package seo

import (
	"context"
	"fmt"
	"strings"

	"github.com/descrybe/descrybe-v2/apps/api/internal/aiprompts"
	"github.com/descrybe/descrybe-v2/apps/api/internal/company"
	"github.com/descrybe/descrybe-v2/apps/api/internal/processing"
)

// FillMetaTemplate builds meta title/description from product fields (free, rule-based).
func FillMetaTemplate(p ProductInput) (title, description string) {
	name := displayTitle(p)
	if name == "" {
		name = "Product"
	}
	cat := strings.TrimSpace(p.Category)
	brand := firstString(p.ProcessedAttrs, p.Attributes, p.MappedData, "brand", "Brand", "manufacturer")

	parts := make([]string, 0, 3)
	if brand != "" && !strings.Contains(strings.ToLower(name), strings.ToLower(brand)) {
		parts = append(parts, brand)
	}
	parts = append(parts, name)
	if cat != "" && !strings.Contains(strings.ToLower(name), strings.ToLower(cat)) {
		parts = append(parts, cat)
	}
	title = truncateRunes(strings.Join(parts, " | "), MetaTitleMaxChars)

	body := strings.TrimSpace(p.ProcessedDesc)
	if body == "" {
		body = strings.TrimSpace(p.Description)
	}
	body = stripTags(body)
	if body == "" {
		var bits []string
		if brand != "" {
			bits = append(bits, brand)
		}
		bits = append(bits, name)
		if cat != "" {
			bits = append(bits, "in "+cat)
		}
		body = strings.Join(bits, " ") + ". Shop quality products with clear specs and fast delivery."
	}
	description = truncateRunes(collapseSpace(body), MetaDescriptionMaxChars)
	return title, description
}

// FillMetaAI uses Completer to rewrite SEO meta (paid path).
func FillMetaAI(ctx context.Context, completer processing.Completer, p ProductInput, prompts aiprompts.Resolved) (title, description string, tokens int, err error) {
	if completer == nil {
		return "", "", 0, fmt.Errorf("ai completer not configured")
	}
	name := displayTitle(p)
	desc := strings.TrimSpace(p.ProcessedDesc)
	if desc == "" {
		desc = strings.TrimSpace(p.Description)
	}
	brand := firstString(p.ProcessedAttrs, p.Attributes, p.MappedData, "brand", "Brand", "manufacturer")
	sysTpl := strings.TrimSpace(prompts.SystemTemplate)
	userTpl := strings.TrimSpace(prompts.UserTemplate)
	if def, ok := aiprompts.DefaultFor(aiprompts.KeySEOMeta); ok {
		if sysTpl == "" {
			sysTpl = def.SystemTemplate
		}
		if userTpl == "" {
			userTpl = def.UserTemplate
		}
	}
	vars := aiprompts.Vars{
		"name":        name,
		"description": truncateRunes(desc, processing.MaxProductDescRunes),
		"category":    strings.TrimSpace(p.Category),
		"brand":       brand,
		"brand_voice": processing.CompactBrandPrompt(p.BrandPrompt),
		"language":    company.LanguageLabel(p.Language),
	}
	system := strings.TrimSpace(aiprompts.Render(sysTpl, vars))
	user := strings.TrimSpace(aiprompts.Render(userTpl, vars))
	if user == "" {
		user = fmt.Sprintf("Name: %s\nCategory: %s\nDesc: %s",
			name, p.Category, truncateRunes(desc, processing.MaxProductDescRunes))
	}

	comp, obj, cerr := processing.CompleteJSON(ctx, completer, system, user, processing.CompleteOptions{
		MaxTokens:   processing.MaxTokensSEO,
		Temperature: processing.DefaultStructuredTemp,
	})
	tokens = comp.TotalTokens
	if cerr != nil && obj == nil {
		if comp.Text == "" {
			return "", "", tokens, cerr
		}
		// Parse failed — fall back to template
		mt, md := FillMetaTemplate(p)
		return mt, md, tokens, nil
	}
	mt, md := metaFieldsFromObj(obj)
	if mt == "" || md == "" {
		t2, d2 := FillMetaTemplate(p)
		if mt == "" {
			mt = t2
		}
		if md == "" {
			md = d2
		}
	}
	return truncateRunes(mt, MetaTitleMaxChars), truncateRunes(md, MetaDescriptionMaxChars), tokens, nil
}

func metaFieldsFromObj(obj map[string]any) (title, desc string) {
	if obj == nil {
		return "", ""
	}
	title, _ = obj["meta_title"].(string)
	desc, _ = obj["meta_description"].(string)
	if title == "" {
		title, _ = obj["metaTitle"].(string)
	}
	if desc == "" {
		desc, _ = obj["metaDescription"].(string)
	}
	return strings.TrimSpace(title), strings.TrimSpace(desc)
}

func truncateRunes(s string, max int) string {
	s = collapseSpace(s)
	r := []rune(s)
	if max <= 0 || len(r) <= max {
		return s
	}
	if max <= 3 {
		return string(r[:max])
	}
	return string(r[:max-1]) + "…"
}

func collapseSpace(s string) string {
	return strings.Join(strings.Fields(s), " ")
}

func stripTags(s string) string {
	var b strings.Builder
	inTag := false
	for _, r := range s {
		switch {
		case r == '<':
			inTag = true
		case r == '>':
			inTag = false
		case !inTag:
			b.WriteRune(r)
		}
	}
	return b.String()
}