package content

import (
	"errors"
	"fmt"
	"io/fs"
	"strings"

	"gopkg.in/yaml.v3"
)

// SettingsFile is where a site declares itself, at the site root.
const SettingsFile = "site.yaml"

// Settings are the site's own declarations (ADR-0039).
//
// Declared keys only: this is not a bag for arbitrary engine internals, which is how a settings file turns
// into unbounded configuration. Section-level and bundle-level settings are not here — a bundle's own
// frontmatter covers it, and the rest of the cascade is still parked.
type Settings struct {
	// Base is the site's canonical origin, without a trailing slash: "https://khosra.example". Empty when
	// the site declares none, in which case the engine emits paths and nothing absolute.
	Base string `yaml:"base"`
	// Title names the site. A theme may put it in a document title or a feed; the engine only carries it.
	Title string `yaml:"title"`
}

// LoadSettings reads site.yaml from the site root.
//
// A missing file is not an error, because a bare site root must still serve (ADR-0026). A malformed one is,
// and the caller treats it as fatal: unlike a single bad bundle, which is skipped loudly (ADR-0029), a
// broken declaration misconfigures every page on the site.
func LoadSettings(fsys fs.FS) (Settings, error) {
	data, err := fs.ReadFile(fsys, SettingsFile)
	if errors.Is(err, fs.ErrNotExist) {
		return Settings{}, nil
	}
	if err != nil {
		return Settings{}, fmt.Errorf("read %s: %w", SettingsFile, err)
	}
	var s Settings
	if err := yaml.Unmarshal(data, &s); err != nil {
		return Settings{}, fmt.Errorf("parse %s: %w", SettingsFile, err)
	}
	s.Base = strings.TrimSuffix(strings.TrimSpace(s.Base), "/")
	s.Title = strings.TrimSpace(s.Title)
	return s, nil
}

// Absolute turns a path the engine emitted into a full URL.
//
// With no declared base it returns the path unchanged, so a site that has not said where it lives still
// links correctly to itself — every internal path is root-relative already.
func Absolute(base, path string) string {
	if base == "" {
		return path
	}
	return base + path
}