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CHANGELOG.md

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+# EPrices v1.0 – Changelog
+
+## v1.0 — 2026-04-05
+
+Initial release of EPrices.
+
+---
+
+### Project & device renames
+
+| Item | Value |
+|---|---|
+| ESPHome node name | `eprices` |
+| Friendly name | `EPrices` |
+| Helper file | `eprices_nvs.h` |
+| C++ namespace | `eprices_nvs` |
+| NVS partition namespace | `eprices` |
+| Secret key prefix | `eprices_` |
+
+---
+
+### Secrets file keys
+
+```yaml
+wifi_ssid
+wifi_password
+eprices_fallback_ap_ssid
+eprices_fallback_ap_password
+eprices_api_encryption_key
+eprices_timezone          # e.g. "Europe/Ljubljana"
+eprices_country_bzn       # e.g. "SI"
+eprices_prov_fee          # e.g. "0.12"  (provider fee as decimal multiplier)
+eprices_vat_rate          # e.g. "0.22"  (VAT rate as decimal multiplier)
+```
+
+---
+
+### Sensors
+
+#### Numeric sensors (`sensor:`)
+
+| Name | Entity ID | Notes |
+|---|---|---|
+| Today Current Price | `sensor.eprices_today_current_price` | |
+| Today Next Price | `sensor.eprices_today_next_price` | |
+| Today Average Price | `sensor.eprices_today_average_price` | |
+| Today Highest Price | `sensor.eprices_today_highest_price` | |
+| Today Lowest Price | `sensor.eprices_today_lowest_price` | |
+| Today Current Hourly Price | `sensor.eprices_today_current_hourly_price` | |
+| Today Next Hourly Price | `sensor.eprices_today_next_hourly_price` | |
+| Today Highest Hourly Price | `sensor.eprices_today_highest_hourly_price` | |
+| Today Lowest Hourly Price | `sensor.eprices_today_lowest_hourly_price` | |
+| Today Current Max Hourly Price Percentage | `sensor.eprices_today_current_max_hourly_price_percentage` | |
+| Tomorrow Current Price | `sensor.eprices_tomorrow_current_price` | Evaluates at now + 86400s |
+| Tomorrow Next Price | `sensor.eprices_tomorrow_next_price` | Evaluates at now + 86400s |
+| Tomorrow Average Price | `sensor.eprices_tomorrow_average_price` | |
+| Tomorrow Highest Price | `sensor.eprices_tomorrow_highest_price` | |
+| Tomorrow Lowest Price | `sensor.eprices_tomorrow_lowest_price` | |
+| Tomorrow Current Hourly Price | `sensor.eprices_tomorrow_current_hourly_price` | Evaluates at now + 86400s |
+| Tomorrow Next Hourly Price | `sensor.eprices_tomorrow_next_hourly_price` | Evaluates at now + 86400s |
+| Tomorrow Highest Hourly Price | `sensor.eprices_tomorrow_highest_hourly_price` | |
+| Tomorrow Lowest Hourly Price | `sensor.eprices_tomorrow_lowest_hourly_price` | |
+| Tomorrow Current Max Hourly Price Percentage | `sensor.eprices_tomorrow_current_max_hourly_price_percentage` | Evaluates at now + 86400s |
+| WiFi Signal | `sensor.eprices_wifi_signal` | dBm, diagnostic |
+| Uptime | `sensor.eprices_uptime` | Human-readable string, diagnostic |
+
+#### Text sensors (`text_sensor:`)
+
+| Name | Entity ID | Notes |
+|---|---|---|
+| Today JSON Hourly Prices EUR⁄kWh | `sensor.eprices_today_json_hourly_prices_eur_kwh` | JSON array, 24 values |
+| Today JSON 15-Min Prices EUR⁄kWh (P1 00:00-07:45) | `sensor.eprices_today_json_15_min_prices_eur_kwh_p1_00_00_07_45` | JSON array, 32 values |
+| Today JSON 15-Min Prices EUR⁄kWh (P2 08:00-15:45) | `sensor.eprices_today_json_15_min_prices_eur_kwh_p2_08_00_15_45` | JSON array, 32 values |
+| Today JSON 15-Min Prices EUR⁄kWh (P3 16:00-23:45) | `sensor.eprices_today_json_15_min_prices_eur_kwh_p3_16_00_23_45` | JSON array, 32 values |
+| Today Highest Price Time | `sensor.eprices_today_highest_price_time` | HH:MM |
