namespace SomhairlesDream.Server

open System
open System.Collections.Concurrent
open System.Collections.Generic
open System.IO
open System.Security.Cryptography
open System.Threading.Tasks
open SomhairlesDream.Modeling
open SomhairlesDream.Shared

type RunStartOutcome =
    | Accepted of RunSnapshot
    | Conflict of RunSnapshot

type ArtifactLookupError =
    | RunNotFound
    | RunNotComplete of RunSnapshot
    | InvalidArtifactPath of string
    | ArtifactNotFound
    | InvalidManifest of string
    | ArtifactMismatch of string

type ArtifactFile =
    { Stream: Stream
      RelativePath: string }

type ArtifactRunCoordinator(
    artifactRoot: string,
    bridgeFactory: unit -> IArtifactBridge,
    clock: unit -> DateTimeOffset,
    staleAfter: TimeSpan
) =
    let root = Path.GetFullPath(artifactRoot)
    let registry = ArtifactRunRegistry(staleAfter, clock)

    let validateIds (ids: RunIds) =
        [| ids.ProjectId; ids.RunId; ids.BaseId; ids.TargetId |]
        |> Array.tryFind (Ids.validateResourceId >> Result.isError)
        |> function
            | Some invalid -> Error $"invalid resource id: {invalid}"
            | None -> Ok ()

    let runDirectory (projectId: string) (runId: string) =
        Path.Combine(root, projectId, runId)

    let failIfNeeded (store: ArtifactRunStore) (ids: RunIds) message =
        let snapshot = store.Snapshot()

        if snapshot.Status = "idle" || snapshot.Status = "running" then
            store.Apply(
                RunEvent.Fail
                    { Ids = ids
                      At = clock ()
                      StepId = snapshot.CurrentStepId
                      Message = message }
            )
            |> ignore

    let safeArtifactPath (runDirectory: string) (relativePath: string) =
        if String.IsNullOrWhiteSpace(relativePath) || Path.IsPathRooted(relativePath) then
            Error "artifact path must be relative"
        else
            let normalized = relativePath.Replace('\\', '/')
            let segments = normalized.Split('/', StringSplitOptions.RemoveEmptyEntries)

            if segments |> Array.exists (fun segment -> segment = ".." || segment = ".") then
                Error "artifact path contains traversal"
            else
                let fullPath = Path.GetFullPath(Path.Combine(runDirectory, normalized.Replace('/', Path.DirectorySeparatorChar)))
                let prefix = Path.GetFullPath(runDirectory).TrimEnd(Path.DirectorySeparatorChar) + string Path.DirectorySeparatorChar

                if fullPath.StartsWith(prefix, StringComparison.Ordinal) then
                    Ok(fullPath, String.Join("/", segments))
                else
                    Error "artifact path escapes run directory"

    let checkpointDigests =
        ConcurrentDictionary<string * string, ConcurrentDictionary<string, string * int64>>()

    let recordCheckpointDigest (ids: RunIds) (relativePath: string) =
        try
            match safeArtifactPath (runDirectory ids.ProjectId ids.RunId) relativePath with
            | Ok(fullPath, normalized) when File.Exists(fullPath) ->
                use stream = File.OpenRead(fullPath)
                use sha = SHA256.Create()

                let digest =
                    (Convert.ToHexString(sha.ComputeHash(stream)).ToLowerInvariant(), stream.Length)

                let digests =
                    checkpointDigests.GetOrAdd(
                        (ids.ProjectId, ids.RunId),
                        fun _ -> ConcurrentDictionary<string, string * int64>()
                    )

                digests[normalized] <- digest
            | _ -> ()
        with _ ->
            ()

    let rejectLinks (runDirectory: string) (fullPath: string) =
        let root = Path.GetFullPath(runDirectory)
        let relative = fullPath.Substring(root.Length + 1)
        let mutable current = root
        let mutable outcome = Ok ()

