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//! C allocates/frees PSRAM; Rust only borrows its immutable initialized contents.
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use super::ffi;
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use crate::error::{Error, Result};
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use std::{ptr::NonNull, slice};
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#[derive(Debug)]
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pub(crate) struct MusicBytes {
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    pointer: NonNull<u8>,
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    length: usize,
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}
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impl MusicBytes {
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    pub(crate) fn load() -> Result<Self> {
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        let mut length = 0;
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        // SAFETY: length is writable for the call. On success C transfers a
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        // fresh, fully initialized PSRAM allocation with no remaining aliases.
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        let pointer = NonNull::new(unsafe { ffi::radio_music_load(&mut length) })
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            .ok_or(Error::new("music partition could not be loaded"))?;
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        let bytes = Self { pointer, length };
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        if length != 4 * 1024 * 1024 {
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            return Err(Error::new("unexpected music partition size"));
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        }
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        Ok(bytes)
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    }
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    pub(crate) fn as_slice(&self) -> &[u8] {
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        // SAFETY: C returned exactly length initialized bytes in one allocation,
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        // bounded to 4 MiB (< isize::MAX). No C aliases remain. The returned
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        // lifetime is tied to self, so Drop cannot free live Rust borrows.
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        unsafe { slice::from_raw_parts(self.pointer.as_ptr(), self.length) }
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    }
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}
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impl Drop for MusicBytes {
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    fn drop(&mut self) {
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        // SAFETY: sole allocation owner; borrows have ended; free on C's allocator.
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        unsafe { ffi::radio_music_free(self.pointer.as_ptr()) };
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    }
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}