//! Book codes and their number spaces.
//!
//! This implements the [book codes][bc] for the book integration.  In this module,
//! we use *book code* to refer to the numberspaced numeric code representing the
//! book record in the common code space, and *identifier* (or *underlying identifier*)
//! for the native identifier of the underlying record.  Identifiers are translated
//! into codes by adding the number space's base, which partitions the code space
//! into different regions.
//!
//! [bc]: https://bookdata.piret.info/data/ids.html#book-codes

/// The "number space" structure for identifier spaces.
pub struct NS<'a> {
    /// The name of this numberspace.
    pub name: &'a str,
    /// The name usable as a part of an identifier name (snake_case).
    pub fn_name: &'a str,
    /// The number space numeric code.
    pub code: i32,
}

/// The multiplier base for distinguishing numbers in a number space.
/// Each space supports up to 100K identifiers.
pub const NS_MULT_BASE: i32 = 100_000_000;

#[allow(dead_code)]
pub const NS_WORK: NS<'static> = NS::new("OL-W", "ol_work", 1);
#[allow(dead_code)]
pub const NS_EDITION: NS<'static> = NS::new("OL-E", "ol_edition", 2);
#[allow(dead_code)]
pub const NS_LOC_REC: NS<'static> = NS::new("LOC", "loc_rec", 3);
#[allow(dead_code)]
pub const NS_GR_WORK: NS<'static> = NS::new("GR-W", "gr_work", 4);
#[allow(dead_code)]
pub const NS_GR_BOOK: NS<'static> = NS::new("GR-B", "gr_book", 5);
#[allow(dead_code)]
pub const NS_LOC_WORK: NS<'static> = NS::new("LOC-W", "loc_work", 6);
#[allow(dead_code)]
pub const NS_LOC_INSTANCE: NS<'static> = NS::new("LOC-I", "loc_instance", 7);
#[allow(dead_code)]
pub const NS_ISBN: NS<'static> = NS::new("ISBN", "isbn", 9);

const NAMESPACES: &'static [&'static NS<'static>] = &[
    &NS_WORK,
    &NS_EDITION,
    &NS_LOC_REC,
    &NS_GR_WORK,
    &NS_GR_BOOK,
    &NS_LOC_WORK,
    &NS_LOC_INSTANCE,
    &NS_ISBN,
];

#[cfg(test)]
use quickcheck::quickcheck;

impl<'a> NS<'a> {
    /// Create a new number space. Internal only.
    const fn new(name: &'a str, fn_name: &'a str, code: i32) -> NS<'a> {
        NS {
            name,
            fn_name,
            code,
        }
    }

    /// Get the name of the number space.
    #[allow(dead_code)]
    pub fn name(&'a self) -> &'a str {
        self.name
    }

    /// Get the numeric code of the number space.
    pub fn code(&'a self) -> i32 {
        self.code
    }

    /// Get the base of the number space. Identifiers are translated into this space
    /// by adding the base.
    pub fn base(&'a self) -> i32 {
        self.code() * NS_MULT_BASE
    }

    /// Convert a numeric identifier to a book code in this number space.
    #[allow(dead_code)]
    pub fn to_code(&'a self, n: i32) -> i32 {
        assert!(n >= 0);
        assert!(n <= NS_MULT_BASE);
        n + self.base()
    }

    /// Extract a numeric identifier from a book code in this number space.
    pub fn from_code(&'a self, n: i32) -> Option<i32> {
        let lo = self.base();
        let hi = lo + NS_MULT_BASE;
        if n >= lo && n < hi {
            Some(n - lo)
        } else {
            None
        }
    }
}

impl NS<'static> {
    pub fn by_name(name: &str) -> Option<&'static NS<'static>> {
        for ns in NAMESPACES {
            if ns.name() == name {
                return Some(ns);
            }
        }

        None
    }
}

/// Get the namespace for a book code.
pub fn ns_of_book_code(code: i32) -> Option<&'static NS<'static>> {
    let pfx = code / NS_MULT_BASE;
    if pfx >= 1 {
        for ns in NAMESPACES {
            if ns.code() == pfx {
                return Some(ns);
            }
        }
    }

    None
}

#[cfg(test)]
quickcheck! {
  fn prop_code_looks_up(code: i32) -> bool {
    if let Some(ns) = ns_of_book_code(code) {
      // mapping worked
      let bc = code % NS_MULT_BASE;
      ns.to_code(bc) == code
    } else {
      // acceptable to not map
      code < NS_MULT_BASE || code > 10*NS_MULT_BASE || code / NS_MULT_BASE == 8
    }
  }
}

#[test]
fn test_to_code() {
    let n = 42;
    let code = NS_LOC_REC.to_code(n);
    assert_eq!(code / NS_MULT_BASE, NS_LOC_REC.code());
}

#[test]
fn test_from_code() {
    let n = 42;
    let code = NS_LOC_REC.to_code(n);
    assert_eq!(NS_LOC_REC.from_code(code), Some(n));
    assert_eq!(NS_EDITION.from_code(code), None);
    assert_eq!(NS_ISBN.from_code(code), None);
}