//! Vertical Stacking layout for nested `Layout`s and/or `Widget`s.
//!
//! # Example
//! ...
const std = @import("std");
const terminal = @import("../terminal.zig");

const isTaggedUnion = @import("../event.zig").isTaggedUnion;
const Error = @import("../event.zig").Error;
const Key = terminal.Key;

const log = std.log.scoped(.layout_vstack);

pub fn Layout(comptime Event: type, comptime Element: type, comptime Renderer: type) type {
    if (!isTaggedUnion(Event)) {
        @compileError("Provided user event `Event` for `Layout(comptime Event: type, comptime Element: type, comptime Renderer: type)` is not of type `union(enum)`.");
    }
    if (!isTaggedUnion(Element)) {
        @compileError("Provided type `Element` for `Layout(comptime Event: type, comptime Element: type, comptime Renderer: type)` is not of type `union(enum)`.");
    }
    if (!std.mem.eql(u8, @typeInfo(Element).Union.fields[0].name, "layout")) {
        @compileError("Expected `layout: Layout` to be the first union element, but has name: " ++ @typeInfo(Element).Union.fields[0].name);
    }
    if (!std.mem.eql(u8, @typeInfo(Element).Union.fields[1].name, "widget")) {
        @compileError("Expected `widget: Widget` to be the first union element, but has name: " ++ @typeInfo(Element).Union.fields[1].name);
    }
    const Elements = std.ArrayList(Element);
    const LayoutType = @typeInfo(Element).Union.fields[0].type;
    const WidgetType = @typeInfo(Element).Union.fields[1].type;
    const Events = std.ArrayList(Event);
    return struct {
        // TODO: current focused `Element`?
        allocator: std.mem.Allocator = undefined,
        size: terminal.Size = undefined,
        elements: Elements = undefined,
        events: Events = undefined,

        pub fn init(allocator: std.mem.Allocator, children: anytype) *@This() {
            const ArgsType = @TypeOf(children);
            const args_type_info = @typeInfo(ArgsType);
            if (args_type_info != .Struct) {
                @compileError("expected tuple or struct argument, found " ++ @typeName(ArgsType));
            }
            const fields_info = args_type_info.Struct.fields;
            var elements = Elements.initCapacity(allocator, fields_info.len) catch @panic("OOM");
            inline for (comptime fields_info) |field| {
                const child = @field(children, field.name);
                const ChildType = @TypeOf(child);
                if (ChildType == WidgetType) {
                    elements.append(.{ .widget = child }) catch {};
                    continue;
                }
                if (ChildType == LayoutType) {
                    elements.append(.{ .layout = child }) catch {};
                    continue;
                }
                @compileError("child: " ++ field.name ++ " is not of type " ++ @typeName(WidgetType) ++ " or " ++ @typeName(LayoutType) ++ " but " ++ @typeName(ChildType));
            }
            const layout = allocator.create(@This()) catch @panic("OOM");
            layout.allocator = allocator;
            layout.elements = elements;
            layout.events = Events.init(allocator);
            return layout;
        }

        pub fn deinit(this: *@This()) void {
            this.events.deinit();
            for (this.elements.items) |*element| {
                switch (element.*) {
                    .layout => |*layout| {
                        layout.deinit();
                    },
                    .widget => |*widget| {
                        widget.deinit();
                    },
                }
            }
            this.elements.deinit();
            this.allocator.destroy(this);
        }

        pub fn handle(this: *@This(), event: Event) !*Events {
            this.events.clearRetainingCapacity();
            // order is important
            switch (event) {
                .resize => |size| {
                    this.size = size;
                    log.debug("Event .resize: {{ .anchor = {{ .col = {d}, .row = {d} }}, .cols = {d}, .rows = {d} }}", .{
                        size.anchor.col,
                        size.anchor.row,
                        size.cols,
                        size.rows,
                    });
                    const len: u16 = @truncate(this.elements.items.len);
                    const element_rows = @divTrunc(size.rows, len);
                    var overflow = size.rows % len;
                    var offset: u16 = 0;
                    // adjust size according to the containing elements
                    for (this.elements.items) |*element| {
                        var rows = element_rows;
                        if (overflow > 0) {
                            overflow -|= 1;
                            rows += 1;
                        }
                        const sub_event: Event = .{
                            .resize = .{
                                .anchor = .{
                                    .col = size.anchor.col,
                                    .row = size.anchor.row + offset,
                                },
                                .cols = size.cols,
                                .rows = rows,
                            },
                        };
                        offset += rows;
                        switch (element.*) {
                            .layout => |*layout| {
                                const events = try layout.handle(sub_event);
                                try this.events.appendSlice(events.items);
                            },
                            .widget => |*widget| {
                                if (widget.handle(sub_event)) |e| {
                                    try this.events.append(e);
                                }
                            },
                        }
                    }
                },
                else => {
                    for (this.elements.items) |*element| {
                        switch (element.*) {
                            .layout => |*layout| {
                                const events = try layout.handle(event);
                                try this.events.appendSlice(events.items);
                            },
                            .widget => |*widget| {
                                if (widget.handle(event)) |e| {
                                    try this.events.append(e);
                                }
                            },
                        }
                    }
                },
            }
            return &this.events;
        }

        pub fn render(this: *@This(), renderer: *Renderer) !void {
            for (this.elements.items) |*element| {
                switch (element.*) {
                    .layout => |*layout| {
                        try layout.render(renderer);
                    },
                    .widget => |*widget| {
                        try widget.render(renderer);
                    },
                }
            }
        }
    };
}