package configkit

import (
	"encoding"
	"math"
	"reflect"
	"slices"
	"strconv"
	"time"
	"unicode/utf8"

	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
)

type projectionLimits struct {
	depth int
	nodes int
}

func defaultProjectionLimits() projectionLimits {
	return projectionLimits{depth: maxDocumentDepth, nodes: maxDocumentNodes}
}

type projectionIssue struct {
	code    Code
	path    Path
	message string
}

type valueVisit struct {
	typeOf reflect.Type
	kind   reflect.Kind
	ptr    uintptr
}

type valueOperation struct {
	schema *schemaDescriptor
	limits projectionLimits
	active map[valueVisit]bool
	nodes  int
}

func projectConfiguration(schema *schemaDescriptor, value reflect.Value, limits projectionLimits) (*document.Node, *projectionIssue) {
	if schema == nil || schema.root == nil || !value.IsValid() || value.Type() != schema.root.typeOf {
		return nil, &projectionIssue{code: CodeSchemaUnsupportedType, message: "configuration value does not match its schema"}
	}
	operation := valueOperation{schema: schema, limits: limits, active: make(map[valueVisit]bool)}
	return operation.project(value, schema.root, Path{}, 0)
}

func cloneConfiguration(schema *schemaDescriptor, value reflect.Value, limits projectionLimits) (reflect.Value, *projectionIssue) {
	if schema == nil || schema.root == nil || !value.IsValid() || value.Type() != schema.root.typeOf {
		return reflect.Value{}, &projectionIssue{code: CodeSchemaUnsupportedType, message: "configuration value does not match its schema"}
	}
	operation := valueOperation{schema: schema, limits: limits, active: make(map[valueVisit]bool)}
	return operation.clone(value, schema.root, Path{}, 0)
}

func (o *valueOperation) project(value reflect.Value, descriptor *typeDescriptor, path Path, depth int) (*document.Node, *projectionIssue) {
	if issue := o.checkDepth(path, depth); issue != nil {
		return nil, issue
	}
	if descriptor.kind == descriptorPointer {
		if value.IsNil() {
			return o.node(document.Null, path, depth)
		}
		leave, issue := o.enter(value, path)
		if issue != nil {
			return nil, issue
		}
		defer leave()
		return o.project(value.Elem(), descriptor.element, path, depth)
	}

