tix-tracker 0.12.0

//! `[capacity]`: capacity ceilings, and the scopes they belong to (WP01).
//!
//! # The shape
//!
//! ```toml
//! [capacity.zulu]                 # the key is only a handle for the record
//! cycle = "Cycle 1"               # …and exactly one of these says which scope
//! capacity = 20
//! unit = "d"                      # declared on the board the calculation runs under
//!
//! [capacity.platform]
//! team = "Platform"
//! capacity = 15
//! unit = "d"
//!
//! [capacity.ada]
//! assignee = "Ada Lovelace <ada@example.com>"
//! capacity = 3
//! unit = "w"
//! ```
//!
//! Five decisions, and each one closes a door rather than opening one:
//!
//! 1. **The scope is a field, and there is exactly one of it.** `cycle`, `team` and
//!    `assignee` are three mutually exclusive keys: naming none is refused
//!    (`` `capacity.<id>.scope` `` must name one) and naming two is refused as
//!    ambiguous. A shape that derived the scope from *where* the entry sits would make
//!    "which dimension is this?" unstateable, and C-003 refuses implicit scope
//!    inheritance outright — so the entry says it, once.
//! 2. **The unit is named, and the board the calculation runs under must declare it.**
//!    `[kanban.<board>.wip.units]` is the unit registry (the WIP mission's — reused, never
//!    re-declared here), and a capacity entry has no board of its own, so the board the
//!    arithmetic actually converts under is the one that has to know the unit. An entry
//!    counting in a unit only *another* board declares is refused at load, naming that
//!    board and the table to declare it in — otherwise it would load clean, refuse to
//!    calculate, and print a remedy for a unit the user had already declared, and a unit
//!    two boards declare with different factors would silently convert under the wrong one.
//!    A capacity with no unit is refused by name; it is *not* defaulted, and no new unit is
//!    ever invented (C-004).
//! 3. **`capacity` is an integer at or above zero.** An enabled entry must state one.
//!    A disabled entry keeps the scope without a ceiling, which is the "omit or disable
//!    without deleting history" case the data model asks for.
//! 4. **One ceiling per scope.** Two entries whose scope **resolves to** one
//!    cycle/team/assignee are refused — including two spellings of one cycle (its name and
//!    its stable id) or of one handle (`ada` and `@ada`) — because two answers to "how much
//!    is this allowed to commit?" is a question with no answer.
//! 5. **Nothing is required to be present.** The section is omitted whole when empty, so
//!    a capacity-free `tix.toml` gains no key and round-trips byte-identically (C-001),
//!    and each entry preserves unknown metadata verbatim so a newer `tix` can add a
//!    field this build carries rather than drops.
//!
//! # Cycle references resolve through the crate's one adapter, over the records
//!
//! A cycle scope reference is what the entry's `cycle` key holds, and it is resolved by
//! [`resolve_cycle`] over a [`ScheduleIndex`] the caller built from the cycle **records**:
//! [`ScheduleIndex::resolve`] for the name half (the same adapter an issue's `cycles`
//! value goes through), [`GeneratedCycleId::parse`] plus [`ScheduleIndex::cycle`] for the
//! stable `\<schedule-id\>:\<sequence\>` id half. The records matter: `Config::cycles` is
//! name-keyed and narrows each record to `PlanningCycle`, which carries no
//! `schedule_id`/`sequence`/`state`, so an index built from those keys alone would see
//! every cycle as hand-written. Feeding the records — `docs/cycles/`, or the legacy
//! `[cycles.<name>]` tables when there is no store, which is the loader's own rule in
//! [`cycle_records`] — makes a generated cycle's **name** classify as
//! [`CycleReference::Generated`] with its id, exactly as
//! [`crate::cycle_schedule::registry::load_index`] answers. There is deliberately no
//! second name resolver in this module: the string that identifies a cycle is
//! issue-181's, not capacity's.
//!
//! # Which half of the validation lives where, and why it must not move
//!
//! The section is checked by **two** halves, and the split is deliberate:
//!
//! * [`validate`] is **rootless** — it reads no file — and is called by
//!   [`crate::config::Config::validate`], i.e. by every *validate-then-save* path in the
//!   crate (`tix wip unit --remove`, the schedule registry, the MCP write tools, planning).
//!   It covers what the configuration alone decides: the entry handle, the extensions
//!   shadow check, exactly one scope with a non-blank unpadded reference, a team label that
//!   exists, an assignee identity the model parses, the ceiling (enabled ⇒ present and
//!   non-negative), the unit (enabled ⇒ present, not blank, **declared by a board**), and a
//!   scope no other entry already took. The declared-unit check belongs here beyond
//!   argument: `tix wip unit --remove` drops a unit and then validates the *same in-memory*
//!   config before writing, so without it the command would persist a file whose next load
//!   refuses — a repository nobody could read again.
//! * [`validate_cycle_references`] needs a **project root**, and is called by the two gates
//!   that have one: [`crate::config::Config::load_with_warning`] (every hand-edited file)
//!   and [`set_capacity`] (every programmatic change). It resolves each cycle reference
//!   against the cycle **records** — `docs/cycles/`, whose generated identities are the only
//!   place a generated cycle's name can be told from a hand-written one — and unifies two
//!   spellings of one cycle into one ceiling. Its validity rule is provenance-independent:
//!   a reference is valid when it resolves through the records **or** when it names a
//!   `[cycles.<name>]` entry in the configuration (which, after a load, holds every stored
//!   cycle's reference name too), so the same entry is accepted whether or not the caller
//!   happened to read a cycle store.
//!
//! Moving the declared-unit check into the records' half (or dropping it from the rootless
//! one) is the failure this split exists to prevent; moving the *record* resolution into
//! the rootless half is impossible, because `Config::validate` has no root. Anything added
//! here should go to the half whose inputs it actually reads.
//!
//! # Closed cycles: what this package guarantees, and what it leaves to WP04
//!
//! A closed cycle's capacity is **historical evidence** (C-008). WP01 guarantees two
//! things and no more:
//!
//! * **No-op.** This section holds no snapshot state, so validating and saving a
//!   `tix.toml` cannot rewrite a snapshot: there is nothing in the record to rewrite.
//!   A change to a *current or future* scope is therefore applied and the closed cycle's
//!   evidence file is left byte-identical — asserted end to end.
//! * **Refusal, on the write path.** [`set_capacity`] is the one way this package changes
//!   capacity, and it calls [`ensure_cycle_editable`] before it writes anything: an
//!   ordinary [`CapacityEdit::Configure`] aimed at a terminal cycle — closed, whose
//!   snapshot is the record, or skipped, which was never generated — is refused, leaving
//!   both the in-memory section and `tix.toml` as they were. The one way through is
//!   [`CapacityEdit::Reopen`], which carries the audit reason of the explicit append-only
//!   `History` event.
//!
//! WP04 owns the other half: capturing the snapshot at close, storing it, and appending
//! the reopen/edit event. This module knows none of that — it only refuses to be a
//! second way in.

