param(
    [string]$ProjectRoot = (Get-Location).Path,
    [string]$Date = (Get-Date -Format 'yyyy-MM-dd'),
    [string[]]$WhatDone,
    [string[]]$Files,
    [switch]$NoGit
)

Set-StrictMode -Version Latest
$ErrorActionPreference = 'Stop'

$projectPath = (Resolve-Path -LiteralPath $ProjectRoot).Path
$changelogDir = Join-Path $projectPath 'changelog'
if (-not (Test-Path -LiteralPath $changelogDir)) {
    New-Item -ItemType Directory -Path $changelogDir | Out-Null
}

$targetFile = Join-Path $changelogDir ("{0}.md" -f $Date)

function Get-GitChangedFiles {
    param([string]$Root)

    if ($NoGit) { return @() }
    if (-not (Get-Command git -ErrorAction SilentlyContinue)) { return @() }

    $inside = & git -C $Root rev-parse --is-inside-work-tree 2>$null
    if ($LASTEXITCODE -ne 0 -or $inside -ne 'true') { return @() }

    $lines = & git -C $Root status --porcelain
    $paths = @()

    foreach ($line in $lines) {
        if ([string]::IsNullOrWhiteSpace($line) -or $line.Length -lt 4) { continue }
        $raw = $line.Substring(3).Trim()

        if ($raw -match ' -> ') {
            $raw = ($raw -split ' -> ')[-1].Trim()
        }

        $raw = $raw.Trim('"')
        if (-not [string]::IsNullOrWhiteSpace($raw)) {
            $paths += $raw
        }
    }

    return $paths | Sort-Object -Unique
}

function Merge-Unique {
    param([string[]]$Existing, [string[]]$Incoming)

    $combined = @()
    $seen = @{}

    foreach ($item in @($Existing + $Incoming)) {
        if ([string]::IsNullOrWhiteSpace($item)) { continue }
        $k = $item.Trim()
        if (-not $seen.ContainsKey($k)) {
            $seen[$k] = $true
            $combined += $k
        }
    }

    return $combined
}

$changedFiles = if ($Files -and $Files.Count -gt 0) { $Files } else { Get-GitChangedFiles -Root $projectPath }

if (-not $WhatDone -or $WhatDone.Count -eq 0) {
    $WhatDone = @('Aktualizacja projektu oraz uporzadkowanie zmian w repozytorium.')
}

$existingWhatDone = @()
$existingFiles = @()

if (Test-Path -LiteralPath $targetFile) {
    $content = Get-Content -LiteralPath $targetFile
    $section = ''

    foreach ($line in $content) {
        if ($line -match '^##\s+Co zrobiono') { $section = 'done'; continue }
        if ($line -match '^##\s+Zmienione pliki') { $section = 'files'; continue }

        if ($line -match '^-\s+(.*)$') {
            $value = $matches[1].Trim()
            if ($section -eq 'done') {
                $existingWhatDone += $value
            } elseif ($section -eq 'files') {
                $existingFiles += $value.Trim('`')
            }
        }
    }
}

$finalWhatDone = Merge-Unique -Existing $existingWhatDone -Incoming $WhatDone
$finalFiles = Merge-Unique -Existing $existingFiles -Incoming $changedFiles

$sb = New-Object System.Text.StringBuilder
[void]$sb.AppendLine("# $Date")
[void]$sb.AppendLine()
[void]$sb.AppendLine('## Co zrobiono')
foreach ($item in $finalWhatDone) {
    [void]$sb.AppendLine("- $item")
}

[void]$sb.AppendLine()
[void]$sb.AppendLine('## Zmienione pliki')
if ($finalFiles.Count -eq 0) {
    [void]$sb.AppendLine('- Brak wykrytych zmian plikow (uzupelnij recznie, jesli potrzeba).')
} else {
    foreach ($file in $finalFiles) {
        [void]$sb.AppendLine(('- `{0}`' -f $file))
    }
}

Set-Content -LiteralPath $targetFile -Value $sb.ToString() -Encoding UTF8
Write-Output ("Changelog updated: {0}" -f $targetFile)