package main

import (
	"crypto/sha256"
	"database/sql"
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"text/tabwriter"
	"time"

	"fn-registry/functions/infra"
)

// SequenceConfig holds tunable parameters for sequence detection.
type SequenceConfig struct {
	WindowSecs     int // max gap between consecutive calls in same sequence
	LookbackDays   int // how far back to scan calls
	MinOccurrences int // minimum occurrences to be a candidate
	MinSessions    int // minimum distinct sessions to be a candidate
	MinSuccessRate float64
}

func defaultSequenceConfig() SequenceConfig {
	return SequenceConfig{
		WindowSecs:     30,
		LookbackDays:   30,
		MinOccurrences: 5,
		MinSessions:    2,
		MinSuccessRate: 0.9,
	}
}

// callRow is a single row from the calls table.
type callRow struct {
	ID         int64
	SessionID  string
	FunctionID string
	Success    int
	TS         int64
}

// seqKey is the canonical identifier for a sequence.
type seqKey struct {
	Hash        string   // sha256[:12] of joined function_ids
	FunctionIDs []string // ordered list
	Length      int
}

// seqStats accumulated across sessions.
type seqStats struct {
	Key          seqKey
	Occurrences  int
	Sessions     map[string]struct{} // distinct session_ids
	SuccessCount int                 // all calls in sequence succeeded
	FirstSeen    int64
	LastSeen     int64
}

// SequenceResult is the final merged record for a sequence.
type SequenceResult struct {
	SeqHash      string
	FunctionIDs  []string
	Length       int
	Occurrences  int
	SessionCount int
	SuccessCount int
	SuccessRate  float64
	FirstSeen    int64
	LastSeen     int64
}

// SequenceCandidate wraps SequenceResult with pipeline-promotion metadata.
type SequenceCandidate struct {
	SequenceResult
	SuggestedName  string
	CoveredBy      string // ID of existing pipeline that covers it, or ""
	ProposalExists bool   // true if a pending proposal already exists
}

// detectSequences reads calls from operations.db, computes sequences, upserts
// into function_sequences, and returns candidates for promotion.
func detectSequences(db *DB, cfg SequenceConfig) ([]SequenceResult, error) {
	cutoff := time.Now().Unix() - int64(cfg.LookbackDays)*86400

	rows, err := db.conn.Query(`
		SELECT id, session_id, function_id, success, ts
		FROM calls
		WHERE function_id != ''
		  AND session_id  != ''
		  AND ts >= ?
		ORDER BY session_id, ts`, cutoff)
	if err != nil {
		return nil, fmt.Errorf("query calls: %w", err)
	}
	defer rows.Close()

	var calls []callRow
	for rows.Next() {
		var c callRow
		if err := rows.Scan(&c.ID, &c.SessionID, &c.FunctionID, &c.Success, &c.TS); err != nil {
			return nil, err
		}
		calls = append(calls, c)
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}

	// Group by session.
	bySession := map[string][]callRow{}
	for _, c := range calls {
		bySession[c.SessionID] = append(bySession[c.SessionID], c)
	}

	// Accumulate sequence stats.
	statsMap := map[string]*seqStats{}

	for sessID, sessionCalls := range bySession {
		// Slide a window of 2 and 3 over consecutive calls within the time gap.
		for i := 0; i < len(sessionCalls); i++ {
			// Try length 2.
			if i+1 < len(sessionCalls) {
				c0, c1 := sessionCalls[i], sessionCalls[i+1]
				if c1.TS-c0.TS <= int64(cfg.WindowSecs) {
					ids := []string{c0.FunctionID, c1.FunctionID}
					acc(statsMap, ids, sessID, c0.Success == 1 && c1.Success == 1, c0.TS, c1.TS)
				}
			}
			// Try length 3.
			if i+2 < len(sessionCalls) {
				c0, c1, c2 := sessionCalls[i], sessionCalls[i+1], sessionCalls[i+2]
				if c1.TS-c0.TS <= int64(cfg.WindowSecs) && c2.TS-c1.TS <= int64(cfg.WindowSecs) {
					ids := []string{c0.FunctionID, c1.FunctionID, c2.FunctionID}
					acc(statsMap, ids, sessID, c0.Success == 1 && c1.Success == 1 && c2.Success == 1, c0.TS, c2.TS)
				}
			}
		}
	}

