package toml

import (
	"fmt"
	"regexp"
	"sort"
	"strings"
	"time"
)

// item represents a TOML item.
type item struct {
	Type itemType
	Data []interface{}
}

// table represents a TOML table.
type table map[string]*item

// itemType identifies the semantic role of a TOML item.
type itemType string

const (
	pString         itemType = "string"          // "various", 'types', """of""", '''strings'''
	pInteger        itemType = "integer"         // 12345, 0xffee12a0, 0o0755, 0b101101011
	pFloat          itemType = "float"           // 10.1234, 143E-12, 43.28377e+4, +inf, -inf, nan
	pBoolean        itemType = "boolean"         // true or false
	pOffsetDateTime itemType = "offset datetime" // 2019-06-18 10:32:15.173645362+0200
	pLocalDateTime  itemType = "datetime"        // 2018-12-25 12:12:18.876772533
	pLocalDate      itemType = "date"            // 2017-05-17
	pLocalTime      itemType = "time"            // 23:01:22
	pArrayOfTables  itemType = "array"           // defined using an [[array.of.tables]]
	pArray          itemType = "static array"    // defined using ["an", "inline", "array"]
	pTable          itemType = "table"           // defined using { "inline" = "table" } or [standard.table]
)

// newItem instantiates a new item struct.
func newItem(itemType itemType, data ...interface{}) *item {
	return &item{Type: itemType, Data: data}
}

// newKey instantiates a new key.
func newKey(key ...string) []string {
	return key
}

// parser holds the state for the TOML parser. All parsing functions are
// methods of this struct.
type parser struct {
	Items      []*item  // a buffer for holding parsed items
	Root       table    // the root-level TOML table (each TOML doc is implicitly a table)
	Current    table    // the currently active TOML table
	CurrentKey []string // the key for the currently active TOML table
}

func newParser() *parser {
	p := &parser{Root: make(table)}
	p.Current = p.Root
	return p
}

func (t *parser) setKeyValuePair(key []string, value *item) error {
	// First make sure the table structure for storing the value exists.
	node, lastKeyPart, err := t.makeTablePath(key)
	if err != nil {
		return fmt.Errorf("invalid key/value pair: %s", err)
	}
	// Check if the key is still free for use.
	if existing, ok := node[lastKeyPart]; ok {
		path := t.formatKeyPath(key, len(key)-1)
		return fmt.Errorf("invalid key/value pair: %s item already exists at key %s", existing.Type, path)
	}
	// It is, store the value in the table.
	node[lastKeyPart] = value
	return nil
}

func (t *parser) openTable(key []string) error {
	t.CurrentKey = nil
	t.Current = t.Root
	// Go over all requested levels of the key. For all levels, except the last
	// one, it is okay if a table already exists. For at least the last level,
	// no table or value must exist, because that would mean we are overwriting
	// an existing key/value pair, which is not allowed.
	node, lastKeyPart, err := t.makeTablePath(key)
	if err != nil {
		return fmt.Errorf("invalid table: %s", err)
	}
	// Check if the key is still free for use.
	if existing, ok := node[lastKeyPart]; ok {
		path := t.formatKeyPath(key, len(key)-1)
		return fmt.Errorf("invalid table: %s item already exists at key %s", existing.Type, path)
	}
	// The subtable does not exist yet. Create the subtable.
	subTable := make(table)
	node[lastKeyPart] = newItem(pTable, subTable)
	node = subTable

	// From here on, key/value pairs are added to the newly defined table.
	t.Current = node
	t.CurrentKey = key
	return nil
}