use std::collections::HashMap;
use std::path::Path;

use indexmap::IndexMap;
use serde::{Deserialize, Serialize};

use crate::config::Config;
use crate::cycle_schedule::identity::{
    CycleReference, GeneratedCycle, GeneratedCycleId, GeneratedCycleState, ScheduleIndex,
};
use crate::cycle_store::{CycleRecord, CycleStore};
use crate::error::{Result, TixError};

/// The scope dimension a capacity ceiling belongs to (C-003, data-model §1).
///
/// `cycle`, `team` and `assignee` are the three the contract names and there is no
/// fourth: "unsupported or implicit scope inheritance is an escalation trigger", so a
/// variant that swept several issues together would be a new semantic rather than a new
/// spelling. The variants serialize as the entry keys of the same name.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum CapacityScopeKind {
    /// One cycle, by the name the registry/records answer to or by generated id.
    Cycle,
    /// One configured team, by its `[teams.<label>]` label.
    Team,
    /// One assignee identity, in the shape an issue's `assignee` field tolerates.
    Assignee,
}

impl CapacityScopeKind {
    /// The stable spelling every surface prints and `tix.toml` stores.
    #[must_use]
    pub const fn as_str(self) -> &'static str {
        match self {
            Self::Cycle => "cycle",
            Self::Team => "team",
            Self::Assignee => "assignee",
        }
    }

    /// Every scope kind, in the order a diagnostic lists them.
    #[must_use]
    pub const fn all() -> [Self; 3] {
        [Self::Cycle, Self::Team, Self::Assignee]
    }
}

impl std::fmt::Display for CapacityScopeKind {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_str(self.as_str())
    }
}

/// Metadata this build does not interpret, preserved verbatim.
///
/// The same guarantee the sibling registries give their records
/// ([`crate::cycle_schedule::config::CycleScheduleExtensions`],
/// [`crate::roadmap::registry::InitiativeExtensions`]): a key a newer `tix` adds must
/// survive an edit-and-save round trip instead of being dropped. The one rule it cannot
/// break is that a preserved key must not **shadow** a built-in field — a file can never
/// deliver such a key (serde matches the known field first), but the public write path
/// could inject one, and `toml` serializes duplicate table keys without complaining, so
/// the write would appear to succeed while the next load failed on a duplicate key.
/// [`validate`] refuses it instead.
#[derive(Debug, Clone, Default, Serialize, Deserialize)]
#[serde(transparent)]
pub struct CapacityExtensions(toml::Table);

impl CapacityExtensions {
    /// Whether no unknown metadata is present.
    #[must_use]
    pub fn is_empty(&self) -> bool {
        self.0.is_empty()
    }

    /// The number of preserved keys.
    #[must_use]
    pub fn len(&self) -> usize {
        self.0.len()
    }

    /// Look up a preserved key.
    #[must_use]
    pub fn get(&self, key: &str) -> Option<&toml::Value> {
        self.0.get(key)
    }

    /// The preserved keys, in canonical order.
    pub fn keys(&self) -> impl Iterator<Item = &str> {
        self.0.keys().map(String::as_str)
    }

    /// Iterate the preserved `(key, value)` pairs in canonical order.
    pub fn iter(&self) -> impl Iterator<Item = (&str, &toml::Value)> {
        self.0.iter().map(|(k, v)| (k.as_str(), v))
    }

    /// The underlying table, for a caller that must serialize it whole.
    #[must_use]
    pub fn table(&self) -> &toml::Table {
        &self.0
    }

    /// Preserve one `(key, value)` pair, returning the previous value if any.
    pub fn insert(&mut self, key: impl Into<String>, value: toml::Value) -> Option<toml::Value> {
        self.0.insert(key.into(), value)
    }
}

impl PartialEq for CapacityExtensions {
    fn eq(&self, other: &Self) -> bool {
        // Compared through the rendered value, so two maps that hold the same keys and
        // values compare equal whatever order they were built in.
        toml::Value::Table(self.0.clone()).to_string()
            == toml::Value::Table(other.0.clone()).to_string()
    }
}

impl Eq for CapacityExtensions {}

impl From<toml::Table> for CapacityExtensions {
    fn from(table: toml::Table) -> Self {
        Self(table)
    }
}

