//! tmuxrdr: the tab row drawn the way tmux draws its status line, for
//! `ui.tab_style = "tmux"`. tmux 3.7c's defaults, as `tmux show -g` reports
//! them: status-left "[#{session_name}] " cut to status-left-length 10;
//! window-status-format "#I:#W#{?window_flags,#{window_flags}, }"; one space
//! between windows; left-justified; plain text in the status line's colours.
//!
//! herdr's render_tab_bar (tabs.rs) keeps the layout, scrolling, mouse hits
//! and the + button, and asks this module for each tab's width, text and
//! style, and to draw the session at the left -- three one-line hooks there.
//!
//! #I is the tab's place in the tab bar, from 1 (base-index 1, as this
//! machine's tmux.conf sets it). #W is the window name: a tab named by hand
//! keeps its name, any other is named after its active pane's directory, as
//! the tmux.conf has it (automatic-rename-format '#{b:pane_current_path}').
//! The server sends only the pane focused overall, not each tab's active one,
//! so this remembers the pane each tab last had focused while it was shown,
//! and falls back to the tab's first pane. It also remembers each workspace's
//! previous tab, for tmux's last-window flag "-". All of it lives in this
//! client process and needs nothing from the server, so it works against a
//! stock herdr server as well.

use std::collections::HashMap;
use std::sync::{LazyLock, Mutex};

use unicode_width::UnicodeWidthChar;

use crate::protocol::ClientShellPane;

use super::*;

/// tmux's status-left-length default.
const STATUS_LEFT_LENGTH: u16 = 10;

/// What this client has seen, across renders. Keyed by herdr's ids, which are
/// unique within a server; a client showing several machines could see the
/// same id twice, and would then mix their history -- a flag, not a failure.
#[derive(Default)]
struct Seen {
    /// workspace -> the tab last seen focused in it
    current: HashMap<String, String>,
    /// workspace -> the tab focused before that: tmux's last window
    last: HashMap<String, String>,
    /// tab -> the pane last seen focused in it
    active_pane: HashMap<String, String>,
}

impl Seen {
    fn observe(&mut self, snapshot: &ClientShellSnapshot) {
        let (Some(workspace), Some(tab)) = (
            snapshot.focused_workspace_id.as_ref(),
            snapshot.focused_tab_id.as_ref(),
        ) else {
            return;
        };
        if let Some(previous) = self.current.insert(workspace.clone(), tab.clone()) {
            if previous != *tab {
                self.last.insert(workspace.clone(), previous);
            }
        }
        if let Some(pane) = snapshot.focused_pane_id.as_ref() {
            self.active_pane.insert(tab.clone(), pane.clone());
        }
    }
}

static SEEN: LazyLock<Mutex<Seen>> = LazyLock::new(Default::default);

/// The tab row's labels for one render, in the order render_tab_bar has its
/// tabs, and the session text for the left.
pub(super) struct TmuxTabs {
    labels: Vec<String>,
    session: String,
}

impl TmuxTabs {
    pub(super) fn new(snapshot: &ClientShellSnapshot, tabs: &[&ClientShellTab]) -> Self {
        let mut seen = SEEN.lock().unwrap_or_else(|poisoned| poisoned.into_inner());
        seen.observe(snapshot);
        let workspace = snapshot.focused_workspace_id.as_deref();
        let last = workspace.and_then(|workspace| seen.last.get(workspace));
        let labels = tabs
            .iter()
            .enumerate()
            .map(|(index, tab)| {
                let name = if tab.custom_label {
                    tab.label.clone()
                } else {
                    window_name(snapshot, tab, &seen).unwrap_or_else(|| tab.label.clone())
                };
                window_status(
                    index + 1,
                    &name,
                    tab.focused,
                    last == Some(&tab.tab_id),
                    tab.zoomed,
                )
            })
            .collect();
        let session_name = snapshot
            .workspaces
            .iter()
            .find(|candidate| Some(candidate.workspace_id.as_str()) == workspace)
            .map_or("", |candidate| candidate.label.as_str());
        Self {
            labels,
            session: truncate_cells(&format!("[{session_name}] "), STATUS_LEFT_LENGTH),
        }
    }

    pub(super) fn width(&self, index: usize) -> u16 {
        display_width(&self.labels[index])
    }

    pub(super) fn cell(
        &self,
        index: usize,
        tab: &ClientShellTab,
        palette: &Palette,
    ) -> (String, Style) {
        // tmux's status line: no fill of its own, the current window brighter.
        let fg = if tab.focused {
            palette.text
        } else {
            palette.overlay1
        };
        (
            self.labels[index].clone(),
            Style::default().fg(fg).bg(palette.panel_bg),
        )
    }