	switch descriptor.kind {
	case descriptorStruct:
		result, issue := o.node(document.Mapping, path, depth)
		if issue != nil {
			return nil, issue
		}
		result.Mapping = make([]document.Entry, 0, len(descriptor.fields))
		seen := make(map[string]bool, len(descriptor.fields))
		for _, member := range descriptor.members {
			memberValue := value.Field(member.index)
			if member.inline {
				if isNilValue(memberValue) {
					continue
				}
				inline, issue := o.project(memberValue, member.descriptor, path, depth)
				if issue != nil {
					return nil, issue
				}
				if inline.Kind != document.Mapping {
					return nil, &projectionIssue{code: CodeSchemaUnsupportedType, path: path.clone(), message: "inline value did not project to a mapping"}
				}
				o.nodes-- // The flattened container is not retained in the output tree.
				for _, entry := range inline.Mapping {
					if seen[entry.Key] {
						return nil, &projectionIssue{code: CodeSchemaAmbiguousField, path: path.Key(entry.Key), message: "inline value conflicts with a declared field"}
					}
					seen[entry.Key] = true
					result.Mapping = append(result.Mapping, entry)
				}
				continue
			}
			childPath := path.Key(member.name)
			if seen[member.name] {
				return nil, &projectionIssue{code: CodeSchemaAmbiguousField, path: childPath, message: "inline value conflicts with a declared field"}
			}
			if issue := o.charge(childPath); issue != nil { // mapping key
				return nil, issue
			}
			child, issue := o.project(memberValue, member.descriptor, childPath, depth+1)
			if issue != nil {
				return nil, issue
			}
			seen[member.name] = true
			result.Mapping = append(result.Mapping, document.Entry{Key: member.name, Value: child})
		}
		return result, nil
	case descriptorMap:
		if value.IsNil() {
			return o.node(document.Null, path, depth)
		}
		leave, issue := o.enter(value, path)
		if issue != nil {
			return nil, issue
		}
		defer leave()
		result, issue := o.node(document.Mapping, path, depth)
		if issue != nil {
			return nil, issue
		}
		result.Mapping = make([]document.Entry, 0, value.Len())
		keys := value.MapKeys()
		slices.SortFunc(keys, func(left, right reflect.Value) int {
			return cmpString(left.String(), right.String())
		})
		for _, key := range keys {
			childPath := path.Key(key.String())
			if issue := o.charge(childPath); issue != nil {
				return nil, issue
			}
			child, issue := o.project(value.MapIndex(key), descriptor.element, childPath, depth+1)
			if issue != nil {
				return nil, issue
			}
			result.Mapping = append(result.Mapping, document.Entry{Key: key.String(), Value: child})
		}
		return result, nil
	case descriptorSlice:
		if value.IsNil() {
			return o.node(document.Null, path, depth)
		}
		leave, issue := o.enter(value, path)
		if issue != nil {
			return nil, issue
		}
		defer leave()
		fallthrough
	case descriptorArray:
		result, issue := o.node(document.Sequence, path, depth)
		if issue != nil {
			return nil, issue
		}
		result.Sequence = make([]*document.Node, 0, value.Len())
		for i := 0; i < value.Len(); i++ {
			childPath := path.Index(i)
			child, issue := o.project(value.Index(i), descriptor.element, childPath, depth+1)
			if issue != nil {
				return nil, issue
			}
			result.Sequence = append(result.Sequence, child)
		}
		return result, nil
	case descriptorDynamic:
		if value.IsNil() {
			return o.node(document.Null, path, depth)
		}
		concrete := value.Elem()
		dynamic, issue := o.dynamicDescriptor(concrete.Type(), path)
		if issue != nil {
			return nil, issue
		}
		return o.project(concrete, dynamic, path, depth)
	case descriptorString:
		node, issue := o.node(document.String, path, depth)
		if issue == nil {
			node.Text = value.String()
		}
		return node, issue
	case descriptorBoolean:
		node, issue := o.node(document.Boolean, path, depth)
		if issue == nil {
			node.Text = strconv.FormatBool(value.Bool())
		}
		return node, issue
	case descriptorSigned:
		node, issue := o.node(document.Number, path, depth)
		if issue == nil {
			node.Text = strconv.FormatInt(value.Int(), 10)
		}
		return node, issue
	case descriptorUnsigned:
		node, issue := o.node(document.Number, path, depth)
		if issue == nil {
			node.Text = strconv.FormatUint(value.Uint(), 10)
		}
		return node, issue
	case descriptorFloat:
		if math.IsNaN(value.Float()) || math.IsInf(value.Float(), 0) {
			return nil, &projectionIssue{code: CodeSchemaNonFinite, path: path.clone(), message: "configuration float must be finite"}
		}
		node, issue := o.node(document.Number, path, depth)
		if issue == nil {
			node.Text = strconv.FormatFloat(value.Float(), 'g', -1, value.Type().Bits())
		}
		return node, issue
	case descriptorDuration:
		node, issue := o.node(document.String, path, depth)
		if issue == nil {
			node.Text = time.Duration(value.Int()).String()
		}
		return node, issue
	case descriptorSecret:
		node, issue := o.node(document.String, path, depth)
		if issue == nil {
			node.Text = value.Interface().(Secret).EnvName()
		}
		return node, issue
	case descriptorText:
		text, issue := marshalCanonicalText(value, path)
		if issue != nil {
			return nil, issue
		}
		node, nodeIssue := o.node(document.String, path, depth)
		if nodeIssue == nil {
			node.Text = text
		}
		return node, nodeIssue
	default:
		return nil, &projectionIssue{code: CodeSchemaUnsupportedType, path: path.clone(), message: "configuration type is not supported"}
	}
}

