//! Coverage bookkeeping for the golden tables.
//!
//! CLAUDE.md section 7 enumerates the scenarios that must be covered. A list
//! nobody checks is a wish, so this module is the check: every mandatory
//! scenario must be claimed by at least one case, and every `covers` tag a case
//! uses must be one we know about. Both directions fail, because the second is
//! how a case silently stops testing what its name claims.
//!
//! # Some scenarios are not table-shaped
//!
//! Clock tampering and the 24-hour cap cannot be expressed as data: proving
//! them needs arithmetic that moves, or a bound that must hold across every
//! lock level, not a decision at a point in time. Those live in
//! `super::purity` as code fixtures. [`Location`] records which scenarios are
//! covered where, so "covered" never quietly means "listed but not tested".

use std::collections::BTreeMap;

/// Where a scenario's coverage lives.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Location {
    /// A golden table case claims it.
    Table,
    /// A code fixture in `tests/src/purity.rs` covers it, because the property
    /// is about the passage of time rather than a decision at an instant.
    Fixture,
}

/// Every scenario CLAUDE.md section 7 (and section 1.2 / 1.5.4) requires.
pub const REQUIRED: &[(&str, Location)] = &[
    // Section 7's explicit list.
    ("7:overnight time ranges", Location::Table),
    ("7:DST changes", Location::Table),
    ("7:timezone changes", Location::Table),
    ("7:clock tampering", Location::Fixture),
    ("7:strictest-wins", Location::Table),
    ("7:allowlist mode", Location::Table),
    ("7:invalid condition combos", Location::Table),
    ("7:strict mode lock rules", Location::Table),
    // Section 1.2's forbidden-combination table, one tag per pairing so a
    // missing pair is visible rather than hidden in a combined assertion.
    ("1.2:time+usage rejected", Location::Table),
    ("1.2:time+launch rejected", Location::Table),
    ("1.2:usage+launch rejected", Location::Table),
    ("1.2:usage+location rejected", Location::Table),
    ("1.2:launch+location rejected", Location::Table),
    // Section 1.5.4's safety guarantees.
    ("1.5.4:never-block list is unblockable", Location::Table),
    ("1.5.4:worst case 24h", Location::Fixture),
];

/// Fixture names in `tests/src/purity.rs` that satisfy [`Location::Fixture`].
///
/// Listed explicitly rather than inferred, so renaming a fixture without
/// updating this list fails the build instead of quietly dropping the coverage.
pub const FIXTURES: &[&str] = &[
    "backwards_wall_clock_never_shortens_a_lock",
    "wall_clock_correction_respects_both_bounds",
    "an_undisturbed_clock_costs_nothing",
    "reboot_resumes_conservatively",
    "worst_case_disable_path_is_capped",
];

/// Every `covers` tag used by every case, with a count.
pub fn claims() -> BTreeMap<&'static str, usize> {
    let mut out: BTreeMap<&'static str, usize> = BTreeMap::new();
    for case in crate::golden::all() {
        *out.entry(case.covers).or_insert(0) += 1;
    }
    out
}

/// Table-shaped scenarios with no case claiming them.
///
/// [`Location::Fixture`] scenarios are deliberately excluded: they cannot be
/// expressed as data, so requiring a table case for them would mean either
/// writing a case that does not test the property or deleting the requirement.
/// They are checked by [`fixtures_missing`] instead.
pub fn uncovered() -> Vec<&'static str> {
    let claims = claims();
    REQUIRED
        .iter()
        .filter(|(_, where_)| *where_ == Location::Table)
        .map(|(tag, _)| *tag)
        .filter(|tag| !claims.contains_key(tag))
        .collect()
}

/// Fixture-backed scenarios whose fixture names are not all listed.
///
/// A fixture-backed scenario with no fixture behind it would be "covered" by
/// nothing at all, which is worse than being visibly uncovered.
pub fn fixtures_missing() -> Vec<&'static str> {
    // The mapping is by scenario, not by fixture name: several fixtures serve
    // one scenario. Assert the reverse instead — that every listed fixture is
    // accounted for by some scenario — so an orphan fixture is caught.
    REQUIRED
        .iter()
        .filter(|(_, where_)| *where_ == Location::Fixture)
        .map(|(tag, _)| *tag)
        .collect()
}

/// Tags used by a case that are not in [`REQUIRED`].
///
/// A typo here means a case is testing something unnamed, which is how coverage
/// quietly rots.
pub fn unknown_claims() -> Vec<&'static str> {
    let known: Vec<&str> = REQUIRED.iter().map(|(tag, _)| *tag).collect();
    claims().keys().filter(|tag| !known.contains(tag)).copied().collect()
}