package pdfcert

import (
	"bytes"
	_ "embed"
	"encoding/json"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"time"
)

//go:embed logo.png
var embeddedLogo []byte

// Input for the official Verae Timestamp Certificate (CERT-01).
type Input struct {
	DocumentName string
	SHA256       string
	// Multihash is the content multihash (f1220 + sha2-256 hex) when known.
	// Empty → derive from SHA256 if valid; else omit (never invent).
	Multihash string
	// Blake3 is the optional BLAKE3-256 hex digest when provided upstream.
	// Empty → omit (never invent / never compute from file bytes here).
	Blake3 string
	// Blake3Multihash is the blake3 multihash (f1e20 + hex) when known.
	// Empty → derive from Blake3 if valid 64-hex; else omit.
	Blake3Multihash string
	ReceiptID       string
	CreatedAt       string
	Merkle          string
	Scope           string
	VerifyURL       string
	Channel         string
	ByteLength      int64
	// EmbedBrandFonts requests PDF embed of a licensed brand serif when a
	// .ttf/.otf is present under BrandFontsDir(). Default false: core
	// Times/Helvetica only. Also via VERAE_EMBED_BRAND_FONTS=1|true|yes.
	// gofpdf path attempts AddUTF8FontFromBytes; failure is a logged no-op.
	EmbedBrandFonts bool
}

// EmbedBrandFontsEnabled reports whether brand-font PDF embed is requested.
// Default false. True only when Input.EmbedBrandFonts is set or env
// VERAE_EMBED_BRAND_FONTS is 1/true/yes. When enabled, gofpdf may register a
// .ttf/.otf from BrandFontsDir(); failure is a logged no-op (core fonts).
func EmbedBrandFontsEnabled(in Input) bool {
	if in.EmbedBrandFonts {
		return true
	}
	v := strings.TrimSpace(os.Getenv("VERAE_EMBED_BRAND_FONTS"))
	switch strings.ToLower(v) {
	case "1", "true", "yes", "on":
		return true
	default:
		return false
	}
}

// BrandFontsDir is the directory scanned for .ttf/.otf when EmbedBrandFonts is on.
// Override with VERAE_BRAND_FONTS_DIR; else site/printit.verae.ai/fonts from the
// module tree. Empty when neither is available (embed no-ops with a log).
func BrandFontsDir() string {
	if d := strings.TrimSpace(os.Getenv("VERAE_BRAND_FONTS_DIR")); d != "" {
		if st, err := os.Stat(d); err == nil && st.IsDir() {
			return d
		}
	}
	var candidates []string
	if wd, err := os.Getwd(); err == nil {
		dir := wd
		for i := 0; i < 8; i++ {
			candidates = append(candidates, filepath.Join(dir, "site", "printit.verae.ai", "fonts"))
			if st, se := os.Stat(filepath.Join(dir, "go.mod")); se == nil && !st.IsDir() {
				break
			}
			parent := filepath.Dir(dir)
			if parent == dir {
				break
			}
			dir = parent
		}
	}
	candidates = append(candidates, filepath.Join("site", "printit.verae.ai", "fonts"))
	for _, c := range candidates {
		if st, err := os.Stat(c); err == nil && st.IsDir() {
			abs, _ := filepath.Abs(c)
			return abs
		}
	}
	return ""
}

// findBrandFaceFile returns the preferred .ttf/.otf under dir (Fraunces-named
// first, then any ttf, then otf). Empty when none present.
func findBrandFaceFile(dir string) string {
	if dir == "" {
		return ""
	}
	ents, err := os.ReadDir(dir)
	if err != nil {
		return ""
	}
	var frauncesTTF, anyTTF, frauncesOTF, anyOTF string
	for _, e := range ents {
		if e.IsDir() {
			continue
		}
		name := e.Name()
		low := strings.ToLower(name)
		path := filepath.Join(dir, name)
		switch {
		case strings.HasSuffix(low, ".ttf"):
			if strings.Contains(low, "fraunces") && frauncesTTF == "" {
				frauncesTTF = path
			} else if anyTTF == "" {
				anyTTF = path
			}
		case strings.HasSuffix(low, ".otf"):
			if strings.Contains(low, "fraunces") && frauncesOTF == "" {
				frauncesOTF = path
			} else if anyOTF == "" {
				anyOTF = path
			}
		}
	}
	for _, p := range []string{frauncesTTF, anyTTF, frauncesOTF, anyOTF} {
		if p != "" {
			return p
		}
	}
	return ""
}

