/*
 * PCF8574 I/O expander @ 0x21.
 *
 * The PCF8574 has no direction register. Every pin is quasi-bidirectional:
 * writing 1 releases the pin to a weak pull-up (and lets it be read as an
 * input), writing 0 drives it hard low. So "output high" and "input" are the
 * same electrical state, and there is no way to read back what you last wrote
 * — reading returns the actual pin level.
 *
 * That is why this driver keeps a shadow byte. Without it, a read-modify-write
 * to set the touch reset line would sample the encoder button and the relay
 * line and write those levels back, which on the relay is a genuine hazard.
 * The shadow starts at 0xFF, matching the chip's power-on state (all pins
 * released high) — which is also the relay-off state for an active-low module.
 */
#pragma once

#include <stdbool.h>
#include <stdint.h>

#include "esp_err.h"

#define PCF8574_I2C_ADDR    0x21

/* Named per docs/HARDWARE.md. */
#define PCF_PIN_TOUCH_RST   0
#define PCF_PIN_RELAY       1   /* this project — heat call, active low */
#define PCF_PIN_TOUCH_INT   2
#define PCF_PIN_LCD_POWER   3
#define PCF_PIN_LCD_RST     4
#define PCF_PIN_ENCODER_SW  5
/* P6, P7 free */

esp_err_t pcf8574_init(void);

/* True once init has succeeded. relay.c checks this before trusting writes. */
bool pcf8574_is_ready(void);

/* Drive one pin. level=false pulls low; level=true releases to the pull-up. */
esp_err_t pcf8574_write(uint8_t pin, bool level);

/* Read the actual level of one pin. */
esp_err_t pcf8574_read(uint8_t pin, bool *level);

/* Write the whole port at once. Updates the shadow. */
esp_err_t pcf8574_write_port(uint8_t value);

/* Last value written, not the pin levels. */
uint8_t pcf8574_shadow(void);