/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

//! Common handling of keyboard input and state management for text input controls

use clipboard_provider::ClipboardProvider;
use dom::bindings::str::DOMString;
use dom::keyboardevent::KeyboardEvent;
use msg::constellation_msg::{ALT, CONTROL, SHIFT, SUPER};
use msg::constellation_msg::{Key, KeyModifiers};
use std::borrow::ToOwned;
use std::cmp::{max, min};
use std::default::Default;
use std::ops::Range;
use std::usize;

#[derive(Copy, Clone, PartialEq)]
pub enum Selection {
    Selected,
    NotSelected
}

#[derive(JSTraceable, PartialEq, Copy, Clone, HeapSizeOf)]
pub enum SelectionDirection {
    Forward,
    Backward,
    None,
}

impl From<DOMString> for SelectionDirection {
    fn from(direction: DOMString) -> SelectionDirection {
        match direction.as_ref() {
            "forward" => SelectionDirection::Forward,
            "backward" => SelectionDirection::Backward,
            _ => SelectionDirection::None,
        }
    }
}

impl From<SelectionDirection> for DOMString {
    fn from(direction: SelectionDirection) -> DOMString {
        match direction {
            SelectionDirection::Forward => DOMString::from("forward"),
            SelectionDirection::Backward => DOMString::from("backward"),
            SelectionDirection::None => DOMString::from("none"),
        }
    }
}

#[derive(JSTraceable, Copy, Clone, HeapSizeOf, PartialEq)]
pub struct TextPoint {
    /// 0-based line number
    pub line: usize,
    /// 0-based column number in UTF-8 bytes
    pub index: usize,
}

/// Encapsulated state for handling keyboard input in a single or multiline text input control.
#[derive(JSTraceable, HeapSizeOf)]
pub struct TextInput<T: ClipboardProvider> {
    /// Current text input content, split across lines without trailing '\n'
    lines: Vec<DOMString>,
    /// Current cursor input point
    pub edit_point: TextPoint,
    /// Beginning of selection range with edit_point as end that can span multiple lines.
    pub selection_begin: Option<TextPoint>,
    /// Is this a multiline input?
    multiline: bool,
    #[ignore_heap_size_of = "Can't easily measure this generic type"]
    clipboard_provider: T,
    /// The maximum number of UTF-16 code units this text input is allowed to hold.
    ///
    /// https://html.spec.whatwg.org/multipage/#attr-fe-maxlength
    pub max_length: Option<usize>,
    pub min_length: Option<usize>,
    pub selection_direction: SelectionDirection,
}

/// Resulting action to be taken by the owner of a text input that is handling an event.
pub enum KeyReaction {
    TriggerDefaultAction,
    DispatchInput,
    RedrawSelection,
    Nothing,
}

impl Default for TextPoint {
    fn default() -> TextPoint {
        TextPoint {
            line: 0,
            index: 0,
        }
    }
}

/// Control whether this control should allow multiple lines.
#[derive(PartialEq, Eq)]
pub enum Lines {
    Single,
    Multiple,
}

/// The direction in which to delete a character.
#[derive(PartialEq, Eq, Copy, Clone)]
pub enum Direction {
    Forward,
    Backward
}


/// Was the keyboard event accompanied by the standard control modifier,
/// i.e. cmd on Mac OS or ctrl on other platforms.
#[cfg(target_os = "macos")]
fn is_control_key(mods: KeyModifiers) -> bool {
    mods.contains(SUPER) && !mods.contains(CONTROL | ALT)
}

#[cfg(not(target_os = "macos"))]
fn is_control_key(mods: KeyModifiers) -> bool {
    mods.contains(CONTROL) && !mods.contains(SUPER | ALT)
}

/// The length in bytes of the first n characters in a UTF-8 string.
///
/// If the string has fewer than n characters, returns the length of the whole string.
fn len_of_first_n_chars(text: &str, n: usize) -> usize {
    match text.char_indices().take(n).last() {
        Some((index, ch)) => index + ch.len_utf8(),
        None => 0
    }
}

