package api

import (
	"context"
	"encoding/json"
	"io"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"sync"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"
	"github.com/pys/pdf-count/internal/config"
	"github.com/pys/pdf-count/internal/domain"
	"github.com/pys/pdf-count/internal/model"
	"github.com/pys/pdf-count/internal/ocr"
	"github.com/pys/pdf-count/internal/pipeline"
	"gopkg.in/yaml.v3"
)

// Server holds the shared, stateless dependencies of the count-api.
type Server struct {
	cfg       config.Config
	predictor *model.Predictor // nil → heuristic fallback
	ocrEngine *ocr.Engine
	openAPI   []byte
}

// NewServer constructs a Server. predictor may be nil when the ONNX model is
// unavailable; the pipeline will fall back to a counting heuristic.
func NewServer(
	cfg config.Config,
	predictor *model.Predictor,
	ocrEngine *ocr.Engine,
	openAPI []byte,
) *Server {
	return &Server{
		cfg:       cfg,
		predictor: predictor,
		ocrEngine: ocrEngine,
		openAPI:   openAPI,
	}
}

// Router registers all HTTP routes.
func (s *Server) Router() http.Handler {
	r := chi.NewRouter()
	r.Use(middleware.RequestID)
	r.Use(middleware.RealIP)
	r.Use(middleware.Logger)
	r.Use(middleware.Recoverer)

	r.Get("/health", s.health)
	r.Get("/ready", s.ready)
	r.Get("/openapi.json", s.openAPIHandler)

	r.Route("/v1", func(r chi.Router) {
		r.Post("/count", s.countSync)
	})

	return r
}

// health returns a simple liveness response.
func (s *Server) health(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

// ready returns 200 once the server is accepting traffic (always ready after init).
func (s *Server) ready(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{"status": "ready"})
}

// openAPIHandler serves the OpenAPI specification as JSON.
func (s *Server) openAPIHandler(w http.ResponseWriter, _ *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(http.StatusOK)
	_, _ = w.Write(s.openAPI)
}

// countSync processes a multipart batch of PDFs synchronously and returns the
// counting results in a single JSON response. No state is persisted.
//
// POST /v1/count
//
//	Query:  include_rejected=true|false
//	Body:   multipart/form-data, field "files" (one or more PDFs)
//	Limits: SYNC_MAX_FILES (default 50), MAX_PDF_SIZE_MB (default 20)
func (s *Server) countSync(w http.ResponseWriter, r *http.Request) {
	includeRejected := r.URL.Query().Get("include_rejected") == "true"
	maxBytes := int64(s.cfg.MaxPDFSizeMB) * 1024 * 1024

	if err := r.ParseMultipartForm(maxBytes * int64(s.cfg.SyncMaxFiles)); err != nil {
		httpError(w, http.StatusBadRequest, "invalid multipart form")
		return
	}

	files := r.MultipartForm.File["files"]
	if len(files) == 0 {
		httpError(w, http.StatusBadRequest, "field 'files' required")
		return
	}
	if len(files) > s.cfg.SyncMaxFiles {
		httpError(w, http.StatusBadRequest, "too many files")
		return
	}

	log.Printf("POST /v1/count: %d archivo(s), include_rejected=%v", len(files), includeRejected)

	type fileInput struct {
		filename string
		data     []byte
		errRes   *domain.PDFResult
	}

	inputs := make([]fileInput, 0, len(files))
	for _, fh := range files {
		name := filepath.Base(fh.Filename)
		f, err := fh.Open()
		if err != nil {
			errRes := domain.PDFResult{Filename: name, Status: domain.StatusError, Error: err.Error()}
			inputs = append(inputs, fileInput{errRes: &errRes})
			continue
		}
		data, err := io.ReadAll(io.LimitReader(f, maxBytes+1))
		_ = f.Close()
		if err != nil {
			errRes := domain.PDFResult{Filename: name, Status: domain.StatusError, Error: err.Error()}
			inputs = append(inputs, fileInput{errRes: &errRes})
			continue
		}
		if int64(len(data)) > maxBytes {
			errRes := domain.PDFResult{Filename: name, Status: domain.StatusError, Error: "file too large"}
			inputs = append(inputs, fileInput{errRes: &errRes})
			continue
		}
		inputs = append(inputs, fileInput{filename: name, data: data})
	}

