git-queue 0.1.0

//! Pure rendering helpers: the status tree, PR titles, and the shared queue
//! navigation block injected into every PR body. Kept side-effect-free so they
//! can be unit-tested without git or the network.

pub const BEGIN: &str = "<!-- git-queue:begin -->";
pub const END: &str = "<!-- git-queue:end -->";

/// One entry in a queue line for rendering purposes.
pub struct Entry {
    pub branch: String,
    pub pr: Option<PrRef>,
    /// The branch currently holds persisted conflict markers.
    pub conflicted: bool,
    /// Paths of the files holding those markers (filled by status/log).
    pub conflicts: Vec<String>,
    /// Commits to render beneath the branch (newest first): `(Stable-Commit-Id?,
    /// subject)`. Empty for `status`; filled by `log`.
    pub commits: Vec<(Option<String>, String)>,
    /// Nesting level: 0 on the main line, +1 for each fork the branch sits
    /// behind. Forked subtrees render indented above their fork parent.
    pub indent: usize,
}

#[derive(Clone)]
pub struct PrRef {
    pub number: u64,
    pub url: String,
    pub state: String, // OPEN | CLOSED | MERGED
    /// APPROVED | CHANGES_REQUESTED | REVIEW_REQUIRED | None
    pub review: Option<String>,
}

/// The commit-status context the merge-order gate posts under.
pub const GATE_CONTEXT: &str = "git-queue/merge-order";

/// One planned merge-order status (the advisory "status gate"), to be posted
/// on the head commit of a PR.
#[derive(Debug, PartialEq)]
pub struct GateStatus {
    /// Head branch of the PR receiving the status.
    pub branch: String,
    /// true -> green ✓ (mergeable now); false -> red ✗ (out of order).
    pub success: bool,
    pub description: String,
    /// "Details" link for the status: the PR that must merge first.
    pub target_url: Option<String>,
}

/// Plan the advisory merge-order statuses for a queue line (bottom-first): the
/// bottom-most OPEN PR gets a success status, every open PR above it gets a
/// failure status naming the PR that must merge first. Merged/closed PRs and
/// branches without a PR get nothing.
pub fn gate_plan(entries: &[Entry]) -> Vec<GateStatus> {
    let mut bottom: Option<&PrRef> = None;
    let mut plan = Vec::new();
    for e in entries {
        let Some(pr) = &e.pr else { continue };
        if pr.state != "OPEN" {
            continue;
        }
        match bottom {
            None => {
                plan.push(GateStatus {
                    branch: e.branch.clone(),
                    success: true,
                    description: "Ready — front of the queue, merge this PR first".to_string(),
                    target_url: None,
                });
                bottom = Some(pr);
            }
            Some(b) => plan.push(GateStatus {
                branch: e.branch.clone(),
                success: false,
                description: format!("Do not merge — merge PR #{} first (queue order)", b.number),
                target_url: (!b.url.is_empty()).then(|| b.url.clone()),
            }),
        }
    }
    plan
}

/// Emoji for a PR's review decision.
fn approval_emoji(review: &Option<String>) -> &'static str {
    match review.as_deref() {
        Some("APPROVED") => "✅",
        Some("CHANGES_REQUESTED") => "♻️",
        _ => "⏳", // REVIEW_REQUIRED / not yet reviewed
    }
}

/// Emoji for a PR's merge state.
fn state_emoji(state: &str) -> &'static str {
    match state {
        "MERGED" => "🟣",
        "CLOSED" => "⚫",
        _ => "🟢", // OPEN
    }
}

/// Numbered title: `[k/n] <subject>`, stripping any prior `[i/j] ` prefix so
/// re-submitting doesn't pile up prefixes.
pub fn numbered_title(subject: &str, index: usize, total: usize) -> String {
    format!("[{}/{}] {}", index + 1, total, strip_prefix(subject))
}

fn strip_prefix(subject: &str) -> &str {
    let s = subject.trim_start();
    if let Some(rest) = s.strip_prefix('[') {
        if let Some(close) = rest.find(']') {
            let inside = &rest[..close];
            if inside.contains('/') && inside.chars().all(|c| c.is_ascii_digit() || c == '/') {
                return rest[close + 1..].trim_start();
            }
        }
    }
    s
}

