#!/bin/bash

# doppio-ssh
#
# Script to run doppio-web over an SSH connection and automatically set up port
# forwarding by finding an open TCP port on the local host and connecting it to the
# remote port chosen by the Doppio server. The script will then open a local web browser
# to view Doppio on the forwarded connection.
#
# By default, this script assumes that 'doppio-web' is available on the PATH on the
# remote host. If it is not, set COMMAND below with the absolute path to the doppio-web
# executable.
#
# Usage is exactly like ssh. All arguments are passed through directly to ssh itself.
# In particular, if you would like to launch X-forwarded applications from Doppio, you
# should pass the -X or -Y argument, or enable the ForwardX11 or ForwardX11Trusted
# option in your ssh config.
#
# Example:
#   doppio-ssh -Y user@host

# Ensure bash exits on error
set -euo pipefail

# The command to run on the remote server
COMMAND="bash -lic 'doppio-web --no-browser'"

# Ensure at least one argument is provided
if [[ $# -lt 1 ]]; then
    echo "Usage: $0 [ssh options] [user@]host"
    exit 1
fi

# Set up a file name for the SSH Control Master
mkdir -p ~/.ssh/controlmasters
CONTROL_SOCKET="$HOME/.ssh/controlmasters/ssh_mux_$$"

# Clean up control socket on exit
cleanup() {
    ssh -S "$CONTROL_SOCKET" -O exit "$@" 2>/dev/null || true
    rm -f "$CONTROL_SOCKET"
}
trap cleanup EXIT

# Generate a random port in the range 1024–65535 using $RANDOM
random_port() {
    local rand=$(( RANDOM + RANDOM )) # Combine two RANDOMs to get up to full range of port numbers
    echo $((1024 + (rand % 64512))) # 64512 = 65535 - 1023 = number of non-privileged ports
}

# Check if nc is available
if command -v nc >/dev/null 2>&1; then
    is_port_free() {
        local port=$1
        ! nc -z 127.0.0.1 "$port" 2>/dev/null
    }
else
    is_port_free() {
        local port=$1
        # Try to bind using a dummy listener (fallback method)
        (echo >"/dev/tcp/127.0.0.1/$port") >/dev/null 2>&1 && return 1 || return 0
    }
fi

# Function to find a free port and establish forwarding
start_port_forwarding() {
    local remote_port=$1
    local try_port=$1
    while :; do
        if is_port_free "$try_port"; then
            ssh -S "$CONTROL_SOCKET" -O forward -L "$try_port:127.0.0.1:$remote_port" "$@" 2>/dev/null
            LOCAL_PORT=$try_port
            printf "Forwarded local port %s to remote port %s\r\n" "$LOCAL_PORT" "$remote_port"
            break
        fi
        try_port=$(random_port)
    done
}

open_browser() {
    local url="$1"
    printf "\r\n"
    printf "doppio-ssh is opening your browser to navigate to: %s\r\n" "$url"
    printf "\r\n"
    printf "If the browser doesn't open, copy and paste the link instead, or\r\n"
    printf "depending on your terminal you might be able to open the link with\r\n"
    printf "Ctrl-click or Cmd-click.\r\n"
    printf "\r\n"
    printf "You will need to copy the access token and paste it into the Doppio\r\n"
    printf "authorisation page. Note: do not press Ctrl+C to copy it because that\r\n"
    printf "will shut down the Doppio server! Use Ctrl+Shift+C, or Cmd+C, or select\r\n"
    printf "and middle mouse click, or whatever other method works on your operating\r\n"
    printf "system.\r\n"
    printf "\r\n"
    if command -v xdg-open >/dev/null 2>&1; then
        xdg-open "$url" >/dev/null 2>&1
    elif command -v open >/dev/null 2>&1; then
        open "$url" >/dev/null 2>&1
    elif grep -qEi "(Microsoft|WSL)" /proc/version &>/dev/null; then
        powershell.exe start "$url" >/dev/null 2>&1
    else
        printf "Could not open your browser. Please open the link manually.\r\n"
        printf "\r\n"
    fi
}

FORWARDING_STARTED=0

# Run the SSH command and process output
ssh -M -S "$CONTROL_SOCKET" "$@" -t "$COMMAND" 2> >(while IFS= read -r line; do
    echo "$line" >&2
done) | while IFS= read -r line; do
    echo "$line"

    if [[ "$FORWARDING_STARTED" -eq 0 ]]; then
        # Strip out ANSI escape sequences
        clean_line=$(echo "$line" | sed -E 's/\x1B\[[0-9;]*[mK]//g')
        if [[ "$clean_line" =~ ^Server\ URL:\ [a-zA-Z]+://[a-zA-Z0-9._-]+:([0-9]+) ]]; then
            REMOTE_PORT="${BASH_REMATCH[1]}"
            FORWARDING_STARTED=1

            # Start port forwarding in the background to avoid missing output lines
            {
                start_port_forwarding "$REMOTE_PORT"
                open_browser "http://127.0.0.1:$LOCAL_PORT/"

                # Prevent new SSH multiplexed connections, but keep the master alive
                ssh -S "$CONTROL_SOCKET" -O stop "$@" 2>/dev/null || true
            } &
        fi
    fi
done

echo "Finished, exiting doppio-ssh"