package seahorse

import (
	"context"
	"database/sql"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"sync"

	_ "modernc.org/sqlite"

	"github.com/sipeed/picoclaw/pkg/logger"
)

// Config holds engine configuration.
type Config struct {
	DBPath                   string   `json:"dbPath"`
	IgnoreSessionPatterns    []string `json:"ignoreSessionPatterns,omitempty"`
	StatelessSessionPatterns []string `json:"statelessSessionPatterns,omitempty"`
}

// CompleteFn is the LLM completion function type.
type CompleteFn func(ctx context.Context, prompt string, opts CompleteOptions) (string, error)

// CompleteOptions holds LLM completion parameters.
type CompleteOptions struct {
	Model       string
	MaxTokens   int
	Temperature float64
}

// IngestResult is the result of message ingestion.
type IngestResult struct {
	MessageCount int `json:"messageCount"`
	TokenCount   int `json:"tokenCount"`
}

// AssembleInput controls context assembly.
type AssembleInput struct {
	Budget int    `json:"budget"`
	Query  string `json:"query,omitempty"`
}

// AssembleResult contains assembled context.
type AssembleResult struct {
	Messages []Message `json:"messages"`
	Summary  string    `json:"summary"` // formatted XML summaries + system prompt addition
}

const numSessionShards = 256

// Engine is the main short-term memory engine.
type Engine struct {
	store             *Store
	compaction        *CompactionEngine
	compactionMu      sync.Mutex
	assembler         *Assembler
	assemblerMu       sync.Mutex
	retrieval         *RetrievalEngine
	config            Config
	complete          CompleteFn
	ignorePatterns    []*regexp.Regexp
	statelessPatterns []*regexp.Regexp
	sessionShards     [numSessionShards]struct {
		mu sync.Mutex
	}
}

// CompactionEngine handles LLM-based summarization (defined in short_compaction.go).
type CompactionEngine struct {
	store          *Store
	config         Config
	complete       CompleteFn
	condensing     sync.Map // map[int64]struct{} — dedup for async condensed goroutines
	shutdownCtx    context.Context
	shutdownCancel context.CancelFunc
}

// Assembler handles budget-aware context assembly (defined in short_assembler.go).
type Assembler struct {
	store  *Store
	config Config
}

// RetrievalEngine handles search and expansion (defined in short_retrieval.go).
type RetrievalEngine struct {
	store  *Store
	config Config
}

// Store returns the underlying store for direct access.
func (r *RetrievalEngine) Store() *Store {
	return r.store
}

// NewEngine creates a new short-term memory engine.
func NewEngine(config Config, completeFn CompleteFn) (*Engine, error) {
	dir := filepath.Dir(config.DBPath)
	if dir != "" && dir != "." {
		if err := os.MkdirAll(dir, 0o755); err != nil {
			return nil, fmt.Errorf("create db directory: %w", err)
		}
	}

	db, err := sql.Open("sqlite", config.DBPath)
	if err != nil {
		return nil, fmt.Errorf("open db: %w", err)
	}

	// Configure SQLite for concurrent access
	if _, err := db.Exec("PRAGMA journal_mode = WAL;"); err != nil {
		db.Close()
		return nil, fmt.Errorf("enable WAL: %w", err)
	}
	if _, err := db.Exec("PRAGMA busy_timeout = 5000;"); err != nil {
		db.Close()
		return nil, fmt.Errorf("set busy_timeout: %w", err)
	}
	if _, err := db.Exec("PRAGMA synchronous = NORMAL;"); err != nil {
		db.Close()
		return nil, fmt.Errorf("set synchronous: %w", err)
	}

	if err := runSchema(db); err != nil {
		db.Close()
		return nil, fmt.Errorf("migrations: %w", err)
	}

	store := &Store{db: db}

	// Prepend hardcoded ignore patterns (spec lines 1326-1328)
	ignorePatterns := make([]string, 0, 1+len(config.IgnoreSessionPatterns))
	ignorePatterns = append(ignorePatterns, "heartbeat")
	ignorePatterns = append(ignorePatterns, config.IgnoreSessionPatterns...)

	retrieval := &RetrievalEngine{store: store, config: config}

	return &Engine{
		store:             store,
		compaction:        nil,
		assembler:         nil,
		retrieval:         retrieval,
		config:            config,
		complete:          completeFn,
		ignorePatterns:    compileSessionPatterns(ignorePatterns),
		statelessPatterns: compileSessionPatterns(config.StatelessSessionPatterns),
	}, nil
}

