package main

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"strings"
	"time"
)

const queryTimeout = 5 * time.Second

// Server holds the HTTP handlers and DB pool.
type Server struct {
	pool *DBPool
}

func NewServer(pool *DBPool) *Server {
	return &Server{pool: pool}
}

// Routes registers all API routes on the given mux.
func (s *Server) Routes(mux *http.ServeMux) {
	mux.HandleFunc("GET /health", s.handleHealth)
	mux.HandleFunc("GET /api/databases", s.handleDatabases)
	mux.HandleFunc("GET /api/databases/{db}/tables", s.handleTables)
	mux.HandleFunc("GET /api/databases/{db}/schema", s.handleSchema)
	mux.HandleFunc("POST /api/databases/{db}/query", s.handleQuery)
	mux.HandleFunc("GET /api/databases/{db}/fts", s.handleFTS)
}

func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

func (s *Server) handleDatabases(w http.ResponseWriter, r *http.Request) {
	entries := s.pool.List()
	type dbInfo struct {
		Alias string `json:"alias"`
		Kind  string `json:"kind"`
	}
	out := make([]dbInfo, len(entries))
	for i, e := range entries {
		out[i] = dbInfo{Alias: e.Alias, Kind: e.Kind}
	}
	writeJSON(w, http.StatusOK, out)
}

func (s *Server) handleTables(w http.ResponseWriter, r *http.Request) {
	dbAlias := resolveDBAlias(r.PathValue("db"))
	db, err := s.pool.Get(dbAlias)
	if err != nil {
		writeError(w, http.StatusNotFound, err.Error())
		return
	}

	ctx, cancel := context.WithTimeout(r.Context(), queryTimeout)
	defer cancel()

	rows, err := db.QueryContext(ctx, "SELECT type, name FROM sqlite_master WHERE type IN ('table','view') ORDER BY type, name")
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}
	defer rows.Close()

	type tableInfo struct {
		Type string `json:"type"`
		Name string `json:"name"`
	}
	var tables []tableInfo
	for rows.Next() {
		var t tableInfo
		if err := rows.Scan(&t.Type, &t.Name); err != nil {
			writeError(w, http.StatusInternalServerError, err.Error())
			return
		}
		tables = append(tables, t)
	}
	if tables == nil {
		tables = []tableInfo{}
	}
	writeJSON(w, http.StatusOK, tables)
}

func (s *Server) handleSchema(w http.ResponseWriter, r *http.Request) {
	dbAlias := resolveDBAlias(r.PathValue("db"))
	db, err := s.pool.Get(dbAlias)
	if err != nil {
		writeError(w, http.StatusNotFound, err.Error())
		return
	}

	ctx, cancel := context.WithTimeout(r.Context(), queryTimeout)
	defer cancel()

	rows, err := db.QueryContext(ctx, "SELECT sql FROM sqlite_master WHERE sql IS NOT NULL ORDER BY type, name")
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}
	defer rows.Close()

	var statements []string
	for rows.Next() {
		var stmt string
		if err := rows.Scan(&stmt); err != nil {
			writeError(w, http.StatusInternalServerError, err.Error())
			return
		}
		statements = append(statements, stmt)
	}
	writeJSON(w, http.StatusOK, map[string]any{
		"statements": statements,
		"count":      len(statements),
	})
}

func (s *Server) handleQuery(w http.ResponseWriter, r *http.Request) {
	dbAlias := resolveDBAlias(r.PathValue("db"))
	db, err := s.pool.Get(dbAlias)
	if err != nil {
		writeError(w, http.StatusNotFound, err.Error())
		return
	}

	var req struct {
		SQL string `json:"sql"`
	}
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid JSON body")
		return
	}
	if req.SQL == "" {
		writeError(w, http.StatusBadRequest, "sql field is required")
		return
	}
	if err := ValidateQuery(req.SQL); err != nil {
		writeError(w, http.StatusBadRequest, err.Error())
		return
	}

	ctx, cancel := context.WithTimeout(r.Context(), queryTimeout)
	defer cancel()

	start := time.Now()
	rows, err := db.QueryContext(ctx, req.SQL)
	if err != nil {
		writeError(w, http.StatusBadRequest, err.Error())
		return
	}
	defer rows.Close()

	columns, err := rows.Columns()
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}

