// Package contract 内部 JSON 序列化辅助（与契约逻辑分离，保持 contract.go 职责单一）。
package contract

import "encoding/json"

// jsonMarshal 统一带缩进关闭的紧凑序列化（HTML 转义开启与标准库默认一致）。
func jsonMarshal(v any) ([]byte, error) {
	return json.Marshal(v)
}

// UnmarshalJSON 从平铺 wire 还原 Data。缺此方法时 encoding/json 只填顶层字段，
// Data 恒为 nil；再 Marshal 会丢掉 results/markdown（gateway 缓存命中改写即踩中）。
func (e *Envelope) UnmarshalJSON(b []byte) error {
	var top envelopeTop
	if err := json.Unmarshal(b, &top); err != nil {
		return err
	}
	e.OK = top.OK
	e.Kind = top.Kind
	e.RequestID = top.RequestID
	e.TookMs = top.TookMs
	e.Usage = top.Usage
	e.Provenance = top.Provenance
	e.Error = top.Error
	switch top.Kind {
	case "search":
		var w searchWire
		if err := json.Unmarshal(b, &w); err != nil {
			return err
		}
		p := &SearchPayload{Query: w.Query, Answer: w.Answer, Results: w.Results}
		p.EnsureEmptySlice()
		e.Data = p
	case "read":
		var w readWire
		if err := json.Unmarshal(b, &w); err != nil {
			return err
		}
		p := readPayloadFromWire(w)
		p.EnsureEmptySlice()
		e.Data = p
	}
	return nil
}

func readPayloadFromWire(w readWire) *ReadPayload {
	p := &ReadPayload{
		Description:   w.Description,
		HTML:          w.HTML,
		ScreenshotURL: w.ScreenshotURL,
		Extracted:     w.Extracted,
		Links:         w.Links,
		Images:        w.Images,
		Warnings:      w.Warnings,
	}
	if w.URL != nil {
		p.URL = *w.URL
	}
	if w.FinalURL != nil {
		p.FinalURL = *w.FinalURL
	}
	if w.Title != nil {
		p.Title = *w.Title
	}
	if w.Markdown != nil {
		p.Markdown = *w.Markdown
	}
	if w.Truncated != nil {
		p.Truncated = *w.Truncated
	}
	if w.CharCount != nil {
		p.CharCount = *w.CharCount
	}
	if w.Metadata != nil {
		p.Metadata = *w.Metadata
	}
	return p
}