xi-core-lib 0.3.0

// Copyright 2016 The xi-editor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use std::borrow::{Borrow, Cow};
use std::cmp::min;
use std::collections::BTreeSet;

use serde_json::Value;

use xi_rope::diff::{Diff, LineHashDiff};
use xi_rope::engine::{Engine, RevId, RevToken};
use xi_rope::rope::count_newlines;
use xi_rope::spans::SpansBuilder;
use xi_rope::{Cursor, DeltaBuilder, Interval, LinesMetric, Rope, RopeDelta, Transformer};
use xi_trace::{trace_block, trace_payload};

use crate::annotations::{AnnotationType, Annotations};
use crate::config::BufferItems;
use crate::edit_types::BufferEvent;
use crate::event_context::MAX_SIZE_LIMIT;
use crate::layers::Layers;
use crate::movement::{region_movement, Movement};
use crate::plugins::rpc::{DataSpan, GetDataResponse, PluginEdit, ScopeSpan, TextUnit};
use crate::plugins::PluginId;
use crate::rpc::SelectionModifier;
use crate::selection::{InsertDrift, SelRegion, Selection};
use crate::styles::ThemeStyleMap;
use crate::view::{Replace, View};
use crate::word_boundaries::WordCursor;

#[cfg(not(feature = "ledger"))]
pub struct SyncStore;
use crate::backspace::offset_for_delete_backwards;
#[cfg(feature = "ledger")]
use fuchsia::sync::SyncStore;

// TODO This could go much higher without issue but while developing it is
// better to keep it low to expose bugs in the GC during casual testing.
const MAX_UNDOS: usize = 20;

enum IndentDirection {
    In,
    Out,
}

pub struct Editor {
    /// The contents of the buffer.
    text: Rope,
    /// The CRDT engine, which tracks edit history and manages concurrent edits.
    engine: Engine,

    /// The most recent revision.
    last_rev_id: RevId,
    /// The revision of the last save.
    pristine_rev_id: RevId,
    undo_group_id: usize,
    /// Undo groups that may still be toggled
    live_undos: Vec<usize>,
    /// The index of the current undo; subsequent undos are currently 'undone'
    /// (but may be redone)
    cur_undo: usize,
    /// undo groups that are undone
    undos: BTreeSet<usize>,
    /// undo groups that are no longer live and should be gc'ed
    gc_undos: BTreeSet<usize>,
    force_undo_group: bool,

    this_edit_type: EditType,
    last_edit_type: EditType,

    revs_in_flight: usize,

    /// Used only on Fuchsia for syncing
    #[allow(dead_code)]
    sync_store: Option<SyncStore>,
    #[allow(dead_code)]
    last_synced_rev: RevId,

    layers: Layers,
}

impl Editor {
    /// Creates a new `Editor` with a new empty buffer.
    pub fn new() -> Editor {
        Self::with_text("")
    }

    /// Creates a new `Editor`, loading text into a new buffer.
    pub fn with_text<T: Into<Rope>>(text: T) -> Editor {
        let engine = Engine::new(text.into());
        let buffer = engine.get_head().clone();
        let last_rev_id = engine.get_head_rev_id();

        Editor {
            text: buffer,
            engine,
            last_rev_id,
            pristine_rev_id: last_rev_id,
            undo_group_id: 1,
            // GC only works on undone edits or prefixes of the visible edits,
            // but initial file loading can create an edit with undo group 0,
            // so we want to collect that as part of the prefix.
            live_undos: vec![0],
            cur_undo: 1,
            undos: BTreeSet::new(),
            gc_undos: BTreeSet::new(),
            force_undo_group: false,
            last_edit_type: EditType::Other,
            this_edit_type: EditType::Other,
            layers: Layers::default(),
            revs_in_flight: 0,
            sync_store: None,
            last_synced_rev: last_rev_id,
        }
    }

    pub(crate) fn get_buffer(&self) -> &Rope {
        &self.text
    }

    pub(crate) fn get_layers(&self) -> &Layers {
        &self.layers
    }

    pub(crate) fn get_layers_mut(&mut self) -> &mut Layers {
        &mut self.layers
    }

    pub(crate) fn get_head_rev_token(&self) -> u64 {
        self.engine.get_head_rev_id().token()
    }

    pub(crate) fn get_edit_type(&self) -> EditType {
        self.this_edit_type
    }

    pub(crate) fn get_active_undo_group(&self) -> usize {
        *self.live_undos.last().unwrap_or(&0)
    }

    pub(crate) fn update_edit_type(&mut self) {
        self.last_edit_type = self.this_edit_type;
        self.this_edit_type = EditType::Other
    }

    pub(crate) fn set_pristine(&mut self) {
        self.pristine_rev_id = self.engine.get_head_rev_id();
    }

    pub(crate) fn is_pristine(&self) -> bool {
        self.engine.is_equivalent_revision(self.pristine_rev_id, self.engine.get_head_rev_id())
    }

