//! Application-level "miscellaneous" state: scroll, input buffer,
//! overlay stack, toasts, editor, and autocomplete.
use std::path::PathBuf;
use std::sync::Arc;
use tokio::sync::RwLock;
use super::types::Overlay;

/// A shared, async-writable cache of directory entries, used to avoid
/// re-reading a directory every render frame.
#[derive(Clone)]
pub struct DirCache {
    entries: Arc<RwLock<Vec<PathBuf>>>,
}

impl DirCache {
    /// Create an empty `DirCache`.
    pub fn new() -> Self {
        DirCache {
            entries: Arc::new(RwLock::new(Vec::new())),
        }
    }

    /// Replace the cached entries (async write).
    pub async fn set(&self, paths: Vec<PathBuf>) {
        let mut w = self.entries.write().await;
        *w = paths;
    }
}

/// A shared, whole-workspace file-path index used for `@file` mention
/// autocomplete. Built once by a background thread at startup (see
/// `AppStateRest::new`) and incrementally appended to when tools create
/// new files (see `tool/fs/write.rs`).
#[derive(Clone)]
pub struct MentionIndex {
    entries: Arc<std::sync::RwLock<Vec<String>>>,
}

impl MentionIndex {
    /// Create an empty `MentionIndex`.
    pub fn new() -> Self {
        MentionIndex {
            entries: Arc::new(std::sync::RwLock::new(Vec::new())),
        }
    }

    /// Replace the indexed paths (used by the startup background walk).
    pub fn set(&self, paths: Vec<String>) {
        if let Ok(mut w) = self.entries.write() {
            *w = paths;
        }
    }

    /// Append a single newly created file's path (used by the `write` tool).
    pub fn push(&self, path: String) {
        if let Ok(mut w) = self.entries.write() {
            w.push(path);
        }
    }

    /// Take a snapshot of the current indexed paths for fuzzy matching.
    pub fn snapshot(&self) -> Vec<String> {
        self.entries.read().map(|r| r.clone()).unwrap_or_default()
    }
}

/// Which source populated the autocomplete dropdown, since selecting a
/// candidate is spliced into the buffer differently for each.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum AutocompleteKind {
    Command,
    FileMention,
}

/// Manages the viewport scroll offset.
#[derive(Debug, Clone)]
pub struct ScrollState {
    pub offset: usize,
    pub max_visible: usize,
}

impl ScrollState {
    /// Create a `ScrollState` with zero offset and 30 rows visible.
    pub fn new() -> Self {
        ScrollState {
            offset: 0,
            max_visible: 30,
        }
    }

    /// Scroll the viewport up by `amount` lines (increasing the offset).
    /// Scroll the viewport up by `amount` lines (increasing the offset).
    pub fn scroll_up(&mut self, amount: usize) {
        self.offset = self.offset.saturating_add(amount);
    }

    /// Scroll the viewport down by `amount` lines (decreasing the offset).
    pub fn scroll_down(&mut self, amount: usize) {
        self.offset = self.offset.saturating_sub(amount);
    }

    /// Update the maximum number of visible lines.
    pub fn set_max_visible(&mut self, max: usize) {
        self.max_visible = max;
    }
}

/// The user's input buffer, cursor position, history, and autocomplete
/// state for the chat prompt.
#[derive(Debug, Clone)]
pub struct InputState {
    pub buffer: String,
    pub cursor: usize,
    pub history: Vec<String>,
    pub history_idx: Option<usize>,
    pub autocomplete_prefix: String,
    pub autocomplete_candidates: Vec<String>,
    pub autocomplete_idx: usize,
    pub autocomplete_visible: bool,
    pub autocomplete_kind: AutocompleteKind,
    pub mention_start: usize,
    pub history_file: Option<PathBuf>,
}

const COMMANDS: &[&str] = &[
    "/help",
    "/quit",
    "/clear",
    "/login",
    "/login zen",
    "/login openai",
    "/edit",
    "/mcp add",
    "/model",
    "/model ls",
    "/model add",

    "/todo",
    "/usage",
    "/compact",
];

impl InputState {
    /// Create an empty input state with no buffer, no history, and no
    /// autocomplete.
    pub fn new() -> Self {
        InputState {
            buffer: String::new(),
            cursor: 0,
            history: Vec::new(),
            history_idx: None,
            autocomplete_prefix: String::new(),
            autocomplete_candidates: Vec::new(),
            autocomplete_idx: 0,
            autocomplete_visible: false,
            autocomplete_kind: AutocompleteKind::Command,
            mention_start: 0,
            history_file: None,
        }
    }

