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use winnow::{
ModalResult, Parser,
combinator::{alt, cut_err, delimited, fail, opt, preceded, repeat},
};
use crate::{
StatefulInput,
expr::Expr,
ident::Ident,
macros::{exp_char, exp_desc, label},
state::{EvalState, FmtState},
utils::delimited_multispace0,
value::Value,
};
/// Index operation for element access.
#[derive(Debug, Clone)]
pub struct Index {
base: Ident,
indices: Vec<IndexType>,
}
/// Type of indexing operation.
#[derive(Debug, Clone)]
pub(crate) enum IndexType {
/// Single element access.
Single(Expr),
/// Range access with bounds.
Range(RangeBounds),
}
/// Range bounds for range access operations.
#[derive(Debug, Clone)]
pub(crate) enum RangeBounds {
/// Range starting from an index to the end.
StartingFrom(Expr),
/// Range from the beginning to an index.
EndingAt(Expr),
/// Range from one index to another.
FromTo(Expr, Expr),
}
impl Index {
pub(crate) fn parse(input: &mut StatefulInput) -> ModalResult<Expr> {
(
Ident::parse_ident,
repeat(
1..,
preceded(
'[',
alt((
// For cases:
// - `x[0]`
// - `x[0:]`
// - `x[0:1]`
(
Expr::parse,
alt((
delimited(
':',
delimited_multispace0(
// Optional end expression for case:
// - `x[0:1]`
// - `x[0:]`
opt(Expr::parse),
),
// Require closing ']'
cut_err(']')
.context(exp_desc!("an expression"))
.context(exp_char!(']')),
)
.map(Some),
// Accept immediate closing ']' for case:
// - `x[0]
']'.value(None),
// Fail otherwise
cut_err(fail)
.context(exp_char!(':'))
.context(exp_char!(']')),
)),
)
.map(
|(start, end): (Expr, Option<Option<Expr>>)| match end {
Some(end) => match end {
Some(end) => {
IndexType::Range(RangeBounds::FromTo(start, end))
}
None => IndexType::Range(RangeBounds::StartingFrom(start)),
},
None => IndexType::Single(start),
},
),
// For case:
// - `x[:5]`
delimited(
':',
// Required expression for range end
Expr::require_parse,
// Peek for closing ']', otherwise fail
cut_err(']').context(exp_char!(']')),
)
.map(|end| IndexType::Range(RangeBounds::EndingAt(end))),
// For case:
// - `x[]`
cut_err(fail)
.context(exp_desc!("An expression"))
.context(exp_char!(':')),
)),
),
),
)
.context(label!("index expression"))
.map(|(ident, indices): (Ident, Vec<IndexType>)| Self {
base: ident,
indices,
})
.map(Expr::Index)
.parse_next(input)
}
pub(crate) fn evaluate(self, state: &mut EvalState) -> Value {
let Some(base_value) = self.base.evaluate(state) else {
return Value::Null;
};
let mut base_value = if matches!(base_value, Value::Map(_) | Value::List(_)) {
base_value.clone()
} else {
return Value::Null;
};
for index in self.indices {
match index {
IndexType::Single(index_expr) => {
let index_value = index_expr.evaluate(state);
match index_value {
// If the index is a string, try to get from map
Value::String(string) => {
if let Value::Map(map) = base_value {
base_value = map.get(&string).cloned().unwrap_or_default();
} else {
return Value::Null;
}
}
// If the index is a non-negative integer, try to get from list
Value::Integer(int) if int >= 0 => {
if let Value::List(list) = base_value {
base_value = list.get(int as usize).cloned().unwrap_or_default();
} else {
return Value::Null;
}
}
_ => {
return Value::Null;
}
}
}
IndexType::Range(range_bounds) => {
if let Value::List(list) = base_value {
let range = match range_bounds {
RangeBounds::StartingFrom(index) => {
let Some(start) = expr_to_usize(index, state) else {
return Value::Null;
};
if start >= list.len() {
return Value::Null;
}
start..list.len()
}
RangeBounds::EndingAt(end) => {
let Some(end) = expr_to_usize(end, state) else {
return Value::Null;
};
if end > list.len() {
return Value::Null;
}
0..end
}
RangeBounds::FromTo(start, end) => {
let Some(start) = expr_to_usize(start, state) else {
return Value::Null;
};
let Some(end) = expr_to_usize(end, state) else {
return Value::Null;
};
if start > end || start >= list.len() || end > list.len() {
return Value::Null;
}
start..end
}
};
base_value = list
.get(range)
.map(|slice| slice.to_vec())
.map(Value::List)
.unwrap_or_default();
}
}
}
}
base_value
}
pub(crate) fn format<W: std::fmt::Write>(
&self,
writer: &mut W,
state: FmtState,
) -> std::fmt::Result {
self.base.format(writer, state)?;
for index in self.indices.iter() {
match index {
IndexType::Single(index) => {
write!(writer, "[")?;
index.format(writer, state)?;
write!(writer, "]")?;
}
IndexType::Range(range_bounds) => {
write!(writer, "[")?;
match range_bounds {
RangeBounds::StartingFrom(start) => {
start.format(writer, state)?;
write!(writer, ":")?;
}
RangeBounds::EndingAt(end) => {
write!(writer, ":")?;
end.format(writer, state)?;
}
RangeBounds::FromTo(start, end) => {
start.format(writer, state)?;
write!(writer, ":")?;
end.format(writer, state)?;
}
}
write!(writer, "]")?;
}
}
}
Ok(())
}
}
fn expr_to_usize(expr: Expr, state: &mut EvalState) -> Option<usize> {
match expr.evaluate(state) {
Value::Integer(int) if int >= 0 => Some(int as usize),
_ => None,
}
}