    /// Set whether or not edits are forced into the same undo group rather than being split by
    /// their EditType.
    ///
    /// This is used for things such as recording playback, where you don't want the
    /// individual events to be undoable, but instead the entire playback should be.
    pub(crate) fn set_force_undo_group(&mut self, force_undo_group: bool) {
        trace_payload("Editor::set_force_undo_group", &["core"], force_undo_group.to_string());
        self.force_undo_group = force_undo_group;
    }

    /// Sets this Editor's contents to `text`, preserving undo state and cursor
    /// position when possible.
    pub fn reload(&mut self, text: Rope) {
        let delta = LineHashDiff::compute_delta(self.get_buffer(), &text);
        self.add_delta(delta);
        self.set_pristine();
    }

    // each outstanding plugin edit represents a rev_in_flight.
    pub fn increment_revs_in_flight(&mut self) {
        self.revs_in_flight += 1;
    }

    // GC of CRDT engine is deferred until all plugins have acknowledged the new rev,
    // so when the ack comes back, potentially trigger GC.
    pub fn dec_revs_in_flight(&mut self) {
        self.revs_in_flight -= 1;
        self.gc_undos();
    }

    fn insert<T: Into<Rope>>(&mut self, view: &View, text: T) {
        let rope = text.into();
        let mut builder = DeltaBuilder::new(self.text.len());
        for region in view.sel_regions() {
            let iv = Interval::new(region.min(), region.max());
            builder.replace(iv, rope.clone());
        }
        self.add_delta(builder.build());
    }

    /// Leaves the current selection untouched, but surrounds it with two insertions.
    fn surround<BT, AT>(&mut self, view: &View, before_text: BT, after_text: AT)
    where
        BT: Into<Rope>,
        AT: Into<Rope>,
    {
        let mut builder = DeltaBuilder::new(self.text.len());
        let before_rope = before_text.into();
        let after_rope = after_text.into();
        for region in view.sel_regions() {
            let before_iv = Interval::new(region.min(), region.min());
            builder.replace(before_iv, before_rope.clone());
            let after_iv = Interval::new(region.max(), region.max());
            builder.replace(after_iv, after_rope.clone());
        }
        self.add_delta(builder.build());
    }

    /// Applies a delta to the text, and updates undo state.
    ///
    /// Records the delta into the CRDT engine so that it can be undone. Also
    /// contains the logic for merging edits into the same undo group. At call
    /// time, self.this_edit_type should be set appropriately.
    ///
    /// This method can be called multiple times, accumulating deltas that will
    /// be committed at once with `commit_delta`. Note that it does not update
    /// the views. Thus, view-associated state such as the selection and line
    /// breaks are to be considered invalid after this method, until the
    /// `commit_delta` call.
    fn add_delta(&mut self, delta: RopeDelta) {
        let head_rev_id = self.engine.get_head_rev_id();
        let undo_group = self.calculate_undo_group();
        self.last_edit_type = self.this_edit_type;
        let priority = 0x10000;
        self.engine.edit_rev(priority, undo_group, head_rev_id.token(), delta);
        self.text = self.engine.get_head().clone();
    }

    pub(crate) fn calculate_undo_group(&mut self) -> usize {
        let has_undos = !self.live_undos.is_empty();
        let force_undo_group = self.force_undo_group;
        let is_unbroken_group = !self.this_edit_type.breaks_undo_group(self.last_edit_type);

        if has_undos && (force_undo_group || is_unbroken_group) {
            *self.live_undos.last().unwrap()
        } else {
            let undo_group = self.undo_group_id;
            self.gc_undos.extend(&self.live_undos[self.cur_undo..]);
            self.live_undos.truncate(self.cur_undo);
            self.live_undos.push(undo_group);
            if self.live_undos.len() <= MAX_UNDOS {
                self.cur_undo += 1;
            } else {
                self.gc_undos.insert(self.live_undos.remove(0));
            }
            self.undo_group_id += 1;
            undo_group
        }
    }

    /// generates a delta from a plugin's response and applies it to the buffer.
    pub fn apply_plugin_edit(&mut self, edit: PluginEdit) {
        let _t = trace_block("Editor::apply_plugin_edit", &["core"]);
        //TODO: get priority working, so that plugin edits don't necessarily move cursor
        let PluginEdit { rev, delta, priority, undo_group, .. } = edit;
        let priority = priority as usize;
        let undo_group = undo_group.unwrap_or_else(|| self.calculate_undo_group());
        match self.engine.try_edit_rev(priority, undo_group, rev, delta) {
            Err(e) => error!("Error applying plugin edit: {}", e),
            Ok(_) => self.text = self.engine.get_head().clone(),
        };
    }