func (t *parser) openArrayOfTables(key []string) error {
	t.CurrentKey = nil
	t.Current = t.Root
	// Go over all requested levels of the key. For all levels, except the last
	// one, it is okay if a table already exists. For the last level, either
	// no item must exist (in which case a table array will be created), or a
	// table array must exist.
	// Other cases would mean we are overwriting an existing key/value pair,
	// which is not allowed.
	node, lastKeyPart, err := t.makeTablePath(key)
	if err != nil {
		return fmt.Errorf("invalid table array: %s", err)
	}
	// At the last key position, there must be either no value yet, or the
	// existing value must be a table array. Other values are invalid.
	if existing, ok := node[lastKeyPart]; ok {
		if existing.Type != pArrayOfTables {
			path := t.formatKeyPath(key, len(key)-1)
			return fmt.Errorf("invalid table array: %s item already exists at key %s", existing.Type, path)
		}
		// A table array exists. Add a new table to this array.
		array := node[lastKeyPart]
		subTable := make(table)
		tables := array.Data
		tables = append(tables, newItem(pTable, subTable))
		array.Data = tables
		node = subTable
	} else {
		// No value exists at the defined key path. Create a new table array.
		subTable := make(table)
		node[lastKeyPart] = newItem(pArrayOfTables, newItem(pTable, subTable))
		node = subTable
	}

	// From here on, key/value pairs are added to the newly defined table.
	t.Current = node
	t.CurrentKey = key
	return nil
}

func (t *parser) makeTablePath(key []string) (table, string, error) {
	node := t.Current
	for i, keyPart := range key {
		// Arrived at the last key part? Then the path towards that key is
		// setup correctly. Return the last part, so the caller can use it.
		isLast := i == len(key)-1
		if isLast {
			return node, keyPart, nil
		}
		if subItem, ok := node[keyPart]; ok {
			// You cannot overwrite an already defined key, regardless its value.
			// When a value already exists at the current key, this can only be a table.
			if subItem.Type != pTable {
				path := t.formatKeyPath(key, i)
				return nil, "", fmt.Errorf("%s item already exists at key %s", subItem.Type, path)
			}
			// All is okay, traverse to the subtable.
			node = subItem.Data[0].(table)
		} else {
			// The subtable does not exist yet. Create the subtable.
			subTable := make(table)
			node[keyPart] = newItem(pTable, subTable)
			node = subTable
		}
	}
	panic("makeTablePath(): empty key provided; a key must have at least one key part")
}

func (t *parser) formatKeyPath(key []string, end int) string {
	var sb strings.Builder
	sb.WriteRune('[')
	if t.CurrentKey != nil {
		for i, keyPart := range t.CurrentKey {
			if i > 0 {
				sb.WriteString("->")
			}
			sb.WriteString(formatKeyName(keyPart))
		}
	}
	for i, keyPart := range key {
		if t.CurrentKey != nil || i > 0 {
			sb.WriteString("->")
		}
		sb.WriteString(formatKeyName(keyPart))
		if i == end {
			break
		}
	}
	sb.WriteRune(']')
	return sb.String()
}

func formatKeyName(key string) string {
	if ok, _ := regexp.Match(`^\w+$`, []byte(key)); ok {
		return key
	}
	return fmt.Sprintf("%q", key)
}

func (t table) String() string {
	return newItem(pTable, t).String()
}

func (parseItem item) String() string {
	switch parseItem.Type {
	case pString:
		return fmt.Sprintf("%q", parseItem.Data[0])
	case pOffsetDateTime:
		return parseItem.Data[0].(time.Time).Format(time.RFC3339Nano)
	case pLocalDateTime:
		return parseItem.Data[0].(time.Time).Format("2006-01-02 15:04:05.999999999")
	case pLocalDate:
		return parseItem.Data[0].(time.Time).Format("2006-01-02")
	case pLocalTime:
		return parseItem.Data[0].(time.Time).Format("15:04:05.999999999")
	case pArrayOfTables:
		fallthrough
	case pArray:
		items := make([]string, len(parseItem.Data))
		for i, value := range parseItem.Data {
			items[i] = value.(*item).String()
		}
		return fmt.Sprintf("[%s]", strings.Join(items, ", "))
	case pTable:
		pairs := parseItem.Data[0].(table)
		keys := make([]string, len(pairs))
		i := 0
		for k := range pairs {
			keys[i] = k
			i++
		}
		sort.Strings(keys)
		items := make([]string, len(pairs))
		for i, k := range keys {
			items[i] = fmt.Sprintf("%q: %s", k, pairs[k].String())
		}
		return fmt.Sprintf("{%s}", strings.Join(items, ", "))
	default:
		return fmt.Sprintf("%v", parseItem.Data[0])
	}
}