+| Today Lowest Price Time | `sensor.eprices_today_lowest_price_time` | HH:MM |
+| Today Highest Hourly Price Time | `sensor.eprices_today_highest_hourly_price_time` | HH:00 |
+| Today Lowest Hourly Price Time | `sensor.eprices_today_lowest_hourly_price_time` | HH:00 |
+| Today Current Price Status | `sensor.eprices_today_current_price_status` | `Valid` / `Missing` / `Stale` |
+| Today Data Loaded Time | `sensor.eprices_today_data_loaded_time` | Stamped on NVS load and HTTP fetch |
+| Today Last API Fetch Time | `sensor.eprices_today_last_api_fetch_time` | Stamped on HTTP fetch only; `Never` if NVS only; diagnostic |
+| Today Price Update Status | `sensor.eprices_today_price_update_status` | `SUCCESS` / `FAILED/WAITING`; diagnostic |
+| Today Price Update Status Message | `sensor.eprices_today_price_update_status_message` | Detailed status string; diagnostic |
+| Today API Fetch Attempts | `sensor.eprices_today_api_fetch_attempts` | HTTP fetch count; resets at midnight; diagnostic |
+| Today Entry Count | `sensor.eprices_today_entry_count` | Number of stored price points; diagnostic |
+| Tomorrow JSON Hourly Prices EUR⁄kWh | `sensor.eprices_tomorrow_json_hourly_prices_eur_kwh` | JSON array, 24 values |
+| Tomorrow JSON 15-Min Prices EUR⁄kWh (P1 00:00-07:45) | `sensor.eprices_tomorrow_json_15_min_prices_eur_kwh_p1_00_00_07_45` | JSON array, 32 values |
+| Tomorrow JSON 15-Min Prices EUR⁄kWh (P2 08:00-15:45) | `sensor.eprices_tomorrow_json_15_min_prices_eur_kwh_p2_08_00_15_45` | JSON array, 32 values |
+| Tomorrow JSON 15-Min Prices EUR⁄kWh (P3 16:00-23:45) | `sensor.eprices_tomorrow_json_15_min_prices_eur_kwh_p3_16_00_23_45` | JSON array, 32 values |
+| Tomorrow Highest Price Time | `sensor.eprices_tomorrow_highest_price_time` | HH:MM |
+| Tomorrow Lowest Price Time | `sensor.eprices_tomorrow_lowest_price_time` | HH:MM |
+| Tomorrow Highest Hourly Price Time | `sensor.eprices_tomorrow_highest_hourly_price_time` | HH:00 |
+| Tomorrow Lowest Hourly Price Time | `sensor.eprices_tomorrow_lowest_hourly_price_time` | HH:00 |
+| Tomorrow Current Price Status | `sensor.eprices_tomorrow_current_price_status` | `Valid` / `Missing` / `Waiting...` |
+| Tomorrow Data Loaded Time | `sensor.eprices_tomorrow_data_loaded_time` | Stamped on NVS load and HTTP fetch; `Outside fetch window` before 13:20 |
+| Tomorrow Last API Fetch Time | `sensor.eprices_tomorrow_last_api_fetch_time` | Stamped on HTTP fetch only; `Never` if NVS only; diagnostic |
+| Tomorrow Price Update Status | `sensor.eprices_tomorrow_price_update_status` | `SUCCESS` / `FAILED/WAITING`; diagnostic |
+| Tomorrow Price Update Status Message | `sensor.eprices_tomorrow_price_update_status_message` | Detailed status string; diagnostic |
+| Tomorrow API Fetch Attempts | `sensor.eprices_tomorrow_api_fetch_attempts` | HTTP fetch count; resets at 13:25; diagnostic |
+| Tomorrow Entry Count | `sensor.eprices_tomorrow_entry_count` | Number of stored price points; diagnostic |
+| Last Reboot | `sensor.eprices_last_reboot` | Boot timestamp; diagnostic |
+| Last Update Source | `sensor.eprices_last_update_source` | `NVS_boot` / `HTTP_today` / `midnight_bridge` etc.; diagnostic |
+| Today NVS Status | `sensor.eprices_today_nvs_status` | NVS load/store result; diagnostic |
+| Tomorrow NVS Status | `sensor.eprices_tomorrow_nvs_status` | NVS load/store result; diagnostic |
+| Today Data Date | `sensor.eprices_today_data_date` | Date of stored today data; diagnostic |
