// Package edgebill stamps digests through the commercial edge (zap.verae.ai)
// so MCP global stamps share one meter with PrintIt / Zapier / Node-RED.
package edgebill

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"strings"
	"time"
)

// Client posts digests to the edge /v1/timestamp API.
type Client struct {
	BaseURL    string
	HTTPClient *http.Client
	Channel    string
}

// DefaultBaseURL is the public edge.
const DefaultBaseURL = "https://zap.verae.ai"

// FromEnv builds a client when VERAE_MCP_EDGE_URL is set (non-empty).
// Empty env disables edge billing (legacy direct VeraeTime only).
func FromEnv() *Client {
	u := strings.TrimRight(strings.TrimSpace(os.Getenv("VERAE_MCP_EDGE_URL")), "/")
	if u == "" {
		return nil
	}
	ch := strings.TrimSpace(os.Getenv("VERAE_MCP_BILLING_CHANNEL"))
	if ch == "" {
		ch = "mcp"
	}
	return &Client{
		BaseURL:    u,
		HTTPClient: &http.Client{Timeout: 90 * time.Second},
		Channel:    ch,
	}
}

// Receipt is a minimal stamp result compatible with tools.ReceiptDTO mapping.
type Receipt struct {
	ReceiptID string
	Hash      string
	Scope     string
	CreatedAt string
	Merkle    string
}

// Stamp posts sha256 to edge /v1/timestamp with the caller credential.
// bearer may be an xVerae- / key- API key or a VeraeTime JWT (sent as Bearer).
func (c *Client) Stamp(ctx context.Context, sha256, bearer string) (*Receipt, error) {
	if c == nil || c.BaseURL == "" {
		return nil, fmt.Errorf("edgebill: not configured")
	}
	h := strings.ToLower(strings.TrimSpace(sha256))
	h = strings.TrimPrefix(h, "sha256:")
	payload, _ := json.Marshal(map[string]any{
		"sha256":  h,
		"digest":  h,
		"data":    h,
		"hashAlg": "SHA256",
		"wait":    true,
		"restamp": false,
	})
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.BaseURL+"/v1/timestamp", bytes.NewReader(payload))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Accept", "application/json")
	req.Header.Set("x-billing-channel", c.Channel)
	req.Header.Set("User-Agent", "verae-mcp-timestamping/edgebill")
	tok := strings.TrimSpace(bearer)
	if tok != "" {
		if strings.HasPrefix(tok, "xVerae-") || strings.HasPrefix(tok, "key-") || strings.HasPrefix(tok, "zmw_") {
			req.Header.Set("x-api-key", tok)
		} else {
			req.Header.Set("Authorization", "Bearer "+tok)
			// Edge also accepts Bearer xVerae- in some paths; keep x-api-key empty.
		}
	}
	hc := c.HTTPClient
	if hc == nil {
		hc = http.DefaultClient
	}
	res, err := hc.Do(req)
	if err != nil {
		return nil, err
	}
	defer res.Body.Close()
	raw, _ := io.ReadAll(res.Body)
	if res.StatusCode >= 300 {
		return nil, fmt.Errorf("edgebill: stamp HTTP %d: %s", res.StatusCode, truncate(raw, 300))
	}
	var body map[string]any
	_ = json.Unmarshal(raw, &body)
	cid := str(body, "certificate")
	if cid == "" {
		cid = str(body, "receipt_id")
	}
	if cid == "" {
		if recs, ok := body["receipts"].([]any); ok && len(recs) > 0 {
			if m, ok := recs[0].(map[string]any); ok {
				cid = str(m, "certificate")
				if cid == "" {
					cid = str(m, "receipt_id")
				}
			}
		}
	}
	if cid == "" {
		return nil, fmt.Errorf("edgebill: response missing certificate: %s", truncate(raw, 200))
	}
	return &Receipt{
		ReceiptID: cid,
		Hash:      h,
		Scope:     "global",
		CreatedAt: firstNonEmpty(str(body, "completedAt"), str(body, "created_at"), str(body, "timestamp")),
		Merkle:    firstNonEmpty(str(body, "blockHash"), str(body, "merkle")),
	}, nil
}

func str(m map[string]any, k string) string {
	if m == nil {
		return ""
	}
	v, ok := m[k]
	if !ok || v == nil {
		return ""
	}
	switch t := v.(type) {
	case string:
		return t
	default:
		return fmt.Sprint(t)
	}
}

func firstNonEmpty(ss ...string) string {
	for _, s := range ss {
		if strings.TrimSpace(s) != "" {
			return s
		}
	}
	return ""
}

func truncate(b []byte, n int) string {
	if len(b) <= n {
		return string(b)
	}
	return string(b[:n]) + "…"
}