        for segment in
            relative.Split(
                [| Path.DirectorySeparatorChar; Path.AltDirectorySeparatorChar |],
                StringSplitOptions.RemoveEmptyEntries
            ) do
            match outcome with
            | Error _ -> ()
            | Ok () ->
                current <- Path.Combine(current, segment)

                let info: FileSystemInfo =
                    if Directory.Exists(current) && not (File.Exists(current)) then
                        DirectoryInfo(current) :> FileSystemInfo
                    else
                        FileInfo(current) :> FileSystemInfo

                if not (isNull info.LinkTarget) then
                    outcome <- Error "artifact path crosses a filesystem link"

        outcome

    let openValidated
        (runDirectory: string)
        (fullPath: string)
        (normalized: string)
        (expectedSha256: string)
        (expectedBytes: int64)
        : Result<ArtifactFile, ArtifactLookupError> =
        match rejectLinks runDirectory fullPath with
        | Error message -> Error(InvalidArtifactPath message)
        | Ok () ->
            try
                if not (File.Exists(fullPath)) then
                    Error ArtifactNotFound
                else
                    let stream =
                        File.Open(fullPath, FileMode.Open, FileAccess.Read, FileShare.Read)

                    try
                        if stream.Length <> expectedBytes then
                            Error(ArtifactMismatch $"artifact byte count mismatch: {normalized}")
                        else
                            use sha = SHA256.Create()

                            let sha256 =
                                Convert.ToHexString(sha.ComputeHash(stream)).ToLowerInvariant()

                            if sha256 <> expectedSha256 then
                                Error(ArtifactMismatch $"artifact hash mismatch: {normalized}")
                            else
                                stream.Seek(0L, SeekOrigin.Begin) |> ignore
                                Ok { Stream = stream :> Stream; RelativePath = normalized }
                    with _ ->
                        stream.Dispose()
                        reraise ()
            with
            | :? FileNotFoundException
            | :? DirectoryNotFoundException -> Error ArtifactNotFound
            | :? IOException as ex -> Error(InvalidArtifactPath $"artifact unavailable: {ex.Message}")

    let verifiedManifest (projectId: string) (runId: string) =
        let path = Path.Combine(runDirectory projectId runId, "manifest.json")

        match ArtifactVerifier.verify path with
        | Ok manifest -> Ok manifest
        | Error message -> Error(InvalidManifest message)

    let memberDigests (manifest: ArtifactManifest) =
        let map = Dictionary<string, string * int64>()

        let add (relativePath: string) (sha256: string) (bytes: int64) =
            map[relativePath] <- (sha256, bytes)

        for step in manifest.Steps do
            add step.ArtifactPath step.Sha256 step.Bytes
            step.Render |> Option.iter (fun render -> add render.ArtifactPath render.Sha256 render.Bytes)

        map

    let completedDigest (projectId: string) (runId: string) (normalized: string) =
        match verifiedManifest projectId runId with
        | Error lookupError -> Error lookupError
        | Ok manifest ->
            match (memberDigests manifest).TryGetValue(normalized) with
            | true, digest -> Ok digest
            | false, _ -> Error ArtifactNotFound

    let checkpointDigest (projectId: string) (runId: string) (normalized: string) =
        match checkpointDigests.TryGetValue((projectId, runId)) with
        | true, digests ->
            match digests.TryGetValue(normalized) with
            | true, digest -> Ok digest
            | false, _ -> Error ArtifactNotFound
        | false, _ -> Error ArtifactNotFound

    let runPipeline (store: ArtifactRunStore) (ids: RunIds) render =
        try
            let options : PipelineOptions =
                { ArtifactRoot = root
                  Ids = ids
                  Render = render
                  Bridge = bridgeFactory ()
                  Clock = clock
                  OnEvent =
                      fun event ->
                          (match event with
                           | Checkpoint value -> recordCheckpointDigest value.Ids value.ArtifactPath
                           | _ -> ())