+| Tomorrow Data Date | `sensor.eprices_tomorrow_data_date` | Date of stored tomorrow data; diagnostic |
+
+#### Buttons
+
+| Name | Entity ID |
+|---|---|
+| Force Today's Update | `button.eprices_force_today_s_update` |
+| Force Tomorrow's Update | `button.eprices_force_tomorrow_s_update` |
+| Reboot Device | `button.eprices_reboot_device` |
+
+---
+
+### Key behaviours
+
+- **Price calculation:** `price_eur_kwh = (raw_eur_mwh / 1000) × (1 + prov_fee) × (1 + vat_rate)`
+- **Negative prices:** formatted as `%.3f` (3 decimal places) to stay within the 255-character HA text sensor state limit; positive prices use `%.4f`
+- **DST-safe:** all price indexing uses UNIX timestamps and binary search — no hour-slot arithmetic
+- **NVS persistence:** prices survive reboots; stale data (date mismatch) is discarded and triggers a fresh HTTP fetch
+- **Today Current Price Status** shows `Stale` if stored date does not match today's date
+- **Tomorrow live sensors** evaluate at `now + 86400s` so they reflect tomorrow at the same local time
+- **Tomorrow Data Loaded Time** shows `Outside fetch window` when device boots before 13:20
+- **API fetch times** reset to `Never` at midnight bridge and on `clear_tomorrow_prices`
+- **API fetch attempt counters** reset to `0` at midnight and publish `0` immediately on boot
+- **Uptime** displayed as human-readable string: `45 s` / `5 min` / `3 h 22 min` / `12 d 4 h` / `4 months 12 d`

ENTSO-E-PRICES-MIGRATION.md

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+# Migrating from Entso-E Prices to EPrices
+
+This document explains the rationale behind EPrices and documents all changes
+relative to the last public release of the predecessor project,
+**entso-e-prices v4.3.1**.
+
+It is intended for users who ran entso-e-prices v4.3.1 and want to migrate
+their Home Assistant automations, dashboards, and energy configurations to EPrices.
+
+---
+
+## Why EPrices was created
+
+The original entso-e-prices project fetched electricity prices from the
+**ENTSOE Transparency Platform XML API**. That API requires a private token,
+has rate limits, and returns data in a complex XML format that required
+significant parsing logic and an external helper file (`entsoe_http_idf.h`).
+Additionally, all automation logic (midnight bridge, retry scheduling, NVS
+management) was split across external HA automations, making the system fragile
+and difficult to maintain.
+
+The goal of EPrices was to:
+
+1. **Eliminate the need for a private API token** — the Energy-Charts API
+   (Fraunhofer ISE) is public, free, and returns clean JSON. No registration,
+   no token rotation, no rate limit concerns.
+
+2. **Move all core logic into the device** — midnight bridge, retry scheduling,
+   NVS persistence, and boot recovery all run on the ESP32 itself. No external
+   HA automations are required for any core functionality.
+
+3. **Simplify the codebase** — the two external helper files
+   (`entsoe_http_idf.h` and `entsoe_storage_v2.h`) were eliminated. All logic
+   is now either inline in `eprices.yaml` or in the single helper `eprices_nvs.h`.
+
+4. **Improve sensor clarity and user experience** — sensor names were
+   systematically restructured with Today/Tomorrow prefixes, redundant words
+   removed, and diagnostic sensors clearly separated from operational ones.
+
+5. **Make the system DST-safe** — the original slot arithmetic
+   `(hour × 4) + (min / 15)` breaks on DST transition days. EPrices uses
+   UNIX timestamps and binary search throughout, making it fully DST-safe.
