package main

import (
	"bufio"
	"encoding/csv"
	"encoding/json"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"sync"
	"unicode/utf8"
)

var (
	rulesMu sync.RWMutex
	rules   = map[string]map[string]Rule{}
)

var langNameRe = regexp.MustCompile(`^[a-z]{2,5}$`)

func rulesDir() string {
	if configuredRulesDir != "" {
		return configuredRulesDir
	}
	return "rules"
}

// readCSVFile reads a CSV file, transparently stripping a leading UTF-8 BOM
// (common when the file has been round-tripped through a spreadsheet app).
func readCSVFile(path string) ([][]string, error) {
	f, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	br := bufio.NewReader(f)
	if bom, err := br.Peek(3); err == nil && bom[0] == 0xEF && bom[1] == 0xBB && bom[2] == 0xBF {
		br.Discard(3)
	}
	r := csv.NewReader(br)
	r.FieldsPerRecord = -1
	return r.ReadAll()
}

// writeCSVFile writes records back out with correct quoting, which is what
// prevents the "double-encoded row" corruption spreadsheet apps tend to cause.
func writeCSVFile(path string, records [][]string) error {
	f, err := os.Create(path)
	if err != nil {
		return err
	}
	w := csv.NewWriter(f)
	if err := w.WriteAll(records); err != nil {
		f.Close()
		return err
	}
	w.Flush()
	if err := w.Error(); err != nil {
		f.Close()
		return err
	}
	return f.Close()
}

// upsertRuleRecord updates the row for `number` in-place, or appends a new
// row if it isn't present yet. records[0] is assumed to be the header.
func upsertRuleRecord(records [][]string, number, text, penalty, escalation string) [][]string {
	for i, rec := range records {
		if i == 0 || len(rec) < 1 {
			continue
		}
		if strings.TrimSpace(rec[0]) != number {
			continue
		}
		for len(rec) < 4 {
			rec = append(rec, "")
		}
		rec[1], rec[2], rec[3] = text, penalty, escalation
		records[i] = rec
		return records
	}
	return append(records, []string{number, text, penalty, escalation})
}

func loadRules(dir string) error {
	entries, err := os.ReadDir(dir)
	if err != nil {
		return err
	}
	out := map[string]map[string]Rule{}
	for _, e := range entries {
		if e.IsDir() || !strings.HasSuffix(e.Name(), ".csv") {
			continue
		}
		lang := strings.TrimSuffix(e.Name(), ".csv")
		records, err := readCSVFile(filepath.Join(dir, e.Name()))
		if err != nil {
			continue
		}
		langMap := map[string]Rule{}
		for i, rec := range records {
			if len(rec) < 4 {
				continue
			}
			if i == 0 {
				lower := strings.ToLower(strings.TrimSpace(rec[0]))
				if lower == "number" || lower == "rule_number" || lower == "rule" {
					continue
				}
			}
			if strings.ContainsAny(rec[0], ",\"") || !utf8.ValidString(rec[0]) {
				log.Printf("rules: skipping malformed row %d in %s: %q", i+1, e.Name(), rec[0])
				continue
			}
			ru := Rule{
				Number:           strings.TrimSpace(rec[0]),
				Text:             strings.TrimSpace(rec[1]),
				SuggestedPenalty: strings.TrimSpace(rec[2]),
				EscalationMode:   strings.TrimSpace(rec[3]),
			}
			if ru.EscalationMode == "" {
				ru.EscalationMode = "same"
			}
			if strings.HasPrefix(ru.EscalationMode, "escalate:") {
				tiers := strings.Split(strings.TrimPrefix(ru.EscalationMode, "escalate:"), "|")
				for j, t := range tiers {
					tiers[j] = strings.TrimSpace(t)
				}
				ru.EscalationTiers = tiers
				ru.EscalationMode = "escalate"
			}
			langMap[ru.Number] = ru
		}
		out[lang] = langMap
	}
	rulesMu.Lock()
	rules = out
	rulesMu.Unlock()
	return nil
}