                          match store.Apply event with
                          | Ok _ -> ()
                          | Error message -> invalidOp message }

            match Pipeline.run options with
            | Ok _ -> ()
            | Error message -> failIfNeeded store ids message
        with ex ->
            failIfNeeded store ids ex.Message

    member _.ArtifactRoot = root

    member _.Start(ids: RunIds, render: bool) : Result<RunStartOutcome, string> =
        match validateIds ids with
        | Error message -> Error message
        | Ok () ->
            match registry.TryCreate(ids) with
            | Some store ->
                Task.Run(fun () -> runPipeline store ids render) |> ignore
                Ok(Accepted(store.Snapshot()))
            | None ->
                match registry.TryFind(ids.ProjectId, ids.RunId) with
                | Some store -> Ok(Conflict(store.Observe(clock ())))
                | None -> Error "run registry entry disappeared"

    member _.TryFind(projectId: string, runId: string) = registry.TryFind(projectId, runId)

    member _.Subscribe(projectId: string, runId: string) =
        registry.TryFind(projectId, runId) |> Option.map (fun store -> store.Subscribe())

    member _.ObserveAll() = registry.ObserveAll(clock ())

    member _.Manifest(projectId: string, runId: string) : Result<ArtifactManifest, ArtifactLookupError> =
        match registry.TryFind(projectId, runId) with
        | None -> Error RunNotFound
        | Some store ->
            let snapshot = store.Observe(clock ())

            if snapshot.Status <> "complete" then
                Error(RunNotComplete snapshot)
            else
                verifiedManifest projectId runId

    member _.Artifact(projectId: string, runId: string, relativePath: string) : Result<ArtifactFile, ArtifactLookupError> =
        match registry.TryFind(projectId, runId) with
        | None -> Error RunNotFound
        | Some store ->
            let snapshot = store.Observe(clock ())

            if snapshot.Status <> "complete" then
                Error(RunNotComplete snapshot)
            else
                let directory = runDirectory projectId runId

                match safeArtifactPath directory relativePath with
                | Error message -> Error(InvalidArtifactPath message)
                | Ok(fullPath, normalized) ->
                    match rejectLinks directory fullPath with
                    | Error message -> Error(InvalidArtifactPath message)
                    | Ok () ->
                        match completedDigest projectId runId normalized with
                        | Error lookupError -> Error lookupError
                        | Ok(sha256, bytes) -> openValidated directory fullPath normalized sha256 bytes

    member _.StepArtifact(projectId: string, runId: string, relativePath: string) : Result<ArtifactFile, ArtifactLookupError> =
        match registry.TryFind(projectId, runId) with
        | None -> Error RunNotFound
        | Some store ->
            let directory = runDirectory projectId runId

            match safeArtifactPath directory relativePath with
            | Error message -> Error(InvalidArtifactPath message)
            | Ok(_, normalized) when not (normalized.EndsWith(".glb", StringComparison.OrdinalIgnoreCase)) ->
                Error(InvalidArtifactPath "step artifacts must be .glb files")
            | Ok(_, normalized) when not (normalized.StartsWith("steps/", StringComparison.Ordinal)) ->
                Error(InvalidArtifactPath "step artifacts must live under steps/")
            | Ok(fullPath, normalized) ->
                let snapshot = store.Observe(clock ())

                let digest =
                    match rejectLinks directory fullPath with
                    | Error message -> Error(InvalidArtifactPath message)
                    | Ok () ->
                        if snapshot.Status = "complete" then
                            completedDigest projectId runId normalized
                        elif snapshot.CompletedSteps |> Array.exists (fun recorded -> recorded = normalized) then
                            checkpointDigest projectId runId normalized
                        else
                            Error ArtifactNotFound

                match digest with
                | Error lookupError -> Error lookupError
                | Ok(sha256, bytes) -> openValidated directory fullPath normalized sha256 bytes