// Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at

//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include <stdint.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <freertos/FreeRTOS.h>
#include <freertos/task.h>

#include "esp_err.h"
#include "esp_partition.h"
#include "esp_spi_flash.h"
#include "esp_image_format.h"
#include "esp_secure_boot.h"
#include "sdkconfig.h"

#include "esp_ota_ops.h"
#include "sys/queue.h"
#include "crc.h"
#include "esp_log.h"

#ifdef CONFIG_IDF_TARGET_ESP8266
#include "spi_flash.h"
esp_err_t bootloader_flash_read(size_t src_addr, void *dest, size_t size, bool allow_decrypt);
#endif

#define OTA_MAX(a,b) ((a) >= (b) ? (a) : (b)) 
#define OTA_MIN(a,b) ((a) <= (b) ? (a) : (b)) 
#define SUB_TYPE_ID(i) (i & 0x0F) 

typedef struct ota_ops_entry_ {
    uint32_t handle;
    const esp_partition_t *part;
    uint32_t erased_size;
    uint32_t wrote_size;
    uint8_t partial_bytes;
    uint8_t partial_data[16];
    LIST_ENTRY(ota_ops_entry_) entries;
} ota_ops_entry_t;

/* OTA selection structure (two copies in the OTA data partition.)
   Size of 32 bytes is friendly to flash encryption */
typedef struct {
    uint32_t ota_seq;
    uint8_t  seq_label[24];
    uint32_t crc;                /* CRC32 of ota_seq field only */
} ota_select;

static LIST_HEAD(ota_ops_entries_head, ota_ops_entry_) s_ota_ops_entries_head =
    LIST_HEAD_INITIALIZER(s_ota_ops_entries_head);

static uint32_t s_ota_ops_last_handle = 0;
static ota_select s_ota_select[2];

const static char *TAG = "esp_ota_ops";

#ifndef CONFIG_ESP8266_BOOT_COPY_APP
static inline int esp_ota_verify_binary(const esp_partition_pos_t *pos, esp_image_header_t *image)
{
    const int32_t entry = image->entry_addr - 0x40200010;

    ESP_LOGD(TAG, "OTA binary start entry 0x%x, partition start from 0x%x to 0x%x\n", entry, pos->offset,
                        pos->offset + pos->size);

    if (pos->offset + pos->size <= 0x100000) {
        if (entry <= 0 || entry <= pos->offset || entry >= pos->offset + pos->size) {
            const char *doc_str = "<<ESP8266_RTOS_SDK/examples/system/ota/README.md>>";

            ESP_LOGE(TAG, "**Important**: The OTA binary link data is error, "
                          "please refer to document %s for how to generate OTA binaries", doc_str);
            return ESP_ERR_INVALID_ARG;
        }
    }

    return ESP_OK;
}
#endif

/* Return true if this is an OTA app partition */
static bool is_ota_partition(const esp_partition_t *p)
{
    return (p != NULL
            && p->type == ESP_PARTITION_TYPE_APP
            && p->subtype >= ESP_PARTITION_SUBTYPE_APP_OTA_0
            && p->subtype < ESP_PARTITION_SUBTYPE_APP_OTA_MAX);
}

esp_err_t esp_ota_begin(const esp_partition_t *partition, size_t image_size, esp_ota_handle_t *out_handle)
{
    ota_ops_entry_t *new_entry;
    esp_err_t ret = ESP_OK;

    if ((partition == NULL) || (out_handle == NULL)) {
        return ESP_ERR_INVALID_ARG;
    }

    partition = esp_partition_verify(partition);
    if (partition == NULL) {
        return ESP_ERR_NOT_FOUND;
    }

    if (!is_ota_partition(partition)) {
        return ESP_ERR_INVALID_ARG;
    }

    if (partition == esp_ota_get_running_partition()) {
        return ESP_ERR_OTA_PARTITION_CONFLICT;
    }

    // If input image size is 0 or OTA_SIZE_UNKNOWN, erase entire partition
    if ((image_size == 0) || (image_size == OTA_SIZE_UNKNOWN)) {
        ret = esp_partition_erase_range(partition, 0, partition->size);
    } else {
        ret = esp_partition_erase_range(partition, 0, (image_size / SPI_FLASH_SEC_SIZE + 1) * SPI_FLASH_SEC_SIZE);
    }

    if (ret != ESP_OK) {
        return ret;
    }

    new_entry = (ota_ops_entry_t *) calloc(sizeof(ota_ops_entry_t), 1);
    if (new_entry == NULL) {
        return ESP_ERR_NO_MEM;
    }

