package config

import (
	"encoding/json"
	"fmt"
	"reflect"
	"sort"
	"strings"
)

var jsonUnmarshalerType = reflect.TypeOf((*json.Unmarshaler)(nil)).Elem()

type documentBinder struct {
	doc   Document
	nodes int
}

func (b *documentBinder) step(path string, depth int) error {
	b.nodes++
	if depth > maxConfigDepth || b.nodes > maxConfigNodes {
		return b.doc.diagnostic(path, "configuration nesting or node limit exceeded", nil)
	}
	return nil
}

func bindDocument[T any](doc Document, defaults T) (T, error) {
	var zero T
	base := reflect.ValueOf(&defaults).Elem()
	if base.Kind() != reflect.Struct && (base.Kind() != reflect.Pointer || base.Type().Elem().Kind() != reflect.Struct) {
		return zero, &Error{Reason: "project configuration must be a struct"}
	}
	result, err := cloneConfiguration(base, 0)
	if err != nil {
		return zero, &Error{Reason: "cannot clone configuration defaults", cause: err}
	}
	b := documentBinder{doc: doc}
	if err = b.bind(doc.Value, result, "", 0, false); err != nil {
		return zero, err
	}
	return result.Interface().(T), nil
}

func (b *documentBinder) decode(v any, dst reflect.Value, path string) (err error) {
	defer func() {
		if recover() != nil {
			err = b.doc.diagnostic(path, "custom value decoder panicked", nil)
		}
	}()
	raw, err := json.Marshal(v)
	if err != nil {
		return b.doc.diagnostic(path, "unsupported configuration value", err)
	}
	if err = json.Unmarshal(raw, dst.Addr().Interface()); err != nil {
		return b.doc.diagnostic(path, "expected a valid "+dst.Type().String(), err)
	}
	return nil
}
func (b *documentBinder) bind(v any, dst reflect.Value, path string, depth int, quoted bool) error {
	if err := b.step(path, depth); err != nil {
		return err
	}
	if text, ok := v.(resolvedText); ok {
		if dst.Kind() != reflect.Pointer && dst.Type() != durationType && dst.CanAddr() && !dst.Addr().Type().Implements(jsonUnmarshalerType) && !dst.Addr().Type().Implements(textType) {
			switch dst.Kind() {
			case reflect.Bool, reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Float32, reflect.Float64:
				if err := parseTextValue(dst, string(text)); err != nil {
					return b.doc.diagnostic(path, "expected a valid "+dst.Type().String(), err)
				}
				return nil
			}
		}
		if dst.Kind() != reflect.Pointer {
			v = string(text)
		}
	}
	if v == nil {
		return b.decode(nil, dst, path)
	} // Preserve encoding/json null semantics.
	if dst.Kind() == reflect.Pointer {
		if dst.IsNil() {
			dst.Set(reflect.New(dst.Type().Elem()))
		}
		return b.bind(v, dst.Elem(), path, depth+1, quoted)
	}
	if dst.Type() == durationType {
		var raw string
		switch x := v.(type) {
		case string:
			raw = x
		case Text:
			raw = string(x)
		default:
			return b.decode(v, dst, path)
		}
		if err := parseTextValue(dst, strings.TrimSpace(raw)); err != nil {
			return b.doc.diagnostic(path, "expected a duration such as 5s", err)
		}
		return nil
	}
	if dst.CanAddr() && dst.Addr().Type().Implements(jsonUnmarshalerType) {
		normalized, err := b.dynamic(v, path, depth+1)
		if err != nil {
			return err
		}
		return b.decode(normalized, dst, path)
	}
	if dst.CanAddr() && dst.Addr().Type().Implements(textType) {
		if text, ok := v.(Text); ok {
			v = string(text)
		}
		return b.decode(v, dst, path)
	}
	if text, ok := v.(Text); ok {
		if dst.Kind() == reflect.String || dst.Kind() == reflect.Interface || (dst.Kind() == reflect.Slice && dst.Type().Elem().Kind() == reflect.Uint8) {
			return b.decode(string(text), dst, path)
		}
		switch dst.Kind() {
		case reflect.Bool, reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Float32, reflect.Float64:
			if err := parseTextValue(dst, strings.TrimSpace(string(text))); err != nil {
				return b.doc.diagnostic(path, "expected a valid "+dst.Type().String(), err)
			}
			return nil
		default:
			return b.doc.diagnostic(path, "expected an object or array, not scalar text", nil)
		}
	}
	if quoted {
		s, ok := v.(string)
		if !ok {
			return b.doc.diagnostic(path, "expected a JSON-encoded string", nil)
		}
		if err := json.Unmarshal([]byte(s), dst.Addr().Interface()); err != nil {
			return b.doc.diagnostic(path, "invalid string-encoded value", err)
		}
		return nil
	}
	switch dst.Kind() {
	case reflect.Struct:
		m, ok := v.(map[string]any)
		if !ok {
			return b.doc.diagnostic(path, "expected an object", nil)
		}
		fields := configurationFields(dst.Type())
		used := map[string]bool{}
		for _, name := range sortedKeys(m) {
			child := joinField(path, name)
			f, ok := fields[name]
			canonical := name
			if !ok {
				for n, field := range fields {
					if strings.EqualFold(n, name) {
						if ok {
							return b.doc.diagnostic(child, "ambiguous field name", nil)
						}
						f, ok, canonical = field, true, n
					}
				}
			}
			if !ok {
				return b.doc.diagnostic(child, unknownFieldReason(name, fields), nil)
			}
			if used[canonical] {
				return b.doc.diagnostic(child, "duplicate field binding", nil)
			}
			used[canonical] = true
			target := dst
			for _, index := range f.Index {
				if target.Kind() == reflect.Pointer {
					if target.IsNil() {
						if !target.CanSet() {
							return b.doc.diagnostic(child, "field cannot be assigned", nil)
						}
						target.Set(reflect.New(target.Type().Elem()))
					}
					target = target.Elem()
				}
				target = target.Field(index)
			}
			if !target.CanSet() {
				return b.doc.diagnostic(child, "field cannot be assigned", nil)
			}
			if err := b.bind(m[name], target, child, depth+1, strings.Contains(","+f.Tag.Get("json")+",", ",string,")); err != nil {
				return err
			}
		}
		return nil
	case reflect.Map:
		m, ok := v.(map[string]any)
		if !ok || dst.Type().Key().Kind() != reflect.String {
			return b.doc.diagnostic(path, "expected an object with string keys", nil)
		}
		if dst.IsNil() {
			dst.Set(reflect.MakeMap(dst.Type()))
		}
		for _, key := range sortedKeys(m) {
			value := reflect.New(dst.Type().Elem()).Elem()
			if err := b.bind(m[key], value, joinField(path, key), depth+1, false); err != nil {
				return err
			}
			k := reflect.New(dst.Type().Key()).Elem()
			k.SetString(key)
			dst.SetMapIndex(k, value)
		}
		return nil
	case reflect.Slice, reflect.Array:
		if _, ok := v.(string); ok && dst.Kind() == reflect.Slice && dst.Type().Elem().Kind() == reflect.Uint8 {
			return b.decode(v, dst, path)
		}
		items, ok := v.([]any)
		if !ok {
			return b.doc.diagnostic(path, "expected an array", nil)
		}
		if dst.Kind() == reflect.Array && len(items) != dst.Len() {
			return b.doc.diagnostic(path, "array length does not match its declared type", nil)
		}
		if dst.Kind() == reflect.Slice {
			dst.Set(reflect.MakeSlice(dst.Type(), len(items), len(items)))
		}
		for i, value := range items {
			if err := b.bind(value, dst.Index(i), fmt.Sprintf("%s[%d]", path, i), depth+1, false); err != nil {
				return err
			}
		}
		return nil
	case reflect.Interface:
		v, err := b.dynamic(v, path, depth+1)
		if err != nil {
			return err
		}
		if dst.Type().NumMethod() == 0 {
			dst.Set(reflect.ValueOf(v))
			return nil
		}
		return b.decode(v, dst, path)
	default:
		return b.decode(v, dst, path)
	}
}
func sortedKeys(m map[string]any) []string {
	keys := make([]string, 0, len(m))
	for k := range m {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	return keys
}
func (b *documentBinder) dynamic(v any, path string, depth int) (any, error) {
	if err := b.step(path, depth); err != nil {
		return nil, err
	}
	switch x := v.(type) {
	case Text:
		return string(x), nil
	case resolvedText:
		return string(x), nil
	case map[string]any:
		out := make(map[string]any, len(x))
		for _, k := range sortedKeys(x) {
			c, err := b.dynamic(x[k], joinField(path, k), depth+1)
			if err != nil {
				return nil, err
			}
			out[k] = c
		}
		return out, nil
	case []any:
		out := make([]any, len(x))
		for i, v := range x {
			c, err := b.dynamic(v, fmt.Sprintf("%s[%d]", path, i), depth+1)
			if err != nil {
				return nil, err
			}
			out[i] = c
		}
		return out, nil
	default:
		return v, nil
	}
}

