feat(build): start of server-side job queue

src/build/build.v

@@ -18,11 +18,11 @@ const (
 
 pub struct BuildConfig {
 pub:
-	id int
-	kind string
-	url string
-	branch string
-	repo string
+	target_id  int
+	kind       string
+	url        string
+	branch     string
+	repo       string
 	base_image string
 }
 

src/build/queue.v

@@ -0,0 +1,70 @@
+module build
+
+import models { Target }
+import cron.expression { CronExpression, parse_expression }
+import time
+import datatypes { MinHeap }
+
+struct BuildJob {
+pub:
+	// Earliest point this
+	timestamp time.Time
+	config    BuildConfig
+}
+
+// Overloaded operator for comparing ScheduledBuild objects
+fn (r1 BuildJob) < (r2 BuildJob) bool {
+	return r1.timestamp < r2.timestamp
+}
+
+pub struct BuildJobQueue {
+	// Schedule to use for targets without explicitely defined cron expression
+	default_schedule CronExpression
+	// Base image to use for targets without defined base image
+	default_base_image string
+mut:
+	// For each architecture, a priority queue is tracked
+	queues map[string]MinHeap<BuildJob>
+	// Each queued build job is also stored in a map, with the keys being the
+	// target IDs. This is used when removing or editing targets.
+	// jobs map[int]BuildJob
+}
+
+pub fn new_job_queue(default_schedule CronExpression, default_base_image string) BuildJobQueue {
+	return BuildJobQueue{
+		default_schedule: default_schedule
+		default_base_image: default_base_image
+	}
+}
+
+// insert a new job into the queue for a given target on an architecture.
+pub fn (mut q BuildJobQueue) insert(target Target, arch string) ! {
+	if arch !in q.queues {
+		q.queues[arch] = MinHeap<BuildJob>{}
+	}
+
+	ce := if target.schedule != '' {
+		parse_expression(target.schedule) or {
+			return error("Error while parsing cron expression '$target.schedule' (id $target.id): $err.msg()")
+		}
+	} else {
+		q.default_schedule
+	}
+
+	timestamp := ce.next_from_now()!
+
+	job := BuildJob{
+		timestamp: timestamp
+		config: BuildConfig{
+			target_id: target.id
+			kind: target.kind
+			url: target.url
+			branch: target.branch
+			repo: target.repo
+			// TODO make this configurable
+			base_image: q.default_base_image
+		}
+	}
+
+	q.queues[arch].insert(job)
+}