// Copyright 2017 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.

//! Segmentation of word boundaries. Note: this current implementation
//! is intended to work for code. Future work is to make it Unicode aware.

use xi_rope::{Cursor, Rope, RopeInfo};

pub struct WordCursor<'a> {
    inner: Cursor<'a, RopeInfo>,
}

impl<'a> WordCursor<'a> {
    pub fn new(text: &'a Rope, pos: usize) -> WordCursor<'a> {
        let inner = Cursor::new(text, pos);
        WordCursor { inner }
    }

    /// Get previous boundary, and set the cursor at the boundary found.
    pub fn prev_boundary(&mut self) -> Option<usize> {
        if let Some(ch) = self.inner.prev_codepoint() {
            let mut prop = get_word_property(ch);
            let mut candidate = self.inner.pos();
            while let Some(prev) = self.inner.prev_codepoint() {
                let prop_prev = get_word_property(prev);
                if classify_boundary(prop_prev, prop).is_start() {
                    break;
                }
                prop = prop_prev;
                candidate = self.inner.pos();
            }
            self.inner.set(candidate);
            return Some(candidate);
        }
        None
    }

    /// Get next boundary, and set the cursor at the boundary found.
    pub fn next_boundary(&mut self) -> Option<usize> {
        if let Some(ch) = self.inner.next_codepoint() {
            let mut prop = get_word_property(ch);
            let mut candidate = self.inner.pos();
            while let Some(next) = self.inner.next_codepoint() {
                let prop_next = get_word_property(next);
                if classify_boundary(prop, prop_next).is_end() {
                    break;
                }
                prop = prop_next;
                candidate = self.inner.pos();
            }
            self.inner.set(candidate);
            return Some(candidate);
        }
        None
    }

    /// Return the selection for the word containing the current cursor. The
    /// cursor is moved to the end of that selection.
    pub fn select_word(&mut self) -> (usize, usize) {
        let initial = self.inner.pos();
        let init_prop_after = self.inner.next_codepoint().map(get_word_property);
        self.inner.set(initial);
        let init_prop_before = self.inner.prev_codepoint().map(get_word_property);
        let mut start = initial;
        let init_boundary = if let (Some(pb), Some(pa)) = (init_prop_before, init_prop_after) {
            classify_boundary_initial(pb, pa)
        } else {
            WordBoundary::Both
        };
        let mut prop_after = init_prop_after;
        let mut prop_before = init_prop_before;
        if prop_after.is_none() {
            start = self.inner.pos();
            prop_after = prop_before;
            prop_before = self.inner.prev_codepoint().map(get_word_property);
        }
        while let (Some(pb), Some(pa)) = (prop_before, prop_after) {
            if start == initial {
                if init_boundary.is_start() {
                    break;
                }
            } else if !init_boundary.is_boundary() {
                if classify_boundary(pb, pa).is_boundary() {
                    break;
                }
            } else if classify_boundary(pb, pa).is_start() {
                break;
            }
            start = self.inner.pos();
            prop_after = prop_before;
            prop_before = self.inner.prev_codepoint().map(get_word_property);
        }
        self.inner.set(initial);
        let mut end = initial;
        prop_after = init_prop_after;
        prop_before = init_prop_before;
        if prop_before.is_none() {
            prop_before = self.inner.next_codepoint().map(get_word_property);
            end = self.inner.pos();
            prop_after = self.inner.next_codepoint().map(get_word_property);
        }
        while let (Some(pb), Some(pa)) = (prop_before, prop_after) {
            if end == initial {
                if init_boundary.is_end() {
                    break;
                }
            } else if !init_boundary.is_boundary() {
                if classify_boundary(pb, pa).is_boundary() {
                    break;
                }
            } else if classify_boundary(pb, pa).is_end() {
                break;
            }
            end = self.inner.pos();
            prop_before = prop_after;
            prop_after = self.inner.next_codepoint().map(get_word_property);
        }
        self.inner.set(end);
        (start, end)
    }
}

#[derive(PartialEq, Eq)]
enum WordBoundary {
    Interior,
    Start, // a boundary indicating the end of a word
    End,   // a boundary indicating the start of a word
    Both,
}

impl WordBoundary {
    fn is_start(&self) -> bool {
        *self == WordBoundary::Start || *self == WordBoundary::Both
    }

    fn is_end(&self) -> bool {
        *self == WordBoundary::End || *self == WordBoundary::Both
    }

    fn is_boundary(&self) -> bool {
        *self != WordBoundary::Interior
    }
}

fn classify_boundary(prev: WordProperty, next: WordProperty) -> WordBoundary {
    use self::WordBoundary::*;
    use self::WordProperty::*;
    match (prev, next) {
        (Lf, _) => Both,
        (_, Lf) => Both,
        (Space, Other) => Start,
        (Space, Punctuation) => Start,
        (Punctuation, Other) => Start,
        (Other, Space) => End,
        (Punctuation, Space) => End,
        (Other, Punctuation) => End,
        _ => Interior,
    }
}

fn classify_boundary_initial(prev: WordProperty, next: WordProperty) -> WordBoundary {
    use self::WordBoundary::*;
    use self::WordProperty::*;
    match (prev, next) {
        (Lf, Other) => Start,
        (Other, Lf) => End,
        (Lf, Space) => Interior,
        (Lf, Punctuation) => Interior,
        (Space, Lf) => Interior,
        (Punctuation, Lf) => Interior,
        (Space, Punctuation) => Interior,
        (Punctuation, Space) => Interior,
        _ => classify_boundary(prev, next),
    }
}

#[derive(Copy, Clone)]
enum WordProperty {
    Lf,
    Space,
    Punctuation,
    Other, // includes letters and all of non-ascii unicode
}

fn get_word_property(codepoint: char) -> WordProperty {
    if codepoint <= ' ' {
        // TODO: deal with \r
        if codepoint == '\n' {
            return WordProperty::Lf;
        }
        return WordProperty::Space;
    } else if codepoint <= '\u{3f}' {
        // Hardcoded: !"#$%&'()*+,-./:;<=>?
        if (0xfc00fffe00000000u64 >> (codepoint as u32)) & 1 != 0 {
            return WordProperty::Punctuation;
        }
    } else if codepoint <= '\u{7f}' {
        // Hardcoded: @[\]^`{|}~
        if (0x7800000178000001u64 >> ((codepoint as u32) & 0x3f)) & 1 != 0 {
            return WordProperty::Punctuation;
        }
    }
    WordProperty::Other
}