package toml

import (
	"fmt"
	"reflect"
	"strings"
)

const fieldTagName = "toml"

// fieldCache maps normalized field names to their position in a struct.
type fieldCache struct {
	named map[string]fieldInfo // fields with an explicit name in tag
	auto  map[string]fieldInfo // fields with auto-assigned normalized names
}

type fieldInfo struct {
	index   []int
	name    string
	ignored bool
}

func makeFieldCache(cfg *Config, rt reflect.Type) fieldCache {
	named, auto := make(map[string]fieldInfo), make(map[string]fieldInfo)

	var descend func([]int, reflect.Type)
	descend = func(index []int, rt reflect.Type) {
		for i := 0; i < rt.NumField(); i++ {
			ft := rt.Field(i)
			// skip unexported fields
			if ft.PkgPath != "" && !ft.Anonymous {
				continue
			}

			col, _ := extractTag(ft.Tag.Get(fieldTagName))

			if ft.Anonymous && ft.Type.Kind() == reflect.Struct && col == "" {
				descend(append(index, ft.Index...), ft.Type)
				continue
			}

			indexx := append(append([]int{}, index...), ft.Index...)
			info := fieldInfo{index: indexx, name: ft.Name, ignored: col == "-"}

			if col == "" || col == "-" {
				name := cfg.NormFieldName(rt, ft.Name)
				// discard any duplicate names
				if _, ok := auto[name]; ok {
					info.ignored = true
				}
				auto[name] = info
			} else {
				if _, ok := named[col]; ok {
					info.ignored = true
				}
				named[col] = info
			}
		}
	}

	descend([]int{}, rt)
	return fieldCache{named, auto}
}

func (fc fieldCache) findField(cfg *Config, rv reflect.Value, name string) (reflect.Value, string, error) {
	info, found := fc.named[name]
	if !found {
		info, found = fc.auto[cfg.NormFieldName(rv.Type(), name)]
	}
	if !found {
		if cfg.MissingField == nil {
			return reflect.Value{}, "", fmt.Errorf("field corresponding to `%s' is not defined in %v", name, rv.Type())
		} else {
			return reflect.Value{}, "", cfg.MissingField(rv.Type(), name)
		}
	} else if info.ignored {
		return reflect.Value{}, "", fmt.Errorf("field corresponding to `%s' in %v cannot be set through TOML", name, rv.Type())
	}
	return rv.FieldByIndex(info.index), info.name, nil
}

func extractTag(tag string) (col, rest string) {
	tags := strings.SplitN(tag, ",", 2)
	if len(tags) == 2 {
		return strings.TrimSpace(tags[0]), strings.TrimSpace(tags[1])
	}
	return strings.TrimSpace(tags[0]), ""
}