// Copyright (c) 2026 Storm Dragon
// Authors: Storm Dragon, Angus Kola
// SPDX-License-Identifier: GPL-3.0-or-later

package app

import (
	"strings"

	"git.stormux.org/storm/cthulhu/internal/ocr"
	"git.stormux.org/storm/cthulhu/internal/review"
)

// Retain an unchanged prefix or suffix exactly. A changed middle keeps the
// nearest legal offset; identical repeated text is deliberately not guessed.
func remapOCROffset(oldText, newText string, offset int) int {
	oldRunes, newRunes := []rune(oldText), []rune(newText)
	offset = max(0, min(offset, len(oldRunes)))
	prefix := 0
	for prefix < len(oldRunes) && prefix < len(newRunes) && oldRunes[prefix] == newRunes[prefix] {
		prefix++
	}
	if offset < prefix {
		return offset
	}
	suffix := 0
	for suffix < len(oldRunes)-prefix && suffix < len(newRunes)-prefix &&
		oldRunes[len(oldRunes)-1-suffix] == newRunes[len(newRunes)-1-suffix] {
		suffix++
	}
	if offset >= len(oldRunes)-suffix {
		return len(newRunes) - (len(oldRunes) - offset)
	}
	return min(offset, len(newRunes))
}

func (session *ocrSession) finish_refresh_locked(job ocrJob, interest review.Interest, capture ocr.Capture, result ocr.Result, err error) {
	session.refreshing = false
	if err != nil {
		session.refreshFailed = true
		session.status_locked("OCR refresh failed; activate after a successful refresh")
		return
	}
	previous := session.cursor.Text()
	offset := remapOCROffset(previous, result.Text, session.cursor.Offset())
	anchor := -1
	if session.selectionAnchor >= 0 {
		anchor = remapOCROffset(previous, result.Text, session.selectionAnchor)
	}
	session.source, session.pixels = interest, capture
	session.cursor = ocr.NewCursor(result)
	position, _ := session.cursor.Set(offset)
	session.selectionAnchor = anchor
	session.refreshFailed = result.Text == ""
	if result.Text == "" {
		session.status_locked("No text recognized")
	} else if result.Text != previous {
		session.status_locked(ocrChangedAnnouncement(previous, result.Text))
	} else if !job.automatic {
		session.status_locked("OCR text unchanged")
	}
	if session.display != nil {
		session.display.EnqueueFrame(session.frame_locked(position))
	}
	session.schedule_refresh_locked()
}

func ocrChangedAnnouncement(previous, current string) string {
	oldRunes, newRunes := []rune(previous), []rune(current)
	index := 0
	for index < len(oldRunes) && index < len(newRunes) && oldRunes[index] == newRunes[index] {
		index++
	}
	if index == len(newRunes) && index < len(oldRunes) {
		return "OCR text removed"
	}
	start, end := index, index
	for start > 0 && newRunes[start-1] != '\n' {
		start--
	}
	for end < len(newRunes) && newRunes[end] != '\n' && end-start < 100 {
		end++
	}
	line := strings.TrimSpace(string(newRunes[start:end]))
	if line == "" {
		return "OCR text changed"
	}
	return line
}