//! Parse the cassiopeia file format
//!
//! Each file is associated with a single project.  This way there is
//! no need to associate session enries with multiple customers and
//! projcets.  Currently there's also no way to cross-relate sessions
//! between projects or clients, although the metadata in the header
//! is available to do so in the future
//!
//! ## Structure
//!
//! `cassiopeia` files should use the `.cass` extension, although this
//! implementation is not opinionated on that.
//!
//! A line starting with `;` is a comment and can be ignored.  A line
//! can have a comment anywhere, which means that everything after it
//! gets ignored.  There are no block comments.
//!
//! A regular statements has two parts: a key, and a value.  Available
//! keys are:
//!
//! - HEADER
//! - START
//! - STOP
//! - FINISH
//!
//! A file has to have at least one `HEADER` key, containing a certain
//! number of fields to be considered valid.  The required number of
//! fields may vary between versions.
//!
//! ### HEADER
//!
//! `cassiopeia` in princpile only needs a single value to parse a
//! file, which is `version`.  It is however recommended to add
//! additional metadata to allow future processing into clients and
//! cross-referencing projects.  Importantly: header keys that are not
//! expected will be ignored.
//!
//! The general header format is a comma-separated list with a key
//! value pair, separated by an equals sign.  You can use spaces in
//! both keys and values without having to escape them or use special
//! quotes.  Leading and trailing spaces will be removed.
//!
//! ```
//! HEADER version=0.0.0,location=Berlin
//! HEADER work schedule=mon tue wed
//! ```
//!
//! When re-writing the file format, known/ accepted keys should go
//! first.  All other unknown keys will be printed alphabetically at
//! the end.  This way it's possible for an outdated implementation to
//! pass through unknown keys, or users to add their own keys.

use chrono::{DateTime, Utc};
use std::{fs::File, io::Read, path::Path};

/// A cassiopeia file that has been successfully parsed
pub struct TimeFile {
    path: PathBuf,
    content: Vec<Statement>,
}

impl TimeFile {
    /// Open an existing `.cass` file on disk.  Panics!
    pub fn open(p: impl Into<Path>) -> Self {
        let mut f = File::open(p).unwrap();
        let mut cont = String::new();
        f.read_to_string(&mut cont).unwrap();
    }
}

/// A statement in a `.cass` line
///
/// While the whole file get's re-written on every run to update
/// version numbers and header values, the structure of the file is
/// preserved.
pub enum Statement {
    /// A blank line
    Blank,
    /// A comment line that is echo-ed back out
    Comment(String),
    /// Header value
    Header(Vec<HeaderVal>),
    /// A session start value
    Start(DateTime<Utc>),
    /// A session stop value
    Stop(DateTime<Utc>),
    /// A project finish value
    Finish(DateTime<Utc>),
}

/// A set of header value
pub struct HeaderVal {
    /// Header key
    key: String,
    /// Header value
    val: String,
}

impl HeaderVal {
    fn new<S: Into<String>>(key: S, val: S) -> Self {
        Self {
            key: key.into(),
            val: val.into(),
        }
    }

    /// Test if a header value is known to this implementation
    fn known(&self) -> bool {
        match self.key {
            "version" => true,
            _ => false,
        }
    }
}

/// A builder for cass files
#[cfg(tests)]
struct FileBuilder {
    acc: Vec<Statement>,
}

impl FileBuilder {
    fn new() -> Self {
        Self { acc: vec![] }
    }

    fn header(mut self, data: Vec<(&str, &str)>) -> Self {
        self.acc.push(Statement::Header(
            data.into_iter()
                .map(|(key, val)| HeaderVal::new(key, val))
                .collect(),
        ));

        self
    }

    fn build(self) -> String {
        format!(";; This file was generated by cassiopeia (reference)\n{}", self.acc.into_iter().map(|s| s.render()).collect::<Vec<_>().join("\n"))
    }
}

#[test]
fn empty_file() {
    let fb = FileBuilder::new().header(vec![("version", "0.3.0"), ("project", "testing")]);
}