    /// Commits the current delta. If the buffer has changed, returns
    /// a 3-tuple containing the delta representing the changes, the previous
    /// buffer, and an `InsertDrift` enum describing the correct selection update
    /// behaviour.
    pub(crate) fn commit_delta(&mut self) -> Option<(RopeDelta, Rope, InsertDrift)> {
        let _t = trace_block("Editor::commit_delta", &["core"]);

        if self.engine.get_head_rev_id() == self.last_rev_id {
            return None;
        }

        let last_token = self.last_rev_id.token();
        let delta = self.engine.try_delta_rev_head(last_token).expect("last_rev not found");
        // TODO (performance): it's probably quicker to stash last_text
        // rather than resynthesize it.
        let last_text = self.engine.get_rev(last_token).expect("last_rev not found");

        // Transpose can rotate characters inside of a selection; this is why it's an Inside edit.
        // Surround adds characters on either side of a selection, that's why it's an Outside edit.
        let drift = match self.this_edit_type {
            EditType::Transpose => InsertDrift::Inside,
            EditType::Surround => InsertDrift::Outside,
            _ => InsertDrift::Default,
        };
        self.layers.update_all(&delta);

        self.last_rev_id = self.engine.get_head_rev_id();
        self.sync_state_changed();
        Some((delta, last_text, drift))
    }

    /// Attempts to find the delta from head for the given `RevToken`. Returns
    /// `None` if the revision is not found, so this result should be checked if
    /// the revision is coming from a plugin.
    pub(crate) fn delta_rev_head(&self, target_rev_id: RevToken) -> Option<RopeDelta> {
        self.engine.try_delta_rev_head(target_rev_id).ok()
    }

    #[cfg(not(target_os = "fuchsia"))]
    fn gc_undos(&mut self) {
        if self.revs_in_flight == 0 && !self.gc_undos.is_empty() {
            self.engine.gc(&self.gc_undos);
            self.undos = &self.undos - &self.gc_undos;
            self.gc_undos.clear();
        }
    }

    #[cfg(target_os = "fuchsia")]
    fn gc_undos(&mut self) {
        // Never run GC on Fuchsia so that peers don't invalidate our
        // last_rev_id and so that merge will work.
    }

    pub fn merge_new_state(&mut self, new_engine: Engine) {
        self.engine.merge(&new_engine);
        self.text = self.engine.get_head().clone();
        // TODO: better undo semantics. This only implements separate undo
        // histories for low concurrency.
        self.undo_group_id = self.engine.max_undo_group_id() + 1;
        self.last_synced_rev = self.engine.get_head_rev_id();
        self.commit_delta();
        //self.render();
        //FIXME: render after fuchsia sync
    }

    /// See `Engine::set_session_id`. Only useful for Fuchsia sync.
    pub fn set_session_id(&mut self, session: (u64, u32)) {
        self.engine.set_session_id(session);
    }

    #[cfg(feature = "ledger")]
    pub fn set_sync_store(&mut self, sync_store: SyncStore) {
        self.sync_store = Some(sync_store);
    }

    #[cfg(not(feature = "ledger"))]
    pub fn sync_state_changed(&mut self) {}

    #[cfg(feature = "ledger")]
    pub fn sync_state_changed(&mut self) {
        if let Some(sync_store) = self.sync_store.as_mut() {
            // we don't want to sync right after recieving a new merge
            if self.last_synced_rev != self.engine.get_head_rev_id() {
                self.last_synced_rev = self.engine.get_head_rev_id();
                sync_store.state_changed();
            }
        }
    }

    #[cfg(feature = "ledger")]
    pub fn transaction_ready(&mut self) {
        if let Some(sync_store) = self.sync_store.as_mut() {
            sync_store.commit_transaction(&self.engine);
        }
    }

    fn delete_backward(&mut self, view: &View, config: &BufferItems) {
        // TODO: this function is workable but probably overall code complexity
        // could be improved by implementing a "backspace" movement instead.
        let mut builder = DeltaBuilder::new(self.text.len());
        for region in view.sel_regions() {
            let start = offset_for_delete_backwards(&view, &region, &self.text, &config);
            let iv = Interval::new(start, region.max());
            if !iv.is_empty() {
                builder.delete(iv);
            }
        }

        if !builder.is_empty() {
            self.this_edit_type = EditType::Delete;
            self.add_delta(builder.build());
        }
    }