    LIST_INSERT_HEAD(&s_ota_ops_entries_head, new_entry, entries);

    if ((image_size == 0) || (image_size == OTA_SIZE_UNKNOWN)) {
        new_entry->erased_size = partition->size;
    } else {
        new_entry->erased_size = image_size;
    }

    new_entry->part = partition;
    new_entry->handle = ++s_ota_ops_last_handle;
    *out_handle = new_entry->handle;
    return ESP_OK;
}

esp_err_t esp_ota_write(esp_ota_handle_t handle, const void *data, size_t size)
{
    const uint8_t *data_bytes = (const uint8_t *)data;
    esp_err_t ret;
    ota_ops_entry_t *it;

    if (data == NULL) {
        ESP_LOGE(TAG, "write data is invalid");
        return ESP_ERR_INVALID_ARG;
    }

    // find ota handle in linked list
    for (it = LIST_FIRST(&s_ota_ops_entries_head); it != NULL; it = LIST_NEXT(it, entries)) {
        if (it->handle == handle) {
            // must erase the partition before writing to it
            assert(it->erased_size > 0 && "must erase the partition before writing to it");

            if(it->wrote_size == 0 && size > 0 && data_bytes[0] != 0xE9) {
                ESP_LOGE(TAG, "OTA image has invalid magic byte (expected 0xE9, saw 0x%02x", data_bytes[0]);
                return ESP_ERR_OTA_VALIDATE_FAILED;
            }

#ifdef CONFIG_IDF_TARGET_ESP32
            if (esp_flash_encryption_enabled()) {
                /* Can only write 16 byte blocks to flash, so need to cache anything else */
                size_t copy_len;

                /* check if we have partially written data from earlier */
                if (it->partial_bytes != 0) {
                    copy_len = OTA_MIN(16 - it->partial_bytes, size);
                    memcpy(it->partial_data + it->partial_bytes, data_bytes, copy_len);
                    it->partial_bytes += copy_len;
                    if (it->partial_bytes != 16) {
                        return ESP_OK; /* nothing to write yet, just filling buffer */
                    }
                    /* write 16 byte to partition */
                    ret = esp_partition_write(it->part, it->wrote_size, it->partial_data, 16);
                    if (ret != ESP_OK) {
                        return ret;
                    }
                    it->partial_bytes = 0;
                    memset(it->partial_data, 0xFF, 16);
                    it->wrote_size += 16;
                    data_bytes += copy_len;
                    size -= copy_len;
                }

                /* check if we need to save trailing data that we're about to write */
                it->partial_bytes = size % 16;
                if (it->partial_bytes != 0) {
                    size -= it->partial_bytes;
                    memcpy(it->partial_data, data_bytes + size, it->partial_bytes);
                }
            }

#endif
            ret = esp_partition_write(it->part, it->wrote_size, data_bytes, size);
            if(ret == ESP_OK){
                it->wrote_size += size;
            }
            return ret;
        }
    }

    //if go to here ,means don't find the handle
    ESP_LOGE(TAG,"not found the handle");
    return ESP_ERR_INVALID_ARG;
}

esp_err_t esp_ota_end(esp_ota_handle_t handle)
{
    ota_ops_entry_t *it;
    esp_err_t ret = ESP_OK;

    for (it = LIST_FIRST(&s_ota_ops_entries_head); it != NULL; it = LIST_NEXT(it, entries)) {
        if (it->handle == handle) {
            break;
        }
    }

    if (it == NULL) {
        return ESP_ERR_NOT_FOUND;
    }

    /* 'it' holds the ota_ops_entry_t for 'handle' */

    // esp_ota_end() is only valid if some data was written to this handle
    if ((it->erased_size == 0) || (it->wrote_size == 0)) {
        ret = ESP_ERR_INVALID_ARG;
        goto cleanup;
    }

    if (it->partial_bytes > 0) {
        /* Write out last 16 bytes, if necessary */
        ret = esp_partition_write(it->part, it->wrote_size, it->partial_data, 16);
        if (ret != ESP_OK) {
            ret = ESP_ERR_INVALID_STATE;
            goto cleanup;
        }
        it->wrote_size += 16;
        it->partial_bytes = 0;
    }

    esp_image_metadata_t data;
    const esp_partition_pos_t part_pos = {
      .offset = it->part->address,
      .size = it->part->size,
    };

    if (esp_image_load(ESP_IMAGE_VERIFY, &part_pos, &data) != ESP_OK) {
        ret = ESP_ERR_OTA_VALIDATE_FAILED;
        goto cleanup;
    }

