package toml

import (
	"bytes"
	"encoding/hex"
	"fmt"
	"reflect"
)

func Unmarshal(data []byte, v interface{}) error {
	if v == nil {
		return fmt.Errorf("cannot unmarshal to nil target")
	}
	rv := reflect.ValueOf(v)
	if rv.Kind() != reflect.Ptr {
		return fmt.Errorf("can only marshal to pointer, not %s", rv.Kind())
	}

	u := &unmarshaler{stack: []reflect.Value{rv.Elem()}}
	parseErr := parser{builder: u}.parse(data)
	if parseErr != nil {
		return parseErr
	}
	return u.err
}

type unmarshaler struct {
	// Each stack frame is a pointer to the root object that should be
	// considered when settings values.
	// It at least contains the root object passed to Unmarshal.
	stack []reflect.Value

	// First error that appeared during the construction of the object.
	// When set all callbacks are no-ops.
	err error

	// State that indicates the parser is processing a [table] name. If false
	// keys are interpreted as part of a key-value.
	parsingTable bool
}

func (u *unmarshaler) KeyValBegin() {
	u.push(u.top())
}

func (u *unmarshaler) KeyValEnd() {
	u.pop()
}

func getOrCreateChild(parent reflect.Value, key string) (reflect.Value, error) {
	if parent.Type().Kind() != reflect.Struct {
		return reflect.Value{}, fmt.Errorf("value of type '%s' cannot have children", parent)
	}
	f := parent.FieldByName(key)
	if !f.IsValid() {
		// TODO: implement alternative names
		return reflect.Value{}, fmt.Errorf("field '%s' not found", key)
	}
	// TODO create things
	return f, nil
}

func (u *unmarshaler) top() reflect.Value {
	return u.stack[len(u.stack)-1]
}

func (u *unmarshaler) push(v reflect.Value) {
	u.stack = append(u.stack, v)
}

func (u *unmarshaler) pop() {
	u.stack = u.stack[:len(u.stack)-1]
}

func (u *unmarshaler) replace(v reflect.Value) {
	u.stack[len(u.stack)-1] = v
}

func (u *unmarshaler) StringValue(v []byte) {
	if u.err != nil {
		return
	}
	u.top().SetString(string(v))
}

func (u *unmarshaler) SimpleKey(v []byte) {
	if u.err != nil {
		return
	}

	target, err := getOrCreateChild(u.top(), string(v))
	if err != nil {
		u.err = err
		return
	}

	u.replace(target)
}

func (u *unmarshaler) StandardTableBegin() {
	if u.err != nil {
		return
	}

	// tables are only top-level
	u.stack = u.stack[:1]

	u.push(u.top())
}

func (u *unmarshaler) StandardTableEnd() {
	if u.err != nil {
		return
	}
}

type builder interface {
	SimpleKey(v []byte)

	StandardTableBegin()
	StandardTableEnd()

	KeyValBegin()
	KeyValEnd()

	StringValue(v []byte)
}

type parser struct {
	builder builder
}

func (p parser) parse(b []byte) error {
	b, err := p.parseExpression(b)
	if err != nil {
		return err
	}
	for len(b) > 0 {
		b, err = p.parseNewline(b)
		if err != nil {
			return err
		}

		b, err = p.parseExpression(b)
		if err != nil {
			return err
		}
	}
	return nil
}

func (p parser) parseNewline(b []byte) ([]byte, error) {
	if b[0] == '\n' {
		return b[1:], nil
	}
	if b[0] == '\r' {
		_, rest, err := scanWindowsNewline(b)
		return rest, err
	}
	return nil, fmt.Errorf("expected newline but got %#U", b[0])
}

func (p parser) parseExpression(b []byte) ([]byte, error) {
	//expression =  ws [ comment ]
	//expression =/ ws keyval ws [ comment ]
	//expression =/ ws table ws [ comment ]

	b = p.parseWhitespace(b)

	if len(b) == 0 {
		return b, nil
	}

	if b[0] == '#' {
		_, rest, err := scanComment(b)
		return rest, err
	}
	if b[0] == '\n' || b[0] == '\r' {
		return b, nil
	}

	var err error
	if b[0] == '[' {
		b, err = p.parseTable(b)
	} else {
		b, err = p.parseKeyval(b)
	}
	if err != nil {
		return nil, err
	}

	b = p.parseWhitespace(b)

	if len(b) > 0 && b[0] == '#' {
		_, rest, err := scanComment(b)
		return rest, err
	}

	return b, nil
}

func (p parser) parseTable(b []byte) ([]byte, error) {
	//table = std-table / array-table
	if len(b) > 1 && b[1] == '[' {
		return p.parseArrayTable(b)
	}
	return p.parseStdTable(b)
}