/// Indexing by handle, so a caller that has validated a config reads
/// `config.capacity["zulu"]` the way it reads any other registry in `tix.toml`.
///
/// Panics on an unknown handle, exactly as indexing an `IndexMap` does: a missing entry
/// is a programming error by the time a caller has a handle, and [`CapacityConfig::get`]
/// is the total alternative.
impl std::ops::Index<&str> for CapacityConfig {
    type Output = CapacityEntry;

    fn index(&self, id: &str) -> &Self::Output {
        &self.0[id]
    }
}

/// The fields [`CapacityEntry`] reads as typed values.
///
/// This is the set serde treats as **known** for the record — the fields that survive
/// through the typed struct rather than being swept into the preserved
/// [`extensions`](CapacityEntry::extensions) table. It must stay in step with the
/// struct: add a field there and add it here, or the shadow check would let the new name
/// through and the next load would fail on a duplicate key.
pub const CAPACITY_ENTRY_KNOWN_FIELDS: &[&str] =
    &["cycle", "team", "assignee", "capacity", "unit", "enabled"];

/// One capacity ceiling, for exactly one scope.
///
/// The three scope keys are `Option<String>` on purpose: "absent" has to be
/// distinguishable from "set", because an entry that names no scope is refused by name
/// (C-003) rather than guessed from the surrounding table. `capacity` is `i64` rather
/// than an unsigned integer so that a negative number is *refused with its field path*
/// instead of failing in the TOML parser, where no diagnostic could name the record.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(default)]
pub struct CapacityEntry {
    /// The cycle this ceiling belongs to: the name a `[cycles.<name>]` record answers
    /// to, or a generated cycle's stable id. See [`resolve_cycle`].
    #[serde(skip_serializing_if = "Option::is_none")]
    pub cycle: Option<String>,
    /// The team this ceiling belongs to: a `[teams.<label>]` key.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub team: Option<String>,
    /// The assignee this ceiling belongs to: an identity in the shape an issue's
    /// `assignee` field tolerates (a handle, or `Name <email>`).
    #[serde(skip_serializing_if = "Option::is_none")]
    pub assignee: Option<String>,
    /// The ceiling itself, at or above zero, counted in [`unit`](Self::unit).
    ///
    /// Required for an enabled entry; a **disabled** entry may omit it, which is how a
    /// scope stays configured without a ceiling in force.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub capacity: Option<i64>,
    /// The estimate unit [`capacity`](Self::capacity) counts in. Required for an enabled
    /// entry, refused when blank, and refused when no board declares it.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub unit: Option<String>,
    /// Whether the ceiling is in force. `false` keeps the numbers for later without
    /// changing today's calculations.
    #[serde(
        default = "crate::config::default_true",
        skip_serializing_if = "crate::config::is_true"
    )]
    pub enabled: bool,
    /// Unknown metadata, preserved verbatim.
    #[serde(flatten)]
    pub extensions: CapacityExtensions,
}

impl Default for CapacityEntry {
    fn default() -> Self {
        Self {
            cycle: None,
            team: None,
            assignee: None,
            capacity: None,
            unit: None,
            enabled: true,
            extensions: CapacityExtensions::default(),
        }
    }
}

impl CapacityEntry {
    /// The `(kind, reference)` this entry names, in scope-kind order.
    ///
    /// Zero entries means "no scope", more than one means "ambiguous"; both are refused
    /// by [`validate`]. A caller that has validated a config always gets exactly one.
    pub fn scopes(&self) -> impl Iterator<Item = (CapacityScopeKind, &str)> {
        [
            (CapacityScopeKind::Cycle, self.cycle.as_deref()),
            (CapacityScopeKind::Team, self.team.as_deref()),
            (CapacityScopeKind::Assignee, self.assignee.as_deref()),
        ]
        .into_iter()
        .filter_map(|(kind, reference)| reference.map(|reference| (kind, reference)))
    }

    /// The scope kind this entry names, when it names exactly one.
    #[must_use]
    pub fn scope_kind(&self) -> Option<CapacityScopeKind> {
        let mut scopes = self.scopes();
        let first = scopes.next()?;
        scopes.next().is_none().then_some(first.0)
    }

    /// The scope reference this entry names, when it names exactly one.
    #[must_use]
    pub fn scope_id(&self) -> Option<&str> {
        let mut scopes = self.scopes();
        let first = scopes.next()?;
        scopes.next().is_none().then_some(first.1)
    }

    /// Whether the ceiling is in force: enabled, with a value and a unit.
    ///
    /// The resolver every surface should ask, so "declared but disabled" cannot be read
    /// as "enforced" by one caller and not another — the same rule
    /// [`crate::wip::config::WipConfig::effective_limit`] follows for limits.
    #[must_use]
    pub fn effective(&self) -> bool {
        self.enabled && self.capacity.is_some() && self.unit.is_some()
    }
}

/// The `[capacity]` section: capacity entries keyed by a handle, in declaration order.
///
/// Serialized transparently as the TOML table `[capacity.<entry-id>]` and omitted whole
/// when empty, so a repository that configures no capacity gains no key on save and a
/// legacy `tix.toml` round-trips byte-identically (C-001).
#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(transparent)]
pub struct CapacityConfig(IndexMap<String, CapacityEntry>);

impl CapacityConfig {
    /// An empty section.
    #[must_use]
    pub fn new() -> Self {
        Self::default()
    }

    /// Whether no capacity is configured: the state that writes nothing.
    #[must_use]
    pub fn is_empty(&self) -> bool {
        self.0.is_empty()
    }

