tix-tracker 0.12.0

//! The template management service (WP03; mission `issue-form-templates-01M3C76V`).
//!
//! This is the **operation layer** over WP01's registry
//! ([`crate::templates::registry`]). It adds no storage of its own and no second
//! issue writer:
//!
//! - every read (`list`, `show`) borrows the registry and returns derived copies;
//! - every write (`create`, `update`, `duplicate`, `delete`) builds a **candidate**
//!   registry, validates the complete definition against the caller's [`Config`],
//!   and only then persists through the existing atomic
//!   [`Config::save`] — a refused or failed operation writes nothing
//!   (`data-model.md` §5, `contracts/template-registry.md`);
//! - identity is the stable ID. A rename replaces the display label and nothing
//!   else, so selection by ID keeps scope, defaults, prompts, references, and
//!   preserved unknown metadata intact (C-002/C-006);
//! - delete removes a **definition** and nothing else. Issues created from a
//!   template live in the issue tree and are never named here, so delete cannot
//!   reach them (C-001).
//!
//! # Read-only versus write operations
//!
//! The split is visible in the signatures:
//!
//! | operation | returns | writes |
//! |---|---|---|
//! | `list`, `show` | `Result<..>` | nothing |
//! | `create`, `update`, `duplicate`, `delete` | `TemplateMutation<..>` | one atomic `tix.toml` save |
//!
//! A read can only be refused (a plain [`TixError`]). A write can also *fail*:
//! the registry already models a refusal differently from an infrastructure
//! failure, and [`TemplateWriteError`] keeps that distinction rather than
//! flattening it.
//!
//! # Auditable, idempotent mutations
//!
//! An accepted mutation returns a [`TemplateOutcome`] carrying exactly one
//! [`TemplateAuditEvent`] — what changed, for which stable ID, under which
//! display name at the time of the operation. A refused or failed operation
//! carries **no** event, because nothing happened. A same-content `update` is a
//! no-op: no save is issued and the outcome reports [`TemplateOutcome::is_noop`].
//! Committing the same registry twice writes the same bytes, so re-applying an
//! operation converges.
//!
//! # Definition-only delete
//!
//! [`TemplateService::delete`] cannot be called without a [`DeleteConfirmed`], a
//! token whose field is private so "I forgot to confirm" is a compile error
//! rather than a defaulted `true`. It removes the definition and nothing else:
//! no issue, comment, relationship, or board data is touched.

use std::fmt;
use std::path::Path;

use crate::config::Config;
use crate::error::{Result, TixError};
use crate::templates::registry::{
    Template, TemplateDefaults, TemplateMetadata, TemplatePrompt, TemplateReference,
    TemplateRegistry, TemplateScope,
};

/// The outcome of a service **write**: an accepted value plus its audit event, or
/// a refusal/failure that wrote nothing.
pub type TemplateMutation<T> = std::result::Result<TemplateOutcome<T>, TemplateWriteError>;

/// Why a template write did not happen.
///
/// The two cases are deliberately distinct. [`Refused`](Self::Refused) is the
/// registry/config declining the change — a bad ID, an unknown scope, an
/// unsupported field: nothing was written, and the caller should show the
/// message. [`Failed`](Self::Failed) is infrastructure — the atomic save could
/// not complete. In both cases `tix.toml` is unchanged; only the remedy differs.
#[derive(Debug)]
pub enum TemplateWriteError {
    /// The candidate was invalid; the registry and `tix.toml` are unchanged.
    Refused(TixError),
    /// The candidate was valid but the atomic save failed; `tix.toml` is unchanged.
    Failed(TixError),
}

impl TemplateWriteError {
    /// The underlying error, whichever kind this is.
    #[must_use]
    pub fn inner(&self) -> &TixError {
        match self {
            Self::Refused(error) | Self::Failed(error) => error,
        }
    }

    /// Consume the error for its underlying [`TixError`].
    #[must_use]
    pub fn into_inner(self) -> TixError {
        match self {
            Self::Refused(error) | Self::Failed(error) => error,
        }
    }