    /// Hide the autocomplete dropdown and clear its state.
    pub fn close_autocomplete(&mut self) {
        self.autocomplete_visible = false;
        self.autocomplete_candidates.clear();
        self.autocomplete_prefix.clear();
        self.autocomplete_idx = 0;
        self.autocomplete_kind = AutocompleteKind::Command;
        self.mention_start = 0;
    }

    /// Open or refresh the autocomplete dropdown by filtering `COMMANDS`
    /// against the current buffer prefix.
    ///
    /// Flow: if buffer is empty or doesn't start with `/`, close and return
    /// → filter `COMMANDS` by prefix match → store candidates → set
    /// `autocomplete_visible` if any candidates found.
    pub fn open_autocomplete(&mut self) {
        let trimmed = self.buffer.trim().to_string();
        if trimmed.is_empty() || !trimmed.starts_with('/') {
            self.close_autocomplete();
            return;
        }

        let prefix = trimmed.to_lowercase();
        self.autocomplete_candidates = COMMANDS
            .iter()
            .filter(|c| c.starts_with(&prefix))
            .map(std::string::ToString::to_string)
            .collect();
        self.autocomplete_prefix = prefix;
        self.autocomplete_kind = AutocompleteKind::Command;
        self.autocomplete_idx = 0;
        self.autocomplete_visible = !self.autocomplete_candidates.is_empty();
    }

    /// Find the `@mention` token (if any) immediately before the cursor.
    ///
    /// Flow: find the nearest `@` before the cursor → if there's whitespace
    /// between that `@` and the cursor, no trigger → the `@` only counts as
    /// a trigger if it's at buffer start or immediately preceded by
    /// whitespace (so `foo@bar` mid-word never triggers).
    ///
    /// Return: `Some((byte offset of '@', query text between '@' and cursor))`
    /// or `None` if the cursor isn't inside a mention token.
    pub fn mention_query_at_cursor(&self) -> Option<(usize, String)> {
        let before_cursor = &self.buffer[..self.cursor];
        let at_pos = before_cursor.rfind('@')?;
        let between = &before_cursor[at_pos + 1..];
        if between.chars().any(char::is_whitespace) {
            return None;
        }
        let boundary_ok = at_pos == 0
            || before_cursor[..at_pos].chars().next_back().is_some_and(char::is_whitespace);
        if !boundary_ok {
            return None;
        }
        Some((at_pos, between.to_string()))
    }

    /// Open or refresh the `@file` mention dropdown from `files`, fuzzy-matched
    /// against the mention query at the cursor.
    ///
    /// Flow: `mention_query_at_cursor` finds the trigger `@` and query text →
    /// if none, close and return → otherwise fuzzy-match `query` against
    /// `files` via `nucleo-matcher`, keep the top 10 by score.
    pub fn open_mention_autocomplete(&mut self, files: &[String]) {
        let Some((start, query)) = self.mention_query_at_cursor() else {
            self.close_autocomplete();
            return;
        };
        use nucleo_matcher::{Config, Matcher};
        use nucleo_matcher::pattern::{CaseMatching, Normalization, Pattern};
        let mut matcher = Matcher::new(Config::DEFAULT.match_paths());
        let pattern = Pattern::parse(&query, CaseMatching::Smart, Normalization::Smart);
        let matches = pattern.match_list(files.iter(), &mut matcher);
        self.autocomplete_candidates = matches.into_iter().take(10).map(|(f, _)| f.clone()).collect();
        self.autocomplete_kind = AutocompleteKind::FileMention;
        self.mention_start = start;
        self.autocomplete_idx = 0;
        self.autocomplete_visible = !self.autocomplete_candidates.is_empty();
    }

    /// Move the autocomplete selection up (forward=false) or down (forward=true).
    /// Wraps around at the boundaries.
    pub fn cycle_autocomplete(&mut self, forward: bool) {
        let n = self.autocomplete_candidates.len();
        if n == 0 { return; }
        if forward {
            self.autocomplete_idx = (self.autocomplete_idx + 1) % n;
        } else {
            self.autocomplete_idx = if self.autocomplete_idx == 0 { n - 1 } else { self.autocomplete_idx - 1 };
        }
    }

