// Copyright (C) 2026 Dcntrlized
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published
// by the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

// Package instance holds the instance's public identity: a small, self-
// contained file at the data root that answers "who am I" for the hub app's
// public profile (hub-app theme M1) and, later, federation attestation.
package instance

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
)

// Identity is the instance's user-visible self-description. Name falls back to
// DCNTRLIZED_INSTANCE_NAME and then the hostname when instance.json is absent;
// Title and Description are optional and only ever come from the file.
type Identity struct {
	Name        string `json:"name"`
	Title       string `json:"title,omitempty"`
	Description string `json:"description,omitempty"`
}

// Path returns the identity file location for the given data root.
func Path(dataRoot string) string {
	return filepath.Join(dataRoot, "instance.json")
}

// Load resolves the instance identity: instance.json when present, else
// DCNTRLIZED_INSTANCE_NAME, else os.Hostname(). Read-on-demand by design —
// no daemon state, so an edited file shows up on the next request.
func Load(dataRoot string) Identity {
	id := defaultIdentity()

	if data, err := os.ReadFile(Path(dataRoot)); err == nil {
		var fromFile Identity
		if json.Unmarshal(data, &fromFile) == nil && fromFile.Name != "" {
			if fromFile.Title != "" {
				id.Title = fromFile.Title
			}
			if fromFile.Description != "" {
				id.Description = fromFile.Description
			}
			id.Name = fromFile.Name
		}
	}
	return id
}

// Save atomically writes the identity file (tmp + rename), chmod 600 like the
// rest of Maestro's file stores. The owner-gated edit endpoint that uses this
// lands with the federation theme; the helper exists so both callers share one
// write path.
func Save(dataRoot string, id Identity) error {
	if id.Name == "" {
		return fmt.Errorf("instance name must not be empty")
	}
	data, err := json.MarshalIndent(id, "", "  ")
	if err != nil {
		return fmt.Errorf("marshal instance identity: %w", err)
	}
	path := Path(dataRoot)
	tmp := path + ".tmp"
	if err := os.WriteFile(tmp, append(data, '\n'), 0o600); err != nil {
		return fmt.Errorf("write instance identity: %w", err)
	}
	if err := os.Rename(tmp, path); err != nil {
		return fmt.Errorf("replace instance identity: %w", err)
	}
	return nil
}

func defaultIdentity() Identity {
	name := os.Getenv("DCNTRLIZED_INSTANCE_NAME")
	if name == "" {
		if host, err := os.Hostname(); err == nil {
			name = host
		}
	}
	return Identity{Name: name}
}