use std::cell::RefCell;
use std::ops::Range;
use std::rc::Rc;

use unicode_segmentation::UnicodeSegmentation;

use gpui::prelude::FluentBuilder as _;
use gpui::{
    App, AppContext as _, Bounds, ClipboardItem, Context, DispatchPhase, ElementId, Entity,
    EntityInputHandler, Font, InteractiveElement as _, IntoElement, KeyDownEvent, MouseButton,
    MouseDownEvent, MouseMoveEvent, MouseUpEvent, ParentElement as _, Pixels, RenderOnce, Role,
    SharedString, StatefulInteractiveElement as _, Styled as _, TextAlign, TextRun, UTF16Selection,
    Window, canvas, div, fill, point, px,
};
use gpui_native_theme::ActiveTheme as _;

use crate::common::h_flex;

/// Input layout information for hit testing and caret positioning.
struct InputLayout {
    line: gpui::ShapedLine,
    bounds: Bounds<Pixels>,
    /// Where the text was painted inside `bounds` (padding minus scroll).
    origin: gpui::Point<Pixels>,
}

/// Input state for a single-line text field.
pub struct InputState {
    text: String,
    /// The caret's byte offset.
    cursor: usize,
    /// The byte offset the selection extends from.
    anchor: usize,
    /// The byte range of in-progress IME composition, if any.
    marked_range: Option<Range<usize>>,
    focus_handle: gpui::FocusHandle,
    layout: Rc<RefCell<Option<InputLayout>>>,
}

impl InputState {
    fn new_inner(cx: &mut App) -> Self {
        Self {
            text: String::new(),
            cursor: 0,
            anchor: 0,
            marked_range: None,
            focus_handle: cx.focus_handle(),
            layout: Rc::new(RefCell::new(None)),
        }
    }

    /// Creates the state entity for an application-owned input.
    pub fn new(cx: &mut App) -> Entity<Self> {
        cx.new(|cx| Self::new_inner(cx))
    }

    /// Creates the state entity with initial text, caret at the end.
    pub fn new_with_text(text: impl Into<String>, cx: &mut App) -> Entity<Self> {
        let text = text.into();
        cx.new(|cx| {
            let mut state = Self::new_inner(cx);
            state.text = text;
            state.cursor = state.text.len();
            state.anchor = state.cursor;
            state
        })
    }

    /// The current text.
    pub fn value(&self) -> &str {
        &self.text
    }

    /// Replaces the whole value and collapses the selection to the end.
    pub fn set_value<V>(&mut self, value: V, window: &mut Window, cx: &mut Context<Self>)
    where
        V: Into<String>,
    {
        self.text = value.into();
        self.cursor = self.text.len();
        self.anchor = self.cursor;
        self.marked_range = None;
        self.notify(window, cx);
    }

    /// The focus handle, for applications that focus the field programmatically.
    pub fn focus_handle(&self) -> gpui::FocusHandle {
        self.focus_handle.clone()
    }

    /// The selected byte range of the buffer.
    fn selection(&self) -> Range<usize> {
        self.cursor.min(self.anchor)..self.cursor.max(self.anchor)
    }

    fn notify(&mut self, window: &mut Window, cx: &mut Context<Self>) {
        cx.notify();
        window.notify_text_input_changed(&self.focus_handle);
    }

    /// Replaces a byte range with `text` and collapses the caret to its end.
    fn replace_range(
        &mut self,
        range: Range<usize>,
        text: &str,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        self.text.replace_range(range.clone(), text);
        self.cursor = range.start + text.len();
        self.anchor = self.cursor;
        self.marked_range = None;
        self.notify(window, cx);
    }

    /// Deletes the selection, or one character/word before the caret.
    fn delete_backward(&mut self, word: bool, window: &mut Window, cx: &mut Context<Self>) {
        if !self.selection().is_empty() {
            let range = self.selection();
            self.replace_range(range, "", window, cx);
        } else if self.cursor > 0 {
            let start = if word {
                previous_word_start(&self.text, self.cursor)
            } else {
                previous_grapheme_start(&self.text, self.cursor)
            };
            self.replace_range(start..self.cursor, "", window, cx);
        }
    }

    /// Deletes the selection, or one character/word after the caret.
    fn delete_forward(&mut self, word: bool, window: &mut Window, cx: &mut Context<Self>) {
        if !self.selection().is_empty() {
            let range = self.selection();
            self.replace_range(range, "", window, cx);
        } else if self.cursor < self.text.len() {
            let end = if word {
                next_word_end(&self.text, self.cursor)
            } else {
                next_grapheme_start(&self.text, self.cursor)
            };
            self.replace_range(self.cursor..end, "", window, cx);
        }
    }

