#!/bin/bash
# tmux-util — small utilities for managing tmux sessions.
#
# Subcommands:
#   go <name>      attach to <name> if it exists, otherwise create it
#   pick           fzf-driven session switcher
#   ls             opinionated session listing (attached, idle, windows, cwd)
#   find <pattern> locate panes whose foreground process matches <pattern>
#   reap           gracefully exit every unattached session (skipping aiv-*)
#   rename         fzf-pick a session, prompt for a new name, rename it
#
# Run with no arguments to print this help.

set -uo pipefail

# -----------------------------------------------------------------------------
# Usage
# -----------------------------------------------------------------------------

usage() {
    cat <<'EOF'
Usage: tmux-util <subcommand> [args]

Subcommands:
  go <name>      Attach to session <name>; create it (in $PWD) if missing.
  pick           Fzf-driven session switcher.
  ls             List sessions with attached / idle / window / cwd columns.
  find <pattern> Locate panes whose foreground process matches <pattern>.
  reap           Send SIGHUP to every unattached session's panes and close
                 the session. Sessions matching $TMUX_UTIL_REAP_SKIP
                 (default: ^aiv-) are skipped.
  rename         Pick a session via fzf, prompt for a new name, rename it.

Run with no arguments to print this help.
EOF
}

# -----------------------------------------------------------------------------
# rename
# -----------------------------------------------------------------------------

cmd_rename() {
    local sessions
    sessions=$(tmux list-sessions \
        -F '#{session_attached} #{session_name}' 2>/dev/null || true)
    if [ -z "$sessions" ]; then
        echo "No tmux sessions to rename."
        return 0
    fi

    local choice
    choice=$(echo "$sessions" | awk '{
        state = ($1 == "1") ? "attached" : "detached"
        printf "%-9s %s\n", state, $2
    }' | fzf --header="Pick a session to rename" | awk '{print $2}')

    if [ -z "$choice" ]; then
        # User cancelled.
        return 0
    fi

    local new_name
    printf 'New name for "%s": ' "$choice"
    read -r new_name

    if [ -z "$new_name" ]; then
        echo "tmux-util rename: empty new name, cancelled." >&2
        return 1
    fi

    if [ "$new_name" = "$choice" ]; then
        echo "tmux-util rename: new name same as old, no change."
        return 0
    fi

    if tmux has-session -t "=$new_name" 2>/dev/null; then
        echo "tmux-util rename: a session named '$new_name' already exists." >&2
        return 1
    fi

    tmux rename-session -t "$choice" "$new_name"
    echo "Renamed: $choice -> $new_name"
}

# -----------------------------------------------------------------------------
# pick
# -----------------------------------------------------------------------------

cmd_pick() {
    local sessions
    sessions=$(tmux list-sessions \
        -F '#{session_attached} #{session_name}' 2>/dev/null || true)
    if [ -z "$sessions" ]; then
        echo "No tmux sessions to pick from."
        return 0
    fi

    # Format for fzf: "<state>  <name>" — name is the second field of the
    # selection line, which we recover after fzf returns.
    local choice
    choice=$(echo "$sessions" | awk '{
        state = ($1 == "1") ? "attached" : "detached"
        printf "%-9s %s\n", state, $2
    }' | fzf --header="Pick a tmux session" | awk '{print $2}')

    if [ -z "$choice" ]; then
        # User cancelled (Ctrl-C or Esc); fzf exits 130, the pipeline
        # returns empty.
        return 0
    fi

    if [ -n "${TMUX:-}" ]; then
        tmux switch-client -t "$choice"
    else
        tmux attach-session -t "$choice"
    fi
}

# -----------------------------------------------------------------------------
# find
# -----------------------------------------------------------------------------

cmd_find() {
    local pattern="${1:-}"
    if [ -z "$pattern" ]; then
        echo "tmux-util find: missing pattern" >&2
        echo "Usage: tmux-util find <pattern>" >&2
        return 2
    fi

    local matches
    matches=$(tmux list-panes -a \
        -F '#{session_name}:#{window_index}.#{pane_index} #{pane_current_command}' \
        2>/dev/null | grep -E "$pattern" || true)

    if [ -z "$matches" ]; then
        return 1
    fi
    echo "$matches"
}

# -----------------------------------------------------------------------------
# go
# -----------------------------------------------------------------------------

cmd_go() {
    local name="${1:-}"
    if [ -z "$name" ]; then
        echo "tmux-util go: missing session name" >&2
        echo "Usage: tmux-util go <name>" >&2
        return 2
    fi

