wsb_github/

service.rs

//! Everything a person does with GitHub here, once.
//!
//! A command line, a daemon serving pages, and any other surface call these
//! and nothing beneath them. Reads come from the mirror: no token, no network,
//! no waiting, and every answer carries how old it is. Writes go to GitHub
//! FIRST and are mirrored from what GitHub hands back — the other order shows
//! a change and takes it away again on the next sync, and a surface that does
//! that is one nobody believes.

use std::collections::BTreeMap;
use std::fs::File;
use std::path::PathBuf;

use anyhow::Context;
use serde::Serialize;

use crate::boards::BoardRef;
use crate::checkout::Repository;
use crate::client::{
    CreateGistRequest, CreateIssueRequest, GitHubClient, GitHubComment, GitHubGist, GitHubIssue,
    GitHubProject, GitHubProjectItem, ProjectFieldWrite, UpdateGistRequest, UpdateIssueRequest,
};
use crate::mirror::{Document, Mirror, Scope, Standing};
use crate::sync::{self, SyncReport};

/// Why an operation did not happen.
///
/// Three different things, and every surface says them differently: a request
/// that was wrong (a draft with no title), GitHub refusing or failing, and the
/// mirror itself failing.
#[derive(Debug)]
pub enum Failure {
    /// The request itself is wrong; nothing was asked of anybody.
    Invalid(String),
    /// Answering needs GitHub, and there is no token to ask with.
    NoToken(String),
    /// GitHub refused or could not be reached.
    GitHub(anyhow::Error),
    /// The mirror could not be read or written.
    Mirror(anyhow::Error),
}

impl Failure {
    /// Whether this is about the token: there is none, or GitHub refused the
    /// one there is — it is invalid, or lacks the access the request needs.
    pub fn is_authorization(&self) -> bool {
        match self {
            Self::NoToken(_) => true,
            Self::GitHub(error) => {
                let message = format!("{error:#}");
                message.contains("status 401") || message.contains("status 403")
            }
            _ => false,
        }
    }
}

impl std::fmt::Display for Failure {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Invalid(message) | Self::NoToken(message) => f.write_str(message),
            Self::GitHub(error) => write!(f, "{error:#}"),
            Self::Mirror(error) => write!(f, "the GitHub mirror failed: {error:#}"),
        }
    }
}

impl std::error::Error for Failure {}

pub type Outcome<T> = std::result::Result<T, Failure>;

fn mirror_failure(error: anyhow::Error) -> Failure {
    Failure::Mirror(error)
}

fn github_failure(error: anyhow::Error) -> Failure {
    Failure::GitHub(error)
}

/// Which issues a read wants.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum IssueState {
    Open,
    Closed,
    All,
}

impl std::str::FromStr for IssueState {
    type Err = String;
    fn from_str(text: &str) -> Result<Self, String> {
        match text {
            "open" => Ok(Self::Open),
            "closed" => Ok(Self::Closed),
            "all" => Ok(Self::All),
            other => Err(format!("unsupported issue state '{other}': open, closed or all")),
        }
    }
}

impl IssueState {
    fn admits(self, issue: &serde_json::Value) -> bool {
        let state = issue.get("state").and_then(|value| value.as_str()).unwrap_or("");
        match self {
            Self::Open => state == "open",
            Self::Closed => state == "closed",
            Self::All => true,
        }
    }
}

/// A repository whose last refresh failed, and why.
#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
pub struct RepoFailure {
    pub repo: String,
    pub error: String,
}

/// Issues across several repositories, as the mirror holds them.
#[derive(Debug, Clone, PartialEq, Serialize)]
pub struct IssueList {
    /// Newest movement first, each carrying `repo`.
    pub issues: Vec<serde_json::Value>,
    pub failures: Vec<RepoFailure>,
    /// Per repository, how current its copy is.
    pub sync: BTreeMap<String, Standing>,
}

/// A list scope's documents and how current they are.
#[derive(Debug, Clone, PartialEq, Serialize)]
pub struct Listed {
    pub items: Vec<serde_json::Value>,
    pub sync: Standing,
}

/// A single-document scope's document — `None` when not read yet — and how
/// current it is.
#[derive(Debug, Clone, PartialEq, Serialize)]
pub struct Single {
    pub item: Option<serde_json::Value>,
    pub sync: Standing,
}