    /// Whether this is a validation refusal rather than an infrastructure failure.
    #[must_use]
    pub const fn is_refusal(&self) -> bool {
        matches!(self, Self::Refused(_))
    }
}

impl From<TixError> for TemplateWriteError {
    /// A bare error from the registry is a **refusal** by default: the registry's
    /// failures are all validation, and the save path maps its own error to
    /// [`TemplateWriteError::Failed`] explicitly.
    fn from(error: TixError) -> Self {
        Self::Refused(error)
    }
}

impl fmt::Display for TemplateWriteError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Refused(error) => write!(f, "template refused: {error}"),
            Self::Failed(error) => write!(f, "template write failed: {error}"),
        }
    }
}

impl std::error::Error for TemplateWriteError {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        Some(self.inner())
    }
}

/// What kind of registry mutation an accepted operation performed.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum TemplateMutationKind {
    /// A new definition was added under a caller-supplied stable ID.
    Create,
    /// An existing definition's name, scope, and data were replaced (ID unchanged).
    Update,
    /// A new definition was copied from an existing one under a new stable ID.
    Duplicate,
    /// A definition was removed. Only the definition.
    Delete,
}

impl TemplateMutationKind {
    /// The stable name of this mutation, for output and matching.
    #[must_use]
    pub const fn as_str(self) -> &'static str {
        match self {
            Self::Create => "create",
            Self::Update => "update",
            Self::Duplicate => "duplicate",
            Self::Delete => "delete",
        }
    }
}

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

/// The auditable record of one **accepted** registry mutation.
///
/// Emitted once per accepted change, and never for a refusal or a no-op. The
/// template ID is identity; the name is the display label *at the time of the
/// operation*, kept for a readable history even after a later rename.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct TemplateAuditEvent {
    kind: TemplateMutationKind,
    template_id: String,
    template_name: String,
}

impl TemplateAuditEvent {
    fn new(kind: TemplateMutationKind, template_id: String, template_name: String) -> Self {
        Self {
            kind,
            template_id,
            template_name,
        }
    }

    /// What kind of mutation this was.
    #[must_use]
    pub const fn kind(&self) -> TemplateMutationKind {
        self.kind
    }

    /// The stable ID of the affected definition.
    #[must_use]
    pub fn template_id(&self) -> &str {
        &self.template_id
    }

    /// The display name the definition carried when the mutation was accepted.
    #[must_use]
    pub fn template_name(&self) -> &str {
        &self.template_name
    }
}

/// An accepted operation's value and its audit event.
///
/// `audit` is `None` exactly when the candidate registry equalled the current
/// one — an idempotent no-op that issued no save.
#[derive(Debug, Clone, PartialEq)]
pub struct TemplateOutcome<T> {
    value: T,
    audit: Option<TemplateAuditEvent>,
}

impl<T> TemplateOutcome<T> {
    fn accepted(value: T, audit: TemplateAuditEvent) -> Self {
        Self {
            value,
            audit: Some(audit),
        }
    }

    fn unchanged(value: T) -> Self {
        Self { value, audit: None }
    }

    /// The operation's result value.
    #[must_use]
    pub fn value(&self) -> &T {
        &self.value
    }

    /// Consume the outcome for its value.
    #[must_use]
    pub fn into_value(self) -> T {
        self.value
    }

    /// The one audit event, or `None` for an idempotent no-op.
    #[must_use]
    pub fn audit(&self) -> Option<&TemplateAuditEvent> {
        self.audit.as_ref()
    }

    /// Whether the operation changed nothing (no save, no event).
    #[must_use]
    pub fn is_noop(&self) -> bool {
        self.audit.is_none()
    }
}

/// Explicit confirmation for a definition-only delete.
///
/// The private field is the whole point: the token cannot be built outside this
/// module, so [`TemplateService::delete`] is not callable without a deliberate
/// confirmation. There is no `Default` and no `From<bool>`.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct DeleteConfirmed(());

impl DeleteConfirmed {
    /// Acknowledge that only the template **definition** is being removed — never
    /// issues created from it and never their provenance.
    #[must_use]
    pub const fn confirmed() -> Self {
        Self(())
    }
}