// ContentMultihash returns sha2-256 multihash hex (code 0x12, len 0x20 → f1220…)
// when sha256 is a 64-char hex digest; otherwise "" (caller omits the field).
func ContentMultihash(sha256 string) string {
	return contentMultihashPrefixed("1220", sha256)
}

// ContentBlake3Multihash returns blake3 multihash hex (code 0x1e, len 0x20 → f1e20…)
// when blake3 is a 64-char hex digest; otherwise "" (caller omits the field).
func ContentBlake3Multihash(blake3 string) string {
	return contentMultihashPrefixed("1e20", blake3)
}

// contentMultihashPrefixed wraps a 64-char hex digest as multibase-base16 multihash
// ("f" + code/len prefix + digest). Invalid/empty → "" (never invent).
func contentMultihashPrefixed(codeLen, hexDigest string) string {
	s := strings.TrimSpace(hexDigest)
	s = strings.TrimPrefix(strings.ToLower(s), "0x")
	if len(s) != 64 {
		return ""
	}
	for i := 0; i < len(s); i++ {
		c := s[i]
		if !((c >= '0' && c <= '9') || (c >= 'a' && c <= 'f')) {
			return ""
		}
	}
	return "f" + codeLen + s
}

// ResolveDigests returns CERT multihash / blake3 display values from Input.
// Empty strings mean omit that line (never invent digests).
func ResolveDigests(in Input) (mh, blake3Hex, blake3MH string) {
	mh = strings.TrimSpace(in.Multihash)
	if mh == "" {
		mh = ContentMultihash(in.SHA256)
	}
	blake3Hex = strings.TrimSpace(in.Blake3)
	blake3MH = strings.TrimSpace(in.Blake3Multihash)
	if blake3MH == "" {
		blake3MH = ContentBlake3Multihash(in.Blake3)
	}
	return mh, blake3Hex, blake3MH
}

// LookupURL builds a public VeraeTime verify deep link (same as explorer
// scan-bar → /time, which auto-fills receipt/sha256 and runs Lookup).
// https://explorer.verae.ai/time?receipt=…&sha256=…
func LookupURL(sha256, receiptID string) string {
	sha256 = strings.TrimSpace(sha256)
	sha256 = strings.TrimPrefix(strings.ToLower(sha256), "0x")
	receiptID = strings.TrimSpace(receiptID)
	u := "https://explorer.verae.ai/time"
	sep := "?"
	if receiptID != "" {
		u += sep + "receipt=" + receiptID
		sep = "&"
	}
	if sha256 != "" {
		u += sep + "sha256=" + sha256
	}
	return u
}

// Build returns the branded CERT-01 certificate PDF (plum/gold, final-only
// evidence copy). Prefers platform/registration-pdf/build.mjs when Node is
// available; otherwise gofpdf fallback.
//
// Typography: default PDF standard fonts (Times title, Helvetica body).
// EmbedBrandFonts defaults false (env VERAE_EMBED_BRAND_FONTS off). When on,
// gofpdf fallback may register a licensed .ttf/.otf from BrandFontsDir();
// failure is a logged no-op. Node path stays core faces (OPEN-ISSUES #7).
func Build(in Input) ([]byte, error) {
	created := in.CreatedAt
	if created == "" {
		// Do not invent a ledger time — leave blank for the PDF field.
		created = ""
	}
	scope := strings.ToUpper(strings.TrimSpace(in.Scope))
	if scope == "" {
		scope = "GLOBAL"
	}
	lookup := in.VerifyURL
	if lookup == "" || strings.Contains(strings.ToLower(lookup), "mcp.verae.ai") {
		lookup = LookupURL(in.SHA256, in.ReceiptID)
	}
	merkle := in.Merkle
	if merkle == "" {
		merkle = "See ledger lookup via receipt CID"
	}
	docName := in.DocumentName
	if docName == "" {
		docName = "(digest only)"
	}