/// What the mirror knows about one repository, for a row that draws it.
#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
pub struct RepoFacts {
    pub open_issues: i64,
    pub open_pulls: i64,
    /// Absent until the repository has been read: a repository wrongly drawn
    /// as public is how something private gets pasted somewhere.
    pub private: Option<bool>,
    pub archived: Option<bool>,
    pub stars: Option<i64>,
    /// CI's verdict on the commit this checkout has the repository at.
    pub checks: Option<String>,
}

/// The boards a project references, and why any could not be shown.
#[derive(Debug, Clone, PartialEq, Serialize)]
pub struct BoardList {
    pub boards: Vec<GitHubProject>,
    pub problems: Vec<String>,
    /// Per owner board-list scope, how current it is.
    pub sync: BTreeMap<String, Standing>,
}

/// Why an owner's boards are listed.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize)]
#[serde(rename_all = "snake_case")]
pub enum Relation {
    /// The account the token belongs to.
    Account,
    /// An organisation that account is a member of.
    Organization,
    /// Neither — it owns a board some project references.
    Referenced,
}

/// One owner of boards, and how current its board list is.
#[derive(Debug, Clone, PartialEq, Serialize)]
pub struct BoardOwner {
    pub login: String,
    pub relation: Relation,
    pub sync: Standing,
}

/// Every board this person reaches, as the mirror holds them.
#[derive(Debug, Clone, PartialEq, Serialize)]
pub struct AllBoards {
    /// The account first, then its organisations, then the owners of
    /// referenced boards that are neither — the order the boards are in.
    pub owners: Vec<BoardOwner>,
    /// Owner by owner, open boards before closed, most recently changed first.
    pub boards: Vec<GitHubProject>,
    /// The node ids of the boards the asking project references, in the order
    /// it lists them.
    pub referenced: Vec<String>,
    /// How current the knowledge of whose boards these are is.
    pub account: Standing,
    pub problems: Vec<String>,
}

/// One board's cards and how current they are.
#[derive(Debug, Clone, PartialEq, Serialize)]
pub struct Cards {
    pub items: Vec<GitHubProjectItem>,
    pub sync: Standing,
}

/// A gist, and whether it came from the mirror or had to be fetched.
#[derive(Debug, Clone, PartialEq, Serialize)]
pub struct GistAnswer {
    pub gist: serde_json::Value,
    pub from_mirror: bool,
}

/// The machine's GitHub, read through the mirror and written through GitHub.
#[derive(Debug, Clone)]
pub struct Service {
    mirror: Mirror,
}

impl Service {
    pub fn new(mirror: Mirror) -> Self {
        Self { mirror }
    }

    pub fn mirror(&self) -> &Mirror {
        &self.mirror
    }

    // ------------------------------------------------------------- reading

    fn standing(&self, scope: &Scope) -> Outcome<Standing> {
        Ok(self.mirror.state(scope).map_err(mirror_failure)?.standing())
    }

    /// Every mirrored issue of these repositories.
    pub fn issues(&self, repos: &[String], wanted: IssueState) -> Outcome<IssueList> {
        let mut issues = Vec::new();
        let mut failures = Vec::new();
        let mut standing = BTreeMap::new();
        for repo in repos {
            let scope = Scope::Issues(repo.clone());
            for mut issue in self.mirror.payloads(&scope).map_err(mirror_failure)? {
                if !wanted.admits(&issue) {
                    continue;
                }
                if let Some(object) = issue.as_object_mut() {
                    object.insert("repo".to_string(), serde_json::json!(repo));
                }
                issues.push(issue);
            }
            let state = self.mirror.state(&scope).map_err(mirror_failure)?;
            // A repository that has never synced is not a failure to report;
            // it is one not reached yet, and its standing says so.
            if let Some(error) = &state.last_error {
                failures.push(RepoFailure {
                    repo: repo.clone(),
                    error: error.clone(),
                });
            }
            standing.insert(repo.clone(), state.standing());
        }
        issues.sort_by(|a, b| updated_of(b).cmp(updated_of(a)));
        Ok(IssueList {
            issues,
            failures,
            sync: standing,
        })
    }

