namespace SomhairlesDream.Server

open System
open System.Collections.Generic
open System.Threading.Channels
open SomhairlesDream.Shared

type RunStore(projectId: string, runId: string, staleAfter: TimeSpan) =
    let gate = obj ()
    let mutable state = RunState.initial projectId runId DateTimeOffset.UtcNow
    let subscribers = ResizeArray<Channel<LiveSnapshot>>()

    let update transition =
        lock gate (fun () ->
            state <- transition state
            for subscriber in subscribers do
                subscriber.Writer.TryWrite(state) |> ignore
            state)

    member _.Snapshot() = lock gate (fun () -> state)

    member _.Start(now: DateTimeOffset) = update (RunState.start now)

    member _.Heartbeat(now: DateTimeOffset) = update (RunState.heartbeat now)

    member _.Observe(now: DateTimeOffset) = update (RunState.statusAt staleAfter now)

    member _.Publish(now: DateTimeOffset, mesh: MeshSnapshot) = update (RunState.publish now mesh)

    member _.Subscribe() : ChannelReader<LiveSnapshot> =
        let channel = Channel.CreateUnbounded<LiveSnapshot>()

        lock gate (fun () ->
            channel.Writer.TryWrite(state) |> ignore
            subscribers.Add(channel)
            channel.Reader)

type ArtifactRunSubscription(reader: ChannelReader<RunSnapshot>, dispose: unit -> unit) =
    let mutable disposed = false

    member _.Reader = reader

    member _.Dispose() =
        if not disposed then
            disposed <- true
            dispose ()

    interface IDisposable with
        member this.Dispose() = this.Dispose()

type ArtifactRunStore(ids: RunIds, staleAfter: TimeSpan, initialAt: DateTimeOffset) =
    let gate = obj ()
    let subscribers = ResizeArray<Channel<RunSnapshot>>()
    let mutable state : RunSnapshot =
        { ProjectId = ids.ProjectId
          RunId = ids.RunId
          BaseId = ids.BaseId
          TargetId = ids.TargetId
          Status = "idle"
          CurrentStepId = None
          CurrentStepIndex = -1
          TotalSteps = 0
          LastHeartbeatAt = None
          UpdatedAt = initialAt
          Message = "waiting for design run"
          ManifestPath = None
          ManifestUrl = None
          Error = None
          IsStale = false }

    let publish next =
        for subscriber in subscribers do
            subscriber.Writer.TryWrite(next) |> ignore

    let eventIds = function
        | RunEvent.Start value -> value.Ids
        | RunEvent.Heartbeat value -> value.Ids
        | RunEvent.Checkpoint value -> value.Ids
        | RunEvent.Complete value -> value.Ids
        | RunEvent.Fail value -> value.Ids

    let eventName = function
        | RunEvent.Start _ -> "start"
        | RunEvent.Heartbeat _ -> "heartbeat"
        | RunEvent.Checkpoint _ -> "checkpoint"
        | RunEvent.Complete _ -> "complete"
        | RunEvent.Fail _ -> "fail"

    let rejectIfNotRunning event =
        if state.Status <> "running" then
            Some $"cannot apply {eventName event} to run in status {state.Status}"
        else
            None

    let checkpointCount () =
        if state.CurrentStepIndex < 0 then 0 else state.CurrentStepIndex + 1

    let commit next =
        state <- next
        publish next
        Ok next

    member _.Snapshot() = lock gate (fun () -> state)