	// Upsert into function_sequences.
	if err := upsertSequences(db.conn, statsMap); err != nil {
		return nil, fmt.Errorf("upsert sequences: %w", err)
	}

	// Return all detected sequences as SequenceResult.
	results := make([]SequenceResult, 0, len(statsMap))
	for _, s := range statsMap {
		rate := 0.0
		if s.Occurrences > 0 {
			rate = float64(s.SuccessCount) / float64(s.Occurrences)
		}
		results = append(results, SequenceResult{
			SeqHash:      s.Key.Hash,
			FunctionIDs:  s.Key.FunctionIDs,
			Length:       s.Key.Length,
			Occurrences:  s.Occurrences,
			SessionCount: len(s.Sessions),
			SuccessCount: s.SuccessCount,
			SuccessRate:  rate,
			FirstSeen:    s.FirstSeen,
			LastSeen:     s.LastSeen,
		})
	}
	return results, nil
}

// filterCandidates applies promotion criteria to the full result set.
func filterCandidates(results []SequenceResult, cfg SequenceConfig) []SequenceResult {
	var out []SequenceResult
	for _, r := range results {
		if r.Occurrences >= cfg.MinOccurrences &&
			r.SessionCount >= cfg.MinSessions &&
			r.SuccessRate >= cfg.MinSuccessRate {
			out = append(out, r)
		}
	}
	return out
}

// enrichCandidates looks up registry.db to check if any existing pipeline
// covers the sequence and whether a pending proposal already exists.
func enrichCandidates(candidates []SequenceResult, registryRoot string) ([]SequenceCandidate, error) {
	regPath := filepath.Join(registryRoot, "registry.db")
	conn, err := sql.Open("sqlite3", regPath+"?_journal_mode=WAL")
	if err != nil {
		return nil, fmt.Errorf("open registry: %w", err)
	}
	defer conn.Close()

	// Load pipelines with their uses_functions.
	type pipe struct {
		ID           string
		UsesFunctions []string
	}
	prows, err := conn.Query("SELECT id, uses_functions FROM functions WHERE kind='pipeline' AND uses_functions != '[]'")
	if err != nil {
		return nil, fmt.Errorf("query pipelines: %w", err)
	}
	var pipelines []pipe
	for prows.Next() {
		var id, raw string
		if err := prows.Scan(&id, &raw); err != nil {
			continue
		}
		var ids []string
		_ = json.Unmarshal([]byte(raw), &ids)
		pipelines = append(pipelines, pipe{id, ids})
	}
	prows.Close()

	// Load existing pending proposals for seq_hash.
	pendingSeqs := map[string]struct{}{}
	propRows, err := conn.Query("SELECT evidence FROM proposals WHERE status='pending' AND kind='new_pipeline'")
	if err == nil {
		for propRows.Next() {
			var rawEvidence string
			if err := propRows.Scan(&rawEvidence); err != nil {
				continue
			}
			var ev map[string]any
			if err := json.Unmarshal([]byte(rawEvidence), &ev); err != nil {
				continue
			}
			if h, ok := ev["sequence_hash"].(string); ok {
				pendingSeqs[h] = struct{}{}
			}
		}
		propRows.Close()
	}

	out := make([]SequenceCandidate, 0, len(candidates))
	for _, c := range candidates {
		cand := SequenceCandidate{
			SequenceResult: c,
			SuggestedName:  suggestPipelineName(c.FunctionIDs),
		}

		// Check coverage: a pipeline covers the sequence if its uses_functions
		// contains all sequence function_ids as a subset.
		seqSet := map[string]struct{}{}
		for _, id := range c.FunctionIDs {
			seqSet[id] = struct{}{}
		}
		for _, p := range pipelines {
			pipeSet := map[string]struct{}{}
			for _, id := range p.UsesFunctions {
				pipeSet[id] = struct{}{}
			}
			covered := true
			for id := range seqSet {
				if _, ok := pipeSet[id]; !ok {
					covered = false
					break
				}
			}
			if covered {
				cand.CoveredBy = p.ID
				break
			}
		}