/// Build the shared queue-navigation block: a formatted, linked list of every
/// PR in the line in merge order (bottom first), with the current PR bolded and
/// marked. Each entry links to the PR's URL when known.
pub fn nav_block(line: &[Entry], current: &str, base: &str, queue_name: &str) -> String {
    let total = line.len();
    let mut lines = vec![
        format!(
            "### 📚 {queue_name} PR &nbsp;·&nbsp; {} of {}",
            position_of(line, current),
            total
        ),
        String::new(),
        "Part of a queue. The PRs merge in FIFO order — the numbered order below, #1 \
         first. Merging one supersedes the PRs after it until the author runs \
         `git queue sync` (rebases the rest onto the merged base) and `git queue submit` \
         (retargets their PRs)."
            .to_string(),
        String::new(),
    ];
    // Bottom-first: index 0 merges first.
    for (i, e) in line.iter().enumerate() {
        let is_current = e.branch == current;
        let target = if i == 0 {
            base
        } else {
            line[i - 1].branch.as_str()
        };
        // Merge-state emoji always; approval emoji only while the PR is open
        // (a merged/closed PR's review status is no longer meaningful).
        let status = match &e.pr {
            Some(p) if p.state == "OPEN" => {
                format!("{}{} ", approval_emoji(&p.review), state_emoji(&p.state))
            }
            Some(p) => format!("{} ", state_emoji(&p.state)),
            None => String::new(),
        };
        // Link text: `#<n> branch` linked to the PR URL if we have one.
        let label = match &e.pr {
            Some(p) if !p.url.is_empty() => format!("[#{} `{}`]({})", p.number, e.branch, p.url),
            Some(p) => format!("#{} `{}`", p.number, e.branch),
            None => format!("`{}` _(not submitted)_", e.branch),
        };
        let arrow = format!(" → `{target}`");
        let line_str = if is_current {
            format!("{status}**{label}{arrow}** &nbsp;👈 **this PR**")
        } else {
            format!("{status}{label}{arrow}")
        };
        lines.push(line_str);
    }
    lines.push(String::new());
    lines.push(
        "<sub>✅ approved · ♻️ changes requested · ⏳ review pending &nbsp;|&nbsp; \
         🟣 merged · 🟢 open · ⚫ closed &nbsp;—&nbsp; status as of the last \
         `git queue submit`.</sub>"
            .to_string(),
    );
    lines.push("<sub>🥞 Managed by git-queue — do not edit this list by hand.</sub>".to_string());
    lines.join("\n")
}

/// 1-based position of `current` within the (bottom-first) line.
fn position_of(line: &[Entry], current: &str) -> usize {
    line.iter()
        .position(|e| e.branch == current)
        .map_or(0, |i| i + 1)
}

/// Compose a PR body: the queue map, then optional "About this queue" and
/// "About this branch" sections, all inside the managed BEGIN..END block —
/// every part regenerates from config on each submit.
pub fn compose_body(queue_description: &str, branch_description: &str, nav: &str) -> String {
    let mut body = format!("{BEGIN}\n{nav}");
    let qd = queue_description.trim();
    if !qd.is_empty() {
        body.push_str(&format!("\n\n# About this queue\n\n{qd}"));
    }
    let bd = strip_block(branch_description);
    // Legacy bodies kept the description under a bare `---` divider outside
    // the managed block; drop that scaffolding if it survived the strip.
    let bd = bd.trim();
    let bd = bd.strip_prefix("---").map(str::trim_start).unwrap_or(bd);
    if !bd.is_empty() {
        body.push_str(&format!("\n\n# About this branch\n\n{bd}"));
    }
    body.push_str(&format!("\n{END}"));
    body
}

/// Remove a previously injected BEGIN..END block (inclusive) from `body`.
pub fn strip_block(body: &str) -> String {
    match (body.find(BEGIN), body.find(END)) {
        (Some(start), Some(end)) if end >= start => {
            let after = end + END.len();
            let mut result = String::new();
            result.push_str(&body[..start]);
            result.push_str(&body[after..]);
            result
        }
        _ => body.to_string(),
    }
}