    /// Moves the caret, extending the selection when `extend`.
    fn move_cursor(
        &mut self,
        to: usize,
        extend: bool,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        self.cursor = to.clamp(0, self.text.len());
        if !extend {
            self.anchor = self.cursor;
        }
        self.notify(window, cx);
    }

    /// Selects `range`.
    fn select_range(&mut self, range: Range<usize>, window: &mut Window, cx: &mut Context<Self>) {
        self.anchor = range.start;
        self.cursor = range.end;
        self.notify(window, cx);
    }

    /// Copies or cuts the selection to the clipboard.
    fn copy_or_cut(&mut self, cut: bool, window: &mut Window, cx: &mut Context<Self>) {
        let range = self.selection();
        if range.is_empty() {
            return;
        }
        cx.write_to_clipboard(ClipboardItem::new_string(
            self.text[range.clone()].to_string(),
        ));
        if cut {
            self.replace_range(range, "", window, cx);
        }
    }
}

impl EntityInputHandler for InputState {
    fn text_for_range(
        &mut self,
        range_utf16: Range<usize>,
        adjusted_range: &mut Option<Range<usize>>,
        _window: &mut Window,
        _cx: &mut Context<Self>,
    ) -> Option<String> {
        let range = utf16_range_to_utf8(&self.text, range_utf16);
        adjusted_range.replace(utf8_range_to_utf16(&self.text, range.clone()));
        Some(self.text[range].to_string())
    }

    fn selected_text_range(
        &mut self,
        _ignore_disabled_input: bool,
        _window: &mut Window,
        _cx: &mut Context<Self>,
    ) -> Option<UTF16Selection> {
        Some(UTF16Selection {
            range: utf8_range_to_utf16(&self.text, self.selection()),
            reversed: self.cursor < self.anchor,
        })
    }

    fn marked_text_range(
        &self,
        _window: &mut Window,
        _cx: &mut Context<Self>,
    ) -> Option<Range<usize>> {
        self.marked_range
            .clone()
            .map(|range| utf8_range_to_utf16(&self.text, range))
    }

    fn unmark_text(&mut self, _window: &mut Window, _cx: &mut Context<Self>) {
        self.marked_range = None;
    }

    fn replace_text_in_range(
        &mut self,
        range_utf16: Option<Range<usize>>,
        text: &str,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        let range = range_utf16.map_or_else(
            || self.selection(),
            |range| utf16_range_to_utf8(&self.text, range),
        );
        self.replace_range(range, text, window, cx);
    }

    fn replace_and_mark_text_in_range(
        &mut self,
        range_utf16: Option<Range<usize>>,
        new_text: &str,
        new_selected_range_utf16: Option<Range<usize>>,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        let range = range_utf16.map_or_else(
            || self.selection(),
            |range| utf16_range_to_utf8(&self.text, range),
        );
        self.text.replace_range(range.clone(), new_text);
        let start = range.start;
        let end = start + new_text.len();
        self.marked_range = Some(start..end);
        let selected_end = new_selected_range_utf16
            .map(|selected| utf16_range_to_utf8(&self.text, selected).end)
            .unwrap_or(end);
        self.cursor = selected_end;
        self.anchor = selected_end;
        self.notify(window, cx);
    }

    fn bounds_for_range(
        &mut self,
        range_utf16: Range<usize>,
        _element_bounds: Bounds<Pixels>,
        _window: &mut Window,
        _cx: &mut Context<Self>,
    ) -> Option<Bounds<Pixels>> {
        let layout = self.layout.borrow();
        let layout = layout.as_ref()?;
        let start = layout
            .line
            .x_for_index(utf16_to_utf8_offset(&self.text, range_utf16.start));
        let end = layout
            .line
            .x_for_index(utf16_to_utf8_offset(&self.text, range_utf16.end));
        // `origin` is already an absolute window point.
        Some(Bounds::from_corners(
            point(layout.origin.x + start.min(end), layout.bounds.top()),
            point(layout.origin.x + start.max(end), layout.bounds.bottom()),
        ))
    }

    fn character_index_for_point(
        &mut self,
        window_point: gpui::Point<Pixels>,
        _window: &mut Window,
        _cx: &mut Context<Self>,
    ) -> Option<usize> {
        let layout = self.layout.borrow();
        let layout = layout.as_ref()?;
        Some(
            layout
                .line
                .closest_index_for_x(window_point.x - layout.origin.x)
                .min(self.text.len()),
        )
    }

    fn text_length_utf16(
        &mut self,
        _window: &mut Window,
        _cx: &mut Context<Self>,
    ) -> Option<usize> {
        Some(self.text.encode_utf16().count())
    }
}

