package compass

import (
	"fmt"
	"os"
	"strings"
	"unicode"

	"github.com/knadh/koanf/providers/env/v2"
	"github.com/knadh/koanf/v2"
)

const envPrefix = "SUMMER_"

func loadEnvVars(k *koanf.Koanf, environ []string) error {
	if k == nil {
		return nil
	}
	return k.Load(env.Provider(".", env.Opt{
		Prefix: envPrefix,
		EnvironFunc: func() []string {
			if environ == nil {
				return []string{}
			}
			return environ
		},
		TransformFunc: transformSummerKey,
	}), nil)
}

func transformSummerKey(key, value string) (string, any) {
	if key == "SUMMER_ENV" {
		return "", nil
	}
	rest, ok := strings.CutPrefix(key, envPrefix)
	if !ok || rest == "" {
		return "", nil
	}
	parts := strings.Split(rest, "__")
	for i, part := range parts {
		parts[i] = strings.ToLower(part)
	}
	return strings.Join(parts, "."), value
}

func readDotEnv(path string) ([]string, error) {
	raw, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, fmt.Errorf("compass: read .env: %w", err)
	}
	var out []string
	for _, line := range strings.Split(string(raw), "\n") {
		line = strings.TrimSpace(line)
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		if after, ok := strings.CutPrefix(line, "export "); ok {
			line = strings.TrimSpace(after)
		}
		key, val, ok := strings.Cut(line, "=")
		if !ok {
			continue
		}
		key = strings.TrimSpace(key)
		if key == "" {
			continue
		}
		val = strings.TrimSpace(val)
		if len(val) >= 2 {
			if (val[0] == '"' && val[len(val)-1] == '"') || (val[0] == '\'' && val[len(val)-1] == '\'') {
				val = val[1 : len(val)-1]
			}
		}
		out = append(out, key+"="+val)
	}
	return out, nil
}

func mergeEnviron(real, dotenv []string) []string {
	present := make(map[string]struct{}, len(real))
	out := make([]string, 0, len(real)+len(dotenv))
	for _, kv := range real {
		key, _, _ := strings.Cut(kv, "=")
		present[key] = struct{}{}
		out = append(out, kv)
	}
	for _, kv := range dotenv {
		key, _, _ := strings.Cut(kv, "=")
		if _, ok := present[key]; ok {
			continue
		}
		out = append(out, kv)
	}
	return out
}

func lookupEnv(environ []string, key string) string {
	for i := len(environ) - 1; i >= 0; i-- {
		k, v, ok := strings.Cut(environ[i], "=")
		if ok && k == key {
			return v
		}
	}
	return ""
}

func sanitizeEnv(env string) (string, error) {
	if env == "" {
		return "", fmt.Errorf("compass: environment name is empty")
	}
	if env == "." || env == ".." || strings.Contains(env, "..") || strings.ContainsAny(env, `/\`) {
		return "", fmt.Errorf("compass: invalid environment name")
	}
	for _, r := range env {
		if unicode.IsLetter(r) || unicode.IsDigit(r) || r == '-' || r == '_' {
			continue
		}
		return "", fmt.Errorf("compass: invalid environment name")
	}
	return env, nil
}