package main

import (
	"bytes"
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"go/format"
	"os"
	"path/filepath"
	"sort"
	"strings"
)

const (
	usage = "Usage: %s -input=/proto-dir-1 -input=/proto-dir-2 -output=/mappings.go\n"

	fileHeader = `// generated by protoc-gen-consul-rate-limit; DO NOT EDIT.
package middleware

import "github.com/hashicorp/consul/agent/consul/rate"
`

	entTags = `//go:build consulent
// +build consulent
`
)

func main() {
	var (
		inputPaths sliceFlags
		outputPath string
	)
	flag.Var(&inputPaths, "input", "")
	flag.StringVar(&outputPath, "output", "", "")
	flag.Parse()

	if len(inputPaths) == 0 || outputPath == "" {
		fmt.Fprintf(os.Stderr, usage, os.Args[0])
		os.Exit(1)
	}

	if err := run(inputPaths, outputPath); err != nil {
		fmt.Fprintf(os.Stderr, "ERROR: %v\n", err)
		os.Exit(1)
	}
}

func run(inputPaths []string, outputPath string) error {
	if !strings.HasSuffix(outputPath, ".go") {
		return errors.New("-output path must end in .go")
	}

	oss, ent, err := collectSpecs(inputPaths)
	if err != nil {
		return err
	}

	ossSource, err := generateOSS(oss)
	if err != nil {
		return err
	}
	if err := os.WriteFile(outputPath, ossSource, 0666); err != nil {
		return fmt.Errorf("failed to write output file: %s - %w", outputPath, err)
	}

	// ent should only be non-zero in the enterprise repository.
	if len(ent) > 0 {
		entSource, err := generateENT(ent)
		if err != nil {
			return err
		}

		if err := os.WriteFile(enterpriseFileName(outputPath), entSource, 0666); err != nil {
			return fmt.Errorf("failed to write output file: %s - %w", outputPath, err)
		}
	}

	return nil
}

// enterpriseFileName adds the _ent filename suffix before the extension.
//
// Example:
//	enterpriseFileName("bar/baz/foo.gen.go") => "bar/baz/foo_ent.gen.go"
func enterpriseFileName(filename string) string {
	fileName := filepath.Base(filename)
	extStart := strings.Index(fileName, ".")
	return filepath.Join(
		filepath.Dir(filename),
		fileName[0:extStart]+"_ent"+fileName[extStart:],
	)
}

type spec struct {
	MethodName    string
	OperationType string
	Enterprise    bool
}

func (s spec) GoOperationType() string {
	switch s.OperationType {
	case "OPERATION_TYPE_WRITE":
		return "rate.OperationTypeWrite"
	case "OPERATION_TYPE_READ":
		return "rate.OperationTypeRead"
	case "OPERATION_TYPE_EXEMPT":
		return "rate.OperationTypeExempt"
	}
	panic(fmt.Sprintf("unknown rate limit operation type: %s", s.OperationType))
}

func collectSpecs(inputPaths []string) ([]spec, []spec, error) {
	var specs []spec
	for _, protoPath := range inputPaths {
		specFiles, err := filepath.Glob(filepath.Join(protoPath, "*", ".ratelimit.tmp"))
		if err != nil {
			return nil, nil, fmt.Errorf("failed to glob directory: %s - %s", protoPath, err)
		}

		for _, file := range specFiles {
			b, err := os.ReadFile(file)
			if err != nil {
				return nil, nil, fmt.Errorf("failed to read ratelimit file: %w", err)
			}

			var fileSpecs []spec
			if err := json.Unmarshal(b, &fileSpecs); err != nil {
				return nil, nil, fmt.Errorf("failed to unmarshal ratelimit file %s - %w", file, err)
			}
			specs = append(specs, fileSpecs...)
		}
	}

	sort.Slice(specs, func(a, b int) bool {
		return specs[a].MethodName < specs[b].MethodName
	})

	var oss, ent []spec
	for _, spec := range specs {
		if spec.Enterprise {
			ent = append(ent, spec)
		} else {
			oss = append(oss, spec)
		}
	}

	return oss, ent, nil
}

func generateOSS(specs []spec) ([]byte, error) {
	var output bytes.Buffer
	output.WriteString(fileHeader)

	fmt.Fprintln(&output, `var rpcRateLimitSpecs = map[string]rate.OperationType{`)
	for _, spec := range specs {
		fmt.Fprintf(&output, `"%s": %s,`, spec.MethodName, spec.GoOperationType())
		output.WriteString("\n")
	}
	output.WriteString("}")

	formatted, err := format.Source(output.Bytes())
	if err != nil {
		return nil, fmt.Errorf("failed to format source: %w", err)
	}
	return formatted, nil
}

func generateENT(specs []spec) ([]byte, error) {
	var output bytes.Buffer
	output.WriteString(entTags)
	output.WriteString(fileHeader)

	output.WriteString("func init() {\n")
	for _, spec := range specs {
		fmt.Fprintf(&output, `rpcRateLimitSpecs["%s"] = %s`, spec.MethodName, spec.GoOperationType())
		output.WriteString("\n")
	}
	output.WriteString("}")

	formatted, err := format.Source(output.Bytes())
	if err != nil {
		return nil, fmt.Errorf("failed to format source: %w", err)
	}
	return formatted, nil
}

type sliceFlags []string

func (i *sliceFlags) Set(value string) error {
	*i = append(*i, value)
	return nil
}

func (i *sliceFlags) String() string { return "" }