gen.go

package main

import (
	"fmt"
	"path/filepath"
	"strconv"

	"github.com/dave/jennifer/jen"
	"github.com/samber/lo"
	"golang.org/x/text/cases"
	"golang.org/x/text/language"
)

const (
	minParams      = 0
	maxParams      = 15
	outdir         = ""
	failureMessage = "failureMessage"
)

const (
	pkgFmt = "fmt"
)

func main() {
	for paramCount := minParams; paramCount <= maxParams; paramCount++ {
		f := jen.NewFile("try")
		name := func(prefix string, n int) string {
			return prefix + strconv.Itoa(n)
		}
		structName := name("from", paramCount)
		T := func(n int) string {
			return name("T", n)
		}

		// struct
		f.Type().
			Id(structName).
			TypesFunc(func(g *jen.Group) {
				for n := 1; n <= paramCount; n++ {
					g.Add(jen.Id(T(n)).Any())
				}
			}).
			StructFunc(func(g *jen.Group) {
				g.Add(jen.Id("err").Error())
				g.Add(jen.Id(failureMessage).String())
				for n := 1; n <= paramCount; n++ {
					g.Add(jen.Id(name("result", n)).Id(T(n)))
				}
			})

		// constructor "from"
		declareConstructor := func(ctorName string) {
			f.Func().
				Id(ctorName).
				TypesFunc(func(g *jen.Group) {
					for n := 1; n <= paramCount; n++ {
						g.Add(jen.Id(T(n)).Any())
					}
				}).
				ParamsFunc(func(g *jen.Group) {
					for n := 1; n <= paramCount; n++ {
						g.Add(jen.Id(name("result", n)).Id(T(n)))
					}
					g.Add(jen.Id("err").Error())
				}).
				Op("*").Id(structName).
				TypesFunc(func(g *jen.Group) {
					for n := 1; n <= paramCount; n++ {
						g.Add(jen.Id(T(n)))
					}
				}).
				Block(
					jen.Return(jen.Op("&").Id(structName).
						TypesFunc(func(g *jen.Group) {
							for n := 1; n <= paramCount; n++ {
								g.Add(jen.Id(T(n)))
							}
						}).
						Values(
							jen.DictFunc(func(d jen.Dict) {
								d[jen.Id("err")] = jen.Id("err")
								for n := 1; n <= paramCount; n++ {
									d[jen.Id(name("result", n))] = jen.Id(name("result", n))
								}
							}),
						)),
				)
			f.Line()
		}
		declareConstructor(name("From", paramCount))
		if paramCount == 1 {
			declareConstructor("From")
		}

		// failure message
		f.Func().
			Params(jen.Id("self").Op("*").Id(structName).TypesFunc(func(g *jen.Group) {
				for n := 1; n <= paramCount; n++ {
					g.Add(jen.Id(T(n)))
				}
			})).
			Id(titleCase(failureMessage)).
			Params(jen.Id("msg").String()).
			Params(jen.Op("*").Id(structName).TypesFunc(func(g *jen.Group) {
				for n := 1; n <= paramCount; n++ {
					g.Add(jen.Id(T(n)))
				}
			})).
			Block(
				jen.Id("self").Dot(failureMessage).Op("=").Id("msg"),
				jen.Return(jen.Id("self")),
			)
		f.Line()

		// unwrap
		f.Func().
			Params(jen.Id("self").Op("*").Id(structName).TypesFunc(func(g *jen.Group) {
				for n := 1; n <= paramCount; n++ {
					g.Add(jen.Id(T(n)))
				}
			})).
			Id("Unwrap").
			Params().
			ParamsFunc(func(g *jen.Group) {
				for n := 1; n <= paramCount; n++ {
					g.Add(jen.Id(T(n)))
				}
			}).
			Block(
				jen.If(
					jen.Id("self").Dot("err").Op("!=").Nil(),
				).Block(
					jen.If(
						jen.Id("self").Dot(failureMessage).Op("!=").Lit(""),
					).Block(
						jen.Panic(jen.Qual(pkgFmt, "Sprintf").Call(
							jen.Lit("%s: %s"),
							jen.Id("self").Dot(failureMessage),
							jen.Id("self").Dot("err"),
						)),
					).Else().Block(
						jen.Panic(jen.Id("self").Dot("err")),
					),
				),
				jen.ReturnFunc(func(g *jen.Group) {
					for n := 1; n <= paramCount; n++ {
						g.Add(jen.Id("self").Dot(name("result", n)))
					}
				}),
			)
		lo.Must0(f.Save(filepath.Join(outdir, fmt.Sprintf("try%d.go", paramCount))))
		fmt.Printf("%#v", f)
	}
}

func titleCase(text string) string {
	return cases.Title(language.English, cases.NoLower).String(text)
}