namespace FundLab.Api

open System
open System.Globalization
open System.IO
open System.Text.Json
open Giraffe
open Microsoft.AspNetCore.Http

type EmptyPortfolioResponse =
    {
        status: string
        message: string
    }

type FundApiResponse =
    {
        id: Guid
        name: string
        currency: string
        initialCash: string
        initialUnitNav: string
        isSynthetic: bool
        availableCash: string
        status: string
    }

type ApiErrorResponse =
    {
        error: string
        message: string
    }

module App =
    let private invariant = CultureInfo.InvariantCulture

    let private cashText (value: decimal) = value.ToString("0.00", invariant)
    let private unitNavText (value: decimal) = value.ToString("0.00000000", invariant)

    let private fundResponse (fund: FundRecord) : FundApiResponse =
        {
            id = fund.Id
            name = fund.Name
            currency = fund.Currency
            initialCash = cashText fund.InitialCash
            initialUnitNav = unitNavText fund.InitialUnitNav
            isSynthetic = fund.IsSynthetic
            availableCash = cashText fund.AvailableCash
            status = fund.Status
        }

    let private errorResponse status error message : HttpHandler =
        setStatusCode status
        >=> json ({
            error = error
            message = message
        } : ApiErrorResponse)

    let private tryStringProperty (root: JsonElement) (name: string) =
        let mutable property = Unchecked.defaultof<JsonElement>

        if root.TryGetProperty(name, &property) && property.ValueKind = JsonValueKind.String then
            property.GetString() |> Option.ofObj
        else
            None

    let private tryBoolProperty (root: JsonElement) (name: string) =
        let mutable property = Unchecked.defaultof<JsonElement>

        if root.TryGetProperty(name, &property) then
            match property.ValueKind with
            | JsonValueKind.True -> Some true
            | JsonValueKind.False -> Some false
            | _ -> None
        else
            None

    let private tryDecimal (label: string) (text: string) =
        if String.IsNullOrWhiteSpace text then
            Error(sprintf "%s must be a decimal string" label)
        else
            match Decimal.TryParse(text, NumberStyles.AllowLeadingSign ||| NumberStyles.AllowDecimalPoint, invariant) with
            | true, value -> Ok value
            | false, _ -> Error(sprintf "%s must be a decimal string" label)

    let private parseFundCommand (body: string) =
        try
            use document = JsonDocument.Parse(body)
            let root = document.RootElement

            if root.ValueKind <> JsonValueKind.Object then
                Error "request body must be a JSON object"
            else
                match tryStringProperty root "name", tryStringProperty root "initialCash", tryStringProperty root "initialUnitNav", tryBoolProperty root "isSynthetic" with
                | Some name, Some initialCashText, Some initialUnitNavText, Some isSynthetic ->
                    match tryDecimal "initialCash" initialCashText, tryDecimal "initialUnitNav" initialUnitNavText with
                    | Ok initialCash, Ok initialUnitNav ->
                        Ok {
                            Name = name
                            InitialCash = initialCash
                            InitialUnitNav = initialUnitNav
                            IsSynthetic = isSynthetic
                        }
                    | Error message, _
                    | _, Error message -> Error message
                | _ ->
                    Error "name, initialCash, initialUnitNav and isSynthetic are required"
        with
        | :? JsonException -> Error "request body must be valid JSON"

    let private invokeHandler handler next ctx = handler next ctx

    let private unauthorized : HttpHandler =
        setStatusCode 401
        >=> setHttpHeader "WWW-Authenticate" "Bearer"
        >=> text "Unauthorized"

    let private requireBearer (next: HttpFunc) (ctx: HttpContext) =
        let expectedToken =
            Environment.GetEnvironmentVariable("FUND_LAB_AUTH_TOKEN")
            |> Option.ofObj
            |> Option.defaultValue ""

        let authorizationHeader = ctx.Request.Headers.Authorization.ToString()

        match Authentication.authorize expectedToken authorizationHeader with
        | AuthDecision.Authorized -> next ctx
        | AuthDecision.Unauthorized -> unauthorized next ctx

    let private health : HttpHandler =
        json ({
            service = "fund-lab-api"
            status = "ok"
        } : HealthResponse)

    let private emptyPortfolio : HttpHandler =
        json ({
             status = "empty"
             message = "尚未创建基金/尚未选择投资"
         } : EmptyPortfolioResponse)

    let private createFund (repository: FundRepository) : HttpHandler =
        fun next ctx ->
            task {
                use reader = new StreamReader(ctx.Request.Body)
                let! body = reader.ReadToEndAsync()
                let idempotencyKey = ctx.Request.Headers["Idempotency-Key"].ToString()

                match parseFundCommand body with
                | Error message ->
                    return! invokeHandler (errorResponse 400 "INVALID_FUND_REQUEST" message) next ctx
                | Ok command ->
                    try
                        match repository.CreateFund(idempotencyKey, command) with
                        | FundWriteResult.Created fund ->
                            return! invokeHandler (setStatusCode 201 >=> json (fundResponse fund)) next ctx
                        | FundWriteResult.Replayed fund ->
                            return! invokeHandler (json (fundResponse fund)) next ctx
                        | FundWriteResult.IdempotencyConflict ->
                            return! invokeHandler (errorResponse 409 "IDEMPOTENCY_CONFLICT" "idempotency key was used with a different request") next ctx
                        | FundWriteResult.Invalid message ->
                            return! invokeHandler (errorResponse 400 "INVALID_FUND_REQUEST" message) next ctx
                    with _ ->
                        return! invokeHandler (errorResponse 500 "PERSISTENCE_ERROR" "fund persistence failed") next ctx
            }

    let private getFund (repository: FundRepository) (fundIdText: string) : HttpHandler =
        fun next ctx ->
            match Guid.TryParse fundIdText with
            | false, _ -> errorResponse 400 "INVALID_FUND_ID" "fund id must be a UUID" next ctx
            | true, fundId ->
                try
                    match repository.GetFund fundId with
                    | Some fund -> json (fundResponse fund) next ctx
                    | None -> errorResponse 404 "FUND_NOT_FOUND" "fund was not found" next ctx
                with _ ->
                    errorResponse 500 "PERSISTENCE_ERROR" "fund persistence failed" next ctx

    let createApplication (repository: FundRepository) : HttpHandler =
        choose [
            GET >=> route "/health" >=> health
            subRoute "/api" (
                requireBearer
                >=> choose [
                    GET >=> route "/portfolio/summary" >=> emptyPortfolio
                    POST >=> route "/funds" >=> createFund repository
                    GET >=> routef "/funds/%s" (getFund repository)
                ]
            )
            setStatusCode 404 >=> text "Not Found"
        ]