Internalize majority of cmd package (#2533)

* internalize majority of cmd package and migrate integration tests

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

* add internal api encoder

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

* create internal representation of all formats

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

* export capability to get default encoders

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

* restore test fixtures

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

---------

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

cmd/syft/internal/options/source.go

@@ -0,0 +1,59 @@
+package options
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+
+	"github.com/scylladb/go-set/strset"
+)
+
+type sourceConfig struct {
+	Name     string      `json:"name" yaml:"name" mapstructure:"name"`
+	Version  string      `json:"version" yaml:"version" mapstructure:"version"`
+	BasePath string      `yaml:"base-path" json:"base-path" mapstructure:"base-path"` // specify base path for all file paths
+	File     fileSource  `json:"file" yaml:"file" mapstructure:"file"`
+	Image    imageSource `json:"image" yaml:"image" mapstructure:"image"`
+}
+
+type fileSource struct {
+	Digests []string `json:"digests" yaml:"digests" mapstructure:"digests"`
+}
+
+type imageSource struct {
+	DefaultPullSource string `json:"default-pull-source" yaml:"default-pull-source" mapstructure:"default-pull-source"`
+}
+
+func defaultSourceConfig() sourceConfig {
+	return sourceConfig{
+		File: fileSource{
+			Digests: []string{"sha256"},
+		},
+		Image: imageSource{
+			DefaultPullSource: "",
+		},
+	}
+}
+
+func (c *fileSource) PostLoad() error {
+	digests := strset.New(c.Digests...).List()
+	sort.Strings(digests)
+	c.Digests = digests
+	return nil
+}
+
+func (c imageSource) PostLoad() error {
+	return checkDefaultSourceValues(c.DefaultPullSource)
+}
+
+var validDefaultSourceValues = []string{"registry", "docker", "podman", ""}
+
+func checkDefaultSourceValues(source string) error {
+	validValues := strset.New(validDefaultSourceValues...)
+	if !validValues.Has(source) {
+		validValuesString := strings.Join(validDefaultSourceValues, ", ")
+		return fmt.Errorf("%s is not a valid default source; please use one of the following: %s''", source, validValuesString)
+	}
+
+	return nil
+}