    /// Common logic for a number of delete methods. For each region in the
    /// selection, if the selection is a caret, delete the region between
    /// the caret and the movement applied to the caret, otherwise delete
    /// the region.
    ///
    /// If `save` is set, save the deleted text into the kill ring.
    fn delete_by_movement(
        &mut self,
        view: &View,
        movement: Movement,
        save: bool,
        kill_ring: &mut Rope,
    ) {
        // We compute deletions as a selection because the merge logic
        // is convenient. Another possibility would be to make the delta
        // builder able to handle overlapping deletions (with union semantics).
        let mut deletions = Selection::new();
        for &r in view.sel_regions() {
            if r.is_caret() {
                let new_region = region_movement(movement, r, view, &self.text, true);
                deletions.add_region(new_region);
            } else {
                deletions.add_region(r);
            }
        }
        if save {
            let saved = self.extract_sel_regions(&deletions).unwrap_or_default();
            *kill_ring = Rope::from(saved);
        }
        self.delete_sel_regions(&deletions);
    }

    /// Deletes the given regions.
    fn delete_sel_regions(&mut self, sel_regions: &[SelRegion]) {
        let mut builder = DeltaBuilder::new(self.text.len());
        for region in sel_regions {
            let iv = Interval::new(region.min(), region.max());
            if !iv.is_empty() {
                builder.delete(iv);
            }
        }
        if !builder.is_empty() {
            self.this_edit_type = EditType::Delete;
            self.add_delta(builder.build());
        }
    }

    /// Extracts non-caret selection regions into a string,
    /// joining multiple regions with newlines.
    fn extract_sel_regions(&self, sel_regions: &[SelRegion]) -> Option<Cow<str>> {
        let mut saved = None;
        for region in sel_regions {
            if !region.is_caret() {
                let val = self.text.slice_to_cow(region);
                match saved {
                    None => saved = Some(val),
                    Some(ref mut s) => {
                        s.to_mut().push('\n');
                        s.to_mut().push_str(&val);
                    }
                }
            }
        }
        saved
    }

    fn insert_newline(&mut self, view: &View, config: &BufferItems) {
        self.this_edit_type = EditType::InsertNewline;
        self.insert(view, &config.line_ending);
    }

    fn insert_tab(&mut self, view: &View, config: &BufferItems) {
        self.this_edit_type = EditType::InsertChars;
        let mut builder = DeltaBuilder::new(self.text.len());
        let const_tab_text = self.get_tab_text(config, None);

        if view.sel_regions().len() > 1 {
            // if we indent multiple regions or multiple lines (below),
            // we treat this as an indentation adjustment; otherwise it is
            // just inserting text.
            self.this_edit_type = EditType::Indent;
        }

        for region in view.sel_regions() {
            let line_range = view.get_line_range(&self.text, region);

            if line_range.len() > 1 {
                self.this_edit_type = EditType::Indent;
                for line in line_range {
                    let offset = view.line_col_to_offset(&self.text, line, 0);
                    let iv = Interval::new(offset, offset);
                    builder.replace(iv, Rope::from(const_tab_text));
                }
            } else {
                let (_, col) = view.offset_to_line_col(&self.text, region.start);
                let mut tab_size = config.tab_size;
                tab_size = tab_size - (col % tab_size);
                let tab_text = self.get_tab_text(config, Some(tab_size));

                let iv = Interval::new(region.min(), region.max());
                builder.replace(iv, Rope::from(tab_text));
            }
        }
        self.add_delta(builder.build());
    }

    /// Indents or outdents lines based on selection and user's tab settings.
    /// Uses a BTreeSet to holds the collection of lines to modify.
    /// Preserves cursor position and current selection as much as possible.
    /// Tries to have behavior consistent with other editors like Atom,
    /// Sublime and VSCode, with non-caret selections not being modified.
    fn modify_indent(&mut self, view: &View, config: &BufferItems, direction: IndentDirection) {
        self.this_edit_type = EditType::Indent;
        let mut lines = BTreeSet::new();
        let tab_text = self.get_tab_text(config, None);
        for region in view.sel_regions() {
            let line_range = view.get_line_range(&self.text, region);
            for line in line_range {
                lines.insert(line);
            }
        }
        match direction {
            IndentDirection::In => self.indent(view, lines, tab_text),
            IndentDirection::Out => self.outdent(view, lines, tab_text),
        };
    }

    fn indent(&mut self, view: &View, lines: BTreeSet<usize>, tab_text: &str) {
        let mut builder = DeltaBuilder::new(self.text.len());
        for line in lines {
            let offset = view.line_col_to_offset(&self.text, line, 0);
            let interval = Interval::new(offset, offset);
            builder.replace(interval, Rope::from(tab_text));
        }
        self.this_edit_type = EditType::InsertChars;
        self.add_delta(builder.build());
    }