    /// How many entries are configured.
    #[must_use]
    pub fn len(&self) -> usize {
        self.0.len()
    }

    /// One entry by its handle.
    #[must_use]
    pub fn get(&self, id: &str) -> Option<&CapacityEntry> {
        self.0.get(id)
    }

    /// One entry by its handle, mutably.
    #[must_use]
    pub fn get_mut(&mut self, id: &str) -> Option<&mut CapacityEntry> {
        self.0.get_mut(id)
    }

    /// The entries, in declaration order.
    pub fn iter(&self) -> impl Iterator<Item = (&str, &CapacityEntry)> {
        self.0.iter().map(|(id, entry)| (id.as_str(), entry))
    }

    /// The entries as a map, for a caller that must serialize or compare them whole.
    #[must_use]
    pub fn entries(&self) -> &IndexMap<String, CapacityEntry> {
        &self.0
    }

    /// The entries mutably, for the declaration-order restoration the loader performs.
    #[must_use]
    pub fn entries_mut(&mut self) -> &mut IndexMap<String, CapacityEntry> {
        &mut self.0
    }

    /// Preserve one entry, returning the previous one if the handle was already used.
    pub fn insert(&mut self, id: impl Into<String>, entry: CapacityEntry) -> Option<CapacityEntry> {
        self.0.insert(id.into(), entry)
    }

    /// Restore the declaration order the `toml` parser loses (it sorts table keys) from
    /// the `[capacity.<entry-id>]` headers in the source document.
    pub fn restore_declaration_order(&mut self, contents: &str) {
        crate::config::restore_section_order(&mut self.0, contents, "capacity");
    }
}

/// Whether the board capacity calculations run under declares `unit`.
///
/// A unit is declared by a board under `[kanban.<board>.wip.units]`; that map is the one
/// owner of "what units exist and how they convert" (`configurable-wip-limits-01M3C6WX`),
/// and capacity reuses it rather than restating it.
///
/// The check is against **that one board** — [`Config::default_config`], the registry the
/// calculation converts under — and not against the union of every board's units. The
/// union was wrong in two ways, and neither showed up until a project declared more than
/// one board:
///
/// * an entry counting in a unit only *another* board declares was accepted at load and
///   could never be calculated: the conversion under the calculation board answers
///   `UnknownUnit`, and the remedy it printed ("declare the unit under
///   `[kanban.<board>.wip.units]`") pointed at a unit the user had already declared;
/// * a unit two boards declare with **different factors** was accepted and then converted
///   under the calculation board's factor — a wrong number, with no diagnostic at all.
///
/// Checking here, where the refusing happens, closes both: an accepted entry counts in a
/// unit the arithmetic can actually resolve, and the factor it resolves to is the one this
/// gate looked at. A capacity entry has no board of its own — a scope names a cycle, a team,
/// or an assignee — so there is no other board it could honestly be judged against.
fn declared_unit(config: &Config, unit: &str) -> bool {
    config.default_config().wip.units.contains_key(unit)
}

/// The cycle records a capacity reference resolves against.
///
/// [`crate::cycle_store::CycleStore::list`] is the canonical reader — the store's records
/// when `docs/cycles/` exists, the implicit `Default` cycle when it does not. The second
/// half is the loader's own fallback: with no store, `Config::cycles` **is** this project's
/// cycle registry (the legacy `[cycles.<name>]` tables the loader keeps), so those names
/// are added as the name-only records they are. An index built from the store alone would
/// call every legacy cycle unknown, which is why the fallback is here and not at the call
/// site.
fn cycle_records(config: &Config, root: &Path) -> Result<Vec<CycleRecord>> {
    let store = CycleStore::new(root);
    let mut records = store.list()?;
    if !store.exists() {
        records.extend(config.cycles.keys().map(|name| CycleRecord {
            name: name.clone(),
            ..CycleRecord::default()
        }));
    }
    Ok(records)
}

/// The [`ScheduleIndex`] a capacity reference resolves against.
///
/// Built from [`cycle_records`]: `CycleStore::list()`'s records — the same input
/// [`crate::cycle_schedule::registry::load_index`] feeds its index — plus, when there is no
/// store, the legacy `[cycles.<name>]` names a store cannot see. So with a store present it
/// *is* `load_index`'s index, and without one it is a strict superset of it: a caller
/// holding either may pass it to [`resolve_cycle`], and both answer `Generated` or `Legacy`
/// identically for anything the store contains. They differ only on a store-less project's
/// legacy names, where the store-only index answers `Unknown` — which is why
/// [`validate_cycle_references`] decides validity by *records or configuration*, never by
/// which provenance the caller happens to have.
pub fn schedule_index(config: &Config, root: &Path) -> Result<ScheduleIndex> {
    Ok(ScheduleIndex::build(config, &cycle_records(config, root)?))
}

/// The stored record a scope reference names, when one exists.
///
/// A generated cycle's stable id names its record directly; a name is the record's own
/// `name`, whatever kind of cycle it belongs to. `None` means the record is not on this
/// project's disk — a legacy `[cycles.<name>]` table, or the implicit `Default` cycle —
/// which is also the answer "no lifecycle state to consult".
fn cycle_record<'a>(
    index: &ScheduleIndex,
    records: &'a [CycleRecord],
    reference: &str,
) -> Option<&'a CycleRecord> {
    if let Ok(id) = GeneratedCycleId::parse(reference)
        && let Some(cycle) = index.cycle(&id)
    {
        return records.iter().find(|record| record.name == cycle.name);
    }
    records.iter().find(|record| record.name == reference)
}