// compileSessionPattern converts a glob pattern to a compiled regex.
// Pattern rules:
//   - *  matches any sequence of non-colon characters ([^:]*)
//   - ** matches any sequence of characters including colons (.*)
//   - All other characters are treated literally
//   - Pattern is anchored (^...$)
func compileSessionPattern(pattern string) *regexp.Regexp {
	var b strings.Builder
	b.WriteByte('^')

	i := 0
	for i < len(pattern) {
		if i+1 < len(pattern) && pattern[i] == '*' && pattern[i+1] == '*' {
			b.WriteString(".*")
			i += 2
			continue
		}
		if pattern[i] == '*' {
			b.WriteString("[^:]*")
			i++
			continue
		}
		b.WriteString(regexp.QuoteMeta(string(pattern[i])))
		i++
	}

	b.WriteByte('$')
	return regexp.MustCompile(b.String())
}

// compileSessionPatterns compiles multiple glob patterns into regex patterns.
func compileSessionPatterns(patterns []string) []*regexp.Regexp {
	result := make([]*regexp.Regexp, 0, len(patterns))
	for _, p := range patterns {
		if p == "" {
			continue
		}
		result = append(result, compileSessionPattern(p))
	}
	return result
}

// shouldIgnoreSession returns true if the session key matches any ignore pattern.
func (e *Engine) shouldIgnoreSession(sessionKey string) bool {
	for _, p := range e.ignorePatterns {
		if p.MatchString(sessionKey) {
			return true
		}
	}
	return false
}

// isStatelessSession returns true if the session key matches any stateless pattern.
func (e *Engine) isStatelessSession(sessionKey string) bool {
	for _, p := range e.statelessPatterns {
		if p.MatchString(sessionKey) {
			return true
		}
	}
	return false
}

// fnv32 computes FNV-1a 32-bit hash for session key sharding.
func fnv32(key string) uint32 {
	h := uint32(2166136261)
	for _, c := range key {
		h ^= uint32(c)
		h *= 16777619
	}
	return h
}

// getSessionMutex returns the sharded mutex for a session key.
func (e *Engine) getSessionMutex(sessionKey string) *sync.Mutex {
	h := fnv32(sessionKey)
	shard := h % numSessionShards
	return &e.sessionShards[shard].mu
}

// Ingest adds messages to a conversation identified by sessionKey.
func (e *Engine) Ingest(ctx context.Context, sessionKey string, messages []Message) (*IngestResult, error) {
	if e.shouldIgnoreSession(sessionKey) {
		return nil, nil
	}
	if e.isStatelessSession(sessionKey) {
		return nil, nil
	}

	mu := e.getSessionMutex(sessionKey)
	mu.Lock()
	defer mu.Unlock()

	conv, err := e.store.GetOrCreateConversation(ctx, sessionKey)
	if err != nil {
		return nil, fmt.Errorf("get conversation: %w", err)
	}

	var totalTokens int
	var msgIDs []int64
	for _, msg := range messages {
		var added *Message
		var err error
		if len(msg.Parts) > 0 {
			added, err = e.store.AddMessageWithParts(ctx, conv.ConversationID, msg.Role, msg.Parts, msg.TokenCount)
		} else {
			added, err = e.store.AddMessage(ctx, conv.ConversationID, msg.Role, msg.Content, msg.TokenCount)
		}
		if err != nil {
			return nil, fmt.Errorf("add message: %w", err)
		}
		totalTokens += msg.TokenCount
		msgIDs = append(msgIDs, added.ID)
	}

	// Append to context_items using actual inserted IDs
	if err := e.store.AppendContextMessages(ctx, conv.ConversationID, msgIDs); err != nil {
		return nil, fmt.Errorf("append context: %w", err)
	}

	logger.InfoCF("seahorse", "ingest", map[string]any{
		"conv_id":  conv.ConversationID,
		"messages": len(messages),
		"tokens":   totalTokens,
	})
	return &IngestResult{
		MessageCount: len(messages),
		TokenCount:   totalTokens,
	}, nil
}

// Close releases resources.
func (e *Engine) Close() error {
	// Signal compaction goroutines to stop
	if e.compaction != nil {
		e.compaction.Close()
	}
	if e.store != nil && e.store.db != nil {
		return e.store.db.Close()
	}
	return nil
}

// GetRetrieval returns the retrieval engine for tool implementations.
func (e *Engine) GetRetrieval() *RetrievalEngine {
	return e.retrieval
}

// Assemble builds budget-constrained context for a session.
func (e *Engine) Assemble(ctx context.Context, sessionKey string, input AssembleInput) (*AssembleResult, error) {
	if e.shouldIgnoreSession(sessionKey) {
		return nil, nil
	}

	conv, err := e.store.GetOrCreateConversation(ctx, sessionKey)
	if err != nil {
		return nil, fmt.Errorf("get conversation: %w", err)
	}

	e.initAssemblerOnce()
	return e.assembler.Assemble(ctx, conv.ConversationID, input)
}