/// Floors `index` to the nearest grapheme-cluster boundary at or below it.
fn previous_grapheme_start(text: &str, index: usize) -> usize {
    text.grapheme_indices(true)
        .rev()
        .find(|(offset, _)| *offset < index)
        .map(|(offset, _)| offset)
        .unwrap_or(0)
}

/// Advances `index` to the next grapheme-cluster boundary.
fn next_grapheme_start(text: &str, index: usize) -> usize {
    text.grapheme_indices(true)
        .find(|(offset, _)| *offset > index)
        .map(|(offset, _)| offset)
        .unwrap_or(text.len())
}

/// The start of the word before `from`.
fn previous_word_start(text: &str, from: usize) -> usize {
    let mut best = 0;
    for (offset, word) in text.split_word_bound_indices() {
        if offset >= from {
            break;
        }
        if !word.starts_with(char::is_whitespace) {
            best = offset;
        }
    }
    best
}

/// The end of the word after `from`.
fn next_word_end(text: &str, from: usize) -> usize {
    for (offset, word) in text.split_word_bound_indices() {
        let end = offset + word.len();
        if end > from && !word.starts_with(char::is_whitespace) {
            return end;
        }
    }
    text.len()
}

/// Converts a UTF-16 offset into a UTF-8 byte offset.
fn utf16_to_utf8_offset(text: &str, utf16_offset: usize) -> usize {
    let mut utf16_count = 0;
    for (byte_offset, char) in text.char_indices() {
        if utf16_count >= utf16_offset {
            return byte_offset;
        }
        utf16_count += char.len_utf16();
    }
    text.len()
}

/// Converts a UTF-8 byte range to a UTF-16 range.
fn utf8_range_to_utf16(text: &str, range: Range<usize>) -> Range<usize> {
    utf16_to_utf8_offset(text, range.start)..utf16_to_utf8_offset(text, range.end)
}

/// Converts a UTF-16 range to a UTF-8 byte range.
fn utf16_range_to_utf8(text: &str, range: Range<usize>) -> Range<usize> {
    utf16_to_utf8_offset(text, range.start)..utf16_to_utf8_offset(text, range.end)
}

/// A single-line text field bound to an application-owned [`InputState`].
#[derive(IntoElement)]
pub struct Input {
    id: ElementId,
    state: Entity<InputState>,
    placeholder: SharedString,
    disabled: bool,
    a11y_label: Option<SharedString>,
}

impl Input {
    /// Creates a text field bound to `state`.
    pub fn new<I>(id: I, state: Entity<InputState>) -> Self
    where
        I: Into<ElementId>,
    {
        Self {
            id: id.into(),
            state,
            placeholder: SharedString::default(),
            disabled: false,
            a11y_label: None,
        }
    }

    /// Sets the placeholder shown when the field is empty and unfocused.
    pub fn placeholder<P>(mut self, placeholder: P) -> Self
    where
        P: Into<SharedString>,
    {
        self.placeholder = placeholder.into();
        self
    }

    /// Renders the field inert, unfocusable, and dimmed; disabled always wins.
    pub fn disabled(mut self, disabled: bool) -> Self {
        self.disabled = disabled;
        self
    }

    /// Overrides the accessibility label.
    pub fn accessibility_label<L>(mut self, label: L) -> Self
    where
        L: Into<SharedString>,
    {
        self.a11y_label = Some(label.into());
        self
    }
}

impl RenderOnce for Input {
    fn render(self, window: &mut Window, cx: &mut App) -> impl IntoElement {
        let theme = cx.theme();
        let colors = theme.colors;
        let radius = theme.radius;
        let focus_handle = self.state.read(cx).focus_handle.clone();
        let layout_cell = self.state.read(cx).layout.clone();

        // Drag selection crosses frames, so it lives in keyed element state.
        let dragging = window.use_keyed_state("input-dragging", cx, |_, _| false);
        let down_dragging = dragging.clone();
        let paint_dragging = dragging.clone();

        let focused = focus_handle.is_focused(window);
        let is_empty = self.state.read(cx).text.is_empty();

        let key_state = self.state.clone();
        let key_focus = focus_handle.clone();
        let down_state = self.state.clone();
        let down_layout = layout_cell.clone();

        let fallback_label = self
            .a11y_label
            .clone()
            .or_else(|| (!self.placeholder.is_empty()).then_some(self.placeholder.clone()))
            .unwrap_or_else(|| SharedString::from(self.id.to_string()));