func getRules(lang string) []Rule {
	rulesMu.RLock()
	defer rulesMu.RUnlock()
	m, ok := rules[lang]
	if !ok {
		m = rules["en"]
	}
	out := make([]Rule, 0, len(m))
	for _, r := range m {
		out = append(out, r)
	}
	return out
}

func registerRuleRoutes(mux *http.ServeMux) {
	mux.HandleFunc("GET /api/rules", requireAuth(handleListRules))
	mux.HandleFunc("GET /api/rules/languages", requireAuth(handleListRuleLanguages))
	mux.HandleFunc("GET /api/rules/numbers", requireAuth(handleListRuleNumbers))
	mux.HandleFunc("PUT /api/rules/{lang}/{number}", requireAdmin(handleUpdateRule))
	mux.HandleFunc("POST /api/rules/reload", requireAdmin(handleReloadRules))
}

func handleListRuleLanguages(w http.ResponseWriter, r *http.Request) {
	rulesMu.RLock()
	defer rulesMu.RUnlock()
	out := make([]string, 0, len(rules))
	for lang := range rules {
		out = append(out, lang)
	}
	writeJSON(w, http.StatusOK, out)
}

func handleListRules(w http.ResponseWriter, r *http.Request) {
	lang := r.URL.Query().Get("lang")
	if lang == "" {
		u := userFromCtx(r)
		lang = u.Language
	}
	writeJSON(w, http.StatusOK, getRules(lang))
}

func handleReloadRules(w http.ResponseWriter, r *http.Request) {
	if err := loadRules(rulesDir()); err != nil {
		writeError(w, http.StatusInternalServerError, "load_error")
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// handleListRuleNumbers returns the union of rule numbers known across every
// loaded language, so the rules-editor UI can show a row even for a rule
// that a given language's file hasn't been given a translation for yet.
func handleListRuleNumbers(w http.ResponseWriter, r *http.Request) {
	rulesMu.RLock()
	seen := map[string]bool{}
	out := make([]string, 0, 64)
	for _, langMap := range rules {
		for number := range langMap {
			if !seen[number] {
				seen[number] = true
				out = append(out, number)
			}
		}
	}
	rulesMu.RUnlock()
	writeJSON(w, http.StatusOK, out)
}

func handleUpdateRule(w http.ResponseWriter, r *http.Request) {
	lang := r.PathValue("lang")
	number := strings.TrimSpace(r.PathValue("number"))
	if !langNameRe.MatchString(lang) {
		writeError(w, http.StatusBadRequest, "invalid_language")
		return
	}
	path := filepath.Join(rulesDir(), lang+".csv")
	if _, err := os.Stat(path); err != nil {
		writeError(w, http.StatusNotFound, "unknown_language")
		return
	}
	if number == "" {
		writeError(w, http.StatusBadRequest, "invalid_number")
		return
	}
	var req struct {
		Text             string `json:"text"`
		SuggestedPenalty string `json:"suggested_penalty"`
		EscalationMode   string `json:"escalation_mode"`
	}
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid_body")
		return
	}
	req.Text = strings.TrimSpace(req.Text)
	if req.Text == "" {
		writeError(w, http.StatusBadRequest, "missing_text")
		return
	}
	if req.EscalationMode == "" {
		req.EscalationMode = "same"
	}

	records, err := readCSVFile(path)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "read_error")
		return
	}
	if len(records) == 0 {
		records = [][]string{{"rule_number", "rule_text", "suggested_penalty", "escalation_mode"}}
	}
	records = upsertRuleRecord(records, number, req.Text, req.SuggestedPenalty, req.EscalationMode)
	if err := writeCSVFile(path, records); err != nil {
		writeError(w, http.StatusInternalServerError, "write_error")
		return
	}
	if err := loadRules(rulesDir()); err != nil {
		writeError(w, http.StatusInternalServerError, "reload_error")
		return
	}

	rulesMu.RLock()
	ru, ok := rules[lang][number]
	rulesMu.RUnlock()
	if !ok {
		writeError(w, http.StatusInternalServerError, "reload_mismatch")
		return
	}
	writeJSON(w, http.StatusOK, ru)
}