[CmdletBinding()]
param()

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

function Get-Sha256([string]$Path) {
    return (Get-FileHash -Algorithm SHA256 -LiteralPath $Path).Hash.ToLowerInvariant()
}

function Get-UserPathValue {
    if ($env:THT_USER_PATH_FILE) {
        if (Test-Path -LiteralPath $env:THT_USER_PATH_FILE) {
            return [System.IO.File]::ReadAllText($env:THT_USER_PATH_FILE)
        }
        return ''
    }
    return [Environment]::GetEnvironmentVariable('Path', 'User')
}

function Set-UserPathValue([string]$Value) {
    if ($env:THT_USER_PATH_FILE) {
        [System.IO.File]::WriteAllText($env:THT_USER_PATH_FILE, $Value)
        return
    }
    [Environment]::SetEnvironmentVariable('Path', $Value, 'User')
}

function Add-InstallDirectoryToUserPath([string]$InstallDirectory) {
    $currentPath = Get-UserPathValue
    $entries = @($currentPath -split ';' | Where-Object { $_ -ne '' })
    if ($entries | Where-Object { $_.TrimEnd('\\') -ieq $InstallDirectory.TrimEnd('\\') }) {
        return $false
    }
    $newPath = (@($entries) + $InstallDirectory) -join ';'
    Set-UserPathValue $newPath
    return $true
}

function Replace-InstalledBinary([string]$StagedBinary, [string]$TargetBinary) {
    $backupBinary = $null
    $replacedExistingBinary = $false
    try {
        if (Test-Path -LiteralPath $TargetBinary -PathType Leaf) {
            $backupBinary = Join-Path (Split-Path -Parent $TargetBinary) ('.tht-previous-' + [guid]::NewGuid() + '.exe')
            [System.IO.File]::Replace($StagedBinary, $TargetBinary, $backupBinary, $true)
            $replacedExistingBinary = $true
        } else {
            [System.IO.File]::Move($StagedBinary, $TargetBinary)
        }

        & $TargetBinary --help | Out-Null
        if ($LASTEXITCODE -ne 0) { throw 'installed tht did not pass its help check' }

        if ($backupBinary -and (Test-Path -LiteralPath $backupBinary -PathType Leaf)) {
            Remove-Item -LiteralPath $backupBinary -Force -ErrorAction Stop
        }
    } catch {
        $installFailure = $_
        if ($replacedExistingBinary -and $backupBinary -and (Test-Path -LiteralPath $backupBinary -PathType Leaf)) {
            try {
                [System.IO.File]::Replace($backupBinary, $TargetBinary, $null, $true)
                $backupBinary = $null
            } catch {
                throw "tht replacement failed; the previous executable remains at $backupBinary. Original failure: $installFailure. Restore failure: $_"
            }
        }
        throw $installFailure
    } finally {
        Remove-Item -LiteralPath $StagedBinary -Force -ErrorAction SilentlyContinue
    }
}

$repositoryRoot = Split-Path -Parent $PSScriptRoot
$buildOutput = $null
$sourceArtifactForInstall = $null
$installDirectory = if ($env:THT_INSTALL_DIRECTORY) {
    $env:THT_INSTALL_DIRECTORY
} else {
    Join-Path $env:LOCALAPPDATA 'ThothII\bin'
}
$installDirectory = [System.IO.Path]::GetFullPath($installDirectory)

if ($env:THT_BUILD_ARTIFACT) {
    $sourceArtifact = $env:THT_BUILD_ARTIFACT
    if (-not (Test-Path -LiteralPath $sourceArtifact -PathType Leaf)) {
        throw 'THT_BUILD_ARTIFACT is not a regular file'
    }
    if (-not $env:THT_BUILD_ARTIFACT_SHA256 -or $env:THT_BUILD_ARTIFACT_SHA256 -notmatch '^[0-9A-Fa-f]{64}$') {
        throw 'THT_BUILD_ARTIFACT_SHA256 must be a 64-character SHA-256 digest'
    }
    if ((Get-Sha256 $sourceArtifact) -ne $env:THT_BUILD_ARTIFACT_SHA256.ToLowerInvariant()) {
        throw 'packaged tht artifact checksum does not match'
    }
    $sourceArtifactForInstall = $sourceArtifact
} else {
    if ($env:PROCESSOR_ARCHITECTURE -notin @('AMD64', 'x86_64')) {
        throw "unsupported Windows processor architecture: $env:PROCESSOR_ARCHITECTURE (supported: AMD64)"
    }
    $buildOutput = Join-Path ([System.IO.Path]::GetTempPath()) ("tht-build-" + [guid]::NewGuid())
    New-Item -ItemType Directory -Path $buildOutput -Force | Out-Null
    $previousOutput = $env:THT_THT_OUTPUT_DIRECTORY
    $env:THT_THT_OUTPUT_DIRECTORY = $buildOutput
    try {
        & bash (Join-Path $repositoryRoot 'scripts/build-tht.sh') --all
        if ($LASTEXITCODE -ne 0) { throw 'the repository-pinned Docker build failed' }
    } finally {
        $env:THT_THT_OUTPUT_DIRECTORY = $previousOutput
    }
    $sourceArtifactForInstall = Join-Path $buildOutput 'tht-windows-amd64.exe'
    if (-not (Test-Path -LiteralPath $sourceArtifactForInstall -PathType Leaf)) {
        throw 'the repository-pinned Docker build did not produce tht-windows-amd64.exe'
    }
}

if ((Get-Item -LiteralPath $sourceArtifactForInstall).Length -eq 0) { throw 'native artifact is empty' }
New-Item -ItemType Directory -Path $installDirectory -Force | Out-Null
$stagedBinary = Join-Path $installDirectory ('.tht-' + [guid]::NewGuid() + '.exe')
try {
    Copy-Item -LiteralPath $sourceArtifactForInstall -Destination $stagedBinary -Force
    & $stagedBinary --help | Out-Null
    if ($LASTEXITCODE -ne 0) { throw 'native artifact did not pass its help check' }
    Replace-InstalledBinary $stagedBinary (Join-Path $installDirectory 'tht.exe')
} finally {
    Remove-Item -LiteralPath $stagedBinary -Force -ErrorAction SilentlyContinue
    if ($buildOutput) { Remove-Item -LiteralPath $buildOutput -Recurse -Force -ErrorAction SilentlyContinue }
}

$pathChanged = Add-InstallDirectoryToUserPath $installDirectory
if ($env:Path -notlike "*$installDirectory*") {
    $env:Path = "$installDirectory;$env:Path"
}
& (Join-Path $installDirectory 'tht.exe') --help | Out-Null
if ($LASTEXITCODE -ne 0) { throw 'installed tht did not pass its help check' }
Write-Output "Installed tht at $(Join-Path $installDirectory 'tht.exe')"
if ($pathChanged) {
    Write-Output 'Added ThothII to your user PATH. Open a new terminal before using tht there.'
}