+
+---
+
+## Summary of all changes from entso-e-prices v4.3.1 to EPrices v1.0
+
+### API
+
+| Item | entso-e-prices v4.3.1 | EPrices v1.0 |
+|---|---|---|
+| Data source | ENTSOE Transparency Platform XML | Energy-Charts JSON (Fraunhofer ISE) |
+| Authentication | Private API token required | No token — public API |
+| Data format | XML | JSON |
+| Price resolution | 15-minute | 15-minute |
+| Base price unit | €/MWh | €/MWh (converted to €/kWh in firmware) |
+
+### Project structure
+
+| Item | entso-e-prices v4.3.1 | EPrices v1.0 |
+|---|---|---|
+| ESPHome node name | `entso-e-prices` | `eprices` |
+| Friendly name | `Entso-E Prices` | `EPrices` |
+| Helper files | `entsoe_http_idf.h` + `entsoe_storage_v2.h` | `eprices_nvs.h` only |
+| NVS namespace | `entsoe2` | `eprices` |
+| Secret key prefix | `entsoe_` | `eprices_` |
+| Provider fee / VAT | Hardcoded in lambdas | Configurable via `secrets.yaml` |
+| Core automation logic | Split across external HA automations | Fully on-device |
+
+### NVS storage
+
+| Item | entso-e-prices v4.3.1 | EPrices v1.0 |
+|---|---|---|
+| Storage format | Fixed 96-slot float blobs | Dynamic timestamp + price arrays |
+| DST handling | Hour-slot arithmetic `(h×4)+(m/15)` — breaks on DST | UNIX timestamp binary search — DST-safe |
+| Boot recovery | Via external HA automation | On-device `boot_recovery_today/tomorrow_script` |
+| Midnight bridge | Via external HA automation | On-device `midnight_bridge_promotion` script |
+
+### Fetch scheduling and retry logic
+
+| Item | entso-e-prices v4.3.1 | EPrices v1.0 |
+|---|---|---|
+| Today fetch trigger | External HA automation | On-device auto-retry (up to 8 attempts) |
+| Tomorrow fetch schedule | External HA automation | On-device 13:25 → 13:55 → 14:55 … 19:55 |
+| Manual force update | Button | Button (unchanged) |
+| Midnight bridge | External HA automation at 00:00 | On-device `on_time: 00:00:00` |
+
+### Sensor naming
+
+All sensors were renamed with a systematic **Today / Tomorrow** prefix.
+The words "electricity" and "energy" were removed from all sensor names.
+"Next Day" was replaced with "Tomorrow" throughout.
+
+#### Numeric sensors
+
+| entso-e-prices v4.3.1 name | EPrices v1.0 name |
+|---|---|
+| `Current Electricity Price` | `Today Current Price` |
+| `Next Electricity Price` | `Today Next Price` |
+| `Average Electricity Price Today` | `Today Average Price` |
+| `Highest Electricity Price Today` | `Today Highest Price` |
+| `Lowest Electricity Price Today` | `Today Lowest Price` |
+| `Current Hourly Electricity Price` | `Today Current Hourly Price` |
+| `Next Hourly Electricity Price` | `Today Next Hourly Price` |
+| `Highest Hourly Electricity Price Today` | `Today Highest Hourly Price` |
+| `Lowest Hourly Electricity Price Today` | `Today Lowest Hourly Price` |
+| `Current Max Hourly Price Percentage` | `Today Current Max Hourly Price Percentage` |
+| `Daily Price Update Attempts` | `Today API Fetch Attempts` *(moved to text_sensor)* |
+| `Today Entry Count` | `Today Entry Count` *(moved to text_sensor)* |
+| `Next Day Current Electricity Price` | `Tomorrow Current Price` |
+| `Next Day Next Electricity Price` | `Tomorrow Next Price` |
+| `Average Electricity Price Tomorrow` | `Tomorrow Average Price` |