        h_flex()
            .id(self.id.clone())
            .relative()
            .overflow_hidden()
            .w_full()
            .h_7()
            .px_2()
            .rounded(radius.control)
            .border_1()
            .border_color(colors.border)
            .bg(colors.input)
            .text_sm()
            .text_color(colors.foreground)
            .role(Role::TextInput)
            .aria_label(fallback_label)
            .when(self.disabled, |input| input.opacity(0.5))
            .when(!self.disabled, |input| {
                input.track_focus(&focus_handle).tab_stop(true)
            })
            .when(focused, |input| input.border_color(colors.ring))
            .when(is_empty && !focused, |input| {
                input.child(
                    div()
                        .text_color(colors.muted_foreground)
                        .child(self.placeholder.clone()),
                )
            })
            .child(
                canvas(
                    {
                        let state = self.state.clone();

                        move |_bounds, window, cx| {
                            let text = state.read(cx).text.clone();
                            let text_style = window.text_style();
                            let font = Font {
                                family: text_style.font_family.clone(),
                                features: text_style.font_features.clone(),
                                weight: text_style.font_weight,
                                style: text_style.font_style,
                                fallbacks: text_style.font_fallbacks.clone(),
                            };
                            let font_size = text_style.font_size.to_pixels(window.rem_size());
                            let runs = [TextRun {
                                len: text.len(),
                                font,
                                color: text_style.color,
                                background_color: None,
                                underline: None,
                                strikethrough: None,
                            }];
                            window
                                .text_system()
                                .shape_line(text.into(), font_size, &runs, None)
                        }
                    },
                    {
                        let state = self.state.clone();
                        let layout_cell = layout_cell.clone();
                        let focus = focus_handle.clone();
                        let dragging = paint_dragging;
                        let disabled = self.disabled;
                        // `line` comes from the prepaint closure above.
                        move |bounds, line, window, cx| {
                            let (font_size, line_height) = {
                                let text_style = window.text_style();
                                (
                                    text_style.font_size.to_pixels(window.rem_size()),
                                    text_style
                                        .line_height
                                        .to_pixels(text_style.font_size, window.rem_size()),
                                )
                            };

                            let padding = px(8.);
                            let selection = state.read(cx).selection();
                            let caret_x = line.x_for_index(selection.end);

                            // Horizontal scroll keeps the caret inside the field.
                            let visible = bounds.size.width - padding * 2.0;
                            let scroll_x = if caret_x > visible {
                                caret_x - visible
                            } else {
                                Pixels::ZERO
                            };

                            let origin = point(
                                bounds.left() + padding - scroll_x,
                                bounds.top() + (bounds.size.height - line_height) / 2.0,
                            );
                            *layout_cell.borrow_mut() = Some(InputLayout {
                                line,
                                bounds,
                                origin,
                            });

                            let layout = layout_cell.borrow();
                            let layout = layout.as_ref().expect("layout just stored");
                            let line = &layout.line;
                            let origin = layout.origin;

                            if focused && !selection.is_empty() {
                                let start_x = line.x_for_index(selection.start);
                                let rect = Bounds::from_corners(
                                    point(origin.x + start_x.min(caret_x), bounds.top() + px(1.)),
                                    point(
                                        origin.x + start_x.max(caret_x),
                                        bounds.bottom() - px(1.),
                                    ),
                                );
                                window.paint_quad(fill(rect, colors.selection));
                            }

                            let _ =
                                line.paint(origin, line_height, TextAlign::Left, None, window, cx);

                            if focused && selection.is_empty() {
                                let caret_top = origin.y + (line_height - font_size) / 2.0;
                                let caret = Bounds::from_corners(
                                    point(origin.x + caret_x, caret_top),
                                    point(origin.x + caret_x + px(1.5), caret_top + font_size),
                                );
                                window.paint_quad(fill(caret, colors.foreground));
                            }

                            if disabled {
                                return;
                            }

                            window.handle_input(
                                &focus,
                                gpui::ElementInputHandler::new(bounds, state.clone()),
                                cx,
                            );