/// The length in bytes of the first n code units a string when encoded in UTF-16.
///
/// If the string is fewer than n code units, returns the length of the whole string.
fn len_of_first_n_code_units(text: &str, n: usize) -> usize {
    let mut utf8_len = 0;
    let mut utf16_len = 0;
    for c in text.chars() {
        utf16_len += c.len_utf16();
        if utf16_len > n {
            break;
        }
        utf8_len += c.len_utf8();
    }
    utf8_len
}

impl<T: ClipboardProvider> TextInput<T> {
    /// Instantiate a new text input control
    pub fn new(lines: Lines, initial: DOMString,
               clipboard_provider: T, max_length: Option<usize>,
               min_length: Option<usize>,
               selection_direction: SelectionDirection) -> TextInput<T> {
        let mut i = TextInput {
            lines: vec!(),
            edit_point: Default::default(),
            selection_begin: None,
            multiline: lines == Lines::Multiple,
            clipboard_provider: clipboard_provider,
            max_length: max_length,
            min_length: min_length,
            selection_direction: selection_direction,
        };
        i.set_content(initial);
        i
    }

    /// Remove a character at the current editing point
    pub fn delete_char(&mut self, dir: Direction) {
        if self.selection_begin.is_none() || self.selection_begin == Some(self.edit_point) {
            self.adjust_horizontal_by_one(dir, Selection::Selected);
        }
        self.replace_selection(DOMString::new());
    }

    /// Insert a character at the current editing point
    pub fn insert_char(&mut self, ch: char) {
        self.insert_string(ch.to_string());
    }

    /// Insert a string at the current editing point
    pub fn insert_string<S: Into<String>>(&mut self, s: S) {
        if self.selection_begin.is_none() {
            self.selection_begin = Some(self.edit_point);
        }
        self.replace_selection(DOMString::from(s.into()));
    }

    pub fn get_sorted_selection(&self) -> Option<(TextPoint, TextPoint)> {
        self.selection_begin.map(|begin| {
            let end = self.edit_point;

            if begin.line < end.line || (begin.line == end.line && begin.index < end.index) {
                (begin, end)
            } else {
                (end, begin)
            }
        })
    }

    // Check that the selection is valid.
    fn assert_ok_selection(&self) {
        if let Some(begin) = self.selection_begin {
            debug_assert!(begin.line < self.lines.len());
            debug_assert!(begin.index <= self.lines[begin.line].len());
        }
        debug_assert!(self.edit_point.line < self.lines.len());
        debug_assert!(self.edit_point.index <= self.lines[self.edit_point.line].len());
    }

    /// Return the selection range as UTF-8 byte offsets from the start of the content.
    ///
    /// If there is no selection, returns an empty range at the insertion point.
    pub fn get_absolute_selection_range(&self) -> Range<usize> {
        match self.get_sorted_selection() {
            Some((begin, end)) => self.get_absolute_point_for_text_point(&begin) ..
                                  self.get_absolute_point_for_text_point(&end),
            None => {
                let insertion_point = self.get_absolute_insertion_point();
                insertion_point .. insertion_point
            }
        }
    }

    pub fn get_selection_text(&self) -> Option<String> {
        let text = self.fold_selection_slices(String::new(), |s, slice| s.push_str(slice));
        if text.is_empty() {
            return None
        }
        Some(text)
    }

    /// The length of the selected text in UTF-16 code units.
    fn selection_utf16_len(&self) -> usize {
        self.fold_selection_slices(0usize,
            |len, slice| *len += slice.chars().map(char::len_utf16).sum())
    }

    /// Run the callback on a series of slices that, concatenated, make up the selected text.
    ///
    /// The accumulator `acc` can be mutated by the callback, and will be returned at the end.
    fn fold_selection_slices<B, F: FnMut(&mut B, &str)>(&self, mut acc: B, mut f: F) -> B {
        match self.get_sorted_selection() {
            Some((begin, end)) if begin.line == end.line => {
                f(&mut acc, &self.lines[begin.line][begin.index..end.index])
            }
            Some((begin, end)) => {
                f(&mut acc, &self.lines[begin.line][begin.index..]);
                for line in &self.lines[begin.line + 1 .. end.line] {
                    f(&mut acc, "\n");
                    f(&mut acc, line);
                }
                f(&mut acc, "\n");
                f(&mut acc, &self.lines[end.line][..end.index])
            }
            None => {}
        }
        acc
    }

    pub fn replace_selection(&mut self, insert: DOMString) {
        if let Some((begin, end)) = self.get_sorted_selection() {
            let allowed_to_insert_count = if let Some(max_length) = self.max_length {
                let len_after_selection_replaced = self.utf16_len() - self.selection_utf16_len();
                if len_after_selection_replaced >= max_length {
                    // If, after deleting the selection, the len is still greater than the max
                    // length, then don't delete/insert anything
                    return
                }

                max_length - len_after_selection_replaced
            } else {
                usize::MAX
            };

            let last_char_index = len_of_first_n_code_units(&*insert, allowed_to_insert_count);
            let chars_to_insert = &insert[..last_char_index];

            self.clear_selection();

            let new_lines = {
                let prefix = &self.lines[begin.line][..begin.index];
                let suffix = &self.lines[end.line][end.index..];
                let lines_prefix = &self.lines[..begin.line];
                let lines_suffix = &self.lines[end.line + 1..];

                let mut insert_lines = if self.multiline {
                    chars_to_insert.split('\n').map(|s| DOMString::from(s)).collect()
                } else {
                    vec!(DOMString::from(chars_to_insert))
                };

