package main

import (
	"bytes"
	"fmt"
	"go/format"
	"os"
	"path/filepath"
	"regexp"
	"sort"
)

func main() {
	controllerDir, err := findControllerDir()
	if err != nil {
		fatal(err)
	}

	ctors, err := findControllerCtors(controllerDir)
	if err != nil {
		fatal(err)
	}

	content, err := renderModule(ctors)
	if err != nil {
		fatal(err)
	}

	outPath := filepath.Join(controllerDir, "module.go")
	if err := os.WriteFile(outPath, content, 0o644); err != nil {
		fatal(err)
	}
}

func findControllerDir() (string, error) {
	wd, err := os.Getwd()
	if err != nil {
		return "", err
	}

	if exists(filepath.Join(wd, "module.go")) && exists(filepath.Join(wd, "routes.go")) {
		return wd, nil
	}

	candidate := filepath.Join(wd, "internal", "controller")
	if exists(filepath.Join(candidate, "module.go")) {
		return candidate, nil
	}

	return "", fmt.Errorf("could not locate internal/controller")
}

func findControllerCtors(dir string) ([]string, error) {
	entries, err := os.ReadDir(dir)
	if err != nil {
		return nil, err
	}

	ctorRe := regexp.MustCompile(`(?m)^func\s+(New[A-Za-z0-9_]*Controller)\s*\(`)

	seen := make(map[string]struct{})
	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}
		name := entry.Name()
		if !hasSuffix(name, "_controller.go") {
			continue
		}
		if name == "module.go" {
			continue
		}

		path := filepath.Join(dir, name)
		data, err := os.ReadFile(path)
		if err != nil {
			return nil, err
		}

		matches := ctorRe.FindAllSubmatch(data, -1)
		for _, m := range matches {
			if len(m) < 2 {
				continue
			}
			seen[string(m[1])] = struct{}{}
		}
	}

	var ctors []string
	for k := range seen {
		ctors = append(ctors, k)
	}
	sort.Strings(ctors)

	return ctors, nil
}

func renderModule(ctors []string) ([]byte, error) {
	var buf bytes.Buffer

	buf.WriteString("// Code generated by cmd/gen/controllers; DO NOT EDIT.\n")
	buf.WriteString("package controller\n\n")
	buf.WriteString("import \"go.uber.org/fx\"\n\n")
	buf.WriteString("var Module = fx.Options(\n")

	if len(ctors) > 0 {
		buf.WriteString("\tfx.Provide(\n")
		for _, ctor := range ctors {
			buf.WriteString("\t\t")
			buf.WriteString(ctor)
			buf.WriteString(",\n")
		}
		buf.WriteString("\t),\n")
	}

	buf.WriteString("\tfx.Invoke(\n\t\tRegisterRoutes,\n\t),\n")
	buf.WriteString(")\n")

	formatted, err := format.Source(buf.Bytes())
	if err != nil {
		return nil, err
	}

	return formatted, nil
}

func exists(path string) bool {
	info, err := os.Stat(path)
	if err != nil {
		return false
	}
	return !info.IsDir()
}

func hasSuffix(s, suffix string) bool {
	return len(s) >= len(suffix) && s[len(s)-len(suffix):] == suffix
}

func fatal(err error) {
	fmt.Fprintln(os.Stderr, err)
	os.Exit(1)
}