    fn outdent(&mut self, view: &View, lines: BTreeSet<usize>, tab_text: &str) {
        let mut builder = DeltaBuilder::new(self.text.len());
        for line in lines {
            let offset = view.line_col_to_offset(&self.text, line, 0);
            let tab_offset = view.line_col_to_offset(&self.text, line, tab_text.len());
            let interval = Interval::new(offset, tab_offset);
            let leading_slice = self.text.slice_to_cow(interval.start()..interval.end());
            if leading_slice == tab_text {
                builder.delete(interval);
            } else if let Some(first_char_col) = leading_slice.find(|c: char| !c.is_whitespace()) {
                let first_char_offset = view.line_col_to_offset(&self.text, line, first_char_col);
                let interval = Interval::new(offset, first_char_offset);
                builder.delete(interval);
            }
        }
        self.this_edit_type = EditType::Delete;
        self.add_delta(builder.build());
    }

    fn get_tab_text(&self, config: &BufferItems, tab_size: Option<usize>) -> &'static str {
        let tab_size = tab_size.unwrap_or(config.tab_size);
        let tab_text = if config.translate_tabs_to_spaces { n_spaces(tab_size) } else { "\t" };

        tab_text
    }

    fn do_insert(&mut self, view: &View, config: &BufferItems, chars: &str) {
        let pair_search = config.surrounding_pairs.iter().find(|pair| pair.0 == chars);
        let caret_exists = view.sel_regions().iter().any(|region| region.is_caret());
        if let (Some(pair), false) = (pair_search, caret_exists) {
            self.this_edit_type = EditType::Surround;
            self.surround(view, pair.0.to_string(), pair.1.to_string());
        } else {
            self.this_edit_type = EditType::InsertChars;
            self.insert(view, chars);
        }
    }

    fn do_paste(&mut self, view: &View, chars: &str) {
        if view.sel_regions().len() == 1 || view.sel_regions().len() != count_lines(chars) {
            self.insert(view, chars);
        } else {
            let mut builder = DeltaBuilder::new(self.text.len());
            for (sel, line) in view.sel_regions().iter().zip(chars.lines()) {
                let iv = Interval::new(sel.min(), sel.max());
                builder.replace(iv, line.into());
            }
            self.add_delta(builder.build());
        }
    }

    pub(crate) fn do_cut(&mut self, view: &mut View) -> Value {
        let result = self.do_copy(view);
        self.delete_sel_regions(&view.sel_regions());
        result
    }

    pub(crate) fn do_copy(&self, view: &View) -> Value {
        if let Some(val) = self.extract_sel_regions(view.sel_regions()) {
            Value::String(val.into_owned())
        } else {
            Value::Null
        }
    }

    fn do_undo(&mut self) {
        if self.cur_undo > 1 {
            self.cur_undo -= 1;
            assert!(self.undos.insert(self.live_undos[self.cur_undo]));
            self.this_edit_type = EditType::Undo;
            self.update_undos();
        }
    }

    fn do_redo(&mut self) {
        if self.cur_undo < self.live_undos.len() {
            assert!(self.undos.remove(&self.live_undos[self.cur_undo]));
            self.cur_undo += 1;
            self.this_edit_type = EditType::Redo;
            self.update_undos();
        }
    }

    fn update_undos(&mut self) {
        self.engine.undo(self.undos.clone());
        self.text = self.engine.get_head().clone();
    }

    fn sel_region_to_interval_and_rope(&self, region: SelRegion) -> (Interval, Rope) {
        let as_interval = Interval::new(region.min(), region.max());
        let interval_rope = self.text.subseq(as_interval);
        (as_interval, interval_rope)
    }

    fn do_transpose(&mut self, view: &View) {
        let mut builder = DeltaBuilder::new(self.text.len());
        let mut last = 0;
        let mut optional_previous_selection: Option<(Interval, Rope)> =
            last_selection_region(view.sel_regions())
                .map(|&region| self.sel_region_to_interval_and_rope(region));

        for &region in view.sel_regions() {
            if region.is_caret() {
                let mut middle = region.end;
                let mut start = self.text.prev_grapheme_offset(middle).unwrap_or(0);
                let mut end = self.text.next_grapheme_offset(middle).unwrap_or(middle);

