#!/bin/bash
# slow-server - start a web server that responds after a configurable delay
#
# Usage:
#   slow-server [port]
#   slow-server -h
#
# Options:
#   port         Port to listen on (default: 8080)
#   -h, --help   Show help message
#
# Starts a socat-based HTTP server where the last path segment of each request
# is the delay in milliseconds. Requests without a numeric path return 404
# e.g. `curl http://localhost:8080/2500` responds after ~2.5 seconds

_slow_server() (
    local SCRIPT_NAME; SCRIPT_NAME="$(basename "${BASH_SOURCE[0]}")"
    case "${BASH_SOURCE[0]}" in /dev/*|/proc/*) SCRIPT_NAME="" ;; esac
    case "$SCRIPT_NAME" in ""|bash|sh|zsh|dash) SCRIPT_NAME="slow-server" ;; esac

    _error() { echo "[ERR][$SCRIPT_NAME] $*" >&2; }

    _show_help() {
        local s; [ -t 1 ] && s=$'\033[4m'
        local r; [ -t 1 ] && r=$'\033[24m'
        cat <<EOF
NAME
  $SCRIPT_NAME - start a web server that responds after a configurable delay
SYNOPSIS
  $SCRIPT_NAME [${s}port${r}]
  $SCRIPT_NAME -h
DESCRIPTION
  Starts a socat-based HTTP server on the given port (default 8080).
  The last path segment of each request is the delay in milliseconds.
  Requests without a numeric path return 404.
EXAMPLES
  $SCRIPT_NAME 3000
  curl http://localhost:3000/2500   # responds after ~2.5 seconds
OPTIONS
  ${s}port${r}   Port to listen on (default: 8080)
  -h, --help   Show this help message
EXIT STATUS
  0  Success (server exited cleanly)
  3  Dependency error (socat missing)
  *  socat exit code on other failures
DEPENDENCIES
  socat, sleep (must support fractional seconds)
EOF
    }

    # Function invoked by socat below on each request. Exported for socat's
    # SYSTEM: subshell to see it
    # shellcheck disable=SC2317,SC2329 # "Command appears to be unreachable. Check usage (or ignore if invoked indirectly)." / "This function is never invoked. Check usage (or ignored if invoked indirectly)." -- invoked indirectly via socat SYSTEM:_slow_response
    _slow_response() {
        _is_number() {
            case "$1" in
                ''|*[!0-9]*)
                    return 1 ;; # not a number
                *)
                    return 0 ;; # is a number
            esac
        }
        local method
        local path
        local _version
        read -r method path _version
        local last; last="$(basename "$path")"
        printf %s "$method $path ($last)" >&2
        # Ignore other paths, return not found
        if ! _is_number "$last"; then
            echo " [ignored]" >&2 # append to previous line
            printf 'HTTP/1.1 404 Not Found\r\n\r\n'
            return 0
        else
            local delay_ms="$last"
            printf '\n' >&2 # move to next line
        fi
        local seconds="$((delay_ms / 1000)).$((delay_ms % 1000))"
        sleep "$seconds"
        printf 'HTTP/1.1 200 OK\r\n\r\n%s\n' "$last"
        echo "Done: $method $path ($delay_ms)" >&2
        unset -f _is_number
    }

    case "$1" in
        -h|--help) _show_help; return 0 ;;
    esac

    # Function arguments
    local port="${1:-8080}"

    # Check for socat dependency
    if ! command -v socat >/dev/null 2>&1; then
        _error "socat is required"
        return 3
    fi

    export -f _slow_response # exported for socat

    # Start simple server
    echo "Starting server at http://localhost:$port"
    socat "TCP-LISTEN:$port,fork,reuseaddr" "SYSTEM:_slow_response"
    # _slow_response and any exports die with the wrapper subshell on return
)

_slow_server "$@"
__slow_server_rc=$?
unset -f _slow_server
if [ -n "${BASH_SOURCE[0]}" ] && [ "${BASH_SOURCE[0]}" != "$0" ]; then
    eval "unset __slow_server_rc; return $__slow_server_rc"
fi
eval "unset __slow_server_rc; exit $__slow_server_rc"