    /// A list scope as it stands.
    pub fn list(&self, scope: &Scope) -> Outcome<Listed> {
        Ok(Listed {
            items: self.mirror.payloads(scope).map_err(mirror_failure)?,
            sync: self.standing(scope)?,
        })
    }

    /// A single-document scope as it stands.
    pub fn single(&self, scope: &Scope) -> Outcome<Single> {
        Ok(Single {
            item: self.mirror.only(scope).map_err(mirror_failure)?,
            sync: self.standing(scope)?,
        })
    }

    /// What the mirror knows about each repository of a checkout, in one read.
    pub fn overview(&self, repositories: &[Repository]) -> Outcome<BTreeMap<String, RepoFacts>> {
        let open_issues = self.mirror.open_counts("issues").map_err(mirror_failure)?;
        let open_pulls = self.mirror.open_counts("pulls").map_err(mirror_failure)?;
        let mut facts = BTreeMap::new();
        for repository in repositories {
            let repo = &repository.name;
            let metadata = self
                .mirror
                .only(&Scope::Repository(repo.clone()))
                .map_err(mirror_failure)?;
            let checks = match &repository.head {
                Some(commit) => self
                    .mirror
                    .only(&Scope::Checks {
                        repo: repo.clone(),
                        commit: commit.clone(),
                    })
                    .map_err(mirror_failure)?,
                None => None,
            };
            facts.insert(
                repo.clone(),
                RepoFacts {
                    open_issues: open_issues.get(repo).copied().unwrap_or(0),
                    open_pulls: open_pulls.get(repo).copied().unwrap_or(0),
                    private: metadata.as_ref().and_then(|m| m.get("private")?.as_bool()),
                    archived: metadata.as_ref().and_then(|m| m.get("archived")?.as_bool()),
                    stars: metadata.as_ref().and_then(|m| m.get("stargazers_count")?.as_i64()),
                    checks: checks
                        .as_ref()
                        .and_then(|c| c.get("state")?.as_str().map(str::to_string)),
                },
            );
        }
        Ok(facts)
    }

    /// The person's gists. Summaries until one is opened.
    pub fn gists(&self) -> Outcome<Listed> {
        self.list(&Scope::Gists)
    }

    /// One gist with its file contents.
    ///
    /// The mirror answers when it holds the whole gist. Often it does not —
    /// the list endpoint omits file contents — and opening one is the moment
    /// where reaching GitHub is right: a person is waiting for exactly this,
    /// and what comes back is stored, so the next open is instant.
    pub async fn gist(&self, client: Option<&GitHubClient>, id: &str) -> Outcome<GistAnswer> {
        if let Some(held) = self.mirror.document(&Scope::Gists, id).map_err(mirror_failure)? {
            if held.complete {
                return Ok(GistAnswer {
                    gist: held.payload,
                    from_mirror: true,
                });
            }
        }
        let client = client.ok_or_else(|| {
            Failure::NoToken(format!(
                "gist {id} is held only as a summary, and there is no GitHub token to read it with \
                 (log in with `gh auth login`)"
            ))
        })?;
        let gist = client.get_gist(id).await.map_err(github_failure)?;
        let payload = self.record_gist(&gist)?;
        Ok(GistAnswer {
            gist: payload,
            from_mirror: false,
        })
    }

    /// Comments on an issue or pull request.
    ///
    /// Opening a thread is what puts it in the sweep: a thread nobody opened
    /// is not worth a request per sweep. The first open reads it now, when a
    /// token is there to read with; after that the mirror answers.
    pub async fn comments(
        &self,
        client: Option<&GitHubClient>,
        repo: &str,
        number: i64,
    ) -> Outcome<Listed> {
        let scope = Scope::Comments {
            repo: repo.to_string(),
            number,
        };
        self.mirror.hold(&scope).map_err(mirror_failure)?;
        let state = self.mirror.state(&scope).map_err(mirror_failure)?;
        if !state.ever_synced() {
            if let Some(client) = client {
                let report = sync::sync_scopes(&self.mirror, client, &[scope.clone()], true).await;
                if let Some((_, error)) = report.failed.first() {
                    return Err(Failure::GitHub(anyhow::anyhow!("{error}")));
                }
            }
        }
        self.list(&scope)
    }

