#!/usr/bin/env pwsh
# CASAN L5 Drift Detector - PowerShell port of drift-detect.sh
# Usage:
#   drift-detect.ps1 <golden-file> <candidate-file> <report-json>
#
# Exit codes: 0=pass/warn, 2=drift-fail

param(
    [Parameter(Mandatory=$true, Position=0)][string]$GoldenFile,
    [Parameter(Mandatory=$true, Position=1)][string]$CandidateFile,
    [Parameter(Mandatory=$true, Position=2)][string]$ReportFile
)

$ErrorActionPreference = "Stop"

$scriptDir   = Split-Path $MyInvocation.MyCommand.Path -Parent
$projectRoot = (Resolve-Path (Join-Path $scriptDir "../../..")).Path
$l5LogDir    = Join-Path $projectRoot ".specify/logs/level5"

foreach ($d in @($l5LogDir, (Split-Path $ReportFile -Parent))) {
    if ($d -and !(Test-Path $d)) { New-Item -ItemType Directory -Force -Path $d | Out-Null }
}

if (!(Test-Path $GoldenFile))    { Write-Error "Golden file not found: $GoldenFile"; exit 1 }
if (!(Test-Path $CandidateFile)) { Write-Error "Candidate file not found: $CandidateFile"; exit 1 }

function Get-Sha256 ([string]$text) {
    $bytes = [System.Text.Encoding]::UTF8.GetBytes($text)
    $hash  = [System.Security.Cryptography.SHA256]::Create().ComputeHash($bytes)
    return ($hash | ForEach-Object { $_.ToString("x2") }) -join ""
}

# Levenshtein-inspired similarity via longest common subsequence on words
function Get-SimilarityRatio ([string]$a, [string]$b) {
    $wordsA = $a -split '\s+' | Where-Object { $_ }
    $wordsB = $b -split '\s+' | Where-Object { $_ }
    if ($wordsA.Count -eq 0 -and $wordsB.Count -eq 0) { return 1.0 }
    if ($wordsA.Count -eq 0 -or $wordsB.Count -eq 0)  { return 0.0 }

    # Simple Jaccard similarity on word sets (fast, portable, no python needed)
    $setA = [System.Collections.Generic.HashSet[string]]$wordsA
    $setB = [System.Collections.Generic.HashSet[string]]$wordsB
    $intersection = ($setA | Where-Object { $setB.Contains($_) }).Count
    $union        = ($setA + $setB | Sort-Object -Unique).Count
    return [math]::Round($intersection / [math]::Max($union, 1), 4)
}

$golden    = Get-Content $GoldenFile    -Raw -Encoding UTF8
$candidate = Get-Content $CandidateFile -Raw -Encoding UTF8
if (!$golden)    { $golden    = "" }
if (!$candidate) { $candidate = "" }

$similarity   = Get-SimilarityRatio $golden $candidate
$lenGolden    = [math]::Max($golden.Length, 1)
$lengthDelta  = [math]::Round([math]::Abs($candidate.Length - $golden.Length) / $lenGolden, 4)

$driftStatus = "pass"
$driftAction = "allow"
if ($similarity -lt 0.70 -or $lengthDelta -gt 0.50) {
    $driftStatus = "fail"; $driftAction = "block_or_fallback"
} elseif ($similarity -lt 0.85 -or $lengthDelta -gt 0.30) {
    $driftStatus = "warn"; $driftAction = "require_review"
}

$timestamp    = (Get-Date).ToUniversalTime().ToString("yyyy-MM-ddTHH:mm:ssZ")
$goldenHash   = Get-Sha256 $golden
$candidHash   = Get-Sha256 $candidate

$report = @"
{
  "timestamp": "$timestamp",
  "harness": "L5-drift-detection",
  "status": "$driftStatus",
  "action": "$driftAction",
  "similarity_ratio": $similarity,
  "length_delta_ratio": $lengthDelta,
  "golden_hash": "$goldenHash",
  "candidate_hash": "$candidHash",
  "golden_file": "$GoldenFile",
  "candidate_file": "$CandidateFile"
}
"@

Set-Content -Path $ReportFile -Value $report -Encoding UTF8

# Append to L5 log
$logLine = "{`"timestamp`":`"$timestamp`",`"harness`":`"L5-drift-detection`",`"status`":`"$driftStatus`",`"similarity`":$similarity,`"length_delta`":$lengthDelta,`"golden`":`"$GoldenFile`",`"candidate`":`"$CandidateFile`"}"
Add-Content -Path (Join-Path $l5LogDir "drift.jsonl") -Value $logLine -Encoding UTF8

Write-Output "DRIFT_$($driftStatus.ToUpper()) similarity=$similarity length_delta=$lengthDelta report=$ReportFile"

if ($driftStatus -eq "fail") { exit 2 }
exit 0