Private/Expand-Template.ps1
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<#
.SYNOPSIS Expands template placeholders in a string using values from a context object. .DESCRIPTION Replaces all template expressions of the form {{ property }} or {{ property.subproperty }} in the input string with corresponding values from the provided context object. Supports both simple and nested properties using dot notation. If a context value is missing, the placeholder is replaced with an empty string. For placeholders ending in '.sha256' (e.g., {{ asset.sha256 }}), if the parent object contains a 'browser_download_url' property, the function will automatically download the file, calculate its SHA256 hash, and cache the result for 24 hours. Returns the expanded string with all placeholders replaced. .PARAMETER Content The template string containing placeholders to expand. .PARAMETER Context The object providing values for template placeholders. Supports nested properties using dot notation. .EXAMPLE Expand-Template -Content 'Hello, {{ user.name }}!' -Context @{ user = @{ name = 'World' } } .EXAMPLE Expand-Template -Content 'SHA256: {{ asset.sha256 }}' -Context @{ asset = @{ browser_download_url = 'https://example.com/file.zip' } } .OUTPUTS System.String. The expanded string with all placeholders replaced. #> function Expand-Template { param([string]$Content, $Context) $Content -replace '{{\s*([\w.]+)\s*}}', { $expr = $_.Groups[1].Value $parts = $expr -split '\.' $val = $Context foreach ($p in $parts) { if ($null -eq $val) { break } $val = $val.$p } if ($null -eq $val) { $lastPart = $parts[-1] if ($lastPart -eq 'sha256' -and $parts.Count -gt 1) { # Special handling for sha256 placeholders $parentParts = $parts[0..($parts.Count - 2)] $parentVal = $Context foreach ($pp in $parentParts) { if ($null -eq $parentVal) { break } $parentVal = $parentVal.$pp } if ($null -ne $parentVal -and $null -ne $parentVal.browser_download_url -and $parentVal.browser_download_url -ne '') { return Get-Sha256FromUrlWithCache -Url $parentVal.browser_download_url } } return '' } else { return $val.ToString() } } } <#+ .SYNOPSIS Downloads a file from a URL, calculates its SHA256 hash, and caches the result for 24 hours. .DESCRIPTION Downloads the file at the specified URL to a temporary location, calculates its SHA256 hash, and caches the hash in a JSON file in the user's TEMP directory. If a cached hash exists and is less than 24 hours old, the cached value is returned. Verbose messages are always written for cache usage, cache errors, downloads, and hash calculations using Write-VerboseMark. .PARAMETER Url The URL of the file to download and hash. .EXAMPLE Get-Sha256FromUrlWithCache -Url 'https://example.com/file.zip' .NOTES Used internally by Expand-Template for {{ ...sha256 }} placeholders. Not intended for direct use outside template expansion. Verbose output is always written using Write-VerboseMark. #> function Get-Sha256FromUrlWithCache { param([string]$Url) $url = $Url.Trim() $cachePath = Join-Path $env:TEMP 'ChocoForge-HashCache.json' $cache = @{} if (Test-Path $cachePath) { try { $rawCache = Get-Content $cachePath -Raw | ConvertFrom-Json if ($rawCache -is [System.Collections.IDictionary]) { foreach ($k in $rawCache.PSObject.Properties.Name) { $cache[$k] = $rawCache.$k } } elseif ($rawCache -is [PSCustomObject]) { foreach ($k in $rawCache.PSObject.Properties.Name) { $cache[$k] = $rawCache.$k } } else { $cache = @{} } } catch { Write-VerboseMark 'Failed to read or parse cache file. Starting with empty cache.' $cache = @{ } } } $now = Get-Date $cacheKey = $url $cachedEntry = $null if ($cache.Keys -contains $cacheKey) { $cachedEntry = $cache[$cacheKey] $cacheTime = Get-Date $cachedEntry.timestamp if ($now - $cacheTime -lt ([TimeSpan]::FromHours(24))) { Write-VerboseMark "Using cached SHA256 for $url." return $cachedEntry.sha256 } else { Write-VerboseMark "Cache expired for $url. Recomputing hash." } } $tempDir = Join-Path $env:TEMP ([System.Guid]::NewGuid().ToString()) New-Item -ItemType Directory -Path $tempDir | Out-Null $fileName = Split-Path $url -Leaf $filePath = Join-Path $tempDir $fileName Write-VerboseMark "Downloading $url to $filePath ..." Invoke-WebRequest -Uri $url -OutFile $filePath -UseBasicParsing -Verbose:$false Write-VerboseMark "Calculating SHA256 for $filePath ..." $sha256 = (Get-FileHash -Path $filePath -Algorithm SHA256).Hash.ToLower() Remove-Item -Path $tempDir -Recurse -Force $cache[$cacheKey] = @{ sha256 = $sha256; timestamp = $now.ToString('o') } try { $cache | ConvertTo-Json -Depth 5 | Set-Content -Path $cachePath -Force Write-VerboseMark "Wrote SHA256 to cache for $url." } catch { Write-VerboseMark 'Failed to write cache file.' } Write-VerboseMark "Returning calculated SHA256 for $url." return $sha256 } |