    member _.Apply(event: RunEvent) : Result<RunSnapshot, string> =
        lock gate (fun () ->
            if eventIds event <> ids then
                Error "run event identity does not match the selected run"
            else
                match event with
                | RunEvent.Start value ->
                    if state.Status <> "idle" then
                        Error $"cannot apply start to run in status {state.Status}"
                    elif value.TotalSteps <= 0 then
                        Error "run must contain at least one step"
                    else
                        commit
                            { state with
                                Status = "running"
                                TotalSteps = value.TotalSteps
                                CurrentStepId = None
                                CurrentStepIndex = -1
                                LastHeartbeatAt = Some value.At
                                UpdatedAt = value.At
                                Message = "design run started"
                                Error = None
                                IsStale = false }
                | RunEvent.Heartbeat value ->
                    match rejectIfNotRunning event with
                    | Some message -> Error message
                    | None ->
                        commit
                            { state with
                                LastHeartbeatAt = Some value.At
                                UpdatedAt = value.At
                                Message = value.Message
                                IsStale = false }
                | RunEvent.Checkpoint value ->
                    match rejectIfNotRunning event with
                    | Some message -> Error message
                    | None when value.TotalSteps <> state.TotalSteps ->
                        Error "checkpoint total steps do not match run"
                    | None when value.StepIndex < 0 || value.StepIndex >= state.TotalSteps ->
                        Error "checkpoint step index is outside the run"
                    | None when value.StepIndex <> checkpointCount () ->
                        Error "checkpoint step index is out of order"
                    | None ->
                        commit
                            { state with
                                CurrentStepId = Some value.StepId
                                CurrentStepIndex = value.StepIndex
                                LastHeartbeatAt = Some value.At
                                UpdatedAt = value.At
                                Message = value.Message
                                IsStale = false }
                | RunEvent.Complete value ->
                    match rejectIfNotRunning event with
                    | Some message -> Error message
                    | None when checkpointCount () <> state.TotalSteps ->
                        Error "cannot complete run before every step is checkpointed"
                    | None ->
                        commit
                            { state with
                                Status = "complete"
                                CurrentStepId = None
                                LastHeartbeatAt = Some value.At
                                UpdatedAt = value.At
                                Message = "design run complete"
                                ManifestPath = Some value.ManifestPath
                                ManifestUrl = Some $"/api/artifacts/manifest?projectId={ids.ProjectId}&runId={ids.RunId}"
                                Error = None
                                IsStale = false }
                | RunEvent.Fail value ->
                    if state.Status <> "idle" && state.Status <> "running" then
                        Error $"cannot apply fail to run in status {state.Status}"
                    else
                        commit
                            { state with
                                Status = "failed"
                                CurrentStepId = value.StepId
                                LastHeartbeatAt = Some value.At
                                UpdatedAt = value.At
                                Message = value.Message
                                Error = Some value.Message
                                IsStale = false })

    member _.Observe(now: DateTimeOffset) =
        lock gate (fun () ->
            let next =
                match state.Status, state.LastHeartbeatAt with
                | "running", Some heartbeat when now - heartbeat > staleAfter && not state.IsStale ->
                    Some
                        { state with
                            UpdatedAt = now
                            Message = "heartbeat timeout"
                            IsStale = true }
                | "running", Some heartbeat when now - heartbeat <= staleAfter && state.IsStale ->
                    Some
                        { state with
                            UpdatedAt = now
                            Message = "heartbeat resumed"
                            IsStale = false }
                | _ -> None

            match next with
            | Some value ->
                state <- value
                publish value
                value
            | None -> state)

    member _.Subscribe() =
        let channel = Channel.CreateUnbounded<RunSnapshot>()

        lock gate (fun () ->
            channel.Writer.TryWrite(state) |> ignore
            subscribers.Add(channel))

        new ArtifactRunSubscription(
            channel.Reader,
            fun () ->
                lock gate (fun () ->
                    subscribers.Remove(channel) |> ignore
                    channel.Writer.TryComplete() |> ignore))

type ArtifactRunRegistry(staleAfter: TimeSpan, clock: unit -> DateTimeOffset) =
    let gate = obj ()
    let runs = Dictionary<string * string, ArtifactRunStore>()

    member _.TryCreate(ids: RunIds) =
        lock gate (fun () ->
            let key = ids.ProjectId, ids.RunId

            match runs.TryGetValue(key) with
            | true, _ -> None
            | false, _ ->
                let store = ArtifactRunStore(ids, staleAfter, clock ())
                runs.Add(key, store)
                Some store)

    member _.GetOrCreate(ids: RunIds) =
        lock gate (fun () ->
            let key = ids.ProjectId, ids.RunId

            match runs.TryGetValue(key) with
            | true, store -> store
            | false, _ ->
                let store = ArtifactRunStore(ids, staleAfter, clock ())
                runs.Add(key, store)
                store)

    member _.TryFind(projectId: string, runId: string) =
        lock gate (fun () ->
            match runs.TryGetValue((projectId, runId)) with
            | true, store -> Some store
            | false, _ -> None)

    member _.ObserveAll(now: DateTimeOffset) =
        lock gate (fun () -> runs.Values |> Seq.map (fun store -> store.Observe(now)) |> Seq.toArray)