                            if *dragging.read(cx) {
                                window.on_mouse_event({
                                    let state = state.clone();
                                    let layout_cell = layout_cell.clone();
                                    move |event: &MouseMoveEvent, phase, window, cx| {
                                        if phase != DispatchPhase::Bubble
                                            || event.pressed_button != Some(MouseButton::Left)
                                        {
                                            return;
                                        }
                                        state.update(cx, |state, cx| {
                                            let index = index_at_x(
                                                &layout_cell,
                                                event.position.x,
                                                state.text.len(),
                                            );
                                            state.cursor = index;
                                            state.notify(window, cx);
                                        });
                                    }
                                });
                            }
                            window.on_mouse_event({
                                let dragging = dragging.clone();
                                move |event: &MouseUpEvent, phase, _window, cx| {
                                    if phase != DispatchPhase::Bubble
                                        || event.button != MouseButton::Left
                                    {
                                        return;
                                    }
                                    dragging.update(cx, |dragging, _| *dragging = false);
                                }
                            });
                        }
                    },
                )
                .absolute()
                .inset_0(),
            )
            .when(!self.disabled, |input| {
                input
                    .on_mouse_down(MouseButton::Left, {
                        let state = down_state;
                        let layout_cell = down_layout;
                        let dragging = down_dragging;
                        move |event: &MouseDownEvent, window, cx| {
                            dragging.update(cx, |dragging, _| *dragging = true);
                            state.update(cx, |state, cx| {
                                let index =
                                    index_at_x(&layout_cell, event.position.x, state.text.len());
                                if event.click_count == 2 {
                                    let start = previous_word_start(&state.text, index);
                                    let end = next_word_end(&state.text, index);
                                    state.select_range(start..end, window, cx);
                                } else if event.modifiers.shift {
                                    state.cursor = index;
                                    state.notify(window, cx);
                                } else {
                                    state.cursor = index;
                                    state.anchor = index;
                                    state.notify(window, cx);
                                }
                            });
                        }
                    })
                    .on_key_down({
                        move |event: &KeyDownEvent, window, cx| {
                            if !key_focus.contains_focused(window, cx) {
                                return;
                            }
                            let keystroke = &event.keystroke;
                            let command =
                                keystroke.modifiers.platform || keystroke.modifiers.control;
                            key_state.update(cx, |state, cx| match keystroke.key.as_str() {
                                "left" => {
                                    let to = if command || keystroke.modifiers.alt {
                                        previous_word_start(&state.text, state.cursor)
                                    } else {
                                        previous_grapheme_start(&state.text, state.cursor)
                                    };
                                    state.move_cursor(to, keystroke.modifiers.shift, window, cx);
                                    cx.stop_propagation();
                                }
                                "right" => {
                                    let to = if command || keystroke.modifiers.alt {
                                        next_word_end(&state.text, state.cursor)
                                    } else {
                                        next_grapheme_start(&state.text, state.cursor)
                                    };
                                    state.move_cursor(to, keystroke.modifiers.shift, window, cx);
                                    cx.stop_propagation();
                                }
                                "home" => {
                                    state.move_cursor(0, keystroke.modifiers.shift, window, cx);
                                    cx.stop_propagation();
                                }
                                "end" => {
                                    state.move_cursor(
                                        state.text.len(),
                                        keystroke.modifiers.shift,
                                        window,
                                        cx,
                                    );
                                    cx.stop_propagation();
                                }
                                "backspace" => {
                                    state.delete_backward(
                                        command || keystroke.modifiers.alt,
                                        window,
                                        cx,
                                    );
                                    cx.stop_propagation();
                                }
                                "delete" => {
                                    state.delete_forward(
                                        command || keystroke.modifiers.alt,
                                        window,
                                        cx,
                                    );
                                    cx.stop_propagation();
                                }
                                "a" if command => {
                                    let len = state.text.len();
                                    state.select_range(0..len, window, cx);
                                    cx.stop_propagation();
                                }
                                "c" if command => {
                                    state.copy_or_cut(false, window, cx);
                                    cx.stop_propagation();
                                }
                                "x" if command => {
                                    state.copy_or_cut(true, window, cx);
                                    cx.stop_propagation();
                                }
                                "v" if command => {
                                    if let Some(item) = cx.read_from_clipboard()
                                        && let Some(text) = item.text()
                                    {
                                        let range = state.selection();
                                        state.replace_range(range, &text, window, cx);
                                    }
                                    cx.stop_propagation();
                                }
                                "enter" | "tab" => {}
                                _ => {
                                    if let Some(text) = &keystroke.key_char
                                        && !command
                                    {
                                        let range = state.selection();
                                        state.replace_range(range, text, window, cx);
                                        cx.stop_propagation();
                                    }
                                }
                            });
                        }
                    })
            })
    }
}

/// The text index at window x, using the last painted layout.
fn index_at_x(layout_cell: &RefCell<Option<InputLayout>>, x: Pixels, text_len: usize) -> usize {
    let layout = layout_cell.borrow();
    let Some(layout) = layout.as_ref() else {
        return 0;
    };
    layout
        .line
        .closest_index_for_x(x - layout.origin.x)
        .min(text_len)
}