/// Resolve a cycle scope reference through the crate's one cycle identity adapter.
///
/// The reference is the name a cycle record answers to — hand-written or generated — or
/// a generated cycle's stable `<schedule-id>:<sequence>` id. Names are decided by
/// [`ScheduleIndex::resolve`]; ids by [`GeneratedCycleId::parse`] plus an existence check
/// through [`ScheduleIndex::cycle`], because `by_reference` is keyed by name. Both halves
/// answer with the same three-answer [`CycleReference`] vocabulary, and an unknown
/// reference stays unknown rather than being rebound to whatever cycle is nearby.
/// Neither rewrites an issue reference or a cycle date.
///
/// `index` is the caller's, built from the cycle records — everything
/// [`ScheduleIndex::build`] reads. [`crate::cycle_schedule::registry::load_index`] builds
/// exactly that from a project root.
#[must_use]
pub fn resolve_cycle(index: &ScheduleIndex, reference: &str) -> CycleReference {
    let resolved = index.resolve(reference);
    if !matches!(resolved, CycleReference::Unknown { .. }) {
        return resolved;
    }
    let Ok(id) = GeneratedCycleId::parse(reference) else {
        return resolved;
    };
    let Some(cycle) = index.cycle(&id) else {
        return resolved;
    };
    CycleReference::Generated {
        name: cycle.name.clone(),
        id,
        schedule_id: cycle.schedule_id.clone(),
    }
}

/// The authorization a capacity change carries (T004, C-008).
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum CapacityEdit<'a> {
    /// An ordinary configuration change: it applies to current and future calculations
    /// only.
    Configure,
    /// The explicit reopen path — the append-only `History` event — carrying the reason
    /// the audit trail stores.
    Reopen {
        /// Why the closed cycle is being reopened. Required, and never blank.
        reason: &'a str,
    },
}

/// The closed-cycle boundary every capacity change goes through (T004, C-008).
///
/// A closed generated cycle's capacity is the historical record: WP04 captures it as an
/// immutable snapshot at close, and this function is how a configuration change is kept
/// away from it. The state is read from the cycle **record** — through
/// [`GeneratedCycle::from_record`], the crate's one parser for it — rather than from a
/// caller-supplied flag, and a partial generated identity is propagated as the finding
/// it is instead of being treated as open.
///
/// * [`CapacityEdit::Configure`] is refused for a terminal cycle: `closed` has a
///   snapshot that must not be rewritten, and `skipped` was never generated, so it has
///   no capacity to configure.
/// * [`CapacityEdit::Reopen`] is the one way through, and it refuses a blank reason
///   because the event it produces is auditable.
///
/// A hand-written cycle carries no lifecycle state at all, so it is always editable.
pub fn ensure_cycle_editable(record: &CycleRecord, edit: &CapacityEdit<'_>) -> Result<()> {
    match edit {
        CapacityEdit::Reopen { reason } => {
            if reason.trim().is_empty() {
                return Err(TixError::Config(
                    "`reopen.reason` must not be blank: a reopen is auditable, and its reason is \
                     stored with the append-only `History` event"
                        .into(),
                ));
            }
            Ok(())
        }
        CapacityEdit::Configure => match GeneratedCycle::from_record(record)? {
            Some(cycle) if cycle.state == GeneratedCycleState::Closed => {
                Err(TixError::Config(format!(
                    "`cycles.{}` is closed; its capacity (`{}`) is the historical record captured \
                     at close, and a configuration change applies to current and future \
                     calculations only — reopen it through the explicit `History` event instead",
                    record.name, cycle.id
                )))
            }
            Some(cycle) if cycle.state == GeneratedCycleState::Skipped => {
                Err(TixError::Config(format!(
                    "`cycles.{}` is skipped; a skipped sequence was never generated, so it has no \
                     capacity to configure",
                    record.name
                )))
            }
            _ => Ok(()),
        },
    }
}

/// Validate the `[capacity]` section against the rest of `config` (FR-001, C-001,
/// C-003, C-004) — **without** a project root.
///
/// This is the half every *validate-then-save* path already calls, because
/// [`Config::validate`](crate::config::Config::validate) is what they validate with:
/// `tix wip unit --remove`, the schedule registry, the MCP write tools, planning. It
/// covers exactly what the configuration alone decides, and nothing that needs
/// `docs/cycles/`:
///
/// * the entry's handle (non-blank, unpadded, no `.`),
/// * a preserved key that would shadow a built-in field,
/// * exactly one scope, with a non-blank, unpadded reference,
/// * a team label that exists in `[teams.*]`,
/// * an assignee identity the model's own parser accepts,
/// * an enabled entry's ceiling (present, not negative) and unit (present, not blank,
///   **declared by a board**) — the check that keeps a change like "remove the unit a
///   ceiling names" from writing a file the next load refuses,
/// * one ceiling per scope, on the identity this gate can see.
///
/// A cycle reference is accepted here when `config.cycles` names it — that is the legacy
/// registry, and after a load it also holds every stored cycle's reference name — and is
/// otherwise **deferred**, not refused: whether a generated cycle answers to a reference
/// is a question for the records, which this gate has no root to read. Deferring is what
/// keeps the verdict provenance-independent: a valid file is never refused because the
/// caller happened to be a save path rather than the loader.
///
/// Nothing here reads a file, which is why a capacity-free section returning immediately
/// makes a repository that configures no capacity provably unaffected.
pub fn validate(capacity: &CapacityConfig, config: &Config) -> Result<()> {
    if capacity.is_empty() {
        return Ok(());
    }
    let mut claimed: HashMap<(CapacityScopeKind, String), String> = HashMap::new();
    for (id, entry) in capacity.iter() {
        let path = format!("capacity.{id}");
        validate_entry_id(id)?;
        check_extensions(&path, &entry.extensions)?;
        let (kind, reference) = validate_scope(&path, entry)?;
        let identity = scope_identity(&path, config, None, kind, &reference)?;
        if let Some(first) = claimed.insert((kind, identity.canonical.clone()), id.to_string()) {
            return Err(duplicate_scope(&path, kind, &reference, &identity, &first));
        }
        validate_ceiling(&path, entry, config)?;
    }
    Ok(())
}