+| `Highest Electricity Price Tomorrow` | `Tomorrow Highest Price` |
+| `Lowest Electricity Price Tomorrow` | `Tomorrow Lowest Price` |
+| `Current Hourly Electricity Price Tomorrow` | `Tomorrow Current Hourly Price` |
+| `Next Hourly Electricity Price Tomorrow` | `Tomorrow Next Hourly Price` |
+| `Highest Hourly Electricity Price Tomorrow` | `Tomorrow Highest Hourly Price` |
+| `Lowest Hourly Electricity Price Tomorrow` | `Tomorrow Lowest Hourly Price` |
+| `Next Day Current Max Hourly Price Percentage` | `Tomorrow Current Max Hourly Price Percentage` |
+| `Next Day Price Update Attempts` | `Tomorrow API Fetch Attempts` *(moved to text_sensor)* |
+| `Tomorrow Entry Count` | `Tomorrow Entry Count` *(moved to text_sensor)* |
+
+#### Text sensors
+
+| entso-e-prices v4.3.1 name | EPrices v1.0 name |
+|---|---|
+| `ENTSO-E Hourly Prices EUR⁄kWh JSON` | `Today JSON Hourly Prices EUR⁄kWh` |
+| `ENTSO-E 15-Min Prices EUR⁄kWh JSON (P1 00:00-07:45)` | `Today JSON 15-Min Prices EUR⁄kWh (P1 00:00-07:45)` |
+| `ENTSO-E 15-Min Prices EUR⁄kWh JSON (P2 08:00-15:45)` | `Today JSON 15-Min Prices EUR⁄kWh (P2 08:00-15:45)` |
+| `ENTSO-E 15-Min Prices EUR⁄kWh JSON (P3 16:00-23:45)` | `Today JSON 15-Min Prices EUR⁄kWh (P3 16:00-23:45)` |
+| `Time Of Highest Energy Price Today` | `Today Highest Price Time` |
+| `Time Of Lowest Energy Price Today` | `Today Lowest Price Time` |
+| `Time Of Highest Hourly Energy Price Today` | `Today Highest Hourly Price Time` |
+| `Time Of Lowest Hourly Energy Price Today` | `Today Lowest Hourly Price Time` |
+| `Price Update Status` | `Today Price Update Status` |
+| `Last Price Update Time` | `Today Data Loaded Time` |
+| `Price Update Status Message` | `Today Price Update Status Message` |
+| `Current Price Status` | `Today Current Price Status` |
+| `ENTSO-E Next Day Hourly Prices EUR⁄kWh JSON` | `Tomorrow JSON Hourly Prices EUR⁄kWh` |
+| `ENTSO-E Next Day 15-Min Prices EUR⁄kWh JSON (P1 00:00-07:45)` | `Tomorrow JSON 15-Min Prices EUR⁄kWh (P1 00:00-07:45)` |
+| `ENTSO-E Next Day 15-Min Prices EUR⁄kWh JSON (P2 08:00-15:45)` | `Tomorrow JSON 15-Min Prices EUR⁄kWh (P2 08:00-15:45)` |
+| `ENTSO-E Next Day 15-Min Prices EUR⁄kWh JSON (P3 16:00-23:45)` | `Tomorrow JSON 15-Min Prices EUR⁄kWh (P3 16:00-23:45)` |
+| `Time Of Highest Energy Price Tomorrow` | `Tomorrow Highest Price Time` |
+| `Time Of Lowest Energy Price Tomorrow` | `Tomorrow Lowest Price Time` |
+| `Time Of Highest Hourly Energy Price Tomorrow` | `Tomorrow Highest Hourly Price Time` |
+| `Time Of Lowest Hourly Energy Price Tomorrow` | `Tomorrow Lowest Hourly Price Time` |
+| `Next Day Price Update Status` | `Tomorrow Price Update Status` |
+| `Next Day Last Price Update Time` | `Tomorrow Data Loaded Time` |
+| `Next Day Price Update Status Message` | `Tomorrow Price Update Status Message` |
+| `Next Day Current Price Status` | `Tomorrow Current Price Status` |
+| `ENTSO-E Last Reboot` | `Last Reboot` |
+| `Entso-E Today NVS Status` | `Today NVS Status` |
+| `Entso-E Tomorrow NVS Status` | `Tomorrow NVS Status` |
+| `ENTSO-E Last Update Source` | `Last Update Source` |
+| `Today Data Date` | `Today Data Date` *(unchanged)* |
+| `Tomorrow Data Date` | `Tomorrow Data Date` *(unchanged)* |
