package main

import (
	"crypto/sha256"
	"database/sql"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"os"
	"regexp"
	"sort"
	"strings"
	"text/tabwriter"
)

// ClusterConfig controls the pattern clustering behaviour.
type ClusterConfig struct {
	MinOccurrences int
	LookbackDays   int
	Tools          []string // tool_used values to consider
}

// PatternCluster is one normalized cluster of inline snippets.
type PatternCluster struct {
	Hash           string
	Representative string
	Occurrences    int
	SessionIDs     []string
	FirstSeen      int64
	LastSeen       int64
}

var (
	reNumber  = regexp.MustCompile(`\b\d+\b`)
	reDQuoted = regexp.MustCompile(`"[^"]*"`)
	reSQuoted = regexp.MustCompile(`'[^']*'`)
	reSpaces  = regexp.MustCompile(`\s+`)
	rePath    = regexp.MustCompile(`/[A-Za-z0-9_./-]{6,}`)
	reHex     = regexp.MustCompile(`\b[0-9a-f]{8,}\b`)
)

// normalizeSnippet collapses noise (numbers, quoted strings, hex, paths,
// whitespace) so that semantically-equivalent snippets hash the same.
func normalizeSnippet(s string) string {
	s = strings.ToLower(s)
	s = reDQuoted.ReplaceAllString(s, `"STR"`)
	s = reSQuoted.ReplaceAllString(s, `'STR'`)
	s = rePath.ReplaceAllString(s, "/PATH")
	s = reHex.ReplaceAllString(s, "HEX")
	s = reNumber.ReplaceAllString(s, "N")
	s = reSpaces.ReplaceAllString(s, " ")
	return strings.TrimSpace(s)
}

func hashSnippet(norm string) string {
	sum := sha256.Sum256([]byte(norm))
	return hex.EncodeToString(sum[:8]) // 16 hex chars, enough collision room
}

// ClusterPatterns groups inline snippets (function_id='') by normalized hash,
// upserts the patterns table, and returns clusters with occurrences >= min.
func ClusterPatterns(db *sql.DB, cfg ClusterConfig) ([]PatternCluster, error) {
	if cfg.MinOccurrences <= 0 {
		cfg.MinOccurrences = 3
	}
	if cfg.LookbackDays <= 0 {
		cfg.LookbackDays = 30
	}
	if len(cfg.Tools) == 0 {
		cfg.Tools = []string{"heredoc_py", "heredoc_bash", "sqlite_direct", "bash_other"}
	}

	placeholders := make([]string, len(cfg.Tools))
	args := make([]any, 0, len(cfg.Tools)+1)
	for i, t := range cfg.Tools {
		placeholders[i] = "?"
		args = append(args, t)
	}
	args = append(args, cfg.LookbackDays)

	q := fmt.Sprintf(`
        SELECT command_snippet, session_id, ts
        FROM calls
        WHERE function_id = ''
          AND command_snippet != ''
          AND tool_used IN (%s)
          AND ts >= CAST(strftime('%%s', 'now', '-' || ? || ' days') AS INTEGER)
        ORDER BY ts ASC`,
		strings.Join(placeholders, ","))

	rows, err := db.Query(q, args...)
	if err != nil {
		return nil, fmt.Errorf("query calls: %w", err)
	}
	defer rows.Close()

	clusters := map[string]*PatternCluster{}
	sessionsSeen := map[string]map[string]struct{}{}

	for rows.Next() {
		var snippet, session string
		var ts int64
		if err := rows.Scan(&snippet, &session, &ts); err != nil {
			return nil, err
		}
		norm := normalizeSnippet(snippet)
		if norm == "" {
			continue
		}
		hash := hashSnippet(norm)
		c, ok := clusters[hash]
		if !ok {
			c = &PatternCluster{
				Hash:           hash,
				Representative: trim(snippet, 240),
				FirstSeen:      ts,
				LastSeen:       ts,
			}
			clusters[hash] = c
			sessionsSeen[hash] = map[string]struct{}{}
		}
		c.Occurrences++
		if ts > c.LastSeen {
			c.LastSeen = ts
		}
		if ts < c.FirstSeen {
			c.FirstSeen = ts
		}
		if session != "" {
			if _, seen := sessionsSeen[hash][session]; !seen {
				sessionsSeen[hash][session] = struct{}{}
				c.SessionIDs = append(c.SessionIDs, session)
			}
		}
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}

	out := make([]PatternCluster, 0, len(clusters))
	for _, c := range clusters {
		if c.Occurrences >= cfg.MinOccurrences {
			out = append(out, *c)
		}
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Occurrences > out[j].Occurrences })
	return out, nil
}

