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//! Incremental extraction of the top-level script string from tool arguments.
//!
//! Only new argument bytes are scanned. Escapes (including surrogate pairs)
//! stay pending across provider deltas; source rows are assembled once rather
//! than reparsing and splitting the entire argument buffer on every update.
//! This is a preview, not validation: execution still uses the completed JSON.
#[derive(Clone, Copy, Debug)]
enum StringRole {
Key,
Script,
Other,
}
#[derive(Clone, Copy, Debug, Default)]
enum Escape {
#[default]
None,
Slash,
Unicode {
value: u16,
digits: u8,
},
}
#[derive(Clone, Debug, Default)]
pub(super) struct ScriptStream {
consumed: usize,
depth: usize,
expecting_key: bool,
key: String,
key_buffer: String,
role: Option<StringRole>,
escape: Escape,
high_surrogate: Option<u16>,
invalid: bool,
lines: Vec<String>,
visible_end: Option<(usize, usize)>,
revision: usize,
}
impl ScriptStream {
/// Consume only the unobserved suffix, including arguments received before
/// the provider named the tool. Returns whether decoded source changed.
pub(super) fn update(&mut self, arguments: &str) -> bool {
let revision = self.revision;
for character in arguments[self.consumed..].chars() {
if self.invalid {
break;
}
self.consume(character);
}
self.consumed = arguments.len();
self.revision != revision
}
/// Full source history, with the same trailing-whitespace policy as cards
/// built from completed arguments. No full-source split or JSON parse.
pub(super) fn lines(&self) -> Vec<String> {
let Some((last, end)) = self.visible_end else {
return Vec::new();
};
let mut lines = self.lines[..=last].to_vec();
lines[last].truncate(end);
lines
}
fn consume(&mut self, character: char) {
if let Some(role) = self.role {
match self.escape {
Escape::Slash => {
self.escape = Escape::None;
let decoded = match character {
'"' => '"',
'\\' => '\\',
'/' => '/',
'b' => '\u{0008}',
'f' => '\u{000c}',
'n' => '\n',
'r' => '\r',
't' => '\t',
'u' => {
self.escape = Escape::Unicode {
value: 0,
digits: 0,
};
return;
}
_ => {
self.invalid = true;
return;
}
};
self.push(role, decoded);
}
Escape::Unicode { value, digits } => {
let Some(hex) = character.to_digit(16) else {
self.invalid = true;
return;
};
let value = (value << 4) | hex as u16;
let digits = digits + 1;
if digits != 4 {
self.escape = Escape::Unicode { value, digits };
return;
}
self.escape = Escape::None;
if (0xd800..=0xdbff).contains(&value) && self.high_surrogate.is_none() {
self.high_surrogate = Some(value);
return;
}
let scalar = match self.high_surrogate.take() {
Some(high) if (0xdc00..=0xdfff).contains(&value) => {
0x10000 + ((u32::from(high) - 0xd800) << 10) + u32::from(value) - 0xdc00
}
Some(_) => {
self.invalid = true;
return;
}
None => u32::from(value),
};
if let Some(decoded) = char::from_u32(scalar) {
self.push(role, decoded);
} else {
self.invalid = true;
}
}
Escape::None => match character {
'\\' => self.escape = Escape::Slash,
'"' if self.high_surrogate.is_none() => {
if matches!(role, StringRole::Key) {
self.key = std::mem::take(&mut self.key_buffer);
self.expecting_key = false;
}
self.role = None;
}
character if character >= '\u{0020}' => self.push(role, character),
_ => self.invalid = true,
},
}
return;
}
match character {
'{' | '[' => {
self.depth += 1;
if self.depth == 1 {
self.expecting_key = true;
}
}
'}' | ']' => self.depth = self.depth.saturating_sub(1),
',' if self.depth == 1 => {
self.expecting_key = true;
self.key.clear();
}
'"' => {
let role = if self.depth == 1 && self.expecting_key {
StringRole::Key
} else if self.depth == 1 && self.key == "script" {
self.lines.clear();
self.visible_end = None;
self.revision += 1;
StringRole::Script
} else {
StringRole::Other
};
self.role = Some(role);
}
_ => {}
}
}
fn push(&mut self, role: StringRole, character: char) {
if self.high_surrogate.is_some() {
self.invalid = true;
return;
}
match role {
StringRole::Key => self.key_buffer.push(character),
StringRole::Other => {}
StringRole::Script => {
if self.lines.is_empty() {
self.lines.push(String::new());
}
if character == '\n' {
if let Some(line) = self.lines.last_mut().filter(|line| line.ends_with('\r')) {
line.pop();
}
self.lines.push(String::new());
} else {
let index = self.lines.len() - 1;
let line = &mut self.lines[index];
line.push(character);
if !character.is_whitespace() {
self.visible_end = Some((index, line.len()));
}
}
self.revision += 1;
}
}
}
}
#[cfg(test)]
#[path = "interactive_presenter_script_stream_tests.rs"]
mod tests;