Task 9: extract SortTasks helpers

1 files changed, 99 insertions, 0 deletions

diff --git a/internal/task/sort.go b/internal/task/sort.go
new file mode 100644
index 0000000..7cd953b
--- /dev/null
+++ b/internal/task/sort.go
@@ -0,0 +1,99 @@
+package task
+
+import (
+	"sort"
+	"strings"
+	"time"
+)
+
+// SortTasks orders tasks by start status, priority, due date, tag names and id.
+// Started tasks are always placed before non-started ones. Tasks without a due
+// date are placed after tasks with a due date. Overdue tasks are placed at the
+// very top regardless of other properties.
+//
+// The sort order is:
+// 1. Overdue tasks (oldest due date first)
+// 2. Started tasks (not completed)
+// 3. High priority tasks
+// 4. Tasks with earlier due dates
+// 5. Tasks sorted alphabetically by tags
+// 6. Tasks sorted by ID (oldest first)
+func SortTasks(tasks []Task) {
+	now := time.Now()
+
+	sort.Slice(tasks, func(i, j int) bool {
+		ti, tj := tasks[i], tasks[j]
+
+		if oi, oj := isOverdue(ti, now), isOverdue(tj, now); oi != oj {
+			return oi
+		}
+
+		startedI := ti.Start != "" && ti.Status != "completed"
+		startedJ := tj.Start != "" && tj.Status != "completed"
+		if startedI != startedJ {
+			return startedI
+		}
+
+		pi, pj := priorityRank(ti.Priority), priorityRank(tj.Priority)
+		if pi != pj {
+			return pi > pj
+		}
+
+		di, iok := parseDueDate(ti.Due)
+		dj, jok := parseDueDate(tj.Due)
+		if iok && !jok {
+			return true
+		}
+		if !iok && jok {
+			return false
+		}
+		if iok && jok && !di.Equal(dj) {
+			return di.Before(dj)
+		}
+
+		tgI, tgJ := joinTags(ti.Tags), joinTags(tj.Tags)
+		if tgI != tgJ {
+			return tgI < tgJ
+		}
+
+		return ti.ID < tj.ID
+	})
+}
+
+func joinTags(tags []string) string {
+	if len(tags) == 0 {
+		return ""
+	}
+	cpy := append([]string(nil), tags...)
+	sort.Strings(cpy)
+	return strings.Join(cpy, " ")
+}
+
+func priorityRank(priority string) int {
+	switch priority {
+	case "H":
+		return 3
+	case "M":
+		return 2
+	case "L":
+		return 1
+	default:
+		return 0
+	}
+}
+
+func parseDueDate(value string) (time.Time, bool) {
+	if value == "" {
+		return time.Time{}, false
+	}
+	parsed, err := time.Parse(DateFormat, value)
+	if err != nil {
+		return time.Time{}, false
+	}
+	return parsed, true
+}
+
+func isOverdue(task Task, now time.Time) bool {
+	due, ok := parseDueDate(task.Due)
+	return ok && now.After(due)
+}