                // FIXME(ajeffrey): effecient append for DOMStrings
                let mut new_line = prefix.to_owned();

                new_line.push_str(&insert_lines[0]);
                insert_lines[0] = DOMString::from(new_line);

                let last_insert_lines_index = insert_lines.len() - 1;
                self.edit_point.index = insert_lines[last_insert_lines_index].len();
                self.edit_point.line = begin.line + last_insert_lines_index;

                // FIXME(ajeffrey): effecient append for DOMStrings
                insert_lines[last_insert_lines_index].push_str(suffix);

                let mut new_lines = vec!();
                new_lines.extend_from_slice(lines_prefix);
                new_lines.extend_from_slice(&insert_lines);
                new_lines.extend_from_slice(lines_suffix);
                new_lines
            };

            self.lines = new_lines;
        }
        self.assert_ok_selection();
    }

    /// Return the length in UTF-8 bytes of the current line under the editing point.
    pub fn current_line_length(&self) -> usize {
        self.lines[self.edit_point.line].len()
    }

    /// Adjust the editing point position by a given of lines. The resulting column is
    /// as close to the original column position as possible.
    pub fn adjust_vertical(&mut self, adjust: isize, select: Selection) {
        if !self.multiline {
            return;
        }

        if select == Selection::Selected {
            if self.selection_begin.is_none() {
                self.selection_begin = Some(self.edit_point);
            }
        } else {
            self.clear_selection();
        }

        assert!(self.edit_point.line < self.lines.len());

        let target_line: isize = self.edit_point.line as isize + adjust;

        if target_line < 0 {
            self.edit_point.index = 0;
            self.edit_point.line = 0;
            return;
        } else if target_line as usize >= self.lines.len() {
            self.edit_point.line = self.lines.len() - 1;
            self.edit_point.index = self.current_line_length();
            return;
        }


        let col = self.lines[self.edit_point.line][..self.edit_point.index].chars().count();

        self.edit_point.line = target_line as usize;
        self.edit_point.index = len_of_first_n_chars(&self.lines[self.edit_point.line], col);
        self.assert_ok_selection();
    }

    /// Adjust the editing point position by a given number of bytes. If the adjustment
    /// requested is larger than is available in the current line, the editing point is
    /// adjusted vertically and the process repeats with the remaining adjustment requested.
    pub fn adjust_horizontal(&mut self, adjust: isize, select: Selection) {
        let direction = if adjust >= 0 { Direction::Forward } else { Direction::Backward };
        if self.adjust_selection_for_horizontal_change(direction, select) {
            return
        }
        self.perform_horizontal_adjustment(adjust, select);
    }

    pub fn adjust_horizontal_by_one(&mut self, direction: Direction, select: Selection) {
        if self.adjust_selection_for_horizontal_change(direction, select) {
            return
        }
        let adjust = {
            let current_line = &self.lines[self.edit_point.line];
            // FIXME: We adjust by one code point, but it proably should be one grapheme cluster
            // https://github.com/unicode-rs/unicode-segmentation
            match direction {
                Direction::Forward => {
                    match current_line[self.edit_point.index..].chars().next() {
                        Some(c) => c.len_utf8() as isize,
                        None => 1,  // Going to the next line is a "one byte" offset
                    }
                }
                Direction::Backward => {
                    match current_line[..self.edit_point.index].chars().next_back() {
                        Some(c) => -(c.len_utf8() as isize),
                        None => -1,  // Going to the previous line is a "one byte" offset
                    }
                }
            }
        };
        self.perform_horizontal_adjustment(adjust, select);
    }

