package template

import (
	"fmt"
)

// CompileTemplate scans once, emitting:
// - data blocks: inner content between a line that's exactly "{" and a line that's exactly "}"
// - matching blocks: gaps between data blocks (excluding the brace lines themselves)
func CompileTemplate(template string) ([]Block, error) {
	var out []Block
	var curlyIndex int

	const OPENING = '{'
	const CLOSING = '}'

	var start int
	var blockType BlockType

	if len(template) > 0 && template[0] == OPENING {
		blockType = DataBlock
	} else {
		blockType = MatchingBlock
	}

	for i, r := range template {

		nextCurlyIndex := curlyIndex

		switch r {
		case OPENING:
			nextCurlyIndex++
		case CLOSING:
			nextCurlyIndex--
		}

		if curlyIndex == 0 && nextCurlyIndex == 1 {
			if i > start {
				block, err := ParseTemplateBlock(template[start:i], blockType)
				if err != nil {
					return nil, fmt.Errorf("cannot parse block: %w", err)
				}
				out = append(out, block)
			}
			start = i
			blockType = DataBlock
		} else if curlyIndex == 1 && nextCurlyIndex == 0 {

			if i > start {
				block, err := ParseTemplateBlock(template[start:i+1], blockType)
				if err != nil {
					return nil, fmt.Errorf("cannot parse block: %w", err)
				}
				out = append(out, block)
			}

			nextChar := ' '
			if i+1 < len(template) {
				nextChar = rune(template[i+1])
			}

			if nextChar == OPENING {
				start = i + 1
				blockType = DataBlock
			} else {
				start = i + 1
				blockType = MatchingBlock
			}
		}

		curlyIndex = nextCurlyIndex
	}

	return out, nil
}