//! Transport-sized request, response, and provider boundary types.

use crate::{CONTENT_BYTES, DATA_BYTES};

/// Exact MAVLink endpoint that owns the virtual-file service.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct Target {
    system: u8,
    component: u8,
}

impl Target {
    /// Creates one exact, non-broadcast endpoint.
    pub const fn new(system: u8, component: u8) -> Self {
        assert!(system != 0 && component != 0, "file target must be exact");
        Self { system, component }
    }

    /// Parses an exact endpoint from an untrusted request.
    pub const fn try_new(system: u8, component: u8) -> Option<Self> {
        if system == 0 || component == 0 {
            None
        } else {
            Some(Self { system, component })
        }
    }

    /// Target system identity.
    pub const fn system(self) -> u8 {
        self.system
    }

    /// Target component identity.
    pub const fn component(self) -> u8 {
        self.component
    }
}

/// Exact MAVLink source that owns an open transfer.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct Principal {
    system: u8,
    component: u8,
}

impl Principal {
    /// Creates one exact source identity.
    pub const fn new(system: u8, component: u8) -> Self {
        assert!(
            system != 0 && component != 0,
            "file principal must be exact"
        );
        Self { system, component }
    }

    /// Parses an exact source identity from an untrusted frame.
    pub const fn try_new(system: u8, component: u8) -> Option<Self> {
        if system == 0 || component == 0 {
            None
        } else {
            Some(Self { system, component })
        }
    }

    pub(crate) const fn target(self) -> Target {
        Target {
            system: self.system,
            component: self.component,
        }
    }

    /// Source system identity.
    pub const fn system(self) -> u8 {
        self.system
    }

    /// Source component identity.
    pub const fn component(self) -> u8 {
        self.component
    }
}

/// File operation carried by `FILE_CONTROL`.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
#[repr(u8)]
pub enum FileOperation {
    /// Opens a stable read snapshot selected by the supplied path.
    OpenRead = 1,
    /// Opens a bounded write staging area selected by the supplied path.
    OpenWrite = 2,
    /// Requests the chunk beginning at `position`.
    Read = 3,
    /// Acknowledges one accepted upload chunk.
    WriteAck = 4,
    /// Completes an open transfer.
    Close = 5,
    /// Discards an open transfer.
    Abort = 6,
}

/// Authoritative result carried by a control response.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
#[repr(u8)]
pub enum FileStatus {
    /// The operation succeeded.
    Ok = 1,
    /// Another principal owns the single transfer slot.
    Busy = 2,
    /// The transfer identity is absent, stale, or owned by another principal.
    InvalidTransfer = 3,
    /// The operation is not valid for the transfer's current mode or state.
    InvalidState = 4,
    /// The open request did not carry one canonical bounded path.
    InvalidPath = 5,
    /// No virtual file exists at the supplied path.
    NotFound = 6,
    /// The declared complete file exceeds the provider's bound.
    TooLarge = 7,
    /// A chunk or read did not start at an admissible position.
    InvalidPosition = 8,
    /// The complete sequential upload disagrees with its declared CRC-32C.
    ChecksumMismatch = 9,
    /// The provider rejected the complete file contents.
    ContentRejected = 10,
    /// Durable storage failed; the resulting durable state may be unknown.
    StorageFailure = 11,
    /// A retry reused an operation identity with different content.
    RequestConflict = 12,
    /// A provider or service invariant failed.
    Internal = 13,
}

/// Bounded opaque response detail or open-request path storage.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct Content {
    length: u8,
    bytes: [u8; CONTENT_BYTES],
}

impl Content {
    /// Empty content.
    pub const EMPTY: Self = Self {
        length: 0,
        bytes: [0; CONTENT_BYTES],
    };

    /// Copies a bounded byte sequence.
    pub fn try_new(bytes: &[u8]) -> Option<Self> {
        if bytes.len() > CONTENT_BYTES {
            return None;
        }
        let mut content = Self::EMPTY;
        content.bytes[..bytes.len()].copy_from_slice(bytes);
        content.length = bytes.len() as u8;
        Some(content)
    }

    /// Parses canonical length-delimited wire content.
    pub(crate) fn from_wire(length: u8, bytes: [u8; CONTENT_BYTES]) -> Option<Self> {
        let length = usize::from(length);
        if length > CONTENT_BYTES || bytes[length..].iter().any(|byte| *byte != 0) {
            return None;
        }
        Some(Self {
            length: length as u8,
            bytes,
        })
    }

    /// Logical initialized bytes.
    pub fn as_bytes(&self) -> &[u8] {
        &self.bytes[..usize::from(self.length)]
    }