		if _, ok := pendingSeqs[c.SeqHash]; ok {
			cand.ProposalExists = true
		}

		out = append(out, cand)
	}
	return out, nil
}

// buildProposalsFromCandidates creates infra.ProposalDraft entries for uncovered,
// non-duplicate candidates.
func buildProposalsFromCandidates(candidates []SequenceCandidate) []infra.ProposalDraft {
	var drafts []infra.ProposalDraft
	for _, c := range candidates {
		if c.CoveredBy != "" || c.ProposalExists {
			continue
		}
		exampleSessions := []string{} // sessions not available at this point; seq_hash is enough
		evidence := map[string]any{
			"rule_id":        "sequence_promote",
			"sequence_hash":  c.SeqHash,
			"function_ids":   c.FunctionIDs,
			"occurrences":    c.Occurrences,
			"sessions_count": c.SessionCount,
			"success_rate":   fmt.Sprintf("%.2f", c.SuccessRate),
			"last_seen":      c.LastSeen,
			"first_seen":     c.FirstSeen,
			"session_ids":    exampleSessions,
			"lookback_days":  30,
		}
		title := fmt.Sprintf("Promote sequence %s to pipeline", joinArrow(c.FunctionIDs))
		desc := fmt.Sprintf(
			"Sequence `%s` appeared %d times across %d sessions "+
				"(success rate %.0f%%). Promote to pipeline `%s` to make it one-shot.",
			joinArrow(c.FunctionIDs), c.Occurrences, c.SessionCount, c.SuccessRate*100, c.SuggestedName,
		)
		drafts = append(drafts, infra.ProposalDraft{
			ID:          deterministicSeqID(c.SeqHash),
			Kind:        "new_pipeline",
			TargetID:    "",
			Title:       title,
			Description: desc,
			RuleID:      "sequence_promote",
			Evidence:    evidence,
		})
	}
	return drafts
}

// ---- Output helpers ----

func printSequenceReport(w *tabwriter.Writer, allResults []SequenceResult, candidates []SequenceCandidate, cfg SequenceConfig) {
	len2 := 0
	len3 := 0
	for _, r := range allResults {
		if r.Length == 2 {
			len2++
		} else {
			len3++
		}
	}

	fmt.Fprintf(w, "SEQUENCE DETECTION — window %ds, lookback %dd\n", cfg.WindowSecs, cfg.LookbackDays)
	fmt.Fprintln(w, "─────────────────────────────────────────────────")
	fmt.Fprintf(w, "Sequences found:\t%d\n", len(allResults))
	fmt.Fprintf(w, "  Length 2:\t%d\n", len2)
	fmt.Fprintf(w, "  Length 3:\t%d\n", len3)
	fmt.Fprintf(w, "Promotion candidates:\t%d\n", len(candidates))
	fmt.Fprintf(w, "  (occ >= %d, sess >= %d, success_rate >= %.0f%%)\n",
		cfg.MinOccurrences, cfg.MinSessions, cfg.MinSuccessRate*100)
	w.Flush()

	if len(candidates) == 0 {
		fmt.Println("\nNo promotion candidates yet.")
		return
	}

	fmt.Println("\nCANDIDATES:")
	for i, c := range candidates {
		ago := humanAgo(c.LastSeen)
		fmt.Printf("[%d] occ=%d sess=%d success=%.0f%% last=%s\n",
			i+1, c.Occurrences, c.SessionCount, c.SuccessRate*100, ago)
		for j, id := range c.FunctionIDs {
			if j == 0 {
				fmt.Printf("    %s\n", id)
			} else {
				fmt.Printf("     → %s\n", id)
			}
		}
		fmt.Printf("    Suggested pipeline name: %s\n", c.SuggestedName)
		if c.CoveredBy != "" {
			fmt.Printf("    Already covered by: %s ✓ SKIP\n", c.CoveredBy)
		} else if c.ProposalExists {
			fmt.Printf("    Pending proposal already exists → SKIP\n")
		} else {
			fmt.Printf("    NOT COVERED → proposal candidate\n")
		}
		fmt.Println()
	}
}