    # `=name` forces exact match in `tmux has-session` (otherwise tmux does
    # prefix matching, which would let `go foo` attach to a session named
    # `foobar`).
    if tmux has-session -t "=$name" 2>/dev/null; then
        if [ -n "${TMUX:-}" ]; then
            tmux switch-client -t "$name"
        else
            tmux attach-session -t "$name"
        fi
    else
        if [ -n "${TMUX:-}" ]; then
            tmux new-session -d -s "$name" -c "$PWD"
            tmux switch-client -t "$name"
        else
            tmux new-session -s "$name" -c "$PWD"
        fi
    fi
}

# -----------------------------------------------------------------------------
# ls
# -----------------------------------------------------------------------------

# Render seconds as a short human duration (e.g. "5s", "12m", "3h", "2d").
format_idle() {
    local s="$1"
    if [ "$s" -lt 60 ]; then
        echo "${s}s"
    elif [ "$s" -lt 3600 ]; then
        echo "$((s / 60))m"
    elif [ "$s" -lt 86400 ]; then
        echo "$((s / 3600))h"
    else
        echo "$((s / 86400))d"
    fi
}

cmd_ls() {
    local sessions
    sessions=$(tmux list-sessions \
        -F '#{session_attached} #{session_name} #{session_activity} #{session_windows}' \
        2>/dev/null || true)

    if [ -z "$sessions" ]; then
        echo "No tmux sessions."
        return 0
    fi

    local now="${TMUX_UTIL_NOW:-$(date +%s)}"

    {
        printf 'STATE\tNAME\tIDLE\tWINDOWS\tCWD\n'
        local attached name activity windows state idle_str cwd
        while IFS=' ' read -r attached name activity windows; do
            [ -n "$name" ] || continue
            state="detached"
            [ "$attached" -gt 0 ] && state="attached"
            idle_str=$(format_idle "$((now - activity))")
            cwd=$(tmux display -p -t "$name" '#{pane_current_path}' 2>/dev/null || echo "?")
            # Replace leading $HOME with ~ for display.
            if [ -n "${HOME:-}" ] && [ "${cwd#$HOME}" != "$cwd" ]; then
                cwd="~${cwd#$HOME}"
            fi
            printf '%s\t%s\t%s\t%s\t%s\n' "$state" "$name" "$idle_str" "$windows" "$cwd"
        done <<<"$sessions"
    } | column -t -s $'\t'
}

# -----------------------------------------------------------------------------
# Reap
# -----------------------------------------------------------------------------

cmd_reap() {
    local skip="${TMUX_UTIL_REAP_SKIP:-^aiv-}"
    local sessions
    sessions=$(tmux list-sessions -F '#{session_name} #{session_attached}' 2>/dev/null \
               | awk '$2 == 0 {print $1}' \
               | grep -vE "$skip" || true)

    if [ -z "$sessions" ]; then
        echo "No unattached sessions to reap."
        return 0
    fi

    local s pids
    while IFS= read -r s; do
        [ -n "$s" ] || continue
        echo "Reaping: $s"
        pids=$(tmux list-panes -s -t "$s" -F '#{pane_pid}' 2>/dev/null)
        if [ -n "$pids" ]; then
            echo "$pids" | xargs -r kill -HUP
        fi
        # Give the session a moment to wind down naturally.
        local i
        for i in 1 2 3; do
            tmux has-session -t "$s" 2>/dev/null || break
            sleep 1
        done
        if tmux has-session -t "$s" 2>/dev/null; then
            echo "  still alive, force killing"
            tmux kill-session -t "$s"
        fi
    done <<<"$sessions"
}

# -----------------------------------------------------------------------------
# Dispatch
# -----------------------------------------------------------------------------

main() {
    if [ "$#" -eq 0 ]; then
        usage
        return 0
    fi

    local sub="$1"
    shift

    case "$sub" in
        -h|--help|help)
            usage
            ;;
        reap)
            cmd_reap "$@"
            ;;
        ls)
            cmd_ls "$@"
            ;;
        go)
            cmd_go "$@"
            ;;
        find)
            cmd_find "$@"
            ;;
        pick)
            cmd_pick "$@"
            ;;
        rename)
            cmd_rename "$@"
            ;;
        *)
            echo "tmux-util: unknown subcommand: $sub" >&2
            usage >&2
            return 2
            ;;
    esac
}

main "$@"