/// The records' half of the section's validation: resolve every cycle reference, and
/// treat two spellings of one cycle as one ceiling (FR-001, C-003).
///
/// Called by the two gates that have a project root —
/// [`Config::load_with_warning`](crate::config::Config::load_with_warning) for every
/// hand-edited file and [`set_capacity`] for every programmatic change — because the
/// records are the only place a generated cycle's identity lives. It is the *extra* half,
/// not a replacement for [`validate`]: a caller runs both. A section with no cycle scope
/// returns without touching the filesystem.
///
/// The validity rule is deliberately provenance-independent: a reference is valid when it
/// resolves through the records **or** when it names a `[cycles.<name>]` entry in the
/// configuration, so a store-less project's legacy table is accepted whether or not the
/// caller read a cycle store (the crate's store-only
/// [`crate::cycle_schedule::registry::load_index`] answers `Unknown` for those names,
/// while [`schedule_index`] adds them). Only a reference that neither resolves nor names a
/// configured cycle is refused — and the message says so, rather than telling a user to
/// add a table their file already has.
pub fn validate_cycle_references(
    capacity: &CapacityConfig,
    config: &Config,
    root: &Path,
) -> Result<()> {
    if !capacity.iter().any(|(_, entry)| entry.cycle.is_some()) {
        return Ok(());
    }
    validate_cycle_identities(capacity, config, &schedule_index(config, root)?)
}

/// The cycle scopes of a section, resolved against an index.
fn validate_cycle_identities(
    capacity: &CapacityConfig,
    config: &Config,
    index: &ScheduleIndex,
) -> Result<()> {
    let mut claimed: HashMap<String, String> = HashMap::new();
    for (id, entry) in capacity.iter() {
        let Some((CapacityScopeKind::Cycle, reference)) = entry.scopes().next() else {
            continue;
        };
        let path = format!("capacity.{id}");
        let identity = scope_identity(
            &path,
            config,
            Some(index),
            CapacityScopeKind::Cycle,
            reference,
        )?;
        if let Some(first) = claimed.insert(identity.canonical.clone(), id.to_string()) {
            return Err(duplicate_scope(
                &path,
                CapacityScopeKind::Cycle,
                reference,
                &identity,
                &first,
            ));
        }
    }
    Ok(())
}

/// Set one capacity ceiling, through the closed-cycle boundary (T004, C-008).
///
/// This is the write path this package exposes, and the call site of
/// [`ensure_cycle_editable`]. A caller hands over the entry it wants and the edit it
/// believes it is making; the change happens only if
///
/// 1. the boundary allows it — an ordinary [`CapacityEdit::Configure`] aimed at a closed
///    cycle (whose ceiling is the historical record) or a skipped one is refused before
///    anything is written, and
/// 2. the whole section still validates with the entry in place — a scope that resolves
///    nowhere, a second ceiling for a scope another entry already holds, or a missing
///    unit leaves both `config` and `tix.toml` exactly as they were.
///
/// `root` is the project root: the cycle records that decide the boundary and the
/// resolution are read from `docs/cycles/` there (the legacy `[cycles.<name>]` tables when
/// there is no store), and the file is written atomically by [`Config::save`]. The change
/// is staged on a copy and committed only once both gates pass, so a refusal cannot leave
/// a half-applied section behind — the shape the other registries' commit boundaries use.
pub fn set_capacity(
    config: &mut Config,
    id: &str,
    entry: CapacityEntry,
    edit: &CapacityEdit<'_>,
    root: &Path,
) -> Result<()> {
    let records = cycle_records(config, root)?;
    let index = ScheduleIndex::build(config, &records);
    if let Some((CapacityScopeKind::Cycle, reference)) = entry.scopes().next()
        && let Some(record) = cycle_record(&index, &records, reference)
    {
        ensure_cycle_editable(record, edit)?;
    }
    let mut candidate = config.clone();
    candidate.capacity.insert(id, entry);
    // Both halves: what the configuration alone decides, and what the records decide.
    validate(&candidate.capacity, &candidate)?;
    validate_cycle_identities(&candidate.capacity, &candidate, &index)?;
    candidate.save(&root.join("tix.toml"))?;
    *config = candidate;
    Ok(())
}

/// The entry handle is a real key: non-blank, unpadded, and free of the one character
/// that would read as a nested table in a header or in a diagnostic path.
///
/// Unlike the stable-id registries this handle is not an identity — nothing points at a
/// capacity entry — so it is free-form otherwise: a user names it whatever reads best in
/// their file.
fn validate_entry_id(id: &str) -> Result<()> {
    if id.trim().is_empty() {
        return Err(TixError::Config(
            "`capacity` must not contain an entry with a blank id".into(),
        ));
    }
    if id.trim() != id {
        return Err(TixError::Config(format!(
            "`capacity` entry id `{id}` has leading or trailing whitespace"
        )));
    }
    if id.contains('.') {
        return Err(TixError::Config(format!(
            "`capacity` entry id `{id}` contains `.`; a dot reads as a nested table in \
             `[capacity.<id>]` and in a diagnostic path"
        )));
    }
    Ok(())
}