+
+#### Buttons
+
+| entso-e-prices v4.3.1 name | EPrices v1.0 name |
+|---|---|
+| `Entso-E Force Update` | `Force Today's Update` |
+| `Entso-E Force Next Day Update` | `Force Tomorrow's Update` |
+| `Entso-E Reboot Device` | `Reboot Device` |
+
+### New sensors in EPrices v1.0 (no equivalent in v4.3.1)
+
+| Sensor | Purpose |
+|---|---|
+| `Today Last API Fetch Time` | Timestamp of last successful HTTP fetch for today |
+| `Tomorrow Last API Fetch Time` | Timestamp of last successful HTTP fetch for tomorrow |
+| `WiFi Signal` | RSSI in dBm |
+| `Uptime` | Human-readable uptime string |
+
+### Sensor output changes
+
+| Sensor | v4.3.1 output | EPrices v1.0 output |
+|---|---|---|
+| `Last Reboot` | `Last reboot: 2026-04-04 20:10:10` | `2026-04-04 20:10:10` |
+| `Today NVS Status` | `Today NVS: Stored 96 pts for 2026-04-04` | `Stored 96 pts for 2026-04-04` |
+| `Tomorrow NVS Status` | `Tomorrow NVS: Stored 96 pts for 2026-04-05` | `Stored 96 pts for 2026-04-05` |
+| `Today Entry Count` | `96.0` | `96` |
+| `Tomorrow Entry Count` | `96.0` | `96` |
+| `Today API Fetch Attempts` | `0.0` | `0` |
+| `Tomorrow API Fetch Attempts` | `0.0` | `0` |
+| `Today Current Price Status` | `Valid` / `Missing` | `Valid` / `Missing` / `Stale` |
+| `Today Data Loaded Time` | Stamped on HTTP fetch only | Stamped on NVS load and HTTP fetch |
+| `Tomorrow Data Loaded Time` | `Never` after NVS boot load | Stamped on NVS load and HTTP fetch |
+
+### HA entity ID changes
+
+All entity IDs changed due to the node name change from `entso-e-prices` to `eprices`.
+
+**Find and replace in all your automations and dashboards:**
+```
+sensor.entso_e_prices_  →  sensor.eprices_
+button.entso_e_prices_  →  button.eprices_
+```
+
+Then apply the individual sensor name slug changes from the tables above.
+
+### NVS data
+
+The NVS namespace changed from `entsoe2` to `eprices`. On first boot after
+flashing EPrices v1.0 the device will not find any stored data and will
+trigger a fresh HTTP fetch automatically. This is expected and safe.
+No manual NVS erase is required.
+
+---
+
+## Migration checklist
+
+- [ ] Flash `eprices.yaml` to the device
+- [ ] Update `secrets.yaml` — rename all `entsoe_` keys to `eprices_`; add `eprices_prov_fee` and `eprices_vat_rate`
+- [ ] In all HA automations: replace `entso_e_prices_` with `eprices_` in all entity IDs
+- [ ] Apply individual sensor name slug renames from the tables above
+- [ ] Remove any external HA automations that handled midnight bridge, boot recovery, or fetch scheduling — these are now all on-device
+- [ ] Verify the device fetches fresh data on first boot (check `Today NVS Status` and `Today Price Update Status Message`)
+- [ ] Update any HA dashboard cards referencing old entity IDs

VERSION.md

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+# EPrices – Version History
+
+## v1.0 — 2026-04-05
+
+First public release.
+
+### What EPrices is
+
+EPrices is an ESPHome firmware for ESP32 that fetches day-ahead electricity
+spot prices from the public Energy-Charts API and exposes them as Home Assistant
+sensors. No API token, no cloud subscription, no external automations required
+for core functionality — just an ESP32, ESPHome, and your WiFi network.
