package goyaml

import (
    "strconv"
    "strings"
    "math"
)


// TODO: merge, timestamps, base 60 floats, omap.


type resolveMapItem struct {
    value interface{}
    tag   string
}

var resolveTable = make([]byte, 256)
var resolveMap = make(map[string]resolveMapItem)


func init() {
    t := resolveTable
    t[int('+')] = 'S' // Sign
    t[int('-')] = 'S'
    for _, c := range "0123456789" {
        t[int(c)] = 'D' // Digit
    }
    for _, c := range "yYnNtTfFoO~" {
        t[int(c)] = 'M' // In map
    }
    t[int('.')] = '.' // Float (potentially in map)
    t[int('<')] = '<' // Merge

    var resolveMapList = []struct {
        v   interface{}
        tag string
        l   []string
    }{
        {true, "!!bool", []string{"y", "Y", "yes", "Yes", "YES"}},
        {true, "!!bool", []string{"true", "True", "TRUE"}},
        {true, "!!bool", []string{"on", "On", "ON"}},
        {false, "!!bool", []string{"n", "N", "no", "No", "NO"}},
        {false, "!!bool", []string{"false", "False", "FALSE"}},
        {false, "!!bool", []string{"off", "Off", "OFF"}},
        {nil, "!!null", []string{"~", "null", "Null", "NULL"}},
        {math.NaN(), "!!float", []string{".nan", ".NaN", ".NAN"}},
        {math.Inf(+1), "!!float", []string{".inf", ".Inf", ".INF"}},
        {math.Inf(+1), "!!float", []string{"+.inf", "+.Inf", "+.INF"}},
        {math.Inf(-1), "!!float", []string{"-.inf", "-.Inf", "-.INF"}},
    }

    m := resolveMap
    for _, item := range resolveMapList {
        for _, s := range item.l {
            m[s] = resolveMapItem{item.v, item.tag}
        }
    }
}

const longTagPrefix = "tag:yaml.org,2002:"

func shortTag(tag string) string {
    if strings.HasPrefix(tag, longTagPrefix) {
        return "!!" + tag[len(longTagPrefix):]
    }
    return tag
}

func resolvableTag(tag string) bool {
    switch tag {
    case "", "!!str", "!!bool", "!!int", "!!float", "!!null":
        return true
    }
    return false
}

func resolve(tag string, in string) (rtag string, out interface{}) {
    tag = shortTag(tag)
    if !resolvableTag(tag) {
        return tag, in
    }

    defer func() {
        if tag != "" && tag != rtag {
            panic("Can't decode " + rtag + " '" + in + "' as a " + tag)
        }
    }()

    if in == "" {
        return "!!null", nil
    }

    c := resolveTable[in[0]]
    if c == 0 {
        // It's a string for sure. Nothing to do.
        return "!!str", in
    }

    // Handle things we can lookup in a map.
    if item, ok := resolveMap[in]; ok {
        return item.tag, item.value
    }

    switch c {
    case 'M':
        // We've already checked the map above.

    case '.':
        // Not in the map, so maybe a normal float.
        floatv, err := strconv.Atof64(in)
        if err == nil {
            return "!!float", floatv
        }
        // XXX Handle base 60 floats here (WTF!)

    case 'D', 'S':
        // Int, float, or timestamp.
        for i := 0; i != len(in); i++ {
            if in[i] == '_' {
                in = strings.Replace(in, "_", "", -1)
                break
            }
        }
        intv, err := strconv.Btoi64(in, 0)
        if err == nil {
            if intv == int64(int(intv)) {
                return "!!int", int(intv)
            } else {
                return "!!int", intv
            }
        }
        floatv, err := strconv.Atof64(in)
        if err == nil {
            return "!!float", floatv
        }
        if strings.HasPrefix(in, "0b") {
            intv, err := strconv.Btoi64(in[2:], 2)
            if err == nil {
                return "!!int", int(intv)
            }
        } else if strings.HasPrefix(in, "-0b") {
            intv, err := strconv.Btoi64(in[3:], 2)
            if err == nil {
                return "!!int", -int(intv)
            }
        }
        // XXX Handle timestamps here.

    case '<':
        // XXX Handle merge (<<) here.

    default:
        panic("resolveTable item not yet handled: " +
            string([]byte{c}) + " (with " + in + ")")
    }
    return "!!str", in
}