#!/bin/bash

#==BEGIN function definition==
yell() { echo "$0: $*" >&2; } # print script path and all args to stderr
die() { yell "$*"; exit 111; } # same as yell() but non-zero exit status
try() { "$@" || die "cannot $*"; } # runs args as command, reports args if command fails
update_pi() {
    # Desc: Calculates control variable (CV) given setpoint (SP) and
    #   process variable (PV). Uses proportional integral (PI)
    #   control.
    # Usage: update_pi arg1 arg2 arg3 arg4 arg5 arg6
    # Version: 0.1.3
    # Input: arg1: path_loop_name (control loop name path)
    #        arg2: var_pv (process variable)
    #        arg3: var_sp (set point)
    #        arg4: tune_p (proportional tuning factor)
    #        arg5: tune_i (integral tuning factor)
    #        arg6: var_cv_bias (control variable bias; prevents initial jerk)
    # Output: stdout: var_cv (control variable)
    #         file: path_var_pv
    #         file: path_var_sp
    #         file: path_tune_p
    #         file: path_tune_i
    #         file: path_var_cv
    #         file: path_sum (saves updated sum state)
    # Example: update_pi /dev/shm/DC1.AC 1.0 3.0 2.0 3.0 
    # Depends: bc, gnu coreutils 8.30, yell(), try()
    local var_sp var_pv var_cv;
    local tune_p tune_i;
    local term_p term_i;
    local error sum sum_cand;
    local path_sum path_var_sp path_var_pv path_tune_p path_tune_i;

    path_loop_name="$1";

    path_var_pv="$path_loop_name".pv
    var_pv="$2"; # read provided process variable
    
    path_var_sp="$path_loop_name".sp
    if [[ -f "$path_var_sp" ]]; then
	var_sp="$(cat "$path_var_sp" | head -n1)";
    else
	var_sp="$3";
    fi;
    
    path_tune_p="$path_loop_name".tune_p
    if [[ -f "$path_tune_p" ]]; then
	tune_p="$(cat "$path_tune_p" | head -n1)";
    else
	tune_p="$4";
    fi;

    path_tune_i="$path_loop_name".tune_i
    if [[ -f "$path_tune_i" ]]; then
	tune_i="$(cat "$path_tune_i" | head -n1)";
    else
	tune_i="$5";
    fi;

    path_var_cv="$path_loop_name".cv

    path_var_cv_bias="$path_loop_name".cv_bias
    var_cv_bias="$6";
    
    path_sum="$path_loop_name".sum
    if [[ -f "$path_sum" ]]; then
	sum="$(cat "$path_sum" | head -n1)";
    else
	sum=0;
    fi;

    #yell "DEBUG:path_loop_name:$path_loop_name";
    #yell "DEBUG:var_pv:$var_pv";
    #yell "DEBUG:var_sp:$var_sp";
    #yell "DEBUG:var_cv:$var_cv";
    #yell "DEBUG:var_cv_bias:$var_cv_bias";
    #yell "DEBUG:tune_p:$tune_p";
    #yell "DEBUG:tune_i:$tune_i";
    
    error="$(try echo "$var_sp - $var_pv" | bc -l)";
    #yell "DEBUG:error:$error";
    sum_cand="$(try echo "$sum + $error" | bc -l)";
    #yell "DEBUG:sum:$sum";
    if [[ "$(try echo "$sum_cand > 2 * $sum " | bc -l)" -eq 1 ]]; then
	sum="$(try echo "$sum + l($error + 1)" | bc -l)"; # dampen integral sum spikes
    else
	sum="$sum_cand";
    fi;
    term_p="$(try echo "$tune_p * $error" | bc -l)";
    #yell "DEBUG:term_p:$term_p";
    term_i="$(try echo "$tune_i * $sum" | bc -l)";
    #yell "DEBUG:term_i:$term_i";
    var_cv="$(try echo "$term_p + $term_i + $var_cv_bias" | bc -l)";
    #yell "DEBUG:var_cv:$var_cv";
    
    # Write variables to memory
    echo "$sum" > "$path_sum";
    echo "$var_sp" > "$path_var_sp";
    echo "$var_pv" > "$path_var_pv";
    echo "$tune_p" > "$path_tune_p";
    echo "$tune_i" > "$path_tune_i";
    echo "$var_cv" > "$path_var_cv";
    echo "$var_cv_bias" > "$path_var_cv_bias";

    # Output control variable to stdout
    echo "$var_cv";

    #yell "DEBUG:=============END_ROUND===============";
} # update specified PI loop
#==END function definition==

#==BEGIN Example code==
path_loop_name="/tmp/DC1.AC";
var_pv=1.0;
var_sp=2.0;
tune_p=1.0;
tune_i=0.1;
var_cv_init=1000;
try rm "$path_loop_name"*

var_pv=4.0;
output="$(update_pi "$path_loop_name" "$var_pv" "$var_sp" "$tune_p" "$tune_i" "$var_cv_init" | tail -n1)";
yell "DEBUG:sum:$(cat "$path_loop_name".sum | head -n1)";
yell "DEBUG:output:$output";
var_pv=4.0;
output="$(update_pi "$path_loop_name" "$var_pv" "$var_sp" "$tune_p" "$tune_i" "$var_cv_init" | tail -n1)";
yell "DEBUG:sum:$(cat "$path_loop_name".sum | head -n1)";
yell "DEBUG:output:$output";
var_pv=4.0;
output="$(update_pi "$path_loop_name" "$var_pv" "$var_sp" "$tune_p" "$tune_i" "$var_cv_init" | tail -n1)";
yell "DEBUG:sum:$(cat "$path_loop_name".sum | head -n1)";
yell "DEBUG:output:$output";
var_pv=4.0;
output="$(update_pi "$path_loop_name" "$var_pv" "$var_sp" "$tune_p" "$tune_i" "$var_cv_init" | tail -n1)";
yell "DEBUG:sum:$(cat "$path_loop_name".sum | head -n1)";
yell "DEBUG:output:$output";
var_pv=4.0;
output="$(update_pi "$path_loop_name" "$var_pv" "$var_sp" "$tune_p" "$tune_i" "$var_cv_init" | tail -n1)";
yell "DEBUG:sum:$(cat "$path_loop_name".sum | head -n1)";
yell "DEBUG:output:$output";
var_pv=1.0;
output="$(update_pi "$path_loop_name" "$var_pv" "$var_sp" "$tune_p" "$tune_i" "$var_cv_init" | tail -n1)";
yell "DEBUG:sum:$(cat "$path_loop_name".sum | head -n1)";
yell "DEBUG:output:$output";
var_pv=1.0;
output="$(update_pi "$path_loop_name" "$var_pv" "$var_sp" "$tune_p" "$tune_i" "$var_cv_init" | tail -n1)";
yell "DEBUG:sum:$(cat "$path_loop_name".sum | head -n1)";
yell "DEBUG:output:$output";
var_pv=1.0;
output="$(update_pi "$path_loop_name" "$var_pv" "$var_sp" "$tune_p" "$tune_i" "$var_cv_init" | tail -n1)";
yell "DEBUG:sum:$(cat "$path_loop_name".sum | head -n1)";
yell "DEBUG:output:$output";
var_pv=1.0;
output="$(update_pi "$path_loop_name" "$var_pv" "$var_sp" "$tune_p" "$tune_i" "$var_cv_init" | tail -n1)";
yell "DEBUG:sum:$(cat "$path_loop_name".sum | head -n1)";
yell "DEBUG:output:$output";
#==END Example code==

# Author: Steven Baltakatei Sandoval
# License: GPLv3+