    // ------------------------------------------------------------- writing

    fn record_issue(&self, repo: &str, issue: &GitHubIssue) -> Outcome<()> {
        let payload = serde_json::to_value(issue).map_err(|e| mirror_failure(e.into()))?;
        self.mirror
            .put_one(
                &Scope::Issues(repo.to_string()),
                Document::of(issue.number.to_string(), payload),
            )
            .map_err(mirror_failure)?;
        Ok(())
    }

    fn record_gist(&self, gist: &GitHubGist) -> Outcome<serde_json::Value> {
        let payload = serde_json::to_value(gist).map_err(|e| mirror_failure(e.into()))?;
        // Whole: this came from the single-gist endpoint or from an edit, so it
        // carries the file contents an editor needs.
        self.mirror
            .put_one(&Scope::Gists, Document::of(gist.id.clone(), payload.clone()))
            .map_err(mirror_failure)?;
        Ok(payload)
    }

    pub async fn create_issue(
        &self,
        client: &GitHubClient,
        owner: &str,
        repo: &str,
        request: &CreateIssueRequest,
    ) -> Outcome<GitHubIssue> {
        if request.title.trim().is_empty() {
            return Err(Failure::Invalid("an issue needs a title".to_string()));
        }
        let issue = client
            .create_issue(owner, repo, request)
            .await
            .map_err(github_failure)?;
        // Mirrored now, not at the next sweep: a person who just created an
        // issue must see it.
        self.record_issue(&format!("{owner}/{repo}"), &issue)?;
        Ok(issue)
    }

    pub async fn update_issue(
        &self,
        client: &GitHubClient,
        owner: &str,
        repo: &str,
        number: i64,
        request: &UpdateIssueRequest,
    ) -> Outcome<GitHubIssue> {
        let issue = client
            .update_issue(owner, repo, number, request)
            .await
            .map_err(github_failure)?;
        self.record_issue(&format!("{owner}/{repo}"), &issue)?;
        Ok(issue)
    }

    pub async fn add_comment(
        &self,
        client: &GitHubClient,
        owner: &str,
        repo: &str,
        number: i64,
        body: &str,
    ) -> Outcome<GitHubComment> {
        if body.trim().is_empty() {
            return Err(Failure::Invalid("a comment needs a body".to_string()));
        }
        let comment = client
            .add_comment(owner, repo, number, body)
            .await
            .map_err(github_failure)?;
        let scope = Scope::Comments {
            repo: format!("{owner}/{repo}"),
            number,
        };
        let payload = serde_json::to_value(&comment).map_err(|e| mirror_failure(e.into()))?;
        self.mirror.hold(&scope).map_err(mirror_failure)?;
        self.mirror
            .put_one(&scope, Document::of(comment.id.to_string(), payload))
            .map_err(mirror_failure)?;
        Ok(comment)
    }

    pub async fn create_gist(
        &self,
        client: &GitHubClient,
        request: &CreateGistRequest,
    ) -> Outcome<serde_json::Value> {
        if request.files.is_empty() {
            return Err(Failure::Invalid("a gist needs at least one file".to_string()));
        }
        let gist = client.create_gist(request).await.map_err(github_failure)?;
        self.record_gist(&gist)
    }

    pub async fn update_gist(
        &self,
        client: &GitHubClient,
        id: &str,
        request: &UpdateGistRequest,
    ) -> Outcome<serde_json::Value> {
        let gist = client.update_gist(id, request).await.map_err(github_failure)?;
        self.record_gist(&gist)
    }

    // -------------------------------------------------------------- boards

    /// The boards a project references, as the mirror knows them.
    pub fn boards(&self, references: &[BoardRef]) -> Outcome<BoardList> {
        let wanted = references.iter().cloned().collect();
        let (boards, problems) =
            sync::resolve_boards(&self.mirror, &wanted).map_err(mirror_failure)?;
        // In the order the project lists them, not the order they resolved.
        let mut ordered = Vec::new();
        for reference in references {
            if let Some(board) = boards
                .iter()
                .find(|board| board.owner == reference.owner && board.number == reference.number)
            {
                ordered.push(board.clone());
            }
        }
        let mut standing = BTreeMap::new();
        for reference in references {
            let scope = Scope::Projects(reference.owner.clone());
            standing.insert(scope.key(), self.standing(&scope)?);
        }
        Ok(BoardList {
            boards: ordered,
            problems,
            sync: standing,
        })
    }