/// A definition handed to `create`/`update`: the mutable fields of a record.
///
/// Every field is optional and means **"supply this"**. `create` fills an absent
/// field with its default (no name, repository scope, no defaults/prompts/
/// references); `update` leaves an absent field exactly as it was. That is what
/// makes a rename a rename: [`TemplateDefinition::rename`] names a new label and
/// touches nothing else, so scope, defaults, prompts, and references survive it
/// (C-002).
///
/// The ID and the preserved extension fields are **not** here: identity is the
/// registry key, and extensions survive an update untouched, so a caller cannot
/// accidentally drop either (C-006).
#[derive(Debug, Clone, PartialEq, Default)]
pub struct TemplateDefinition {
    name: Option<String>,
    scope: Option<TemplateScope>,
    defaults: Option<TemplateDefaults>,
    prompts: Option<Vec<TemplatePrompt>>,
    references: Option<Vec<TemplateReference>>,
}

impl TemplateDefinition {
    /// A named, scoped definition with no defaults, prompts, or references.
    #[must_use]
    pub fn new(name: impl Into<String>, scope: TemplateScope) -> Self {
        Self {
            name: Some(name.into()),
            scope: Some(scope),
            ..Self::default()
        }
    }

    /// A definition with no display name; the stable ID is shown in its place.
    #[must_use]
    pub fn unnamed(scope: TemplateScope) -> Self {
        Self {
            scope: Some(scope),
            ..Self::default()
        }
    }

    /// A rename: a new display label and nothing else.
    ///
    /// The only field carried is the name, so an update through it cannot change
    /// the scope, defaults, prompts, or references of the record it renames.
    #[must_use]
    pub fn rename(name: impl Into<String>) -> Self {
        Self {
            name: Some(name.into()),
            ..Self::default()
        }
    }

    /// Set the normal create-request defaults.
    #[must_use]
    pub fn with_defaults(mut self, defaults: TemplateDefaults) -> Self {
        self.defaults = Some(defaults);
        self
    }

    /// Set the ordered structured prompts.
    #[must_use]
    pub fn with_prompts(mut self, prompts: Vec<TemplatePrompt>) -> Self {
        self.prompts = Some(prompts);
        self
    }

    /// Set the typed references.
    #[must_use]
    pub fn with_references(mut self, references: Vec<TemplateReference>) -> Self {
        self.references = Some(references);
        self
    }

    /// A fresh record for `create`, with no preserved metadata.
    fn into_template(self) -> Template {
        Template {
            name: self.name,
            scope: self.scope.unwrap_or_default(),
            defaults: self.defaults.unwrap_or_default(),
            prompts: self.prompts.unwrap_or_default(),
            references: self.references.unwrap_or_default(),
            ..Template::default()
        }
    }

    /// Apply the supplied fields to an existing record, leaving the rest as-is.
    fn apply_to(self, template: &mut Template) {
        if let Some(name) = self.name {
            template.name = Some(name);
        }
        if let Some(scope) = self.scope {
            template.scope = scope;
        }
        if let Some(defaults) = self.defaults {
            template.defaults = defaults;
        }
        if let Some(prompts) = self.prompts {
            template.prompts = prompts;
        }
        if let Some(references) = self.references {
            template.references = references;
        }
    }
}

/// A definition shown to a caller: the stable ID and the full stored record.
///
/// The record carries the display name, scope, defaults, prompts, references, and
/// any preserved unknown metadata, so a surface renders everything without
/// reaching back into the registry (T013).
#[derive(Debug, Clone, PartialEq)]
pub struct TemplateDetail {
    id: String,
    template: Template,
}

impl TemplateDetail {
    fn new(id: String, template: Template) -> Self {
        Self { id, template }
    }

    /// The immutable stable ID.
    #[must_use]
    pub fn id(&self) -> &str {
        &self.id
    }