func (p parser) parseArrayTable(b []byte) ([]byte, error) {
	//array-table = array-table-open key array-table-close
	//array-table-open  = %x5B.5B ws  ; [[ Double left square bracket
	//array-table-close = ws %x5D.5D  ; ]] Double right square bracket

	b = b[2:]
	b = p.parseWhitespace(b)
	b, err := p.parseKey(b)
	if err != nil {
		return nil, err
	}
	b = p.parseWhitespace(b)
	b, err = expect(']', b)
	if err != nil {
		return nil, err
	}
	return expect(']', b)
}

func (p parser) parseStdTable(b []byte) ([]byte, error) {
	//std-table = std-table-open key std-table-close
	//std-table-open  = %x5B ws     ; [ Left square bracket
	//std-table-close = ws %x5D     ; ] Right square bracket

	p.builder.StandardTableBegin()
	defer p.builder.StandardTableEnd()

	b = b[1:]
	b = p.parseWhitespace(b)
	b, err := p.parseKey(b)
	if err != nil {
		return nil, err
	}
	b = p.parseWhitespace(b)

	return expect(']', b)
}

func (p parser) parseKeyval(b []byte) ([]byte, error) {
	//keyval = key keyval-sep val

	p.builder.KeyValBegin()
	defer p.builder.KeyValEnd()

	b, err := p.parseKey(b)
	if err != nil {
		return nil, err
	}

	//keyval-sep = ws %x3D ws ; =

	b = p.parseWhitespace(b)
	b, err = expect('=', b)
	if err != nil {
		return nil, err
	}
	b = p.parseWhitespace(b)

	return p.parseVal(b)
}

func (p parser) parseVal(b []byte) ([]byte, error) {
	// val = string / boolean / array / inline-table / date-time / float / integer
	if len(b) == 0 {
		return nil, fmt.Errorf("expected value, not eof")
	}

	var err error
	c := b[0]

	switch c {
	// strings
	case '"':
		var v []byte
		if scanFollowsMultilineBasicStringDelimiter(b) {
			v, b, err = p.parseMultilineBasicString(b)
		} else {
			v, b, err = p.parseBasicString(b)
		}
		if err == nil {
			p.builder.StringValue(v)
		}
		return b, err
	case '\'':
		var v []byte
		if scanFollowsMultilineLiteralStringDelimiter(b) {
			v, b, err = p.parseMultilineLiteralString(b)
		} else {
			v, b, err = p.parseLiteralString(b)
		}
		if err == nil {
			p.builder.StringValue(v)
		}
		return b, err
	case 't':
		if !scanFollowsTrue(b) {
			return nil, fmt.Errorf("expected 'true'")
		}
		return b[4:], nil
	case 'f':
		if !scanFollowsFalse(b) {
			return nil, fmt.Errorf("expected 'false'")
		}
		return b[5:], nil
	case '[':
		return p.parseValArray(b)
	case '{':
		return p.parseInlineTable(b)

	// TODO date-time

	// TODO float

	// TODO integer
	default:
		return nil, fmt.Errorf("unexpected char")
	}
}

func (p parser) parseLiteralString(b []byte) ([]byte, []byte, error) {
	v, rest, err := scanLiteralString(b)
	if err != nil {
		return nil, nil, err
	}
	return v[1 : len(v)-1], rest, nil
}

func (p parser) parseInlineTable(b []byte) ([]byte, error) {
	//inline-table = inline-table-open [ inline-table-keyvals ] inline-table-close
	//inline-table-open  = %x7B ws     ; {
	//inline-table-close = ws %x7D     ; }
	//inline-table-sep   = ws %x2C ws  ; , Comma
	//inline-table-keyvals = keyval [ inline-table-sep inline-table-keyvals ]

	b = b[1:]

	first := true
	var err error
	for len(b) > 0 {
		b = p.parseWhitespace(b)
		if b[0] == '}' {
			break
		}

		if !first {
			b, err = expect(',', b)
			if err != nil {
				return nil, err
			}
			b = p.parseWhitespace(b)
		}
		b, err = p.parseKeyval(b)
		if err != nil {
			return nil, err
		}

		first = false
	}
	return expect('}', b)
}

func (p parser) parseValArray(b []byte) ([]byte, error) {
	//array = array-open [ array-values ] ws-comment-newline array-close
	//array-open =  %x5B ; [
	//array-close = %x5D ; ]
	//array-values =  ws-comment-newline val ws-comment-newline array-sep array-values
	//array-values =/ ws-comment-newline val ws-comment-newline [ array-sep ]
	//array-sep = %x2C  ; , Comma
	//ws-comment-newline = *( wschar / [ comment ] newline )

	b = b[1:]

	first := true
	var err error
	for len(b) > 0 {
		b, err = p.parseOptionalWhitespaceCommentNewline(b)
		if err != nil {
			return nil, err
		}