    /// Logical byte count.
    pub(crate) const fn len(self) -> u8 {
        self.length
    }

    /// Whether the logical content is empty.
    pub(crate) const fn is_empty(self) -> bool {
        self.length == 0
    }

    /// Zero-padded wire storage.
    pub(crate) const fn wire_bytes(self) -> [u8; CONTENT_BYTES] {
        self.bytes
    }
}

/// Canonical absolute ASCII virtual-file path.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct FilePath(Content);

impl FilePath {
    /// Validates a bounded absolute path without normalization or allocation.
    pub(crate) fn try_from_content(content: Content) -> Option<Self> {
        let bytes = content.as_bytes();
        if bytes.len() < 2 || bytes[0] != b'/' || bytes[bytes.len() - 1] == b'/' {
            return None;
        }
        let mut segment_start = 1;
        for (index, byte) in bytes.iter().copied().enumerate().skip(1) {
            if byte == b'/' {
                if index == segment_start || reserved_segment(&bytes[segment_start..index]) {
                    return None;
                }
                segment_start = index + 1;
            } else if !matches!(byte, b'a'..=b'z' | b'A'..=b'Z' | b'0'..=b'9' | b'.' | b'_' | b'-')
            {
                return None;
            }
        }
        if reserved_segment(&bytes[segment_start..]) {
            return None;
        }
        Some(Self(content))
    }

    /// Canonical path bytes.
    pub fn as_bytes(&self) -> &[u8] {
        self.0.as_bytes()
    }
}

fn reserved_segment(segment: &[u8]) -> bool {
    segment == b"." || segment == b".."
}

/// One decoded control request.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct ControlRequest {
    /// Request-selected operation.
    pub operation: FileOperation,
    /// Exact addressed service endpoint.
    pub target: Target,
    /// Transfer-relative byte position.
    pub position: u32,
    /// Complete file size declared by an open-write request.
    pub file_size: u32,
    /// Complete CRC-32C declared by an open-write request.
    pub checksum_crc32c: u32,
    /// Nonzero client-selected transfer identity.
    pub transfer_id: u16,
    /// Canonical path bytes for opens; empty for all other requests.
    pub content: Content,
}

/// One decoded upload data request.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct DataRequest {
    /// Exact addressed service endpoint.
    pub target: Target,
    /// Transfer-relative byte position.
    pub position: u32,
    /// Nonzero client-selected transfer identity.
    pub transfer_id: u16,
    /// Fixed wire chunk. Its logical length comes from the open file size.
    pub data: [u8; DATA_BYTES],
}

/// Request accepted by [`crate::FileService`].
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum FileRequest {
    /// Control operation.
    Control(ControlRequest),
    /// Write data.
    Data(DataRequest),
}

/// One control response.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct ControlResponse {
    /// Operation whose outcome is reported.
    pub operation: FileOperation,
    /// Requester addressed by the response.
    pub target: Target,
    /// Next accepted position or request position on failure.
    pub position: u32,
    /// Complete opened file size.
    pub file_size: u32,
    /// Complete opened file CRC-32C.
    pub checksum_crc32c: u32,
    /// Client-selected transfer identity.
    pub transfer_id: u16,
    /// Authoritative outcome.
    pub status: FileStatus,
    /// Bounded provider detail.
    pub content: Content,
}

/// One read-data response.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct DataResponse {
    /// Requester addressed by the response.
    pub target: Target,
    /// Position of the first logical byte.
    pub position: u32,
    /// Transfer identity.
    pub transfer_id: u16,
    /// Zero-padded wire data; logical length derives from the opened file size.
    pub data: [u8; DATA_BYTES],
}

/// Response produced by [`crate::FileService`].
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum FileResponse {
    /// Control outcome.
    Control(ControlResponse),
    /// Read data.
    Data(DataResponse),
}

/// Stable metadata returned when a provider pins a readable file.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct FileMetadata {
    /// Exact complete byte length.
    pub size: u32,
    /// CRC-32C of the complete pinned bytes.
    pub checksum_crc32c: u32,
}

/// Format-agnostic provider rejection.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct FileFailure {
    /// Stable generic failure classification.
    status: FileStatus,
    /// Bounded format-specific detail.
    content: Content,
}

impl FileFailure {
    /// Constructs a provider failure. Success statuses are rejected.
    pub const fn new(status: FileStatus, content: Content) -> Option<Self> {
        match status {
            FileStatus::Ok => None,
            _ => Some(Self { status, content }),
        }
    }

    /// Stable generic failure classification.
    pub(crate) const fn status(self) -> FileStatus {
        self.status
    }

    /// Bounded format-specific detail.
    pub(crate) const fn content(self) -> Content {
        self.content
    }
}