Add application config loading

internal/config/config.go

@@ -0,0 +1,168 @@
+package config
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/scriptorium/internal/defaults"
+	renderformat "gitea.maximumdirect.net/eric/scriptorium/internal/format"
+	"gopkg.in/yaml.v3"
+)
+
+const DefaultConfigPath = "/etc/scriptorium/config.yml"
+
+var (
+	ErrConfigNotFound    = errors.New("config file not found")
+	ErrInvalidConfigYAML = errors.New("invalid config YAML")
+	ErrInvalidConfig     = errors.New("invalid config")
+)
+
+// Config is the on-disk YAML shape for application-level settings.
+type Config struct {
+	PromptDir  string         `yaml:"prompt_dir"`
+	ProfileDir string         `yaml:"profile_dir"`
+	SchemaDir  string         `yaml:"schema_dir"`
+	Server     ServerConfig   `yaml:"server"`
+	Defaults   DefaultsConfig `yaml:"defaults"`
+}
+
+type ServerConfig struct {
+	Addr string `yaml:"addr"`
+}
+
+type DefaultsConfig struct {
+	RenderFormat string `yaml:"render_format"`
+}
+
+// AppSettings is the resolved application settings used by adapters.
+type AppSettings struct {
+	PromptDir           string
+	ProfileDir          string
+	SchemaDir           string
+	ServerAddr          string
+	DefaultRenderFormat renderformat.PreparedRunOutputFormat
+}
+
+// CLIOverrides can be applied after config load to enforce precedence.
+type CLIOverrides struct {
+	PromptDir    string
+	ProfileDir   string
+	SchemaDir    string
+	ServerAddr   string
+	RenderFormat string
+}
+
+// BuiltInDefaults returns compile-time application defaults.
+func BuiltInDefaults() AppSettings {
+	return AppSettings{
+		SchemaDir:           defaults.SchemaDirDefault,
+		ServerAddr:          defaults.HTTPAddrDefault,
+		DefaultRenderFormat: renderformat.DefaultPreparedRunOutputFormat,
+	}
+}
+
+// LoadConfig loads and resolves app settings from YAML.
+//
+// If explicit is false and the file does not exist, built-in defaults are returned.
+// If explicit is true, missing file is an error.
+func LoadConfig(path string, explicit bool) (AppSettings, error) {
+	resolved := BuiltInDefaults()
+	configPath := strings.TrimSpace(path)
+	if configPath == "" {
+		configPath = DefaultConfigPath
+	}
+	configPath = filepath.Clean(configPath)
+
+	raw, err := os.ReadFile(configPath)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			if explicit {
+				return AppSettings{}, fmt.Errorf("%w: %s", ErrConfigNotFound, configPath)
+			}
+			return resolved, nil
+		}
+		return AppSettings{}, fmt.Errorf("failed to read config file %q: %w", configPath, err)
+	}
+
+	cfg, err := decodeConfig(raw)
+	if err != nil {
+		return AppSettings{}, err
+	}
+
+	resolved, err = applyConfig(resolved, cfg)
+	if err != nil {
+		return AppSettings{}, err
+	}
+	return resolved, nil
+}
+
+// ApplyCLIOverrides applies CLI-provided overrides over resolved config settings.
+func ApplyCLIOverrides(base AppSettings, overrides CLIOverrides) (AppSettings, error) {
+	out := base
+
+	if v := strings.TrimSpace(overrides.PromptDir); v != "" {
+		out.PromptDir = filepath.Clean(v)
+	}
+	if v := strings.TrimSpace(overrides.ProfileDir); v != "" {
+		out.ProfileDir = filepath.Clean(v)
+	}
+	if v := strings.TrimSpace(overrides.SchemaDir); v != "" {
+		out.SchemaDir = filepath.Clean(v)
+	}
+	if v := strings.TrimSpace(overrides.ServerAddr); v != "" {
+		out.ServerAddr = v
+	}
+	if rawFormat := strings.TrimSpace(overrides.RenderFormat); rawFormat != "" {
+		parsed, err := renderformat.ParsePreparedRunOutputFormat(rawFormat)
+		if err != nil {
+			return AppSettings{}, fmt.Errorf("%w: defaults.render_format: %v", ErrInvalidConfig, err)
+		}
+		out.DefaultRenderFormat = parsed
+	}
+
+	return out, nil
+}
+
+func decodeConfig(raw []byte) (Config, error) {
+	var cfg Config
+	decoder := yaml.NewDecoder(bytes.NewReader(raw))
+	decoder.KnownFields(true)
+	if err := decoder.Decode(&cfg); err != nil {
+		if errors.Is(err, io.EOF) {
+			return Config{}, nil
+		}
+		return Config{}, fmt.Errorf("%w: %v", ErrInvalidConfigYAML, err)
+	}
+	return cfg, nil
+}
+
+func applyConfig(base AppSettings, cfg Config) (AppSettings, error) {
+	out := base
+
+	if v := strings.TrimSpace(cfg.PromptDir); v != "" {
+		out.PromptDir = filepath.Clean(v)
+	}
+	if v := strings.TrimSpace(cfg.ProfileDir); v != "" {
+		out.ProfileDir = filepath.Clean(v)
+	}
+	if v := strings.TrimSpace(cfg.SchemaDir); v != "" {
+		out.SchemaDir = filepath.Clean(v)
+	}
+	if v := strings.TrimSpace(cfg.Server.Addr); v != "" {
+		out.ServerAddr = v
+	}
+	if rawFormat := strings.TrimSpace(cfg.Defaults.RenderFormat); rawFormat != "" {
+		parsed, err := renderformat.ParsePreparedRunOutputFormat(rawFormat)
+		if err != nil {
+			return AppSettings{}, fmt.Errorf("%w: defaults.render_format: %v", ErrInvalidConfig, err)
+		}
+		out.DefaultRenderFormat = parsed
+	}
+
+	return out, nil
+}