    /// Every board of the token's account, of each of its organisations, and
    /// of the owner of every board `references` names — with which of them
    /// those references are.
    ///
    /// Boards belong to owners, not to projects, so this is the same list from
    /// whichever project it is asked; the references only mark the boards that
    /// project works with. An owner whose list has never been read is reported
    /// beside the boards that could be listed, never dropped silently.
    pub fn all_boards(&self, references: &[BoardRef]) -> Outcome<AllBoards> {
        let account = self.standing(&Scope::Viewer)?;
        let viewer = sync::viewer(&self.mirror).map_err(mirror_failure)?;
        let mut problems = Vec::new();

        let mut owners: Vec<(String, Relation)> = Vec::new();
        match viewer {
            Some(viewer) => {
                owners.push((viewer.login, Relation::Account));
                let mut organizations = viewer.organizations;
                organizations.sort_by_key(|login| login.to_lowercase());
                owners.extend(organizations.into_iter().map(|login| (login, Relation::Organization)));
            }
            None => problems.push(match &account.last_error {
                Some(error) => format!("whose boards these are could not be read: {error}"),
                None => "who the GitHub token belongs to has not been read yet, so only referenced \
                         boards are listed"
                    .to_string(),
            }),
        }
        for reference in references {
            if !owners.iter().any(|(login, _)| *login == reference.owner) {
                owners.push((reference.owner.clone(), Relation::Referenced));
            }
        }

        let mut listed = Vec::new();
        let mut boards = Vec::new();
        let mut unread = std::collections::BTreeSet::new();
        for (login, relation) in owners {
            let scope = Scope::Projects(login.clone());
            match sync::owner_boards(&self.mirror, &login).map_err(mirror_failure)? {
                Ok(mut held) => {
                    held.sort_by(|a, b| a.closed.cmp(&b.closed).then(b.updated_at.cmp(&a.updated_at)));
                    boards.extend(held);
                }
                Err(reason) => {
                    problems.push(reason);
                    unread.insert(login.clone());
                }
            }
            listed.push(BoardOwner {
                sync: self.standing(&scope)?,
                login,
                relation,
            });
        }

        let mut referenced = Vec::new();
        for reference in references {
            match boards
                .iter()
                .find(|board| board.owner == reference.owner && board.number == reference.number)
            {
                Some(board) => referenced.push(board.id.clone()),
                // An owner whose list was never read is already reported.
                None if unread.contains(&reference.owner) => {}
                None => problems.push(format!("{} has no board {}", reference.owner, reference.number)),
            }
        }

        Ok(AllBoards {
            owners: listed,
            boards,
            referenced,
            account,
            problems,
        })
    }

    /// One board's cards, in TODAY'S shape.
    ///
    /// Every card is parsed into the type this version defines: a row an
    /// older version wrote takes the defaults of the fields it did not have,
    /// and a payload that does not parse AT ALL is raised — half a board is
    /// the silent wrong answer.
    pub fn cards(&self, board: &str) -> Outcome<Cards> {
        let scope = Scope::ProjectItems(board.to_string());
        let items = self
            .mirror
            .payloads(&scope)
            .map_err(mirror_failure)?
            .into_iter()
            .map(|payload| {
                serde_json::from_value::<GitHubProjectItem>(payload).map_err(|e| {
                    Failure::Mirror(anyhow::anyhow!(
                        "a mirrored card of {board} cannot be read by this version ({e}); \
                         sync the board to read it again"
                    ))
                })
            })
            .collect::<Outcome<Vec<_>>>()?;
        Ok(Cards {
            items,
            sync: self.standing(&scope)?,
        })
    }

    /// Bring every board current now — who the token is, each owner's list,
    /// the cards being kept — without the rest of the machine's mirror.
    pub async fn refresh_boards(&self, client: &GitHubClient, references: &[BoardRef]) -> SyncReport {
        let references = references.iter().cloned().collect();
        sync::sync_boards(&self.mirror, client, &references, true).await
    }