/// Refuse a preserved key that would shadow a built-in field.
fn check_extensions(path: &str, extensions: &CapacityExtensions) -> Result<()> {
    for key in extensions.keys() {
        if CAPACITY_ENTRY_KNOWN_FIELDS.contains(&key) {
            return Err(TixError::Config(format!(
                "`{path}.{key}` collides with a built-in field; rename the extension key"
            )));
        }
    }
    Ok(())
}

/// Exactly one of `cycle`, `team`, `assignee`: the entry's scope.
fn validate_scope(path: &str, entry: &CapacityEntry) -> Result<(CapacityScopeKind, String)> {
    let named: Vec<(CapacityScopeKind, &str)> = entry.scopes().collect();
    match named.len() {
        0 => Err(TixError::Config(format!(
            "`{path}.scope` must name exactly one scope: set `cycle`, `team`, or `assignee`"
        ))),
        1 => {
            let (kind, reference) = named[0];
            if reference.trim().is_empty() {
                return Err(TixError::Config(format!(
                    "`{path}.{kind}` must not be blank"
                )));
            }
            if reference.trim() != reference {
                return Err(TixError::Config(format!(
                    "`{path}.{kind}` (`{reference}`) has leading or trailing whitespace"
                )));
            }
            Ok((kind, reference.to_string()))
        }
        _ => {
            let listed = named
                .iter()
                .map(|(kind, _)| format!("`{kind}`"))
                .collect::<Vec<_>>()
                .join(" and ");
            Err(TixError::Config(format!(
                "`{path}.scope` names more than one scope ({listed}); an entry targets exactly one \
                 cycle, team, or assignee"
            )))
        }
    }
}

/// The identity a scope reference **resolves to**, for the one-ceiling-per-scope rule.
///
/// `canonical` is what two entries are compared on: a cycle's stable id or resolved name,
/// an assignee's canonical handle, a team label. `label` is the human spelling to print,
/// which differs from the literal a user wrote whenever two spellings resolve to one
/// identity (`@ada` and `ada`, a generated cycle's name and its id) — the case the
/// duplicate diagnostic has to explain.
struct ScopeIdentity {
    canonical: String,
    label: String,
}

/// The message every repeated-scope refusal uses.
fn duplicate_scope(
    path: &str,
    kind: CapacityScopeKind,
    reference: &str,
    identity: &ScopeIdentity,
    first: &str,
) -> TixError {
    let note = if identity.label == reference {
        String::new()
    } else {
        format!(" (`{reference}` resolves to `{}`)", identity.label)
    };
    TixError::Config(format!(
        "`{path}.{kind}` (`{reference}`) repeats the scope \
         `capacity.{first}.{kind}` already configures{note}; one ceiling per scope"
    ))
}

/// Resolve a scope reference to the identity the one-ceiling rule compares.
///
/// `index` is `Some` at the records' gate and `None` where only the configuration is
/// available. The cycle arm is the one that differs, and that difference is the whole
/// point of the split: with an index, a reference that resolves neither through the
/// records nor through `config.cycles` is refused by name; without one, a reference the
/// configuration does not name is accepted under a reference-shaped identity and left for
/// the records' gate to judge.
fn scope_identity(
    path: &str,
    config: &Config,
    index: Option<&ScheduleIndex>,
    kind: CapacityScopeKind,
    reference: &str,
) -> Result<ScopeIdentity> {
    match kind {
        CapacityScopeKind::Cycle => {
            if let Some(index) = index {
                return Ok(match resolve_cycle(index, reference) {
                    CycleReference::Generated { id, .. } => ScopeIdentity {
                        canonical: format!("cycle-id:{id}"),
                        label: id.to_string(),
                    },
                    CycleReference::Legacy { name } => ScopeIdentity {
                        canonical: format!("cycle-name:{name}"),
                        label: name,
                    },
                    // Not in the records: the configuration's own cycle registry is the
                    // second half of the validity rule, so a legacy table — or a stored
                    // cycle's name the loader copied in — is still a valid reference.
                    CycleReference::Unknown { .. } if config.cycles.contains_key(reference) => {
                        ScopeIdentity {
                            canonical: format!("cycle-name:{reference}"),
                            label: reference.to_string(),
                        }
                    }
                    CycleReference::Unknown { .. } => {
                        return Err(TixError::Config(format!(
                            "`{path}.cycle` (`{reference}`) does not name a cycle; add \
                             `[cycles.\"{reference}\"]`, or name a generated cycle's \
                             `<schedule-id>:<sequence>` id or its `cycles` value"
                        )));
                    }
                });
            }
            if config.cycles.contains_key(reference) {
                return Ok(ScopeIdentity {
                    canonical: format!("cycle-name:{reference}"),
                    label: reference.to_string(),
                });
            }
            // Only the records can say whether a generated cycle answers to this, and this
            // gate has no root: defer rather than refuse a reference the loader accepts.
            Ok(ScopeIdentity {
                canonical: format!("cycle-ref:{reference}"),
                label: reference.to_string(),
            })
        }
        CapacityScopeKind::Team => {
            if !config.teams.contains_key(reference) {
                return Err(TixError::Config(format!(
                    "`{path}.team` (`{reference}`) is not a configured team; add \
                     `[teams.{reference}]`"
                )));
            }
            Ok(ScopeIdentity {
                canonical: format!("team:{reference}"),
                label: reference.to_string(),
            })
        }
        CapacityScopeKind::Assignee => {
            // The model's own parser folds the spellings: `ada` and `@ada` are one
            // identity, so they are one scope here too.
            let Some(canonical) = crate::assignee::parse_assignee(reference) else {
                return Err(TixError::Config(format!(
                    "`{path}.assignee` (`{reference}`) is not an assignee identity; use a handle \
                     (`ada`, `@ada`) or `Ada Lovelace <ada@example.com>`"
                )));
            };
            Ok(ScopeIdentity {
                canonical: format!("assignee:{canonical}"),
                label: canonical,
            })
        }
    }
}