func (o *valueOperation) clone(value reflect.Value, descriptor *typeDescriptor, path Path, depth int) (reflect.Value, *projectionIssue) {
	if issue := o.checkDepth(path, depth); issue != nil {
		return reflect.Value{}, issue
	}
	if descriptor.kind == descriptorPointer {
		if value.IsNil() {
			return reflect.Zero(value.Type()), nil
		}
		leave, issue := o.enter(value, path)
		if issue != nil {
			return reflect.Value{}, issue
		}
		defer leave()
		child, issue := o.clone(value.Elem(), descriptor.element, path, depth)
		if issue != nil {
			return reflect.Value{}, issue
		}
		result := reflect.New(value.Type().Elem())
		result.Elem().Set(child)
		return result, nil
	}

	switch descriptor.kind {
	case descriptorStruct:
		result := reflect.New(value.Type()).Elem()
		for _, member := range descriptor.members {
			memberPath, memberDepth := path, depth
			if !member.inline {
				memberPath, memberDepth = path.Key(member.name), depth+1
			}
			cloned, issue := o.clone(value.Field(member.index), member.descriptor, memberPath, memberDepth)
			if issue != nil {
				return reflect.Value{}, issue
			}
			result.Field(member.index).Set(cloned)
		}
		return result, nil
	case descriptorMap:
		if value.IsNil() {
			return reflect.Zero(value.Type()), nil
		}
		leave, issue := o.enter(value, path)
		if issue != nil {
			return reflect.Value{}, issue
		}
		defer leave()
		result := reflect.MakeMapWithSize(value.Type(), value.Len())
		for _, key := range value.MapKeys() {
			cloned, issue := o.clone(value.MapIndex(key), descriptor.element, path.Key(key.String()), depth+1)
			if issue != nil {
				return reflect.Value{}, issue
			}
			result.SetMapIndex(key, cloned)
		}
		return result, nil
	case descriptorSlice:
		if value.IsNil() {
			return reflect.Zero(value.Type()), nil
		}
		leave, issue := o.enter(value, path)
		if issue != nil {
			return reflect.Value{}, issue
		}
		defer leave()
		result := reflect.MakeSlice(value.Type(), value.Len(), value.Len())
		for i := 0; i < value.Len(); i++ {
			cloned, issue := o.clone(value.Index(i), descriptor.element, path.Index(i), depth+1)
			if issue != nil {
				return reflect.Value{}, issue
			}
			result.Index(i).Set(cloned)
		}
		return result, nil
	case descriptorArray:
		result := reflect.New(value.Type()).Elem()
		for i := 0; i < value.Len(); i++ {
			cloned, issue := o.clone(value.Index(i), descriptor.element, path.Index(i), depth+1)
			if issue != nil {
				return reflect.Value{}, issue
			}
			result.Index(i).Set(cloned)
		}
		return result, nil
	case descriptorDynamic:
		if value.IsNil() {
			return reflect.Zero(value.Type()), nil
		}
		concrete := value.Elem()
		dynamic, issue := o.dynamicDescriptor(concrete.Type(), path)
		if issue != nil {
			return reflect.Value{}, issue
		}
		cloned, issue := o.clone(concrete, dynamic, path, depth)
		if issue != nil {
			return reflect.Value{}, issue
		}
		result := reflect.New(value.Type()).Elem()
		result.Set(cloned)
		return result, nil
	case descriptorSecret:
		result := reflect.New(value.Type()).Elem()
		reference := value.Interface().(Secret)
		if reference.specified {
			result.Set(reflect.ValueOf(SecretEnv(reference.EnvName())))
		}
		return result, nil
	case descriptorText:
		text, issue := marshalCanonicalText(value, path)
		if issue != nil {
			return reflect.Value{}, issue
		}
		result := reflect.New(value.Type()).Elem()
		unmarshaler := result.Addr().Interface().(encoding.TextUnmarshaler)
		if err := unmarshaler.UnmarshalText([]byte(text)); err != nil {
			return reflect.Value{}, &projectionIssue{code: CodeSchemaCodec, path: path.clone(), message: "custom text scalar could not be reconstructed"}
		}
		return result, nil
	case descriptorFloat:
		if math.IsNaN(value.Float()) || math.IsInf(value.Float(), 0) {
			return reflect.Value{}, &projectionIssue{code: CodeSchemaNonFinite, path: path.clone(), message: "configuration float must be finite"}
		}
		fallthrough
	default:
		result := reflect.New(value.Type()).Elem()
		result.Set(value)
		return result, nil
	}
}