/// Render the status tree, top of queue first. `entries` is bottom-first;
/// `base` is the branch the line merges into (labelled "trunk" when it is the
/// trunk). The current branch gets a `❯` marker in the left margin. With
/// `color`: bold branch names, tinted PR states and warnings, and a distinct
/// colour for commit ids.
pub fn status_tree(
    entries: &[Entry],
    current: &str,
    base: &str,
    base_is_trunk: bool,
    color: bool,
    // `Some(repo url)` when the terminal renders OSC 8 hyperlinks: PR numbers
    // become clickable links to their PRs.
    link_base: Option<&str>,
) -> String {
    let paint = |code: &str, s: &str| -> String {
        if color {
            format!("\u{1b}[{code}m{s}\u{1b}[0m")
        } else {
            s.to_string()
        }
    };
    let mut out = String::new();
    // Entries arrive top-down (leaves first, base-most branch last); forked
    // subtrees sit directly above their fork parent, one indent level in.
    for e in entries.iter() {
        let is_current = e.branch == current;
        let margin = if is_current {
            paint("1;32", "❯ ")
        } else {
            "  ".to_string()
        };
        let pad = "  ".repeat(e.indent);
        let node = if is_current { "◉" } else { "◯" };
        let name = paint("1", &e.branch);
        let link = |n: u64| -> String {
            match link_base {
                Some(base_url) => {
                    format!("\u{1b}]8;;{base_url}/pull/{n}\u{1b}\\#{n}\u{1b}]8;;\u{1b}\\")
                }
                None => format!("#{n}"),
            }
        };
        let pr = match &e.pr {
            // status/log never touch the network: the number is cached
            // locally, but the live state is only known after submit/sync —
            // show just the number rather than a cryptic placeholder.
            Some(p) if p.state == "?" => format!("  {}", link(p.number)),
            Some(p) => {
                let state = match p.state.as_str() {
                    "OPEN" => paint("32", "OPEN"),
                    "MERGED" => paint("35", "MERGED"),
                    "CLOSED" => paint("31", "CLOSED"),
                    other => other.to_string(),
                };
                format!("  {} [{state}]", link(p.number))
            }
            None => String::new(),
        };
        let warn = if e.conflicted {
            paint("33", "  ⚠ conflicts")
        } else {
            String::new()
        };
        out.push_str(&format!("{margin}{pad}{node} {name}{pr}{warn}\n"));
        for path in &e.conflicts {
            out.push_str(&format!(
                "      {pad}{}\n",
                paint("33", &format!("⚠ {path}"))
            ));
        }
        for (id, subject) in &e.commits {
            // Abbreviate the id to `q-` + 8 chars.
            let abbrev = match id {
                Some(id) => {
                    let short: String = id.chars().take(10).collect();
                    paint("36", &format!("{short:<10}"))
                }
                None => paint("2", "(no id)   "),
            };
            out.push_str(&format!("      {pad}{abbrev}  {subject}\n"));
        }
    }
    out.push_str("  ┴\n");
    let label = if base_is_trunk { "trunk" } else { "base" };
    out.push_str(&format!("    {base} ({label})\n"));
    out
}

/// A classified line of a unified diff, so the TUI diff pane can colour
/// `+`/`-`/hunk lines (ADR: our own colouring, no syntax highlighting) and
/// render binary changes as a placeholder. The mapping to terminal styles
/// lives in the view; this classification is pure and unit-tested.
#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub enum DiffLine {
    /// An added line (`+…`, but not the `+++` file header).
    Added,
    /// A removed line (`-…`, but not the `---` file header).
    Removed,
    /// A hunk header (`@@ … @@`).
    Hunk,
    /// File-level metadata (`diff --git`, `index`, `--- `, `+++ `, mode and
    /// rename/copy lines).
    FileHeader,
    /// A binary-file change git renders as a placeholder rather than content.
    Binary,
    /// An unchanged context line (or anything unrecognised).
    Context,
}

