package migrate

import "strings"

// splitSQL splits a SQL string into individual statements.
// Handles $$ ... $$ dollar-quoted blocks, $tag$ ... $tag$ tagged quotes,
// -- line comments, /* ... */ block comments, and '...' string literals
// so that semicolons inside any of these constructs are not treated as
// statement boundaries.
func SplitSQL(sql string) []string {
	var statements []string
	var current strings.Builder
	inDollarQuote := false
	dollarTag := ""

	i := 0
	for i < len(sql) {
		// Handle line comments (-- to end of line)
		if !inDollarQuote && i+1 < len(sql) && sql[i] == '-' && sql[i+1] == '-' {
			for i < len(sql) && sql[i] != '\n' {
				current.WriteByte(sql[i])
				i++
			}
			continue
		}

		// Handle block comments (/* ... */)
		if !inDollarQuote && i+1 < len(sql) && sql[i] == '/' && sql[i+1] == '*' {
			end := strings.Index(sql[i+2:], "*/")
			if end >= 0 {
				current.WriteString(sql[i : i+end+4])
				i += end + 4
				continue
			}
		}

		// Handle single-quoted string literals ('...')
		if !inDollarQuote && sql[i] == '\'' {
			j := i + 1
			for j < len(sql) {
				if sql[j] == '\'' {
					if j+1 < len(sql) && sql[j+1] == '\'' {
						j += 2 // skip doubled quote ''
						continue
					}
					break
				}
				j++
			}
			current.WriteString(sql[i : j+1])
			i = j + 1
			continue
		}

		// Check for dollar-quote start/end
		if !inDollarQuote && sql[i] == '$' {
			j := i + 1
			for j < len(sql) && (sql[j] == '_' || (sql[j] >= 'a' && sql[j] <= 'z') || (sql[j] >= 'A' && sql[j] <= 'Z') || (sql[j] >= '0' && sql[j] <= '9')) {
				j++
			}
			if j < len(sql) && sql[j] == '$' {
				dollarTag = sql[i : j+1]
				current.WriteString(dollarTag)
				inDollarQuote = true
				i = j + 1
				continue
			}
		}
		if inDollarQuote && strings.HasPrefix(sql[i:], dollarTag) {
			current.WriteString(dollarTag)
			i += len(dollarTag)
			inDollarQuote = false
			dollarTag = ""
			continue
		}

		if !inDollarQuote && sql[i] == ';' {
			statements = append(statements, current.String())
			current.Reset()
			i++
			continue
		}

		current.WriteByte(sql[i])
		i++
	}

	if strings.TrimSpace(current.String()) != "" {
		statements = append(statements, current.String())
	}

	return statements
}