package main

import (
	"encoding/json"
	"net/http"
	"regexp"
	"strings"
)

// guessLang heuristically detects a language from source content.
func guessLang(s string) string {
	src := strings.TrimSpace(s)
	if src == "" {
		return ""
	}

	// JSON: must start with { or [ and parse
	if src[0] == '{' || src[0] == '[' {
		var v any
		if json.Unmarshal([]byte(src), &v) == nil {
			return "json"
		}
	}

	rules := []struct {
		lang string
		re   *regexp.Regexp
	}{
		{"python", regexp.MustCompile(`(?m)^\s*(def |class |import |from \w+ import |@decorator)`)},
		{"python", regexp.MustCompile(`(^|\n)\s*#!.*python`)},
		{"go", regexp.MustCompile(`(?m)^\s*(package \w+|import \(|func (\w+|\() )`)},
		{"rust", regexp.MustCompile(`(?m)(\bfn \w+|let mut \b|\bimpl \b|\bmatch \w+ \{|use std::)`)},
		{"javascript", regexp.MustCompile(`(?m)(\bconst \w+ = |require\(|import \w+ from |=> \{|\bconsole\.log\()` )},
		{"java", regexp.MustCompile(`(?m)(\bpublic (static |final |class )|\bSystem\.out\.print|import java\.)`)},
		{"c", regexp.MustCompile(`(?m)(#include\s*<\w+\.h>|printf\(|\bint main\()` )},
		{"cpp", regexp.MustCompile(`(?m)(#include\s*<(iostream|vector|string)>|std::|\bcout\s*<<)`)},
		{"bash", regexp.MustCompile(`(?m)^(#!.*bash|#!.*sh|\w+\(\)\s*\{)` )},
		{"sql", regexp.MustCompile(`(?i)\b(SELECT .+ FROM|INSERT INTO|CREATE TABLE|UPDATE \w+ SET)\b`)},
		{"yaml", regexp.MustCompile(`(?m)^(\w[\w-]*:\s*(\||\S)|  \w[\w-]*: |---\s*$)`)},
		{"markdown", regexp.MustCompile("(?m)^(#{1,6} \\S|\\|.*\\||-\\s\\[\\s?\\]|```)")},
	}

	scores := map[string]int{}
	for _, r := range rules {
		n := len(r.re.FindAllString(src, -1))
		if n > 0 {
			// later generic rules shouldn't drown out earlier specific ones
			scores[r.lang] += n
		}
	}

	best, bestN := "", 0
	for lang, n := range scores {
		if n > bestN {
			best, bestN = lang, n
		}
	}
	if bestN == 0 {
		return "text"
	}
	return best
}

func (a *apiServer) handleGuessLang(w http.ResponseWriter, r *http.Request) {
	setRateLimitHeaders(w, 1, 5)
	if !rateLimitGuess(r) {
		writeRateLimited(w, 1)
		return
	}
	var req struct {
		Content string `json:"content"`
	}
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeErr(w, http.StatusBadRequest, "invalid json body")
		return
	}
	lang := guessLang(req.Content)
	writeJSON(w, http.StatusOK, map[string]any{"language": lang})
}