		if len(b) == 0 {
			return nil, unexpectedCharacter{b: b}
		}

		if b[0] == ']' {
			break
		}
		if b[0] == ',' {
			if first {
				return nil, fmt.Errorf("array cannot start with comma")
			}
			b = b[1:]
			b, err = p.parseOptionalWhitespaceCommentNewline(b)
			if err != nil {
				return nil, err
			}
		}

		b, err = p.parseVal(b)
		if err != nil {
			return nil, err
		}
		b, err = p.parseOptionalWhitespaceCommentNewline(b)
		if err != nil {
			return nil, err
		}
		first = false
	}

	return expect(']', b)
}

func (p parser) parseOptionalWhitespaceCommentNewline(b []byte) ([]byte, error) {
	var err error
	b = p.parseWhitespace(b)
	if len(b) > 0 && b[0] == '#' {
		_, b, err = scanComment(b)
		if err != nil {
			return nil, err
		}
	}
	if len(b) > 0 && (b[0] == '\n' || b[0] == '\r') {
		b, err = p.parseNewline(b)
		if err != nil {
			return nil, err
		}
	}
	return b, nil
}

func (p parser) parseMultilineLiteralString(b []byte) ([]byte, []byte, error) {
	token, rest, err := scanMultilineLiteralString(b)
	if err != nil {
		return nil, nil, err
	}

	i := 3

	// skip the immediate new line
	if token[i] == '\n' {
		i++
	} else if token[i] == '\r' && token[i+1] == '\n' {
		i += 2
	}

	return token[i : len(b)-3], rest, err
}

func (p parser) parseMultilineBasicString(b []byte) ([]byte, []byte, error) {
	//ml-basic-string = ml-basic-string-delim [ newline ] ml-basic-body
	//ml-basic-string-delim
	//ml-basic-string-delim = 3quotation-mark
	//ml-basic-body = *mlb-content *( mlb-quotes 1*mlb-content ) [ mlb-quotes ]
	//
	//mlb-content = mlb-char / newline / mlb-escaped-nl
	//mlb-char = mlb-unescaped / escaped
	//mlb-quotes = 1*2quotation-mark
	//mlb-unescaped = wschar / %x21 / %x23-5B / %x5D-7E / non-ascii
	//mlb-escaped-nl = escape ws newline *( wschar / newline )

	token, rest, err := scanMultilineBasicString(b)
	if err != nil {
		return nil, nil, err
	}
	var builder bytes.Buffer

	i := 3

	// skip the immediate new line
	if token[i] == '\n' {
		i++
	} else if token[i] == '\r' && token[i+1] == '\n' {
		i += 2
	}

	// The scanner ensures that the token starts and ends with quotes and that
	// escapes are balanced.
	for ; i < len(token)-3; i++ {
		c := token[i]
		if c == '\\' {
			// When the last non-whitespace character on a line is an unescaped \,
			// it will be trimmed along with all whitespace (including newlines) up
			// to the next non-whitespace character or closing delimiter.
			if token[i+1] == '\n' || (token[i+1] == '\r' && token[i+2] == '\n') {
				i++ // skip the \
				for ; i < len(token)-3; i++ {
					c := token[i]
					if !(c == '\n' || c == '\r' || c == ' ' || c == '\t') {
						break
					}
				}
				continue
			}

			// handle escaping
			i++
			c = token[i]
			switch c {
			case '"', '\\':
				builder.WriteByte(c)
			case 'b':
				builder.WriteByte('\b')
			case 'f':
				builder.WriteByte('\f')
			case 'n':
				builder.WriteByte('\n')
			case 'r':
				builder.WriteByte('\r')
			case 't':
				builder.WriteByte('\t')
			case 'u':
				x, err := hexToString(token[i+3:len(token)-3], 4)
				if err != nil {
					return nil, nil, err
				}
				builder.WriteString(x)
				i += 4
			case 'U':
				x, err := hexToString(token[i+3:len(token)-3], 8)
				if err != nil {
					return nil, nil, err
				}
				builder.WriteString(x)
				i += 8
			default:
				return nil, nil, fmt.Errorf("invalid escaped character: %#U", c)
			}
		} else {
			builder.WriteByte(c)
		}
	}

	return builder.Bytes(), rest, nil
}

func (p parser) parseKey(b []byte) ([]byte, error) {
	//key = simple-key / dotted-key
	//simple-key = quoted-key / unquoted-key
	//
	//unquoted-key = 1*( ALPHA / DIGIT / %x2D / %x5F ) ; A-Z / a-z / 0-9 / - / _
	//quoted-key = basic-string / literal-string
	//dotted-key = simple-key 1*( dot-sep simple-key )
	//
	//dot-sep   = ws %x2E ws  ; . Period