+
+Prices are fetched for today and tomorrow in 15-minute resolution, converted
+from raw €/MWh to €/kWh with your provider fee and VAT applied, and stored
+persistently in ESP32 NVS flash so they survive reboots without re-fetching.
+
+### Core features
+
+- 15-minute and hourly resolution price arrays exposed as JSON text sensors
+- Current, next, average, highest and lowest price sensors for both today and tomorrow
+- Tomorrow live sensors evaluate at `now + 86400s` — showing tomorrow at the same local time
+- NVS persistence — prices survive reboots without re-fetching
+- Midnight bridge — tomorrow's data automatically promoted to today at 00:00
+- Auto-retry logic — up to 8 HTTP fetch attempts for both today and tomorrow
+- DST-safe — UNIX timestamps and binary search throughout, no hour-slot arithmetic
+- Staleness detection — `Today Current Price Status` shows `Stale` if stored date mismatches today
+- Full diagnostic sensor suite — NVS status, fetch attempts, API fetch times, data loaded
+  times, WiFi signal, human-readable uptime
+- Supports any Energy-Charts bidding zone (SI, DE-LU, AT, FR, HR, HU and more)
+- Provider fee and VAT rate configurable via `secrets.yaml` — no code changes needed
+
+### Sensor highlights
+
+- **Today/Tomorrow JSON Hourly Prices EUR⁄kWh** — 24-value JSON arrays
+- **Today/Tomorrow JSON 15-Min Prices EUR⁄kWh (P1/P2/P3)** — three 32-value JSON arrays
+  covering 00:00-07:45, 08:00-15:45 and 16:00-23:45
+- **Today/Tomorrow Data Loaded Time** — stamped on both NVS load and HTTP fetch
+- **Today/Tomorrow Last API Fetch Time** — stamped on HTTP fetch only; `Never` if NVS only
+- **Today/Tomorrow API Fetch Attempts** — HTTP-only counter, resets at midnight
+- **Uptime** — human-readable: `45 s` → `5 min` → `3 h 22 min` → `12 d 4 h` → `4 months 12 d`
+
+### Files
+
+| File | Purpose |
+|---|---|
+| `eprices.yaml` | Main ESPHome configuration |
+| `eprices_nvs.h` | NVS helper — save/load price arrays to ESP32 flash |
+| `secrets.yaml` | Local secrets — not committed to git |
+| `CHANGELOG.md` | Full sensor and entity ID reference for v1.0 |
+| `README.md` | Installation guide and full sensor reference |
+| `ENTSO-E-PRICES-MIGRATION.md` | Optional — migration guide from the predecessor project |

eprices_nvs.h

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+#pragma once
+// EPrices NVS helper
+// Namespace: "eprices"
+// Keys: td_count, td_date, td_prices, td_ts
+//       tm_count, tm_date, tm_prices, tm_ts
+
+#include <vector>
+#include <string>
+#include <cstdint>
+#include "esphome/core/log.h"
+#include "nvs_flash.h"
+#include "nvs.h"
+
+namespace eprices_nvs {
+
+static const char *TAG  = "eprices_nvs";
+static const char *NS   = "eprices";
+
+// ---- internal: ensure NVS is initialised once ----
+inline bool ensure_init() {
+  static bool done = false;
+  if (done) return true;
+  esp_err_t e = nvs_flash_init();
+  if (e == ESP_ERR_NVS_NO_FREE_PAGES || e == ESP_ERR_NVS_NEW_VERSION_FOUND) {
+    nvs_flash_erase();
+    e = nvs_flash_init();
+  }
+  done = (e == ESP_OK);
+  if (!done) ESP_LOGE(TAG, "nvs_flash_init failed: %s", esp_err_to_name(e));
+  return done;
+}
+
+// ---- save ----
+inline bool save(const char *count_key, const char *date_key,
+                 const char *prices_key, const char *ts_key,
+                 int count, const std::string &date,
+                 const std::vector<float>   &prices,
+                 const std::vector<int64_t> &timestamps) {
+  if (!ensure_init()) return false;
+  nvs_handle_t h;
