package main

import (
	"encoding/json"
	"flag"
	"fmt"
	"io"
	"net/http"
	"os"
	"strings"
	"time"

	"github.com/google/go-cmp/cmp"
	"github.com/google/go-cmp/cmp/cmpopts"
)

// /api/version is intentionally excluded — it returns each binary's own build
// identity (tag/commit/build_date), which differs by design between independently
// built backends. Pass -route /api/version to inspect it manually.
var allRoutes = []string{"/api/adults", "/api/juniors", "/api/payments"}

// defaultAllowlist holds dotted key paths to strip before diffing.
// render_time.total is forward-compatible insurance: today it lives in the Jinja
// template context only (app.py inject_render_time) and is logged via
// middleware/timer.go on the Go side, so it isn't in any JSON response. If either
// side ever surfaces it under a render_time envelope, the scrubber handles it.
var defaultAllowlist = []string{"render_time.total"}

func main() {
	pyURL := flag.String("py", "http://localhost:5001", "Python backend base URL")
	goURL := flag.String("go", "http://localhost:8080", "Go backend base URL")
	route := flag.String("route", "", "single route to diff, e.g. /api/adults (default: all)")
	timeout := flag.Duration("timeout", 30*time.Second, "per-request HTTP timeout")
	flag.Parse()

	client := &http.Client{Timeout: *timeout}

	targets := allRoutes
	if *route != "" {
		targets = []string{*route}
	}

	matched, diffs, errs := 0, 0, 0

	for _, r := range targets {
		pyMap, err1 := fetch(client, *pyURL+r)
		goMap, err2 := fetch(client, *goURL+r)

		if err1 != nil || err2 != nil {
			fmt.Printf("=== %s ===\n", r)
			if err1 != nil {
				fmt.Printf("ERROR (py): %v\n", err1)
			}
			if err2 != nil {
				fmt.Printf("ERROR (go): %v\n", err2)
			}
			fmt.Println()
			errs++
			continue
		}

		scrub(pyMap, defaultAllowlist)
		scrub(goMap, defaultAllowlist)

		diff := cmp.Diff(pyMap, goMap, cmpopts.EquateEmpty())
		if diff == "" {
			fmt.Printf("=== %s ===\nOK\n\n", r)
			matched++
		} else {
			fmt.Printf("=== %s ===\n%s\n", r, diff)
			diffs++
		}
	}

	total := len(targets)
	fmt.Printf("parity: %d/%d routes match", matched, total)
	if diffs > 0 {
		fmt.Printf(", %d diff", diffs)
		if diffs > 1 {
			fmt.Print("s")
		}
	}
	if errs > 0 {
		fmt.Printf(", %d error", errs)
		if errs > 1 {
			fmt.Print("s")
		}
	}
	fmt.Println()

	if errs > 0 {
		os.Exit(2)
	}
	if diffs > 0 {
		os.Exit(1)
	}
}

func fetch(client *http.Client, url string) (map[string]any, error) {
	resp, err := client.Get(url) //nolint:noctx
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("read body: %w", err)
	}
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("HTTP %d: %s", resp.StatusCode, strings.TrimSpace(string(body)))
	}
	var m map[string]any
	if err := json.Unmarshal(body, &m); err != nil {
		return nil, fmt.Errorf("decode JSON: %w", err)
	}
	return m, nil
}

// scrub removes keys from m whose dotted paths appear in paths.
// A bare segment (no dot) deletes a top-level key.
// A two-segment path "parent.child" deletes child from m["parent"] if it is a map.
func scrub(m map[string]any, paths []string) {
	for _, path := range paths {
		parts := strings.SplitN(path, ".", 2)
		if len(parts) == 1 {
			delete(m, parts[0])
		} else {
			if child, ok := m[parts[0]].(map[string]any); ok {
				delete(child, parts[1])
			}
		}
	}
}