                // Note: this matches Emac's behavior. It swaps last
                // two characters of line if at end of line.
                if start >= last {
                    let end_line_offset =
                        view.offset_of_line(&self.text, view.line_of_offset(&self.text, end));
                    // include end != self.text.len() because if the editor is entirely empty, we dont' want to pull from empty space
                    if (end == middle || end == end_line_offset) && end != self.text.len() {
                        middle = start;
                        start = self.text.prev_grapheme_offset(middle).unwrap_or(0);
                        end = middle.wrapping_add(1);
                    }

                    let interval = Interval::new(start, end);
                    let before = self.text.slice_to_cow(start..middle);
                    let after = self.text.slice_to_cow(middle..end);
                    let swapped: String = [after, before].concat();
                    builder.replace(interval, Rope::from(swapped));
                    last = end;
                }
            } else if let Some(previous_selection) = optional_previous_selection {
                let current_interval = self.sel_region_to_interval_and_rope(region);
                builder.replace(current_interval.0, previous_selection.1);
                optional_previous_selection = Some(current_interval);
            }
        }
        if !builder.is_empty() {
            self.this_edit_type = EditType::Transpose;
            self.add_delta(builder.build());
        }
    }

    fn yank(&mut self, view: &View, kill_ring: &mut Rope) {
        // TODO: if there are multiple cursors and the number of newlines
        // is one less than the number of cursors, split and distribute one
        // line per cursor.
        self.insert(view, kill_ring.clone());
    }

    fn replace(&mut self, view: &mut View, replace_all: bool) {
        if let Some(Replace { chars, .. }) = view.get_replace() {
            // todo: implement preserve case
            // store old selection because in case nothing is found the selection will be preserved
            let mut old_selection = Selection::new();
            for &region in view.sel_regions() {
                old_selection.add_region(region);
            }
            view.collapse_selections(&self.text);

            if replace_all {
                view.do_find_all(&self.text);
            } else {
                view.do_find_next(&self.text, false, true, true, &SelectionModifier::Set);
            }

            match last_selection_region(view.sel_regions()) {
                Some(_) => self.insert(view, chars),
                None => return,
            };
        }
    }

    fn transform_text<F: Fn(&str) -> String>(&mut self, view: &View, transform_function: F) {
        let mut builder = DeltaBuilder::new(self.text.len());

        for region in view.sel_regions() {
            let selected_text = self.text.slice_to_cow(region);
            let interval = Interval::new(region.min(), region.max());
            builder.replace(interval, Rope::from(transform_function(&selected_text)));
        }
        if !builder.is_empty() {
            self.this_edit_type = EditType::Other;
            self.add_delta(builder.build());
        }
    }

    /// Changes the number(s) under the cursor(s) with the `transform_function`.
    /// If there is a number next to or on the beginning of the region, then
    /// this number will be replaced with the result of `transform_function` and
    /// the cursor will be placed at the end of the number.
    /// Some Examples with a increment `transform_function`:
    ///
    /// "|1234" -> "1235|"
    /// "12|34" -> "1235|"
    /// "-|12" -> "-11|"
    /// "another number is 123|]" -> "another number is 124"
    ///
    /// This function also works fine with multiple regions.
    fn change_number<F: Fn(i128) -> Option<i128>>(&mut self, view: &View, transform_function: F) {
        let mut builder = DeltaBuilder::new(self.text.len());
        for region in view.sel_regions() {
            let mut cursor = WordCursor::new(&self.text, region.end);
            let (mut start, end) = cursor.select_word();

            // if the word begins with '-', then it is a negative number
            if start > 0 && self.text.byte_at(start - 1) == (b'-') {
                start -= 1;
            }

            let word = self.text.slice_to_cow(start..end);
            if let Some(number) = word.parse::<i128>().ok().and_then(&transform_function) {
                let interval = Interval::new(start, end);
                builder.replace(interval, Rope::from(number.to_string()));
            }
        }

        if !builder.is_empty() {
            self.this_edit_type = EditType::Other;
            self.add_delta(builder.build());
        }
    }

    // capitalization behaviour is similar to behaviour in XCode
    fn capitalize_text(&mut self, view: &mut View) {
        let mut builder = DeltaBuilder::new(self.text.len());
        let mut final_selection = Selection::new();

        for &region in view.sel_regions() {
            final_selection.add_region(SelRegion::new(region.max(), region.max()));
            let mut word_cursor = WordCursor::new(&self.text, region.min());

            loop {
                // capitalize each word in the current selection
                let (start, end) = word_cursor.select_word();

                if start < end {
                    let interval = Interval::new(start, end);
                    let word = self.text.slice_to_cow(start..end);

                    // first letter is uppercase, remaining letters are lowercase
                    let (first_char, rest) = word.split_at(1);
                    let capitalized_text =
                        [first_char.to_uppercase(), rest.to_lowercase()].concat();
                    builder.replace(interval, Rope::from(capitalized_text));
                }

                if word_cursor.next_boundary().is_none() || end > region.max() {
                    break;
                }
            }
        }

        if !builder.is_empty() {
            self.this_edit_type = EditType::Other;
            self.add_delta(builder.build());
        }

