refactor: make internals easier to test and add unit tests (#2)

This PR refactors most of the internals to make them easier to test (and also because the names didn't make sense). It adds unit tests for all internal components.

Reviewed-on: #2
Co-authored-by: Emmanuel BENOÎT <tseeker@nocternity.net>
Co-committed-by: Emmanuel BENOÎT <tseeker@nocternity.net>

pkg/plugin/plugin.go

@@ -1,122 +1,20 @@
-// Package plugin implements a helper that can be used to implement a Nagios,
-// Centreon, Icinga... service monitoring plugin.
-package plugin // import nocternity.net/gomonop/pkg/perfdata
+package plugin // import nocternity.net/gomonop/pkg/plugin
 
-import (
-	"container/list"
-	"fmt"
-	"os"
-	"strings"
+import "nocternity.net/gomonop/pkg/results"
 
-	"nocternity.net/gomonop/pkg/perfdata"
-)
+// Plugin represents the interface to a monitoring plugin.
+type Plugin interface {
+	// Results accesses the results of the monitoring plugin.
+	Results() *results.Results
 
-// Status represents the return status of the monitoring plugin. The
-// corresponding integer value will be used as the program's exit code,
-// to be interpreted by the monitoring system.
-type Status int
+	// CheckArguments ensures that the arguments that were passed to the plugin
+	// actually make sense. Errors should be stored in the plugin's results.
+	CheckArguments() bool
 
-// Plugin exit statuses.
-const (
-	OK Status = iota
-	WARNING
-	CRITICAL
-	UNKNOWN
-)
-
-// String representations of the plugin statuses.
-func (s Status) String() string {
-	return [...]string{"OK", "WARNING", "ERROR", "UNKNOWN"}[s]
+	// RunCheck actually runs whatever checks are implemented by the plugin and
+	// updates the results accordingly.
+	RunCheck()
 }
 
-// Plugin represents the monitoring plugin's state, including its name,
-// return status and message, additional lines of text, and performance
-// data to be encoded in the output.
-type Plugin struct {
-	name      string
-	status    Status
-	message   string
-	extraText *list.List
-	perfData  map[string]*perfdata.PerfData
-}
-
-// New creates the plugin with `name` as its name and an unknown status.
-func New(name string) *Plugin {
-	p := new(Plugin)
-	p.name = name
-	p.status = UNKNOWN
-	p.message = "no status set"
-	p.perfData = make(map[string]*perfdata.PerfData)
-	return p
-}
-
-// SetState sets the plugin's output code to `status` and its message to
-// the specified `message`.
-func (p *Plugin) SetState(status Status, message string) {
-	p.status = status
-	p.message = message
-}
-
-// AddLine adds the specified string to the extra output text buffer.
-func (p *Plugin) AddLine(line string) {
-	if p.extraText == nil {
-		p.extraText = list.New()
-	}
-	p.extraText.PushBack(line)
-}
-
-// AddLinef formats the input and adds it to the text buffer.
-func (p *Plugin) AddLinef(format string, data ...interface{}) {
-	p.AddLine(fmt.Sprintf(format, data...))
-}
-
-// AddLines add the specified `lines` to the output text.
-func (p *Plugin) AddLines(lines []string) {
-	for _, line := range lines {
-		p.AddLine(line)
-	}
-}
-
-// AddPerfData adds performance data described by the "pd" argument to the
-// output's performance data. If two performance data records are added for
-// the same label, the program panics.
-func (p *Plugin) AddPerfData(pd *perfdata.PerfData) {
-	_, exists := p.perfData[pd.Label]
-	if exists {
-		panic("duplicate performance data " + pd.Label)
-	}
-	p.perfData[pd.Label] = pd
-}
-
-// Done generates the plugin's text output from its name, status, text data
-// and performance data, before exiting with the code corresponding to the
-// status.
-func (p *Plugin) Done() {
-	var strBuilder strings.Builder
-	strBuilder.WriteString(p.name)
-	strBuilder.WriteString(" ")
-	strBuilder.WriteString(p.status.String())
-	strBuilder.WriteString(": ")
-	strBuilder.WriteString(p.message)
-	if len(p.perfData) > 0 {
-		strBuilder.WriteString(" | ")
-		needSep := false
-		for _, data := range p.perfData {
-			if needSep {
-				strBuilder.WriteString(", ")
-			} else {
-				needSep = true
-			}
-			strBuilder.WriteString(data.String())
-		}
-	}
-	if p.extraText != nil {
-		for em := p.extraText.Front(); em != nil; em = em.Next() {
-			strBuilder.WriteString("\n")
-			//nolint:forcetypeassert // we want to panic if this isn't a string
-			strBuilder.WriteString(em.Value.(string))
-		}
-	}
-	fmt.Println(strBuilder.String())
-	os.Exit(int(p.status))
-}
+// Builder is a function that can be called in order to instantiate a plugin.
+type Builder func() Plugin