	proc := s.newProcessor(includeRejected)
	results := make([]domain.PDFResult, len(inputs))
	failed := 0

	concurrency := s.syncConcurrency()
	sem := make(chan struct{}, concurrency)
	var wg sync.WaitGroup
	var mu sync.Mutex

	for i, in := range inputs {
		if in.errRes != nil {
			results[i] = *in.errRes
			mu.Lock()
			failed++
			mu.Unlock()
			continue
		}
		wg.Add(1)
		go func(idx int, in fileInput) {
			defer wg.Done()
			sem <- struct{}{}
			defer func() { <-sem }()
			res := proc.ProcessPDF(in.filename, in.data)
			mu.Lock()
			results[idx] = res
			if res.Status == domain.StatusError {
				failed++
			}
			mu.Unlock()
		}(i, in)
	}
	wg.Wait()

	log.Printf("POST /v1/count completado: %d procesados, %d fallidos", len(results)-failed, failed)

	writeJSON(w, http.StatusOK, domain.CountResponse{
		Results:   results,
		Processed: len(results) - failed,
		Failed:    failed,
	})
}

// syncConcurrency returns the effective parallelism for /v1/count requests.
func (s *Server) syncConcurrency() int {
	c := s.cfg.SyncProcessConcurrency
	if c <= 0 {
		c = s.cfg.OCRPoolSize
	}
	if c <= 0 {
		c = 4
	}
	pool := s.cfg.OCRPoolSize
	if pool <= 0 {
		pool = 4
	}
	if c > pool {
		c = pool
	}
	return c
}

func (s *Server) newProcessor(includeRejected bool) *pipeline.Processor {
	return pipeline.NewProcessor(s.predictor, s.ocrEngine, pipeline.Options{
		DPI:               s.cfg.OCRDPI,
		Lang:              s.cfg.OCRLang,
		DBSCANEps:         s.cfg.DBSCANEps,
		DBSCANMinSamples:  s.cfg.DBSCANMinSamples,
		IncludeRejected:   includeRejected,
		LogPipelineTiming: s.cfg.LogPipelineTiming,
	})
}

// writeJSON encodes v as JSON and writes it with the given HTTP status.
func writeJSON(w http.ResponseWriter, status int, v interface{}) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

// httpError writes a JSON error response.
func httpError(w http.ResponseWriter, status int, msg string) {
	writeJSON(w, status, map[string]string{"error": msg})
}

// LoadOpenAPI reads an OpenAPI spec from path.
// YAML files are converted to JSON on the fly. Returns a minimal stub on error.
func LoadOpenAPI(path string) []byte {
	data, err := os.ReadFile(path)
	if err != nil {
		return []byte(`{"openapi":"3.1.0","info":{"title":"count-api","version":"1.0.0"}}`)
	}
	if strings.HasSuffix(strings.ToLower(path), ".yaml") || strings.HasSuffix(strings.ToLower(path), ".yml") {
		var doc interface{}
		if err := yaml.Unmarshal(data, &doc); err == nil {
			if j, err := json.Marshal(doc); err == nil {
				return j
			}
		}
	}
	return data
}

// ListenAndServe starts the HTTP server and blocks until ctx is cancelled.
func ListenAndServe(ctx context.Context, addr string, handler http.Handler) error {
	srv := &http.Server{Addr: addr, Handler: handler}
	go func() {
		<-ctx.Done()
		_ = srv.Shutdown(context.Background())
	}()
	if err := srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
		return err
	}
	return nil
}