	var resultRows [][]any
	for rows.Next() {
		vals := make([]any, len(columns))
		ptrs := make([]any, len(columns))
		for i := range vals {
			ptrs[i] = &vals[i]
		}
		if err := rows.Scan(ptrs...); err != nil {
			writeError(w, http.StatusInternalServerError, err.Error())
			return
		}
		// Convert []byte to string for JSON serialization.
		for i, v := range vals {
			if b, ok := v.([]byte); ok {
				vals[i] = string(b)
			}
		}
		resultRows = append(resultRows, vals)
	}
	if resultRows == nil {
		resultRows = [][]any{}
	}

	durationMs := time.Since(start).Milliseconds()
	writeJSON(w, http.StatusOK, map[string]any{
		"columns":     columns,
		"rows":        resultRows,
		"count":       len(resultRows),
		"duration_ms": durationMs,
	})
}

func (s *Server) handleFTS(w http.ResponseWriter, r *http.Request) {
	dbAlias := resolveDBAlias(r.PathValue("db"))
	db, err := s.pool.Get(dbAlias)
	if err != nil {
		writeError(w, http.StatusNotFound, err.Error())
		return
	}

	q := r.URL.Query().Get("q")
	if q == "" {
		writeError(w, http.StatusBadRequest, "q parameter is required")
		return
	}

	table := r.URL.Query().Get("table")
	if table == "" {
		table = "functions"
	}

	// Map table to its FTS table and columns to return.
	ftsTable := table + "_fts"
	var selectCols string
	switch table {
	case "functions":
		selectCols = "id, name, kind, purity, domain, description"
	case "types":
		selectCols = "id, name, algebraic, domain, description"
	case "unit_tests":
		selectCols = "id, name, function_id, lang"
	default:
		writeError(w, http.StatusBadRequest, fmt.Sprintf("unsupported FTS table: %s", table))
		return
	}

	limit := r.URL.Query().Get("limit")
	if limit == "" {
		limit = "20"
	}

	query := fmt.Sprintf(
		"SELECT %s FROM %s WHERE id IN (SELECT id FROM %s WHERE %s MATCH ?) LIMIT %s",
		selectCols, table, ftsTable, ftsTable, limit,
	)

	ctx, cancel := context.WithTimeout(r.Context(), queryTimeout)
	defer cancel()

	start := time.Now()
	rows, err := db.QueryContext(ctx, query, q)
	if err != nil {
		writeError(w, http.StatusBadRequest, err.Error())
		return
	}
	defer rows.Close()

	columns, err := rows.Columns()
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}

	var resultRows [][]any
	for rows.Next() {
		vals := make([]any, len(columns))
		ptrs := make([]any, len(columns))
		for i := range vals {
			ptrs[i] = &vals[i]
		}
		if err := rows.Scan(ptrs...); err != nil {
			writeError(w, http.StatusInternalServerError, err.Error())
			return
		}
		for i, v := range vals {
			if b, ok := v.([]byte); ok {
				vals[i] = string(b)
			}
		}
		resultRows = append(resultRows, vals)
	}
	if resultRows == nil {
		resultRows = [][]any{}
	}

	durationMs := time.Since(start).Milliseconds()
	writeJSON(w, http.StatusOK, map[string]any{
		"columns":     columns,
		"rows":        resultRows,
		"count":       len(resultRows),
		"duration_ms": durationMs,
	})
}

// resolveDBAlias converts URL path segment to pool alias.
// "registry" → "registry", "ops:app_name" → "ops:app_name"
// URL-encoded colons: "ops%3Aapp_name" → already decoded by net/http.
func resolveDBAlias(raw string) string {
	return raw
}

// CORS middleware for browser access.
func corsMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Access-Control-Allow-Origin", "*")
		w.Header().Set("Access-Control-Allow-Methods", "GET, POST, OPTIONS")
		w.Header().Set("Access-Control-Allow-Headers", "Content-Type")
		if r.Method == http.MethodOptions {
			w.WriteHeader(http.StatusNoContent)
			return
		}
		next.ServeHTTP(w, r)
	})
}

func writeJSON(w http.ResponseWriter, status int, data any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	json.NewEncoder(w).Encode(data)
}

func writeError(w http.ResponseWriter, status int, msg string) {
	writeJSON(w, status, map[string]string{"error": msg})
}

// sanitizeFTS escapes special FTS5 characters in user input.
func sanitizeFTS(input string) string {
	// Wrap each term in double quotes to treat as literal.
	terms := strings.Fields(input)
	for i, t := range terms {
		terms[i] = `"` + strings.ReplaceAll(t, `"`, `""`) + `"`
	}
	return strings.Join(terms, " ")
}