    /// The stored record.
    #[must_use]
    pub fn template(&self) -> &Template {
        &self.template
    }

    /// The display label, falling back to the stable ID.
    #[must_use]
    pub fn display_name(&self) -> &str {
        self.template.display_name(&self.id)
    }

    /// The explicit scope.
    #[must_use]
    pub fn scope(&self) -> &TemplateScope {
        &self.template.scope
    }

    /// The normal create-request defaults.
    #[must_use]
    pub fn defaults(&self) -> &TemplateDefaults {
        &self.template.defaults
    }

    /// The ordered structured prompts.
    #[must_use]
    pub fn prompts(&self) -> &[TemplatePrompt] {
        &self.template.prompts
    }

    /// The typed references.
    #[must_use]
    pub fn references(&self) -> &[TemplateReference] {
        &self.template.references
    }

    /// Preserved unknown metadata, never interpreted.
    #[must_use]
    pub fn extensions(&self) -> &TemplateMetadata {
        &self.template.extensions
    }
}

/// The template service: the caller's registry-bearing [`Config`] and the
/// `tix.toml` path to save it through.
///
/// The service borrows the caller's config mutably because an accepted mutation
/// *is* `config.issue_templates` changing; it never reaches around the registry
/// to write anything else. There is no separate file and no hosted state — the
/// existing atomic [`Config::save`] is the persistence (C-001).
pub struct TemplateService<'a> {
    config: &'a mut Config,
    path: &'a Path,
}

impl<'a> TemplateService<'a> {
    /// A service over a caller's config and `tix.toml` path.
    #[must_use]
    pub fn new(config: &'a mut Config, path: &'a Path) -> Self {
        Self { config, path }
    }

    /// The registry, for a surface that must enumerate or render it directly.
    #[must_use]
    pub fn registry(&self) -> &TemplateRegistry {
        &self.config.issue_templates
    }

    // -- read-only --------------------------------------------------------

    /// Every stored definition, with its stable ID, in declaration order (T013).
    ///
    /// Declaration order is the registry's order, which the TOML loader restores
    /// from the document's section headers, so the list is deterministic across
    /// load/save round trips.
    #[must_use]
    pub fn list(&self) -> Vec<TemplateDetail> {
        self.config
            .issue_templates
            .iter()
            .map(|(id, template)| TemplateDetail::new(id.to_string(), template.clone()))
            .collect()
    }

    /// Resolve one definition by stable ID, or by a display name that names
    /// exactly one record, and return the full detail (T013).
    ///
    /// The ID is authoritative and is tried first; a name is a convenience, so an
    /// ambiguous name is refused rather than guessed. Unknown references are a
    /// `not found` error that names the request.
    pub fn show(&self, reference: &str) -> Result<TemplateDetail> {
        let (id, template) = self.select(reference)?;
        Ok(TemplateDetail::new(id, template))
    }

    // -- mutations --------------------------------------------------------

    /// Create a definition under the caller's stable ID (T014).
    ///
    /// The ID must be a well-formed handle no stored template already uses; the
    /// complete definition is validated before the atomic save, so a rejected
    /// create writes nothing.
    pub fn create(&mut self, id: &str, definition: TemplateDefinition) -> TemplateMutation<String> {
        let mut candidate = self.config.issue_templates.clone();
        candidate
            .insert(id, definition.into_template())
            .map_err(TemplateWriteError::Refused)?;

        let id = id.to_string();
        let name = display_name_of(&candidate, &id);
        self.commit(candidate)?;
        Ok(TemplateOutcome::accepted(
            id.clone(),
            TemplateAuditEvent::new(TemplateMutationKind::Create, id, name),
        ))
    }

    /// Replace an existing definition's supplied fields in place (T014).
    ///
    /// Only the fields the caller supplies change; an absent field is left as it
    /// was. The stable ID never changes — identity survives a rename (C-002) —
    /// and the record's preserved extension fields are left untouched (C-006). A
    /// same-content update is a no-op: no save, no audit event.
    pub fn update(
        &mut self,
        reference: &str,
        definition: TemplateDefinition,
    ) -> TemplateMutation<String> {
        let (id, _source) = self.select(reference)?;

        let mut candidate = self.config.issue_templates.clone();
        let template = candidate
            .get_mut(&id)
            .expect("the selected template is in the registry");
        definition.apply_to(template);
        // `extensions` is deliberately not assigned: unknown metadata survives
        // an update unchanged.