func (o *valueOperation) dynamicDescriptor(current reflect.Type, path Path) (*typeDescriptor, *projectionIssue) {
	if current == secretType {
		return nil, &projectionIssue{code: CodeSchemaDynamicType, path: path.clone(), message: "dynamic configuration values cannot establish secret-reference semantics"}
	}
	builder := schemaBuilder{cache: o.schema.types, building: make(map[reflect.Type]bool)}
	descriptor, issue := builder.describe(current, path)
	if issue != nil {
		return nil, &projectionIssue{code: CodeSchemaDynamicType, path: path.clone(), message: "dynamic configuration value has an unsupported type"}
	}
	if descriptorContainsSecret(descriptor, make(map[*typeDescriptor]bool)) {
		return nil, &projectionIssue{code: CodeSchemaDynamicType, path: path.clone(), message: "dynamic configuration values cannot establish secret-reference semantics"}
	}
	return descriptor, nil
}

func descriptorContainsSecret(descriptor *typeDescriptor, visited map[*typeDescriptor]bool) bool {
	if descriptor == nil || visited[descriptor] {
		return false
	}
	if descriptor.kind == descriptorSecret {
		return true
	}
	visited[descriptor] = true
	if descriptorContainsSecret(descriptor.element, visited) {
		return true
	}
	for _, member := range descriptor.members {
		if descriptorContainsSecret(member.descriptor, visited) {
			return true
		}
	}
	return false
}

func (o *valueOperation) node(kind document.Kind, path Path, depth int) (*document.Node, *projectionIssue) {
	if issue := o.checkDepth(path, depth); issue != nil {
		return nil, issue
	}
	if issue := o.charge(path); issue != nil {
		return nil, issue
	}
	return &document.Node{Kind: kind}, nil
}

func (o *valueOperation) charge(path Path) *projectionIssue {
	o.nodes++
	if o.limits.nodes >= 0 && o.nodes > o.limits.nodes {
		return &projectionIssue{code: CodeSchemaProjectionLimit, path: path.clone(), message: "configuration projection exceeds the node limit"}
	}
	return nil
}

func (o *valueOperation) checkDepth(path Path, depth int) *projectionIssue {
	if depth > o.limits.depth {
		return &projectionIssue{code: CodeSchemaProjectionLimit, path: path.clone(), message: "configuration projection exceeds the depth limit"}
	}
	return nil
}

func (o *valueOperation) enter(value reflect.Value, path Path) (func(), *projectionIssue) {
	visit, ok := visitFor(value)
	if !ok {
		return func() {}, nil
	}
	if o.active[visit] {
		return nil, &projectionIssue{code: CodeSchemaCycle, path: path.clone(), message: "configuration values must not contain cycles"}
	}
	o.active[visit] = true
	return func() { delete(o.active, visit) }, nil
}

func visitFor(value reflect.Value) (valueVisit, bool) {
	if isNilValue(value) {
		return valueVisit{}, false
	}
	visit := valueVisit{typeOf: value.Type(), kind: value.Kind()}
	switch value.Kind() {
	case reflect.Pointer, reflect.Slice:
		if value.Kind() == reflect.Slice && value.Len() == 0 {
			return valueVisit{}, false
		}
		visit.ptr = value.Pointer()
	case reflect.Map:
		if value.Len() == 0 {
			return valueVisit{}, false
		}
		visit.ptr = uintptr(value.UnsafePointer())
	default:
		return valueVisit{}, false
	}
	return visit, visit.ptr != 0
}

func isNilValue(value reflect.Value) bool {
	switch value.Kind() {
	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Pointer, reflect.Slice:
		return value.IsNil()
	default:
		return false
	}
}