// Compact compresses conversation history for a session.
func (e *Engine) Compact(ctx context.Context, sessionKey string, input CompactInput) (*CompactResult, error) {
	if e.shouldIgnoreSession(sessionKey) || e.isStatelessSession(sessionKey) {
		return &CompactResult{}, nil
	}

	conv, err := e.store.GetOrCreateConversation(ctx, sessionKey)
	if err != nil {
		return nil, fmt.Errorf("get conversation: %w", err)
	}

	e.initCompactionOnce()
	return e.compaction.Compact(ctx, conv.ConversationID, input)
}

// CompactUntilUnder aggressively compacts until context is under budget.
// Used for emergency compaction after LLM overflow (retry reason).
func (e *Engine) CompactUntilUnder(ctx context.Context, sessionKey string, budget int) (*CompactResult, error) {
	if e.shouldIgnoreSession(sessionKey) || e.isStatelessSession(sessionKey) {
		return &CompactResult{}, nil
	}

	conv, err := e.store.GetOrCreateConversation(ctx, sessionKey)
	if err != nil {
		return nil, fmt.Errorf("get conversation: %w", err)
	}

	e.initCompactionOnce()
	return e.compaction.CompactUntilUnder(ctx, conv.ConversationID, budget)
}

// initCompactionOnce lazily initializes the compaction engine.
func (e *Engine) initCompactionOnce() {
	if e.compaction == nil {
		e.compactionMu.Lock()
		defer e.compactionMu.Unlock()
		if e.compaction == nil {
			shutdownCtx, shutdownCancel := context.WithCancel(context.Background())
			e.compaction = &CompactionEngine{
				store:          e.store,
				config:         e.config,
				complete:       e.complete,
				shutdownCtx:    shutdownCtx,
				shutdownCancel: shutdownCancel,
			}
		}
	}
}

// initAssemblerOnce lazily initializes the assembler.
func (e *Engine) initAssemblerOnce() {
	if e.assembler == nil {
		e.assemblerMu.Lock()
		defer e.assemblerMu.Unlock()
		if e.assembler == nil {
			e.assembler = &Assembler{store: e.store, config: e.config}
		}
	}
}

// IngestMessages is an alias for Ingest.
func (e *Engine) IngestMessages(ctx context.Context, sessionKey string, messages []Message) (*IngestResult, error) {
	return e.Ingest(ctx, sessionKey, messages)
}

// ClearSession removes all stored data for a session (messages, summaries, context).
// If the session has no prior seahorse record, it is a no-op.
func (e *Engine) ClearSession(ctx context.Context, sessionKey string) error {
	conv, err := e.store.GetConversationBySessionKey(ctx, sessionKey)
	if err != nil {
		return err
	}
	if conv == nil {
		return nil // session never ingested, nothing to clear
	}
	return e.store.ClearConversation(ctx, conv.ConversationID)
}

// Bootstrap reconciles a session's messages with the database.
// Called once at startup for each known session.
// Bootstrap reconciles JSONL history with SQLite by ingesting only the delta.
// Simple approach: find longest matching prefix and append delta.
// If any mismatch is detected, clear and rebuild.
func (e *Engine) Bootstrap(ctx context.Context, sessionKey string, messages []Message) error {
	if e.shouldIgnoreSession(sessionKey) {
		return nil
	}
	if e.isStatelessSession(sessionKey) {
		return nil
	}
	if len(messages) == 0 {
		return nil
	}

	conv, err := e.store.GetOrCreateConversation(ctx, sessionKey)
	if err != nil {
		return fmt.Errorf("bootstrap: get conversation: %w", err)
	}

	// Get messages already in DB
	dbMsgs, err := e.store.GetMessages(ctx, conv.ConversationID, len(messages), 0)
	if err != nil {
		return fmt.Errorf("bootstrap: get messages: %w", err)
	}

	// Fast path: DB has same count and exact match → no-op
	if len(dbMsgs) == len(messages) {
		matched := true
		for i := 0; i < len(messages); i++ {
			if !messageMatches(dbMsgs[i], messages[i]) {
				matched = false
				break
			}
		}
		if matched {
			return nil // DB is up to date
		}
	}

	// Find longest matching prefix from the start
	anchor := -1
	compareLen := len(dbMsgs)
	if compareLen > len(messages) {
		compareLen = len(messages)
	}

	for i := 0; i < compareLen; i++ {
		if messageMatches(dbMsgs[i], messages[i]) {
			anchor = i
		} else {
			// Mismatch detected - log details and rebuild
			logger.InfoCF("seahorse", "bootstrap: mismatch detected", map[string]any{
				"conv_id":     conv.ConversationID,
				"index":       i,
				"db_role":     dbMsgs[i].Role,
				"db_content":  truncate(dbMsgs[i].Content, 50),
				"db_parts":    len(dbMsgs[i].Parts),
				"msg_role":    messages[i].Role,
				"msg_content": truncate(messages[i].Content, 50),
				"msg_parts":   len(messages[i].Parts),
			})
			break
		}
	}