    /// Accept the currently selected autocomplete candidate.
    ///
    /// `Command` candidates replace the whole buffer; `FileMention`
    /// candidates splice `@path ` in at the mention's start position so the
    /// rest of the sentence around it is preserved.
    ///
    /// Return: `true` if a candidate was selected, `false` if none existed.
    pub fn select_autocomplete(&mut self) -> bool {
        let Some(candidate) = self.autocomplete_candidates.get(self.autocomplete_idx).cloned() else {
            return false;
        };
        match self.autocomplete_kind {
            AutocompleteKind::Command => {
                self.buffer = candidate;
                self.cursor = self.buffer.len();
            }
            AutocompleteKind::FileMention => {
                // Cursor movement (Left/Right) does not close the dropdown, so
                // by the time Enter is pressed `mention_start` may no longer
                // describe a valid range against the current cursor/buffer
                // (e.g. the cursor moved left past the '@'). Splicing on a
                // stale range would panic (`start > end`) or, even when it
                // doesn't panic, produce a nonsensical replacement. Treat a
                // stale mention context the same as "nothing selected".
                if self.cursor < self.mention_start || self.mention_start > self.buffer.len() {
                    self.close_autocomplete();
                    return false;
                }
                let replacement = format!("@{candidate} ");
                self.buffer.replace_range(self.mention_start..self.cursor, &replacement);
                self.cursor = self.mention_start + replacement.len();
            }
        }
        self.close_autocomplete();
        true
    }

    /// Legacy inline tab-complete — opens the dropdown on first Tab press,
    /// then cycles forward on subsequent presses.
    pub fn tab_complete(&mut self) {
        // Legacy inline tab-complete — used as a fallback when the dropdown
        // isn't visible yet. Opens the dropdown on the first Tab press.
        if self.autocomplete_visible {
            self.cycle_autocomplete(true);
        } else {
            self.open_autocomplete();
        }
    }

    /// Move the cursor left by one character (if not at the start).
    pub fn char_left(&mut self) {
        if self.cursor > 0 {
            self.cursor -= 1;
        }
    }

    /// Move the cursor right by one character (if not at the end).
    pub fn char_right(&mut self) {
        if self.cursor < self.buffer.len() {
            self.cursor += 1;
        }
    }

    /// Insert a character at the cursor position.
    pub fn insert(&mut self, c: char) {
        self.buffer.insert(self.cursor, c);
        self.cursor += 1;
    }

    /// Delete the character to the left of the cursor (backspace).
    pub fn delete_left(&mut self) {
        if self.cursor > 0 {
            self.cursor -= 1;
            self.buffer.remove(self.cursor);
        }
    }

    /// Delete the character at the cursor position (forward delete).
    pub fn delete_right(&mut self) {
        if self.cursor < self.buffer.len() {
            self.buffer.remove(self.cursor);
        }
    }

    pub fn submit(&mut self) -> String {
        let result = self.buffer.clone();
        if !result.is_empty() {
            if self.history.last() != Some(&result) {
                self.history.push(result.clone());
                if let Some(ref path) = self.history_file {
                    if let Ok(mut file) = std::fs::OpenOptions::new()
                        .create(true)
                        .append(true)
                        .open(path)
                    {
                        use std::io::Write;
                        let _ = writeln!(file, "{result}");
                    }
                }
            }
            self.history_idx = None;
        }
        self.buffer.clear();
        self.cursor = 0;
        result
    }

    /// Navigate backward through input history.
    pub fn history_up(&mut self) {
        if self.history.is_empty() {
            return;
        }
        let idx = match self.history_idx {
            Some(i) if i > 0 => i - 1,
            None => self.history.len() - 1,
            Some(_) => return,
        };
        self.history_idx = Some(idx);
        self.buffer = self.history[idx].clone();
        self.cursor = self.buffer.len();
    }

    /// Navigate forward through input history (back toward the newest entry).
    pub fn history_down(&mut self) {
        match self.history_idx {
            Some(i) if i < self.history.len() - 1 => {
                let idx = i + 1;
                self.history_idx = Some(idx);
                self.buffer = self.history[idx].clone();
                self.cursor = self.buffer.len();
            }
            Some(_) => {
                self.history_idx = None;
                self.buffer.clear();
                self.cursor = 0;
            }
            None => {}
        }
    }
}

