/// Loads shared fixtures from ../fixtures/<name>.json and decodes them into the course's types.
module Snake.Tests.Fixtures

open System.IO
open System.Text.Json
open Expecto
open Snake.Model
open Snake.View

let private dir =
    Path.GetFullPath(Path.Combine(Directory.GetCurrentDirectory(), "..", "fixtures"))

let load (name: string) : JsonElement =
    use doc = JsonDocument.Parse(File.ReadAllText(Path.Combine(dir, name + ".json")))
    doc.RootElement.Clone()

/// The cases array of a fixture.
let cases (name: string) : JsonElement list =
    (load name).GetProperty("cases").EnumerateArray() |> List.ofSeq

/// Decode a nullable JSON value into an Option.
let opt (f: JsonElement -> 'a) (v: JsonElement) : 'a option =
    if v.ValueKind = JsonValueKind.Null then None else Some(f v)

let prop (key: string) (v: JsonElement) : JsonElement = v.GetProperty(key)
let str (v: JsonElement) : string = v.GetString()
let num (v: JsonElement) : int = v.GetInt32()
let u32 (v: JsonElement) : uint32 = v.GetUInt32()
let bool (v: JsonElement) : bool = v.GetBoolean()
let list (f: JsonElement -> 'a) (v: JsonElement) : 'a list = v.EnumerateArray() |> Seq.map f |> List.ofSeq

/// The i-th argument of a case.
let arg (i: int) (c: JsonElement) : JsonElement = (prop "args" c)[i]
let expected (c: JsonElement) : JsonElement = prop "expected" c
let name (c: JsonElement) : string = str (prop "name" c)

let point (v: JsonElement) : Point = { X = num (prop "x" v); Y = num (prop "y" v) }

let direction (v: JsonElement) : Direction =
    match str v with
    | "Up" -> Up
    | "Down" -> Down
    | "Left" -> Left
    | "Right" -> Right
    | other -> failwith $"unknown direction: {other}"

let status (v: JsonElement) : Status =
    match str v with
    | "Playing" -> Playing
    | "Paused" -> Paused
    | "GameOver" -> GameOver
    | "Won" -> Won
    | other -> failwith $"unknown status: {other}"

let action (v: JsonElement) : Action =
    match str (prop "tag" v) with
    | "Tick" -> Tick
    | "Turn" -> Turn(direction (prop "dir" v))
    | "TogglePause" -> TogglePause
    | "Restart" -> Restart
    | "Frame" -> Frame
    | other -> failwith $"unknown action tag: {other}"

/// JSON uses camelCase field names; the F# record uses PascalCase.
let gameState (v: JsonElement) : GameState =
    { Width = num (prop "width" v)
      Height = num (prop "height" v)
      Snake = list point (prop "snake" v)
      Dir = direction (prop "dir" v)
      NextDir = direction (prop "nextDir" v)
      Apple = opt point (prop "apple" v)
      Seed = u32 (prop "seed" v)
      Score = num (prop "score" v)
      Status = status (prop "status" v)
      Frame = num (prop "frame" v) }

let shape (v: JsonElement) : Shape =
    let n key = num (prop key v)
    let s key = str (prop key v)

    match s "tag" with
    | "Rect" -> Rect(n "x", n "y", n "w", n "h", s "color")
    | "Text" -> Text(n "x", n "y", s "text", s "color", n "size", s "align")
    | other -> failwith $"unknown shape tag: {other}"

/// One test per case of a fixture, named "<label>: <case name>".
let fixtureTests (fixture: string) (label: string) (body: JsonElement -> unit) : Test list =
    [ for c in cases fixture -> testCase $"{label}: {name c}" (fun () -> body c) ]