Add basic resolver for configuration file cascade

resolver/resolver.go

@@ -0,0 +1,167 @@
+package resolver
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+const separator = string(filepath.Separator)
+
+// SourceFile represents a file that is used to compile a configuration file.
+// The source file knows what group it is part of.
+type SourceFile struct {
+	Group    string
+	Path     string
+	Override bool
+}
+
+// ConfigFile represents a configuration file to be installed.
+type ConfigFile struct {
+	Path    string
+	Removed bool
+	Sources []*SourceFile
+}
+
+// Configurations holds a mapping of configuration file destinations mapped to
+// the ConfigFile struct representing that file.
+type Configurations map[string]*ConfigFile
+
+// Files gets the list of all configuration files.
+func (c Configurations) Files() []string {
+	files := make([]string, len(c))
+
+	for path := range c {
+		files = append(files, path)
+	}
+
+	return files
+}
+
+// Filter filters down a Configurations list to only configs with the specified prefix
+func (c Configurations) Filter(prefix string) Configurations {
+	for path := range c {
+		if !strings.HasPrefix(path, prefix) {
+			delete(c, path)
+		}
+	}
+
+	return c
+}
+
+// resolveSources inserts or updates a Configurations list from a list of
+// configuration sources relative to the source root. Sources not belonging to
+// the specified group will be ignored.
+func resolveSources(configs Configurations, sources []string, group string) {
+	for _, source := range sources {
+		if !strings.HasPrefix(source, group) {
+			continue
+		}
+
+		destPath := strings.TrimPrefix(source, group+separator)
+
+		sourceFile := &SourceFile{
+			Group: group,
+			Path:  source,
+		}
+
+		// The config file was added in a previous group mapping
+		if file, ok := configs[destPath]; ok {
+			file.Sources = append(file.Sources, sourceFile)
+			continue
+		}
+
+		configs[destPath] = &ConfigFile{
+			Path:    destPath,
+			Sources: []*SourceFile{sourceFile},
+		}
+	}
+}
+
+// resolveOverrides scans a Configurations list for config files that have
+// associated override files. The override files will be removed as individual
+// configurations and their sources will be inserted into config file they are
+// associated to.
+func resolveOverrides(configs Configurations, overrideSuffix string) {
+	for path, config := range configs {
+		if strings.HasSuffix(path, "."+overrideSuffix) {
+			continue
+		}
+
+		overridePath := path + overrideSuffix
+		overrideConfig, exists := configs[overridePath]
+
+		if !exists {
+			continue
+		}
+
+		for _, source := range overrideConfig.Sources {
+			source.Override = true
+		}
+
+		config.Sources = append(config.Sources, overrideConfig.Sources...)
+		delete(configs, overridePath)
+	}
+}
+
+// resolveRemoved inserts entries into a Configurations list for files that
+// previously were installed but are no longer present to be installed.
+func resolveRemoved(configs Configurations, oldConfigs []string) {
+	for _, oldConfig := range oldConfigs {
+		if _, ok := configs[oldConfig]; ok {
+			continue
+		}
+
+		configs[oldConfig] = &ConfigFile{
+			Path:    oldConfig,
+			Removed: true,
+		}
+	}
+}
+
+// Config specifies the configuration object to be pased into the
+// ResolveConfigurations function.
+type Config struct {
+	SourcePath     string
+	OverrideSuffix string
+
+	// Groups to resolve
+	Groups []string
+
+	// CurrentConfigs is a list of files that are currently installed. This
+	// list will be used to determine which configurations have been removed.
+	CurrentConfigs []string
+
+	// FilterPrefix specifies the prefix that should be used to filter down the
+	// list of installable configurations.
+	FilterPrefix string
+}
+
+// ResolveConfigurations walks the source tree and builds a Configuration
+// object, resolving group sources along the way.
+func ResolveConfigurations(config Config) Configurations {
+	sources := []string{}
+	configs := Configurations{}
+
+	walker := func(path string, info os.FileInfo, err error) error {
+		if err != nil || info.IsDir() {
+			return nil
+		}
+
+		srcPath := strings.TrimPrefix(path, config.SourcePath+separator)
+		sources = append(sources, srcPath)
+
+		return nil
+	}
+
+	filepath.Walk(config.SourcePath, walker)
+
+	for _, group := range config.Groups {
+		resolveSources(configs, sources, group)
+	}
+
+	//resolveRemoved(configs, config.CurrentConfigs)
+	resolveOverrides(configs, config.OverrideSuffix)
+
+	return configs
+}