/// The "miscellaneous" slice of app state: which overlay is showing,
/// toasts, thinking/connected flags, effort level, editor state, and tick.
#[derive(Debug, Clone)]
pub struct MiscState {
    pub overlay: Overlay,
    pub toasts: Vec<super::types::Toast>,
    pub last_staleness_sweep_ms: i64,
    pub thinking: bool,
    pub effort_level: usize,
    pub selected_index: usize,
    pub editor: Option<super::super::mode::editor::EditorState>,
    pub api_connected: bool,
    #[allow(dead_code)]
    pub api_context_length: Option<u32>,
    pub tick_count: u64,
    pub todo_content: String,
    pub lesson_running: bool,
    pub pending_clipboard_copy: Option<String>,
}

impl MiscState {
    /// Create a fresh `MiscState` with no overlay, no toasts, and default
    /// effort level 1.
    pub fn new() -> Self {
        MiscState {
            overlay: Overlay::None,
            toasts: Vec::new(),
            last_staleness_sweep_ms: 0,
            thinking: false,
            effort_level: 1,
            selected_index: 0,
            editor: None,
            api_connected: false,
            api_context_length: None,
            tick_count: 0,
            todo_content: String::new(),
            lesson_running: false,
            pending_clipboard_copy: None,
        }
    }

    pub fn push_toast(&mut self, toast: super::types::Toast) {
        self.toasts.push(toast);
    }

    /// Remove and return all toasts whose lifetime has expired at `now_ms`.
    ///
    /// Return: the expired toasts (after removal).
    pub fn drain_expired_toasts(&mut self, now_ms: i64) -> Vec<super::types::Toast> {
        let expired: Vec<_> = self.toasts.iter().filter(|t| t.expired(now_ms)).cloned().collect();
        self.toasts.retain(|t| !t.expired(now_ms));
        expired
    }
}

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

    fn input_with(buffer: &str, cursor: usize) -> InputState {
        let mut input = InputState::new();
        input.buffer = buffer.to_string();
        input.cursor = cursor;
        input
    }

    #[test]
    fn mention_at_buffer_start_triggers() {
        let input = input_with("@mai", 4);
        assert_eq!(input.mention_query_at_cursor(), Some((0, "mai".to_string())));
    }

    #[test]
    fn mention_after_space_mid_sentence_triggers() {
        let input = input_with("look at @read", 13);
        assert_eq!(input.mention_query_at_cursor(), Some((8, "read".to_string())));
    }

    #[test]
    fn mid_word_at_does_not_trigger() {
        let input = input_with("foo@bar", 7);
        assert_eq!(input.mention_query_at_cursor(), None);
    }

    #[test]
    fn whitespace_between_at_and_cursor_does_not_trigger() {
        let input = input_with("@foo bar", 8);
        assert_eq!(input.mention_query_at_cursor(), None);
    }

    #[test]
    fn select_file_mention_splices_into_buffer() {
        let mut input = input_with("look at @rea and fix it", 12);
        input.autocomplete_candidates = vec!["src/main.rs".to_string()];
        input.autocomplete_idx = 0;
        input.autocomplete_kind = AutocompleteKind::FileMention;
        input.mention_start = 8;
        assert!(input.select_autocomplete());
        assert_eq!(input.buffer, "look at @src/main.rs  and fix it");
        assert_eq!(input.cursor, 8 + "@src/main.rs ".len());
    }

    #[test]
    fn select_file_mention_with_stale_cursor_before_mention_start_does_not_panic() {
        // Simulates: user typed "foo @rea" (mention_start = 4, cursor = 8,
        // dropdown open), then pressed Left 5 times without closing the
        // dropdown, moving the cursor to byte 3 (before the '@'). Selecting
        // now must not panic on `replace_range(4..3, ...)`.
        let mut input = input_with("foo @rea", 3);
        input.autocomplete_candidates = vec!["src/main.rs".to_string()];
        input.autocomplete_idx = 0;
        input.autocomplete_kind = AutocompleteKind::FileMention;
        input.mention_start = 4;
        assert!(!input.select_autocomplete());
        assert!(!input.autocomplete_visible);
    }

    #[test]
    fn select_command_still_replaces_whole_buffer() {
        let mut input = input_with("/mo", 3);
        input.autocomplete_candidates = vec!["/model".to_string()];
        input.autocomplete_idx = 0;
        input.autocomplete_kind = AutocompleteKind::Command;
        assert!(input.select_autocomplete());
        assert_eq!(input.buffer, "/model");
        assert_eq!(input.cursor, "/model".len());
    }

    #[test]
    fn misc_state_starts_with_no_pending_clipboard_copy() {
        let misc = MiscState::new();
        assert!(misc.pending_clipboard_copy.is_none());
    }
}