<#
.SYNOPSIS
    Fails if the rule engine has acquired a dependency it must not have.

.DESCRIPTION
    Constitution Principle IV: the pure rule engine must not depend on Microsoft
    Graph, authentication, Azure Automation, or console rendering. Directory
    structure alone does not enforce that — one convenient call is all it takes to
    make the engine untestable offline, and the failure is silent until someone
    tries to run the tests without a tenant.

    This check is the enforcement. It runs in CI (pipelines/validate.yml) and is
    cheap enough to run locally on every change.

.EXAMPLE
    ./tests/Test-EnginePurity.ps1
#>
[CmdletBinding()]
param(
    [string] $EnginePath = (Join-Path (Split-Path $PSScriptRoot -Parent) 'src/RuleEngine'),
    [switch] $PassThru
)

$ErrorActionPreference = 'Stop'

$forbidden = @(
    @{ Name = 'Microsoft Graph call'; Regex = 'Invoke-MgGraphRequest|Connect-MgGraph|graph\.microsoft\.com|Invoke-PersonaGraphRequest' }
    @{ Name = 'Authentication layer'; Regex = 'Connect-Persona\w+' }
    @{ Name = 'Data provider layer'; Regex = 'Get-Persona(Users|GroupMembership|DirectoryRoles)' }
    @{ Name = 'Persistence layer'; Regex = 'Set-UserPersonaAttribute|New-PersonaWriteBody|Compare-PersonaValue' }
    @{ Name = 'Console rendering'; Regex = 'Write-Host|Write-UserPersonaResult|Write-PersonaSummary' }
    @{ Name = 'Direct HTTP'; Regex = 'Invoke-RestMethod|Invoke-WebRequest|System\.Net\.Http' }
    @{ Name = 'Filesystem access'; Regex = 'Get-Content|Set-Content|Out-File|Export-Csv' }
    @{ Name = 'Non-deterministic input'; Regex = 'Get-Random|Get-Date|\[datetime\]::(Now|UtcNow|Today)|New-Guid' }
)

if (-not (Test-Path $EnginePath)) {
    Write-Host "Engine path '$EnginePath' does not exist yet - nothing to check." -ForegroundColor Yellow
    if ($PassThru) { return @() }
    exit 0
}

$findings = [System.Collections.Generic.List[object]]::new()

foreach ($file in Get-ChildItem -Path $EnginePath -Filter '*.ps1' -File -Recurse) {

    # Tokenize rather than scan raw text. Comments in this codebase legitimately
    # name the forbidden functions when explaining why the engine does not call
    # them, and a text scan cannot tell a trailing comment from code. The parser
    # can, exactly.
    $tokens = $null
    $parseErrors = $null
    $null = [System.Management.Automation.Language.Parser]::ParseFile(
        $file.FullName, [ref]$tokens, [ref]$parseErrors)

    if ($parseErrors.Count -gt 0) {
        $findings.Add([pscustomobject]@{
                File       = $file.Name
                Line       = $parseErrors[0].Extent.StartLineNumber
                Dependency = 'Parse error'
                Text       = $parseErrors[0].Message
            })
        continue
    }

    # Rebuild each line from its non-comment tokens.
    $codeByLine = @{}
    foreach ($token in $tokens) {
        if ($token.Kind -eq 'Comment') { continue }

        $line = $token.Extent.StartLineNumber
        if (-not $codeByLine.ContainsKey($line)) { $codeByLine[$line] = [System.Text.StringBuilder]::new() }
        $null = $codeByLine[$line].Append($token.Text).Append(' ')
    }

    foreach ($line in ($codeByLine.Keys | Sort-Object)) {
        $code = $codeByLine[$line].ToString()

        foreach ($rule in $forbidden) {
            if ($code -match $rule.Regex) {
                $findings.Add([pscustomobject]@{
                        File       = $file.Name
                        Line       = $line
                        Dependency = $rule.Name
                        Text       = $code.Trim()
                    })
            }
        }
    }
}

if ($findings.Count -gt 0) {
    Write-Host "Engine purity check FAILED - $($findings.Count) violation(s) of Principle IV:" -ForegroundColor Red
    $findings | Format-Table -AutoSize | Out-String | Write-Host
    Write-Host 'The rule engine must remain testable offline with synthetic data.' -ForegroundColor Red
    if ($PassThru) { return $findings }
    exit 1
}

Write-Host 'Engine purity check passed: the rule engine has no forbidden dependencies.' -ForegroundColor Green
if ($PassThru) { return @() }
exit 0