	// If we hit a mismatch before reaching the end of DB messages, delete delta and re-ingest
	// Note: anchor can be -1 if first message didn't match (history completely changed)
	if anchor >= 0 && anchor < len(dbMsgs)-1 && len(dbMsgs) > 0 {
		anchorID := dbMsgs[anchor].ID
		logger.InfoCF("seahorse", "bootstrap: history edit detected", map[string]any{
			"conv_id":     conv.ConversationID,
			"db_count":    len(dbMsgs),
			"anchor":      anchor,
			"anchor_id":   anchorID,
			"msg_count":   len(messages),
			"delta_start": anchor + 1,
		})

		// Delete messages after anchor (also clears context_items)
		if err := e.store.DeleteMessagesAfterID(ctx, conv.ConversationID, anchorID); err != nil {
			return fmt.Errorf("bootstrap: delete messages: %w", err)
		}

		// Re-ingest from anchor+1 to end
		delta := messages[anchor+1:]
		if len(delta) > 0 {
			_, err := e.Ingest(ctx, sessionKey, delta)
			if err != nil {
				return fmt.Errorf("bootstrap: re-ingest: %w", err)
			}
		}
		return nil
	}

	// Normal case: append delta after anchor
	if anchor >= 0 && anchor < len(messages)-1 {
		delta := messages[anchor+1:]
		if len(delta) > 0 {
			_, err := e.Ingest(ctx, sessionKey, delta)
			if err != nil {
				return fmt.Errorf("bootstrap: ingest delta: %w", err)
			}
		}
	} else if anchor == -1 && len(dbMsgs) > 0 {
		// First message changed (history completely different) - rebuild from scratch
		logger.InfoCF("seahorse", "bootstrap: history replaced, rebuilding", map[string]any{
			"conv_id":   conv.ConversationID,
			"db_count":  len(dbMsgs),
			"msg_count": len(messages),
		})
		// Delete all existing messages
		if err := e.store.DeleteMessagesAfterID(ctx, conv.ConversationID, 0); err != nil {
			return fmt.Errorf("bootstrap: delete all messages: %w", err)
		}
		// Re-ingest everything
		if len(messages) > 0 {
			_, err := e.Ingest(ctx, sessionKey, messages)
			if err != nil {
				return fmt.Errorf("bootstrap: re-ingest all: %w", err)
			}
		}
	} else if anchor == -1 && len(dbMsgs) == 0 {
		// DB is empty, ingest everything
		_, err := e.Ingest(ctx, sessionKey, messages)
		if err != nil {
			return fmt.Errorf("bootstrap: ingest all: %w", err)
		}
	}

	return nil
}

// truncate shortens a string for logging.
func truncate(s string, maxLen int) string {
	if len(s) <= maxLen {
		return s
	}
	return s[:maxLen] + "..."
}

// messageMatches compares two messages using (role, content) or (role, parts).
// TokenCount is NOT compared because it may be re-estimated differently
// during bootstrap (e.g., via tokenizer.EstimateMessageTokens).
// For messages with Parts (tool_use, tool_result), compare Parts instead of Content
// since AddMessageWithParts stores empty Content in DB.
func messageMatches(a, b Message) bool {
	if a.Role != b.Role {
		return false
	}
	// If either message has Parts, compare Parts
	if len(a.Parts) > 0 || len(b.Parts) > 0 {
		return partsMatch(a.Parts, b.Parts)
	}
	// Simple text messages: compare Content
	return a.Content == b.Content
}

// partsMatch compares two slices of MessagePart for equality.
func partsMatch(a, b []MessagePart) bool {
	if len(a) != len(b) {
		return false
	}
	for i := range a {
		if a[i].Type != b[i].Type {
			return false
		}
		switch a[i].Type {
		case "text":
			if a[i].Text != b[i].Text {
				return false
			}
		case "tool_use":
			if a[i].Name != b[i].Name || a[i].Arguments != b[i].Arguments || a[i].ToolCallID != b[i].ToolCallID {
				return false
			}
		case "tool_result":
			if a[i].ToolCallID != b[i].ToolCallID || a[i].Text != b[i].Text {
				return false
			}
		case "media":
			if a[i].MediaURI != b[i].MediaURI || a[i].MimeType != b[i].MimeType {
				return false
			}
		}
	}
	return true
}