// Faux implements a pretty terrible subset of YAML
// because apparently no YAML parser for Zig is good yet
// and I am honestly already growing quite angered about it.
//
// It's insanely simple, it's meant to be simple, and it
// will stay that way.
//
// I like to see it as it's own format, atp.
//
// Also, important note, the day that a proper YAML parser
// comes out for Zig, this library must be pulled off
// immediately and destroyed. yes.
//

const std = @import("std");

fn parseSimpleKV(
    allocator: std.mem.Allocator,
    input: []const u8,
) !Map {
    var map = Map.init(allocator);
    var lines = std.mem.tokenizeScalar(u8, input, '\n');

    while (lines.next()) |line| {
        const hash_index = std.mem.indexOfScalar(u8, line, '#') orelse line.len;
        const trimmed = std.mem.trim(u8, line[0..hash_index], " \t\r");

        if (trimmed.len == 0) continue;

        const colon_index = std.mem.indexOfScalar(u8, trimmed, ':') orelse continue;

        const key = std.mem.trim(u8, trimmed[0..colon_index], " \t");
        var value = std.mem.trim(u8, trimmed[colon_index + 1 ..], " \t");

        if (value.len >= 2 and ((value[0] == '"' and value[value.len - 1] == '"') or
            (value[0] == '\'' and value[value.len - 1] == '\'')))
        {
            const inner = value[1 .. value.len - 1];
            value = try unescapeString(allocator, inner, value[0]);
        } else {
            value = try unescapeString(allocator, value, 0);
        }

        try map.put(key, value);
    }

    return map;
}

fn unescapeString(
    allocator: std.mem.Allocator,
    s: []const u8,
    quote: u8,
) ![]const u8 {
    var buffer = std.ArrayList(u8).init(allocator);
    var i: usize = 0;

    while (i < s.len) : (i += 1) {
        if (s[i] == '\\' and i + 1 < s.len) {
            i += 1;
            switch (s[i]) {
                'n' => try buffer.append('\n'),
                'r' => try buffer.append('\r'),
                't' => try buffer.append('\t'),
                '\\' => try buffer.append('\\'),
                '"' => if (quote == '"' or quote == 0) try buffer.append('"') else {
                    try buffer.append('\\');
                    try buffer.append('"');
                },
                '\'' => if (quote == '\'' or quote == 0) try buffer.append('\'') else {
                    try buffer.append('\\');
                    try buffer.append('\'');
                },
                else => {
                    try buffer.append('\\');
                    try buffer.append(s[i]);
                },
            }
        } else {
            try buffer.append(s[i]);
        }
    }

    return buffer.toOwnedSlice();
}

fn populateStructFromMap(comptime T: type, dest: *T, map: Map, allocator: std.mem.Allocator) !void {
    const fields = std.meta.fields(T);
    inline for (fields) |field| {
        const key = field.name;
        const field_type = field.type;

        @field(dest, key) = if (map.get(key)) |raw|
            try parseValue(field_type, raw, allocator)
        else
            field.defaultValue() orelse return error.MissingField;
    }
}

fn parseValue(comptime T: type, raw: []const u8, allocator: std.mem.Allocator) !T {
    const info = @typeInfo(T);
    return switch (info) {
        .bool => std.mem.eql(u8, raw, "true"),

        .pointer => if (T == []const u8 or T == []u8)
            try allocator.dupe(u8, raw)
        else
            error.PointersUnsupported,

        .@"enum" => std.meta.stringToEnum(T, raw) orelse error.InvalidEnumValue,

        .optional => blk: {
            if (std.mem.eql(u8, raw, "null"))
                break :blk null;

            const child = info.optional.child;
            const parsed = try parseValue(child, raw, allocator);
            break :blk parsed;
        },

        else => error.NotImplemented,
    };
}

const Map = std.StringHashMap([]const u8);
map: Map,
arena: std.heap.ArenaAllocator,

const Faux = @This();

pub fn parse(source: []const u8, allocator: std.mem.Allocator) !Faux {
    var f = Faux{
        .arena = std.heap.ArenaAllocator.init(allocator),
        .map = undefined,
    };

    f.map = try parseSimpleKV(f.arena.allocator(), source);
    return f;
}

pub fn toStructure(self: *Faux, comptime T: type) !T {
    var t: T = undefined;
    try populateStructFromMap(T, &t, self.map, self.arena.allocator());
    return t;
}

pub fn deinit(self: *Faux) void {
    self.arena.deinit();
}