        // at the end of the transformation carets are located at the end of the words that were
        // transformed last in the selections
        view.collapse_selections(&self.text);
        view.set_selection(&self.text, final_selection);
    }

    fn duplicate_line(&mut self, view: &View, config: &BufferItems) {
        let mut builder = DeltaBuilder::new(self.text.len());
        // get affected lines or regions
        let mut to_duplicate = BTreeSet::new();

        for region in view.sel_regions() {
            let (first_line, _) = view.offset_to_line_col(&self.text, region.min());
            let line_start = view.offset_of_line(&self.text, first_line);

            let mut cursor = match region.is_caret() {
                true => Cursor::new(&self.text, line_start),
                false => {
                    // duplicate all lines together that are part of the same selections
                    let (last_line, _) = view.offset_to_line_col(&self.text, region.max());
                    let line_end = view.offset_of_line(&self.text, last_line);
                    Cursor::new(&self.text, line_end)
                }
            };

            if let Some(line_end) = cursor.next::<LinesMetric>() {
                to_duplicate.insert((line_start, line_end));
            }
        }

        for (start, end) in to_duplicate {
            // insert duplicates
            let iv = Interval::new(start, start);
            builder.replace(iv, self.text.slice(start..end));

            // last line does not have new line character so it needs to be manually added
            if end == self.text.len() {
                builder.replace(iv, Rope::from(&config.line_ending))
            }
        }

        self.this_edit_type = EditType::Other;
        self.add_delta(builder.build());
    }

    pub(crate) fn do_edit(
        &mut self,
        view: &mut View,
        kill_ring: &mut Rope,
        config: &BufferItems,
        cmd: BufferEvent,
    ) {
        use self::BufferEvent::*;
        match cmd {
            Delete { movement, kill } => self.delete_by_movement(view, movement, kill, kill_ring),
            Backspace => self.delete_backward(view, config),
            Transpose => self.do_transpose(view),
            Undo => self.do_undo(),
            Redo => self.do_redo(),
            Uppercase => self.transform_text(view, |s| s.to_uppercase()),
            Lowercase => self.transform_text(view, |s| s.to_lowercase()),
            Capitalize => self.capitalize_text(view),
            Indent => self.modify_indent(view, config, IndentDirection::In),
            Outdent => self.modify_indent(view, config, IndentDirection::Out),
            InsertNewline => self.insert_newline(view, config),
            InsertTab => self.insert_tab(view, config),
            Insert(chars) => self.do_insert(view, config, &chars),
            Paste(chars) => self.do_paste(view, &chars),
            Yank => self.yank(view, kill_ring),
            ReplaceNext => self.replace(view, false),
            ReplaceAll => self.replace(view, true),
            DuplicateLine => self.duplicate_line(view, config),
            IncreaseNumber => self.change_number(view, |s| s.checked_add(1)),
            DecreaseNumber => self.change_number(view, |s| s.checked_sub(1)),
        }
    }

    pub fn theme_changed(&mut self, style_map: &ThemeStyleMap) {
        self.layers.theme_changed(style_map);
    }

    pub fn plugin_n_lines(&self) -> usize {
        self.text.measure::<LinesMetric>() + 1
    }

    pub fn update_spans(
        &mut self,
        view: &mut View,
        plugin: PluginId,
        start: usize,
        len: usize,
        spans: Vec<ScopeSpan>,
        rev: RevToken,
    ) {
        let _t = trace_block("Editor::update_spans", &["core"]);
        // TODO: more protection against invalid input
        let mut start = start;
        let mut end_offset = start + len;
        let mut sb = SpansBuilder::new(len);
        for span in spans {
            sb.add_span(Interval::new(span.start, span.end), span.scope_id);
        }
        let mut spans = sb.build();
        if rev != self.engine.get_head_rev_id().token() {
            if let Ok(delta) = self.engine.try_delta_rev_head(rev) {
                let mut transformer = Transformer::new(&delta);
                let new_start = transformer.transform(start, false);
                if !transformer.interval_untouched(Interval::new(start, end_offset)) {
                    spans = spans.transform(start, end_offset, &mut transformer);
                }
                start = new_start;
                end_offset = transformer.transform(end_offset, true);
            } else {
                error!("Revision {} not found", rev);
            }
        }
        let iv = Interval::new(start, end_offset);
        self.layers.update_layer(plugin, iv, spans);
        view.invalidate_styles(&self.text, start, end_offset);
    }