    /// Bring one board's cards current before it is shown, if due — or whether
    /// due or not, with `force` — and nothing else.
    ///
    /// The board is one the mirror already lists, so its owner's list has
    /// nothing to add. Reading more inside the request that opens a board made
    /// that request slow enough for its caller to give up, and a cancelled
    /// read left the board "not read yet" until the next scheduled pass
    /// (20 Oct 2026). A board's cards need nothing but the board.
    pub async fn refresh_board(
        &self,
        client: &GitHubClient,
        board: &GitHubProject,
        force: bool,
    ) -> SyncReport {
        sync::sync_scopes(&self.mirror, client, &[Scope::ProjectItems(board.id.clone())], force).await
    }

    fn record_card(&self, board: &str, item: &GitHubProjectItem) -> Outcome<()> {
        let payload = serde_json::to_value(item).map_err(|e| mirror_failure(e.into()))?;
        self.mirror
            .put_one(
                &Scope::ProjectItems(board.to_string()),
                Document::of(item.id.clone(), payload),
            )
            .map_err(mirror_failure)?;
        Ok(())
    }

    /// Set one field of one card, or take its value off with `None`.
    ///
    /// Clearing is its own act rather than an empty value: an empty text IS a
    /// value, and a board that could not tell "no due date" from "a due date
    /// of nothing" shows a column of blanks where it means to show none.
    pub async fn set_field(
        &self,
        client: &GitHubClient,
        board: &str,
        item: &str,
        field: &str,
        value: Option<&ProjectFieldWrite>,
    ) -> Outcome<GitHubProjectItem> {
        let updated = match value {
            Some(value) => client.set_project_field(board, item, field, value).await,
            None => client.clear_project_field(board, item, field).await,
        }
        .map_err(github_failure)?;
        self.record_card(board, &updated)?;
        Ok(updated)
    }

    /// Order a card: behind `after`, or first with `None`.
    pub async fn move_card(
        &self,
        client: &GitHubClient,
        board: &str,
        item: &str,
        after: Option<&str>,
    ) -> Outcome<GitHubProjectItem> {
        if after == Some(item) {
            return Err(Failure::Invalid("a card cannot be moved behind itself".to_string()));
        }
        let updated = client
            .move_project_item_after(board, item, after)
            .await
            .map_err(github_failure)?;
        self.record_card(board, &updated)?;
        Ok(updated)
    }

    /// Archive a card, or bring it back. Stated rather than toggled: a toggle
    /// acts on what the caller last saw.
    pub async fn set_archived(
        &self,
        client: &GitHubClient,
        board: &str,
        item: &str,
        archived: bool,
    ) -> Outcome<GitHubProjectItem> {
        let updated = client
            .archive_project_item(board, item, archived)
            .await
            .map_err(github_failure)?;
        self.record_card(board, &updated)?;
        Ok(updated)
    }

    /// Rewrite a draft card's title and body, whole.
    pub async fn edit_draft(
        &self,
        client: &GitHubClient,
        board: &str,
        item: &str,
        content: &str,
        title: &str,
        body: &str,
    ) -> Outcome<GitHubProjectItem> {
        if title.trim().is_empty() {
            return Err(Failure::Invalid(
                "a draft card needs a title; an untitled card is one nobody can find".to_string(),
            ));
        }
        let updated = client
            .update_project_draft(item, content, title, body)
            .await
            .map_err(github_failure)?;
        self.record_card(board, &updated)?;
        Ok(updated)
    }

    /// A card that lives only on the board.
    pub async fn add_draft(
        &self,
        client: &GitHubClient,
        board: &str,
        title: &str,
        body: &str,
    ) -> Outcome<GitHubProjectItem> {
        if title.trim().is_empty() {
            return Err(Failure::Invalid("a draft card needs a title".to_string()));
        }
        let added = client
            .add_project_draft(board, title, body)
            .await
            .map_err(github_failure)?;
        self.record_card(board, &added)?;
        Ok(added)
    }

    /// A card for an issue or pull request that already exists, by its URL.
    pub async fn add_existing(
        &self,
        client: &GitHubClient,
        board: &str,
        url: &str,
    ) -> Outcome<GitHubProjectItem> {
        let added = client
            .add_project_item_by_url(board, url)
            .await
            .map_err(github_failure)?;
        self.record_card(board, &added)?;
        Ok(added)
    }