// Match encoding/json's field promotion: the shallowest declaration wins;
// explicit tags win ties, and ambiguous fields remain unavailable.
func configurationFields(t reflect.Type) map[string]reflect.StructField {
	type candidate struct {
		field  reflect.StructField
		tagged bool
	}
	candidates := map[string][]candidate{}
	var visit func(reflect.Type, []int, map[reflect.Type]bool)
	visit = func(current reflect.Type, prefix []int, visiting map[reflect.Type]bool) {
		if visiting[current] {
			return
		}
		visiting[current] = true
		defer delete(visiting, current)
		for i := 0; i < current.NumField(); i++ {
			f := current.Field(i)
			name := strings.Split(f.Tag.Get("json"), ",")[0]
			if name == "-" {
				continue
			}
			child := f.Type
			if child.Kind() == reflect.Pointer {
				child = child.Elem()
			}
			if f.PkgPath != "" && (!f.Anonymous || child.Kind() != reflect.Struct) {
				continue
			}
			f.Index = append(append([]int(nil), prefix...), i)
			if name == "" && f.Anonymous && child.Kind() == reflect.Struct {
				visit(child, f.Index, visiting)
				continue
			}
			tagged := name != ""
			if name == "" {
				name = f.Name
			}
			candidates[name] = append(candidates[name], candidate{f, tagged})
		}
	}
	visit(t, nil, map[reflect.Type]bool{})
	fields := map[string]reflect.StructField{}
	for name, list := range candidates {
		sort.Slice(list, func(i, j int) bool {
			if len(list[i].field.Index) != len(list[j].field.Index) {
				return len(list[i].field.Index) < len(list[j].field.Index)
			}
			return list[i].tagged && !list[j].tagged
		})
		if len(list) > 1 && len(list[0].field.Index) == len(list[1].field.Index) && list[0].tagged == list[1].tagged {
			continue
		}
		fields[name] = list[0].field
	}
	return fields
}