/**
 * @file gpio_linux.c
 * @brief GPIO implementation for Linux using libgpiod and KED function pointer injection.
 */

#include "../../ked/peripherals/gpio/gpio.h"
#include <gpiod.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

/**
 * @brief Internal Linux GPIO context.
 *
 * Holds the active chip and line handles.
 * This implementation assumes one active GPIO at a time (can be extended to multiple if needed).
 */
typedef struct {
    struct gpiod_chip* chip;
    struct gpiod_line* line;
} gpio_linux_ctx_t;

static gpio_linux_ctx_t gpio_ctx;

/* === Centralized Error Handling === */

/**
 * @brief Centralized error handler for GPIO-related failures.
 *
 * Logs the error to stderr and can be extended to trigger hooks or diagnostics.
 *
 * @param err The GPIO error code encountered.
 */
static void gpio_linux_handle_error(gpio_error_t err) {
    fprintf(stderr, "[GPIO/Linux] ERROR: %d\n", err);
    // Future: report to diagnostic logger or panic handler
}

/* === GPIO Operation Implementations === */

/**
 * @brief Set the output level of the GPIO line.
 *
 * @param value 1 = HIGH, 0 = LOW
 */
static void gpio_linux_set(uint8_t value) {
    if (gpio_ctx.line) {
        gpiod_line_set_value(gpio_ctx.line, value);
    } else {
        gpio_linux_handle_error(T_GPIO_ERR_NOT_AVAILABLE);
    }
}

/**
 * @brief Read the current logic level of the GPIO line.
 *
 * @return Logic level (1 = HIGH, 0 = LOW)
 */
static uint8_t gpio_linux_read(void) {
    if (!gpio_ctx.line) {
        gpio_linux_handle_error(T_GPIO_ERR_NOT_AVAILABLE);
        return 0;
    }
    return (uint8_t)gpiod_line_get_value(gpio_ctx.line);
}

/**
 * @brief Toggle the current logic level of the GPIO line.
 */
static void gpio_linux_toggle(void) {
    if (!gpio_ctx.line) {
        gpio_linux_handle_error(T_GPIO_ERR_NOT_AVAILABLE);
        return;
    }
    uint8_t current = (uint8_t)gpiod_line_get_value(gpio_ctx.line);
    gpiod_line_set_value(gpio_ctx.line, !current);
}

/**
 * @brief Update GPIO configuration dynamically.
 *
 * Currently not supported on Linux – placeholder only.
 */
static gpio_error_t gpio_linux_update(void) {
    // TODO: implement runtime reconfiguration if needed
    return T_GPIO_ERR_UNSUPPORTED_MODE;
}

/* === Static GPIO Function Table Instance === */

/**
 * @brief Shared Linux GPIO function table for all gpio_t instances.
 *
 * Each GPIO object holds a pointer to this table via its `vtable` field.
 * This avoids redundant copies of function pointers per object.
 */
static const gpio_fn_ptr_t gpio_linux_fn = {
    .set      = gpio_linux_set,
    .read     = gpio_linux_read,
    .toggle   = gpio_linux_toggle,
    .update   = gpio_linux_update,
    .on_error = gpio_linux_handle_error
};

/* === Public API Implementation === */

/**
 * @brief Initialize the GPIO using the given Linux gpio_t config and callback struct.
 *
 * This sets direction, bias, and binds callbacks to the gpio_fn_ptr_t table.
 *
 * @param gpio Pointer to GPIO configuration structure
 * @param callbacks Optional pointer to gpio_fn_ptr_t to receive platform-specific handlers
 * @return T_GPIO_ERR_OK on success, or appropriate error code
 */
gpio_error_t ked_gpio_init(gpio_t* gpio) {
    gpio_ctx.chip = gpiod_chip_open(gpio->chipname);
    if (!gpio_ctx.chip) {
        gpio_linux_handle_error(T_GPIO_ERR_NOT_AVAILABLE);
        return T_GPIO_ERR_NOT_AVAILABLE;
    }

    gpio_ctx.line = gpiod_chip_get_line(gpio_ctx.chip, gpio->line_offset);
    if (!gpio_ctx.line) {
        gpiod_chip_close(gpio_ctx.chip);
        gpio_linux_handle_error(T_GPIO_ERR_NOT_AVAILABLE);
        return T_GPIO_ERR_NOT_AVAILABLE;
    }

    struct gpiod_line_request_config req_cfg = {
        .consumer = "ked_gpio",
        .request_type = (gpio->direction == T_GPIO_DIRECTION_OUTPUT)
            ? GPIOD_LINE_REQUEST_DIRECTION_OUTPUT
            : GPIOD_LINE_REQUEST_DIRECTION_INPUT,
        .flags = 0
    };

    if (gpio->bias == T_GPIO_BIAS_PULL_UP)
        req_cfg.flags |= GPIOD_LINE_REQUEST_FLAG_BIAS_PULL_UP;
    else if (gpio->bias == T_GPIO_BIAS_PULL_DOWN)
        req_cfg.flags |= GPIOD_LINE_REQUEST_FLAG_BIAS_PULL_DOWN;
    else if (gpio->bias == T_GPIO_BIAS_DISABLE)
        req_cfg.flags |= GPIOD_LINE_REQUEST_FLAG_BIAS_DISABLE;
    else if (gpio->bias == T_GPIO_BIAS_DEFAULT)
        req_cfg.request_type = GPIOD_LINE_REQUEST_DIRECTION_AS_IS;

    if (gpiod_line_request(gpio_ctx.line, &req_cfg, 0) < 0) {
        gpiod_chip_close(gpio_ctx.chip);
        gpio_linux_handle_error(T_GPIO_ERR_BUS_BUSY);
        return T_GPIO_ERR_BUS_BUSY;
    }

    gpio->func     = &gpio_linux_fn;

    return T_GPIO_ERR_OK;
}

/**
 * @brief Deinitialize GPIO from platform and free resources.
 *
 * @param gpio Unused in this implementation
 * @param callbacks Pointer to callback table that includes `deinit`
 */
void ked_gpio_deinit(gpio_t* gpio) {
    if (gpio_ctx.line) {
        gpiod_line_release(gpio_ctx.line);
        gpio_ctx.line = NULL;
    }
    if (gpio_ctx.chip) {
        gpiod_chip_close(gpio_ctx.chip);
        gpio_ctx.chip = NULL;
    }
}