	b, err := p.parseSimpleKey(b)
	if err != nil {
		return nil, err
	}

	for {
		b = p.parseWhitespace(b)
		if len(b) > 0 && b[0] == '.' {
			b, err = expect('.', b)
			if err != nil {
				return nil, err
			}
			b = p.parseWhitespace(b)
			b, err = p.parseSimpleKey(b)
			if err != nil {
				return nil, err
			}
		} else {
			break
		}
	}

	return b, nil
}

func (p parser) parseSimpleKey(b []byte) (rest []byte, err error) {
	//simple-key = quoted-key / unquoted-key
	//unquoted-key = 1*( ALPHA / DIGIT / %x2D / %x5F ) ; A-Z / a-z / 0-9 / - / _
	//quoted-key = basic-string / literal-string

	if len(b) == 0 {
		return nil, unexpectedCharacter{b: b}
	}

	var v []byte
	if b[0] == '\'' {
		v, rest, err = scanLiteralString(b)
	} else if b[0] == '"' {
		v, rest, err = p.parseBasicString(b)
	} else if isUnquotedKeyChar(b[0]) {
		v, rest, err = scanUnquotedKey(b)
	} else {
		return nil, unexpectedCharacter{b: b}
	}
	p.builder.SimpleKey(v)
	return
}

func (p parser) parseBasicString(b []byte) ([]byte, []byte, error) {
	//basic-string = quotation-mark *basic-char quotation-mark
	//quotation-mark = %x22            ; "
	//basic-char = basic-unescaped / escaped
	//basic-unescaped = wschar / %x21 / %x23-5B / %x5D-7E / non-ascii
	//escaped = escape escape-seq-char
	//escape-seq-char =  %x22         ; "    quotation mark  U+0022
	//escape-seq-char =/ %x5C         ; \    reverse solidus U+005C
	//escape-seq-char =/ %x62         ; b    backspace       U+0008
	//escape-seq-char =/ %x66         ; f    form feed       U+000C
	//escape-seq-char =/ %x6E         ; n    line feed       U+000A
	//escape-seq-char =/ %x72         ; r    carriage return U+000D
	//escape-seq-char =/ %x74         ; t    tab             U+0009
	//escape-seq-char =/ %x75 4HEXDIG ; uXXXX                U+XXXX
	//escape-seq-char =/ %x55 8HEXDIG ; UXXXXXXXX            U+XXXXXXXX

	token, rest, err := scanBasicString(b)
	if err != nil {
		return nil, nil, err
	}
	var builder bytes.Buffer

	// The scanner ensures that the token starts and ends with quotes and that
	// escapes are balanced.
	for i := 1; i < len(token)-1; i++ {
		c := token[i]
		if c == '\\' {
			i++
			c = token[i]
			switch c {
			case '"', '\\':
				builder.WriteByte(c)
			case 'b':
				builder.WriteByte('\b')
			case 'f':
				builder.WriteByte('\f')
			case 'n':
				builder.WriteByte('\n')
			case 'r':
				builder.WriteByte('\r')
			case 't':
				builder.WriteByte('\t')
			case 'u':
				x, err := hexToString(token[i+1:len(token)-1], 4)
				if err != nil {
					return nil, nil, err
				}
				builder.WriteString(x)
				i += 4
			case 'U':
				x, err := hexToString(token[i+1:len(token)-1], 8)
				if err != nil {
					return nil, nil, err
				}
				builder.WriteString(x)
				i += 8
			default:
				return nil, nil, fmt.Errorf("invalid escaped character: %#U", c)
			}
		} else {
			builder.WriteByte(c)
		}
	}

	return builder.Bytes(), rest, nil
}

func hexToString(b []byte, length int) (string, error) {
	if len(b) < length {
		return "", fmt.Errorf("unicode point needs %d hex characters", length)
	}
	// TODO: slow
	b, err := hex.DecodeString(string(b[:length]))
	if err != nil {
		return "", err
	}
	return string(b), nil
}

func (p parser) parseWhitespace(b []byte) []byte {
	//ws = *wschar
	//wschar =  %x20  ; Space
	//wschar =/ %x09  ; Horizontal tab

	_, rest := scanWhitespace(b)
	return rest
}

func expect(x byte, b []byte) ([]byte, error) {
	if len(b) == 0 || b[0] != x {
		return nil, unexpectedCharacter{r: x, b: b}
	}
	return b[1:], nil
}

type unexpectedCharacter struct {
	r byte
	b []byte
}

func (u unexpectedCharacter) Error() string {
	if len(u.b) == 0 {
		return fmt.Sprintf("expected %#U, not EOF", u.r)

	}
	return fmt.Sprintf("expected %#U, not %#U", u.r, u.b[0])
}