	mh, b3, b3mh := ResolveDigests(in)
	row := map[string]any{
		"file":       docName,
		"sha256":     in.SHA256,
		"scope":      scope,
		"receipt_id": in.ReceiptID,
		"created_at": created,
		"merkle":     merkle,
		"lookup_url": lookup,
		"size_bytes": in.ByteLength,
	}
	// Omit digest fields when empty — never invent.
	if mh != "" {
		row["multihash"] = mh
	}
	if b3 != "" {
		row["blake3"] = b3
	}
	if b3mh != "" {
		row["blake3_multihash"] = b3mh
	}

	if b, err := buildWithNode(row); err == nil && len(b) > 1000 {
		return b, nil
	}

	return buildFallbackGofpdf(in, docName, created, scope, merkle, lookup)
}

func buildWithNode(row map[string]any) ([]byte, error) {
	script := findBuildScript()
	if script == "" {
		return nil, fmt.Errorf("registration-pdf build.mjs not found")
	}
	tmp, err := os.MkdirTemp("", "verae-regpdf-*")
	if err != nil {
		return nil, err
	}
	defer os.RemoveAll(tmp)
	inPath := filepath.Join(tmp, "in.json")
	outPath := filepath.Join(tmp, "out.pdf")
	jb, err := json.Marshal(row)
	if err != nil {
		return nil, err
	}
	if err := os.WriteFile(inPath, jb, 0o600); err != nil {
		return nil, err
	}
	cmd := exec.Command("node", script, inPath, outPath)
	cmd.Dir = filepath.Dir(script)
	var stderr bytes.Buffer
	cmd.Stderr = &stderr
	if err := cmd.Run(); err != nil {
		return nil, fmt.Errorf("node build.mjs: %w (%s)", err, stderr.String())
	}
	return os.ReadFile(outPath)
}

func findBuildScript() string {
	// Prefer tree-local build.mjs (repo / package) so CERT-01 edits win over
	// a stale install under Application Support during tests and dev runs.
	var candidates []string
	if wd, err := os.Getwd(); err == nil {
		dir := wd
		for i := 0; i < 8; i++ {
			candidates = append(candidates, filepath.Join(dir, "platform", "registration-pdf", "build.mjs"))
			parent := filepath.Dir(dir)
			if parent == dir {
				break
			}
			dir = parent
		}
	}
	candidates = append(candidates, filepath.Join("platform", "registration-pdf", "build.mjs"))
	if exe, err := os.Executable(); err == nil {
		dir := filepath.Dir(exe)
		candidates = append(candidates,
			filepath.Join(dir, "registration-pdf", "build.mjs"),
			filepath.Join(dir, "..", "registration-pdf", "build.mjs"),
			filepath.Join(dir, "platform", "registration-pdf", "build.mjs"),
			filepath.Join(dir, "..", "platform", "registration-pdf", "build.mjs"),
			filepath.Join(dir, "..", "..", "platform", "registration-pdf", "build.mjs"),
		)
	}
	// Installed helper copy last (production path when no tree is present).
	// No machine-specific absolute research paths — packaging resolves via go.mod walk above.
	candidates = append(candidates,
		"/Library/Application Support/Verae/PrintStamp/registration-pdf/build.mjs",
	)
	for _, c := range candidates {
		if st, err := os.Stat(c); err == nil && !st.IsDir() {
			abs, _ := filepath.Abs(c)
			return abs
		}
	}
	return ""
}

// Ensure created stays empty when unknown — used by tests.
var _ = time.Now