add(taskwarrior): get exported taskwarrior tasks

This implementation uses a filter struct to create taskwarrior filters
(like you would do in the command line) to export the filtered tasks
into json which are parsed as go structs.

internal/taskwarrior/task.go

@@ -1 +1,46 @@
 package taskwarrior
+
+import (
+	"bytes"
+	"encoding/json"
+	"os/exec"
+)
+
+/// A task with an Id of 0 is either `completed` or `deleted` which is also
+/// mentioned in the Status field
+
+type Task struct {
+	Id          uint
+	Project     string
+	Tags        []string
+	Description string
+	Annotations []Annotation
+	Status      string
+	Due         string
+	Entry       string
+	Modified    string
+	End         string
+	Uuid        string
+	Urgency     float32
+}
+
+type Annotation struct {
+	Description string
+	Entry       string
+}
+
+func GetTasks(filter Filter) ([]Task, error) {
+	filter.filter = append(filter.filter, "export")
+	cmd := exec.Command("task", filter.filter...)
+	out, err := cmd.Output()
+	if err != nil {
+		return nil, err
+	}
+	var tasks []Task
+	decoder := json.NewDecoder(bytes.NewBuffer(out))
+	decoder.DisallowUnknownFields()
+	if err = decoder.Decode(&tasks); err != nil {
+		return nil, err
+	}
+	return tasks, nil
+}