package infra

import (
	"bufio"
	"database/sql"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strings"

	_ "github.com/mattn/go-sqlite3"
)

// CapabilityGroupAudit holds the audit result for a single capability group.
type CapabilityGroupAudit struct {
	Group           string   `json:"group"`            // slug del grupo (tag canonico)
	DeclaredInIndex bool     `json:"declared_in_index"` // aparece en docs/capabilities/INDEX.md
	DocExists       bool     `json:"doc_exists"`        // existe docs/capabilities/<group>.md
	FunctionCount   int      `json:"function_count"`    // funciones con ese tag en registry.db
	Issues          []string `json:"issues"`            // lista de problemas detectados
	OK              bool     `json:"ok"`                // true si Issues esta vacio
}

// indexLinkRe matches markdown links [slug](target.md). Go regexp has no
// backreferences, so we capture both sides and compare in code.
var indexLinkRe = regexp.MustCompile(`\[([a-z][a-z0-9_-]*)\]\(([a-z][a-z0-9_-]*)\.md\)`)

// AuditCapabilityGroups audits the drift between:
//  1. Groups declared in docs/capabilities/INDEX.md (parsed via link regex).
//  2. Tags present in functions.tags of registry.db (via json_each).
//  3. Doc pages existing as docs/capabilities/<group>.md on disk.
//
// Returns one CapabilityGroupAudit per group/candidate, ordered by Group ASC.
// Tags with count >= 3 that are not declared in INDEX are surfaced as
// "ungrouped_candidate". Doc files not listed in INDEX are surfaced as
// "doc_orphan".
func AuditCapabilityGroups(root string) ([]CapabilityGroupAudit, error) {
	// --- 1. Open registry.db (read-only) ---
	dbPath := filepath.Join(root, "registry.db")
	dsn := fmt.Sprintf("file:%s?mode=ro&_foreign_keys=on", dbPath)
	db, err := sql.Open("sqlite3", dsn)
	if err != nil {
		return nil, fmt.Errorf("audit_capability_groups: open db: %w", err)
	}
	defer db.Close()
	if err := db.Ping(); err != nil {
		return nil, fmt.Errorf("audit_capability_groups: ping db: %w", err)
	}

	// --- 2. Query all tags with their function counts ---
	tagCounts, err := queryTagCounts(db)
	if err != nil {
		return nil, fmt.Errorf("audit_capability_groups: query tags: %w", err)
	}

	// --- 3. Parse INDEX.md for declared group slugs ---
	indexPath := filepath.Join(root, "docs", "capabilities", "INDEX.md")
	indexSlugs, err := parseIndexSlugs(indexPath)
	if err != nil {
		return nil, fmt.Errorf("audit_capability_groups: parse INDEX.md: %w", err)
	}

	// --- 4. Scan docs/capabilities/ for existing .md files (excluding INDEX.md) ---
	capDir := filepath.Join(root, "docs", "capabilities")
	docSlugs, err := scanDocSlugs(capDir)
	if err != nil {
		return nil, fmt.Errorf("audit_capability_groups: scan docs: %w", err)
	}

	// --- 5. Build audit entries ---
	// We collect all relevant slugs: declared in INDEX, present as doc, or tags >= 3.
	allSlugs := make(map[string]struct{})
	for s := range indexSlugs {
		allSlugs[s] = struct{}{}
	}
	for s := range docSlugs {
		allSlugs[s] = struct{}{}
	}
	for tag, count := range tagCounts {
		if count >= 3 {
			allSlugs[tag] = struct{}{}
		}
	}

	results := make([]CapabilityGroupAudit, 0, len(allSlugs))
	for slug := range allSlugs {
		_, declaredInIndex := indexSlugs[slug]
		_, docExists := docSlugs[slug]
		count := tagCounts[slug]

		var issues []string
		if declaredInIndex {
			if !docExists {
				issues = append(issues, "doc_missing")
			}
			if count == 0 {
				issues = append(issues, "no_functions")
			} else if count < 3 {
				issues = append(issues, "below_minimum")
			}
		} else if docExists {
			// Doc exists but not in INDEX
			issues = append(issues, "doc_orphan")
		} else if count >= 3 {
			// Tag with enough functions but no declaration or doc
			issues = append(issues, "ungrouped_candidate")
		}

		results = append(results, CapabilityGroupAudit{
			Group:           slug,
			DeclaredInIndex: declaredInIndex,
			DocExists:       docExists,
			FunctionCount:   count,
			Issues:          issues,
			OK:              len(issues) == 0,
		})
	}

	sort.Slice(results, func(i, j int) bool {
		return results[i].Group < results[j].Group
	})

	return results, nil
}

// queryTagCounts returns a map of tag → function count using json_each on functions.tags.
func queryTagCounts(db *sql.DB) (map[string]int, error) {
	rows, err := db.Query(`
		SELECT j.value AS tag, COUNT(*) AS cnt
		FROM functions f, json_each(f.tags) j
		GROUP BY j.value
	`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	counts := make(map[string]int)
	for rows.Next() {
		var tag string
		var cnt int
		if err := rows.Scan(&tag, &cnt); err != nil {
			continue
		}
		counts[tag] = cnt
	}
	return counts, rows.Err()
}

// parseIndexSlugs reads INDEX.md and extracts group slugs from links of the
// form [slug](slug.md). Returns the set of declared slugs.
func parseIndexSlugs(indexPath string) (map[string]struct{}, error) {
	f, err := os.Open(indexPath)
	if err != nil {
		if os.IsNotExist(err) {
			// No INDEX.md — return empty set, not an error.
			return make(map[string]struct{}), nil
		}
		return nil, err
	}
	defer f.Close()

	slugs := make(map[string]struct{})
	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		line := scanner.Text()
		matches := indexLinkRe.FindAllStringSubmatch(line, -1)
		for _, m := range matches {
			// Self-referencing link only: [slug](slug.md), not external.
			label := strings.TrimSpace(m[1])
			target := strings.TrimSpace(m[2])
			if label != "" && label == target {
				slugs[label] = struct{}{}
			}
		}
	}
	return slugs, scanner.Err()
}

// scanDocSlugs returns the set of slugs that have a corresponding .md file in
// capDir, excluding INDEX.md itself.
func scanDocSlugs(capDir string) (map[string]struct{}, error) {
	entries, err := os.ReadDir(capDir)
	if err != nil {
		if os.IsNotExist(err) {
			return make(map[string]struct{}), nil
		}
		return nil, err
	}

	slugs := make(map[string]struct{})
	for _, e := range entries {
		if e.IsDir() {
			continue
		}
		name := e.Name()
		if !strings.HasSuffix(name, ".md") {
			continue
		}
		slug := strings.TrimSuffix(name, ".md")
		if slug == "INDEX" {
			continue
		}
		slugs[slug] = struct{}{}
	}
	return slugs, nil
}