#ifndef CONFIG_ESP8266_BOOT_COPY_APP
    if (esp_ota_verify_binary(&part_pos, &data.image) != ESP_OK) {
        ret = ESP_ERR_OTA_VALIDATE_FAILED;
        goto cleanup;
    }
#endif

#ifdef CONFIG_SECURE_BOOT_ENABLED
    ret = esp_secure_boot_verify_signature(it->part->address, data.image_len);
    if (ret != ESP_OK) {
        ret = ESP_ERR_OTA_VALIDATE_FAILED;
        goto cleanup;
    }
#endif

 cleanup:
    LIST_REMOVE(it, entries);
    free(it);
    return ret;
}

static uint32_t ota_select_crc(const ota_select *s)
{
    return crc32_le(UINT32_MAX, (uint8_t *)&s->ota_seq, 4);
}

static bool ota_select_valid(const ota_select *s)
{
    return s->ota_seq != UINT32_MAX && s->crc == ota_select_crc(s);
}

static esp_err_t rewrite_ota_seq(uint32_t seq, uint8_t sec_id, const esp_partition_t *ota_data_partition)
{
    esp_err_t ret;

    if (sec_id == 0 || sec_id == 1) {
        s_ota_select[sec_id].ota_seq = seq;
        s_ota_select[sec_id].crc = ota_select_crc(&s_ota_select[sec_id]);
        ret = esp_partition_erase_range(ota_data_partition, sec_id * SPI_FLASH_SEC_SIZE, SPI_FLASH_SEC_SIZE);
        if (ret != ESP_OK) {
            return ret;
        } else {
            return esp_partition_write(ota_data_partition, SPI_FLASH_SEC_SIZE * sec_id, &s_ota_select[sec_id].ota_seq, sizeof(ota_select));
        }
    } else {
        return ESP_ERR_INVALID_ARG;
    }
}

uint8_t get_ota_partition_count(void)
{
    uint16_t ota_app_count = 0;
    while (esp_partition_find_first(ESP_PARTITION_TYPE_APP, ESP_PARTITION_SUBTYPE_APP_OTA_MIN + ota_app_count, NULL) != NULL) {
            assert(ota_app_count < 16 && "must erase the partition before writing to it");
            ota_app_count++;
    }
    return ota_app_count;
}

static esp_err_t esp_rewrite_ota_data(esp_partition_subtype_t subtype)
{
    esp_err_t ret;
    const esp_partition_t *find_partition = NULL;
    uint16_t ota_app_count = 0;
    uint32_t i = 0;
    uint32_t seq;

    find_partition = esp_partition_find_first(ESP_PARTITION_TYPE_DATA, ESP_PARTITION_SUBTYPE_DATA_OTA, NULL);
    if (find_partition != NULL) {
        ota_app_count = get_ota_partition_count();
        //esp32_idf use two sector for store information about which partition is running
        //it defined the two sector as ota data partition,two structure ota_select is saved in the two sector
        //named data in first sector as s_ota_select[0], second sector data as s_ota_select[1]
        //e.g.
        //if s_ota_select[0].ota_seq == s_ota_select[1].ota_seq == 0xFFFFFFFF,means ota info partition is in init status
        //so it will boot factory application(if there is),if there's no factory application,it will boot ota[0] application 
        //if s_ota_select[0].ota_seq != 0 and s_ota_select[1].ota_seq != 0,it will choose a max seq ,and get value of max_seq%max_ota_app_number
        //and boot a subtype (mask 0x0F) value is (max_seq - 1)%max_ota_app_number,so if want switch to run ota[x],can use next formulas.
        //for example, if s_ota_select[0].ota_seq = 4, s_ota_select[1].ota_seq = 5, and there are 8 ota application, 
        //current running is (5-1)%8 = 4,running ota[4],so if we want to switch to run ota[7],
        //we should add s_ota_select[0].ota_seq (is 4) to 4 ,(8-1)%8=7,then it will boot ota[7]
        //if      A=(B - C)%D
        //then    B=(A + C)%D + D*n ,n= (0,1,2...)
        //so current ota app sub type id is x , dest bin subtype is y,total ota app count is n
        //seq will add (x + n*1 + 1 - seq)%n
        if (SUB_TYPE_ID(subtype) >= ota_app_count) {
            return ESP_ERR_INVALID_ARG;
        }
#ifdef CONFIG_IDF_TARGET_ESP32
        const void *result = NULL;
        static spi_flash_mmap_memory_t ota_data_map;
        ret = esp_partition_mmap(find_partition, 0, find_partition->size, SPI_FLASH_MMAP_DATA, &result, &ota_data_map);
        if (ret != ESP_OK) {
            result = NULL;
            return ret;
        } else {
            memcpy(&s_ota_select[0], result, sizeof(ota_select));
            memcpy(&s_ota_select[1], result + SPI_FLASH_SEC_SIZE, sizeof(ota_select));
            spi_flash_munmap(ota_data_map);
        }
#endif

