//! Errors the `ffprobe` wrapper can produce.

use std::path::PathBuf;

/// Result alias for every fallible operation in this crate.
pub type Result<T> = std::result::Result<T, Error>;

/// Everything that can go wrong probing a file.
///
/// Nothing here has a default. A file `ffprobe` cannot read is an error, never
/// a `ProbedFile` full of zeroes — importing on top of a default-valued struct
/// would silently record a 0-byte SDR file with no audio and pass every policy
/// rule that inspects a field it does not have (DESIGN.md §5.6, §5.7).
#[derive(Debug, thiserror::Error)]
#[non_exhaustive]
pub enum Error {
    /// `ffprobe` could not be started at all: not installed, or not on `PATH`.
    #[error("could not run {binary}")]
    Spawn {
        /// The binary that was attempted.
        binary: String,
        /// The underlying spawn failure.
        #[source]
        source: std::io::Error,
    },

    /// `ffprobe` started but exited non-zero — an unreadable or corrupt file.
    #[error("ffprobe rejected {path}: {stderr}")]
    Rejected {
        /// The file that was probed.
        path: PathBuf,
        /// Exit status, absent when the process was killed by a signal.
        status: Option<i32>,
        /// `ffprobe`'s own diagnostics, truncated to something loggable.
        stderr: String,
    },

    /// `ffprobe` did not finish within the configured timeout.
    #[error("ffprobe timed out probing {path}")]
    Timeout {
        /// The file that was probed.
        path: PathBuf,
    },

    /// Reading the child process failed after it was spawned.
    #[error("reading ffprobe output for {path} failed")]
    Io {
        /// The file that was probed.
        path: PathBuf,
        /// The underlying IO failure.
        #[source]
        source: std::io::Error,
    },

    /// `ffprobe` printed something that is not the JSON shape expected.
    #[error("ffprobe output for {path} did not parse")]
    Decode {
        /// The file that was probed.
        path: PathBuf,
        /// The deserialisation failure.
        #[source]
        source: serde_json::Error,
    },

    /// `ffprobe` read the file, but as a still image or as text.
    ///
    /// ffmpeg's `tty` demuxer parses any text file at all as ANSI art video,
    /// and the image demuxers turn a poster into a one-frame film. Both would
    /// otherwise pass for importable media.
    #[error("{path} is not a video file: ffprobe read it as {format}")]
    NotVideo {
        /// The file that was probed.
        path: PathBuf,
        /// The container format `ffprobe` matched.
        format: String,
    },

    /// `ffprobe` read the file but it carries no video stream.
    #[error("{path} has no video stream")]
    NoVideoStream {
        /// The file that was probed.
        path: PathBuf,
    },

    /// A container that reports neither a duration nor a stream long enough to
    /// derive one. The runtime sanity check has nothing to work with.
    #[error("{path} reports no duration")]
    NoDuration {
        /// The file that was probed.
        path: PathBuf,
    },

    /// Feature selection was handed a set of paths with no readable video file
    /// among them.
    #[error("no video file among the candidates")]
    NoCandidates,
}

impl Error {
    /// Whether this failure is a fact about one file rather than about the
    /// prober.
    ///
    /// Feature selection walks a torrent full of `.nfo`, `.jpg` and `.txt`
    /// files, so a file that is not importable media is expected and gets
    /// skipped. A missing binary, a timeout or unparseable output is not about
    /// the file at all, and swallowing it would report "no video file" for a
    /// torrent that has one.
    #[must_use]
    pub const fn is_about_the_file(&self) -> bool {
        matches!(
            self,
            Self::Rejected { .. }
                | Self::NotVideo { .. }
                | Self::NoVideoStream { .. }
                | Self::NoDuration { .. }
        )
    }
}