package nginx

import (
	"bufio"
	"io"
	"regexp"
	"strings"
)

// Decoder implements parser.Decoder
type Decoder struct{ reader io.Reader }

// Decode is the main function of the parser.Decoder interface
func (d *Decoder) Decode(v interface{}) error {

	// check 'v'
	if v == nil {
		return ErrNullReceiver
	}
	vcast, ok := v.(*Line)
	if !ok {
		return ErrInvalidReceiver
	}
	vcast.Lines = make([]*Line, 0)

	r := bufio.NewReader(d.reader)
	n := -1 // line number

	// regexes
	reSection := regexp.MustCompile(`(?m)^([a-z0-9_-]+)\s*([^\{]*)\s*\{$`)
	reAssign := regexp.MustCompile(`(?m)^([a-z0-9_-]+)\s+([^;#]+);$`)
	reInclude := regexp.MustCompile(`(?m)^include\s+([^;#]+);$`)

	// actual section stack
	stack := make([]*Line, 0)
	eof := false

	for {
		n++
		if eof {
			break
		}

		l := &Line{Type: NONE}

		// 1. read line
		notrim, err := r.ReadString('\n')
		if err == io.EOF {
			if len(notrim) > 0 {
				eof = true
			} else {
				break
			}
		} else if err != nil {
			return &LineError{n, err}
		}
		notrim = strings.Trim(notrim, "\r\n")

		// 2. ignore empty
		line := strings.Trim(notrim, " \t\r\n")
		if len(line) < 1 {
			continue
		}

		// 2. comment
		if line[0] == '#' {
			l.Type = COMMENT
			l.Components = []string{line[1:]}
		} else if line[0] == ';' {
			l.Type = COLONCOMMENT
			l.Components = []string{line[1:]}
		} else if line[0] == '}' {
			l.Type = SECTIONEND
			if len(stack) < 1 {
				return &LineError{n, ErrUnexpectedSectionClose}
			}
		}

		// 3. section
		if l.Type == NONE {
			match := reSection.FindStringSubmatch(line)
			if match != nil {
				l.Type = SECTION
				l.Components = make([]string, 0)
				l.Components = append(l.Components, match[1])

				if len(match[2]) > 0 {
					l.Components = append(l.Components, strings.Trim(match[2], " \t"))
				}

				l.Lines = make([]*Line, 0)
				stack = append(stack, l)
			}
		}

		// 4. include
		if l.Type == NONE {
			match := reInclude.FindStringSubmatch(line)
			if match != nil {
				l.Type = INCLUDE
				l.Components = []string{match[1]}
			}
		}

		// 5. assignment
		if l.Type == NONE {
			match := reAssign.FindStringSubmatch(line)
			if match != nil {
				l.Type = ASSIGNMENT
				l.Components = match[1:]
			}
		}

		// 6. invalid type
		if l.Type == NONE {
			return &LineError{n, ErrInvalidSyntax}
		}

		// 7. pop section
		if l.Type == SECTIONEND {
			cur := stack[len(stack)-1]      // pop
			stack = stack[0 : len(stack)-1] // pop

			var last []*Line
			if len(stack) > 0 {
				last = stack[len(stack)-1].Lines
			} else {
				last = vcast.Lines
			}
			last = append(last, cur)

			continue
		}

		// 8. add to section / or receiver
		stacklen := len(stack)
		if stacklen > 0 && l.Type == SECTION {
			stacklen--
		}

		if stacklen > 0 {
			tail := stack[stacklen-1]
			tail.Lines = append(tail.Lines, l)
		} else {
			vcast.Lines = append(vcast.Lines, l)
		}

	}

	// fail on unclosed section
	if len(stack) > 0 {
		return ErrUnclosedSection
	}

	return nil
}