//go:build ignore

// Command gen writes docs/config.md from the config structs: a heading per table and option, named by its toml key, with its doc comment and default value.
package main

import (
	"bytes"
	"encoding"
	"fmt"
	"go/ast"
	"go/parser"
	"go/token"
	"log"
	"os"
	"path/filepath"
	"reflect"
	"strings"

	"github.com/BurntSushi/toml"
	"github.com/ayn2op/discordo/internal/config"
)

const header = "<!-- GENERATED BY go generate; DO NOT EDIT. -->\n\n"

// docs maps "Type.Field" to the doc comment of that struct field.
var docs = map[string]string{}

type field struct {
	key, doc string
	value    reflect.Value
}

// fields returns the fields of the struct v, with those of embedded structs in place.
func fields(v reflect.Value) []field {
	var fs []field
	t := v.Type()
	for i := range t.NumField() {
		f := t.Field(i)
		if f.Anonymous {
			fs = append(fs, fields(v.Field(i))...)
			continue
		}
		fs = append(fs, field{f.Tag.Get("toml"), docs[t.Name()+"."+f.Name], v.Field(i)})
	}
	return fs
}

// isTable reports whether v is written as a table rather than as a value.
func isTable(v reflect.Value) bool {
	switch v.Interface().(type) {
	case toml.Marshaler, encoding.TextMarshaler:
		return false
	}
	return v.Kind() == reflect.Struct
}

// write writes a section for each option of the table v at path: its doc comment, then its default value or, for a table, its own options.
func write(w *bytes.Buffer, path string, v reflect.Value) {
	if path != "" {
		path += "."
	}
	for _, f := range fields(v) {
		name := path + f.key
		fmt.Fprintf(w, "%s %s\n\n", strings.Repeat("#", strings.Count(name, ".")+1), name)
		if f.doc != "" {
			fmt.Fprintf(w, "%s\n", f.doc)
		}
		if isTable(f.value) {
			write(w, name, f.value)
			continue
		}
		// The encoder only writes whole documents, so the value is what follows the key.
		var line bytes.Buffer
		if err := toml.NewEncoder(&line).Encode(map[string]any{f.key: f.value.Interface()}); err != nil {
			log.Fatal(err)
		}
		_, value, _ := strings.Cut(line.String(), " = ")
		fmt.Fprintf(w, "Default: `%s`\n\n", strings.TrimSpace(value))
	}
}

func main() {
	names, _ := filepath.Glob("*.go")
	for _, name := range names {
		file, err := parser.ParseFile(token.NewFileSet(), name, nil, parser.ParseComments)
		if err != nil {
			log.Fatal(err)
		}
		ast.Inspect(file, func(n ast.Node) bool {
			spec, ok := n.(*ast.TypeSpec)
			if !ok {
				return true
			}
			if s, ok := spec.Type.(*ast.StructType); ok {
				for _, f := range s.Fields.List {
					for _, name := range f.Names {
						docs[spec.Name.Name+"."+name.Name] = f.Doc.Text()
					}
				}
			}
			return false
		})
	}

	w := bytes.NewBufferString(header)
	write(w, "", reflect.ValueOf(config.Default()))
	if err := os.WriteFile("../../docs/config.md", append(bytes.TrimSpace(w.Bytes()), '\n'), 0o644); err != nil {
		log.Fatal(err)
	}
}