#ifdef CONFIG_IDF_TARGET_ESP8266
        ret = spi_flash_read(find_partition->address, &s_ota_select[0], sizeof(ota_select));
        if (ret != ESP_OK) {
            ESP_LOGE(TAG, "read failed");
            return ret;
        }

        ret = spi_flash_read(find_partition->address + 0x1000, &s_ota_select[1], sizeof(ota_select));
        if (ret != ESP_OK) {
            ESP_LOGE(TAG, "read failed");
            return ret;
        }
#endif

        if (ota_select_valid(&s_ota_select[0]) && ota_select_valid(&s_ota_select[1])) {
            seq = OTA_MAX(s_ota_select[0].ota_seq, s_ota_select[1].ota_seq);
            while (seq > (SUB_TYPE_ID(subtype) + 1) % ota_app_count + i * ota_app_count) {
                i++;
            }

            if (s_ota_select[0].ota_seq >= s_ota_select[1].ota_seq) {
                return rewrite_ota_seq((SUB_TYPE_ID(subtype) + 1) % ota_app_count + i * ota_app_count, 1, find_partition);
            } else {
                return rewrite_ota_seq((SUB_TYPE_ID(subtype) + 1) % ota_app_count + i * ota_app_count, 0, find_partition);
            }

        } else if (ota_select_valid(&s_ota_select[0])) {
            while (s_ota_select[0].ota_seq > (SUB_TYPE_ID(subtype) + 1) % ota_app_count + i * ota_app_count) {
                i++;
            }
            return rewrite_ota_seq((SUB_TYPE_ID(subtype) + 1) % ota_app_count + i * ota_app_count, 1, find_partition);

        } else if (ota_select_valid(&s_ota_select[1])) {
            while (s_ota_select[1].ota_seq > (SUB_TYPE_ID(subtype) + 1) % ota_app_count + i * ota_app_count) {
                i++;
            }
            return rewrite_ota_seq((SUB_TYPE_ID(subtype) + 1) % ota_app_count + i * ota_app_count, 0, find_partition);

        } else {
            /* Both OTA slots are invalid, probably because unformatted... */
            return rewrite_ota_seq(SUB_TYPE_ID(subtype) + 1, 0, find_partition);
        }

    } else {
        return ESP_ERR_NOT_FOUND;
    }
}

esp_err_t esp_ota_set_boot_partition(const esp_partition_t *partition)
{
    const esp_partition_t *find_partition = NULL;
    if (partition == NULL) {
        return ESP_ERR_INVALID_ARG;
    }

    esp_image_metadata_t data;
    const esp_partition_pos_t part_pos = {
        .offset = partition->address,
        .size = partition->size,
    };
    if (esp_image_load(ESP_IMAGE_VERIFY, &part_pos, &data) != ESP_OK) {
        return ESP_ERR_OTA_VALIDATE_FAILED;
    }