func printSequenceReportJSON(allResults []SequenceResult, candidates []SequenceCandidate, cfg SequenceConfig) error {
	out := map[string]any{
		"window_secs":           cfg.WindowSecs,
		"lookback_days":         cfg.LookbackDays,
		"min_occurrences":       cfg.MinOccurrences,
		"min_sessions":          cfg.MinSessions,
		"min_success_rate":      cfg.MinSuccessRate,
		"sequences_total":       len(allResults),
		"sequences_length_2":    countByLen(allResults, 2),
		"sequences_length_3":    countByLen(allResults, 3),
		"candidates_total":      len(candidates),
		"candidates":            candidates,
	}
	enc := json.NewEncoder(os.Stdout)
	enc.SetIndent("", "  ")
	return enc.Encode(out)
}

// ---- DB helpers ----

func upsertSequences(conn *sql.DB, statsMap map[string]*seqStats) error {
	tx, err := conn.Begin()
	if err != nil {
		return err
	}
	stmt, err := tx.Prepare(`
		INSERT INTO function_sequences
		    (seq_hash, function_ids, length, occurrences, sessions_count, success_count, first_seen, last_seen)
		VALUES (?, ?, ?, ?, ?, ?, ?, ?)
		ON CONFLICT(seq_hash) DO UPDATE SET
		    occurrences    = occurrences + excluded.occurrences,
		    sessions_count = MAX(sessions_count, excluded.sessions_count),
		    success_count  = success_count + excluded.success_count,
		    last_seen      = MAX(last_seen, excluded.last_seen),
		    first_seen     = MIN(first_seen, excluded.first_seen)`)
	if err != nil {
		_ = tx.Rollback()
		return err
	}
	defer stmt.Close()

	for _, s := range statsMap {
		raw, _ := json.Marshal(s.Key.FunctionIDs)
		_, err := stmt.Exec(
			s.Key.Hash,
			string(raw),
			s.Key.Length,
			s.Occurrences,
			len(s.Sessions),
			s.SuccessCount,
			s.FirstSeen,
			s.LastSeen,
		)
		if err != nil {
			_ = tx.Rollback()
			return err
		}
	}
	return tx.Commit()
}

// ---- Pure helpers ----

func seqHash(ids []string) string {
	key := strings.Join(ids, "|")
	h := sha256.Sum256([]byte(key))
	return fmt.Sprintf("%x", h)[:12]
}

func acc(m map[string]*seqStats, ids []string, sessID string, success bool, firstTS, lastTS int64) {
	h := seqHash(ids)
	s, ok := m[h]
	if !ok {
		cp := make([]string, len(ids))
		copy(cp, ids)
		s = &seqStats{
			Key:      seqKey{Hash: h, FunctionIDs: cp, Length: len(ids)},
			Sessions: map[string]struct{}{},
		}
		m[h] = s
	}
	s.Occurrences++
	s.Sessions[sessID] = struct{}{}
	if success {
		s.SuccessCount++
	}
	if s.FirstSeen == 0 || firstTS < s.FirstSeen {
		s.FirstSeen = firstTS
	}
	if lastTS > s.LastSeen {
		s.LastSeen = lastTS
	}
}

// suggestPipelineName derives a pipeline name from function IDs by extracting
// meaningful tokens and joining them.
func suggestPipelineName(ids []string) string {
	// Strip lang/domain suffix: "redeploy_cpp_app_windows_bash_infra" → "redeploy_cpp_app_windows"
	// Strategy: remove last two underscore-separated tokens if they look like lang/domain.
	langs := map[string]bool{"go": true, "py": true, "bash": true, "typescript": true}
	domains := map[string]bool{
		"core": true, "infra": true, "finance": true, "datascience": true,
		"cybersecurity": true, "shell": true, "tui": true, "pipelines": true,
		"browser": true, "notebook": true,
	}

	strip := func(id string) string {
		parts := strings.Split(id, "_")
		n := len(parts)
		if n >= 2 && langs[parts[n-1]] {
			parts = parts[:n-1]
			n--
		}
		if n >= 2 && domains[parts[n-1]] {
			parts = parts[:n-1]
		}
		return strings.Join(parts, "_")
	}

