//! Provides the [`Trace`] type (byte offsets and syntax information about tokens).

use std::{
    num::NonZeroUsize,
    ops::{Index, Range},
};

use crate::let_else::assume;
use crate::token::AttributeTraceIdx;

/// Provides byte offsets and syntax information about a [`Token`].
///
/// [`Token`]: crate::token::Token
#[allow(missing_docs)]
#[derive(Eq, PartialEq, Debug)]
pub enum Trace {
    Char(Range<usize>),
    StartTag(StartTagTrace),
    EndTag(EndTagTrace),
    Comment(CommentTrace),
    Doctype(DoctypeTrace),
    EndOfFile(usize),
}

/// Provides byte offsets and syntax information for a [`StartTag`] token.
///
/// [`StartTag`]: crate::token::StartTag
#[derive(Eq, PartialEq, Debug)]
pub struct StartTagTrace {
    /// The span of the tag.
    pub span: Range<usize>,

    /// The span of the tag name.
    pub name_span: Range<usize>,

    /// List of [`AttributeTrace`]s for the attributes that were present in the source.
    pub attribute_traces: AttributeTraceList,
}

/// Provides byte offsets for an [`EndTag`] token.
///
/// [`EndTag`]: crate::token::EndTag
#[derive(Eq, PartialEq, Debug)]
pub struct EndTagTrace {
    /// The span of the tag.
    pub span: Range<usize>,

    /// The span of the tag name.
    pub name_span: Range<usize>,
}

/// Provides byte offsets for a [`Token::Comment`].
///
/// [`Token::Comment`]: crate::token::Token::Comment
#[derive(Eq, PartialEq, Debug)]
pub struct CommentTrace {
    /// The offset of the comment data.
    pub data_span: Range<usize>,
}

/// Provides byte offsets for a [`Doctype`] token.
///
/// [`Doctype`]: crate::token::Doctype
#[derive(Eq, PartialEq, Debug)]
pub struct DoctypeTrace {
    pub(crate) span: Range<usize>,
    // Using NonZeroUsize to optimize the size of the struct.
    name_span: Option<Range<std::num::NonZeroUsize>>,
    public_id_span: Option<Range<std::num::NonZeroUsize>>,
    system_id_span: Option<Range<std::num::NonZeroUsize>>,
}

impl DoctypeTrace {
    /// Returns the span of the DOCTYPE.
    pub fn span(&self) -> Range<usize> {
        self.span.clone()
    }

    /// Returns the span of the name.
    pub fn name_span(&self) -> Option<Range<usize>> {
        self.name_span
            .as_ref()
            .map(|range| range.start.get()..range.end.get())
    }

    /// Returns the span of the public identifier.
    pub fn public_id_span(&self) -> Option<Range<usize>> {
        self.public_id_span
            .as_ref()
            .map(|range| range.start.get()..range.end.get())
    }

    /// Returns the span of the system identifier.
    pub fn system_id_span(&self) -> Option<Range<usize>> {
        self.system_id_span
            .as_ref()
            .map(|range| range.start.get()..range.end.get())
    }
}

/// Internal [`DoctypeTrace`] methods.
///
/// Note that even though it stands to reason that the offsets provided to the `set_`
/// methods can never be zero, we intentionally don't use `new_unchecked` since
/// actually verifying that the offsets provided to the respective Emitter methods can
/// never be zero would non-trivial (since the tokenizer state machine has 80 states).
impl DoctypeTrace {
    #[inline]
    pub(crate) fn new(span_start: usize) -> Self {
        Self {
            span: span_start..0,
            name_span: None,
            public_id_span: None,
            system_id_span: None,
        }
    }

    #[inline]
    pub(crate) fn set_name_start(&mut self, start: usize) {
        let start = NonZeroUsize::new(start).expect("expected offset to be non-zero");
        self.name_span = Some(start..start);
    }

    #[inline]
    pub(crate) fn set_public_id_start(&mut self, start: usize) {
        let start = NonZeroUsize::new(start).expect("expected offset to be non-zero");
        self.public_id_span = Some(start..start);
    }