func marshalCanonicalText(value reflect.Value, path Path) (string, *projectionIssue) {
	var marshaler encoding.TextMarshaler
	if value.CanInterface() {
		marshaler, _ = value.Interface().(encoding.TextMarshaler)
	}
	if marshaler == nil {
		addressable := reflect.New(value.Type())
		addressable.Elem().Set(value)
		marshaler, _ = addressable.Interface().(encoding.TextMarshaler)
	}
	if marshaler == nil {
		return "", &projectionIssue{code: CodeSchemaCodec, path: path.clone(), message: "custom text scalar has no usable text marshaler"}
	}
	text, err := marshaler.MarshalText()
	if err != nil || !utf8.Valid(text) {
		return "", &projectionIssue{code: CodeSchemaCodec, path: path.clone(), message: "custom text scalar could not be projected"}
	}
	return string(text), nil
}

func cmpString(left, right string) int {
	switch {
	case left < right:
		return -1
	case left > right:
		return 1
	default:
		return 0
	}
}

type documentDeltaKind uint8

const (
	documentAdded documentDeltaKind = iota + 1
	documentRemoved
	documentReplaced
)

type documentDelta struct {
	path Path
	kind documentDeltaKind
}

func compareDocumentTrees(before, after *document.Node) []documentDelta {
	var deltas []documentDelta
	compareDocumentNode(before, after, Path{}, &deltas)
	slices.SortFunc(deltas, func(left, right documentDelta) int {
		if order := cmpString(left.path.String(), right.path.String()); order != 0 {
			return order
		}
		return int(left.kind) - int(right.kind)
	})
	return deltas
}

func compareDocumentNode(before, after *document.Node, path Path, deltas *[]documentDelta) {
	if before == nil && after == nil {
		return
	}
	if before == nil {
		*deltas = append(*deltas, documentDelta{path: path.clone(), kind: documentAdded})
		return
	}
	if after == nil {
		*deltas = append(*deltas, documentDelta{path: path.clone(), kind: documentRemoved})
		return
	}
	if before.Kind != after.Kind {
		*deltas = append(*deltas, documentDelta{path: path.clone(), kind: documentReplaced})
		return
	}
	switch before.Kind {
	case document.Mapping:
		beforeEntries := make(map[string]*document.Node, len(before.Mapping))
		afterEntries := make(map[string]*document.Node, len(after.Mapping))
		keys := make(map[string]bool, len(before.Mapping)+len(after.Mapping))
		for _, entry := range before.Mapping {
			beforeEntries[entry.Key] = entry.Value
			keys[entry.Key] = true
		}
		for _, entry := range after.Mapping {
			afterEntries[entry.Key] = entry.Value
			keys[entry.Key] = true
		}
		ordered := make([]string, 0, len(keys))
		for key := range keys {
			ordered = append(ordered, key)
		}
		slices.Sort(ordered)
		for _, key := range ordered {
			compareDocumentNode(beforeEntries[key], afterEntries[key], path.Key(key), deltas)
		}
	case document.Sequence:
		if !documentNodesEqual(before, after) {
			*deltas = append(*deltas, documentDelta{path: path.clone(), kind: documentReplaced})
		}
	default:
		if before.Text != after.Text {
			*deltas = append(*deltas, documentDelta{path: path.clone(), kind: documentReplaced})
		}
	}
}

func documentNodesEqual(left, right *document.Node) bool {
	if left == nil || right == nil {
		return left == right
	}
	if left.Kind != right.Kind || left.Text != right.Text || len(left.Mapping) != len(right.Mapping) || len(left.Sequence) != len(right.Sequence) {
		return false
	}
	if left.Kind == document.Mapping {
		leftMap := make(map[string]*document.Node, len(left.Mapping))
		for _, entry := range left.Mapping {
			leftMap[entry.Key] = entry.Value
		}
		for _, entry := range right.Mapping {
			if !documentNodesEqual(leftMap[entry.Key], entry.Value) {
				return false
			}
		}
	}
	for i := range left.Sequence {
		if !documentNodesEqual(left.Sequence[i], right.Sequence[i]) {
			return false
		}
	}
	return true
}