#ifdef CONFIG_SECURE_BOOT_ENABLED
    esp_err_t ret = esp_secure_boot_verify_signature(partition->address, data.image_len);
    if (ret != ESP_OK) {
        return ESP_ERR_OTA_VALIDATE_FAILED;
    }
#endif
    // if set boot partition to factory bin ,just format ota info partition
    if (partition->type == ESP_PARTITION_TYPE_APP) {
        if (partition->subtype == ESP_PARTITION_SUBTYPE_APP_FACTORY) {
            find_partition = esp_partition_find_first(ESP_PARTITION_TYPE_DATA, ESP_PARTITION_SUBTYPE_DATA_OTA, NULL);
            if (find_partition != NULL) {
                return esp_partition_erase_range(find_partition, 0, find_partition->size);
            } else {
                return ESP_ERR_NOT_FOUND;
            }
        } else {
            // try to find this partition in flash,if not find it ,return error
            find_partition = esp_partition_find_first(ESP_PARTITION_TYPE_DATA, ESP_PARTITION_SUBTYPE_DATA_OTA, NULL);
            if (find_partition != NULL) {
                return esp_rewrite_ota_data(partition->subtype);
            } else {
                return ESP_ERR_NOT_FOUND;
            }
        }
    } else {
        return ESP_ERR_INVALID_ARG;
    }
}

static const esp_partition_t *find_default_boot_partition(void)
{
    // This logic matches the logic of bootloader get_selected_boot_partition() & load_boot_image().

    // Default to factory if present
    const esp_partition_t *result = esp_partition_find_first(ESP_PARTITION_TYPE_APP, ESP_PARTITION_SUBTYPE_APP_FACTORY, NULL);
    if (result != NULL) {
        return result;
    }

    // Try first OTA slot if no factory partition
    for (esp_partition_subtype_t s = ESP_PARTITION_SUBTYPE_APP_OTA_MIN; s != ESP_PARTITION_SUBTYPE_APP_OTA_MAX; s++) {
        result = esp_partition_find_first(ESP_PARTITION_TYPE_APP, s, NULL);
        if (result != NULL) {
            return result;
        }
    }

    // Test app slot if present
    result = esp_partition_find_first(ESP_PARTITION_TYPE_APP, ESP_PARTITION_SUBTYPE_APP_TEST, NULL);
    if (result != NULL) {
        return result;
    }

    ESP_LOGE(TAG, "invalid partition table, no app partitions");
    return NULL;
}

const esp_partition_t *esp_ota_get_boot_partition(void)
{
    esp_err_t ret;
    const esp_partition_t *find_partition = NULL;

    uint16_t ota_app_count = 0;
    find_partition = esp_partition_find_first(ESP_PARTITION_TYPE_DATA, ESP_PARTITION_SUBTYPE_DATA_OTA, NULL);

    if (find_partition == NULL) {
        ESP_LOGE(TAG, "not found ota data");
        return NULL;
    }

#ifdef CONFIG_IDF_TARGET_ESP32
    const void *result = NULL;
    static spi_flash_mmap_memory_t ota_data_map;
    ret = esp_partition_mmap(find_partition, 0, find_partition->size, SPI_FLASH_MMAP_DATA, &result, &ota_data_map);
    if (ret != ESP_OK) {
        spi_flash_munmap(ota_data_map);
        ESP_LOGE(TAG, "mmap ota data filed");
        return NULL;
    } else {
        memcpy(&s_ota_select[0], result, sizeof(ota_select));
        memcpy(&s_ota_select[1], result + 0x1000, sizeof(ota_select));
        spi_flash_munmap(ota_data_map);

#endif

#ifdef CONFIG_IDF_TARGET_ESP8266
    ret = spi_flash_read(find_partition->address, &s_ota_select[0], sizeof(ota_select));
    if (ret != ESP_OK) {
        ESP_LOGE(TAG, "read failed");
        return NULL;
    }

    ret = spi_flash_read(find_partition->address + 0x1000, &s_ota_select[1], sizeof(ota_select));
    if (ret != ESP_OK) {
        ESP_LOGE(TAG, "read failed");
        return NULL;
    }
#endif
    ota_app_count = get_ota_partition_count();
    ESP_LOGD(TAG, "found ota app max = %d", ota_app_count);

