EasyLayout.fs

module EasyLayout
 
open System
open System.Drawing
open Microsoft.FSharp.Quotations
open Microsoft.FSharp.Quotations.Patterns
open Microsoft.FSharp.Quotations.DerivedPatterns
open MonoTouch.Foundation
open MonoTouch.UIKit
 
module private Utilities =
 
    let rec eval e =
        match e with
        | FieldGet (Some o, f) -> f.GetValue (eval o)
        | FieldGet (None, f) -> f.GetValue (null)
        | PropertyGet (None, p, i) -> p.GetValue (null, i |> Seq.map eval |> Seq.toArray)
        | PropertyGet (Some o, p, i) -> p.GetValue (eval o, i |> Seq.map eval |> Seq.toArray)
        | Value (x, _) -> x
        | _ -> failwithf "Don't know how to eval %A" e
 
    let toAttr m =
        match m with
        | "X" | "Left" -> NSLayoutAttribute.Left
        | "Y" | "Top" -> NSLayoutAttribute.Top
        | "Width" -> NSLayoutAttribute.Width
        | "Height" -> NSLayoutAttribute.Height
        | "Bottom" -> NSLayoutAttribute.Bottom
        | "Right" -> NSLayoutAttribute.Right
        | "CenterX" | "RectangleF.get_CenterX" -> NSLayoutAttribute.CenterX
        | "CenterY" | "RectangleF.get_CenterY" -> NSLayoutAttribute.CenterY
        | "Baseline" | "RectangleF.get_Baseline" -> NSLayoutAttribute.Baseline
        | _ -> NSLayoutAttribute.NoAttribute
 
    let (|ConstrainableProp|_|) (m:Reflection.MemberInfo) =
        match toAttr m.Name with NSLayoutAttribute.NoAttribute -> None | others -> Some(others)
    
    let (|FrameProp|_|) (pi:Reflection.PropertyInfo) = if pi.Name = "Frame" then Some(pi) else None
 
    let (|GetFrameProp|_|) e =
        match e with
        | Let (_, PropertyGet (Some o, FrameProp(fn), _), PropertyGet (_, ConstrainableProp(pn), _)) -> Some (eval o :?> NSObject, pn)
        | Call (_, ConstrainableProp(pn), [PropertyGet (Some o, FrameProp(fn), _)]) -> Some (eval o :?> NSObject, pn)
        | _ -> None 
 
    let compileLeftSide = function
        | GetFrameProp (x) -> x
        | side -> failwithf "Left hand side of constraint is expected to be a UIView.Frame property. It was: %A" side

    let (|NamedMethod|_|) name (m:Reflection.MethodInfo) = if m.Name = name then Some(m) else None

    let (|Mul|_|) = function
        | GetFrameProp (x, p) -> Some (x, p, 1.0f)
        | Call (_, NamedMethod "op_Multiply" _, [l; GetFrameProp (x, p)]) -> Some (x, p, Convert.ToSingle (eval l))
        | Call (_, NamedMethod "op_Multiply" _, [GetFrameProp (x, p); l]) -> Some (x, p, Convert.ToSingle (eval l))
        | _ -> None
 
    let compileRightSide side =
        match side with
        | Mul x -> (Some x, 0.0f)
        | Call (_, NamedMethod "op_Addition" _, [Mul(x); c]) -> (Some x, Convert.ToSingle (eval c))
        | Call (_, NamedMethod "op_Subtraction" _, [Mul(x); c]) -> (Some x, -Convert.ToSingle (eval c))
        | Value (x, _) -> (None, Convert.ToSingle (x))
        | FieldGet _ -> (None, Convert.ToSingle (eval side))
        | _ -> failwithf "Unrecognized right hand side: %A." side
 
    let compileConstraint left right rel =
        let (firstObj, firstAttr) = compileLeftSide left
        let (maybeObj, add) = compileRightSide right
        match maybeObj with
        | None -> NSLayoutConstraint.Create (firstObj, firstAttr, rel, null, NSLayoutAttribute.NoAttribute, 0.0f, add)
        | Some (secObj, secAttr, mul) -> NSLayoutConstraint.Create (firstObj, firstAttr, rel, secObj, secAttr, mul, add)
 
    let (|ToRel|_|) (m:System.Reflection.MethodInfo) =
        match m.Name with
        | "op_Equality" -> Some NSLayoutRelation.Equal
        | "op_LessThanOrEqual" -> Some NSLayoutRelation.LessThanOrEqual
        | "op_GreaterThanOrEqual" -> Some NSLayoutRelation.GreaterThanOrEqual
        | _ -> None
 
    let rec compileConstraints expr  =
        match expr with
        | NewArray (_, es) -> es |> Seq.collect compileConstraints |> Seq.toList
        | IfThenElse (i, t, e) -> compileConstraints i @ compileConstraints t @ compileConstraints e
        | Call (_, ToRel(m), [l; r]) -> [compileConstraint l r m]
        | Value _ -> []
        | _ -> failwithf "Unable to recognize constraints in expression: %A" expr
 
type RectangleF with
    member this.CenterX = this.X + this.Width / 2.0f
    member this.CenterY = this.Y + this.Height / 2.0f
    member this.Baseline = 0.0f
 
type UIView with
    /// <summary>
    /// <para>Constrains the layout of subviews according to equations and
    /// inequalities specified in <paramref name="constraints"/>.  Issue
    /// multiple constraints per call using the &amp;&amp; operator.</para>
    /// <code><@ button.Frame.Left &gt;= text.Frame.Right + 22 &amp;&amp;
    /// button.Frame.Width = View.Frame.Width * 0.42f @></code>
    /// </summary>
    /// <param name="constraints">Constraint equations and inequalities.</param>
    member this.ConstrainLayout (constraints) =
        let cs = Utilities.compileConstraints constraints |> Seq.toArray
        this.AddConstraints (cs)
        for x in cs do
            (x.FirstItem :?> UIView).TranslatesAutoresizingMaskIntoConstraints <- false
        cs