// Package engine 依据已发布规则和持久化快照计算有限推进命令；不调用业务处理器或外部系统。
package engine

import (
	"bytes"
	"encoding/json"
	"errors"
	"math/big"
	"strings"

	"git.yuntuo.hk/k2safe/orbit/internal/jsonwire"
	"git.yuntuo.hk/k2safe/orbit/weave/definition"
)

type values map[string]json.RawMessage

func copyJSON(raw json.RawMessage) json.RawMessage { return append(json.RawMessage(nil), raw...) }
func copyValues(in values) values {
	out := make(values, len(in)+8)
	for k, v := range in {
		out[k] = v
	}
	return out
}

// 表达式来自已验证且由Program持有的不可变定义；每个值仍按运行数据上限检查。
func resolve(v definition.Value, expected definition.Type, env values) (json.RawMessage, error) {
	raw, err := evaluate(v, env, 0)
	if err != nil {
		return nil, err
	}
	if err := definition.ValidateData(expected, raw); err != nil {
		return nil, err
	}
	return raw, nil
}
func evaluate(v definition.Value, env values, depth int) (json.RawMessage, error) {
	if depth > 8 {
		return nil, errors.New("expression depth exceeded")
	}
	var out json.RawMessage
	switch v.Kind {
	case "LITERAL":
		out = copyJSON(v.Literal)
	case "REFERENCE":
		if v.Reference == nil {
			return nil, errors.New("reference required")
		}
		raw, ok := env[v.Reference.Source]
		if !ok {
			return nil, errors.New("reference unavailable")
		}
		for _, key := range v.Reference.Path {
			var object map[string]json.RawMessage
			if json.Unmarshal(raw, &object) != nil {
				return nil, errors.New("reference is not an object")
			}
			raw, ok = object[key]
			if !ok {
				return nil, errors.New("reference field missing")
			}
		}
		out = copyJSON(raw)
	case "OBJECT":
		object := make(map[string]json.RawMessage, len(v.Fields))
		size := 0
		for k, child := range v.Fields {
			raw, err := evaluate(child, env, depth+1)
			if err != nil {
				return nil, err
			}
			size += len(raw)
			if size > definition.MaxSpecificationBytes {
				return nil, errors.New("resolved object exceeds bounds")
			}
			object[k] = raw
		}
		raw, err := jsonwire.Marshal(object)
		if err != nil {
			return nil, err
		}
		out = raw
	case "ARRAY":
		array := make([]json.RawMessage, len(v.Items))
		size := 0
		for i, child := range v.Items {
			raw, err := evaluate(child, env, depth+1)
			if err != nil {
				return nil, err
			}
			size += len(raw)
			if size > definition.MaxSpecificationBytes {
				return nil, errors.New("resolved array exceeds bounds")
			}
			array[i] = raw
		}
		raw, err := jsonwire.Marshal(array)
		if err != nil {
			return nil, err
		}
		out = raw
	default:
		return nil, errors.New("unknown expression")
	}
	if len(out) == 0 || len(out) > definition.MaxSpecificationBytes {
		return nil, errors.New("resolved value exceeds bounds")
	}
	return out, nil
}
func compare(p definition.Predicate, env values) (bool, error) {
	switch p.Op {
	case "AND", "OR", "NOT":
		for _, child := range p.Arguments {
			ok, err := compare(child, env)
			if err != nil {
				return false, err
			}
			if p.Op == "NOT" {
				return !ok, nil
			}
			if p.Op == "AND" && !ok {
				return false, nil
			}
			if p.Op == "OR" && ok {
				return true, nil
			}
		}
		return p.Op == "AND", nil
	}
	if p.Left == nil || p.Right == nil {
		return false, errors.New("comparison operands missing")
	}
	left, err := resolve(*p.Left, definition.Type{Kind: "JSON"}, env)
	if err != nil {
		return false, err
	}
	right, err := resolve(*p.Right, definition.Type{Kind: "JSON"}, env)
	if err != nil {
		return false, err
	}
	decode := func(raw []byte) (any, error) {
		var v any
		d := json.NewDecoder(bytes.NewReader(raw))
		d.UseNumber()
		err := d.Decode(&v)
		return v, err
	}
	a, err := decode(left)
	if err != nil {
		return false, err
	}
	b, err := decode(right)
	if err != nil {
		return false, err
	}
	var order int
	switch v := a.(type) {
	case string:
		w, ok := b.(string)
		if !ok {
			return false, errors.New("comparison type mismatch")
		}
		order = strings.Compare(v, w)
	case json.Number:
		w, ok := b.(json.Number)
		if !ok {
			return false, errors.New("comparison type mismatch")
		}
		x, ok := new(big.Rat).SetString(string(v))
		if !ok {
			return false, errors.New("invalid exact number")
		}
		y, ok := new(big.Rat).SetString(string(w))
		if !ok {
			return false, errors.New("invalid exact number")
		}
		order = x.Cmp(y)
	case bool:
		w, ok := b.(bool)
		if !ok || p.Op != "EQ" && p.Op != "NE" {
			return false, errors.New("comparison type mismatch")
		}
		if v != w {
			order = 1
		}
	case nil:
		if b != nil || p.Op != "EQ" && p.Op != "NE" {
			return false, errors.New("comparison type mismatch")
		}
	default:
		return false, errors.New("comparison requires scalars")
	}
	switch p.Op {
	case "EQ":
		return order == 0, nil
	case "NE":
		return order != 0, nil
	case "LT":
		return order < 0, nil
	case "LE":
		return order <= 0, nil
	case "GT":
		return order > 0, nil
	case "GE":
		return order >= 0, nil
	}
	return false, errors.New("unknown comparison")
}