    /// Take a card off the board. The issue itself is untouched — a board
    /// owns cards, not issues — and a draft has nowhere else to be.
    pub async fn remove_card(&self, client: &GitHubClient, board: &str, item: &str) -> Outcome<()> {
        client
            .delete_project_item(board, item)
            .await
            .map_err(github_failure)?;
        // Gone from the mirror now rather than at the next sync: a card that
        // stayed until then is one somebody removes twice.
        self.mirror
            .remove_one(&Scope::ProjectItems(board.to_string()), item)
            .map_err(mirror_failure)?;
        Ok(())
    }

    /// Add a column to a board's single-select field.
    pub async fn add_column(
        &self,
        client: &GitHubClient,
        board: &str,
        field: &str,
        name: &str,
        color: &str,
        description: &str,
    ) -> Outcome<(GitHubProject, Vec<GitHubProjectItem>)> {
        let _lock = self.column_lock().await?;
        let updated = client
            .add_project_column(board, field, name, color, description)
            .await
            .map_err(github_failure)?;
        let items = client.project_items(board).await.map_err(github_failure)?;
        self.record_board(&updated, &items)?;
        Ok((updated, items))
    }

    /// Remove a column. GitHub clears that value from affected cards; every
    /// card is read again before the mirror changes, so they land in no column.
    pub async fn remove_column(
        &self,
        client: &GitHubClient,
        board: &str,
        field: &str,
        option: &str,
    ) -> Outcome<(GitHubProject, Vec<GitHubProjectItem>)> {
        let _lock = self.column_lock().await?;
        let updated = client
            .remove_project_column(board, field, option)
            .await
            .map_err(github_failure)?;
        let items = client.project_items(board).await.map_err(github_failure)?;
        self.record_board(&updated, &items)?;
        Ok((updated, items))
    }

    /// Store a board and the complete card set GitHub returned after it
    /// changed, as one act.
    fn record_board(&self, board: &GitHubProject, items: &[GitHubProjectItem]) -> Outcome<()> {
        let board_value = serde_json::to_value(board).map_err(|e| mirror_failure(e.into()))?;
        let documents = items
            .iter()
            .map(|item| {
                serde_json::to_value(item)
                    .map(|value| Document::of(item.id.clone(), value))
                    .map_err(|e| mirror_failure(e.into()))
            })
            .collect::<Outcome<Vec<_>>>()?;
        self.mirror
            .put_project_write(
                &Scope::Projects(board.owner.clone()),
                Document::of(board.id.clone(), board_value),
                &Scope::ProjectItems(board.id.clone()),
                &documents,
            )
            .map_err(mirror_failure)
    }

    /// Serialise column writes across every process on the machine.
    ///
    /// GitHub replaces a single-select field's WHOLE option list. Two writers
    /// that both read the same list and each wrote it back with one change
    /// would have the later erase the earlier — and the writers are separate
    /// processes, a command line and a daemon, so the lock is a file.
    async fn column_lock(&self) -> Outcome<ColumnLock> {
        let path = self.mirror.path().with_extension("columns.lock");
        tokio::task::spawn_blocking(move || ColumnLock::acquire(path))
            .await
            .map_err(|e| Failure::Mirror(anyhow::anyhow!("the column lock could not be taken: {e}")))?
            .map_err(mirror_failure)
    }
}

/// An exclusive lock on a file, held while this value lives.
struct ColumnLock {
    file: File,
}

impl ColumnLock {
    fn acquire(path: PathBuf) -> anyhow::Result<Self> {
        let file = std::fs::OpenOptions::new()
            .create(true)
            .truncate(false)
            .write(true)
            .open(&path)
            .with_context(|| format!("cannot open {}", path.display()))?;
        file.lock()
            .with_context(|| format!("cannot lock {}", path.display()))?;
        Ok(Self { file })
    }
}

impl Drop for ColumnLock {
    fn drop(&mut self) {
        // Closing the file releases the lock as well; unlocking first says so
        // in the code rather than leaving it to the descriptor's end.
        let _ = self.file.unlock();
    }
}

fn updated_of(issue: &serde_json::Value) -> &str {
    issue
        .get("updated_at")
        .and_then(|value| value.as_str())
        .unwrap_or("")
}

#[cfg(test)]
#[path = "service_tests.rs"]
mod tests;