	tokens := make([]string, 0, len(ids))
	seen := map[string]bool{}
	for _, id := range ids {
		base := strip(id)
		// Take the first meaningful token (verb) from each.
		parts := strings.SplitN(base, "_", 2)
		verb := parts[0]
		if !seen[verb] {
			tokens = append(tokens, verb)
			seen[verb] = true
		}
		if len(tokens) < 3 {
			// Also add the full base but trimmed.
			if !seen[base] {
				seen[base] = true
			}
		}
	}
	// Build: first_second_third_bash_pipelines style.
	// Fallback: just join stripped names with _and_.
	stripped := make([]string, len(ids))
	for i, id := range ids {
		stripped[i] = strip(id)
	}
	return strings.Join(stripped, "_then_") + "_bash_pipelines"
}

func joinArrow(ids []string) string {
	return strings.Join(ids, " → ")
}

func humanAgo(ts int64) string {
	diff := time.Now().Unix() - ts
	if diff < 60 {
		return fmt.Sprintf("%ds ago", diff)
	}
	if diff < 3600 {
		return fmt.Sprintf("%dm ago", diff/60)
	}
	if diff < 86400 {
		return fmt.Sprintf("%dh ago", diff/3600)
	}
	return fmt.Sprintf("%dd ago", diff/86400)
}

func countByLen(results []SequenceResult, l int) int {
	n := 0
	for _, r := range results {
		if r.Length == l {
			n++
		}
	}
	return n
}

func deterministicSeqID(seqHash string) string {
	return "auto_seq_" + seqHash
}

// ---- CLI runner ----

func runSequences(
	dbPath string,
	detect bool,
	report bool,
	propose bool,
	formatJSON bool,
	rootOverride string,
	cfg SequenceConfig,
) {
	if !detect {
		fmt.Fprintln(os.Stderr, "sequences: specify --detect to run detection")
		os.Exit(2)
	}

	db, err := openDB(dbPath)
	if err != nil {
		fmt.Fprintf(os.Stderr, "error: open call_monitor db: %v\n", err)
		os.Exit(1)
	}
	defer db.Close()

	allResults, err := detectSequences(db, cfg)
	if err != nil {
		fmt.Fprintf(os.Stderr, "error: detect sequences: %v\n", err)
		os.Exit(1)
	}

	rawCandidates := filterCandidates(allResults, cfg)

	root := resolveRegistryRoot(rootOverride)
	var enriched []SequenceCandidate

	if _, err := os.Stat(filepath.Join(root, "registry.db")); err == nil {
		enriched, err = enrichCandidates(rawCandidates, root)
		if err != nil {
			// Non-fatal: report without enrichment.
			fmt.Fprintf(os.Stderr, "warning: enrich candidates: %v\n", err)
			for _, r := range rawCandidates {
				enriched = append(enriched, SequenceCandidate{SequenceResult: r, SuggestedName: suggestPipelineName(r.FunctionIDs)})
			}
		}
	} else {
		for _, r := range rawCandidates {
			enriched = append(enriched, SequenceCandidate{SequenceResult: r, SuggestedName: suggestPipelineName(r.FunctionIDs)})
		}
	}

	if report || !propose {
		if formatJSON {
			if err := printSequenceReportJSON(allResults, enriched, cfg); err != nil {
				fmt.Fprintf(os.Stderr, "error: json output: %v\n", err)
				os.Exit(1)
			}
		} else {
			tw := tabwriter.NewWriter(os.Stdout, 0, 0, 2, ' ', 0)
			printSequenceReport(tw, allResults, enriched, cfg)
		}
	}

	if propose {
		if _, err := os.Stat(filepath.Join(root, "registry.db")); err != nil {
			fmt.Fprintf(os.Stderr, "error: registry.db not found — cannot write proposals\n")
			os.Exit(1)
		}
		drafts := buildProposalsFromCandidates(enriched)
		if len(drafts) == 0 {
			fmt.Println("sequences --propose: no new proposals to write (all candidates covered or already pending).")
			return
		}
		inserted, total, err := infra.PersistProposalDrafts(root, drafts)
		if err != nil {
			fmt.Fprintf(os.Stderr, "error: persist proposals: %v\n", err)
			os.Exit(1)
		}
		fmt.Printf("sequences --propose: %d new proposals inserted (out of %d candidates)\n", inserted, total)
	}
}