/// Classify one raw line of `git show`/`git diff` output. The `---`/`+++`
/// file headers are matched before the `+`/`-` content cases, so they never
/// read as removed/added lines.
pub fn classify_diff_line(line: &str) -> DiffLine {
    if line.starts_with("@@") {
        DiffLine::Hunk
    } else if line.starts_with("diff --git")
        || line.starts_with("index ")
        || line.starts_with("--- ")
        || line.starts_with("+++ ")
        || line.starts_with("new file")
        || line.starts_with("deleted file")
        || line.starts_with("old mode")
        || line.starts_with("new mode")
        || line.starts_with("rename ")
        || line.starts_with("copy ")
        || line.starts_with("similarity ")
        || line.starts_with("dissimilarity ")
    {
        DiffLine::FileHeader
    } else if line.starts_with("Binary files") || line.starts_with("GIT binary patch") {
        DiffLine::Binary
    } else if line.starts_with('+') {
        DiffLine::Added
    } else if line.starts_with('-') {
        DiffLine::Removed
    } else {
        DiffLine::Context
    }
}

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

    #[test]
    fn classifies_diff_lines_headers_before_content() {
        use DiffLine::*;
        assert_eq!(classify_diff_line("@@ -1,3 +1,4 @@ fn main"), Hunk);
        assert_eq!(classify_diff_line("diff --git a/x b/x"), FileHeader);
        assert_eq!(classify_diff_line("index 0000..1111 100644"), FileHeader);
        // The file headers must win over the +/- content rules.
        assert_eq!(classify_diff_line("--- a/x"), FileHeader);
        assert_eq!(classify_diff_line("+++ b/x"), FileHeader);
        assert_eq!(classify_diff_line("new file mode 100644"), FileHeader);
        assert_eq!(classify_diff_line("+added line"), Added);
        assert_eq!(classify_diff_line("-removed line"), Removed);
        assert_eq!(classify_diff_line(" context"), Context);
        assert_eq!(classify_diff_line("Binary files a/i.png and b/i.png differ"), Binary);
    }

    #[test]
    fn strips_prior_number_prefix() {
        assert_eq!(numbered_title("[2/9] Add widget", 0, 3), "[1/3] Add widget");
        assert_eq!(numbered_title("Add widget", 2, 3), "[3/3] Add widget");
        // Not a number prefix -> left intact.
        assert_eq!(numbered_title("[wip] thing", 0, 1), "[1/1] [wip] thing");
    }

    #[test]
    fn compose_builds_sections_and_stays_idempotent() {
        // A branch description that still contains an old managed block.
        let branch_desc = format!("{BEGIN}\nold\n{END}\n\n---\n\nHello");
        let composed = compose_body("The plan.", &branch_desc, "new-nav");
        assert!(composed.starts_with(BEGIN));
        assert!(composed.ends_with(END));
        assert!(composed.contains("new-nav"));
        assert!(!composed.contains("old"), "old nav must be stripped");
        assert!(composed.contains("# About this queue\n\nThe plan."));
        assert!(composed.contains("# About this branch\n\nHello"));
        assert_eq!(composed.matches(BEGIN).count(), 1);
    }

    #[test]
    fn compose_omits_empty_sections() {
        let composed = compose_body("", "", "nav");
        assert_eq!(composed, format!("{BEGIN}\nnav\n{END}"));
        let q_only = compose_body("Q.", "", "nav");
        assert!(q_only.contains("About this queue") && !q_only.contains("About this branch"));
    }

    fn entry(branch: &str, number: u64, url: &str, state: &str, review: Option<&str>) -> Entry {
        Entry {
            branch: branch.to_string(),
            pr: Some(PrRef {
                number,
                url: url.to_string(),
                state: state.to_string(),
                review: review.map(|s| s.to_string()),
            }),
            conflicted: false,
            conflicts: Vec::new(),
            commits: Vec::new(),
            indent: 0,
        }
    }