    if (s_ota_select[0].ota_seq == 0xFFFFFFFF && s_ota_select[1].ota_seq == 0xFFFFFFFF) {
        ESP_LOGD(TAG, "finding factory app......");
        return find_default_boot_partition();
    } else if (ota_select_valid(&s_ota_select[0]) && ota_select_valid(&s_ota_select[1])) {
        ESP_LOGD(TAG, "finding ota_%d app......", \
                 ESP_PARTITION_SUBTYPE_APP_OTA_MIN + ((OTA_MAX(s_ota_select[0].ota_seq, s_ota_select[1].ota_seq) - 1) % ota_app_count));

        return esp_partition_find_first(ESP_PARTITION_TYPE_APP, \
                                        ESP_PARTITION_SUBTYPE_APP_OTA_MIN + ((OTA_MAX(s_ota_select[0].ota_seq, s_ota_select[1].ota_seq) - 1) % ota_app_count), NULL);
    } else if (ota_select_valid(&s_ota_select[0])) {
        ESP_LOGD(TAG, "finding ota_%d app......", \
                 ESP_PARTITION_SUBTYPE_APP_OTA_MIN + (s_ota_select[0].ota_seq - 1) % ota_app_count);

        return esp_partition_find_first(ESP_PARTITION_TYPE_APP, \
                                        ESP_PARTITION_SUBTYPE_APP_OTA_MIN + (s_ota_select[0].ota_seq - 1) % ota_app_count, NULL);

    } else if (ota_select_valid(&s_ota_select[1])) {
        ESP_LOGD(TAG, "finding ota_%d app......", \
                 ESP_PARTITION_SUBTYPE_APP_OTA_MIN + (s_ota_select[1].ota_seq - 1) % ota_app_count);

        return esp_partition_find_first(ESP_PARTITION_TYPE_APP, \
                                        ESP_PARTITION_SUBTYPE_APP_OTA_MIN + (s_ota_select[1].ota_seq - 1) % ota_app_count, NULL);

    } else {
        ESP_LOGE(TAG, "ota data invalid, no current app. Assuming factory");
        return find_default_boot_partition();
    }
}


const esp_partition_t* esp_ota_get_running_partition(void)
{
    /* Find the flash address of this exact function. By definition that is part
       of the currently running firmware. Then find the enclosing partition. */

    size_t phys_offs = spi_flash_cache2phys(esp_ota_get_running_partition);

    assert (phys_offs != SPI_FLASH_CACHE2PHYS_FAIL); /* indicates cache2phys lookup is buggy */

    esp_partition_iterator_t it = esp_partition_find(ESP_PARTITION_TYPE_APP,
                                                     ESP_PARTITION_SUBTYPE_ANY,
                                                     NULL);
    assert(it != NULL); /* has to be at least one app partition */

    while (it != NULL) {
        const esp_partition_t *p = esp_partition_get(it);
        if (p->address <= phys_offs && p->address + p->size > phys_offs) {
            esp_partition_iterator_release(it);
            return p;
        }
        it = esp_partition_next(it);
    }

    abort(); /* Partition table is invalid or corrupt */
}


const esp_partition_t* esp_ota_get_next_update_partition(const esp_partition_t *start_from)
{
    const esp_partition_t *default_ota = NULL;
    bool next_is_result = false;
    if (start_from == NULL) {
        start_from = esp_ota_get_running_partition();
    } else {
        start_from = esp_partition_verify(start_from);
    }
    assert (start_from != NULL);
    /* at this point, 'start_from' points to actual partition table data in flash */


    /* Two possibilities: either we want the OTA partition immediately after the current running OTA partition, or we
       want the first OTA partition in the table (for the case when the last OTA partition is the running partition, or
       if the current running partition is not OTA.)

       This loop iterates subtypes instead of using esp_partition_find, so we
       get all OTA partitions in a known order (low slot to high slot).
    */

    for (esp_partition_subtype_t t = ESP_PARTITION_SUBTYPE_APP_OTA_0;
         t != ESP_PARTITION_SUBTYPE_APP_OTA_MAX;
         t++) {
        const esp_partition_t *p = esp_partition_find_first(ESP_PARTITION_TYPE_APP, t, NULL);
        if (p == NULL) {
            continue;
        }

        if (default_ota == NULL) {
            /* Default to first OTA partition we find,
               will be used if nothing else matches */
            default_ota = p;
        }

        if (p == start_from) {
            /* Next OTA partition is the one to use */
            next_is_result = true;
        }
        else if (next_is_result) {
            return p;
        }
    }

    return default_ota;

}