    #[inline]
    pub(crate) fn set_system_id_start(&mut self, start: usize) {
        let start = NonZeroUsize::new(start).expect("expected offset to be non-zero");
        self.system_id_span = Some(start..start);
    }

    #[inline]
    pub(crate) fn set_name_end(&mut self, end: usize) {
        assume!(Some(span), &mut self.name_span);
        span.end = NonZeroUsize::new(end).expect("expected offset to be non-zero");
    }

    #[inline]
    pub(crate) fn set_public_id_end(&mut self, end: usize) {
        assume!(Some(span), &mut self.public_id_span);
        span.end = NonZeroUsize::new(end).expect("expected offset to be non-zero");
    }

    #[inline]
    pub(crate) fn set_system_id_end(&mut self, end: usize) {
        assume!(Some(span), &mut self.system_id_span);
        span.end = NonZeroUsize::new(end).expect("expected offset to be non-zero");
    }
}

/// The syntax of the attribute value.
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub enum AttrValueSyntax {
    /// An unquoted attribute value, e.g. `id=foo`.
    Unquoted,
    /// A single-quoted attribute value, e.g. `id='foo'`.
    SingleQuoted,
    /// A double-quoted attribute value, e.g. `id="foo"`.
    DoubleQuoted,
}

/// Provides byte offsets and the [`AttrValueSyntax`] for an attribute that was present in the source.
#[derive(Eq, PartialEq, Debug)]
pub struct AttributeTrace {
    pub(crate) value_syntax: Option<AttrValueSyntax>,
    pub(crate) name_span: Range<usize>,
    /// We intentionally don't use `Option<Range<O>>` here to spare us a byte (and padding) per attribute.
    /// For the empty attribute syntax this is just `O::default()..O::default()`.
    pub(crate) value_span: Range<usize>,
}

impl AttributeTrace {
    /// [`AttributeTrace`] intentionally doesn't implement Default
    /// (since it's part of the public API and it wouldn't make sense semantically).
    pub(crate) fn new() -> Self {
        Self {
            value_syntax: None,
            name_span: Default::default(),
            value_span: Default::default(),
        }
    }

    /// Returns the span of the attribute name.
    pub fn name_span(&self) -> Range<usize> {
        self.name_span.clone()
    }

    /// For explicitly defined values returns the span of the attribute value.
    ///
    /// Returns `None` for attributes using the empty attribute syntax (e.g. `disabled` in `<input disabled>`).
    pub fn value_span(&self) -> Option<Range<usize>> {
        if self.value_syntax.is_none() {
            return None;
        }
        Some(self.value_span.clone())
    }

    /// Returns the attribute value syntax in case the value is explicitly defined.
    ///
    /// Returns `None` for attributes using the empty attribute syntax (e.g. `disabled` in `<input disabled>`).
    pub fn value_syntax(&self) -> Option<AttrValueSyntax> {
        self.value_syntax
    }
}

/// List of [`AttributeTrace`]s for the attributes that were present in the source.
#[derive(Eq, PartialEq, Debug)]
pub struct AttributeTraceList {
    /// We don't use `HashMap<String, AttributeTrace>` since this would require
    /// the attribute names to be cloned (which would be less efficient).
    traces: Vec<AttributeTrace>,
}

impl Index<AttributeTraceIdx> for AttributeTraceList {
    type Output = AttributeTrace;

    fn index(&self, index: AttributeTraceIdx) -> &Self::Output {
        &self.traces[index.0.get() - 1]
    }
}

impl AttributeTraceList {
    pub(crate) fn new() -> Self {
        Self {
            traces: Default::default(),
        }
    }

    pub(crate) fn insert(&mut self, trace: AttributeTrace) -> AttributeTraceIdx {
        self.traces.push(trace);
        let len = self.traces.len();
        AttributeTraceIdx(
            // SAFETY: len cannot be zero because we push before calling Vec::len.
            unsafe { std::num::NonZeroUsize::new_unchecked(len) },
        )
    }
}