+  esp_err_t e = nvs_open(NS, NVS_READWRITE, &h);
+  if (e != ESP_OK) { ESP_LOGW(TAG, "save open failed: %s", esp_err_to_name(e)); return false; }
+
+  nvs_set_i32(h, count_key, (int32_t)count);
+  nvs_set_blob(h, date_key, date.c_str(), date.size() + 1);
+  if (count > 0) {
+    nvs_set_blob(h, prices_key, prices.data(),     (size_t)count * sizeof(float));
+    nvs_set_blob(h, ts_key,     timestamps.data(), (size_t)count * sizeof(int64_t));
+  }
+  nvs_commit(h);
+  nvs_close(h);
+  ESP_LOGI(TAG, "save(%s): %d entries for %s", count_key, count, date.c_str());
+  return true;
+}
+
+// ---- load: returns false if missing, stale or corrupt ----
+inline bool load(const char *count_key, const char *date_key,
+                 const char *prices_key, const char *ts_key,
+                 const std::string &expected_date,
+                 std::vector<float>   &out_prices,
+                 std::vector<int64_t> &out_timestamps,
+                 int &out_count) {
+  if (!ensure_init()) return false;
+  nvs_handle_t h;
+  esp_err_t e = nvs_open(NS, NVS_READONLY, &h);
+  if (e != ESP_OK) { ESP_LOGW(TAG, "load open failed: %s", esp_err_to_name(e)); return false; }
+
+  int32_t count = 0;
+  e = nvs_get_i32(h, count_key, &count);
+  if (e != ESP_OK || count <= 0 || count > 110) {
+    ESP_LOGW(TAG, "load(%s): bad count %d", count_key, (int)count);
+    nvs_close(h); return false;
+  }
+
+  char date_buf[12] = {};
+  size_t date_len = sizeof(date_buf);
+  nvs_get_blob(h, date_key, date_buf, &date_len);
+  if (expected_date != std::string(date_buf)) {
+    ESP_LOGW(TAG, "load(%s): stale %s != %s", count_key, date_buf, expected_date.c_str());
+    nvs_close(h); return false;
+  }
+
+  std::vector<float>   pv((size_t)count);
+  std::vector<int64_t> ts((size_t)count);
+  size_t sp = (size_t)count * sizeof(float);
+  size_t st = (size_t)count * sizeof(int64_t);
+  nvs_get_blob(h, prices_key, pv.data(), &sp);
+  nvs_get_blob(h, ts_key,     ts.data(), &st);
+  nvs_close(h);
+
+  out_prices     = pv;
+  out_timestamps = ts;
+  out_count      = (int)count;
+  ESP_LOGI(TAG, "load(%s): %d entries for %s", count_key, (int)count, expected_date.c_str());
+  return true;
+}
+
+// ---- clear one slot (set count=0) ----
+inline void clear_slot(const char *count_key) {
+  if (!ensure_init()) return;
+  nvs_handle_t h;
+  if (nvs_open(NS, NVS_READWRITE, &h) == ESP_OK) {
+    nvs_set_i32(h, count_key, 0);
+    nvs_commit(h);
+    nvs_close(h);
+  }
+}
+
+// ---- public wrappers ----
+inline bool save_today(int count, const std::string &date,
+                       const std::vector<float> &p, const std::vector<int64_t> &ts) {
+  return save("td_count","td_date","td_prices","td_ts", count, date, p, ts);
+}
+inline bool save_tomorrow(int count, const std::string &date,
+                          const std::vector<float> &p, const std::vector<int64_t> &ts) {
+  return save("tm_count","tm_date","tm_prices","tm_ts", count, date, p, ts);
+}
+inline bool load_today(const std::string &expected_date,
+                       std::vector<float> &p, std::vector<int64_t> &ts, int &cnt) {
+  return load("td_count","td_date","td_prices","td_ts", expected_date, p, ts, cnt);
+}
+inline bool load_tomorrow(const std::string &expected_date,
+                          std::vector<float> &p, std::vector<int64_t> &ts, int &cnt) {
+  return load("tm_count","tm_date","tm_prices","tm_ts", expected_date, p, ts, cnt);
+}
+inline void clear_tomorrow_slot() { clear_slot("tm_count"); }
+
+} // namespace eprices_nvs