    pub fn update_annotations(
        &mut self,
        view: &mut View,
        plugin: PluginId,
        start: usize,
        len: usize,
        annotation_spans: Vec<DataSpan>,
        annotation_type: AnnotationType,
        rev: RevToken,
    ) {
        let _t = trace_block("Editor::update_annotations", &["core"]);

        let mut start = start;
        let mut end_offset = start + len;
        let mut sb = SpansBuilder::new(len);
        for span in annotation_spans {
            sb.add_span(Interval::new(span.start, span.end), span.data);
        }
        let mut spans = sb.build();
        if rev != self.engine.get_head_rev_id().token() {
            if let Ok(delta) = self.engine.try_delta_rev_head(rev) {
                let mut transformer = Transformer::new(&delta);
                let new_start = transformer.transform(start, false);
                if !transformer.interval_untouched(Interval::new(start, end_offset)) {
                    spans = spans.transform(start, end_offset, &mut transformer);
                }
                start = new_start;
                end_offset = transformer.transform(end_offset, true);
            } else {
                error!("Revision {} not found", rev);
            }
        }
        let iv = Interval::new(start, end_offset);
        view.update_annotations(plugin, iv, Annotations { items: spans, annotation_type });
    }

    pub(crate) fn get_rev(&self, rev: RevToken) -> Option<Cow<Rope>> {
        let text_cow = if rev == self.engine.get_head_rev_id().token() {
            Cow::Borrowed(&self.text)
        } else {
            match self.engine.get_rev(rev) {
                None => return None,
                Some(text) => Cow::Owned(text),
            }
        };

        Some(text_cow)
    }

    pub fn plugin_get_data(
        &self,
        start: usize,
        unit: TextUnit,
        max_size: usize,
        rev: RevToken,
    ) -> Option<GetDataResponse> {
        let _t = trace_block("Editor::plugin_get_data", &["core"]);
        let text_cow = self.get_rev(rev)?;
        let text = &text_cow;
        // convert our offset into a valid byte offset
        let offset = unit.resolve_offset(text.borrow(), start)?;

        let max_size = min(max_size, MAX_SIZE_LIMIT);
        let mut end_off = offset.saturating_add(max_size);
        if end_off >= text.len() {
            end_off = text.len();
        } else {
            // Snap end to codepoint boundary.
            end_off = text.prev_codepoint_offset(end_off + 1).unwrap();
        }

        let chunk = text.slice_to_cow(offset..end_off).into_owned();
        let first_line = text.line_of_offset(offset);
        let first_line_offset = offset - text.offset_of_line(first_line);

        Some(GetDataResponse { chunk, offset, first_line, first_line_offset })
    }
}

#[derive(PartialEq, Eq, Clone, Copy, Debug, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum EditType {
    /// A catchall for edits that don't fit elsewhere, and which should
    /// always have their own undo groups; used for things like cut/copy/paste.
    Other,
    /// An insert from the keyboard/IME (not a paste or a yank).
    #[serde(rename = "insert")]
    InsertChars,
    #[serde(rename = "newline")]
    InsertNewline,
    /// An indentation adjustment.
    Indent,
    Delete,
    Undo,
    Redo,
    Transpose,
    Surround,
}

impl EditType {
    /// Checks whether a new undo group should be created between two edits.
    fn breaks_undo_group(self, previous: EditType) -> bool {
        self == EditType::Other || self == EditType::Transpose || self != previous
    }
}

fn last_selection_region(regions: &[SelRegion]) -> Option<&SelRegion> {
    for region in regions.iter().rev() {
        if !region.is_caret() {
            return Some(region);
        }
    }
    None
}

fn n_spaces(n: usize) -> &'static str {
    let spaces = "                                ";
    assert!(n <= spaces.len());
    &spaces[..n]
}

/// Counts the number of lines in the string, not including any trailing newline.
fn count_lines(s: &str) -> usize {
    let mut newlines = count_newlines(s);
    if s.as_bytes().last() == Some(&0xa) {
        newlines -= 1;
    }
    1 + newlines
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn plugin_edit() {
        let base_text = "hello";
        let mut editor = Editor::with_text(base_text);
        let mut builder = DeltaBuilder::new(base_text.len());
        builder.replace(0..0, "s".into());
        let delta = builder.build();
        let rev = editor.get_head_rev_token();

        let edit_one = PluginEdit {
            rev,
            delta,
            priority: 55,
            after_cursor: false,
            undo_group: None,
            author: "plugin_one".into(),
        };

        editor.apply_plugin_edit(edit_one.clone());
        editor.apply_plugin_edit(edit_one);

        assert_eq!(editor.get_buffer().to_string(), "sshello");
    }

}