text = String::new();
    if toks.peek().unwrap().kind == '-' {
        toks.next();
        text.push('-');
        if toks.peek().unwrap().kind == '-' {
            toks.next();
            text.push('-');
            text.push_str(&interpolated_ident_body(toks, scope, super_selector, span)?.node);
            return Ok(Spanned { node: text, span });
        }
    }

    let Token { kind: first, pos } = match toks.peek() {
        Some(v) => *v,
        None => return Err(("Expected identifier.", span).into()),
    };

    if is_name_start(first) {
        text.push(toks.next().unwrap().kind);
    } else if first == '\\' {
        toks.next();
        text.push_str(&escape(toks, true)?);
    // TODO: peekmore
    // (first == '#' && scanner.peekChar(1) == $lbrace)
    } else if first == '#' {
        toks.next();
        if toks.peek().is_none() {
            return Err(("Expected identifier.", pos).into());
        }
        let Token { kind, pos } = toks.peek().unwrap();
        if kind == &'{' {
            toks.next();
            text.push_str(
                &match parse_interpolation(toks, scope, super_selector)?.node {
                    Value::Ident(s, ..) => s,
                    v => v.to_css_string(span)?,
                },
            );
        } else {
            return Err(("Expected identifier.", *pos).into());
        }
    } else {
        return Err(("Expected identifier.", pos).into());
    }

    let body = interpolated_ident_body(toks, scope, super_selector, pos)?;
    span = span.merge(body.span);
    text.push_str(&body.node);
    Ok(Spanned { node: text, span })
}

pub(crate) fn eat_ident_no_interpolation<I: Iterator<Item = Token>>(
    toks: &mut PeekMoreIterator<I>,
    unit: bool,
) -> SassResult<Spanned<String>> {
    let mut span = toks.peek().unwrap().pos();
    let mut text = String::new();
    if toks.peek().unwrap().kind == '-' {
        toks.next();
        text.push('-');
        if toks.peek().unwrap().kind == '-' {
            toks.next();
            text.push('-');
            text.push_str(&ident_body_no_interpolation(toks, unit, span)?.node);
            return Ok(Spanned { node: text, span });
        }
    }

    let first = match toks.peek() {
        Some(v) => v,
        None => return Err(("Expected identifier.", span).into()),
    };

    if is_name_start(first.kind) {
        text.push(toks.next().unwrap().kind);
    } else if first.kind == '\\' {
        toks.next();
        text.push_str(&escape(toks, true)?);
    } else {
        return Err(("Expected identifier.", first.pos()).into());
    }

    let body = ident_body_no_interpolation(toks, unit, span)?;
    span = span.merge(body.span);
    text.push_str(&body.node);
    Ok(Spanned { node: text, span })
}

pub(crate) fn parse_quoted_string<I: Iterator<Item = Token>>(
    toks: &mut PeekMoreIterator<I>,
    scope: &Scope,
    q: char,
    super_selector: &Selector,
) -> SassResult<Spanned<Value>> {
    let mut s = String::new();
    let mut span = if let Some(tok) = toks.peek() {
        tok.pos()
    } else {
        todo!()
    };
    while let Some(tok) = toks.next() {
        span = span.merge(tok.pos());
        match tok.kind {
            '"' if q == '"' => break,
            '\'' if q == '\'' => break,
            '#' => {
                if toks.peek().unwrap().kind == '{' {
                    toks.next();
                    let interpolation = parse_interpolation(toks, scope, super_selector)?;
                    s.push_str(&match interpolation.node {
                        Value::Ident(s, ..) => s,
                        v => v.to_css_string(interpolation.span)?,
                    });
                    continue;
                } else {
                    s.push('#');
                    continue;
                }
            }
            '\n' => return Err(("Expected \".", tok.pos()).into()),
            '\\' => {
                let first = match toks.peek() {
                    Some(c) => c,
                    None => {
                        s.push('\u{FFFD}');
                        continue;
                    }
                };

                if first.kind == '\n' {
                    return Err(("Expected escape sequence.", first.pos()).into());
                }

                if first.kind.is_ascii_hexdigit() {
                    let mut value = 0;
                    for _ in 0..6 {
                        let next = match toks.peek() {
                            Some(c) => c,
                            None => break,
                        };
                        if !next.kind.is_ascii_hexdigit() {
                            break;
                        }
                        value = (value << 4) + as_hex(toks.next().unwrap().kind as u32);
                    }

                    if toks.peek().is_some() && toks.peek().unwrap().kind.is_ascii_whitespace() {
                        toks.next();
                    }

                    if value == 0 || (value >= 0xD800 && value <= 0xDFFF) || value >= 0x0010_FFFF {
                        s.push('\u{FFFD}');
                    } else {
                        s.push(std::char::from_u32(value).unwrap());
                    }
                } else {
                    s.push(toks.next().unwrap().kind);
                }
            }
            _ => s.push(tok.kind),
        }
    }
    Ok(Spanned {
        node: Value::Ident(s, QuoteKind::Quoted),
        span,
    })
}