use serde::{Deserialize, Serialize};
use std::fs::File;
use std::io::Read;
use std::path::PathBuf;
use std::time::{SystemTime, UNIX_EPOCH};
use time::{OffsetDateTime, format_description::well_known::Rfc2822};

#[derive(Serialize, Deserialize)]
pub struct Metadata {
    pub id: String,
    #[serde(alias = "createdOn")]
    pub created_on: u64,
}

impl Metadata {
    /// Reads `Metadata` from a file or creates a new one.
    ///
    /// This method will create new metadata if it can't read the file,
    /// whether it's because of malformed JSON, UTF-8 or because the file
    /// is not readable.
    pub fn read_or_create(file_path: &PathBuf) -> Metadata {
        if let Some(metadata) = Metadata::read_metadata_file(file_path) {
            metadata
        } else {
            let timestamp = SystemTime::now().duration_since(UNIX_EPOCH).map_or_else(
                |_| 0,
                |duration| u64::try_from(duration.as_millis()).unwrap_or(0),
            );

            Metadata {
                id: timestamp.to_string(),
                created_on: timestamp,
            }
        }
    }

    /// Returns the metadata `created_on` as an RFC-2822 string.
    pub fn created_on_utc(&self) -> Option<String> {
        let date =
            OffsetDateTime::from_unix_timestamp_nanos((self.created_on * 1_000_000).into()).ok()?;
        date.format(&Rfc2822).ok()
    }

    fn read_metadata_file(file_path: &PathBuf) -> Option<Metadata> {
        let mut file = File::open(file_path).ok()?;
        let mut contents = String::new();
        file.read_to_string(&mut contents).ok()?;
        serde_json::from_str(&contents).ok()
    }
}

#[cfg(test)]
mod tests {
    use std::fs::write;

    use super::*;

    use test_utilities::*;

    #[test]
    fn test_reads_metadata_if_file_exists() {
        let test_dir = setup_test_dir();
        create_test_file(
            &test_dir.join("metadata.json"),
            "\
{
    \"id\": \"cool\",
    \"created_on\": 1736105008957
}",
        );

        let metadata = Metadata::read_or_create(&test_dir.join("metadata.json"));

        assert_eq!(metadata.id, "cool");
        assert_eq!(metadata.created_on, 1_736_105_008_957);
        cleanup_test_dir(&test_dir);
    }

    #[test]
    fn test_creates_metadata_if_file_does_not_exist() {
        let test_dir = setup_test_dir();

        assert!(!test_dir.join("metadata.json").exists());
        let metadata = Metadata::read_or_create(&test_dir.join("metadata.json"));
        assert_eq!(metadata.created_on.to_string(), metadata.id);
        cleanup_test_dir(&test_dir);
    }

    #[test]
    fn test_creates_metadata_if_file_is_malformed() {
        let test_dir = setup_test_dir();
        write(test_dir.join("metadata.json"), vec![0xFF, 0xFF]).expect("Failed to write file");

        let metadata = Metadata::read_or_create(&test_dir.join("metadata.json"));
        assert_eq!(metadata.created_on.to_string(), metadata.id);
        cleanup_test_dir(&test_dir);
    }

    #[test]
    fn test_it_returns_created_on_as_rfc_2822_utc() {
        let metadata = Metadata {
            id: "cool".to_string(),
            created_on: 1_736_035_200_000,
        };

        if let Some(created_on_utc) = metadata.created_on_utc() {
            assert_eq!(created_on_utc, "Sun, 05 Jan 2025 00:00:00 +0000");
        } else {
            panic!("Could not generate RFC-2822 string");
        }
    }
}