        if candidate == self.config.issue_templates {
            return Ok(TemplateOutcome::unchanged(id));
        }
        let name = display_name_of(&candidate, &id);
        self.commit(candidate)?;
        Ok(TemplateOutcome::accepted(
            id.clone(),
            TemplateAuditEvent::new(TemplateMutationKind::Update, id, name),
        ))
    }

    /// Duplicate a definition under a new stable ID (T015).
    ///
    /// The copy carries the source's scope, defaults, prompts, references, and
    /// preserved extensions verbatim; only the ID is new, and the source is left
    /// exactly as it was. `new_id` overrides the deterministic `<source>-copy`
    /// allocation; `name` overrides the label when given. The new definition is
    /// reported explicitly in the outcome value.
    pub fn duplicate(
        &mut self,
        reference: &str,
        new_id: Option<&str>,
        name: Option<&str>,
    ) -> TemplateMutation<TemplateDetail> {
        let (source_id, source) = self.select(reference)?;
        let target_id = match new_id {
            Some(id) => id.to_string(),
            None => self.allocate_duplicate_id(&source_id),
        };

        let mut copy = source;
        if let Some(name) = name {
            copy.name = Some(name.trim().to_string());
        }

        let mut candidate = self.config.issue_templates.clone();
        candidate
            .insert(target_id.clone(), copy)
            .map_err(TemplateWriteError::Refused)?;

        let detail = TemplateDetail::new(
            target_id.clone(),
            candidate_template(&candidate, &target_id),
        );
        let name = detail.display_name().to_string();
        self.commit(candidate)?;
        Ok(TemplateOutcome::accepted(
            detail,
            TemplateAuditEvent::new(TemplateMutationKind::Duplicate, target_id, name),
        ))
    }

    /// Delete a template **definition** after explicit confirmation (T016).
    ///
    /// Only the definition is removed. Issues created from the template are files
    /// in the issue tree that this service never names, so their bytes and their
    /// provenance are untouched. Deleting an unknown reference is refused —
    /// nothing was stored to remove. The removed definition is reported.
    pub fn delete(
        &mut self,
        reference: &str,
        _confirmation: DeleteConfirmed,
    ) -> TemplateMutation<TemplateDetail> {
        let (id, _source) = self.select(reference)?;

        let mut candidate = self.config.issue_templates.clone();
        let removed = candidate
            .remove(&id)
            .expect("the selected template is in the registry");
        let detail = TemplateDetail::new(id.clone(), removed);

        let name = detail.display_name().to_string();
        self.commit(candidate)?;
        Ok(TemplateOutcome::accepted(
            detail,
            TemplateAuditEvent::new(TemplateMutationKind::Delete, id, name),
        ))
    }

    // -- internals --------------------------------------------------------

    /// Resolve a reference to `(stable ID, record)`.
    ///
    /// The ID wins; a display name is accepted only when exactly one record
    /// carries it. Anything else is a `not found` or an ambiguity error, never a
    /// guess.
    fn select(&self, reference: &str) -> Result<(String, Template)> {
        if let Some(template) = self.config.issue_templates.get(reference) {
            return Ok((reference.to_string(), template.clone()));
        }
        let matches: Vec<(&str, &Template)> = self
            .config
            .issue_templates
            .iter()
            .filter(|(_, template)| template.name.as_deref() == Some(reference))
            .collect();
        match matches.as_slice() {
            [] => Err(TixError::NotFound(format!(
                "no template with id or name `{reference}`"
            ))),
            [(id, template)] => Ok(((*id).to_string(), (*template).clone())),
            many => {
                let ids: Vec<&str> = many.iter().map(|(id, _)| *id).collect();
                Err(TixError::Config(format!(
                    "template name `{reference}` is ambiguous; it matches ids {}",
                    ids.join(", ")
                )))
            }
        }
    }

