package envconf

import ("strings"
        "unicode"
        "strconv"
        "time"
        "errors"
        "fmt"
        "os")

type cEntry struct {
    value string
    parsed cValue
    dtype DataType
    unset bool
    empty bool
}

type cValue struct {
    intval int64
    durval time.Duration
    strval string
    err error
}

type Config struct {
    parsed bool
    env map[string]cEntry
}

func NewConfig()(*Config) {
    config := new(Config)
    config.parsed = false
    config.env = make(map[string]cEntry)
    for _,v := range os.Environ() {
        splitted := strings.SplitN(v, "=", 2)
        if len(splitted) == 2 {
            key := strings.TrimSpace(strings.ToLower(splitted[0]))
            if unicode.IsLetter(getFirstRune(key)) {
                var entry cEntry
                entry.value = splitted[1]
                entry.dtype = TypeNone
                entry.unset = false
                entry.empty = false
                config.env[key] = entry
            }
        }
    }
    return config
}

func (c *Config) Define(key string, dtype DataType) {
    entry, ok := c.env[key]
    if ok {
        entry.dtype = dtype
    } else {
        var entry cEntry
        entry.dtype = dtype
        entry.unset = true
        entry.empty = true
        c.env[key] = entry
    }
}

func (c *Config) DefineDefault(key string, val string, dtype DataType) {
    entry, ok := c.env[key]
    if ok {
        if entry.unset {
            entry.empty = false
            entry.value = val
            entry.dtype = dtype
        }
    } else {
        var entry cEntry
        entry.dtype = dtype
        entry.unset = true
        entry.empty = false
        c.env[key] = entry
    }
}

func (c *Config) Parse() {
    parsers := make(map[DataType](func(string)(cValue)))
    parsers[TypeInt] = parseInt
    parsers[TypeDuration] = parseDuration

    for k,v := range c.env {
        parser, ok := parsers[v.dtype]
        if ok {
            if v.empty {
                if v.unset {
                    v.parsed.err = errors.New(fmt.Sprintf("Environment variable %s not found. It should have been of type %s", k, v.dtype))
                }
            } else {
                v.parsed = parser(v.value)
            }
        }
    }
}

func parseInt(str string)(ret cValue) {
    ret.intval, ret.err = strconv.ParseInt(str, 10, 64)
    return
}

func parseDuration(str string)(ret cValue) {
    ret.durval, ret.err = time.ParseDuration(str)
    return
}

func getFirstRune(str string)(rune) {
    for _,v := range str {
        return v
    }
    return rune(0)
}