package openapi

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

// DiffBlock represents a single file change in a git diff.
type DiffBlock struct {
	File    string
	Content string // The full diff content for this file
}

// DiffParser parses a stream of git diff output.
type DiffParser struct {
	onBlock func(DiffBlock)
	current *DiffBlock
	sb      strings.Builder
}

// NewDiffParser creates a new DiffParser.
func NewDiffParser(onBlock func(DiffBlock)) *DiffParser {
	return &DiffParser{onBlock: onBlock}
}

// Parse reads from r and calls onBlock for each completed diff block.
func (p *DiffParser) Parse(r io.Reader) error {
	scanner := bufio.NewScanner(r)
	for scanner.Scan() {
		p.Feed(scanner.Text())
	}
	p.Flush()
	return scanner.Err()
}

// Feed processes a single line of diff output.
func (p *DiffParser) Feed(line string) {
	if strings.HasPrefix(line, "diff --git ") {
		p.Flush()
		p.current = &DiffBlock{}
		// Extract file path from "diff --git a/path/to/file b/path/to/file"
		parts := strings.Split(line, " ")
		if len(parts) >= 4 {
			p.current.File = strings.TrimPrefix(parts[3], "b/")
		}
	}

	if p.current != nil {
		p.sb.WriteString(line)
		p.sb.WriteString("\n")
	}
}

// Flush finalizes the current block and emits it.
func (p *DiffParser) Flush() {
	if p.current != nil {
		p.current.Content = p.sb.String()
		p.onBlock(*p.current)
		p.current = nil
		p.sb.Reset()
	}
}