    /// A deterministic new ID for a duplicate: `<source>-copy`, then
    /// `<source>-copy-2`, `-3`, … for the first handle no stored template uses.
    ///
    /// Deterministic rather than random because a template ID is a human handle:
    /// the same duplicate run twice on the same source names the same target, and
    /// a collision is resolved by counting rather than by redrawing.
    #[must_use]
    fn allocate_duplicate_id(&self, source: &str) -> String {
        let registry = &self.config.issue_templates;
        let first = format!("{source}-copy");
        if !registry.contains(&first) {
            return first;
        }
        let mut suffix = 2u32;
        loop {
            let candidate = format!("{source}-copy-{suffix}");
            if !registry.contains(&candidate) {
                return candidate;
            }
            suffix += 1;
        }
    }

    /// Validate the whole candidate registry against this config and persist it
    /// through the existing atomic save.
    ///
    /// The save is a clone-validate-save-swap: the in-memory config is only
    /// replaced once the bytes are on disk, so a refusal or an I/O failure leaves
    /// both the registry and `tix.toml` exactly as they were.
    fn commit(&mut self, next: TemplateRegistry) -> std::result::Result<(), TemplateWriteError> {
        let mut candidate = self.config.clone();
        candidate.issue_templates = next;
        candidate.validate().map_err(TemplateWriteError::Refused)?;
        candidate
            .save(self.path)
            .map_err(TemplateWriteError::Failed)?;
        *self.config = candidate;
        Ok(())
    }
}

/// The display name of a stored template.
fn display_name_of(registry: &TemplateRegistry, id: &str) -> String {
    registry.get(id).map_or_else(
        || id.to_string(),
        |template| template.display_name(id).to_string(),
    )
}

/// The stored template for `id`.
fn candidate_template(registry: &TemplateRegistry, id: &str) -> Template {
    registry
        .get(id)
        .expect("the just-inserted template is in the registry")
        .clone()
}

#[cfg(test)]
mod tests {
    #[allow(clippy::wildcard_imports)]
    use super::*;
    use crate::config::Config;
    use std::fs;

    fn fixture(raw: &str) -> (tempfile::TempDir, Config) {
        let dir = tempfile::TempDir::new().unwrap();
        let path = dir.path().join("tix.toml");
        fs::write(&path, raw).unwrap();
        let config = Config::load(dir.path()).unwrap();
        (dir, config)
    }

    fn definition(name: &str) -> TemplateDefinition {
        TemplateDefinition::new(name, TemplateScope::repository())
    }

    #[test]
    fn create_then_show_round_trips_and_reloads() {
        let (dir, mut config) = fixture("issues_dir = \"docs/issues\"\n");
        let path = dir.path().join("tix.toml");

        let mut service = TemplateService::new(&mut config, &path);
        let outcome = service.create("bug", definition("Bug report")).unwrap();
        assert_eq!(
            outcome.audit().unwrap().kind(),
            TemplateMutationKind::Create
        );
        assert_eq!(outcome.value(), "bug");

        let detail = service.show("bug").unwrap();
        assert_eq!(detail.id(), "bug");
        assert_eq!(detail.display_name(), "Bug report");
        assert!(detail.scope().is_repository());

        // The write reached disk and survives a reload.
        let reloaded = Config::load(dir.path()).unwrap();
        assert_eq!(
            reloaded.issue_templates.get("bug").unwrap().name.as_deref(),
            Some("Bug report")
        );
    }

    #[test]
    fn a_same_content_update_is_a_noop() {
        let (dir, mut config) = fixture("issues_dir = \"docs/issues\"\n");
        let path = dir.path().join("tix.toml");
        let mut service = TemplateService::new(&mut config, &path);
        service.create("bug", definition("Bug report")).unwrap();

        let outcome = service.update("bug", definition("Bug report")).unwrap();
        assert!(outcome.is_noop());
    }
}