    /// Draws the session at the left of `content` and returns what is left.
    pub(super) fn render_session(
        &self,
        buffer: &mut Buffer,
        content: Rect,
        palette: &Palette,
    ) -> Rect {
        let width = display_width(&self.session).min(content.width);
        put_text(
            buffer,
            content.x,
            content.y,
            width,
            &self.session,
            Style::default().fg(palette.overlay1).bg(palette.panel_bg),
        );
        Rect {
            x: content.x.saturating_add(width),
            width: content.width.saturating_sub(width),
            ..content
        }
    }
}

/// tmux's "#I:#W#{?window_flags,#{window_flags}, }": its flags in tmux's
/// order -- current "*" or last "-", then zoomed "Z" -- or a space when none.
fn window_status(index: usize, name: &str, current: bool, last: bool, zoomed: bool) -> String {
    let mut flags = String::new();
    if current {
        flags.push('*');
    } else if last {
        flags.push('-');
    }
    if zoomed {
        flags.push('Z');
    }
    if flags.is_empty() {
        flags.push(' ');
    }
    format!("{index}:{name}{flags}")
}

/// #{b:pane_current_path} for a tab: its active pane's foreground directory,
/// basename only.
fn window_name(
    snapshot: &ClientShellSnapshot,
    tab: &ClientShellTab,
    seen: &Seen,
) -> Option<String> {
    let remembered = if tab.focused {
        snapshot.focused_pane_id.as_deref()
    } else {
        seen.active_pane.get(&tab.tab_id).map(String::as_str)
    };
    let in_tab = |pane: &&ClientShellPane| pane.tab_id == tab.tab_id;
    let pane = remembered
        .and_then(|id| {
            snapshot
                .panes
                .iter()
                .filter(in_tab)
                .find(|pane| pane.pane_id == id)
        })
        .or_else(|| snapshot.panes.iter().find(in_tab))?;
    let dir = pane.foreground_cwd.as_deref().or(pane.cwd.as_deref())?;
    Some(basename(dir))
}

/// basename(3): the last component; "/" for the root.
fn basename(path: &str) -> String {
    let trimmed = path.trim_end_matches('/');
    if trimmed.is_empty() {
        return "/".into();
    }
    trimmed.rsplit('/').next().unwrap_or(trimmed).to_string()
}

/// The longest prefix of `text` that fits in `cells` columns, as tmux cuts
/// status-left.
fn truncate_cells(text: &str, cells: u16) -> String {
    let mut used = 0_u16;
    let mut out = String::new();
    for ch in text.chars() {
        let width = UnicodeWidthChar::width(ch).unwrap_or(0) as u16;
        if used + width > cells {
            break;
        }
        used += width;
        out.push(ch);
    }
    out
}

#[cfg(test)]
mod tests {
    use super::{basename, truncate_cells, window_status};

    #[test]
    fn window_status_matches_tmux_default_format() {
        assert_eq!(window_status(1, "zsh", true, false, false), "1:zsh*");
        assert_eq!(window_status(2, "vim", false, true, false), "2:vim-");
        assert_eq!(window_status(3, "logs", false, false, false), "3:logs ");
        assert_eq!(window_status(4, "x", true, false, true), "4:x*Z");
        assert_eq!(window_status(5, "x", false, true, true), "5:x-Z");
        assert_eq!(window_status(6, "x", false, false, true), "6:xZ");
    }

    #[test]
    fn basename_is_tmux_b_modifier() {
        assert_eq!(basename("/Users/sz/x"), "x");
        assert_eq!(basename("/private/tmp/"), "tmp");
        assert_eq!(basename("/"), "/");
    }

    #[test]
    fn session_is_cut_to_status_left_length() {
        assert_eq!(truncate_cells("[0] ", 10), "[0] ");
        assert_eq!(truncate_cells("[delta-channels] ", 10), "[delta-cha");
        assert_eq!(truncate_cells("[日本語ab] ", 10), "[日本語ab]");
    }
}