Add --oneshot option

README.md

@@ -18,6 +18,15 @@ gleam run   # Run the project
 gleam shell # Run an Erlang shell
 ```
 
+## Oneshot buildograms
+
+You can use the `--oneshot` command line flag to instead of a server just
+render one SVG immediately for a given repository.
+
+```shell session
+$ podman run --rm ghcr.io/fabjan/buildogram:latest run --oneshot=fabjan/buildogram 2>/dev/null > test.svg
+```
+
 ## Deploying
 
 For each release, a container image is pushed to [buildogram packages](https://github.com/fabjan/buildogram/pkgs/container/buildogram).

src/buildogram.gleam

@@ -20,14 +20,16 @@ import gleam/erlang
 import gleam/erlang/os
 import gleam/erlang/process
 import gleam/http/elli
+import buildogram/diagram
+import buildogram/github
 import buildogram/http_server
 import buildogram/http_client
 import outil.{CommandError, CommandResult, print_usage_and_exit}
 import outil/opt
 import snag.{Snag}
 
 fn log(s) {
-  io.println("[main] " <> s)
+  io.println_error("[main] " <> s)
 }
 
 pub fn get_env(
@@ -53,6 +55,13 @@ pub fn main_cmd(args: List(String)) -> CommandResult(Nil, Snag) {
   let cache_size = get_env("BUILDOGRAM_CACHE_SIZE", int.parse, 100)
   use cache_size, cmd <- opt.int(cmd, "cache", "HTTP cache size", cache_size)
 
+  use one_shot, cmd <- opt.string(
+    cmd,
+    "oneshot",
+    "Just print the SVG for the given GitHub repo and exit",
+    "",
+  )
+
   try port = port(cmd)
   try cache_size = cache_size(cmd)
 
@@ -62,6 +71,11 @@ pub fn main_cmd(args: List(String)) -> CommandResult(Nil, Snag) {
     http_client.start(cache_size)
     |> cmd_snag("starting HTTP client")
 
+  let _ = case one_shot(cmd) {
+    Ok(repo) if repo != "" -> print_svg_and_exit(client, repo)
+    _ -> Nil
+  }
+
   // Start the web server process
   try server =
     http_server.stack(client)
@@ -91,3 +105,20 @@ fn cmd_snag(res: Result(a, b), context: String) -> CommandResult(a, Snag) {
 fn cmd_result(res: Result(a, b)) -> CommandResult(a, b) {
   result.map_error(res, fn(e) { CommandError(e) })
 }
+
+fn print_svg_and_exit(client, repo_path: String) -> Nil {
+  case github.get_all_runs(client, repo_path) {
+    Ok(runs) -> {
+      let svg = diagram.bar_chart(runs, 400, 100)
+      io.println(svg)
+      halt(0)
+    }
+    Error(Snag(issue, _)) -> {
+      io.println_error("Error: " <> issue)
+      halt(1)
+    }
+  }
+}
+
+external fn halt(Int) -> Nil =
+  "erlang" "halt"

src/buildogram/diagram.gleam

@@ -25,7 +25,7 @@ import buildogram/timestamp
 import buildogram/util
 
 fn log(s) {
-  io.println("[diagram] " <> s)
+  io.println_error("[diagram] " <> s)
 }
 
 /// Render an SVG bar chart from the given workflow runs.

src/buildogram/github.gleam

@@ -27,7 +27,7 @@ import buildogram/timestamp.{Timestamp, decode_timestamp}
 import buildogram/util
 
 fn log(s) {
-  io.println("[github] " <> s)
+  io.println_error("[github] " <> s)
 }
 
 /// WorkflowRun is a full pipeline run.

src/buildogram/http_client.gleam

@@ -90,7 +90,7 @@ type HttpClient {
 }
 
 fn log(s) {
-  io.println("[http_client] " <> s)
+  io.println_error("[http_client] " <> s)
 }
 
 fn handle_get(get: HttpGet, state: HttpClient) -> actor.Next(HttpClient) {

src/buildogram/http_server.gleam

@@ -28,7 +28,7 @@ import buildogram/http_client.{HttpGet}
 import buildogram/util
 
 fn log(s) {
-  io.println("[http_server] " <> s)
+  io.println_error("[http_server] " <> s)
 }
 
 /// Configure middleware etc.

test/diagram_test.gleam

@@ -15,8 +15,6 @@ pub fn one_run_test() {
 
   let diagram = diagram.bar_chart(runs, 1, 1)
 
-  io.println(diagram)
-
   // each run yields a rect in the SVG
   count_rects(diagram)
   |> should.equal(1)
@@ -29,8 +27,6 @@ pub fn multi_attempt_run_test() {
 
   let diagram = diagram.bar_chart(runs, 1, 1)
 
-  io.println(diagram)
-
   // each run yields a rect in the SVG
   count_rects(diagram)
   |> should.equal(2)
@@ -65,23 +61,21 @@ pub fn many_runs_test() {
 
   let diagram = diagram.bar_chart(runs, 1, 1)
 
-  io.println(diagram)
-
   // each run yields a rect in the SVG
   count_rects(diagram)
   |> should.equal(15)
 }
 
 pub fn unexpected_conclusion_test() {
+  io.println_error("Heads up: this test will print to stderr!")
+
   let runs = [
     [fake_run(0, 5, "unexpected", None)],
     [fake_run(0, 5, "wjin beof8y23bu", None)],
   ]
 
   let diagram = diagram.bar_chart(runs, 1, 1)
 
-  io.println(diagram)
-
   // each run yields a rect in the SVG
   count_rects(diagram)
   |> should.equal(2)
@@ -95,8 +89,6 @@ pub fn empty_runs_test() {
 
   let diagram = diagram.bar_chart(runs, 1, 1)
 
-  io.println(diagram)
-
   // each run yields a rect in the SVG
   count_rects(diagram)
   |> should.equal(0)