use smallvec::SmallVec; use super::{Edit, PartialEdit}; /// Events emitted by `StreamingParser` for edit-mode input.#[derive(Debug, PartialEq, Eq)]pub enum EditEvent {    /// A chunk of `old_text` for an edit operation.    OldTextChunk {        edit_index: usize,        chunk: String,        done: bool,    },    /// A chunk of `new_text` for an edit operation.    NewTextChunk {        edit_index: usize,        chunk: String,        done: bool,    },} /// Events emitted by `StreamingParser` for write-mode input.#[derive(Debug, PartialEq, Eq)]pub enum WriteEvent {    /// A chunk of content for write/overwrite mode.    ContentChunk { chunk: String },} /// Tracks the streaming state of a single edit to detect deltas.#[derive(Default, Debug)]struct EditStreamState {    old_text_emitted_len: usize,    old_text_done: bool,    new_text_emitted_len: usize,    new_text_done: bool,    hold_until_complete: bool,    buffer_new_text_until_old_text_done: bool,} /// Converts incrementally-growing tool call JSON into a stream of chunk events.////// The tool call streaming infrastructure delivers partial JSON objects where/// string fields grow over time. This parser compares consecutive partials,/// computes the deltas, and emits `EditEvent`s or `WriteEvent`s that downstream/// pipeline stages (`StreamingFuzzyMatcher` for old_text, `StreamingDiff` for/// new_text) can consume incrementally.////// Because partial JSON comes through a fixer (`partial-json-fixer`) that/// closes incomplete escape sequences, a string can temporarily contain wrong/// trailing characters (e.g. a literal `\` instead of `\n`).  We handle this/// by holding back trailing backslash characters in non-finalized chunks: if/// a partial string ends with `\` (0x5C), that byte is not emitted until the/// next partial confirms or corrects it.  This avoids feeding corrupted bytes/// to downstream consumers.#[derive(Default, Debug)]pub struct StreamingParser {    edit_states: Vec<EditStreamState>,    content_emitted_len: usize,} impl StreamingParser {    /// Push a new set of partial edits (from edit mode) and return any events.    ///    /// Each call should pass the *entire current* edits array as seen in the    /// latest partial input. The parser will diff it against its internal state    /// to produce only the new events.    pub fn push_edits(&mut self, edits: &[PartialEdit]) -> SmallVec<[EditEvent; 4]> {        let mut events = SmallVec::new();         for (index, partial) in edits.iter().enumerate() {            if index >= self.edit_states.len() {                // A new edit appeared — finalize the previous one if there was one.                if let Some(previous) = self.finalize_previous_edit(                    index,                    edits                        .get(index.saturating_sub(1))                        .and_then(|edit| edit.old_text.as_deref()),                    edits                        .get(index.saturating_sub(1))                        .and_then(|edit| edit.new_text.as_deref()),                ) {                    events.extend(previous);                }                self.edit_states.push(EditStreamState::default());            }             let state = &mut self.edit_states[index];             if state.old_text_emitted_len == 0                && state.new_text_emitted_len == 0                && !state.old_text_done                && partial.new_text.is_some()                && !state.buffer_new_text_until_old_text_done            {                if partial                    .old_text                    .as_ref()                    .is_some_and(|old_text| !old_text.is_empty())                {                    state.hold_until_complete = true;                } else {                    state.buffer_new_text_until_old_text_done = true;                }            }             if state.hold_until_complete {                continue;            }             // Process old_text changes.            if let Some(old_text) = &partial.old_text                && !state.old_text_done            {                if partial.new_text.is_some() && !state.buffer_new_text_until_old_text_done {                    // new_text appeared after old_text, so old_text is done — emit everything.                    let start = find_char_boundary(old_text, state.old_text_emitted_len);                    let chunk = old_text[start..].to_string();                    state.old_text_done = true;                    state.old_text_emitted_len = old_text.len();                    events.push(EditEvent::OldTextChunk {                        edit_index: index,                        chunk,                        done: true,                    });                } else {                    let safe_end = safe_emit_end_for_edit_text(old_text);                    let safe_start = find_char_boundary(old_text, state.old_text_emitted_len);                     if safe_end > safe_start {                        let chunk = old_text[safe_start..safe_end].to_string();                        state.old_text_emitted_len = safe_end;                        events.push(EditEvent::OldTextChunk {                            edit_index: index,                            chunk,                            done: false,                        });                    }                }            }             // Process new_text changes.            if let Some(new_text) = &partial.new_text                && state.old_text_done                && !state.new_text_done            {                let safe_end = safe_emit_end_for_edit_text(new_text);                let safe_start = find_char_boundary(new_text, state.new_text_emitted_len);                 if safe_end > safe_start {                    let chunk = new_text[safe_start..safe_end].to_string();                    state.new_text_emitted_len = safe_end;                    events.push(EditEvent::NewTextChunk {                        edit_index: index,                        chunk,                        done: false,                    });                }            }        }         events    }     /// Push new content and return any events.    ///    /// Each call should pass the *entire current* content string. The parser    /// will diff it against its internal state to emit only the new chunk.    pub fn push_content(&mut self, content: &str) -> SmallVec<[WriteEvent; 1]> {        let mut events = SmallVec::new();         let safe_end = safe_emit_end(content);        let safe_start = find_char_boundary(content, self.content_emitted_len);        if safe_end > safe_start {            let chunk = content[safe_start..safe_end].to_string();            self.content_emitted_len = safe_end;            events.push(WriteEvent::ContentChunk { chunk });        }         events    }     /// Finalize all edits with the complete input. This emits `done: true`    /// events for any in-progress old_text or new_text that hasn't been    /// finalized yet.    ///    /// `final_edits` should be the fully deserialized final edits array. The    /// parser compares against its tracked state and emits any remaining deltas    /// with `done: true`.    pub fn finalize_edits(&mut self, edits: &[Edit]) -> SmallVec<[EditEvent; 4]> {        let mut events = SmallVec::new();         for (index, edit) in edits.iter().enumerate() {            if index >= self.edit_states.len() {                // This edit was never seen in partials — emit it fully.                if let Some(previous) = self.finalize_previous_edit(                    index,                    edits                        .get(index.saturating_sub(1))                        .map(|edit| edit.old_text.as_str()),                    edits                        .get(index.saturating_sub(1))                        .map(|edit| edit.new_text.as_str()),                ) {                    events.extend(previous);                }                self.edit_states.push(EditStreamState::default());            }             let state = &mut self.edit_states[index];             if state.hold_until_complete {                state.old_text_done = true;                state.old_text_emitted_len = edit.old_text.len();                state.new_text_done = true;                state.new_text_emitted_len = edit.new_text.len();                state.hold_until_complete = false;                state.buffer_new_text_until_old_text_done = false;                events.push(EditEvent::OldTextChunk {                    edit_index: index,                    chunk: edit.old_text.clone(),                    done: true,                });                events.push(EditEvent::NewTextChunk {                    edit_index: index,                    chunk: edit.new_text.clone(),                    done: true,                });                continue;            }             if !state.old_text_done {                let start = find_char_boundary(&edit.old_text, state.old_text_emitted_len);                let chunk = edit.old_text[start..].to_string();                state.old_text_done = true;                state.old_text_emitted_len = edit.old_text.len();                events.push(EditEvent::OldTextChunk {                    edit_index: index,                    chunk,                    done: true,                });            }             if !state.new_text_done {                let start = find_char_boundary(&edit.new_text, state.new_text_emitted_len);                let chunk = edit.new_text[start..].to_string();                state.new_text_done = true;                state.new_text_emitted_len = edit.new_text.len();                events.push(EditEvent::NewTextChunk {                    edit_index: index,                    chunk,                    done: true,                });            }        }         events    }     /// Finalize content with the complete input.    pub fn finalize_content(&mut self, content: &str) -> SmallVec<[WriteEvent; 1]> {        let mut events = SmallVec::new();         let start = find_char_boundary(content, self.content_emitted_len);        if content.len() > start {            let chunk = content[start..].to_string();            self.content_emitted_len = content.len();            events.push(WriteEvent::ContentChunk { chunk });        }         events    }     /// When a new edit appears at `index`, finalize the edit at `index - 1`    /// by emitting a `NewTextChunk { done: true }` if it hasn't been finalized.    fn finalize_previous_edit(        &mut self,        new_index: usize,        old_text: Option<&str>,        new_text: Option<&str>,    ) -> Option<SmallVec<[EditEvent; 2]>> {        if new_index == 0 || self.edit_states.is_empty() {            return None;        }         let previous_index = new_index - 1;        if previous_index >= self.edit_states.len() {            return None;        }         let state = &mut self.edit_states[previous_index];        let mut events = SmallVec::new();         if state.hold_until_complete {            let old_text = old_text.unwrap_or_default();            let new_text = new_text.unwrap_or_default();            state.old_text_done = true;            state.old_text_emitted_len = old_text.len();            state.new_text_done = true;            state.new_text_emitted_len = new_text.len();            state.hold_until_complete = false;            state.buffer_new_text_until_old_text_done = false;            events.push(EditEvent::OldTextChunk {                edit_index: previous_index,                chunk: old_text.to_string(),                done: true,            });            events.push(EditEvent::NewTextChunk {                edit_index: previous_index,                chunk: new_text.to_string(),                done: true,            });            return Some(events);        }         if !state.old_text_done {            let old_text = old_text.unwrap_or_default();            let start = find_char_boundary(old_text, state.old_text_emitted_len);            state.old_text_done = true;            state.old_text_emitted_len = old_text.len();            events.push(EditEvent::OldTextChunk {                edit_index: previous_index,                chunk: old_text[start..].to_string(),                done: true,            });        }         if !state.new_text_done {            let new_text = new_text.unwrap_or_default();            let start = find_char_boundary(new_text, state.new_text_emitted_len);            state.new_text_done = true;            state.new_text_emitted_len = new_text.len();            state.buffer_new_text_until_old_text_done = false;            events.push(EditEvent::NewTextChunk {                edit_index: previous_index,                chunk: new_text[start..].to_string(),                done: true,            });        }         Some(events)    }} /// Returns the byte position up to which it is safe to emit from a partial/// string.  If the string ends with a backslash (`\`, 0x5C), that byte is/// held back because it may be an artifact of the partial JSON fixer closing/// an incomplete escape sequence (e.g. turning a half-received `\n` into `\\`)./// The next partial will reveal the correct character.////// The returned position is always a valid UTF-8 character boundary.fn safe_emit_end(text: &str) -> usize {    if text.ends_with('\\') {        text.len() - 1    } else {        text.len()    }} fn safe_emit_end_for_edit_text(text: &str) -> usize {    let safe_end = safe_emit_end(text);    // Use string slicing to check the last character, ensuring we respect UTF-8 boundaries.    if safe_end > 0 && text[..safe_end].ends_with('\n') {        safe_end - 1    } else {        safe_end    }} /// Finds a valid UTF-8 character boundary at or before the target position.////// When streaming partial JSON, the text structure can change between updates/// (e.g., an escape sequence being completed). This means a byte position that/// was valid in one partial may land inside a multi-byte character in the next./// This function finds the nearest valid boundary at or before the target.fn find_char_boundary(text: &str, target: usize) -> usize {    if target >= text.len() {        return text.len();    }    if text.is_char_boundary(target) {        return target;    }    // Walk backwards to find a valid boundary.    let mut pos = target;    while pos > 0 && !text.is_char_boundary(pos) {        pos -= 1;    }    pos} #[cfg(test)]mod tests {    use super::*;    use proptest::prelude::*;     fn emitted_len_inside_multibyte_char() -> impl Strategy<Value = (String, String)> {        (1usize..8, prop::sample::select(&["。", "—", "é", "🦀"])).prop_map(            |(emitted_len, multibyte_char)| {                let first = "a".repeat(emitted_len);                let second = format!("{}{}", "a".repeat(emitted_len - 1), multibyte_char);                (first, second)            },        )    }     fn boundary_sensitive_text() -> impl Strategy<Value = String> {        prop_oneof![            emitted_len_inside_multibyte_char().prop_map(|(first, _)| first),            emitted_len_inside_multibyte_char().prop_map(|(_, second)| second),            prop::sample::select(&[                "",                "a",                "ab",                "ab\\",                "a。",                "a—",                "hello,\\",                "hello,\n",                "hello,\nworld",            ])            .prop_map(ToString::to_string),        ]    }     fn partial_edit() -> impl Strategy<Value = PartialEdit> {        (            prop::option::of(boundary_sensitive_text()),            prop::option::of(boundary_sensitive_text()),        )            .prop_map(|(old_text, new_text)| PartialEdit { old_text, new_text })    }     #[test]    fn test_first_edit_with_new_text_in_first_chunk_is_held_until_finalize() {        let mut parser = StreamingParser::default();         let events = parser.push_edits(&[PartialEdit {            old_text: Some("old".into()),            new_text: Some("new".into()),        }]);        assert!(events.is_empty());         let events = parser.push_edits(&[PartialEdit {            old_text: Some("old text".into()),            new_text: Some("new text".into()),        }]);        assert!(events.is_empty());         let events = parser.finalize_edits(&[Edit {            old_text: "old text".into(),            new_text: "new text".into(),        }]);        assert_eq!(            events.as_slice(),            &[                EditEvent::OldTextChunk {                    edit_index: 0,                    chunk: "old text".into(),                    done: true,                },                EditEvent::NewTextChunk {                    edit_index: 0,                    chunk: "new text".into(),                    done: true,                },            ]        );    }     #[test]    fn test_single_edit_streamed_incrementally() {        let mut parser = StreamingParser::default();         // old_text arrives in chunks: "hell" → "hello w" → "hello world"        let events = parser.push_edits(&[PartialEdit {            old_text: Some("hell".into()),            new_text: None,        }]);        assert_eq!(            events.as_slice(),            &[EditEvent::OldTextChunk {                edit_index: 0,                chunk: "hell".into(),                done: false,            }]        );         let events = parser.push_edits(&[PartialEdit {            old_text: Some("hello w".into()),            new_text: None,        }]);        assert_eq!(            events.as_slice(),            &[EditEvent::OldTextChunk {                edit_index: 0,                chunk: "o w".into(),                done: false,            }]        );         // new_text appears → old_text finalizes

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