#!/bin/sh
set -eu

INTERVAL_SECONDS="${INTERVAL_SECONDS:-5}"
HIGH_TEMP_C="${HIGH_TEMP_C:-75}"
LOW_TEMP_C="${LOW_TEMP_C:-65}"
PWM_CHANNEL="${PWM_CHANNEL:-2}"
PWM_FULL="${PWM_FULL:-255}"
PWM_AUTO_ENABLE="${PWM_AUTO_ENABLE:-5}"
PWM_MANUAL_ENABLE="${PWM_MANUAL_ENABLE:-1}"
LAST_MODE=""

log() {
    if command -v logger >/dev/null 2>&1; then
        logger -t syno-fan-guard "$*"
    fi
    printf '%s\n' "$*"
}

hwmon_by_name() {
    target="$1"
    for hwmon in /sys/class/hwmon/hwmon*; do
        [ -r "$hwmon/name" ] || continue
        [ "$(cat "$hwmon/name" 2>/dev/null)" = "$target" ] || continue
        printf '%s\n' "$hwmon"
        return 0
    done
    return 1
}

read_cpu_temp_mc() {
    cpu_hwmon="$(hwmon_by_name k10temp || true)"
    if [ -n "$cpu_hwmon" ]; then
        for sensor in temp2_input temp1_input temp3_input; do
            path="$cpu_hwmon/$sensor"
            [ -r "$path" ] || continue
            value="$(cat "$path" 2>/dev/null || printf 0)"
            case "$value" in
                ''|*[!0-9-]*) continue ;;
            esac
            [ "$value" -gt 0 ] || continue
            printf '%s\n' "$value"
            return 0
        done
    fi
    printf '0\n'
}

fan_hwmon() {
    hwmon_by_name nct6795
}

write_if_needed() {
    path="$1"
    value="$2"
    [ -w "$path" ] || return 1
    current="$(cat "$path" 2>/dev/null || printf '')"
    [ "$current" = "$value" ] && return 0
    printf '%s\n' "$value" > "$path"
}

apply_once() {
    verbose="${1:-0}"
    fan_hwmon_path="$(fan_hwmon)"
    pwm_path="$fan_hwmon_path/pwm${PWM_CHANNEL}"
    enable_path="$fan_hwmon_path/pwm${PWM_CHANNEL}_enable"
    rpm_path="$fan_hwmon_path/fan${PWM_CHANNEL}_input"
    temp_mc="$(read_cpu_temp_mc)"
    temp_c=$((temp_mc / 1000))
    rpm=0
    [ -r "$rpm_path" ] && rpm="$(cat "$rpm_path" 2>/dev/null || printf 0)"
    enable="$(cat "$enable_path" 2>/dev/null || printf '?')"
    pwm="$(cat "$pwm_path" 2>/dev/null || printf '?')"

    if [ "$temp_c" -ge "$HIGH_TEMP_C" ]; then
        write_if_needed "$enable_path" "$PWM_MANUAL_ENABLE"
        write_if_needed "$pwm_path" "$PWM_FULL"
        if [ "$LAST_MODE" != "force-full" ] || [ "$verbose" = "1" ]; then
            log "force-full temp=${temp_c}C rpm=${rpm} pwm=${pwm} enable=${enable}"
        fi
        LAST_MODE="force-full"
        return 0
    fi

    if [ "$temp_c" -le "$LOW_TEMP_C" ] && [ "$enable" != "$PWM_AUTO_ENABLE" ]; then
        write_if_needed "$enable_path" "$PWM_AUTO_ENABLE"
        log "restore-auto temp=${temp_c}C rpm=${rpm} pwm=${pwm} enable=${enable}"
        LAST_MODE="auto"
        return 0
    fi

    if [ "$verbose" = "1" ]; then
        log "observe temp=${temp_c}C rpm=${rpm} pwm=${pwm} enable=${enable}"
    fi
    LAST_MODE="observe"
}

case "${1:-run}" in
    once|status)
        apply_once 1
        ;;
    run)
        log "start high=${HIGH_TEMP_C}C low=${LOW_TEMP_C}C channel=${PWM_CHANNEL}"
        while :; do
            apply_once 0 || true
            sleep "$INTERVAL_SECONDS"
        done
        ;;
    *)
        printf 'Usage: %s [run|once|status]\n' "$0" >&2
        exit 2
        ;;
esac