    #[test]
    fn gate_plan_marks_bottom_ready_and_blocks_the_rest() {
        let line = vec![
            entry("api", 10, "https://x/pull/10", "OPEN", None),
            entry("service", 11, "https://x/pull/11", "OPEN", None),
            entry("ui", 12, "https://x/pull/12", "OPEN", None),
        ];
        let plan = gate_plan(&line);
        assert_eq!(plan.len(), 3);
        assert!(plan[0].success);
        assert_eq!(plan[0].branch, "api");
        assert_eq!(plan[0].target_url, None);
        for s in &plan[1..] {
            assert!(!s.success);
            assert!(s.description.contains("#10"), "{}", s.description);
            assert_eq!(s.target_url.as_deref(), Some("https://x/pull/10"));
        }
    }

    #[test]
    fn gate_plan_skips_merged_and_promotes_next_open_pr() {
        let line = vec![
            entry("api", 10, "https://x/pull/10", "MERGED", None),
            entry("service", 11, "https://x/pull/11", "OPEN", None),
            entry("ui", 12, "https://x/pull/12", "OPEN", None),
        ];
        let plan = gate_plan(&line);
        assert_eq!(plan.len(), 2);
        assert!(plan[0].success);
        assert_eq!(plan[0].branch, "service");
        assert!(!plan[1].success);
        assert!(
            plan[1].description.contains("#11"),
            "{}",
            plan[1].description
        );
    }

    #[test]
    fn gate_plan_ignores_closed_prs_and_unsubmitted_branches() {
        let mut line = vec![
            entry("api", 10, "https://x/pull/10", "CLOSED", None),
            entry("service", 11, "https://x/pull/11", "OPEN", None),
        ];
        line.push(Entry {
            branch: "ui".to_string(),
            pr: None,
            conflicted: false,
            conflicts: Vec::new(),
            commits: Vec::new(),
            indent: 0,
        });
        let plan = gate_plan(&line);
        assert_eq!(plan.len(), 1);
        assert!(plan[0].success);
        assert_eq!(plan[0].branch, "service");
    }

    #[test]
    fn gate_plan_is_empty_when_no_pr_is_open() {
        let line = vec![
            entry("api", 10, "https://x/pull/10", "MERGED", None),
            entry("service", 11, "https://x/pull/11", "CLOSED", None),
        ];
        assert!(gate_plan(&line).is_empty());
        assert!(gate_plan(&[]).is_empty());
    }

    #[test]
    fn gate_plan_descriptions_fit_github_status_limit() {
        // The GitHub statuses API caps descriptions at 140 characters.
        let line = vec![
            entry(
                "api",
                4_294_967_295,
                "https://x/pull/4294967295",
                "OPEN",
                None,
            ),
            entry("ui", 12, "https://x/pull/12", "OPEN", None),
        ];
        for s in gate_plan(&line) {
            assert!(s.description.len() <= 140, "{}", s.description);
        }
    }

    #[test]
    fn nav_block_links_marks_current_and_shows_status() {
        let line = vec![
            entry("api", 10, "https://x/pull/10", "MERGED", Some("APPROVED")),
            entry(
                "service",
                11,
                "https://x/pull/11",
                "OPEN",
                Some("CHANGES_REQUESTED"),
            ),
            entry("ui", 12, "https://x/pull/12", "OPEN", None),
        ];
        let nav = nav_block(&line, "service", "main", "payments");
        assert!(nav.contains("📚 payments PR"), "{nav}");
        // Merged PR: state emoji only (approval no longer meaningful).
        assert!(
            nav.contains("🟣 [#10 `api`](https://x/pull/10) → `main`"),
            "{nav}"
        );
        // Current PR: emojis, then bolded label targeting the branch below.
        assert!(
            nav.contains("♻️🟢 **[#11 `service`](https://x/pull/11) → `api`**"),
            "{nav}"
        );
        // Not-yet-reviewed open PR.
        assert!(nav.contains("⏳🟢 [#12 `ui`]"), "{nav}");
        assert!(nav.contains("👈 **this PR**"));
        assert!(nav.contains("2 of 3"));
        assert!(nav.contains("FIFO"), "merge order described as FIFO");
        assert!(
            !nav.contains("bottom-first"),
            "confusing bottom-first wording removed"
        );
    }
}