package main

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

// A check evaluates the saved settings like an apply would (option types and
// the router's assertions) without building anything: router-check.service
// runs `nix eval` on the configuration and leaves its verdict in
// <state>/check/result.json.

type CheckResult struct {
	OK    bool      `json:"ok"`
	Error string    `json:"error,omitempty"`
	Etag  string    `json:"etag"` // of the settings that were evaluated
	Time  time.Time `json:"time"`
}

func (s System) checkResultPath() string { return filepath.Join(s.StateDir, "check", "result.json") }

func (s System) readCheck() (CheckResult, bool) {
	var r CheckResult
	data, err := os.ReadFile(s.checkResultPath())
	if err != nil || json.Unmarshal(data, &r) != nil {
		return r, false
	}
	return r, true
}

func (s System) checkRunning() bool {
	return unitProperty("router-check.service", "ActiveState") == "activating"
}

// checkSettings starts a check unless one runs or the last result is for the
// current settings, and waits a while for it.
func (a *app) checkSettings() (any, error) {
	data, err := os.ReadFile(a.sys.settingsPath())
	if err != nil {
		return nil, err
	}
	current := etag(data)
	if r, ok := a.sys.readCheck(); ok && r.Etag == current && !a.sys.checkRunning() {
		return a.checkReport(r, true), nil
	}
	if !a.sys.checkRunning() {
		if _, err := command("systemctl", "start", "--no-block", "router-check.service"); err != nil {
			return nil, err
		}
	}
	for range 50 {
		time.Sleep(time.Second)
		if a.sys.checkRunning() {
			continue
		}
		if r, ok := a.sys.readCheck(); ok {
			return a.checkReport(r, r.Etag == current), nil
		}
		break
	}
	return CheckResponse{Status: "running", Next: "Still evaluating; call check_settings again in a few seconds."}, nil
}

func (a *app) checkReport(r CheckResult, current bool) CheckResponse {
	out := CheckResponse{Status: "done", OK: &r.OK, ForTheSavedSettings: &current, CheckedAt: &r.Time}
	if r.OK {
		out.Message = "The settings evaluate: the router's assertions pass."
	} else {
		out.Error = r.Error
	}
	if !current {
		out.Note = "The settings changed during or after this check; call check_settings again."
	}
	return out
}