// UpsertPatterns writes clusters to the patterns table (idempotent).
func UpsertPatterns(db *sql.DB, clusters []PatternCluster) error {
	tx, err := db.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()

	stmt, err := tx.Prepare(`
        INSERT INTO patterns (pattern_hash, representative_snippet, occurrences,
                              session_ids_json, first_seen, last_seen, proposal_id)
        VALUES (?, ?, ?, ?, ?, ?, '')
        ON CONFLICT(pattern_hash) DO UPDATE SET
            occurrences = excluded.occurrences,
            session_ids_json = excluded.session_ids_json,
            last_seen = excluded.last_seen
    `)
	if err != nil {
		return err
	}
	defer stmt.Close()

	for _, c := range clusters {
		ids, _ := json.Marshal(c.SessionIDs)
		if _, err := stmt.Exec(
			c.Hash, c.Representative, c.Occurrences, string(ids),
			c.FirstSeen, c.LastSeen,
		); err != nil {
			return err
		}
	}
	return tx.Commit()
}

func splitCSV(s string) []string {
	out := []string{}
	for _, p := range strings.Split(s, ",") {
		p = strings.TrimSpace(p)
		if p != "" {
			out = append(out, p)
		}
	}
	return out
}

func trim(s string, max int) string {
	s = strings.TrimSpace(s)
	if len(s) <= max {
		return s
	}
	return s[:max]
}

// runClusterPatterns is the CLI entry point.
func runClusterPatterns(dbPath string, cfg ClusterConfig, persist, formatJSON bool) {
	db, err := openDB(dbPath)
	if err != nil {
		fmt.Fprintf(os.Stderr, "open db: %v\n", err)
		os.Exit(1)
	}
	defer db.Close()

	clusters, err := ClusterPatterns(db.conn, cfg)
	if err != nil {
		fmt.Fprintf(os.Stderr, "cluster: %v\n", err)
		os.Exit(1)
	}

	if persist {
		if err := UpsertPatterns(db.conn, clusters); err != nil {
			fmt.Fprintf(os.Stderr, "persist patterns: %v\n", err)
			os.Exit(1)
		}
	}

	if formatJSON {
		enc := json.NewEncoder(os.Stdout)
		enc.SetIndent("", "  ")
		enc.Encode(clusters)
		return
	}

	tw := tabwriter.NewWriter(os.Stdout, 0, 0, 2, ' ', 0)
	fmt.Fprintf(tw, "=== %d pattern clusters (min %d occurrences, last %dd) ===\n",
		len(clusters), cfg.MinOccurrences, cfg.LookbackDays)
	if len(clusters) == 0 {
		fmt.Fprintln(tw, "(no clusters found)")
		tw.Flush()
		return
	}
	fmt.Fprintln(tw, "HASH\tOCCURRENCES\tSESSIONS\tFIRST_SEEN\tLAST_SEEN\tSNIPPET")
	for _, c := range clusters {
		snippet := strings.ReplaceAll(c.Representative, "\n", "\\n")
		if len(snippet) > 70 {
			snippet = snippet[:70] + "..."
		}
		fmt.Fprintf(tw, "%s\t%d\t%d\t%d\t%d\t%s\n",
			c.Hash, c.Occurrences, len(c.SessionIDs),
			c.FirstSeen, c.LastSeen, snippet)
	}
	tw.Flush()

	if persist {
		fmt.Println()
		fmt.Printf("upserted %d clusters into patterns table\n", len(clusters))
	}
}