    /// Return whether to cancel the caret move
    fn adjust_selection_for_horizontal_change(&mut self, adjust: Direction, select: Selection)
                                              -> bool {
        if select == Selection::Selected {
            if self.selection_begin.is_none() {
                self.selection_begin = Some(self.edit_point);
            }
        } else {
            if let Some((begin, end)) = self.get_sorted_selection() {
                self.edit_point = match adjust {
                    Direction::Backward => begin,
                    Direction::Forward => end,
                };
                self.clear_selection();
                return true
            }
        }
        false
    }

    fn perform_horizontal_adjustment(&mut self, adjust: isize, select: Selection) {
        if adjust < 0 {
            let remaining = self.edit_point.index;
            if adjust.abs() as usize > remaining && self.edit_point.line > 0 {
                self.adjust_vertical(-1, select);
                self.edit_point.index = self.current_line_length();
                self.adjust_horizontal(adjust + remaining as isize + 1, select);
            } else {
                self.edit_point.index = max(0, self.edit_point.index as isize + adjust) as usize;
            }
        } else {
            let remaining = self.current_line_length() - self.edit_point.index;
            if adjust as usize > remaining && self.lines.len() > self.edit_point.line + 1 {
                self.adjust_vertical(1, select);
                self.edit_point.index = 0;
                // one shift is consumed by the change of line, hence the -1
                self.adjust_horizontal(adjust - remaining as isize - 1, select);
            } else {
                self.edit_point.index = min(self.current_line_length(),
                                            self.edit_point.index + adjust as usize);
            }
        }
        self.assert_ok_selection();
    }

    /// Deal with a newline input.
    pub fn handle_return(&mut self) -> KeyReaction {
        if !self.multiline {
            KeyReaction::TriggerDefaultAction
        } else {
            self.insert_char('\n');
            KeyReaction::DispatchInput
        }
    }

    /// Select all text in the input control.
    pub fn select_all(&mut self) {
        self.selection_begin = Some(TextPoint {
            line: 0,
            index: 0,
        });
        let last_line = self.lines.len() - 1;
        self.edit_point.line = last_line;
        self.edit_point.index = self.lines[last_line].len();
        self.assert_ok_selection();
    }

    /// Remove the current selection.
    pub fn clear_selection(&mut self) {
        self.selection_begin = None;
    }

    /// Process a given `KeyboardEvent` and return an action for the caller to execute.
    pub fn handle_keydown(&mut self, event: &KeyboardEvent) -> KeyReaction {
        if let Some(key) = event.get_key() {
            self.handle_keydown_aux(event.printable(), key, event.get_key_modifiers())
        } else {
            KeyReaction::Nothing
        }
    }

    pub fn handle_keydown_aux(&mut self,
                              printable: Option<char>,
                              key: Key,
                              mods: KeyModifiers) -> KeyReaction {
        let maybe_select = if mods.contains(SHIFT) { Selection::Selected } else { Selection::NotSelected };
        match (printable, key) {
            (Some('a'), _) if is_control_key(mods) => {
                self.select_all();
                KeyReaction::RedrawSelection
            },
            (Some('c'), _) if is_control_key(mods) => {
                if let Some(text) = self.get_selection_text() {
                    self.clipboard_provider.set_clipboard_contents(text);
                }
                KeyReaction::DispatchInput
            },
            (Some('v'), _) if is_control_key(mods) => {
                let contents = self.clipboard_provider.clipboard_contents();
                self.insert_string(contents);
                KeyReaction::DispatchInput
            },
            (Some(c), _) => {
                self.insert_char(c);
                KeyReaction::DispatchInput
            }
            (None, Key::Delete) => {
                self.delete_char(Direction::Forward);
                KeyReaction::DispatchInput
            }
            (None, Key::Backspace) => {
                self.delete_char(Direction::Backward);
                KeyReaction::DispatchInput
            }
            (None, Key::Left) => {
                self.adjust_horizontal_by_one(Direction::Backward, maybe_select);
                KeyReaction::RedrawSelection
            }
            (None, Key::Right) => {
                self.adjust_horizontal_by_one(Direction::Forward, maybe_select);
                KeyReaction::RedrawSelection
            }
            (None, Key::Up) => {
                self.adjust_vertical(-1, maybe_select);
                KeyReaction::RedrawSelection
            }
            (None, Key::Down) => {
                self.adjust_vertical(1, maybe_select);
                KeyReaction::RedrawSelection
            }
            (None, Key::Enter) | (None, Key::KpEnter) => self.handle_return(),
            (None, Key::Home) => {
                self.edit_point.index = 0;
                KeyReaction::RedrawSelection
            }
            (None, Key::End) => {
                self.edit_point.index = self.current_line_length();
                self.assert_ok_selection();
                KeyReaction::RedrawSelection
            }
            (None, Key::PageUp) => {
                self.adjust_vertical(-28, maybe_select);
                KeyReaction::RedrawSelection
            }
            (None, Key::PageDown) => {
                self.adjust_vertical(28, maybe_select);
                KeyReaction::RedrawSelection
            }
            _ => KeyReaction::Nothing,
        }
    }

