use std::fs::File;
use std::path::Path;
use std::time::SystemTime;

use semver::Version;
use serde_derive::{Deserialize, Serialize};

use crate::error::*;

#[derive(Debug, PartialEq, Eq, Default, Serialize, Deserialize)]
pub struct AssetsMetadata {
    bat_version: Option<String>,
    creation_time: Option<SystemTime>,
}

const FILENAME: &str = "metadata.yaml";

impl AssetsMetadata {
    #[cfg(feature = "build-assets")]
    pub(crate) fn new(current_version: &str) -> AssetsMetadata {
        AssetsMetadata {
            bat_version: Some(current_version.to_owned()),
            creation_time: Some(SystemTime::now()),
        }
    }

    #[cfg(feature = "build-assets")]
    pub(crate) fn save_to_folder(&self, path: &Path) -> Result<()> {
        let file = File::create(path.join(FILENAME))?;
        serde_yaml::to_writer(file, self)?;

        Ok(())
    }

    fn try_load_from_folder(path: &Path) -> Result<Self> {
        let file = File::open(path.join(FILENAME))?;
        Ok(serde_yaml::from_reader(file)?)
    }

    /// Load metadata about the stored cache file from the given folder.
    ///
    /// There are several possibilities:
    ///   - We find a `metadata.yaml` file and are able to parse it
    ///     - return the contained information
    ///   - We find a `metadata.yaml` file, but are not able to parse it
    ///     - return a [`Error::SerdeYamlError`]
    ///   - We do not find a `metadata.yaml` file but a `syntaxes.bin` or `themes.bin` file
    ///     - assume that these were created by an old version of bat and return
    ///       [`AssetsMetadata::default()`] without version information
    ///   - We do not find a `metadata.yaml` file and no cached assets
    ///     - no user provided assets are available, return `None`
    pub fn load_from_folder(path: &Path) -> Result<Option<Self>> {
        match Self::try_load_from_folder(path) {
            Ok(metadata) => Ok(Some(metadata)),
            Err(e) => {
                if let Error::SerdeYamlError(_) = e {
                    Err(e)
                } else if path.join("syntaxes.bin").exists() || path.join("themes.bin").exists() {
                    Ok(Some(Self::default()))
                } else {
                    Ok(None)
                }
            }
        }
    }

    pub fn is_compatible_with(&self, current_version: &str) -> bool {
        let current_version =
            Version::parse(current_version).expect("bat follows semantic versioning");
        let stored_version = self
            .bat_version
            .as_ref()
            .and_then(|ver| Version::parse(ver).ok());

        if let Some(stored_version) = stored_version {
            current_version.major == stored_version.major
                && current_version.minor == stored_version.minor
        } else {
            false
        }
    }
}