/// An enabled entry needs a non-negative ceiling in a declared unit; a disabled one may
/// keep the scope alone.
fn validate_ceiling(path: &str, entry: &CapacityEntry, config: &Config) -> Result<()> {
    match entry.capacity {
        Some(value) if value < 0 => {
            return Err(TixError::Config(format!(
                "`{path}.capacity` ({value}) must not be negative"
            )));
        }
        None if entry.enabled => {
            return Err(TixError::Config(format!(
                "`{path}.capacity` must be set for an enabled entry; set `enabled = false` to keep \
                 the scope without a ceiling"
            )));
        }
        _ => {}
    }
    match entry.unit.as_deref() {
        Some(unit) if unit.trim().is_empty() => {
            Err(TixError::Config(format!("`{path}.unit` must not be blank")))
        }
        Some(unit) if unit.trim() != unit => Err(TixError::Config(format!(
            "`{path}.unit` (`{unit}`) has leading or trailing whitespace"
        ))),
        Some(unit) if !declared_unit(config, unit) => Err(TixError::Config(format!(
            "`{path}.unit` (`{unit}`) is not a declared estimate unit on board `{board}`, which \
             is the board capacity calculations run under; declare `{unit}` under \
             `[kanban.{board}.wip.units]`",
            board = crate::workflow::active_board_name(config)
        ))),
        Some(_) => Ok(()),
        None if entry.enabled => Err(TixError::Config(format!(
            "`{path}.unit` must name the estimate unit `capacity` counts in; a capacity with no \
             unit cannot be calculated"
        ))),
        None => Ok(()),
    }
}

#[cfg(test)]
mod tests {
    #[allow(clippy::wildcard_imports)]
    use super::*;

    fn closed_record() -> CycleRecord {
        CycleRecord {
            name: "Platform sprint".into(),
            start_date: Some("2026-01-05".into()),
            due_date: Some("2026-01-19".into()),
            schedule_id: Some("cs-1".into()),
            sequence: Some(1),
            state: Some("closed".into()),
            ..CycleRecord::default()
        }
    }

    #[test]
    fn a_closed_cycle_is_refused_a_configuration_edit_but_not_a_reopen() {
        let error = ensure_cycle_editable(&closed_record(), &CapacityEdit::Configure)
            .expect_err("a closed cycle is historical evidence");
        let message = error.to_string();
        assert!(message.contains("closed"), "{message}");
        assert!(message.contains("cs-1:000001"), "{message}");

        assert!(
            ensure_cycle_editable(&closed_record(), &CapacityEdit::Reopen { reason: "  " })
                .is_err(),
            "a reopen without a reason is not auditable"
        );
        ensure_cycle_editable(
            &closed_record(),
            &CapacityEdit::Reopen {
                reason: "recounting after an import",
            },
        )
        .expect("an explicit, reasoned reopen is the way through");
    }

    #[test]
    fn a_hand_written_cycle_has_no_state_to_refuse() {
        let record = CycleRecord {
            name: "Cycle 1".into(),
            ..CycleRecord::default()
        };
        ensure_cycle_editable(&record, &CapacityEdit::Configure)
            .expect("a hand-written cycle has no lifecycle state");
    }

    #[test]
    fn an_active_cycle_is_editable_and_a_skipped_one_is_not() {
        let active = CycleRecord {
            state: Some("active".into()),
            ..closed_record()
        };
        ensure_cycle_editable(&active, &CapacityEdit::Configure).expect("active is current work");

        let skipped = CycleRecord {
            state: Some("skipped".into()),
            ..closed_record()
        };
        let message = ensure_cycle_editable(&skipped, &CapacityEdit::Configure)
            .expect_err("a skipped sequence was never generated")
            .to_string();
        assert!(message.contains("skipped"), "{message}");
    }

    #[test]
    fn a_partial_generated_identity_is_a_finding_at_the_boundary() {
        let record = CycleRecord {
            state: None,
            ..closed_record()
        };
        assert!(
            ensure_cycle_editable(&record, &CapacityEdit::Configure).is_err(),
            "half an identity must not read as an open cycle"
        );
    }

    #[test]
    fn the_scope_accessors_report_none_when_the_entry_is_ambiguous() {
        let mut entry = CapacityEntry::default();
        assert_eq!(entry.scope_kind(), None);
        assert_eq!(entry.scope_id(), None);

        entry.cycle = Some("Cycle 1".into());
        assert_eq!(entry.scope_kind(), Some(CapacityScopeKind::Cycle));
        assert_eq!(entry.scope_id(), Some("Cycle 1"));

        entry.team = Some("Platform".into());
        assert_eq!(entry.scope_kind(), None, "two scopes are not a scope");
        assert_eq!(entry.scope_id(), None);
    }

    #[test]
    fn a_disabled_entry_without_numbers_is_not_effective() {
        let mut entry = CapacityEntry {
            team: Some("Platform".into()),
            ..CapacityEntry::default()
        };
        assert!(!entry.effective(), "no ceiling is configured yet");
        entry.capacity = Some(0);
        assert!(!entry.effective(), "no unit means it cannot be calculated");
        entry.unit = Some("d".into());
        assert!(entry.effective());
        entry.enabled = false;
        assert!(!entry.effective(), "a disabled entry enforces nothing");
    }
}