    /// Whether the content is empty.
    pub fn is_empty(&self) -> bool {
        self.lines.len() <= 1 && self.lines.get(0).map_or(true, |line| line.is_empty())
    }

    /// The length of the content in bytes.
    pub fn len(&self) -> usize {
        self.lines.iter().fold(0, |m, l| {
            m + l.len() + 1 // + 1 for the '\n'
        }) - 1
    }

    /// The length of the content in bytes.
    pub fn utf16_len(&self) -> usize {
        self.lines.iter().fold(0, |m, l| {
            m + l.chars().map(char::len_utf16).sum::<usize>() + 1 // + 1 for the '\n'
        }) - 1
    }

    /// The length of the content in chars.
    pub fn char_count(&self) -> usize {
        self.lines.iter().fold(0, |m, l| {
            m + l.chars().count() + 1 // + 1 for the '\n'
        }) - 1
    }

    /// Get the current contents of the text input. Multiple lines are joined by \n.
    pub fn get_content(&self) -> DOMString {
        let mut content = "".to_owned();
        for (i, line) in self.lines.iter().enumerate() {
            content.push_str(&line);
            if i < self.lines.len() - 1 {
                content.push('\n');
            }
        }
        DOMString::from(content)
    }

    /// Set the current contents of the text input. If this is control supports multiple lines,
    /// any \n encountered will be stripped and force a new logical line.
    pub fn set_content(&mut self, content: DOMString) {
        self.lines = if self.multiline {
            content.split('\n').map(DOMString::from).collect()
        } else {
            vec!(content)
        };
        self.edit_point.line = min(self.edit_point.line, self.lines.len() - 1);
        self.edit_point.index = min(self.edit_point.index, self.current_line_length());
        self.selection_begin = None;
        self.assert_ok_selection();
    }

    /// Get the insertion point as a byte offset from the start of the content.
    pub fn get_absolute_insertion_point(&self) -> usize {
        self.get_absolute_point_for_text_point(&self.edit_point)
    }

    /// Convert a TextPoint into a byte offset from the start of the content.
    pub fn get_absolute_point_for_text_point(&self, text_point: &TextPoint) -> usize {
        self.lines.iter().enumerate().fold(0, |acc, (i, val)| {
            if i < text_point.line {
                acc + val.len() + 1 // +1 for the \n
            } else {
                acc
            }
        }) + text_point.index
    }

    /// Convert a byte offset from the start of the content into a TextPoint.
    pub fn get_text_point_for_absolute_point(&self, abs_point: usize) -> TextPoint {
        let mut index = abs_point;
        let mut line = 0;

        let last_line_idx = self.lines.len() - 1;
        self.lines.iter().enumerate().fold(0, |acc, (i, val)| {
            if i != last_line_idx {
                let line_end = max(val.len(), 1);
                let new_acc = acc + line_end;
                if abs_point > new_acc && index > line_end {
                    index -= line_end + 1;
                    line += 1;
                }
                new_acc
            } else {
                acc
            }
        });

        TextPoint {
            line: line, index: index
        }
    }

    pub fn set_selection_range(&mut self, start: u32, end: u32) {
        let mut start = start as usize;
        let mut end = end as usize;
        let text_end = self.get_content().len();

        if end > text_end {
            end = text_end;
        }
        if start > end {
            start = end;
        }

        match self.selection_direction {
            SelectionDirection::None |
            SelectionDirection::Forward => {
                self.selection_begin = Some(self.get_text_point_for_absolute_point(start));
                self.edit_point = self.get_text_point_for_absolute_point(end);
            },
            SelectionDirection::Backward => {
                self.selection_begin = Some(self.get_text_point_for_absolute_point(end));
                self.edit_point = self.get_text_point_for_absolute_point(start);
            }
        }
        self.assert_ok_selection();
    }

    pub fn get_selection_start(&self) -> u32 {
        let selection_start = match self.selection_begin {
            Some(selection_begin_point) => {
                self.get_absolute_point_for_text_point(&selection_begin_point)
            },
            None => self.get_absolute_insertion_point()
        };

        selection_start as u32
    }
}
