// Package main is a tiny HTTP service that exposes daily contribution counts
// for a single allowlisted Gitea user, including activity from private repos.
//
// It reads directly from the Gitea database (the `action` table) using a
// read-only DB user. Output is JSON: [{"date":"2026-05-04","count":3}, ...].
//
// Pair with templates/profile-snippet.tmpl on the Gitea side to render a
// GitHub-style heatmap with hover tooltips on a user profile page.
package main

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"net/http"
	"os"
	"os/signal"
	"strings"
	"syscall"
	"time"

	_ "github.com/lib/pq"
)

// ---- config ---------------------------------------------------------------

type config struct {
	DatabaseURL   string
	AllowedUsers  map[string]bool
	AllowedOrigin string
	Listen        string
	OpTypes       string // comma-separated list of integer op_type values
	WindowDays    int
}

func loadConfig() (*config, error) {
	c := &config{
		DatabaseURL:   os.Getenv("DATABASE_URL"),
		AllowedOrigin: getEnv("ALLOWED_ORIGIN", "*"),
		Listen:        getEnv("LISTEN", ":8080"),
		// Default: commit pushes (5), tag pushes (9), mirror sync push (18).
		// See README for the full Gitea op_type reference and why these are
		// the closest analog to "GitHub-style contributions".
		OpTypes:    getEnv("OP_TYPES", "5,9,18"),
		WindowDays: 371, // 53 weeks * 7 days
	}
	if c.DatabaseURL == "" {
		return nil, errors.New("DATABASE_URL is required")
	}
	users := strings.TrimSpace(os.Getenv("ALLOWED_USERS"))
	if users == "" {
		return nil, errors.New("ALLOWED_USERS is required (comma-separated lowercase usernames)")
	}
	c.AllowedUsers = map[string]bool{}
	for _, u := range strings.Split(users, ",") {
		u = strings.TrimSpace(strings.ToLower(u))
		if u != "" {
			c.AllowedUsers[u] = true
		}
	}
	// Validate OP_TYPES contains only digits, commas, and whitespace. This is
	// admin-controlled config but it gets interpolated into SQL, so be paranoid.
	for _, r := range c.OpTypes {
		if !((r >= '0' && r <= '9') || r == ',' || r == ' ') {
			return nil, fmt.Errorf("OP_TYPES may only contain digits and commas, got: %q", c.OpTypes)
		}
	}
	if strings.TrimSpace(strings.Trim(c.OpTypes, ", ")) == "" {
		return nil, errors.New("OP_TYPES must contain at least one value")
	}
	return c, nil
}

func getEnv(key, fallback string) string {
	if v := os.Getenv(key); v != "" {
		return v
	}
	return fallback
}

// ---- handler --------------------------------------------------------------

type heatmapHandler struct {
	db  *sql.DB
	cfg *config
	log *slog.Logger
}

type dayCount struct {
	Date  string `json:"date"`
	Count int    `json:"count"`
}

func (h *heatmapHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}

	// Path: /heatmap/{username}.json  (the .json suffix is optional)
	username := strings.TrimPrefix(r.URL.Path, "/heatmap/")
	username = strings.TrimSuffix(username, ".json")
	username = strings.ToLower(strings.TrimSpace(username))

	if username == "" {
		http.Error(w, "username required", http.StatusBadRequest)
		return
	}
	if !h.cfg.AllowedUsers[username] {
		// 404, not 403, to avoid confirming whether a username exists.
		http.Error(w, "not found", http.StatusNotFound)
		return
	}

	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
	defer cancel()

	counts, err := h.queryHeatmap(ctx, username)
	if err != nil {
		h.log.Error("heatmap query failed", "user", username, "err", err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}
	if counts == nil {
		counts = []dayCount{}
	}

	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("Cache-Control", "public, max-age=3600")
	w.Header().Set("Access-Control-Allow-Origin", h.cfg.AllowedOrigin)
	w.Header().Set("Vary", "Origin")
	if err := json.NewEncoder(w).Encode(counts); err != nil {
		h.log.Error("encode failed", "err", err)
	}
}

func (h *heatmapHandler) queryHeatmap(ctx context.Context, username string) ([]dayCount, error) {
	var userID int64
	err := h.db.QueryRowContext(ctx,
		`SELECT id FROM "user" WHERE lower_name = $1`,
		username,
	).Scan(&userID)
	if err != nil {
		return nil, fmt.Errorf("lookup user %q: %w", username, err)
	}

	cutoff := time.Now().UTC().AddDate(0, 0, -h.cfg.WindowDays).Unix()

	// OP_TYPES is validated at config load to contain only digits and commas,
	// so this fmt.Sprintf interpolation is safe. It's not a parameter because
	// PostgreSQL doesn't accept lists as a single placeholder.
	query := fmt.Sprintf(`
		SELECT to_char(to_timestamp(created_unix) AT TIME ZONE 'UTC', 'YYYY-MM-DD') AS day,
		       COUNT(*)::int
		FROM "action"
		WHERE act_user_id = $1
		  AND created_unix >= $2
		  AND op_type IN (%s)
		GROUP BY day
		ORDER BY day
	`, h.cfg.OpTypes)

	rows, err := h.db.QueryContext(ctx, query, userID, cutoff)
	if err != nil {
		return nil, fmt.Errorf("query: %w", err)
	}
	defer rows.Close()

	var out []dayCount
	for rows.Next() {
		var d dayCount
		if err := rows.Scan(&d.Date, &d.Count); err != nil {
			return nil, fmt.Errorf("scan: %w", err)
		}
		out = append(out, d)
	}
	return out, rows.Err()
}

// ---- main -----------------------------------------------------------------

func main() {
	logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))

	cfg, err := loadConfig()
	if err != nil {
		logger.Error("config error", "err", err)
		os.Exit(1)
	}

	db, err := sql.Open("postgres", cfg.DatabaseURL)
	if err != nil {
		logger.Error("db open failed", "err", err)
		os.Exit(1)
	}
	defer db.Close()
	db.SetMaxOpenConns(4)
	db.SetMaxIdleConns(2)
	db.SetConnMaxLifetime(time.Hour)

	pingCtx, pingCancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer pingCancel()
	if err := db.PingContext(pingCtx); err != nil {
		logger.Error("db ping failed", "err", err)
		os.Exit(1)
	}

	h := &heatmapHandler{db: db, cfg: cfg, log: logger}

	mux := http.NewServeMux()
	mux.Handle("/heatmap/", h)
	mux.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
		ctx, cancel := context.WithTimeout(r.Context(), 2*time.Second)
		defer cancel()
		if err := db.PingContext(ctx); err != nil {
			http.Error(w, "db unhealthy", http.StatusServiceUnavailable)
			return
		}
		_, _ = w.Write([]byte("ok\n"))
	})

	srv := &http.Server{
		Addr:              cfg.Listen,
		Handler:           mux,
		ReadHeaderTimeout: 5 * time.Second,
		ReadTimeout:       10 * time.Second,
		WriteTimeout:      10 * time.Second,
		IdleTimeout:       60 * time.Second,
	}

	go func() {
		logger.Info("listening",
			"addr", cfg.Listen,
			"users", len(cfg.AllowedUsers),
			"op_types", cfg.OpTypes,
		)
		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
			logger.Error("server error", "err", err)
			os.Exit(1)
		}
	}()

	stop := make(chan os.Signal, 1)
	signal.Notify(stop, os.Interrupt, syscall.SIGTERM)
	<-stop
	logger.Info("shutting down")

	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	if err := srv.Shutdown(ctx); err != nil {
		logger.Error("shutdown error", "err", err)
	}
}